Dissertations / Theses on the topic 'Sexual dimorphism'

It is taken for granted in human societies that men are, on average, slightly taller, larger and heavier than women, despite a considerable overlap in their respective weight distributions. However, among mammals in general, intersexual size differences within a single species do not always favour males and range from leopard seals, with the female 20% longer and correspondingly heavier than the conspecific male, to gorillas with the male almost twice the size of his mate. There is ample evidence that body size plays a fundamental role in relation to an animal's survival. Consequently, when males and females of the same species attain different adult body weights, these should be seen in the overall context of divergent life history strategies, as emphasised by the typically later achievement of sexual maturity in the larger bodied sex. Most explanations of sexual size dimorphism in primates tend to be male-centred. They typically emphasize competition between males for females and protection of the social group by larger bodied males. However, such accounts are commonly marred by circular arguments and post hoc rationalisations. They are also self-defeating in their neglect of the possible effects of natural selection acting on females. The present research examines the ontogeny of sexual size dimorphism in terms of the divergent energetic needs of males and females. An allometric approach has been adopted, and the frustrations of circularity overcome by exploiting the special relation which exists between brain size and body weight. The results indicate that, at least for simian primates, body size reduction in females has played a major role in the evolution of sexual size dimorphism. For several species of larger bodied primates this difference has apparently been enhanced by body size increase in males. The scaling of molar tooth area with body weight corroborates these findings.

Phenotypic differences between the sexes evolve largely because selection favours a different complement of traits in either sex. Theory suggests that, despite its frequency, sexual dimorphism should be generally constrained from evolving because the sexes share much of their genome. While selection can lead to adaptation in one sex, correlated responses to selection can be maladaptive in the other. In this thesis I use Drosophila to examine the extent to which the shared genome constrains the evolution of sexual dimorphism and whether the sex chromosomes might play a special role in resolving intralocus sexual conflict. Gene expression data shows that intersexual genetic correlations are generally high, suggesting that genes often affect both sexes. The intersexual genetic correlation is negatively associated with sex-bias in expression in D. melanogaster, and the rate of change in sex-bias between D. melanogaster and six closely related species, showing that a sex-specific genetic architecture is a prerequisite for the evolution of sex difference. In further studies I find that genetic variance affecting lifespan is found in the male-limited Y chromosome within a population, which could offer a route to the evolution of further sexual dimorphism in lifespan, though the amount of variance was small suggesting adaptive potential from standing genetic variance is limited. Genetic variance on the X chromosome is also expected to be depleted once the sex chromosomes evolve, but here I find no evidence of depletion in either sex. Dosage compensation does not appear to double the male X-linked genetic variance, but this effect may be complex to detect. Finally, the X chromosome appears to be enriched for sex-specific genetic variance, and the consequences of this are explored using a variety of analytical methods to test biologically meaningful aspects of G-matrix structure. In summary, this thesis suggests that the evolution of sexual dimorphism is generally constrained by the shared genome, but intralocus sexual conflict could be resolved by novel mutations on the Y chromosomes, and by standing sex-specific genetic variance on the X chromosome. It highlights a special role for the X chromosome in the evolution of sexual dimorphism.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 27, 2007) Vita. Includes bibliographical references.

Heterochromatin is implicated in the negative regulation of gene expression. To understand the effects of heterochromatin on RNA polymerase-II (RNAPII) mediated transcription, this study focused on the FXN gene where abnormal silencing induced by expanded (GAA)n repeats causes Friedreich's ataxia (FRDA), an incurable neurological disorder. Here, the silenced FXN locus was found to be modified by the heterochromatic histone marks H3K9me3, H3K27me3 and bound by HP1β. This pathological heterochromatinisation was partially reversed by the histone deacetlyase inhibitor nicotinamide, which upregulated FXN expression to potentially therapeutic levels in vitro, ex vivo and in vivo. In addition, RNAPII was shown to be stalled in the first exon of the FXN gene and degraded by the proteasome in FRDA but not in healthy cells. This was linked to increased proteasome binding at the -silenced FXN locus in a pattern reminiscent of the heterochromatin marks. Importantly, proteasome inhibition restored stalled RNAPII levels in FRDA and upregulated FXN to potentially therapeutic levels in vitro. Moreover, experiments with healthy human cells and wild-type mouse thymus revealed enriched levels of proteasome binding in other heterochromatic regions (e.g. pericentromeric repeats and SINEs) which were also de-repressed by proteasome inhibition; suggesting that the effect seen on the pathological FXN locus represented a specific example of a more generalised phenomenon. Overall, this introduces a novel mechanism whereby heterochromatin might be maintained in a silent state. In this thesis, heterochromatin effects were also investigated in relation to sexually dimorphic gene expression. Microarray analyses revealed hundreds of autosomal genes sensitive to sex chromosome-complement rather than gender. HP1β-repressed genes and SINE elements were over-represented within this gene group suggesting a potential link between heterochromatin, proteasome-dependent silencing and sexually dimorphic gene expression. The results reveal a novel layer in the regulation of sexually dimorphic genes with implications for understanding sex-bias in physiology and disease.

Objective: The purpose of this study to assess the relationship between masticatory function and symphyseal biomechanical properties using a longitudinal sample. Known differences in male and female maximum bite forces manifest during adolescence. If symphyseal bending rigidity is affected by function during ontongeny, we would expect variation in male and female growth allometries of certain biomechanical properties of the symphysis. Methods and Materials: Subjects were chosen from the Iowa Growth Study records for completeness and quality of radiographic images longitudinally. 19 females and 20 males were chosen. Lateral ceph images from 9 timepoints (age 3-20) were used to trace the external cortical outline of the symphysis. The biomechanical parameters (second moments of area (Ix, Iy, Imax, Imin)) were calculated from the external contours of the symphysis. Mandibular length was used as a proxy for overall mandibular size. All variables were scaled and growth allometries calculated by a reduced major axis regression. Clarke's T-test was used to test for significance. ANCOVA was used assess the interaction between symphyseal properties and sex, mandibular length, and sex+mandibular length. Results: No significant differences in symphyseal growth allometries of males and females were found (p>.05). No significant interactions between symphyseal properties and sex, and sex+mandibular length. (p>.05). A significant interaction between symphyseal properties and mandibular length was found (p<.05). Conclusions: Despite greater bite forces in males that manifest during adolescence, there were no differences in symphyseal growth allometries between males and females. Perhaps function does not play a significant role in development of symphyseal form. Perhaps the subtle effects of function on symphyseal morphology cannot be assessed by using only external cortical outlines for evaluation of symphyseal biomechanical parameters.

The accurate determination of sex is the first analytic task of physical anthropologists in the study of human skeletal remains. Correct sex determinations are essential because most other skeletal analyses rely on this to be accurately determined. Although morphological features of the skull and pelvis have been traditionally used for sex determination, certain metric analyses have also been useful. In the absence of the most commonly used bones, metric measurements obtained from the tarsals have the ability to provide accurate information regarding sex. Metric sex assessments are based on the levels of sexual dimorphism between males and females. This thesis evaluates the presence of sexual dimorphism in the tarsals and their dimensions of length, width, and height and assesses which bones and dimensions are most useful for sex determination using a modern skeletal sample (n = 160) comprised of individuals of known sex and age. Summary statistics were calculated for males and females separately to assess the sexual variation for each measure. Pearsonâs Correlation Coefficient was used to establish correlations between sex and each measurement. Logistic regression analysis was used to determine the levels of sexual dimorphism in the bones and dimensions for the sample. Accuracy of sex estimations was compared between the left and right sides for each bone to determine if one side was more sexually dimorphic than the other. Logistic regression coefficients from the most accurate bones and dimensions were generated from the sample, which can be used to develop equations to accurately sex other samples of similar Euro-American ancestry. The most sexually dimorphic tarsals were the talus and first cuneiform. Tarsals from the right side were slightly more sexually dimorphic than those from the left. Length and height dimensions were more variable than breadth dimensions. Correct classifications for individual variables were as high as 87.8 %, with the highest overall percentage of correct classification of 93.5% obtained from a combination of all height measurements from the right tarsals for the total sample. This has implications for sexing skeletal remains from archaeological samples when other more commonly used bones are absent or poorly preserved.

Thesis (M. S.)--Biomedical Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Boyan, Barbara; Committee Member: Bonassar, Lawrence; Committee Member: Sambanis, Anthanassios; Committee Member: Schwartz, Zvi; Committee Member: Wick, Timothy.

La produzione locale ed il metabolismo degli steroidi nel Sistema Nervoso Centrale, la Neurosteroidigenesi, si pensa possa giocare un ruolo chiave nello sviluppo e nel corretto funzionamento del cervello. Un numero in crescita di studi sembra confermare l’importanza di questo processo svelando diverse condizioni fisio-patologiche dove i neurosteroidi sembrano un punto cardine. Sebbene in tempi recenti ci siano stati degli sforzi isolati di confermare diversi enzimi chiave della steroidogenesi in specifiche strutture cerebrali, ad oggi nessuno studio sistematico è stato effettuato per comprendere le complesse pathways della steroidogenesi cerebrale. La difficoltà di questi studi è stata resa maggiore sino ad ora dalla bassa espressione genica degli enzimi e degli ormoni coinvolti, e dalla difficoltà nel reperire tessuto umano encefalico. Lo scopo della nostra ricerca è stato di quantificare tramite la Real-Time quantitative PCR (qPCR) un set di 63 geni di specifico interesse nella steroidogenesi, dalla biosintesi de-novo a partire dal colesterolo, ai passaggi metabolici chiave per formare i neurosteroidi bioattivi (Cytochrome P450 family, Aldo-Keto reductase family, hydroxysteroid dehydrogenase family, hormone receptors, GABA receptors...). Le PCR quantitative sono state eseguite su RNA estratto dal materiale umano congelato (116 campioni, 9 tessuti da 24 autopsie in 7 gruppi d’età ed accoppiati per i diversi sessi) da controlli “non dementi” ottenuti dalla Netherlands Brain Bank, per un totale oltre le 20000 reazioni chimiche. Il tessuto umano raccolto per lo studio includeva: cervelletto, nucleo caudato, giro frontale mediale, giro frontale superiore, giro superiore occipitale, giro superiore parietale, giro cingolato, talamo (pulvinar) e materia bianca. Globalmente parlando, abbiamo esaminato la domanda controversa di quali steroidi sono prodotti direttamente nel cervello umano e quali siano prodotti negli organi periferici endocrini, come il surrene, e poi successivamente modificati nel tessuto cerebrale. Per questo fine abbiamo analizzato l’espressione di enzimi chiave coinvolti nella formazione di corticosteroidi e degli ormoni sessuali. In maniera opposta al controllo positivo surrenalico, le espressioni degli mRNA CYP17A1 (converte gli steroidi C21 in C19), SULT2A1 (DHEA sulfotransferasi), CYP11β1 (11β-idrossilasi) e CYP11β2 (aldosterone sintetasi) non sono stati trovati nel cervello umano (con l’eccezione del cervelletto). In aggiunta grossi livelli di espressione sono stati riscontrati per STS (sulfatasi steroidea) enzima chiave per attivare i solfati steroidei non biologicamente attivi nelle aree esaminate nello studio. Possiamo quindi ipotizzare che la trasformazione periferica e non la sintesi de-novo siano la fonte primaria di aldosterone, cortisolo e DHEA nel cervello umano. Riportiamo inoltre la prima cartografia su larga scala della steroidogenesi steroidea cerebrale che sembra suggerire un dimorfismo sessuale tessuto-specifico negli enzimi neurosteroidogenetici come l’aromatasi, il P450scc (Cholesterol side-chain cleavage enzyme), STS (steroid sulfatase), 3β-HSD [trasformazione del pregnenolone e DHEA in progesterone ed androstenedione rispettivamente], AR (androgen receptor), ESR (estrogen receptor), CYP21A2 (trasformazione del progesterone e 17-α idrossiprogesterone in 11-deossicorticosterone and 11-deossicortisolo), e molti recettori GABA. Concludendo, questa è la prima volta che una ricerca quantitativa e comprensiva sulla trascrizione genetica della steroidogenesi nel cervello umano sia stata portata a termine, usando un approccio metodologico di largo uso, negli stessi “set” di campioni individuali, rendendo così possibile un confronto diretto tra tessuto cerebrale nei due sessi. I risultati della nostra espressione genica hanno mostrato per la prima volta un dimorfismo sessuale nella sintesi steroidea nel cervello umano. I neurosteroidi posso quindi avere effetti immediati e sesso-specifici su alcune pathways neuronali. Il nostro lavoro sembra indicare che la neurosteroidogenesi sia un processo ubiquitario nel sistema nervoso centrale e non limitato a strutture specifiche. La differenza riscontrata nei set enzimatici nelle diverse regioni cerebrali indica un’interazione molto complessa tra di esse. Questo processo generalizzato è differente in strutture specifiche con ruoli importanti come il cervelletto.
Local production and metabolism of steroids in the Central Nervous System: Neurosteroidogenesis, is believed to be a crucial process in normal brain development and function. Increasing number of studies tend to confirm the importance of this process, through the number of physiopathological conditions in which neurosteroids seem to play a key role. Although in recent years isolated efforts have sought to establish the expression of several key steroidogenic enzymes in specific brain structures, to date, no systematic study has been undertaken to understand the intricate pathways of neurosteroidogenesis in the brain. Such efforts have so far been hindered technically by low enzymatic gene expression and hormones production. The difficult access to human encephalic tissue is also a major drawback for this kind of studies. The aim of our work was to quantify by the means of Real-Time quantitative PCR (qPCR) a set of 63 genes of interest corresponding to a broad selection of steroidogenic enzymes, implicated in de novo biosynthesis from cholesterol, so well as key transformation steps for bioactive neurosteroids (Cytochrome P450 family, Aldo-Keto reductase family, hydroxysteroid dehydrogenase family, hormone receptors, GABA receptors...). qPCRs have been performed on RNA extracted from fresh frozen material (116 samples, 9 tissues from 24 autopsies in 7 age groups paired by sex), from non-dement controls obtained from the Netherlands Brain Bank, for a total of more than 20,000 reactions. Human brain tissues harvested for this study included cerebellum, caudate nucleus, medial frontal gyrus, superior frontal gyrus, superior occipital gyrus, superior parietal gyrus, cingulate gyrus, thalamus (pulvinar) and white matter. Overall, we investigated the controversial question of which steroids are directly produced in the human brain and which are produced in peripheral endocrine organs like the adrenal gland and subsequently modified in the brain tissue, we analyzed the expression of key enzymes involved in corticosteroid and sex steroids formation. In contrast to the adrenal gland, that served as positive control, CYP17A1 [conversion of C21 steroids into C19 steroids], SULT2A1 (“DHEA sulfotransferase”), CYP11β1 (11β-hydroxylase) and CYP11β2 (aldosterone synthase) mRNAs expressions were not detected in the human brain (with the exception of the cerebellum). Furthermore, strong mRNA expression of STS (steroid sulfatase) has been confirmed in the areas examined in the study. We therefore conclude that local peripheral transformation, and not de novo synthesis, could be the main source of aldosterone, cortisol and DHEA in the human brain. We reported the first large scale undertaking of human brain cartography which suggested a tissue-specific sexual dimorphism in gene expression of some neurosteroidogenic enzymes, such as P450 aromatase, P450scc (Cholesterol side-chain cleavage enzyme), STS (steroid sulfatase), 3β-HSD [transformation of pregnenolone and DHEA into progesterone and androstenedione respectively], AR (androgen receptor), ESR (estrogen receptor), CYP21A2 [transformation of progesterone and 17-α hydroxyprogesterone to 11-deoxycorticosterone and 11-deoxycortisol], and many GABA receptors. Neuroactive steroids are endogenous neuromodulators. They have potent effects on neurotransmission mediated by γ-aminobutyric acid type A (GABAA) receptors. In this work, statistical analysis revealed significant sex differences of mRNA expression in human thalamus. The expression of STS, 3β-HSD2, CYP19A1, HSD11β1, AR, GR, and GABRA4 was higher in women, while CYP21A2, HSD17β3, HSD11β2, PGR and GABRδ were more expressed in men. We therefore hypothesize that two sex-dependant pathways inhibit the neurotransmission via interaction with the GABAA receptor to modulate the flow of visceral information to the thalamus. Women appear to preferentially modulate GABRA4 through synthesis of DHEA and estrogen, while the formation of TH-PROG, TH-DOC and their precursors was the men tendency with GABRδ modulation. THPROG and THDOC are potent modulators of the GABAA receptor. GABA mediates most of the inhibitory neurotransmission in the mammalian brain. Both THDOC and THPROG have significant sedative effects in vivo. THDOC is a metabolite of the mineralocorticoid DOC and is responsible for the sedative and anti-seizure activity of DOC in animal models. DOC can be metabolised from progesterone, and CYP21A2 mediates this conversion. CYP21A2 mRNA was detected in all samples studied. In the human brain, we found a higher gene expression of CYP21A2 in men than women (with the exception of cerebellum and caudate nucleus). In absence of CYP11B2 which converts DOC in corticosterone, we can conclude that THDOC is the principal DOC metabolite. In men brain, the tendency seems to be the formation of progesterone metabolites which act as potent modulators of GABAR. Recently the Purkinje cell, an important cerebellar neuron, has been identified as a major site for neurosteroid formation in vertebrates. The cerebellum contains more than half the neurons in the brain. Interestingly, gene expression profile of the cerebellum seems to be unusual compared to the other brain specimens analyzed. Indeed, this is the only tissue that expresses genes of de novo synthesis like CYP17A1, SULT2A1 or CYP11B2. Furthermore, we observed the strongest mRNA expression of key genes: 3β-HSD2 and GABRδ (δ-containing GABAR are the most sensitive to modulation by steroids). These data suggest that the cerebellum could have a crucial role in the steroidogenesis in human brain. To conclude, this is the first time, to our knowledge, that a comprehensive quantitative survey of steroidogenic gene transcription in the human CNS has been performed, using a common methodological approach in the same set of individual samples, permitting direct comparison of brain tissue and sex. Our gene expression results demonstrated for the first time a sexual dimorphism on steroid synthesis in the human brain. Neurosteroids can have immediate and sex specific effects on selected neuronal pathways. Our work tends to show that neurosteroidogenesis is an ubiquitous process in the CNS, and is not limited to specific structures. The difference in the enzymatic set in the different regions studied suggests a complex interplay among them. This generalized process is not incompatible with the existence of specialized structures with more predominant roles like the cerebellum.

Comparative neuroanatomy studies have helped us see the major structures and similarities between mammals, and allowed for the confirmations of hypotheses via direct observation. Variety in brain specialization can be seen in Cetartiodactyla, between the terrestrial artiodactyls and aquatic cetaceans. Compared to the primate brain, adapted to grasp using articulated fingers with opposable thumbs, the pure quadrupedal locomotion of ungulates and the absence of articulated movements in the limbs of cetaceans most certainly shows variations in the related brain areas. From this principle, the study of the brain of the swine, bovine, sheep or any other cetartiodactyl can help understand the basic organization coding the brain of mammals. Some species have been used more than others among cetartiodactyls. The sheep Ovis aries has been the subject of a fair amount of cytoarchitectural studies and functional investigations of the cortex, but also the hypothalamus. Other more exotic terrestrial species like the giraffe Giraffa camelopardalis, have much more rarely had their brain thoroughly studied and published. For this reason we studied the cortical folding of the giraffe brain, its brain weight and encephalization quotient (EQ), and we reviewed the literature concerning its encephalon as far as 1839. This showed that, although a relatively very small absolute number of specimen have been collected over the years, the giraffe brain was quite typical of ungulates, with a deep gyrification, and an absolute weight of 720 g. The brain of the swine Sus scrofa received comparatively little attention, regarding even basic data. To provide weighed data on the brain of the pig, we weighted the brain of 48 animals to reach a robust value for the average brain weight of the domestic swine a different age categories. The average adult brain weight was 135 g, which was compared to the literature, as well as published EQs. The relatively low EQ (0.38) could be related to the domestication and heavy breeding that meat production necessitated to improve body weight. One of the findings of the cyctochemical exploration of the mammalian brain is the existence of sexually dimorphic structures. Groups of cells were found to be much larger in volume or cell number in the brain of males or females. Although their precise function is still unknown, most of them are directly involved in reproduction behaviors. Hormones have a crucial role in shaping the developing brain, and in particular androgens. The effects of male and female steroids on the development of the brain and its sexual differentiation can be put in perspective in the study of intersex freemartin bovines. During twin pregnancy of a bovine with a male and a female fetus, male sexual hormones circulating during intrauterine development in the female fetus can masculinize its genital apparatus and alter its phenotype, resulting in an intersex animal. We investigated the hypothalamus cytoarchitecture of freemartin heifers and compared them to male and female hypothalami. We found sex differences between male and female suprachiasmatic (SCN) and vasopressin-oxytocin containing (VON) nuclei. Moreover, the freemartin hypothalamus showed differences more complex than a simple masculinized female brain. While the VON was in size and cell count between male and female values, the SCN of freemartins was larger than both males and females. Using modern multivariate statistical methods, we also investigated the cytoarchitecture of male, female and freemartin cerebellar cortex. We found differences among cellular layers in size, regularity and density of the cells, across sex categories, showing that a multivariate multi-aspect approach can yield valuable results at the cellular level for large cohorts, and that a multi-disciplinary team can produce finer studies.
La neuroanatomia comparata consente di caratterizzare le strutture nervose mettendo in luce le somiglianze e le differenze tra i mammiferi. Un aspetto interessante di questo studio comparato riguarda il cervello dei Cetartiodattili sia terrestri (artiodattili) sia marini (cetacei) in cui la locomozione quadrupedale degli ungulati e l'assenza di movimenti articolati nell’arto dei cetacei mostrano variazioni morfologiche rispetto ai primati nelle aree cerebrali correlate i quali presentano un arto specializzato con dita articolate e pollici opponibili capaci di afferrare oggetti molto piccoli con precisione. Da questo punto di vista uno studio neuroanatomico dell’encefalo di artiodattili come il suino, il bovino e la pecora può aiutarci a comprendere l'organizzazione della citoarchitettura nei diversi mammiferi. La pecora Ovis aries come modello animale è stata oggetto di una discreta quantità di studi anatomici e indagini funzionali sul ruolo della corteccia cerebrale e dell'ipotalamo. Altre specie di artiodattili terrestri come la giraffa Giraffa camelopardalis, sono state meno studiate e sono rare le pubblicazioni che ne hanno studiato il cervello. Per questo motivo, uno degli obiettivi di questa tesi è stato quello di caratterizzare le circonvoluzioni corticali dell’encefalo della giraffa, valutare il suo peso ed il suo quoziente di encefalizzazione (EQ). I risultati hanno permesso di affermare che il cervello della giraffa presenta caratteristiche comuni a quelle degli altri ungulati con una notevole girificazione e un peso medio di 720 g. Un altro obiettivo è stato quello di analizzare l’encefalo del suino Sus scrofa. Per ottenere risultati significativi, abbiamo pesato il cervello di 48 animali appartenenti a diverse categorie di età. Il peso medio del cervello adulto è risultato di 135 g. L'EQ relativamente basso (0,38) ottenuto da questo mammifero potrebbe essere spiegato con le esigenze di produzione spinta che l'allevamento intensivo comporta, incrementando la selezione di animali sempre più pesanti. Uno degli aspetti molto studiati in questi ultimi anni da un punto di vista neuroanatomia riguarda la caratterizzazione delle aree sessualmente dimorfiche nell’encefalo dei mammiferi. Il bovino Bos taurus rappresenta un modello interessante per lo studio dei dimorfismi cereberali perché questo mammifero possiede un cervello grande, altamente convoluto, una gravidanza di 9 mesi. Inoltre in questa specie si manifesta la sindrome del freemartinismo. Tale sindrome si presenta perchè durante la gravidanza gemellare di un feto maschile e uno femminile, gli ormoni maschili del maschio a causa della anastomosi plaecentare circolano nel feto femminile mascolinizzando. Così il feto femmina è un individuo intersesso interessante perché il suo cervello femminile si è sviluppato naturalmente in un ambiente ormonale maschile. L’obiettivo che ci siamo posti è stato quello di studiare la citoarchitettura dell'ipotalamo di giovenche freemartin e confrontare i dati ottenuti con quelli analizzati nell’ipotalamo di bovini maschi e femmine. Questo studio ci ha permesso di caratterizzare i dimorfismi sessuali tra maschili e femminili presenti nel nucleo suprachiasmatico (SCN) e nel nucleo contenete vasopressina-ossitocina (VON). L’ipotalamo dei freemartin mostrava per quanti riguarda il nucleo VON valori intermedi in termini di dimensioni e numero di cellule tra i valori maschili e femminili. Il SCN dei freemartins è risultato più grande rispetto a quello dei bovini maschi e femmine. Un ulteriore obiettivo è stato quello di studiare la morfologia della citoarchitettura della corteccia cerebellare tra bovini maschi, femmine e freemartin. Applicando un metodo statistico multivariato e multi-aspetto, abbiamo caratterizzato le differenze di genere tra gli strati del cervelletto in termini di dimensioni, regolarità e densità delle cellule.

The genus, Leucadendron, of the Cape Proteaceae family, is made up of over 70 dioecious species that vary in their degree of sexual dimorphism. Males are generally more highly ramified (branched) with smaller leaves compared to corresponding females. It has been hypothesised that sexual dimorphism in Leucadendrons is linked to serotiny (a fire-adapted reproductive strategy), where highly serotinous females may incur extra resource costs in order to keep their transpiring cones alive between fires. This hypothesis predicts that the female morphology might be associated with more efficient resource acquisition compared to males in order to support their greater resource requirements. Another hypothesis suggests that selection for greater floral display in males has lead to a higher degree of ramification as male cones are borne terminally on branches. This highly branched morphology may be associated with subsequent physiological costs. The idea that different male and female morphologies might be associated with different physiological costs or benefits was tested in this experiment with a focus on plant hydraulics. Hydraulic supply is known to affect photosynthetic capacity and maximum assimilation rate. Using a specially designed vacuum chamber, leaf-specific and xylem-specific hydraulic conductance was measured in males and females of the highly dimorphic Leucadendron rubrum and non/marginally dimorphic Leucadendron daphnoides. Using microscopic imagery, xylem anatomy was analysed in an attempt to explain the hydraulic conductance results.

Biology
M.S.
Sexual dimorphism, i.e., differences in morphology, physiology, and behavior between conspecific males and females, is ubiquitous, extensive, and often species-specific, indicative of its rapidly evolving nature. Ever since Darwin first described a general theory of sexual selection to explain the extraordinary differences between males and females of the same species, biologists have proposed a variety of mechanisms ranging from runaway selection to good genes to sexual conflict. While a popular approach is studying the effects of sexual selection on different components of fitness, the results of these studies are generally difficult to interpret and are typically not generalizable across populations, let alone taxa. Recent advances in the “omics” field are transforming the way that we study patterns and processes involved in sexual selection. At the molecular level, sexual dimorphism is present in gene expression differences between the sexes, providing a powerful framework to study sexual selection. By studying genes that are sex-biased in expression, we will better understand the underlying genetic basis of traits that are sexually dimorphic. Alreadly, studies of sex-biased genes in model organisms, particularly Drosophila, have revealed that male-biased genes are among the most rapidly evolving functional classes of genes. However, while a number of intrinsic factors appear to correlate with evolutionary rate (e.g., gene expression level, codon bias), it is unclear whether any of these factors drive the rapid divergence of male-biased genes. Another important discovery is the prevalence of sex-biased gene expression. However, even with widespread sexual dimorphism at the phenotypic level, it remains unknown the extent to which sex-biased gene expression exists in humans and their primate relatives. In fact, studies of sexual dimorphism on a molecular level in primates have been very few, even though understanding this phenomenon in humans could further our knowledge of the nature of sex-biased phenotypes and diseases. In this thesis, I advance our knowledge of the genetic bases and mechanisms that shape sexual dimorphism. First, I review a classic framework that biologists have traditionally applied to define and partition fitness measures between males and females in the model system, Drosophila. Second, I apply a molecular framework to compare the relative roles of intrinsic factors on the evolutionary rate of rapidly evolving male-biased genes in Drosophila. Third, I review the current state of our knowledge of sexual dimorphism and sex-biased gene expression in humans. Fourth, I present a bioinformatics framework to identify the extent of sex-biased expression in primate tissue and to examine the selective forces involved in their evolution. Overall, I demonstrate the effectiveness of using a functional comparative genomics approach in studying the nature of sexual dimorphism at the molecular level across multiple taxa.
Temple University--Theses

In this thesis, I investigate the relationship between two variables for which persistent directional sexual selection is an evolutionary driver: condition dependence and sexual dimorphism. This joint dependence on sexual selection predicts that among traits within a given species, greater dimorphism should be associated with stronger condition dependence. Very few studies have tested this prediction, and those that have focus on species with highly exaggerated and strongly dimorphic traits between the sexes. Here, I quantified variation in a suite of morphological traits in a dipteran species – the antler fly, Protopiophila litigata – in which sexual dimorphism is less extensive. I manipulated condition via different larval diets and then quantified the effects on adult body size and shape in both sexes. Across traits, I found that the extent of sexual dimorphism was positively associated with the strength of condition dependence in males but not in females. These results suggest a shared developmental basis to condition dependence and sexual dimorphism in body shape, and suggest that this has arisen via sexual selection in males despite the absence of extremely dimorphic shared traits.

This study examined indicators of male-female differences in the os Coxa, specifically in the shape of the ilium and iliac crest for the purpose of skeletal sex estimation. The iliac crest is a curved, or “S” shaped, epiphysis which extends along the cranial margin of the ilium, posteriorly from the anterior superior iliac spine to the posterior superior iliac spine of the os Coxae. Forty two metric variables characterizing the shape of the os Coxa and iliac crest were derived from a digital database of 150 adult White human os Coxae, including 75 males and 75 females, from the Hamann-Todd osteological collection at the Cleveland Museum of Natural History. The os Coxae were all digitized using a MicroScribe-3DX digitizer, and the data was stored in an excel spreadsheet, which facilitated further mathematical analysis to define and calculate all variables. A single point of origin defined as the most superior point in the midline of the pubic symphysis, was common to each variable. This study hypothesized that these variables will better define variation in form, and that they will better characterize sexual dimorphism in the iliac crest. Thus serve as an aid in sex estimation. Additionally, the qualitative observation of the sciatic notch was compared to the quantitative observations. Statistical analyses, including descriptive statistics, univariate sectioning points, independent t-tests, and proportional analyses, were used to test the potential application of the findings of this study to sex identification in osteological investigation. The results of this research suggested that there were slight indications of sexual dimorphism in several of the iliac blade dimensions along with the central chords of the iliac crest and their associated angles. Despite indications of differences in the female and male form, the measurements proved to be too variable, thus making accuracy and reliability unattainable. Further investigations are required to better understand the presented findings.
Thesis (M.A.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Anthropology

Studies of sexual dimorphism in the corpus callosum (CC) have employed a variety of methodologies for measurement and normalization but have yielded disparate results. The present work demonstrates how in some cases different manipulations of the same raw data, corresponding to different commonly used methodologies, produce discordant results. Midsagittal CC area was measured from magnetic resonance images (MRIs) of 137 young normal volunteers. Three strategies intended to normalize for average differences in brain size between the sexes, as well as five different normalization variables, were contrasted and evaluated. The stereotaxic method normalizes for inter-subject differences in overall brain size by scaling MRIs into a standardized space. The ratio method uses one of five different indices of brain size and divides it into CC area. The covariate method uses one of these indices as a covariate in statistical analyses. Male subjects show significantly larger absolute total area, as well as anterior third and posterior midbody. However, in 2 of 3 normalization strategies, namely the stereotaxic and ratio methods, females show relatively larger total area, anterior midbody and splenium. The covariate method did not show any significant differences at the .05 level. Results suggest that different approaches to normalization and analysis are not necessarily equivalent and interchangeable.

Sex in the jewel wasp Nasonia vitripennis is determined by whether eggs are haploid or diploid: the radically different male and female phenotypes share the same genome, showing that their sexual dimorphism is not genetic but rather a specific case of phenotypic plasticity. As a consequence, all of Nasonia’s genes are selected for both male and female fitness. The impact of this diverging selective pressure on the evolution of its genome and whether it is comparable to organisms with sex chromosomes are questions still largely unanswered. In this thesis, I develop and apply a set of tools for the integrative analysis of different aspects of Nasonia’s biology. I characterize the improved gene set of Nasonia and identify several lineage-specific gene family expansions. I provide an algorithm for detection and comparison of splicing and transcription signal from transcriptomic data in non-model organisms. Finally, I identify the different regulatory processes that enable generation of disparate phenotypes using network analyses on Nasonia’s developmental transcriptome. Nasonia’s transcriptome shows high amounts of sex-bias not tied to linkage groups or alternative splicing. Early development shows a prevalence of sex-biased interactions between transcripts rather than single-gene upregulation, and sex-biased networks are enriched in lineage-specific regulators.

Thesis (M.S.)--Marshall University, 2004.
Title from document title page. Document formatted into pages; contains viii, 72 p. including illustrations. Includes abstract. Includes bibliographical references (p. 33-37).

The aims of this project were to investigate the binding characteristics of the cytosolic oestrogen receptor in the uterus, brain and thymus of immature Wistar rats. The specificities of the receptor in the uterus are well established. The specificities of the cytosolic receptor in the uterus and thymus of immature female Wistar rats were tested against a range of steroids and the values found for the thymus compared with those for the uterus. The concentrations and dissociation constant (Kd) of the cytosolic oestrogen receptor were determined in uterus, brain and thymus of male and female rats at 5,18 and 30 days of age. Clomiphene citrate (CC), an oestrogen antagonist/partial agonist, oestradiol (E2), CC+E2 or 4-hydroxyandrostenedione (4-OHA), an aromatase inhibitor, were administered to animals at 15 days in order to study the effects of these compounds on receptor binding characteristics at 30 days. Significant differences in specificity were found between the thymus and uterus, the cytosolic oestrogen receptor in the thymus exhibited significantly higher affinity for corticosterone than it did in the uterus. Male animals were heavier than females at 30 days. Uterus and thymus weights increased exponentially between 5 and 30 days. The tissue-to-body weight ratio increased in uterus between 18 and 30 days and increased in the thymus in both sexes between 5 and 18 days. In males at 30 days, the tissue-to-body weight ratio of the thymus was significantly lower than in females of the same age. Cytosolic oestrogen receptor concentrations in the uterus, brain and thymus differed between some age and/or sex groups. Cytosolic oestrogen receptor concentrations increased exponentially in the uterus between the different age groups. Cytosolic oestrogen receptor concentrations in both thymus and hypothalamus at 5 days were significantly higher in females than in males of the same age group. No differences in cytosolic oestrogen receptor concentrations were found between the sexes in the cortex at 5 and 18 days but at 30 days, receptors were not detectable in this brain area. The Kd for moxestrol, a synthetic oestrogen agonist that is not bound by alphafetoprotein present in the blood of immature rats, was similar in all tissues. E2 and CC+E'-' treatmentsr esulted in decreasedb ody and thymus weight in both sexes,i ncreased uterus weight and decreased thymus weight in both sexes but led to increased uterus weight. CC treatment decreased the concentration of the receptors in the female thymus only-, E2 and CC+E2 treatments decreased the concentratIon of the receptor to levels that were undetectable in hypothalamus and thymus in both sexes, 4-OHA treatment increased thymus weight and cytosolic receptor concentrations in the hypothalamus and thymus of males only. These results suggest that cytosolic oestrogen receptors in uterus, brain and thymus are similar and that sex differences in these tissues are mediated by differential exposure to oestradiol during the early postnatal period. The thymus is crucial to the development of the immune response. The finding that the cytosolic oestrogen receptor differed from the uterus receptor in its affinity for corticosterone and that sex differences in cytosolic oestrogen receptor concentrations were present in the thymus at 5 days could be relevant to the sex dimorphisms that exist in autoirnmune disease manifestation.

Bibliography: pages 128-138.
This study focuses on the mating dynamics of South African forest millipedes Centrobolus (Diplopoda: Spirobolida: Pachybolidae). The main objectives were to investigate the two most common mechanisms of sexual selection, sperm competition and cryptic female choice. The approach was to (1) quantify sexual dimorphism and find the selection pressures operating on the sexes, (2) determine the functional significance of male and female genitalia, (3) understand why there should be a conflict of sexual interests in prolonged copulations, and (4) resolve the mechanisms of sperm competition and cryptic female choice by comparing male mating strategies and sperm precedence to female mating strategies and sperm usage. All hypotheses tested in this thesis are centered on whether there is a conflict of interests between the sexes.

The determinants of sexual dimorphism in a family of false scorpions (Pseudoscorpionida, Chernetidae) were investigated experimentally and with a literature analysis of comparative morphometric and habitat data. Species vary in the extent to which males and females differ in size of the conspicuous, prehensile pedipalps. Patterns within the Chernetidae suggest that dimorphism is a highly variable condition, relatively unconstrained by phylogenetic influences. The evolution of species with enlarged male pedipalps appears to be associated with a change from nonpairing to pairing sperm transfer behavior, and aggressive mate acquisition by males. Experiments with Dinocheirus arizonensis demonstrate a high correlation between male combat ability and chela size. Comparison of male and female life histories show prolonged development in males, and morphological comparisons implicate pedipalp dimorphism as a causative factor in this developmental rate difference. Prolonged development may be particularly costly to males, given the pattern of female sexual receptivity in this species. Females were found to become unreceptive soon after mating and remain so throughout a protected period of brood development. Experimental manipulations suggest that the male developmental rate cost is only outweighed under high density conditions when superior combat ability results in increased mating success. Repeated measures experiments failed to show any correlation between male pedipalp size and number of spermatophores accepted by a female. Parent-offspring regressions suggest the existence of additive genetic variance for male chela size and indicate a strong genetic correlation between this trait and cephalothorax length. Full-sib phenotypic correlations suggest that in D. arizonensis sexual divergence through sexual selection may be constrained by a high genetic correlation between males and females. Finally, the role of phoresy in the colonization of ephemeral, patchy habitats is investigated. Results support the hypothesis that attachment of pseudoscorpions to larger, more mobile arthropods represents a behavior functioning specifically for dispersal.

By performing a comparative analysis and using phylogenetic relationships of the Cervidaefamily this study aimed to address whether or not sexual selection may play a role in the extinctionof species by making species more vulnerable to extinction. The role of sexual selection in makingspecies more vulnerable to extinction is largely unexplored, and several factors such as ecologicaland life history traits may increase the risk of extinction.In all species of the family Cervidae (Gilbert et al. 2006, Geist 1998,Groves and Grubb2011,Meijaardand Groves2004,Price et al. 2005, Goss 1983) sexually selected characters plays amain role in determining species status and thus potentially their probability of extinction. In thisstudy the intensity of sexual selection (measured as sexual size dimorphism, antler size and matingsystem) and the rate of extinction (IUCN classification and anthropogenic effect) were counted asfactors to determine the role of sexual selection intensity in both species-rich and species-poorclades.By using the programme MESQUITE and phylogenetic trees, the results show an associationbetween species with larger body size and dimorphism, living in open habitats and having largerantler size expanded to more than three tines; such species are mostly non-territorial and formharems during the rutting season. The small species are territorial, live in closed habitats, aremonomorphic and have small antler size limited to two tines or less. Moreover species that aremore subjected to habitat degradation and anthropogenic effects tend to become smaller in size.Extinction risk for the species-rich clades with small sized, territorial and small antler sizedspecies is lower than for those consisting of species with larger antler size, larger body size, livingin open habitats and using harems as mating system.To sum up, the intensity of sexual selection in larger species in deer family put them in risk ofextinction; but on the other site, small species are more adapted to the environment by choosingdifferent strategy in mating system, and reducing antler and body size thus diminishing theextinction risk.

Nutritional aspects of size-related sex differences in the diets of free-living mink were investigated in laboratory-based feeding trials with adult farm-bred mink maintained on 'natural' diets. As preliminary studies had shown that carcase utility was virtually complete, the rations presented comprised the minced whole carcasses of wild rabbit Oryctolagus cunniculus, eel Anquilla anguilla, laboratory rats and mice, and domestic fowl. Determinations of gross composition revealed significant differences between these diets; the smaller prey types, including rodents, birds and fish, were found to have a higher ratio of Apparent Digestible Energy to Nitrogen than larger items such as rabbits, although comparisons with data presented by other workers demonstrated that the variations between species within these prey groups are as great as, or greater than, those between the diets themselves. From the results of the feeding trials, it was also apparent that such diets do not differ significantly, either in digestibility or biological value and attempts to classify particular prey items in terms of their nutritional value are, therefore, of limited application in analyses of the feeding ecology of a generalist predator. Nutrient intake was related to diet composition and varied widely between trials, although the mass-specific requirements of females were higher than those of males. Comparisons of gut morphology indicated that, in females, hypertrophy of the alimentary tract may develop in response to increased energy demands. A similar adaptation was evident in both males and females from wild populations, suggesting that the natural diets of free-living mink are generally of a lower quality than the rations fed to commercially raised animals. Feeding trials were also carried out on growing kits from 56 to 105 days post partum. Sex differences in nutrient metabolism were not significant but the growth rates of males were higher than those of females. In both sexes the growth rates of kits feeding on 'natural' diets were lower than those of animals raised on commercial rations. This effect was most pronounced in males, a finding which supports the hypothesis that the degree of sexual dimorphism in this species is dependent on the extent to which the growth potential of males is constrained by dietary regime during the early phases of development.

Ontogeny of sexual dimorphism within the Paraclinini is quite complex both within and among species. Differential growth in males is not the main cause of adult dimorphism. Rather, allometric shifts in both sexes produce adult shapes with approximately equal frequency. A trait that appears exaggerated in one sex is not always produced ontogenetically by acceleration in growth of that trait. Larger male head size, for example, may result from neoteny in females (relative to juveniles) as often as acceleration in male growth. Females, rather than looking like large juveniles, are actually more different in shape from juveniles than are males. On this time scale then, females should be considered the divergent sex. Phylogenetic analysis revealed three main lineages within the tribe. These groups are probably stable, though positions of some of the other species may change as more data become available. The most primitive species are grandicomis, nigripinnis, and cingulatus. The position of Exerpes within the clade indicates that its single species should be included in the genus Paraclinus. Fairly extreme sexual dimorphism within Paraclinini seems to be the ancestral condition and has been variously modified within the clade. The trend is toward less extreme male and female difference with occasional reversal of a dimorphic character. The decrease in amount of dimorphism seems to have occurred primarily through neoteny (relative to ancestral allometry), acceleration, and post-displacement. Juvenile growth has also changed relative to ancestral juveniles, affecting of adult as well as juvenile proportions. These evolutionary changes are independent of and in no way reflect the ontogenetic paths producing dimorphism within a species.

Women in modern populations tend to have more stenotic intercondylar fossae than men, which may contribute to an increased probability of anterior cruciate ligament (ACL) injury. We hypothesized that morphological differences are attributable to sexual dimorphism and similar patterns will be observed in past populations. This hypothesis is tested by comparing bilateral femoral intercondylar notch width indices (NWI = intercondylar notch width/bicondylar width) using independent samples t-tests between males and females in a sample of 322 prehistoric Native American individuals from the southwest U.S. Contrary to our predictions, no significant differences in NWI were observed between the sexes for the left (ρ=0.323) or right (ρ=0.278) femur. There was significant directional asymmetry in the development of the distal femur (ρ=0.005), no difference in NWI across age groups (ρ=0.363), and significant differences across sites (ρ=0.001). Differences in NWI between physiographic regions were found to be significant (ρ<0.001). These results suggest that developmental plasticity may play a larger role in the size and geometry of the femoral intercondylar fossa than sexual dimorphism.

Evolution through natural selection enables species to adapt to their surroundings and optimise themselves for reproduction and survival. Sexual selection, on the other hand, reflects modifications to improve reproductive fitness of individuals within species. Animal morphology, therefore, often represents a compromise between these two selective pressures. Bandicoots and bilbies (Marsupialia; Peramelemorphia) are small to medium sized omnivorous marsupials, of which roughly 30 species inhabit varied habitats throughout Australia and Papua New Guinea. This study sought to quantify craniodental variation in a range of bandicoot and bilby species to investigate the relationship between natural selection and sexual dimorphism in this clade of animals. Micro-CT and laser scanning techniques were employed to obtain three-dimensional scans of the crania and dentition of the 25 study species and subspecies (total n=124; 63 female and 61 male). Landmark analysis was conducted on 54 landmarks placed on the cranium and upper dentition to pinpoint areas of variation within and between the genera, species and sexes. Interspecific variation in cranial morphology between genera and species does reflect taxonomic groups and likely reflects adaptation by natural selection for different ecologies in different clades. Macrotis was the closest to the consensus shape for Peramelemorphia. Within family Peramelidae, genera formed discrete clusters, reflecting diagnostic differences in cranial shape between the two genera, separating Australian the short-nosed bandicoots (Isoodon) from the long-nosed or barred bandicoots (Perameles). The Peroryctidae clustered together, with Peroryctes nested within Echymipera, and Microperoryctes between Echymipera and Macrotis. Echymipera kalubu was the only exception and nested within Macrotis, quite distinct from the other species of Echymipera. Intraspecific variation showed strong evidence of sexual dimorphism in the species Macrotis lagotis and Isoodon fusciventer, while most other species did not have sexual dimorphism. In the two species that did show dimorphism in skull shape, there is also significant dimorphism in body mass, with males typically being larger. Shape changes did have allometric correlations with skull size, in PC axis 1 in M. lagotis and interestingly in PC axis 2 in I. fusciventer. In P. papillon, one of the smallest species, there was a trend towards female biased sexual dimorphism both size and skull shape, though this was not significant in our sample. This study highlights the large range of expressions of craniodental sexual dimorphism present in Peramelemorphia, and quantifies distinctions between expression within and between genera.

Le déterminisme génétique du sexe nécessite souvent l’évolution d’une région non-recombinante (NR) formant ainsi paire de chromosomes sexuels. Bien que la reproduction sexuée ait une origine commune à tous les eucaryotes, l’évolution des chromosomes sexuels s’est quant à elle effectuée de manière répétée et indépendante. Les chromosomes du sexe ont été particulièrement étudiés dans les systèmes diploïdes (chromosomes sexuels XY et ZW) des plantes et animaux. Le récent séquençage du génome d’Ectocarpus, modèle d’étude des algues brunes, donne non seulement une chance unique d’analyser les chromosomes sexuels dans un groupe phylogénétiquement distant des opisthocontes et de la lignée verte ; mais il donne aussi l’opportunité d’examiner un système haploïde de chromosomes sexuels (système UV). Chez Ectocarpus l’expression du sexe a lieu pendant la phase haploïde du cycle de vie, avec les chromosomes U et V, respectivement spécifiques aux femelles et aux mâles. L’analyse des chromosomes sexuels chez Ectocarpus a montré que la taille de la région NR est restée modeste pour un système vieux de plus de 70 millions d’années. Une analyse des dimorphismes sexuels a été effectuée ainsi que l’étude comparative des transcriptomes mâle et femelle d’Ectocarpus. Le développement parthénogénétique est, dans certaines populations d’Ectocarpus, un dimorphisme sexuel. Le lien génétique entre parthénogenèse et sexe a été analysé et suggère qu’un locus contrôlant la parthénogenèse est localisé au niveau de la partie recombinante du chromosome sexuel d’Ectocarpus. De plus, une analyse de fitness indique que le locus de la parthénogenèse est soumis à une sélection antagoniste entre les deux sexes
Genetic sex determination is usually controlled by sex chromosomes carrying a non-recombining sex-determining region (SDR). Despite the common origin of sex (meiosis) in Eukaryotes, the evolution of sex chromosomes has evolved repeatedly and independently. Our knowledge in sex chromosomes comes mainly from the analysis of diploid systems (XY and ZW sex chromosomes) in animals and land plants. However the recent genome sequencing of the brown alga Ectocarpus, not only opens up the possibility of studying sex chromosomes in a phylogenetic distant group but also of analysing a haploid sex chromosome system (UV sex chromosomes). Indeed in Ectocarpus sex is expressed during the haploid phase of the life cycle, where U and V sex chromosomes are restricted to female and male, respectively. The Ectocarpus sex chromosomes have some unusual evolutionary features such as the size of the non-recombining region, which is surprisingly small for a 70 million year old system. Also the evolutionary aspect of sexual dimorphism was studied by analyzing male and female transcriptomes and by identifying several subtle sexual dimorphic traits. Parthenogenetic capacity is a sexual dimorphic trait in some populations of Ectocarpus. The genetic link between parthenogenesis and sex was analysed and a locus that controls parthenogenetic was located to the Ectocarpus sex chromosome, in the recombining pseudoautosomal region. Fitness analysis strongly suggested that the parthenogenetic locus is a sexual antagonistic locus