Dissertationen zum Thema „Frogs Evolution“

Thesis (M.S.)--Missouri University of Science and Technology, 2010.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed June 7, 2010) Includes bibliographical references.

Most theoretical models predict an optimal offspring size that maximises parental fitness. Variation in the quality of the offspring environment can result in multiple offspring size optima and therefore variation of offspring provisioning can evolve. Variation in offspring provisioning is common and found across a variety of taxa. It can be defined as between populations, explained by optimality models, or between and within individuals, neither so easily explained by optimality models. My research focused on the evolution of variable offspring provisioning by testing theoretical models relating to variation in offspring provisioning between and within individuals. Using comparative methods, I found a positive relationship between intraclutch variation in offspring provisioning and variation in the quality of the offspring environment in a suite of pond breeding frogs. This positive relationship provided evidence that patterns of variable offspring provisioning are related to the offspring environment. This study also identified a species (Crinia georgiana) with high variation in offspring provisioning on which to focus further investigations. High variation in offspring provisioning occured between and within individuals of this species independent of female phenotype and a trade-off in offspring size and number existed. In laboratory studies, increased yolk per offspring led to increased fitness per offspring. Parental fitness calculations revealed that in high quality conditions production of small more numerous offspring resulted in higher parental fitness, but in lower quality conditions the production of large offspring resulted in the highest parental fitness. This was confirmed in field experiments under natural conditions using molecular markers to trace offspring to clutches of known provisioning, allowing me to measure exact parental fitness. The strategy of high variation in offspring size within clutches can be of benefit when the future of the offspring environment is not known to the parents: as a form of bet-hedging. Further study of the offspring environment revealed that conditions such as density dependent fitness loss, spatial variation in habitat quality, and non-random offspring dispersal, can combine to create the conditions predicted by theoretical models to maintain a strategy of variable offspring provisioning in the population. My research provides a comprehensive empirical test of the theory of variable offspring provisioning

Le Plateau des Guyanes a été géologiquement stable au cours de l'ère Cénozoïque, exempt de l'influence de l'orogénèse des Andes et de la mise en place du bassin de l'Amazone. Cette région est-elle biogéographiquement homogène au sein de l'Amazonie ? Quelles sont les modalités spatio-temporelles de diversification au sein de cette région ? Afin de répondre à ces questions, j'ai exploré sa biorégionalisation sur la base de la distribution des amphibiens anoures. Cette approche a permis de définir trois biorégions dans l'est du Plateau des Guyanes, et de révéler une forte sous-estimation de l'endémisme. Ensuite, j'ai étudié les patrons de diversification au sein du genre endémique Anomaloglossus. Ce volet a permis de dévoiler l'existence de spéciation cryptique au sein du genre, avec un patron biogéographique composé de quatre zones de diversification au sein du Plateau des Guyanes et une origine du genre dans les tepuis
The Guiana Shield has been geologically stable during the Cenozoic era, exempt of the influence of the uplift of the Andes and the setting up of the Amazon basin. Is this region biogeographically homogeneous within Amazonia? What are the spatio-temporal diversification modalities within this region? To answer these questions, I explored bioregionalisation within Amazonia and the Guiana Shield based on the dis- tribution of anuran amphibians. This approach enabled to define three bioregions in the eastern Guiana Shield and to reveal a high underestimation of endemism. Then, I studied the diversification patterns within the endemic frog genus Anomaloglossus. This part en- abled to reveal cryptic speciation within the genus, and a biogeographic pattern composed of four areas of diversification in the Guiana Shield, with an origin of the genus in the western highlands (tepuis)

The upland (Pseudacris feriarum) and midland (P. triseriata) chorus frogs are closely related cryptic species that are best distinguished genetically. The distribution of these species within the Commonwealth of Kentucky has previously been defined by only a handful of genetic samples, making delineation of range limits for each species difficult. Accurate understanding of species distributions, and the genetic structure within them, are vitally important for conservation management of amphibian species. In this study, I have collected genetic samples from across the putative ranges of P. triseriata and P. feriarum in Kentucky and used next-generation sequencing technology to generate more fine-scale estimates of species ranges. The genetic data generated in this study support the delineation of two species in Kentucky, and the species assignments of all individuals and populations are in general concordance with the previously hypothesized species distributions. However, I have identified two previously unrecognized contact zones for these species and revealed areas of hybridization. By delineating species distributions and identifying potentially important regions of genetic admixture, this study will be informative to future conservation management and conservation genetic research of chorus frogs in Kentucky.

The primitive New Zealand frog Leiopelma hochstetteri shows exceptional karyotypic variation. On the North Island, females carry univalent W chromosome and both sexes have 0 to 15 supernumerary chromosomes. Frogs from Great Barrier Island have a conventional 2n = 22 karyotype, with no sex chromosome differentiation in C-banded mitotic chromosomes. However, the lampbrush chromosomes of a Great Barrier Island female show evidence of heterogamety. This suggests that presumed ancestral female heterogamety has persisted on Great Barrier Island and given rise to a WZZ-female/ZZ-male sex chromosome system on the North Island.
A repeated sequence, Lh1, varies greatly within populations in copy number and distribution on genomic EcoRI fragments. In situ hybridization revealed the variable presence of large Lh1 arrays on supernumerary chromosomes and two autosomes. The extensive Lh1 variability implies that, like the supernumeraries, it is more selfish than functional in the L. hochstetteri genome.

The Amazon rainforest along the Andean foothills contains exceptionally high diversity, much of it recent. The complex geology of the Andes and paleoclimate fluctuations preclude complex dispersal scenarios. This, in turn, has contributed to idiosyncratic speciation modes among shallowly-diverged Amazonian taxa. The poison frog genus Ameerega recently radiated throughout the Andes and Amazon (MRCA ~8.7 mya), with some taxa diverging as recently as the late Pliocene and early Pleistocene. Some species-level relationships remain poorly resolved, especially among recently diverged taxa. Here, I define ancestral populations and address the phylogenetic relationships among three recently diverged Peruvian Ameerega species (A. cainarachi, A. petersi, and A. smaragdina), using multiple species tree methods, including one that accounts for reticulate evolution. I complement species tree inference with assessments of behavioral divergence and niche overlap to better resolve species boundaries. I further explore the phylogeographic history of these species of Ameerega with demographic inference, considering evidence for population expansions. These analyses provide the basis to address speciation hypotheses in the Andean lowlands, including the refugial hypothesis and dispersal-vicariance hypothesis. I find support to synonymize A. smaragdina with A. petersi, and that divergent and convergent reticulation processes and historical range expansion impacted the A. petersi group’s speciation history. In addition, I use species distribution modeling (SDM) to infer the A. petersi group’s range dynamics since the mid-Pleistocene (785 kya). SDMs reveal periods of range expansion, contraction, and shifts, tracking climate fluctuations during the Pleistocene. In order to explicitly consider the relative roles of climate and geography in structuring genetic diversity at different time periods, I use a landscape genetics approach and consider 21 isolation-by-resistance hypotheses. These hypotheses include climatic resistance layers from five time periods in the Pleistocene, a stability layer, two geographic layers that reflect the two species’ natural history (distance-from-river and mid-elevation resistance), and composite layers that pair geographic and environmental layers. I find that climate stability and river proximity best explain gene flow. I find that phylogeographic, niche modeling, and landscape genetic evidence supports a dispersal-vicariance model of speciation in the A. petersi group.

The endemic New Zealand frog, Leiopelma hochstetteri, is characterized by variable numbers of mitotically-stable B chromosomes. In order to assess whether the B chromosomes had been derived from the autosome complement, B DNA was isolated and amplified by micromanipulation in conjunction with degenerate oligonucleotide-primed PCR. Southern hybridization patterns of B DNA probes to genomic DNA from males and females characterized by differing numbers of B's demonstrated that the B chromosomes were derived from the univalent W chromosome which is specific to females. The presence of homologous B specific sequences in B chromosomes from geographically-distinct populations show that only a single univalent W to B event had occurred. Furthermore, a plesiomorphic homology shows that the B chromosomes originated soon after the univalent W had been derived from the ancestral WZ/ZZ karyotype, which is still present in frogs from Great Barrier Island. Finally, sequence analysis of the probes reveals that B DNA is composed of repeat sequences, and has the ability to form stable hairpin structures in vivo. The molecular dynamics of these structures may reflect the inherent propensity to undergo rapid change in nucleotide sequence and chromosome structure.

A major goal of ecology and evolutionary biology is to explain patterns of species richness among clades. Differences in rates of net diversification (speciation minus extinction over time) may often explain these patterns, but the factors that drive variation in diversification rates remain uncertain. Three important candidates are climatic niche position (e.g., whether clades are primarily temperate or tropical), rates of climatic niche change among species within clades, and microhabitat (e.g., aquatic, terrestrial, arboreal). The first two factors have been tested separately in several studies, but the relative importance of all three is largely unknown. Here we explore the correlates of diversification among families of frogs, which collectively represent approximate to 88% of amphibian species. We assemble and analyze data on phylogeny, climate, and microhabitat for thousands of species. We find that the best-fitting phylogenetic multiple regression model includes all three types of variables: microhabitat, rates of climatic niche change, and climatic niche position. This model explains 67% of the variation in diversification rates among frog families, with arboreal microhabitat explaining approximate to 31%, niche rates approximate to 25%, and climatic niche position approximate to 11%. Surprisingly, we show that microhabitat can have a much stronger influence on diversification than climatic niche position or rates of climatic niche change.

Les signaux acoustiques utilisés dans la communication intra-spécifique, et cruciaux pour le succès reproducteur des individus, sont susceptibles d'être soumis à des pressions de sélection environnementales, et donc d'être adaptatifs. Les grenouilles vocalisant dans les torrents doivent faire face au bruit intense produit par le cours d'eau qui peut masquer leurs chants. Chez ces grenouilles, les vocalisations minimisant ce masquage ont donc pu être sélectionnées. La nature adaptative des chants des grenouilles torrenticoles a été examinée. La définition d'une guilde de grenouilles torrenticoles a été établie et une phylogénie moléculaire a été construite. Les changements de sites de reproduction et l'évolution des vocalisations chez ces grenouilles ont été pistés. Enfin, l'hypothèse d'adaptation acoustique (AAH) a été testée. Plusieurs types de chants ont évolué au sein des torrents, et l'AAH est supportée pour certaines caractéristiques dde chants et rejetée pour d'autres
Acoustic signals used in intra-specific communication and crucial for reproductive success may be under environmental selective pressures and are thus potientially adaptive. Anurans vocalizing near torrents have to cope with the loud noise produced buy the fast flowing waters, which may mask their calls. In these frogs, vocalizations minimizing masking by noise may thus have been selected. I investigated the presumptive adaptive nature of vocalizations in torrent dwelling frogs in the family Ranidae. I first defined a torrent dwelling frog guild and built a molecular pylogeny of the study group. I then used Ancestral State Reconstruction methods to track evolutionary changes in calling site preferences and vocalization characteristics in these frogs. Finally, I tested the Acoustic Adaptation Hypothesis (AAH) with comparative methods. Several kinds of advertisement calls evolved in torrents ranids and the AAH is supported for some vocalization characteristics and rejected for others

Evolutionary transitions between the two major predator avoidance strategies aposematism and crypsis are expected to be associated with changes in many important traits of animals. However, empirical studies on populations experiencing ongoing or recent transitions between these strategies are rare. This thesis investigates the co-evolution of traits among populations of the Strawberry poison frog D.pumilio in Bocas del Toro, Panama. I found that all investigated populations were genetically distinct but that colour and pattern did not correlate with genetic or geographic distance, which suggests that selection needs to be invoked to explain the observed variation. Based on the chromatic contrast between frog dorsal colour and the natural habitat substrates used by the frogs, the populations were defined as bright or dull coloured. I found that frogs from bright coloured populations were larger. This is expected if aposematism is enhanced by large signals while crypsis is enhanced by small size. Further, individuals from bright coloured populations had a coarser black dorsal pattern, which is expected if crypsis is impaired by a bold pattern. The importance of pattern coarseness was confirmed by an avian detection experiment showing that coarse patterned dark green prey were more easily detected than dark green prey without pattern or with fine pattern. I put forward the hypothesis that enhanced protection, gained by aposematism, may affect behaviours that influence dispersal and pairing patterns. Indeed, males from bright coloured populations displayed at more exposed sites and showed a tendency to be more explorative and aggressive. In summary, my results show that the bright and dull coloured populations most likely represent an aposematic and a cryptic strategy, respectively. Furthermore, I show that evolutionary changes between aposematism and crypsis can be associated with coevolution of both morphology and behaviour. I argue that this coevolution may increase the likelihood of both pre- and post-zygotic reproductive isolation. This is because greater phenotypic differences between populations increase the likelihood of selection against badly adapted migrants and hybrids with intermediate traits.

Understanding how migration, genetic drift, and natural selection interact to maintain the genetic and phenotypic variation we observe in natural populations is a central goal of population genetics. Amphibians provide excellent model organisms for investigating the interplay between these evolutionary forces because amphibians are generally characterized by limited dispersal abilities, high philopatry, and are obligately associated with the areas around suitable habitats (e.g. breeding ponds). Thus, on relatively small geographic scales, the relative effects of all of these evolutionary forces can be studied together. Here, we study the interaction of migration, genetic drift, natural selection, and historical process in the ornate chorus frog (Pseudacris ornata). We report the development and characterization of 10 polymorphic microsatellite genetic markers. Number of alleles per locus ranged from 2 to 21 averaging 9.2 and expected heterozygosities ranged from 0.10 to 0.97 averaging 0.52. However, in an analysis of two populations, three locus-by-population comparisons exhibited significant heterozygote deficiencies and indicated that null alleles may be present some loci. Furthermore, we characterized genetic structure and historical biogeographic patterns in P. ornata using these microsatellite markers along with mitochondrial DNA sequence data. Our data indicate that in these frogs, migration may play a large role in determining population structure as pairwise estimates of FST were relatively small ranging from 0.04 to 0.12 (global FST = 0.083). Additionally, we observed an overall pattern of isolation-by-distance in neutral genetic markers across the species range. Moreover, our data suggest that the Apalachicola River basin does not impede gene flow in P. ornata as it does in many vertebrate taxa. Interestingly, we identified significant genetic structure between populations separated by only 6 km. However, this fine scale genetic structure was only present in the more urbanized of two widespread sampling localities. Finally, in this study, we demonstrated that there was a significant correlation between the frequency of green frogs and latitude. There was a higher frequency of green frogs in southern samples and a lower frequency of green frogs in northern samples. However, when we interpreted this phenotypic cline in light of the overall pattern of isolation-by-distance, it was apparent that the neutral evolutionary forces of genetic drift and migration could explain the cline, and the invocation of natural selection was not necessary.
M.S.
Department of Biology
Sciences
Biology MS

Vertebrate genomes exhibit global methylation of cytosine residues where they occur in a cytosine-guanine dinucleotide (CpG) context and this epigenetic mark is generally thought to be repressive to transcription. Punctuating this pervasive DNA methylation landscape are short, contiguous regions of non-methylated DNA which are found at two thirds of mammalian gene promoters. These non-methylated regions exhibit CpG content close to expected levels as they escape the depletion of CpGs observed across the methylated fraction of the genome. The unique nucleotide properties of these CpG island (CGI) regions enable their identification by computational prediction in mammalian genomes. Owing to a lack of high-resolution genome-wide DNA methylation profiles in non-mammalian species, these CGI predictions have often been used as a proxy for non-methylated DNA in these organisms. In contrast to mammals, CGI predictions in cold-blooded vertebrates rarely coincide with gene promoters, leading to the belief that CGls are significantly divergent between vertebrate species, and that unique promoter-associated features may have been acquired during warmblooded vertebrate evolution. This thesis is primarily concerned with the location, establishment and biological function of non-methylated islands of DNA in vertebrate genomes. To experimentally determine genome-wide profiles of non-methylated DNA, a novel biochemical technique was established called biotinylated ZF-CxxC affinity purification (Bio-CAP), and development of this method is discussed in Chapter 3. Experimental analysis of non-methylated DNA profiles in this thesis initially addresses two main questions: (1) 'How does the non-methylated DNA landscape compare genome-wide for seven vertebrates considering distinct tissue types and developmental stages?' (2) 'How are vertebrate non-methylated regions of DNA defined and interpreted in the nuclear environment?' To address the first question, non-methylated DNA was profiled by Bio-CAP sequencing across the genomes of seven diverse vertebrate species, representing all major branch points of vertebrate evolution, and the results are discussed in Chapters 4 and S. Contrary to previously held dogma, experimentally determined nonmethylated islands of DNA (NMls) constitute an ancient epigenetic feature of vertebrate gene regulatory elements. However, despite having numerous high-resolution maps of vertebrate non-methylated DNA, the means by which NMls are identified and maintained in the nuclear environment remains poorly understood. To address the second question and identify features which determine the methylation state of DNA, exogenous DNA sequences were introduced into mouse embryonic stem (ES) c~.II~. Non-methylated DNA was profiled by Bio-CAP sequencing to investigate how different features, such as sequence-specific binding motifs, chromatin architecture and nucleotide composition of a given DNA sequence impact local DNA methylation patterns. Interestingly, the majority of exogenous promoters were appropriately non-methylated in mouse ES cells, germline and somatic cells suggesting that gene promoters have retained strong signals for the nonmethylated state across millions of years of evolution (discussed in Chapter 6). During mouse embryogenesis, genome-scale DNA demethylation and remethylation events occur to remodel the epigenetic landscape and loss of DNA methylation during this time leads to embryonic lethality. To investigate the biological function of non-methylated DNA, the third question addressed in this thesis is (3) 'What is the developmental importance of non-methylated islands of DNA during vertebrate embryogenesis?' To investigate this, members of the ZF-CxxC domain-containing family of chromatin modifiers were ablated in zebrafish embryos to perturb the chromatin landscape at NMls, and therefore interfere with their function during early development (Chapter 7). Early embryonic development and patterning was disrupted in knockdown embryos, suggesting that interpretation of non-methylated DNA and placement of chromatin modifications at NMls is essential for normal zebrafish embryogenesis. Together this work sheds light on the evolutionary origins of NMls, the mechanisms involved in the recognition and establishment of nonmethylated loci and provides an insight into the function of non-methylated DNA during early embryonic development.

Vietnam has the greatest biodiversity of any country in Indochina. This diversity may be due to its topographically complex nature, with hills and mountains, drained by several independent river systems, covering three quarters of its area. Topographic complexity has undoubtedly had profound effects on the flora and fauna of the region. Recent surveys have uncovered several cryptic species in what were previously considered single widespread species. These discoveries have led some researchers to propose that widespread forest species do not, in fact, exist in Southeast Asia. To test these hypotheses, I examined patterns of mitochondrial phylogeny in several groups of frogs, both at and below the species level. Additionally, these analyses helped clarify the otherwise chaotic picture of anuran taxonomy and systematics. The stream–tied waterfall frogs of the genera Amolops and Odorrana were examined, the monophyly of the ranid subfamily Amolopinae was rejected, and taxonomic adjustments were made. The phylogeny of the Vietnamese narrow–mouthed frogs of the genus Microhyla was recovered and the current taxonomy examined. Patterns of maternal dispersal and genetic differentiation in mitochondrial DNA were further examined within Microhyla heymonsi, revealing geographic structuring and the existence of two sympatric lineages. Lastly, frogs of the Polypedates leucomystax complex were examined and two major, largely sympatric lineages recovered. Within these groups, 11 separate mitochondrial lineages identified. These represented separate species on the basis of advertisement call and allozyme evidence. The relationship of genetic differentiation and river systems was also investigated and common patterns among the different groups were explored. Clear genetic breaks occurred across both the Red River and the Annamite Mountain range, though most common patterns were groupings of populations along river drainages. While several cryptic species were identified, widespread groups likely representing single species still exist, and a phylogenetic component to broad distribution were noted.

Classified in the Lissamphibia, modern amphibians are the only non-amniote tetrapods living today. They consist of three morphologically distinct groups: the tailless frogs and toads (Anura), the limbless caecilians (Gymnophiona), and the tailed salamanders and newts (Urodela). With 205 species, the caecilians are highly specialized worm-like forms that live a fossorial lifestyle, with a relatively narrow distribution in the tropic rainforests of South America, Africa and Asia (Duellman and Trueb, 1994; Amphibiaweb, 2015). Salamanders, with 683 species, are widely distributed in the North America, Asia and Europe, with a few plethodontids extending to Central and South America (Duellman and Trueb, 1994; Amphibiaweb, 2015). Frogs are the most diverse amphibian groups, with 6644 species distributed over all continents except Antarctica (Duellman and Trueb, 1994; Amphibiaweb, 2015). Both frogs and salamanders develop a wide array of lifestyles, ranging from terrestrial, aquatic, fossorial to aboreal lifestyles (Duellman and Trueb, 1994). During ontogeny, amphibian larvae usually undergo a drastic post-embryonic shift into an adult form, a term known as metamorphosis. In salamanders, another developmental pathway – neoteny – also occurs, in which the larval morphology is retained in sexually mature adults (Duellman and Trueb, 1994; Rose, 2003). Because of the diverse lifestyles and developmental pathways, frogs and salamanders are often used as model systems in many fields of biology (e.g., evo-devo). Over a century, but especially in the past two decades, a wealth of frog and salamander fossils has been discovered from the Mesozoic and Cenozoic of East Asia (e.g., Noble, 1924; Young, 1936; Borsuk-Bialynicka, 1978; Gao, 1986; Dong and Wang, 1998; Gao and Shubin, 2001, 2003, 2012; Gao and Wang, 2001; Gao and Chen, 2004; Wang and Rose, 2005; Wang and Evans, 2006b; Zhang et al., 2009; Chen et al., 2016; this study). Some of these fossils represent the earliest members of many crown clades, including the earliest crown salamanders from the Middle Jurassic (~165 Ma, Gao and Shubin, 2003), the earliest salamandroid from the Late Jurassic, the earliest sirenid from the Late Jurassic (this study), and the earliest spadefoot toads from the late Paleocence (Chen et al., 2016). Other fossils also bear important anatomical, temporal and geographical information in understanding their evolution. Unfortunately, the importance of many of these fossils remains obscure in a phylogenetic context. For example, an early-middle Oligocene Mongolian spadefoot toad Macropelobates osborni (Noble, 1924) was discovered outside the current distribution of spadefoot toads, yet its phylogenetic position and its implication on spadefoot toad biogeography remain not well understood. A major reason for the poor understanding of these fossils can be attributed to a trend of dichotomy between morphological and molecular phylogenies on amphibians. Whereas morphologists and paleontologists sometimes use a relatively small morphological dataset to reconstruct relationships (e.g., Gao and Shubin, 2012; Henrici, 2013), large-scale phylogenies are almost always conducted with molecular data with only living taxa (e.g., Roelants and Bossuyt, 2005; Pyron and Wiens, 2011). Very few studies on amphibian phylogeny have combined morphological and molecular data together, and even fewer also combined fossils. Because of this, the positions of many important fossils remains unclear, and the evolutionary scenarios inferred from only living species can sometimes be inconsistent with fossil evidence. In this thesis, I adopt a total-evidence approach to understand the evolution of amphibians, especially frogs and salamanders. I will incorporate information from fossils, morphology and molecules together to reconstruct the relationships. Compared with studies with each individual datasets, this approach incorporates all available data in a single analysis, with a goal to reach robust and congruent results that allow further discussions on character evolution and biogeographic reconstruction. The inclusion of fossils directly into the combined analysis provides the time dimension that is independent from molecular data (Norell, 1992). The anatomical combination of fossils can represent intermediate forms that help to solve the “long branch” problems caused by highly specialized modern taxa. The morphological dataset, despite its much smaller size with molecular data, is the only link between fossils and modern taxa. The inclusion of key morphological characters in both reconstructing phylogenetic hypotheses and examining character evolution provide consistent results that allow discussion on the homology/homoplasy of a certain character without ambiguity. The molecular sequence data provides overwhelmingly large data on modern taxa for phylogenetic reconstructions compared with morphological data, which helps to reach a robust hypothesis. Although fossils contain no molecular data, the inclusion of molecular sequence data into the combined analysis does have an effect on the positions of fossil taxa. By altering the relationship “framework” of modern taxa, the character optimization of fossils and other taxa of a combined analysis also varies compared with results of morphology-only analysis, thus changing the positions of fossils. In the following five chapters, I will describe a number of fossil amphibian species, reconstruct three combined phylogenies, and use the results for discussions on character evolution and biogeography. In Chapter 1 and Chapter 2, I focus on a frog clade called spadefoot toads (Anura: Pelobatoidea). In Chapter 1, I provide descriptions on three important fossil spadefoot toads from the Cenozoic of East Asia and North America: Macropelobates osborni from the early-middle Oligocene of Mongolia, Prospea holoserisca from the latest Paleocene of Mongolia, and Scaphiopus skinneri from the middle Oligocene of the United States. In Chapter 2, I conduct a combined phylogenetic analysis of archaeobatrachian frogs, and discuss the evolution of the bony spade and the historical biogeography of spadefoot toads based on the results of the phylogeny. In Chapter 3, I describe a new fossil frog from the Early Cretaceous of Inner Mongolia, China. The unique morphology of the new fossil is distinct from previous Early Cretaceous frogs from the Jehol Biota of China. Results of the combined analysis show that the new frog represents a basal member of the Pipanura. Comparisons between the Early Cretaceous frogs from China, Spain and Brazil show a high diversity of species coupled with a high degree of endemism during the Early Cretaceous. I discuss in the phylogenetic context how early frogs gradually reach their postcranial body plan with a shortened vertebral column, loss of ribs, and specialized pelvic regions. In Chapter 4, I provide a brief review of Mesozoic fossil salamanders from northern China, and describe a new fossil from the Late Jurassic of Liaoning Province, China. I conduct a combined phylogeny of higher-level relationships of salamanders. The new fossil, despite its general-looking appearance, represents a basal member of the highly specialized eel-like neotenic family Sirenidae on the cladogram. I discuss character evolutions in the Sirenidae, and how the neotenic developmental pathway evolved in early salamanders. In Chapter 5, I conduct a combined phylogenetic analysis of the salamander suborder Cryptobranchoidea, consisting of the neotenic giant salamanders (Cryptobranchidae) and the metamorphic Asiatic salamanders (Hynobiidae). The new morphological matrix includes new characters that were previously less sampled in the hynobranchial region. The monophyly of the Hynobiidae are confirmed by the new analysis, and four unequivocal synapomorphies are found for the clade. An S-DIVA biogeographic reconstruction is conducted to disscuss the distributional patterns of the Hynobiidae.

Vol. [2] comprises 6 reprints of published monographs in box folder; but numbered within the publications submitted listing (90 items), and within the 3 categories identified; at the beginning of vol. 1.
Includes bibliographical references.
2 v. (various pagings) :
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Comprises 90 contributions to the biology and systematics of frogs, with particular emphasis upon those concerning the fauna of Australia and New Guinea. Provides an understanding of the state of knowledge when the author commenced his studies; permitting the extent of his work, an the nature of its significance, to be evaluated.
Thesis (D.Sc.)--University of Adelaide, Dept. of Environmental Biology, 2002

Living organisms are under selection not only for one, but also for several inheritable characters at the same time. Well-sampled and well-supported phylogenies are necessary for the studies of character evolution and their history. The poison frogs (Dendrobatidae) are a well-known example of aposematism in anurans. They include ~270 species of Neotropical frogs with aposematic (toxic and conspicuous) and non-defended (palatable and cryptic) species. The origin of aposematism in poison frogs is puzzling, because of its predicted low probability of establishment due to the prey's increased conspicuousness. Previous studies suggested a single origin of toxicity and warning coloration. By expanding taxon sampling of the group, I reexamined the phylogenetic correlation between the origins of toxicity and warning coloration. I found four or five independent origins of aposematism; by using simulations, I rejected hypotheses of one, two, or three origins of aposematism (P < 0.002). I also found that diet specialization is linked with the evolution of aposematism and has evolved independently at least two times. Poison frogs are endemic to the Neotropic, which is one of the Earth's largest reservoir of biodiversity. I reconstructed the biogeography of the poison frog clade and rejected an Amazonian center-of-origin in favor of a model expanding over the Neotropics. I inferred 14 dispersals into and 18 out of Amazonia to adjacent regions; the Andes were the major source of dispersals into Amazonia. Significant percentage of dendrobatid diversity in Amazonia and Chocó resulted from repeated immigrations, with radiations at <10.0 million years ago. In contrast, the Andes, Venezuelan Highlands, and Guiana Shield have undergone extended in situ diversification at near constant rate since the Oligocene. Poison frogs have significant variation on their physiological characteristics. I measured resting and active metabolic rates of 54 species. I traced metabolic measurements along aposematism, diet specialization, molecular rates, and body mass. I found a synergistic and co-adapted functionality of active metabolic rates with all previous traits that is perhaps the consequence of the increase in complexity in most biological systems. My thesis has expanded the knowledge of the biology, phylogenetic history, and biogeography of the poison frogs.
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Sexually selected traits are among the most costly, complex, and conspicuous elements of the phenotype. In polygynous reproductive systems, they evolve under strong selection by females. Why females favor those traits, however, is an on-going debate. Here, I use túngara frogs as a model system to study the evolution of communication under sexual selection. The wealth of available information on the behavior, neurophysiology, and reproductive biology of túngara frogs make them an ideal system to understand the patterns of signal evolution and explore the processes that have shaped them. In chapter 1 and 2, I review the taxonomy of túngara frogs (Engystomops) from western Ecuador. I describe three new species including their external morphology and advertisement calls. In chapter 3, I explore the phylogenetic relationships of túngara frogs, testing the support for alternative relationships previously reported for this group. The new phylogeny provides the framework for the comparative analysis carried out in chapters 4 and 5. In chapter 4, I present new female preference and male advertisement call data to test the sensory exploitation hypothesis of sexual selection. Using ancestral character reconstruction, I found that female preferences for complex calls did not originated before the appearance of complex calls, as predicted by sensory exploitation. Instead, my results suggest that the origin of complex calls and their preference originated at similar times. Finally, in chapter 5, I analyze the macroevolutionary patterns of call variation in male túngara frogs. A generalized least squares model demonstrates that advertisement calls have a strong phylogenetic signal. Although most species in Engystomops have distinctive calls, they share a common acoustic structure with two components that evolve at different rates. I did not found evidence of greater call differentiation among sympatric species relative to allopatric species.

Sexual selection is responsible for a great diversity of elaborate male traits. A general female preference for males that have exaggerated traits drives this process, but the reasons females exhibit this preference are often unclear. Recent advances in understanding signal evolution have emerged from studies of receiver psychology that focus on how receivers perceive and process communication signals. I apply the perspective of receiver psychology to understand female preference for elaborate signals in túngara frogs (Physalaemus pustulosus). Male túngara frogs produce advertisement calls of variable complexity. Females exhibit a strong preference for complex to simple calls, but previous studies have not found consistent patterns of preference between calls of variable complexity. In my doctoral research, I investigate the function of variable complexity in túngara frogs. Specifically, I address the following questions: 1) Are calls of variable complexity especially relevant to females in certain contexts? Do males respond to female behavior by increasing their production of complex calls? 2) Does male to female proximity influence female response to call complexity? 3) Are females constrained by their perceptual biology in discriminating differences in call complexity? 4) Can females remember attractive males over silences between bouts of advertising? Is working memory for attractive males dependent upon signal complexity? And 5) Does signal memorability increase with signal complexity in a linear relationship? These studies provide several new perspectives to an understanding of female preference for elaborate signals. Phonotaxis experiments demonstrate that females use elicitation behaviors to influence male production of complex calls, that proximity influences female response to signal elaboration, that females are constrained by their perceptual biology in discriminating between complex calls, that memory can influence the evolution of signal complexity, and that memorability and signal complexity share a non-linear relationship.
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Flamboyant colors are widespread throughout the animal kingdom. While many of these traits arise through sexual selection, bright coloration can also evolve through natural selection. Many aposematic species, for example, use conspicuous warning coloration to communicate their noxiousness to predators. Recent research suggests these signals can also function in the context of mate choice. Studies of warning color evolution can therefore provide new insights into how the interplay of natural and sexual selection impact the trajectory of conspicuous signal evolution. For my dissertation, I investigated the potential for male-male competition to impact the warning color evolution of a species of poison frog. I focused my work on an exceptionally bright and toxic population of the strawberry poison frog (Oophaga pumilio) where males are brighter than females, a classic signature of sexual selection. In Chapter 1, I used theoretical models of predator and frog visual systems to determine which can see the variation in bright warning coloration within this population. I found that birds, the presumed major predator, likely cannot see this variation, indicating that sexual selection can work under the radar of predators in this species. In Chapter 2, I tested the aggressive responses of males using a two-way choice paradigm that manipulated the perceived brightness of stimulus males. I found that males directed more of their behaviors to bright stimulus frogs, and brighter focal frogs more readily approached stimuli and directed more of their attention to the brighter rival. In Chapter 3, I tested the outcomes of dyadic interactions between males of varying brightness and observed male reactions to simulated intruders in their territories. I found that brighter males initiated aggressive interactions with rivals more readily, and brightness asymmetries between males settled interactions in a way that is consistent with classic hypotheses about male sexual signals. In Chapter 4 I sought to describe physiological correlates of male warning color brightness. While male brightness did not co-vary with classic measures of body condition (circulating testosterone and skin carotenoids), it did correlate with toxins sequestered from the diet and thus appears to be a reliable signal of toxicity in this population.
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Circuits underlying motor patterns of closely related species provide an ideal framework in which to study how evolution shapes behavioral variation. Male African clawed frogs (Xenopus and Silurana) advertisement call to attract female mates and silence male rivals. Males of each species produce a unique vocal pattern that serves as a species-identifier. Xenopus laevis is the most well-studied species in terms of its vocal behavior and underlying anatomy and physiology. The clade that includes X. laevis, or X. laevis senso lato, also includes 3 other species that diverged ~8.5 million years ago. All 4 of these species produce advertisement calls that include fast trills – trains of fast rate (~60 Hz) sound pulses. However, their calls differ substantially between species in measures of trill duration and period. I examined the premotor circuit underlying vocal patterning in three of these species: X. laevis, X. petersii, and X. victorianus. I used extracellular recordings to find that a premotor nucleus, DTAM, which is part of the vocal central pattern generator, is the likely source of species-variation of vocal patterns. Species-specific trill duration and period are intrinsic to the region of the hindbrain that includes DTAM. Next, I used blind whole-cell patch recordings in DTAM of X. laevis and X. petersii to examine the cells that encode trill duration and period. I identified homologous populations of premotor vocal cells in both species that code for trill duration and period in a species-specific manner. Together, these results support an autonomous role of the DTAM circuit for generation of species variation in call duration and period.

A primary goal of population genetics is to identify the role of microevolutionary forces in producing observed patterns of molecular and phenotypic variation. I conducted four studies in the northern leopard frog, Rana pipiens, to determine just how mutation, migration, genetic drift, and selection influenced, genetic structure of mitochondrial DNA (mtDNA), nuclear DNA, and a single locus polymorphism that determines dorsal coloration. In the first study, I surveyed the literature concerning color and pattern polymorphisms in anurans. I conclude that anuran polymorphisms remain a rich but largely unexploited system for studying the evolution of phenotypic variation in nature. In the second study, I compared mitochondrial DNA variation from 35 populations distributed across the species' range. A phylogenetic analysis indicated R. pipiens is split into two deeply divergent mtDNA groups, a western group and an eastern group. Phylogeographic and demographic analyses indicated that although restricted gene flow with isolation by distance explained the majority of the processes influencing current genetic structure, population bottlenecks and expansions also played an important role. In the third study, I investigated mtDNA and microsatellite variation in Pacific Northwest populations of R. pipiens, where a recent range contraction had occurred. I found that peripheral populations had reduced levels of genetic variation compared to more interior populations. Moreover, I found that historic samples from peripheral population already had reduced levels of genetic variation. Therefore, low diversity in the remnant populations could not be ascribed to the recent range contraction. In the fourth study, I compared genetic structure from a suite of putatively neutral molecular markers with that derived from the color polymorphism locus. Genetic structure at the color locus, assessed both spatially and temporally, was indistinguishable from structure at neutral loci. This study exemplifies the importance of investigating for evidence of selective maintenance before studies attempt to measure the selective mechanisms maintaining a polymorphism. Overall, my research helps to elucidate how biogeographic and microevolutionary forces influence a wide-spread North American species, R. pipiens.
Graduation date: 2004