Academic literature on the topic 'Cospeciation'

The first phylogeny reconstructed solely for amblyceran genera is presented. This study, based on an extensive comparison of adult morphology and a rigorous cladistic analysis, considers generic exemplars from 4 families of amblyceran lice (Menoponidae, Boopiidae, Laemobothriidae and Ricinidae). The monophyly and evolutionary relationships of these families are strongly supported and there is good support for Menoponidae and Boopiidae as sister taxa. The relationships of the families are not concordant with the traditional hypothesis of a basal Menoponidae. The study identifies 4 supra-generic groups within the Menoponidae, which are discussed with reference to previous classifications and studies which have included amblyceran taxa. A preliminary assessment of host-parasite cospeciation is also provided. Whether a similar phylogeny would be produced from molecular data is investigated. The relationships of genera based on morphology are compared with phylogenies generated from the nuclear gene elongation factor 1a and the mitochondrial gene cytochrome oxidase I. Different methods of reconstruction used to assess their phylogeny and raw signal find that the data are largely incongruent, although there is little support for the topologies generated from the sequence data. The monophyly and relationships of families are compared between datasets and differences in rate heterogeneity between the data are also discussed. A first phylogeny for the genus Austromenopon (Amblycera: Menoponidae) and their close allies (based on the results of the morphological analysis) is reconstructed from molecular data using the mitochondrial genes COI and 12S rRNA. The molecular phylogenies obtained are generally incongruent, with most branch support located nearer the tips of the tree. No analysis recovered a monophyletic Austromenopon, although there is good support for a subset of the Austromenopon taxa, which repeatedly group together.

This work further elucidates processes involved in promoting and sustaining evolutionary diversification within the gall-inducing thrips that specialise on Australian Acacia. A phylogenetic approach was taken to determine modes of diversification available to these insects. The extension and revision of the gall-thrips phylogeny is central to the work and primarily focuses on cryptic populations of the Kladothrips rugosus and Kladothrips waterhousei species complexes. Parallel diversification, where the radiation of the K. rugosus and K. waterhousei lineages broadly mirror one another, offered a rare opportunity to test hypotheses of coevolution between gall-thrips and their Acacia hosts. In the absence of a reliable host Acacia phylogeny, indirect inference of insect/plant cospeciation can be arrived at as these two complexes share the same set of host species. The expectation is that if the phylogenies for the gall-thrips complexes show a significant level of concordance, then cospeciation between insect and host-plant can be inferred. Results indicate that the K. rugosus species complex comprise populations at species level. A significant level of phylogenetic concordance between the two species complexes is consistent with gall-thrips lineages tracking the diversification of their Acacia hosts. Given the less than strict form of insect/host cospeciation, factors impacting host diversification become important to gall-thrips diversification. Gall-thrips radiated over a period during the expansion of the Australian arid-zone. Cycles of host range expansion and fragmentation during the Quaternary could have played a major role in gall-thrips diversity. An interesting feature of resourse sharing amongst the K. rugosus and K. waterhousei complex members is the apparent absence of competitive exclusion between them. The persistence of this sympatry over millions of years is an unusual feature and merits further investigation.

Nematodes in the genus Steinernema (Nematoda: Steinernematidae) and their associated bacteria Xenorhabdus spp. (Gamma-Proteobacteria) are an emergent model of terrestrial animal-microbe symbiosis. Although interest in this association initially arose out of their potential as biocontrol agents against insect pests (Tanada and Kaya, 1993), this mutualistic partnership is currently viewed more broadly under the umbrella of basic sciences to inform ecology, evolution, biochemistry, molecular, among other disciplines (Burnell and Stock, 2000; Forst and Clarke, 2002).Despite advances in the discovery and field application of this nematode-bacterium partnership, and the growing popularity of this model system, relatively little has been published to uncover the evolutionary facets of their association. This study adds to the body of knowledge regarding nematode-bacteria symbiosis by 1) producing novel, multi-gene phylogenies for Steinernema and Xenorhabdus; 2) proposing a possible scenario for historical association in the form of a cophylogenetic hypothesis; 3) describing a newly discovered Steinernema species from France.

Tephritidae, commonly known as “fruit flies” is a large and complex family. Most, particularly the frugivorous species, are notorious pests. These include Ceratitis capitata (Wiedemann) (Mediterranean fruit fly), Bactrocera oleae (Rossi) (olive fly), Rhagoletis cerasi (L.) (cherry fly), Rhagoletis completa (Cresson) (walnut husk fly) and other exotic species. Other species, however, live on the flower heads of Asteraceae. Since the beginning of the last century, some authors (Petri 1909, Stammer, 1929) report the presence of symbiotic bacteria in flies belonging to the subfamily Tephritinae. Recently the olive fly symbiont has been described and designated as ‘Candidatus Erwinia dacicola’ by (Capuzzo et al., 2005). The present work aims to study the relationships between species of the family Tephritidae and their symbiotic bacteria. It is based upon three main studies, the first of which has already been published. 1.- The first study is the continuation of Alessia Piscedda PhD. thesis and deals with the identity of symbiotic bacteria, in 25 flies belonging to the subfamily Tephritinae (Diptera: Tephritidae), which were collected mainly in northern Italy. In order to detect and identify symbiotic bacteria, the first tract of the midgut of flies emerging from previously sterilized pupae, was plated on different microbiological media, LIVE/DAD BacLight staining was performed and biomolecular techniques were used. According to Stammer, (1929) the presence of non culturable symbiotic bacteria has been detected in species of genera Tephritis, Campiglossa, Trupanea, Acanthiophilus, Sphenella, and Oxyna. Symbiotic bacteria have also been found in other genera (Capitites, Dioxyna, Noeeta), which were not studied by Stammer. Sequencing 1000 bp of the small subunit rDNA gene from these symbiotic bacteria has indicated that they belong to the family Enterobacteriaceae and a novel candidate organism has been proposed for the symbiotic bacteria of the genus Tephritis, under the designation ‘Candidatus Stammerula tephritidis’. These analyses have been extended to other tribes of the subfamily Tephritinae (Xyphosiini, Myopitini e Terellini), using the same techniques reported above, but non symbiotic bacteria have been detected in these tribes, as suggested by Stammer (1929). 2.- The second study of the present work analyzes the phylogenetic relationships between tephritid flies of the subfamily Tephritinae. Two regions of the mitochondrial DNA, 16S rDNA e COI-tRNALeu-COII, were examined. The phylogenetic trees obtained from a Bayesian Inference and a Maximum-Likelihood analysis have suggested, as a rule, the presence of five monophyletic clusters corresponding to the fives tribes of this subfamily: Tephritini, Myopitini, Xyphosiini, Noeetini e Terellini. The phylogenetic tree obtained from the analysis of the COI-tRNALeu-COII showed more highly resolved trees and the internal nodes more highly supported than the phylogeny inferred from the 16S data set, and defined the relationships among the tribes better. Cophylogenetic analysis has been carried out, and the presence of congruence between hosts and symbionts, even if imperfect, has been suggested. The reconstructions obtained showed two principal events. The most important and probably earliest event corresponds with the acquisition of symbiotic bacteria by the common ancestor of the tribe. The presence of non-strict congruence is probably due to other events such as losses, duplications and hostswitchings. Indeed, these bacteria are extracellular symbionts and some opportunities for host-switching occur during the biological cycle of the fly. In the larval stadium, for instance, bacteria are located in the intestinal caeca (Petri 1909; Stammer, 1929), without the protection of the peritrophic membrane and are thus, in contact with free living bacteria present in the intestinal lumen. The contemporaneous presence of different species in the same host plant could also be an opportunity for host-switching. Considering all of these aspects, the presence of congruence, even if not strict, results particularly interesting and a physiological compatibility between host and symbiont seems to appear. 3.- In the third part of my PhD. thesis, the phylogenetic analysis of insects has been extended to Paleartic species belonging to other subfamilies (Trypetinae e Dacinae). It has been based on the analysis of two regions of the mitochondrial DNA: 16S e COI-tRNALeu-COII. The availability of sequences of the 16S rDNA of several species in GenBank, has allowed extending this data set. These phylogenetic analysis still in progress, confirms the traditional classification based on a morphological approach but suggests also interesting relationships among the tribes. I have also attempted to associate the phylogeny obtained with morphological symbiotic arrangements and biological characteristics. Interestingly, it was pointed out that all the species of the subfamily Tephritinae that overwinter as adults, present symbiotic bacteria in the first tract of the midgut. The presence of these bacteria seems to be essential for the overwintering adults. Indeed, while the diet of larval stages includes relatively rich substrates such as flower tissue and seeds, glyciphagous adults have access to less resources. Thus the presence of bacteria could be more critical for their survival than that in the earlier stages.
I tefritidi costituiscono un’importante famiglia di ditteri fitofagi molti dei quali rivestono un notevole interesse economico in quanto dannosi alle colture agrarie. Le specie di maggior importanza sono quelle che si riproducono a carico del frutto tra cui Ceratitis capitata (Wiedemann) (mosca mediterranea della frutta), Bactrocera oleae (Rossi) (olivo), Rhagoletis cerasi (L.) (ciliegia), Rhagoletis completa (Cresson) (noce) e altre specie esotiche. Altre specie invece, come quelle appartenenti alla sottofamiglia Tephritinae vivono soprattutto a carico dei capolini fiorali delle Composite (Asteraceae). Nella famiglia dei tefritidi sono presenti simbiosi batteriche note per alcune specie da quasi un secolo (Petri, 1909; Stammer, 1929). Recentemente, grazie alle tecniche biomolecolari, è stata identificata e sequenziata la specie batterica simbionte della mosca dell’olivo. Per tale simbionte, che è risultato appartenere alle Enterobacteriaceae è stato proposto il nome “Candidatus Erwinia dacicola”. Il presente lavoro ha come obiettivo l’approfondimento delle conoscenze sulle relazioni tra i ditteri tefritidi e i loro batteri simbionti e si articola in tre parti la prima delle quali è già stata oggetto di una pubblicazione. 1. In continuazione della tesi di dottorato della dottoressa Alessia Piscedda, l’identità dei batteri simbionti è stata studiata in 25 specie della sottofamiglia Tephritinae (Diptera: Tephritidae) provenienti da diverse zone del nordest d’Italia e da paesi limitrofi. Per queste specie si è provveduto alla coltivazione del contenuto del mesointestino di mosche provenienti da pupe preventivamente sterilizzate, all’osservazione di preparati microscopici di questo stesso tratto dell’intestino con LIVE/DAD BacLight e all’utilizzo di tecniche biomolecolari. In accordo con quanto riportato da Stammer (1929) le indagini hanno consentito di accertare la presenza di batteri simbionti non coltivabili in numerose specie dei generi: Tephritis, Campiglossa., Trupanea, Acanthiophilus, Sphenella, e Oxyna. Simbiosi batteriche sono state rinvenute anche in alcuni generi non considerati da Stammer (Capitites, Dioxyna, Noeeta). I batteri, di cui è stato sequenziato un frammento del 16S rDNA di oltre 1000 bp, risultano specifici per ogni specie di insetto ospite e, come il simbionte della mosca dell’olivo (Bactrocera oleae), appartengono tutti alla famiglia delle Enterobacteriaceae. I batteri simbionti riscontrati nelle specie del genere Tephritis per la loro affinità filogenetica sono stati designati come “Candidatus Stammerula tephritidis”. L’estensione dell’indagine ad altre tribù paleartiche della sottofamiglia Tephritinae (Xyphosiini, Myopitini e Terellini) con le medesime tecniche, sia tradizionali che biomolecolari, non ha evidenziato la presenza di batteri simbionti come suggerito da Stammer (1929). 2. Nella seconda parte del lavoro sono state studiate le relazioni filogenetiche tra i tefritidi, appartenenti alla sottofamiglia Tephritinae, analizzando due regioni del DNA mitocondriale, 16S rDNA e COI-LeutRNA-COII. Gli alberi filogenetici risultati da una analisi bayesiana e di maximum-likelihood hanno evidenziato la presenza di 5 cluster monofilettici e di regola altamente supportati corrispondenti alle 5 tribù della sottofamiglia Tephritinae: Tephritini, Myopitini, Xyphosiini, Noeetini e Terellini. La ricostruzione filogenetica ottenuta dal COI-tRNALeu-COII data set è risultata più risolta e supportata nei nodi interni rispetto a quella del 16S rDNA, contribuendo maggiormente a definire i rapporti di parentela tra le tribù. La disponibilità di una filogenesi dei batteri simbionti e dei loro insetti ospiti ha consentito inoltre lo studio della congruenza filogenetica. I diversi test di cofilogenesi addottati hanno evidenziato la presenza di una congruenza, seppur imperfetta, tra ospiti e simbionti. Dalle ricostruzioni si riconoscono due principali eventi di acquisizione il più importante e antico dei quali è quello avvenuto a carico dell’antenato comune della Tribù Tephritini. La causa di una non perfetta congruenza è da imputare all’esistenza di perdite, riacquisizioni e trasferimenti orizzontali. È importante ricordare che, essendo tali simbionti extracellulari, il ciclo biologico di questi insetti potenzialmente offre parecchie occasioni per trasferimenti orizzontali accidentali. Essendo nello stadio larvale i simbionti presenti nei cechi gastrici, parzialmente a contatto con il bolo alimentare, risulterebbero vulnerabili e sostituibili da altri batteri. Anche la frequentazione, da parte di specie diverse, delle stesse piante ospiti potrebbe essere occasione per trasferimenti orizzontali e sostituzioni. A fronte di queste molteplici possibilità la congruenza filogenetica riscontrata, seppure imperfetta, risulta a maggior ragione particolarmente interessante e va probabilmente spiegata con il coinvolgimento di altri fattori quali l’esistenza di una compatibilità fisiologica tra l’insetto ospite ed il battere. 3. Nella terza parte del lavoro l’analisi filogenetica degli insetti è stata ampliata a specie paleartiche appartenenti ad altre sottofamiglie (Trypetinae e Dacinae) sempre basandosi su due regione del DNA mitocondriale (16S e COI-LeutRNA-COII). La disponibilità in GenBank di sequenze del 16S di altre specie appartenenti a diverse regioni zoogeografiche ha consentito di allargare almeno per questo gene il data set. L’elaborazione dei dati, ancora parzialmente in corso, conferma in generale la tradizionale classificazione condotta su base morfologica ma offre anche spunti di discussione per eventuali riarrangiamenti di alcuni taxa. É stato realizzato anche un tentativo di affiancare alla ricostruzione filogenetica, oltre agli aspetti legati al ciclo biologico della specie, anche le diverse caratteristiche morfologiche degli organi adibiti ad ospitare i batteri simbionti nell’adulto. Risulta interessante notare come, tutte le specie paleartiche analizzate che svernano come adulti, ospitano batteri simbionti. Al contrario (tranne in un caso), tutte le specie che non svernano come adulto, sono risultate prive di batteri simbionti. Tali acquisizioni lasciano supporre che la presenza dei simbionti a livello del mesointestino, più che una opportunità per integrare la dieta larvale probabilmente già relativamente ricca, possano rappresentare, per quelle specie che hanno scelto di svernare allo stadio di adulto, una componente indispensabile.

碩士
東海大學
生命科學系
96
Symbiotic life style is a major adaptation of organisms that can increase their diversity. Many insects, especially hemipterans, are associated with the primary as well as secondary endosymbionts. The primary endosymbiont (bacteriome-associated) of insects provides their hosts with nutrition whereas the function of secondary endosymbionts is not clear. Here we used molecular phylogenetic analyses to describe the characteristics of bacterial endosymbionts in the red striped spittlebug, Okiscarta uchidae, and to investigate their phylogenetic placement within the eubacteria. We also evaluated relative evolutionary rates of endosymbionts and their free-living and pathogenic relatives. TEMs suggested that there were at least two types of endosymbionts in the bacteriomes, one of them are bacterial symbionts and the other are yeast-like organisms. Phylogenetic results suggested that there are four distinct symbiont lineages, three of them belonging to γ-proteobacteria and the other one clustered witnin the phylum Bacteroidetes. Results obtained from in situ hybridization suggested that five of the isolated endosymbionts were located inside the bacteriomes. In this study, we found that the evolutionary rates of identified symbionts were frequently the lowest among free-living, pathogenic and symbiont bacteria of insects, suggesting that they are most likely to be the “secondary” endosymbionts of O. uchidae.

The relative role of cospeciation and host switching in the phylogenetic history of ascomycete foliar symbionts is addressed in the orders Leotiales and Rhytismatales, fungi associated predominantly with Pinaceae (Coniferales). Emphasis is placed on comparing the evolution of the sister genera Pseudotsuga and Larix (Pinaceae) with that of the pathogenic and endophytic fungi in the genus Rhabdocline. Pinaceae evolved during the Mesozoic and divergence of all extant genera and several infrageneric lineages (esp. in Pinus) occurred prior to the Tertiary, with subsequent species radiations following climatic changes of the Eocene. The youngest generic pair to evolve from Pinaceae, Larix and Pseudotsuga, diverged near the Cretaceous-Tertiary boundary in East Asia or western North America. Rhabdocline is comprised of seven species and subspecies, six known from two species of Pseudotsuga and one, the asexual species Meria laricis, from three species of Larix. Evidence from host distributions and from nuclear ribosomal DNA suggests that Rhabdocline speciated in western North America and has been involved in several host switches. The ancestor of Meria laricis appears to have switched from P. menziesii to its current western North American hosts, L. occidentalis, L. lyallii, and very recently may have extended its host range to the European species, L. decidua. The occurrence of two lineages of R. weirii ssp. weirii on both North American species of Pseudotsuga is also probably the result of a recent host switch. Evidence of hostmediated divergence is seen in R. parkeri, which has different internal transcribed spacer types in the geographically isolated coastal and interior forms of P. menziesii. The wide host ranges of fungal genera closely related to Rhabdocline indicates that host switching is a prevalent pattern in the evolution of foliar symbionts in Leotiales and Rhytismatales. The prevalence of host switching in this group relative to other endosymbiotic organisms can probably be attributed to differences in dispersal mechanisms. Spores of foliar fungi are dispersed horizontally by wind and rain, rather than vertically from parent to offspring. Over evolutionary time, this provides more opportunities to shift to new hosts, particularly when the hosts are closely related and have overlapping distributions.
Graduation date: 1998

This chapter highlights the use of consensus techniques and other approaches for understanding historical biogeographic relationships and patterns of associations between parasites and their hosts. It deals primarily with analyses that are often placed under the heading of cospeciation or codivergence, situations in which hosts and their parasites appear to have intimate, long-standing historical connections and in which speciation in the host may result in speciation in the parasite. This type of association appears to obtain for many internal parasites and for certain external parasites, such as lice. In addition, or on the other hand, there is a whole class of host associations, such as those between herbivorous insects and their food plants, in which the relationship of the parasite and the host generally does not show such long-term fidelity but involves many apparent host shifts. These latter situations are often referred to under the more liberal heading of coevolution.

This chapter discusses how the methods for testing theories of cospeciation are not well suited to test coevolutionary theories of ecological association, adaptation, and more loosely constrained patterns of host association. It is, nonetheless, desirable to evaluate such theories in a rigorous historical context. Indeed, the ability to use the results of cladistic analyses to evaluate ecological and adaptational theories represents a truly powerful application of the method. This area of inquiry has become a standard approach in contemporary phylogenetic research, to the extent that one's chances of publishing a study in a high-profile journal may be diminished if the tree is not couched as a test of such a hypothesis. Within the cladistic framework, two interrelated approaches to evaluating adaptational hypotheses have been proposed: mapping and optimization. The chapter then describes methodological approaches that are best suited to extrinsic data, but which also apply to the optimization of heritable traits that were not part of an analysis. The rationale is based on the desire to provide an independent test of theories about the evolution or association of attributes within individual lineages when there is no straightforward way to produce a hierarchic scheme for those attributes.