京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18105号 / 理博第3983号 / 新制||理||1574(附属図書館) / 30963 / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 朝倉 彰, 講師 宮崎 勝己, 教授 疋田 努 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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.

In this paper, we present a method and a corresponding tool called Tarzan for cophylogeny analysis of phylogenetic trees where the nodes are labelled with divergence timing information. The tool can be used for example to infer the common history of hosts and their parasites, of insect-plant relations or symbiotic relationships. Our method does the reconciliation analysis using an event-based concept where each event is assigned a cost and cost minimal solutions are sought. The events that are used by Tarzan are cospeciations, sortings, duplications, and (host) switches. Different from existing tools, Tarzan can handle more complex timing information of the phylogenetic trees for the analysis. This is important because several recent studies of cophylogenetic relationship have shown that timing information can be very important for the correct interpretation of results from cophylogenetic analysis. We present two examples (one host-parasite system and one insect-plant system) that show how divergence timing information can be integrated into reconciliation analysis and how this influences the results.

Host-parasite associations are born by cospeciations or by host switches. Feather lice have traditionally been used as model parasites for studying these events and underlying ecological factors. By now tens of analyses have addressed comparisons of host and parasite phylogenies to study cospeciations and host switches in lice, however, these analyses are strongly biased towards the temperate zone. Tropical environment could provide new insight into the origin of host-parasite interactions, because it is ecologically unique. This work aims to supplement the knowledge of host-parasite associations in lice using coevolution analyses of two feather lice genera and their passerine hosts in tropical rainforest in Cameroon. It shows that lice in the tropics cospeciate rarely. To assess whether host switches are non-random and occur preferentially between hosts with specific traits, this work also analyses relations between parasite genetic distances and hosts' trait similarities. No effect of host morphology and spatial distribution was found. However, genetic distances of the lice strongly correlate with genetic distances of their hosts.