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Maaria Kankare 2004: Phylogeny and host associations of Cotesia parasitoids attacking checkerspot butterflies. PhD-Thesis.

The genus Cotesia (Hymenoptera: Braconidae) is a large group (~1500-2000 species wordwide) of primary parasitoids entirely associated with Lepidopteran hosts. The purpose of this thesis was to study the evolutionary relationships and host associations among the Cotesia parasitizing Melitaeini butterflies at different spatial scales. First, a molecular phylogeny of Cotesia was constructed using mtDNA sequence and microsatellite data with material reared from a large number of populations of several host species in Europe, Asia, and North America. The results strongly suggested the presence of several previously unrecognized, cryptic species of Cotesia, which tend to be entirely restricted to just one host species.

Second, the ecological and genetic structure of the Melitaeini-Cotesia community in Catalonia, northern Spain, was studied within a relatively small geographical area that should pose little physical barriers to gene flow. This study revealed the presence of seven biologically distinct species of Cotesia based on mtDNA sequence data, microsatellite data, and behavioural experiments. In particular, two nominal Cotesia species, Cotesia melitaearum agg. and C. acuminata agg., were each represented by a series of cryptic species with narrow host ranges.

Third, the pattern of genetic variation and evolutionary divergence in C. melitaearum agg. was studied in a greater detail. Mitochondrial DNA haplotypes of wasps reared from M. cinxia and E. aurinia showed a complex geographic pattern presumably reflecting long-term history. In contrast, the microsatellite data yielded two hostassociated clades, each including populations across Europe and suggesting that currently there is no gene flow between the parasitoid populations attacking these two host species. The results of this study supported the previous conclusions that checkerspot-associated Cotesia include many previously unrecognized cryptic species, and that the degree of genetic differentiation among the host-associated parasitoid taxa varies with the phylogenetic relatedness of the hosts.

Finally, at the smallest spatial scale the spatial genetic structure of C. melitaearum agg. was compared with that of Hyposoter horticola (Ichneumonidae: Campopleginae), another primary parasitoid species attacking the host species M. cinxia in the Åland Islands in Finland. Analysis of their genetic population structures revealed a distinct spatial pattern in C. melitaearum agg. but a very weak pattern in H. horticola. The results were consistent with expectations based on the biology of these two species. The population sizes are much greater and the dispersal range is much longer in H. horticola than in C. melitaearum agg.

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