Evolution of New Zealand's Marine Caddisflies: A Phylogenetic and Phylogeographic Assessment of the Chathamiidae (Insecta: Trichoptera)

Abstract

The Chathamiidae are an interesting family of caddisflies, unusual as all of the five known species are believed to breed entirely within the marine intertidal, comprising one of very few known marine insect groups. Additionally the family approaches almost complete endemicity status in New Zealand, and may represent an ancient lineage representative of ancient vicariance from Gondwana. However one species, the common and widespread Philanisus plebeius is also known to have a disjunct population in New South Wales Australia, hypothesised to represent a recent anthropogenic dispersal. This thesis, using DNA information, examined the Chathamiidae at varying phylogenetic levels. Firstly the species Philanisus plebeius was incorporated into a thorough intraspecific phylogeography, including samples from both New Zealand and Australia. The population as a whole was genetically diverse, with the population divisible into two major haplogroups, each restricted to discrete geographic areas with no overlap being observed. One of these groups was restricted to just two localities in the central eastern North Island, whereas the remainder included most remaining samples from both Islands of New Zealand, and also Australia. All Australian samples were found to comprise a single haplotype, differing by a single base pair from the most common haplotype in New Zealand. It was decided that the Australian population therefore represents a recent dispersal event from New Zealand, although unless the Australian haplotype remains undiscovered in New Zealand the level of divergence found is not congruent with a human introduction. One sequence intermediate between the two major haplogroups was identified from a single haplotype from Tauranga. It seemed that much of the population of Philanisus plebeius has been affected by recent demographic expansion, likely due to the effects of the last glacial maximum (LGM). The five species of the Chathamiidae were then analysed in a phylogeny. It was found that the genus Chathamia was polyphyletic, with the species C. integripennis nested within the genus Philanisus. The remaining species, C. brevipennis from the Chatham Islands, was basal to all the remaining members of the family. A strict molecular clock found a recent Pleistocene age (roughly 0.5 Ma) for divergence of the Kermadec Island species Philanisus fasciatus, and a Pliocene-Pleistocene age (roughly 3 Ma) for the Chatham Island species Chathamia brevipennis. For a comparison with the species C. brevipennis, the other Chatham Island caddisfly taxa Oecetis chathamensis, and Hydrobiosis lindsayi were compared with New Zealand relatives; indicated to have late and early Pleistocene ages respectively. A short sequence of the gene COI was amplified for the species Philanisus mataua, however this was found to contain two sequences reflecting either heteroplasmy or sample contamination, inhibiting confident phylogenetic placement. Additionally a larval sample from Sydney was demonstrated to represent C. integripennis, recorded outside of Northern New Zealand for the first time. Finally the Chathamiidae was included in a higher level phylogeny with related families, and was show to comprise a monophyletic group, sister to the Australasian family of the Conoesucidae. A relaxed molecular clock estimated a Cretaceous (roughly 90 Ma) age for the Chathamiidae, congruent with a vicariant age in New Zealand.