Exploring Phylogeographic Congruence in a Continental Island System.

Julia Goldberg,Steven A Trewick

doi:10.3390/insects2030369

Abstract

A prediction in phylogeographic studies is that patterns of lineage diversity and timing will be similar within the same landscape under the assumption that these lineages have responded to past environmental changes in comparable ways. Eight invertebrate taxa from four different orders were included in this study of mainland New Zealand and Chatham Islands lineages to explore outcomes of island colonization. These comprised two orthopteran genera, one an endemic forest-dwelling genus of cave weta (Rhaphidophoridae, Talitropsis) and the other a grasshopper (Acrididae, Phaulacridum) that inhabits open grassland; four genera of Coleoptera including carabid beetles (Mecodema), stag beetles (Geodorcus), weevils (Hadramphus) and clickbeetles (Amychus); the widespread earwig genus Anisolabis (Dermaptera) that is common on beaches in New Zealand and the Chatham Islands, and an endemic and widespread cockroach genus Celatoblatta (Blattodea). Mitochondrial DNA data were used to reconstruct phylogeographic hypotheses to compare among these taxa. Strikingly, despite a maximum age of the Chathams of ∼4 million years there is no concordance among these taxa, in the extent of genetic divergence and partitioning between Chatham and Mainland populations. Some Chatham lineages are represented by insular endemics and others by haplotypes shared with mainland populations. These diverse patterns suggest that combinations of intrinsic (taxon ecology) and extrinsic (extinction and dispersal) factors can result in apparently very different biogeographic outcomes.

Highlights

A null hypothesis in biogeography is that different taxon groups will show similar patterns of distribution and phylogeny if their evolution has responded to the same historic processes
Emergence of the Chatham Island archipelago from the southern ocean about 4 million years ago (Ma) might be expected to have yielded a set of Chatham Island endemic taxa that were divergent in terms of genetics and morphology, from neighboring New Zealand populations from which they were derived
Such results are in keeping with previous studies of taxa that incorporate New Zealand and Chatham Island sampling, where divergence estimates range from populations with identical cpDNA haplotypes in the fern Asplenium hookerianum [52], to 2% mtDNA sequence divergence in a skink Oligosoma nigriplantare nigriplantare [53], and plants with up to 6.4% sequence divergence [54]

Summary

Introduction

A null hypothesis in biogeography is that different taxon groups will show similar patterns of distribution and phylogeny if their evolution has responded to the same historic processes. Some biogeographers have used such a proposal as the basis of a putative test of the role of vicariance in biogeography, under the assumption that patterns associated with dispersal would not be coincident [1,2,3]. Early in the application of phylogeographic approaches it was expected that dispersal could be expected to yield congruent biogeographic patterns, where the taxa involved were responding to a common cause [4] and in many contexts the perceived distinction between vicariance and dispersal processes in biogeography is illusional [5]. On oceanic islands a general trend in the phylogeographic history of taxa colonizing successive islands as they emerged, has been revealed (e.g., [8,9]). Distinguishing between random effects and those linked to species traits is very difficult, especially because traits associated with dispersal might be selected against after colonization [10,12,13]

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Conclusion