Phylogeographic patterns of HawaiianMegalagriondamselflies (Odonata: Coenagrionidae) correlate with Pleistocene island boundaries

Abstract

The Pleistocene geological history of the Hawaiian Islands is becoming well understood. Numerous predictions about the influence of this history on the genetic diversity of Hawaiian organisms have been made, including the idea that changing sea levels would lead to the genetic differentiation of populations isolated on individual volcanoes during high sea stands. Here, we analyse DNA sequence data from two closely related, endemic Hawaiian damselfly species in order to test these predictions, and generate novel insights into the effects of Pleistocene glaciation and climate change on island organisms. Megalagrion xanthomelas and Megalagrion pacificum are currently restricted to five islands, including three islands of the Maui Nui super-island complex (Molokai, Lanai, and Maui) that were connected during periods of Pleistocene glaciation, and Hawaii island, which has never been subdivided. Maui Nui and Hawaii are effectively a controlled, natural experiment on the genetic effects of Pleistocene sea level change. We confirm well-defined morphological species boundaries using data from the nuclear EF-1alpha gene and show that the species are reciprocally monophyletic. We perform phylogeographic analyses of 663 base pairs (bp) of cytochrome oxidase subunit II (COII) gene sequence data from 157 individuals representing 25 populations. Our results point to the importance of Pleistocene land bridges and historical island habitat availability in maintaining inter-island gene flow. We also propose that repeated bottlenecks on Maui Nui caused by sea level change and restricted habitat availability are likely responsible for low genetic diversity there. An island analogue to northern genetic purity and southern diversity is proposed, whereby islands with little suitable habitat exhibit genetic purity while islands with more exhibit genetic diversity.

Delimiting species boundaries for endangered Canary Island grasshoppers based on DNA sequence data

“…The two islands are only 8.7 km apart, with La Graciosa islet in between (although it is remarkable that Pamphagidae are absent in the latter). Pleistocene land bridges and historical habitat availability have been recognized as major factors in Hawaiian inter-island gene flow in Megalagrion damselflies (Jordan et al 2005). In the Canaries, the eastern islands of Fuerteventura, Lanzarote and all nearby islets (including Montañ a Clara and Lobos) were connected by land bridges due to sea level oscillation during Pleistocene glaciations.…”

Phylogenetics of the Antopocerus-Modified Tarsus Clade of Hawaiian Drosophila: Diversification across the Hawaiian Islands

“…The change in the rate of speciation indicates that something in the environment or biology of the lineage changed. Based on previous studies on Hawaiian Drosophila , we predict three factors may have driven this diversification: (1) The hirsute tarsus subgroup may have expanded their host range to exploit a previously unused resources that allowed them to adaptively radiate across the Hawaiian Islands; (2) novel secondary sexual characters provide new substrates for sexual selection to drive divergence; (3) around the time the hirsute tarsus clade started to diversify there was an increase in available landscape – the current high islands were forming and increased topographic diversity has been shown to increase biodiversity in other Hawaiian lineages [4], [81]. This may be due to the availability of open niches reducing the extinction rate or an increased speciation rate as new niches become available.…”

A geographic cline induced by negative frequency-dependent selection

“…Some of these clines appear to be difficult to explain by the effects of gene flow, since gene flow is highly effective at relatively small scales in these species [21,22] (but see [23-26]). Instead, "balancing selection," which maintains genetic variation within a population, may be a plausible explanation for the geographic-scale clines to be established and maintained [6].…”