Phylogeography of Solomon Islands blossom bats reflects oceanic divides and Pleistocene connections

Abstract

Aim: Periodic lowering of sea levels and formation of land bridges can reshape phylogeographic patterns of insular biotas. Using archipelago-wide sampling, we aimed to test if phylogeography of an old-endemic bat lineage reflected Pleistocene land bridges. Location: Solomon Islands and Papua New Guinea. Taxon: Melonycteris and Nesonycteris bats (Pteropodidae). Methods: We sequenced genome-wide RADseq data for 49 specimens from 15 islands. We assessed phylogenetic relationships using maximum likelihood in RAxML and quartet-based methods in SVDquartets, population structure using Structure, and admixture using maximum likelihood methods in TreeMix. We tested for genetic and geographic distance correlations using distance-based redundancy analyses (dbRDA), identifying best-fit models using stepwise model selection. Results: Phylogenetic analyses identified five Nesonycteris clades corresponding to Greater Bukida, Guadalcanal, Makira, Malaita and New Georgia group. Makira samples were sister to remaining Nesonycteris. Structure identified four populations: New Ireland Melonycteris melanops; and Nesonycteris from Greater Bukida (including Guadalcanal); Malaita and Makira; and New Georgia group. Genetic backgrounds of Mono, Ngella and Guadalcanal separated from remaining Greater Bukida islands. Makira and Malaita separated into two populations. New Georgia group lacked structure, and genetic and geographic distances were not correlated. The best-fit geographic distance models for Nesonycteris and a Greater Bukida subset were least shore-to-shore distance; and Euclidean and least-cost distances respectively. Main Conclusions: Influences of modern and Pleistocene island isolation and connectivity were evident in the overall Phylogeography of Nesonycteris. The lack of structure or geographic distance correlations within the New Georgia group indicated all islands were interconnected during the Last Glacial Maximum or contemporary oceanic divides are ineffective barriers. Conversely, genetic divergence across Greater Bukida islands reflected land-bridge constrained dispersal. A Makira clade sister to all Nesonycteris possibly indicates an origin on Makira. Alternately it reflects Makira's long-isolated geographic status, as similar results exist for a range of taxa.