Local endemism and within‐island diversification of shrews illustrate the importance of speciation in building Sundaland mammal diversity

Abstract

Island systems are important models for evolutionary biology because they provide convenient, discrete biogeographic units of study. Continental islands with a history of intermittent dry land connections confound the discrete definitions of islands and have led zoologists to predict (1) little differentiation of terrestrial organisms among continental shelf islands and (2) extinction, rather than speciation, to be the main cause of differences in community composition among islands. However, few continental island systems have been subjected to well-sampled phylogeographic studies, leaving these biogeographic assumptions of connectivity largely untested. We analyzed nine unlinked loci from shrews of the genus Crocidura from seven mountains and two lowland localities on the Sundaic continental shelf islands of Sumatra and Java. Coalescent species delimitation strongly supported all currently recognized Crocidura species from Sumatra (six species) and Java (five species), as well as one undescribed species endemic to each island. We find that nearly all species of Crocidura in the region are endemic to a single island and several of these have their closest relative(s) on the same island. Intra-island genetic divergence among allopatric, conspecific populations is often substantial, perhaps indicating species-level diversity remains underestimated. One recent (Pleistocene) speciation event generated two morphologically distinct, syntopic species on Java, further highlighting the prevalence of within-island diversification. Our results suggest that both between- and within-island speciation processes generated local endemism in Sundaland, supplementing the traditional view that the region's fauna is relictual and primarily governed by extinction. This article is protected by copyright. All rights reserved.

Coalescent species delimitation of a Sumatran parachuting frog

“…The two previous studies that included R. catamitus samples lacked sampling from the northern half of Sumatra; thus, little is known regarding the range‐wide genetic structure of this species. We hypothesise that R. catamitus is composed of several lineages across Sumatra, and may harbour more than one species, as has been observed in other Sumatran fauna (Demos, Giarla, Handika, & Rowe, ). The existence of a cryptic species on the island of Sumatra would add to growing evidence that within‐island diversification has contributed substantially to biodiversity on Sumatra (Demos et al., ).…”

“…We hypothesise that R. catamitus is composed of several lineages across Sumatra, and may harbour more than one species, as has been observed in other Sumatran fauna (Demos, Giarla, Handika, & Rowe, ). The existence of a cryptic species on the island of Sumatra would add to growing evidence that within‐island diversification has contributed substantially to biodiversity on Sumatra (Demos et al., ). In this study, we use mitochondrial DNA, genome‐wide single nucleotide polymorphisms (SNPs), and morphological data to investigate the following questions: (i) how many lineages compose R. catamitus ?…”

“…Although Pleistocene climate change did not drive diversification in this group, the gradual cooling of Sumatra during the Pliocene, and the glacial cycles of the Pleistocene likely reinforced the divergence between the northern lineage from the central and southern lineages. PrePleistocene diversification may be more common than previously thought on Sumatra and has been observed in several taxa (Demos et al., ; Harrison et al., ; Lim, Rahman, Lim, Moyle, & Sheldon, ; Moyle et al., ; Quek et al., ; Sheldon, Lim, & Moyle, ).…”

“…More population level studies are needed to identify divergent lineages across large land masses such as Sumatra, where in situ diversification may be common (de Bruyn et al., ; Lohman et al., ). Indeed, mounting evidence suggests that within‐island diversification has been an important process for generating biodiversity on Sumatra and surrounding land masses (de Bruyn et al., ; Demos et al., ; Esselstyn, Achmadi, Siler, & Evans, ).…”

Historical and recent impacts on genetic structure of an island rabbit

“…Previous genetic studies on island populations have mainly focused on genetic diversity and the phylogenetic relationships among islands (Hinten et al 2003, Salgueiro et al 2004, Kamada et al 2012, Kawai et al 2013. Recently, there have been several studies about the intra-island genetic structure of mammals, many of which have been conducted on large islands such as Tasmania, Australia (Jones et al 2004, Miller et al 2011; Java and Sumatra, Indonesia (Demos et al 2016); the South Island of New Zealand (O' Donnell et al 2016); Madagascar (Jansa et al 2008, Rakotoarisoa et al 2013; and Hokkaido, Japan (Kawai et al 2013). Studies focusing on the intra-island genetic structures of small islands (<500 km 2 ) have been rare.…”