Abstract
We demonstrate the controversial origin of a biological species within an area of a few kilometres in the absence of physical barriers. We employed nuclear rRNA/mitochondrial and genome-wide SNP approaches to infer relationships of four species of net-winged beetles characterised by female neoteny. Three species are distributed at low elevations and a single population colonised a 40 km2 highland plateau and established distinct biological species despite incomplete genetic isolation. The speciation process is extreme in the highly localised spatial scale, due to the low dispersal power of neotenics, and provides clear support for a microallopatric model based on ecological conditions. In contrast with neutral evolution in a homogenous environment, as demonstrated by the genetic divergence and morphological similarity of two widely distributed low-mountain species, the environmental characteristics of the high-mountain plateau led to the origin of a species adapted to the local mimetic pattern and characterised by morphologically distinct genitalia. We conclude that the low dispersal propensity promotes neutral genetic differentiation in the first stage, but environmental characteristics play an important role the final phase of the speciation process. The unexpected speciation at such an extreme geographic scale points to the in situ origin and uniqueness of the mountain fauna.
Highlights
Regions with regard to tectonic history and position close to the equator[14,15]
We need to expand the spectrum of model groups to investigate the power of individual factors in the speciation process, but research using non-model organisms has suffered from a restricted development of appropriate molecular marker systems with the resolution to study the origins of reproductive isolation
We allowed up to 25% missing data to obtain the higher numbers of loci and single nucleotide polymorphisms (SNPs) in the dataset
Summary
Regions with regard to tectonic history and position close to the equator[14,15]. The tropical rainforests depend on climatic conditions which are generally unstable[16], but the monsoon dependant rainforests in South East Asia have long history starting with the origin of the monsoon system after the collision of India and Asia[17,18]. We present a clade of four closely related species of Scarelus net-winged beetles (Fig. 1) as a model system for diversification at an extremely small geographic scale. The phylogenetic analyses identified the deeply split clades of species occurring in each region, the geographically structured species distribution even within individual areas[23,24], and in all cases the ranges of neotenics are limited to long-term stable ecosystems[22]. Colour patterns adapted to syntopically occurring mimetic complexes have been hypothesised as factors starting the speciation process in net-winged beetles previously[26], with the aposematic signal shown to constitute a barrier to gene-flow in other animal groups[27]. We use large numbers of anonymous genetic markers (RAD) as well as mitochondrial and nuclear markers to ask whether it is possible to identify genetic structure within this system, including the origin of the highland species and to see if adaptation to local mimicry patterns and morphology fits with genetic divergence and plays a role in the diversification process
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