Phylogeographic structure and ecological niche modelling reveal signals of isolation and postglacial colonisation in the European stag beetle

Abstract

Lucanus cervus (L.), the stag beetle, is a saproxylic beetle species distributed widely across Europe. Throughout its distribution the species has exhibited pronounced declines and is widely considered threatened. Conservation efforts may be hindered by the lack of population genetic data and understanding of the spatial scale of population connectivity. To address this knowledge gap this research details the first broad scale phylogeographic study of L . cervus based on mitochondrial DNA (mtDNA) sequencing and microsatellite analysis of samples collected from 121 localities across Europe. Genetic data were complemented by palaeo-distribution models of spatial occupancy during the Last Glacial Maximum to strengthen inferences of refugial areas. A salient feature of the mtDNA was the identification of two lineages. Lineage I was widespread across Europe while lineage II was confined to Greece. Microsatellites supported the differentiation of the Greek samples and alongside palaeo-distribution models indicated this area was a glacial refuge. The genetic endemism of the Greek samples, and demographic results compatible with no signatures of spatial expansion likely reflects restricted dispersal into and out of the area. Lineage I exhibited a shallow star like phylogeny compatible with rapid population expansion across Europe. Demographic analysis indicated such expansions occurred after the Last Glacial Maximum. Nuclear diversity and hindcast species distribution models indicated a central Italian refuge for lineage I. Palaeo-distribution modelling results also suggested a western refuge in northern Iberia and south-west France. In conclusion the results provide evidence of glacial divergence in stag beetle while also suggesting high, at least on evolutionary timescales, gene flow across most of Europe. The data also provide a neutral genetic framework against which patterns of phenotypic variation may be assessed.

Supporting dataset and methods for body sizes and concentrations of chemical elements measured in elytra and abdomens of Stag Beetles Lucanus cervus

“…All the Stag Beetles were collected by researchers very familiar with the appearance of this species, so confusion with other species of large beetles can be ruled out. Stag Beetles from most of the populations examined here, formed the basis of a recent study on the genetic diversity of this species in Europe, and many of the individual beetles were from an existing collection [8] . In addition, although there are four other members of genus Lucanus in Europe – L. (Pseudolucanus) barbarossa, L. pontbrianti, L. tetraodon and L. ibericus – the materials used for this article were collected outside the geographical ranges of those species.…”

“…For the analysis we used intact abdomens ( n = 124) with dry internal organs and gut contents, and both elytra ( n = 271); other parts (legs) of the majority of these beetles were also used in the genetic study by Cox et al. [8] . The samples were dried and kept at room temperature until the chemical analysis.…”

Genetic structure of recently fragmented suburban populations of European stag beetle

“…Overijse holds the highest gene diversity and allelic richness of the three populations, though slightly lower levels than those found in surrounding areas of West Europe (Cox et al, 2019).…”

“…Population genetic studies of saproxylic insects have typically reported weak genetic structuring over larger geographical ranges than studied here (Komonen & Muller, 2018). Similarly, Cox et al (2019) reported low levels of genetic structure across European stag beetle. This weak genetic structure has often been interpreted as indicating that the species have better than thought dispersal abilities and/or that there exist enough connectivity corridors between populations.…”

“…Similarly, Cox et al. (2019) reported low levels of genetic structure across European stag beetle. This weak genetic structure has often been interpreted as indicating that the species have better than thought dispersal abilities and/or that there exist enough connectivity corridors between populations.…”