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

Date Published: April 25, 2019

Publisher: Public Library of Science

Author(s): Karen Cox, Niall McKeown, Gloria Antonini, Deborah Harvey, Emanuela Solano, An Van Breusegem, Arno Thomaes, Chung-Ping Lin.


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.

Partial Text

The stag beetle, Lucanus cervus L. (Coleoptera: Lucanidae) is distributed widely across Europe [1]. Past and current forest management practices, such as logging, wood harvesting, and removal of old trees and dead wood, have had detrimental effects on saproxylic biodiversity [2, 3]. In light of such declines the stag beetle is listed as “near threatened” in the European Red List [3] and has been protected by the Habitats Directive of the European Union since 1992 [4]. Conservation efforts may be hindered by a lack of information on the spatial scale at which populations may be connected on ecological and evolutionary timescales. Since dispersal distances in the species seem to range from a few hundred meters up to a maximum of five kilometres [5], distances between aggregates or populations cannot exceed these limits if sufficient gene flow is to be maintained within a metapopulation. Harvey et al. [1] reported that, since L. cervus shows an aggregated distribution, wood management may be critical for the species to counter local extinction. Furthermore, in species with presumed high levels of genetic structuring a significant loss of cryptic diversity is expected under changing conditions, such as climate change, when conservation policies do not incorporate these genetic differences [6, 7]. On a broader geographical scale the identification of intraspecific Evolutionarily Significant Units (ESUs), their evolutionary history and spatial distribution provide vital information to optimise conservation strategies which minimise genetic diversity loss at species level [8]. In addition to providing information for spatial management strategies, such phylogeographic approaches can also provide insight into how species have responded to historical climate change, and accordingly inform predictions of future climate change effects.

This study is the first phylogeographic investigation of stag beetle to incorporate both regional and fine scale sampling, and analysis of both mtDNA and nuclear genetic markers. mtDNA analysis revealed a clear spatial pattern wherein most of the European range was dominated by a single clade (lineage I). A second clade (lineage II) was found to be restricted to samples from Greece, with the differentiation of Greek samples also apparent at microsatellite loci. Microsatellite analysis further differentiated samples mainly from Central Italy that was part of lineage I on the basis of mtDNA. Nuclear data also subdivided Lineage I in two clusters. Apart from an increase in genetic clusters, differentiation among populations using nuclear markers was low to moderately high and was in agreement with the spatial structure results.