| Summary: | Saproxylic beetles feed on decayed dead wood, representing some of the most ecologically important fauna in mature forests dominated by veteran trees, though this habitat is a shadow of its former self in Britain and Europe; confined to a handful of unconnected sites it remains nationally important for the diverse community assemblage it supports. Saproxylics can mediate and manipulate the fungal decay of wood, though this knowledge about the keystone status of saproxylic beetles is still poorly understood, despite some saproxylic beetles being some of the largest and most charismatic invertebrates in Europe. Habitats for saproxylics have been carved up over the course of human development, whilst forestry management practices encouraged the ‘tidying up’ of woodland by removing dead wood, leading to localised extinctions of saproxylics throughout Britain and Europe. Even in cases where extinction/threatened statuses are formally recognised servicing of conservation plans is constrained by limited understanding of their biodiversity. In this research the development and application of a suite of morphological, genetic, and ecological simulation approaches to characterise various components of saproxylic beetle diversity is described. This study focusses on three saproxylics: the Stag Beetle (Lucanus cervus), the Noble Chafer (Gnorimus nobilis), and the Bee Beetles (Trichius spp.). For Stag Beetles, the first microsatellites were developed and utilised along with mitochondrial (mtDNA) Cytochrome Oxidase 1 sequencing to perform a preliminary genetic analysis. mtDNA supported the predominance of a single clade across the species’ distribution which exhibited signatures of historical expansion/contractions linked to glacial/interglacial periods. Both mtDNA and microsatellites revealed a markedly lower level of genetic variation among UK samples compared to continental European counterparts and the implications for sustainability and remedial actions are discussed. For Gnorimus nobilis, a rot-hole specialist confined in England to traditional orchards, geometric and mtDNA sequence analysis characterised and confirmed differences between it and its relative, the Variable Chafer (G. variabilis), as well as supporting recognition of other proposed sub-species. A salient feature of the intraspecific genetic variation was the deep divergence between the Eastern and Western clades, indicating historical vicariance and limited post-glacial overlap between clades. For Trichius, analysis of three distinct species revealed three reciprocally monophyletic mtDNA clades. However, despite support for three distinct morphotypes, there was a high level of mtDNA/ morphological incongruence, i.e. multiple morphotypes were associated with a single clade. Nuclear DNA sequencing supported the hypothesis that the pattern has been generated by historical vicariance and introgression upon secondary contact. Species Distribution Modelling of multiple saproxylics (n=14) indicated that many species had similar glacial refugia: a northern refugium across France and Germany was predicted for many species. In addition, many species were predicted to find the Mediterranean region increasingly unsuitable under climate change simulations, but are also predicted to find suitable climates opening up toward the north-east of Europe. The project represents the first combined study of morphological taxonomy, phylogeography, population genetics and habitat modelling in rot-hole associated beetle species across Europe, and should help direct conservation efforts for these and other saproxylic beetles.
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