The EU-protected slug geomalacus maculosus: an investigation into its phylogenetics, population densities in conifer plantations and its gut microbial community
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Geomalacus maculosus is an EU protected Lusitanian slug species which is only found in Ireland and Northern Iberia. It inhabits largely undisturbed habitats such as blanket bogs and forests where it feeds on lower plants growing on tree trunks or rocks. A phylogenetic study was carried out with a view to assess the genetic variability throughout the species’ range and to determine the origin of the Irish population. It was shown that the Irish G. maculosus population has a low genetic variability compared to the highly structured Iberian populations and a great genetic similarity to specimens from Northern Asturias and Cantabria was observed. A mark-recapture study using visible implant elastomers as markers was carried out for the duration of one year to assess the methodology and to investigate habitat requirements and population dynamics of G. maculosus and of the sympatric slug species Lehmannia marginata. Their population densities were found to be highly variable and a thick epiphyte cover of the trunk was identified as an important factor for both species. Capture success was heavily influenced by weather conditions and the employed markers were found to be durable and easy to use. The microbial diversity within the faeces of Irish G. maculosus specimens was explored with view to identifying habitat specific and core microbiome members. The influence of kinship, diet and environment on the composition of their faecal microbiome was investigated. The microbial communities were found to be highly variable indicating that their composition is heavily influenced by the bacteria present in the species’ microhabitat. Two core OTUs were found within all slugs which are likely beneficial symbionts of G. maculosus and we suggest that they could have been vertically transmitted from the egg.