Strong Population Genetic Structure for the Endangered Micro-Trapdoor Spider Moggridgea rainbowi (Mygalomorphae, Migidae) in Unburnt Habitat after Catastrophic Bushfires

Abstract

Catastrophic wildfires impacted large areas of western Kangaroo Island (KI), South Australia in 2019–2020, burning habitat for many species, including large proportions of the distributional range of the KI micro-trapdoor spider Moggridgea rainbowi, which led to it being listed as Endangered under Australia’s Environment Protection and Biodiversity Conservation Act (EPBC Act). In order to assess population genetic structure in M. rainbowi and detect diagnosable lineages and their distributional patterns across KI, 28 individuals were genotyped for 2495 loci, sampling from all known populations of the species. Population genetic and phylogenetic analyses of nuclear and mitochondrial sequence data provided strong support for three Evolutionarily Significant Units (ESUs) within M. rainbowi; two populations on eastern KI and a heavily fire-impacted western population. High levels of divergence and fixed allelic differences between 5 and 16% indicate a lack of gene flow between ESUs and long periods of isolation. Distributional patterns of these lineages match likely locations of isolation events caused by successive changes to sea level during the Quaternary (2.58 million years ago to present), which led to KI being intermittently connected to the mainland or separated into one or more islands. Our findings have strong conservation implications for M. rainbowi and highlight the importance of inclusion of population genetic structure to inform conservation strategies and to conserve lineage biodiversity at the species level and below.