MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12882

Every beach an island – deep population divergence and possible loss of genetic diversity in Tylos granulatus, a sandy shore isopod

Nozibusiso A. Mbongwa, Cang Hui, Andrea Pulfrich, Sophie von der Heyden*

*Email: svdh@sun.ac.za

ABSTRACT: Biogeographic and phylogeographic patterns of sandy beach species are poorly understood, although these ecosystems are heavily impacted by anthropogenic pressures and are of elevated conservation concern. To contribute towards plugging the sandy beach knowledge gap, this study made use of phylogeographic approaches to determine levels of genetic structuring and diversity for Tylos granulatus, a large isopod with direct development distributed in South Africa and Namibia. Individuals (n = 214) were sampled from nine locations encompassing the entire distribution range and sequence data generated for mtDNA COI and 16S. Results revealed high levels of populations structuring between populations (ΦST = 0.11 – 0.96. P <0.05), two deeply divergent lineages of T. granulatus and a new phylogeographic break in southern Africa. Northern populations are genetically more diverse suggesting more stable evolutionary history compared to those in the south. Importantly, the patterns of divergence suggest unique evolutionary signals over short spatial scales (<80km), with nearly all T. granulatus populations effectively isolated from each other. This, in combination with increasing anthropogenic disturbance throughout their range, leaves this species extremely vulnerable to local and potentially, regional loss and extinction of genetic diversity. We suggest that T. granulatus serves as a valuable bioindicator, which if recognised for protection, will broadly capture biological and evolutionary patterns of other sandy beach macrofauna in the region. Our work adds to a growing field of sandy beach science and contributes towards a better understanding of the significance, vulnerability and complexity of sandy beach ecosystems for conservation and management aims.