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Marine Ecology Progress Series

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MEPS 614:111-123 (2019)  -  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. Mbongwa1, Cang Hui2, Andrea Pulfrich3, Sophie von der Heyden1,*

1Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa
2Department of Mathematical Sciences, University of Stellenbosch, and African Institute for Mathematical Sciences, Matieland 7602, South Africa
3Pisces Environmental Services (Pty) Ltd, PO Box 302, McGregor 6708, South Africa
*Corresponding author:

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 filling the knowledge gap on sandy beaches, we 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 9 locations encompassing the entire distribution range, and sequence data were generated for mtDNA cytochrome c oxidase subunit I (COI) and 16S. Results revealed high levels of population structuring between populations (ΦST = 0.11-0.96, p < 0.05), 2 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 (<80 km), 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.


KEY WORDS: Anthropogenic pressures · Marine isopod · Sandy beach ecosystems · Population differentiation · Evolutionary lineages · Conservation genetics · Population decline


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Cite this article as: Mbongwa NA, Hui C, Pulfrich A, von der Heyden S (2019) Every beach an island—deep population divergence and possible loss of genetic diversity in Tylos granulatus, a sandy shore isopod. Mar Ecol Prog Ser 614:111-123. https://doi.org/10.3354/meps12882

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