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Abstract

The extensive coastlines of South Africa and Namibia extends from the Atlantic to the Indian Ocean and encompass several major biogeographic provinces, each characterized by unique faunal and floral assemblages. Recent biogeographic studies have led to competing biogeographic models of the southern African coastline. This has stimulated phylogeographic work to determine whether the distribution of genetic diversity within coastal invertebrate species match the proposed biogeographic regions. The lack of congruence between studies and the discovery of cryptic diversity indicating the possible existence of cryptic species in coastal isopods in the region underscore the need for additional phylogeographic research in southern Africa, particularly for organisms that have been shown to both harbor cryptic diversity and to retain signatures of past geological and oceanographic processes in their phylogeographic patterns. Isopods in the genus Ligia exhibit several biological traits that suggest they may be informative on phylogeographic patterns. They inhabit patchy rocky beaches, are direct developers, avoid the open water, and exhibit several biological traits that severely constrain their dispersal potential (e.g. poor desiccation resistance). These traits are thought to lead to long term isolation of populations, the retention of geological and oceanographic signatures in phylogeographic patterns of Ligia, and the presence of cryptic lineages. In this study, we used mitochondrial and nuclear markers to characterize Ligia collected in 18 localities across Namibia to the KwaZulu-Natal region of South Africa. We report the presence of cryptic lineages within Ligia species in the region, as well as distributional patterns that differ from those reported from other coastal taxa, but that broadly matches a widely used biogeographic model for the region. 18 biogeographic models of the southern African coastline. This has stimulated phylogeographic 19 work to determine whether the distribution of genetic diversity within coastal invertebrate 20 species match the proposed biogeographic regions. The lack of congruence between studies and 21 the discovery of cryptic diversity indicating the possible existence of cryptic species in coastal 22 isopods in the region underscore the need for additional phylogeographic research in southern 23 Africa. This is particularly true for organisms shown to both harbor cryptic diversity and to 24 retain signatures of past geological and oceanographic processes in their phylogeographic 25 patterns. Isopods in the genus Ligia exhibit several biological traits that suggest they may be 26 informative on phylogeographic patterns. They inhabit patchy rocky beaches, are direct 27 developers, avoid the open water, and exhibit several biological traits that severely constrain 28 their dispersal potential (e.g. poor desiccation resistance). These traits are thought to lead to long 29 term isolation of populations, the retention of geological and oceanographic signatures in 30 phylogeographic patterns...