Genetic and morphological variation in four populations of the surf clam Donax serra (Röding) from southern African sandy beaches

Abstract

The surf clam Donax serra (Bivalvia, Donacidae) dominates sandy-beach communities of two southern African biogeographical regions, a cold (Benguela current) and warm province (Agulhas current). Morphometric and behavioural differences led to a controversial discussion of whether or not populations from the two provinces belong to the same species. Shell size measurements confirmed morphological differences: clams from the cold province were significantly rounder, flatter and less wedge-shaped than clams from the warm province. In this study a genetic approach was used to relate phenotypic differences to genetic variability of four populations of D. serra separated by up to 2500 km of shoreline. Genetic analysis of 22 protein-coding loci was carried out by starch-gel electrophoresis. Populations studied are conspecific (genetic distances range from 0.003 to 0.044) and possess genetic variation (alleles per locus: 1.73-1.91; mean heterozygosity: 18-22%; percentage polymorphism: 45.5-59.1%) in the range of most other marine bivalves, which allows for potential adaptation to environmental changes. Wright's fixation indices show little to moderate genetic divergence among the subpopulations relative to the limiting amount under complete fixation (F ST = 0.016-0.089), moderate divergence of individuals relative to the total population (F IS = 0.265-0.452), and comparably high divergence of individuals relative to the compound population (F IT = 0.300-0.473). The effective number of individuals exchanged between populations in each generation is high enough (1. 44-8.65) to counteract genetic drift. We propose that the observed differences represent phenotypic plasticity enabling this species to inhabit * Corresponding author.

Patterns, processes and regulatory mechanisms in sandy beach macrofauna: a multi-scale analysis

“…Phenotypic plasticity and genetic stasis may be characteristic of sandy beach species. Soares et al (1998Soares et al ( , 1999 and Laudien et al (2003) showed no large scale genetic differentiation in the whelk Bullia digitalis (aplanktonic larval phase) and the surf clam Donax serra (planktonic larval phase) in South Africa. Both studies ascribed this to a high degree of plasticity in their behaviour, ecophysiology and morphology, which allowed them to rapidly adapt to environmental changes.…”

Oceanic circulation, local upwelling and palaeoclimatic changes linked to the phylogeography of the Cape sea urchin Parechinus angulosus

“…We propose that, apart from the direction of oceanic currents, the majority of the fine-scale structure seen among sampling sites is likely attributed to local upwelling cells (possibly also coupled to larval behav-iour; see Ross et al 2009 and references therein), and this could be further affected by the periodic formation of extensive coastal dune fields in the region (Roberts et al 2011). In the Namaqua Province, where several strong upwelling cells are present (Shannon 1985, Laudien et al 2003, Parechinus angulosus shows strong population differentiation (Table 2 & Fig. 4) while seasonal upwelling along the Agulhas Province is more wind-dependent and not as intense, providing a more permeable barrier to larval dispersal and thus less structure among sampling sites (Shannon & Nelson 1996).…”

“…The western shoreline known as the cool-temperate Namaqua Province (Lüderitz, Namibia to Cape Point, South Africa) has typically more mixed rocky and sandy habitats, with the oceanic circulation in this region dominated by the northward flowing ~12°C Ben guela Current ( Fig. 1; Griffiths et al 2010) and several strong upwelling cells (Shannon 1985, Laudien at al. 2003.…”

Population structure, growth and production of the surf clam Donax serra (Bivalvia, Donacidae) on two Namibian sandy beaches

“…the reproductive biology (Laudien, Brey, & Arntz, 2001). Growth rates and population structure were studied elsewhere in southern Africa (Donn, 1986;Schoeman, 1994;de Villiers, 1975), but these results cannot simply be transferred to Namibian populations, since it was reported that populations from the southeast and West Coast of southern Africa differ in behaviour and morphometrics (Donn, 1990;Laudien, Flint, van der Bank, & Brey, 2003;Soares, Callahan, & de Ruyck, 1998). Further, genetic differentiation exists between Namibian subpopulations (Laudien et al, 2003).…”