Abstract
Sea cucumbers are increasingly exploited for human consumption and for their curative properties, and many wild populations are now depleted or in danger of extinction. While aquaculture is seen as an alternative to fisheries and as a mean to restore wild populations, more knowledge is needed on their reproductive strategies to render this practice efficient, notably for fissiparous holothurians, which are some of the mobile animals able of asexual reproduction by transverse fission. Little information is available on their population genetic diversity and structure. Here, the clonal structure of populations of the fissiparous sea cucumber Stichopus chloronotus has been investigated using nine microsatellite loci and a random sampling, at different spatial (intra‐reef and inter‐reef) and temporal (inter‐season and inter‐year) scales. Our findings highlight the importance of asexual reproduction in maintaining these populations, and the prevalence of the “initial seedling recruitment” strategy (ISR), leading to a high stability of clonal composition over seasons and years. It also seemed that clonal propagation was limited to the reef scale (<10 km) while reefs were connected by sexual dispersal. This is the first time that clonal structure in sea cucumbers has been studied at such a fine scale, with a specific sampling strategy. It provides key findings on the genetic diversity and structure of fissiparous sea cucumbers, which will be useful for the management of wild populations and aquaculture.
Highlights
Studying and understanding the way species reproduce are an academic matter, but are of practical importance for species management because of the consequences on population genetic diversity, connectivity, and dynamics
The importance of asexual reproduction to maintain populations of S. chloronotus and their weak clonal richness: While well-adapted to local conditions, this lack of genetic diversity may reduce their abilities to adapt to new environmental conditions
The high stability of clonal composition through time: The maintenance of the same predominant clones over seasons and years with weak inputs through sexual reproduction indicates the prevalence of the Initial Seedling Recruitment strategy in S. chloronotus
Summary
Studying and understanding the way species reproduce (sexually, asexually, or both) are an academic matter, but are of practical importance for species management because of the consequences on population genetic diversity, connectivity, and dynamics. In the Western Indian Ocean, it is notably fished in Mauritius, Madagascar, and Kenya, for exportation to the Asian market (Conand et al, 2007; Muthiga & Conand, 2014; Purcell, Hair, et al, 2012; Purcell, Samyn, et al, 2012) Aquaculture production of this species is under consideration, but requires a better understanding of the relative contribution of sexual and asexual reproductions in the maintenance and the genetic diversity of its populations to be efficient. We investigate the clonal diversity and composition in populations of the fissiparous holothurian S. chloronotus from Reunion Island (Western Indian Ocean), where fishing is forbidden and does not represent a selection pressure This was done through space and time and at a finer scale than previously achieved, to assess the relative roles of asexual and sexual reproductions in the maintenance of these populations and their genetic diversity. Performing a random sampling scheme, we studied the genetic structure (1) at different spatial scales, from the intra-reef to the inter-reef, to estimate clonal dispersal distances, and (2) at different temporal scales, from the inter-season (cold and warm seasons) to the inter-year (two years apart), to study clonal persistence through time
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