Happy as a clam, despite genetic uniformity


Corbicula fluminea. photo courtesy of Noel M. Burkhead - U.S. Geological Survey

Corbicula fluminea, photo courtesy of Noel M. Burkhead – U.S. Geological Survey

Introduced populations of non-native species are often associated with low genetic diversity, as measured by neutral genetic loci, and, thus, considered a paradox (but see Roman and Darling 2007). The study by Lise-Marie Pigneur and colleagues documents an extreme example of this putatively paradoxical phenomenon in the invasive clam genus Corbicula. The authors document four, undiversified genetic lineages in Europe and the Americas, whereas the native range, in the northwest Pacific, is characterized by higher levels of genetic diversity. Yet, the relationship between genetic diversity and invasion success is not as straight-forward as it might seem.

The apparent importance of the flexibility of reproductive mode to the success of low diversity invasions suggests that there is much to learn regarding how evolutionary history and life history characteristics affect the invasiveness of species. (Roman and Darling 2007)

The mixed mating system exhibited in the native range of these Corbicula clams may hold an enticing clue as to the success of the invasive lineages. The dioecious sexual lineages are strictly diploid, whereas the hermaphroditic asexual, or more specifically androgenetic (i.e., male parthenogenesis), lineages can be diploid, triploid or tetraploid. But, interestingly, the unreduced spermatozoon from one androgenetic lineage can fertilize an egg of another androgenetic lineage. The resultant progeny exhibit the nuclear genome from one and the mitochondrial genome from another lineage, a phenomenon termed egg parasitism or mitochondrial capture (e.g., Hedtke et al. 2008, Pigneur et al. 2012). Thus, despite reduced genetic diversity, androgenesis in Corbicula clams may combine clonality with the ability of rare genetic material exchange.

Associated with other life history traits of Corbicula lineages, it might have been a determinant mechanism that contributed to the invasiveness of undiversified populations of these clams. (Pigneur et al. 2014)

The role of life history traits coupled with labile reproductive systems in invasion success and invasive histories warrants further attention, especially in aquatic and marine environments.
J Roman and JA Darling (2007) Paradox lost: genetic diversity and the success of aquatic invasions. TREE 22: 454-464; http://dx.doi.org/10.1016/j.tree.2007.07.002
SM Hedtke, M Glaubrecht, DM Hills (2008) Rare gene capture in predominantly adrogenetic species. PNAS 108: 9520-9524; doi:10.1073/pnas.1106742108
L-M Pigneur, SM Hedtke, E Etoundi, K Van Doninck (2012) Androgenesis: a review through the study of the selfish shellfish Corbicula spp. Heredity 108: 581-591; doi:10.1038/hdy.2012.3
L-M Pigneur, E Etoundi, DC Aldridge, J Marescaux, N Yasuda and K Van Doninck (2014) Genetic uniformity and long-distance clonal dispersal in the invasive and androgenetic Corbicula clams.  Molecular Ecology 23: 5102-5116; doi: 10.1111/mec.12912

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