Reduction in post-invasion genetic diversity in Crangonyx pseudogracilis (Amphipoda: Crustacea): a genetic bottleneck or the work of hitchhiking vertically transmitted microparasites?

Abstract

Parasites can strongly influence the success of biological invasions. However, as invading hosts and parasites may be derived from a small subset of genotypes in the native range, it is important to examine the distribution and invasion of parasites in the context of host population genetics. We demonstrate that invasive European populations of the North American Crangonyx pseudogracilis have experienced a reduction in post-invasion genetic diversity. We predict that vertically transmitted parasites may evade the stochastic processes and selective pressures leading to enemy release. As microsporidia may be vertically or horizontally transmitted, we compared the diversity of these microparasites in the native and invasive ranges of the host. In contrast to the reduction in host genetic diversity, we find no evidence for enemy release from microsporidian parasites in the invasive populations. Indeed, a single, vertically transmitted, microsporidian sex ratio distorter dominates the microsporidian parasite assemblage in the invasive range and appears to have invaded with the host. We propose that overproduction of female offspring as a result of parasitic sex ratio distortion may facilitate host invasion success. We also propose that a selective sweep resulting from the increase in infected individuals during the establishment may have contributed to the reduction in genetic diversity in invasive Crangonyx pseudogracilis populations.

Microsporidian disease of the invasive amphipod Dikerogammarus villosus and the potential for its transfer to local invertebrate fauna

“…Third, we have an indirect suggestion that vertical transmission is weak: the proportion of infected young individuals is lower than the proportion of infected individuals observed in large adults; in case of vertical infection as the main route of transmission, such a phenomenon should not have been observed. Nevertheless, even a small amount of vertical transmission could be helpful for parasite establishment in an invasive population, because it reduces parasite loss after the demographic bottleneck experienced by the host during the invasive process (Slothouber-Galbreath et al 2010). Cucumispora dikerogammari therefore benefits from both modes of transmission.…”

Sterile Surfaces of <i>Mnemiopsis leidyi</i> (Ctenophora) in Bacterial Suspension—A Key to Invasion Success?

“…There is precedence for this: Sánchez et al [30] described enhanced invasive activity of New World Artemia species given their lack of susceptibility to Mediterranean parasites. Diversity of parasitic microsporidia has also been observed to be reduced in invasive amphipods [31]. Based on this, we hypothesize that symbiont-host associations of an invasive host species routinely change in quantity and quality upon invading novel habitats, and that this specifically happens in one of the most invasive coastal marine animals: the lobate Comb Jelly, Mnemiopsis leidyi, native at the coasts of North-and South America.…”

Biology of a new xenoma-forming gonadotropic microsporidium in the invasive blotchfin dragonet Callionymus filamentosus

“…Thus, vertically transmitted alien parasites are naturally pre-adapted to evade selective pressures leading to enemy release (Slothouber-Galbreath et al 2010). Since microsporidia can transmit between hosts in both horizontal and vertical (transovarian) routes (Dunn & Smith 2001), it follows that they have an increased likelihood of being present during invasion of their natural host.…”

“…Since microsporidia can transmit between hosts in both horizontal and vertical (transovarian) routes (Dunn & Smith 2001), it follows that they have an increased likelihood of being present during invasion of their natural host. Indeed, they tend to be retained during invasion of their hosts: native and alien host populations of the freshwater gammarid amphipod Cragonyx pseudogracilis Bousfield, 1958 were found to harbor identical microsporidium species in both native and naturalized habitats (Slothouber-Galbreath et al 2010). Nevertheless, since successful establishment is dependent on a variety of factors, 'non-permissive' conditions to a given parasite may persist for an extended period while its host establishes a 'parasitefree' population.…”