Contrasting temporal dynamics and spatial patterns of population genetic structure correlate with differences in demography and habitat between two closely-related African freshwater snails

Abstract

The relationship between habitat stability, demography, and population genetic structure was explored by comparing temporal microsatellite variability spanning a decade in two closely-related hermaphroditic freshwater snails from Cameroon, Bulinus forskalii and Bulinus camerunensis . Although both species show similar levels of preferential selfing, microsatellite analysis revealed significantly greater allelic richness and gene diversity in populations of the highly endemic B. camerunensis compared to those of the geographically-widespread B. forskalii . Additionally, B. camerunensis populations showed significantly lower spatial genetic differentiation, higher dispersal rates, and greater temporal stability compared to B. forskalii populations over a similar spatial scale. This suggests that a more stable demography and greater gene flow account for the elevated genetic diversity observed in this geographicallyrestricted snail. This contrasts sharply with a metapopulation model (which includes extinction/contraction, recolonization/expansion, and passive dispersal) invoked to account for population structuring in B. forskalii . As intermediate hosts for medically important schistosome parasites, these findings have ramifications for determining the scale at which local adaptation may occur in the coevolution of these snails and their parasites.

Large-scale and small-scale population genetic structure of the medically important gastropod species Bulinus truncatus (Gastropoda, Heterobranchia)

“…In this study we found an excess of homozygotes and low levels of genetic diversity in all populations, which is consistent with previous studies on highly selfing freshwater snails (e.g. [ 23 , 24 , 65 – 67 , 69 , 70 ]). However, variable inbreeding coefficients between geographic locations have been observed in our study (e.g.…”

“…The genetic differentiation between the two populations from Egypt was low (0.022, not significant), and this was also true between three of the Senegalese populations (Sen_DIAM, Sen_MBO and Sen_NDO; F st 0.140–0.256, significant difference), indicating relatively high amounts of gene flow on a regional scale of 100 km (cf. Gow et al [ 23 , 24 ] in Cameroonian B. truncatus populations). In Senegal, the low differentiation might also be a relic of the Diama dam construction (see below) that was followed by a rapid expansion of snail populations, leading to highly inbred and genetically similar snail populations in the lower valley of the SRB, as was found for Biomphalaria pfeifferi in the same area [ 60 ].…”

“…Secondly, gastropods disperse over large distances on the feet and feathers of birds [63,64] or through humans [61]. The combination of these phenomena can lead to the biotic homogenisation of snail populations over large distances [23,61,64,65]. On the contrary, genetic differentiation on very small scales can also occur due to genetic drift.…”

“…Little is known about the population genetic structure of B. truncatus and the role of snail genetics in determining parasite susceptibility [21][22][23][24][25]. Furthermore, a reference genome has only recently become available for Biomphalaria glabrata (Say, 1818) [26] but remains absent for other intermediate host species.…”

Spatio-temporal population genetic structure, relative to demographic and ecological characteristics, in the freshwater snail Biomphalaria pfeifferi in Man, western Côte d’Ivoire

“…Some populations are however more closely related, and one remains somewhat apart. On the whole, all the results on population genetic structure are consistent with a system working as a metapopulation from a demographical point of view, with frequent extinction and colonization events, as observed in previous work conducted in this species (Charbonnel et al 2002a;Gow et al 2007;Campbell et al 2010;Mintsa Nguema et al 2013). However, the spatial and temporal differentiation, even if strong considering the spatial scale at which the study was conducted and affected by low effective population size, is maintained below that expected under fixation of alleles in all populations / loci by migration.…”