RESUMO
Population genetic studies are efficient for inferring the invasion history based on a comparison of native and invasive populations, especially when conducted at species scale. An expected outcome in invasive populations is variability loss, and this is especially true in self-fertilizing species. We here focus on the self-fertilizing Pseudosuccinea columella, an invasive hermaphroditic freshwater snail that has greatly expanded its geographic distribution and that acts as intermediate host of Fasciola hepatica, the causative agent of human and veterinary fasciolosis. We evaluated the distribution of genetic diversity at the largest geographic scale analysed to date in this species by surveying 80 populations collected during 16 years from 14 countries, using eight nuclear microsatellites and two mitochondrial genes. As expected, populations from North America, the putative origin area, were strongly structured by selfing and history and harboured much more genetic variability than invasive populations. We found high selfing rates (when it was possible to infer it), none-to-low genetic variability and strong population structure in most invasive populations. Strikingly, we found a unique genotype/haplotype in populations from eight invaded regions sampled all over the world. Moreover, snail populations resistant to infection by the parasite are genetically distinct from susceptible populations. Our results are compatible with repeated introductions in South America and flash worldwide invasion by this unique genotype/haplotype. Our study illustrates the population genetic consequences of biological invasion in a highly selfing species at very large geographic scale. We discuss how such a large-scale flash invasion may affect the spread of fasciolosis.
Assuntos
Genética Populacional , Autofertilização , Caramujos/genética , Animais , Genes Mitocondriais , Genótipo , Haplótipos , Espécies Introduzidas , Repetições de Microssatélites , América do Norte , América do SulRESUMO
The delimitation of cryptic species within the genus Lymnaea, which are the main vectors of fascioliasis, remains a topic of controversy. An analysis of genetic variability based on 12 enzyme loci revealed different fixed alleles at 9 loci between two sympatric samples of Lymnaea viatrix at the type locality in Lima, Peru. The absence of heterozygotes within this locality indicates the presence of isolated populations or cryptic species within L. viatrix. Significant genetic differences were also found between these two L. viatrix samples from Lima and other populations of L. viatrix in South America and in addition to species such as L. truncatula, L. cubensis and L. columella. Moreover, the lack of variability within each Lymnaea samples studied indicates the existence of a high selfing rate in each species.
Assuntos
Lymnaea/genética , Animais , Vetores de Doenças , Fasciolíase/transmissão , Genótipo , América do Sul , Especificidade da EspécieRESUMO
A population of Pseudosuccinea columella was raised under laboratory conditions and its life tables were determined in isolated and paired snails. Isolated snails were significantly larger in shell size than paired snails from five weeks of age onward. Also, statistically significant differences were found for the number of eggs per mass per individual from week 5 to 9, isolated snails exhibiting the highest values. The intrinsic and finite rates of increase were greater in isolated than in paired snails. Either an inhibition of the reproductive output between individuals or the advantage of selfing may be the cause of the differences in this species, acting as a possible mechanism that increase the fitness of isolated snails.
Assuntos
Lymnaea/fisiologia , Animais , Tábuas de Vida , Reprodução/fisiologia , Isolamento SocialRESUMO
Life history traits of Fossaria cubensis were compared between isolated and paired snails after infection with three miracidia of Fasciola hepatica. Four experimental groups were tested: isolated-unexposed, paired-unexposed, isolated-infected, and paired-infected. A repeated-measures ANOVA showed statistically significant interactions among isolation, infection, and age effects for shell size, number of egg masses per snail, number of eggs per snail, and number of viable eggs per snail. Isolated-unexposed snails exhibited the higher values of these variables and those of survival and finite and intrinsic rates of natural increase. Infection stimulated shell growth during the prepatent period, but differences were present only in paired snails since isolation causes a similar effect. Reproduction, in terms of the number of egg masses per snail and the number of eggs per mass per snail, decreases in the presence of parasitic infection, whereas isolation stimulates it. These effects were observed from early stages of infection.
Assuntos
Fasciola hepatica , Fasciolíase/fisiopatologia , Caramujos/fisiologia , Caramujos/parasitologia , Isolamento Social , Animais , Reprodução , Caramujos/crescimento & desenvolvimentoRESUMO
The effect of exposing the lymnaeid snail Fossaria cubensis to the trematode Fasciola hepatica on the snail population's life-history traits was studied under laboratory conditions. Exposed individuals showed a lower survival rate than control snails, although from week 7 onward a slower decrease of this parameter in relation to the control group was observed. There were higher values of fecundity rate for the controls compared to the exposed group except during weeks 9, 10, 11 and 12, which was the time that followed the period when almost all of the infected snails died. Both the intrinsic and finite rates of natural increase were significantly higher for the control group, but exposed snails still attained a lower mean generation time. Age-specific trade-offs were found, mainly for the weekly increase in size versus the number of eggs per mass, the weekly increase in size versus the number of viable eggs per mass, the number of masses versus the hatching probability and the number of eggs versus the hatching probability. All these negative associations were significant for juveniles of both control and exposed snails and not for adults; however, exposed young individuals exhibited much higher values of the correlation coefficient than control animals.
Assuntos
Fasciola hepatica/fisiologia , Caramujos/parasitologia , Animais , Interações Hospedeiro-Parasita , Caramujos/fisiologiaRESUMO
In Cuba, several species of freshwater gastropods belonging to the genus Biomphalaria have been described according to morphological characters. However, the taxonomy of this group remains unclear and a number of synonyms are often cited in the literature. This is the case for B. havanensis whose taxonomical status is not well established. Multilocus enzyme electrophoresis at 18 loci was carried out on adult snails of B. havanensis from the type locality in Havana and from several other sites harbouring a morphologically slightly different form, referred to here as Biomphalaria sp. Another local distinct species B. helophila was used as an outgroup. Allelic distribution showed the presence of nine and 12 diagnostic loci between B. havanensis and Biomphalaria sp. and B. helophila, respectively. We detected eight fixed alleles between Biomphalaria sp. and B. helophila. The genetic divergence estimated by absolute genetic distances strongly supports the assumption that Biomphalaria sp. is quite different from the sympatric B. havanensis, morphologically the closest species.