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1.
J Evol Biol ; 28(12): 2337-48, 2015 12.
Artigo em Inglês | MEDLINE | ID: mdl-26356354

RESUMO

Parthenogenesis (reproduction through unfertilized eggs) encompasses a variety of reproduction modes with (automixis) or without (apomixis) meiosis. Different modes of automixis have very different genetic and evolutionary consequences but can be particularly difficult to tease apart. In this study, we propose a new method to discriminate different types of automixis from population-level genetic data. We apply this method to diploid Artemia parthenogenetica, a crustacean whose reproductive mode remains controversial despite a century of intensive cytogenetic observations. We focus on A. parthenogenetica from two western Mediterranean populations. We show that they are diploid and that markers remain heterozygous in cultures maintained up to ~36 generations in the laboratory. Moreover, parallel patterns of population-wide heterozygosity levels between the two natural populations strongly support the conclusion that diploid A. parthenogenetica reproduce by automictic parthenogenesis with central fusion and low, but nonzero recombination. This settles a century-old controversy on Artemia, and, more generally, suggests that many automictic organisms harbour steep within-chromosome gradients of heterozygosity due to a transition from clonal transmission in centromere-proximal regions to a form of inbreeding similar to self-fertilization in centromere-distal regions. Such systems therefore offer a new avenue for contrasting the genomic consequences of asexuality and inbreeding.


Assuntos
Artemia/fisiologia , Alelos , Animais , Diploide , Heterozigoto , Partenogênese
2.
Heredity (Edinb) ; 102(5): 442-52, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19240752

RESUMO

Powerful and accurate detection of first-generation (F1) hybrids and backcrosses in nature is needed to achieve a better understanding of the function and dynamics of introgression. To document the frequency of ongoing interspecific gene exchange between two Mediterranean evergreen oaks, the cork oak (Quercus suber) and the holm oak (Q. ilex), we analyzed 1487 individuals originating from across the range of the two species using eight microsatellite loci and two Bayesian clustering approaches (implemented in the programs STRUCTURE and NEWHYBRIDS). Simulated data were used to assess the differences between the two clustering methods and to back up the choice of the threshold value for the posterior probability to discriminate admixed from pure individuals. We found that the use of STRUCTURE resulted in the highest power to detect hybrids, whereas NEWHYBRIDS provided the highest accuracy. Irrespective of the approach, the two species were clearly distinguished as independent genetic entities without any prior information. In contrast with previous reports, we found no evidence for unidirectional introgression. The overall hybridization rate was very low (<2% of introgressed individuals). Only two individuals were identified as F1 hybrids and five as early backcrosses. This work shows that the combined application of the two complementary Bayesian approaches and their systematic validation with simulations, fit for the case at hand, helps gain resolution in the identification of admixed individuals.


Assuntos
Hibridização Genética , Quercus/genética , Repetições de Microssatélites
3.
Heredity (Edinb) ; 92(4): 316-22, 2004 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-14735141

RESUMO

We have conducted a thorough study of the mating system of Lymnaea truncatula, the intermediate host of the liver fluke, using three approaches: (i) a population genetics study, (ii) controlled pairings in the laboratory and (iii) a progeny-array analysis. The population genetics study revealed high levels of inbreeding in the studied populations, with strong clues that the extensive heterozygote deficiencies observed are due to selfing. However, Wahlund effects may also arise due to recolonisations from different source populations after bottleneck events. A breeding experiment helped to disentangle the mating system and the Wahlund effects, and showed that high levels of selfing occurred in isolation and in controlled pairings. However, the progeny-array analysis performed after a high-density culturing of the snails suggests that substantial outcrossing may also occur.


Assuntos
Endogamia , Lymnaea/genética , Animais , Impressões Digitais de DNA , Água Doce , Genética Populacional , Lymnaea/crescimento & desenvolvimento , Repetições de Microssatélites/genética , Densidade Demográfica , Reprodução
4.
Acta Trop ; 64(3-4): 191-203, 1997 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-9107366

RESUMO

A population genetic study using starch gel electrophoresis was performed on populations of several species of lymnaeid snails acting as intermediate hosts for Fasciola hepatica (Trematoda, Plathyhelminth). Lymnaea viatrix was collected in 16 sites from the Bolivian Northern Altiplano. L. cubensis were obtained in one site from Venezuela, one site from Guadeloupe, three sites from Cuba and one site from the Dominican Republic. L. truncatula were collected in one site from France, one from Portugal and one from Morocco. Multilocus enzyme electrophoresis (MEE) were determined for 282 snails at 18 loci. A complete monomorphism was encountered at each geographic site. However, among these 18 loci, 13 are polymorphic and low and high levels of genetic divergence were observed between samples. Two genotypic groups can be differentiated by their multilocus genotypes. The western genotypic group associates together samples from Venezuela, Guadeloupe, Cuba and Dominican Republic (L. cubensis) while samples from France, Portugal and Morocco (L. truncatula) belong to the eastern genotypic group. Surprisingly, the Northern Bolivian Altiplano populations (L. viatrix) do not present any genetic divergence with the Portuguese sample. Therefore, the Bolivian snails belong entirely to the eastern genetic group. Within each group slight genetic divergences were observed. These results strongly support the European origin of the lymnaeid snails from the Northern Bolivian Altiplano.


Assuntos
Reservatórios de Doenças/classificação , Genética Populacional , Lymnaea/classificação , Lymnaea/genética , Animais , Bolívia , Cuba , República Dominicana , Eletroforese em Gel de Poliacrilamida , Fasciolíase/epidemiologia , França , Guadalupe , Humanos , Lymnaea/parasitologia , Marrocos , Filogenia , Polimorfismo Genético , Portugal , Venezuela
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