RESUMO
Neutral patterns of population genetic diversity in species with complex life cycles are difficult to anticipate. Cyclical parthenogenesis (CP), in which organisms undergo several rounds of clonal reproduction followed by a sexual event, is one such life cycle. Many species, including crop pests (aphids), human parasites (trematodes) or models used in evolutionary science (Daphnia), are cyclical parthenogens. It is therefore crucial to understand the impact of such a life cycle on neutral genetic diversity. In this paper, we describe distributions of genetic diversity under conditions of CP with various clonal phase lengths. Using a Markov chain model of CP for a single locus and individual-based simulations for two loci, our analysis first demonstrates that strong departures from full sexuality are observed after only a few generations of clonality. The convergence towards predictions made under conditions of full clonality during the clonal phase depends on the balance between mutations and genetic drift. Second, the sexual event of CP usually resets the genetic diversity at a single locus towards predictions made under full sexuality. However, this single recombination event is insufficient to reshuffle gametic phases towards full-sexuality predictions. Finally, for similar levels of clonality, CP and acyclic partial clonality (wherein a fixed proportion of individuals are clonally produced within each generation) differentially affect the distribution of genetic diversity. Overall, this work provides solid predictions of neutral genetic diversity that may serve as a null model in detecting the action of common evolutionary or demographic processes in cyclical parthenogens (for example, selection or bottlenecks).
Assuntos
Variação Genética , Genética Populacional , Partenogênese/genética , Animais , Simulação por Computador , Deriva Genética , Estágios do Ciclo de Vida , Cadeias de Markov , Modelos Genéticos , Modelos EstatísticosRESUMO
Little is known about the processes shaping population structure in saltmarshes. It is expected that the sea should act as a powerful agent of dispersal. Yet, in contrast, import of external propagules into a saltmarsh is thought to be small. To determine the level of connectivity between saltmarsh ecosystems at a macro-geographical scale, we characterized and compared the population structure of two polyploid saltmarsh species, Puccinellia maritima and Triglochin maritima based on a seascape genetics approach. A discriminant analysis of principal components highlighted a genetic structure for both species arranged according to a regional pattern. Subsequent analysis based on isolation-by-distance and isolation-by-resistance frameworks indicated a strong role of coastal sediment transport processes in delimiting regional structure in P. maritima, while additional overland propagule dispersal was indicated for T. maritima. The identification and comparison of regional genetic structure and likely determining factors presented here allows us to understand the biogeographical units along the UK coast, between which barriers to connectivity occur not only at the species level but at the ecosystem scale. This information is valuable in plant conservation and community ecology and in the management and restoration of saltmarsh ecosystems.
Assuntos
Alismatales/genética , Ecossistema , Genética Populacional , Poaceae/genética , DNA de Plantas/genética , Análise Discriminante , Repetições de Microssatélites , Modelos Genéticos , Poliploidia , Análise de Componente Principal , Plantas Tolerantes a Sal/genética , Reino UnidoRESUMO
The grass Puccinellia maritima is an important saltmarsh ecosystem engineer exhibiting wide morphological variation, which is partially genetically determined. Nevertheless, nothing is known about its population genetics or how neutral genetic variation is distributed throughout its geographical range. Here, we describe 12 polymorphic microsatellites pooled into two multiplexes for this octoploid species. Assessment of 24 samples from three populations revealed 4 to 29 alleles per locus, with variation in allele presence and abundance between populations. The transferability of these markers is reported based on their cross-amplification in six other Puccinellia species of different ploidy levels.
