Résultat de la recherche
Asynchronous life cycles contribute to reproductive isolation between two Alpine butterflies
Geographic isolation often leads to the emergence of distinct genetic lineages that are at least partially reproductively isolated. Zones of secondary contact between such lineages are natural experiments that allow investigation of how reproductive isolation evolves and co-existence is maintained. While temporal isolation through allochrony has been suggested to promote reproductive isolation in sympatry, its potential for isolation upon secondary contact is far less understood. Sampling two contact zones of a pair of mainly allopatric Alpine butterflies over several years and taking advantage of museum samples, we show that the contact zones have remained geographically stable over several decades. Furthermore, they seem to be maintained by the asynchronous life cycles of the two butterflies, with one reaching adulthood primarily in even and the other primarily in odd years. Genomic inferences document that allochrony is leaky and that gene flow from allopatric sites scales with the degree of geographic isolation. Overall, we show that allochrony has the potential to contribute to the maintenance of secondary contact zones of lineages that diverged in allopatry.
The evolution of quantitative traits in reponse to drought in "Arabidopsis lyrata"
In spite of the great advances in population genetic and quantitative genetics over the last decades, many central questions of these fields are still not satisfactorily answered. In particular, we still have a poor understanding of how species are limited in their adaptation to changing environmental conditions and to habitats present beyond their natural distribution. In addition, our knowledge about the effect of habitat heterogeneity on the maintenance of genetic variation remains poor. In the context of global climate changes, many species will have to respond to different environmental conditions in order to survive. Therefore, understanding species’ ability to adapt and how high levels of the genetic variance necessary for adaptation can be maintained within populations is highly important. Such knowledge will be very useful for building new conservation strategies.
During this thesis I have investigated these questions using the Arabidospsis lyrata plant system. Its ability to grow on different substrates and the development of comprehensive genomic resources makes it a powerful system for studying adaptation. Several seed families occurring in a heterogeneous landscape and across two latitudinal clines in North America were raised in a common garden environment and in two different treatments: wet and dry. By measuring several traits all related to drought adaptation and by performing intense linear and multivariate statics, I discovered that genetic constraints and low levels of genetic variation are limiting northern populations to adapt to higher latitudes. In addition, I observed that habitat heterogeneity did not greatly impact the adaptive potential of this species. Results of this thesis offer a greater understanding of adaptive limits met at distribution edges. This new knowledge will help constructing models evaluating the impact of global changes on many plant and animal populations.