Quantification of Reproductive Isolating Barriers Between Two Naturally Hybridizing Killifish Species

Sexual selection and speciation in the Anthropocene

Anthropogenic change threatens global biodiversity by causing severe ecological disturbance and extinction. Here, we consider the effects of anthropogenic change on one process that generates biodiversity. Sexual selection (a potent evolutionary force and driver of speciation) is highly sensitive to the environment and, thus, vulnerable to anthropogenic ecological change. Anthropogenic alterations to sexual display and mate preference can make it harder to distinguish between conspecific and heterospecific mates or can weaken divergence via sexual selection, leading to higher rates of hybridization and biodiversity loss. Occasionally, anthropogenically altered sexual selection can abet diversification, but this appears less likely than biodiversity loss. In our rapidly changing world, a full understanding of sexual selection and speciation requires a global change perspective.

Using asexual vertebrates to study genome evolution and animal physiology: Banded (Fundulus diaphanus) x Common Killifish (F. heteroclitus) hybrid lineages as a model system

Wild, asexual, vertebrate hybrids have many characteristics that make them good model systems for studying how genomes evolve and epigenetic modifications influence animal physiology. In particular, the formation of asexual hybrid lineages is a form of reproductive incompatibility, but we know little about the genetic and genomic mechanisms by which this mode of reproductive isolation proceeds in animals. Asexual lineages also provide researchers with the ability to produce genetically identical individuals, enabling the study of autonomous epigenetic modifications without the confounds of genetic variation. Here, we briefly review the cellular and molecular mechanisms leading to asexual reproduction in vertebrates and the known genetic and epigenetic consequences of the loss of sex. We then specifically discuss what is known about asexual lineages of Fundulus diaphanus x F. heteroclitus to highlight gaps in our knowledge of the biology of these clones. Our preliminary studies of F. diaphanus and F. heteroclitus karyotypes from Porter's Lake (Nova Scotia, Canada) agree with data from other populations, suggesting a conserved interspecific chromosomal arrangement. In addition, genetic analyses suggest that: (a) the same major clonal lineage (Clone A) of F. diaphanus x F. heteroclitus has remained dominant over the past decade, (b) some minor clones have also persisted, (c) new clones may have recently formed, and iv) wild clones still mainly descend from F. diaphanus ♀ x F. heteroclitus ♂ crosses (96% in 2017-2018). These data suggest that clone formation may be a relatively rare, but continuous process, and there are persistent environmental or genetic factors causing a bias in cross direction. We end by describing our current research on the genomic causes and consequences of a transition to asexuality and the potential physiological consequences of epigenetic variation.