Biology subjects

Cathy Haag-Liautard

Publications and source records attributed to Cathy Haag-Liautard.

2 recordsLinked to original sources

bioRxiv2016

Transition from environmental to partial genetic sex determination in Daphnia through the evolution of a female-determining incipient W-chromosome

Sex chromosomes can evolve during the evolution of genetic sex determination (GSD) from environmental sex determination (ESD). Despite theoretical attention, early mechanisms involved in the transition from ESD to GSD have yet to be studied in nature. No mixed ESD-GSD animal species have been reported, except for some species of Daphnia, small freshwater crustaceans in which sex is usually determined solely by the environment, but in which a dominant female sex-determining locus is present in some populations. This locus follows Mendelian single-locus inheritance, but has otherwise not been characterized genetically. We now show that the sex-determining genomic region maps to the same low-recombining peri-centromeric region of linkage group 3 (LG3) in three highly divergent populations of D. magna, and spans 3.6 Mb. Despite low levels of recombination, the associated region contains signs of historical recombination, suggesting a role for selection acting on several genes thereby maintaining linkage disequilibrium among the 36 associated SNPs. The region carries numerous genes involved in sex differentiation in other taxa, including transformer2 and sox9. Taken together, the region determining the NMP phenotype shows characteristics of a sex-related supergene, suggesting that LG3 is potentially an incipient W chromosome despite the lack of significant additional restriction of recombination between Z and W. The occurrence of the female-determining locus in a pre-existing low recombining region illustrates one possible form of recombination suppression in sex chromosomes. D. magna is a promising model for studying the evolutionary transitions from ESD to GSD and early sex chromosome evolution.

Preprint↗

bioRxiv2015

Distinguishing contemporary hybridization from past introgression with post-genomic ancestry-informative SNPs in strongly differentiated Ciona species

Biological introductions bring into contact species that can still hybridize. The evolutionary outcomes of such secondary contacts may be diverse (e.g. adaptive introgression from or into the introduced species) but are not yet well examined in the wild. The recent secondary contact between the non-native sea squirt Ciona robusta (formerly known as C. intestinalis type A) and its native congener C. intestinalis (formerly known as C. intestinalis type B), in the western English Channel, provides an excellent case study to examine. To examine contemporary hybridization between the two species, we developed a panel of 310 ancestry-informative SNPs from a population transcriptomic study. Hybridization rates were examined on 449 individuals sampled in 8 sites from the sympatric range and 5 sites from allopatric ranges. The results clearly showed an almost complete absence of contemporary hybridization between the two species in syntopic localities, with only one first generation hybrid and no other genotype compatible with recent backcrosses. Despite the almost lack of contemporary hybridization, shared polymorphisms were observed in sympatric and allopatric populations of both species. Furthermore, one allopatric population from SE Pacific exhibited a higher rate of shared polymorphisms compared to all other C. robusta populations. Altogether, these results indicate that the observed level of shared polymorphism is more probably the outcome of ancient gene flow spread afterwards at a worldwide scale. They also emphasise efficient reproductive barriers preventing hybridization between introduced and native species, which suggests hybridization should not impede too much the expansion and the establishment of the non-native species in its introduction range.

Evolutionary Biology↗