Houbin, C. | Search bioRxiv

bioRxiv2025

Sex chromosomes and chromosomal rearrangements are key to behavioural sexual isolation in Jaera albifrons marine isopods

The lack of sexual attraction between individuals from different populations is a direct barrier to gene flow between these populations. Here we focus on the evolution of this class of isolating mechanism, behavioural sexual isolation, through the empirical study of two closely related species of small marine isopods. The males of Jaera albifrons and J. praehirsuta similarly engage females in tactile courtship by brushing a specific region of the females back, but they do so with divergent sets of specialised setae and spines, and female choice results in strong reproductive isolation. Using bi-allelic SNP genotypes obtained from double-digest RAD sequencing of individuals from natural populations and controlled crosses, we found that secondary contacts between J. albifrons and J. praehirsuta resulted in different levels of heterospecific gene flow depending on the ecological context. Comparison of the genomic landscapes of differentiation in the two most contrasting situations (extremely low heterospecific gene flow in one region of western France, but strong introgressive hybridisation in another), combined with linkage map analyses, allowed us to conclude that genomic regions resistant to interspecies gene flow are primarily located either on the sex chromosomes or on rearranged chromosomes (several fusion-scissions and one reciprocal translocation). These genomic regions show low recombination, and in two cases QTL analyses found genetic variation associated with several male courtship traits. These results suggest that a long period of allopatry may have allowed the divergent co-evolution of male traits and female preferences, with genetic bases located at least in part in non-recombining regions on sex chromosomes and rearranged chromosomes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=182 SRC="FIGDIR/small/631900v4_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@6b7df8org.highwire.dtl.DTLVardef@11b4d00org.highwire.dtl.DTLVardef@15c760aorg.highwire.dtl.DTLVardef@1498d45_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2018

Sexual isolation with and without ecological isolation between sympatric isopods Jaera albifrons and J. praehirsuta

Sexual isolation is often coupled with other barriers, and sexual isolation mechanisms can be intrinsically tied to ecological conditions or natural selection against heterospecific gene flow. The independence and relative strength of sexual isolation are thus difficult to assess. Here we take advantage of a pair of isopod species (Jaera albifrons and J. praehirsuta) that show sexual isolation and coexist in populations where they share the same habitat or not (i.e. without or with ecological isolation). Using no-choice trials and a free-choice experimental population, we estimated the strength of sexual isolation between J. albifrons and J. praehirsuta individuals originating from these different ecological contexts. We found that sexual isolation is strong in presence and absence of ecological isolation, but that it is asymmetric and fails to prevent gene flow entirely. Post-zygotic barriers were low, and there was no sexual isolation within J. praehirsuta across habitats. The J. albifrons / J. praehirsuta species pair thus provides an example where the role of sexual isolation as a barrier to gene flow i) does not depend upon current ecological isolation, ii) seems to have evolved independently of local ecological conditions and hybridization costs, but iii) is unable to complete speciation entirely on its own.

evolutionary biology↗