Long term effects of genomic admixture in hybrid populations between two swordtail species (Xiphophorus birchmanni, Lechner & Radda, 1987 X Xiphophorus malinche, Rauchengerger, Kallman & Morizot, 1990) in seminatural mesocosms

The role and occurrence of hybridization in evolution processes received a lot of attention recently. The interaction between the parental genomes can produce different outcomes such as genetic incompatibilities, adaptive or deleterious introgression or broad small epigenetic effects. The Xiphophorus genus is known to have underwent various events of hybridization during his evolution history, and this study focuses on the species Xiphophorus malinche and Xiphophorus birchmanni, which inhabit the streams of the Sierra Madre Oriental in Mexico. In this work data collected from a ten year-long experiment are analyzed. An initial homogeneous population of F1 hybrids was put in a set of seminatural mesocosms. These populations were free to evolve naturally and twice a year all the fish were collected and marked, and fin clips for DNA analysis were taken. In 2019, after 4 years since the beginning of the experiment, the populations already show significant shifts from an homogeneous distribution of ancestry in a lot of loci. The survival performances positively correlate with the percentage of malinche ancestry in the genome, probably as a consequence that the set of tanks is located at high altitude. An interesting region is found on the sex chromosome (21) and shows an antagonistic selection for the ancestry between males and females , with birchmanni ancestry favoured in the former and malinche in the latter, different ancestries in the region correlate with differential growth rates in females.