Expansion of frozen hybrids in the guppy ectoparasite,Gyrodactylus turnbulli

Abstract

18Hybridization is one of the major factors contributing to the emergence of highly successful parasites. 19Hybrid vigor can play an important role in this process, but its contribution to the evolutionary 20 success of parasites has not been demonstrated. Here, we identify an invasion of a "frozen hybrid" 21 genotype in natural populations of Gyrodactylus turnbulli, ectoparasitic flatworms with facultative 22 sexual reproduction and significant impact on cultured fish. We re-sequenced genomes of these 23 parasites infecting guppies from six Trinidad and Tobago populations, and found surprisingly high 24 discrepancy in genome-wide nucleotide diversity between islands. The elevated heterozygosity on 25 Tobago is maintained by predominantly clonal reproduction of hybrids formed from two diverged 26 genomes. Hybridization has been followed by spread of the hybrids across the island, implying a 27 selective advantage compared to native genotypes. Our results highlight the potential consequences 28 of heterosis in the epidemiology of parasite hybrids and its impact on population genomic diversity. 29 30 conditions (Laine et al., 2019). The probability of hybridization increases when species co-infect the 46 same host, and such systems may be considered hotspots for studying its phenotypic effects. 47 157

Transmission dynamics of ectoparasitic gyrodactylids (Platyhelminthes, Monogenea): An integrative review

“…Hybridization represents a tractable research direction in the study of gyrodactylid transmission. At a macroevolutionary scale, recent hybridization has played an important role in shaping genetic variation of G. turnbulli and G. bullatarudis , followed by clonal reproduction and recombination, respectively, in each species (Konczal et al ., 2020 b , 2021). However, parasite strains of hybrid origin may additionally show enhanced phenotypic features such as higher infectivity, expanded host range and increased transmission potential as it is suggested in other pathogens (Ravel et al ., 2006).…”