“Rapid changes in the sex linkage of male coloration in introduced guppy populations”

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Swanne P. Gordon, Andrés López-Sepulcre, Diana Rumbo, and David N. Reznick

Not only body color, but also its sex linkage relationships evolves rapidly in guppies introduced to new environments

Trinidadian female guppies (Poecilia reticulata) undergoing testosterone hormone treatment.
(Credit: Swanne P. Gordon)

Many animals have a pair of sex chromosomes, where in one of the sexes (the male in mammals and many fish) one of them tends to be smaller (the Y chromosome) and recombines less with its pair (the X chromosome). Some male-specific traits are found in the Y chromosome and can thus only be inherited by males, while others are found in other parts of the genome, and can therefore be inherited by females. In guppies, males show bright colorations while females are drab. Most of this coloration is solely Y-linked in populations that coexist with a diverse community of predators. However, this is not the case in populations with lower predation pressure and stronger sexual selection. In this study researchers Swanne Gordon (University of Jyväskylä), Andrés Lopez-Sepulcre (CNRS Paris), Diana Rumbo, and David Reznick (University of California, Riverside) investigate how fast these differences in sex-linkage among populations can evolve. They show in several experimental populations of rapidly evolving Trinidadian guppies (Poecilia reticulata) introduced from high to low predation environments that changes in the sex linkage of traits can also occur very fast in rapidly evolving populations. More specifically, body coloration changes from being linked to the non-recombining parts of the Y-chromosome to being mainly X- or autosomally-linked in as little as 20 years, and shows substantial changes already after just one year (or three generations). These results have important consequences for our understanding of sexual selection and rapid evolution, since different degrees of sex linkage can affect rates of evolution. Moreover, they give new insights into the origin and evolution of sex chromosomes, where the prevailing theory so far points to an overall loss, rather than gain, of recombination over time. Read the Article