ABOVE: Five morphs of Poecilia parae—from top: melanzona yellow, melanzona blue, melanzona red, parae, immaculata—and a female (bottom) of the same species
CLARA LACEY
The paper
B.A. Sandkam et al., “Extreme Y chromosome polymorphism corresponds to five male reproductive morphs of a freshwater fish,” Nat Eco Evol, 5:939–48, 2021.
One of the key stages in the evolution of different sex chromosomes is a loss of recombination—the exchange of DNA during meiosis—that is both an important mechanism for maintaining genetic diversity in populations and for purging damaging mutations. This loss has led to the gradual depletion of functional gene content from the Y chromosome in many species, says Judith Mank, an evolutionary geneticist at the University of British Columbia who studies sexual dimorphism.
Nevertheless, some species have high levels of male phenotypic variability that appear to be Y-linked. The freshwater fish and guppy relative Poecilia parae, for example, has five different male morphs ...
