In male swordtails (
Xiphophorus nigrensis
) there are three size classes that derive from allelic variation at the pituitary locus on the Y chromosome. Progeny analysis and preference tests suggest that females prefer to mate with larger males. In the closely related
X. pygmaeus
, there is no allelic variation at this locus; this species consists of males similar in size only to smaller
X. nigrensis
males. In addition to being smaller than most
X. nigrensis
males, these
X. pygmaeus
males also lack both the swordtail and a major component of the courtship display common in most
X. nigrensis
males. Usually, female
X. pygmaeus
prefer to mate with heterospecific males rather than conspecifics, regardless of body size and the presence of a swordtail. However, the smallest
X. nigrensis
males lack the same courtship component as do the
X. pygmaeus
males, and in this comparison female
X. pygmaeus
show no preference. Although sexual selection, through its action on divergence of courtship displays, has been implicated as a factor leading to speciation, in this case sexual selection could lead to the congealing of gene pools between heterospecifics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.