Selection experiment on guppy ornamental traits

Female preferences for male ornamental traits can arise from indirect
benefits, such as increased attractiveness or better viability of
progeny, but empirical evidence for such benefits is
inconsistent. Artificial selection offers a powerful way to investigate
indirect effects of male ornaments. Here, we selected for the area of
orange spots on male guppies, a trait subject to female preferences in our
population, in replicated up- and down-selected lines. We found a
significant direct response to selection, and a correlated response in
female preferences, with females from down-selected lines showing less
interest in more orange males. Nevertheless, up-selected males sired more
offspring in direct competition with low-selected males, irrespective of
female origin. We did not find a significantly correlated
response to selection among any other fitness correlates we measured. Our
results imply that female preferences for orange spots can lead to
increased reproductive success of their sons, with no effect on general
viability of progeny. Furthermore, while we demonstrate that female
preferences may evolve via linkage disequilibrium with the preferred
trait, the potential for runaway selection by positive feedback may be
constrained by the lack of corresponding linkage with male reproductive
competitiveness.