A study from Courtney L. Fitzpatrick and her lab in the Texas A&M University Department of Biology challenges a long-standing assumption about how sexual traits evolve. The research, accepted for publication in The American Naturalist, suggests that elaborate sexual traits may develop not only through competition, but to help individuals locate mates.
Sexual selection theory has traditionally focused on competition for reproductive opportunities. In many species, one sex, often males, competes for access to mates, which can lead to the evolution of striking traits such as colorful displays, ornaments or elaborate courtship behaviors.
This new study suggests another pathway. In some populations, individuals may fail to reproduce not because they lose competitions with rivals, but because they rarely encounter potential mates at all. This “absolute mate limitation” can occur when populations are sparse or individuals move across large areas. Traits that make individuals easier to detect — such as visual, acoustic or chemical signals — may improve their chances of reproducing.
Using a mathematical model, the researchers examined how sexual traits which increase mating success but reduce survival chances might evolve in the sex traditionally considered “limiting,” such as females in many polygynous species. Their results show that even when females are not competing with one another for mates, selection can still favor conspicuous signals if doing so increases the likelihood of encountering a partner.
The model also shows the evolution of these traits depends on ecological factors like population density and movement patterns, highlighting how environmental conditions can shape sexual selection.
Together, the findings expand scientists’ understanding of how sexual traits evolve, suggesting that the need to simply locate a mate may be enough to drive the development of elaborate signals in nature.