One would think that when it comes to reproduction, males and females would share a common goal -- passing the genetic heritage of the species on to the next generation. Yet hidden within the mating game is a primal conflict whose goal is to enhance the survival of one set of genes over the other.
Sexual conflict, observable from molecular to behavioral levels in a wide range of species -- including humans -- occurs when characteristics aiding the reproductive success of one sex reduce the fitness of the other.
In an article in today's issue of Nature, Dr. Sergey Gavrilets (ecology and evolutionary biology/mathematics) of the University of Tennessee at Knoxville develops a mathematical model to explain growing evidence for the extremely rapid evolution of fertilization-related traits among species ranging from insects to marine invertebrates.
The model supports his view that this acceleration in the evolution of sex traits -- and of divergent species -- is related more to sexual conflict than to what is usually viewed as natural selection.
The root of sexual conflict lies in what each sex invests in reproduction: the female invests mainly in the survival of her offspring, while the male invests in multiple opportunities for fertilization. Mating is thus costlier for females, who will try to restrict sexual activity to save energy for nurturing the young.
Conflict over mating rate leads to selection for new traits in males to attract females to mate at a rate beyond what is optimal -- and for females to evolve resistance to "attractive" male traits.
Gavrilets' paper provides the first formal model describing the dynamics that lead to an accelerated evolution of sexual traits, tying this rapid rate to population size.
"The model shows that continual change in such traits at a constant speed is expected whenever females (or eggs) experience fitness loss from having too many compatible males (or sperms). The plausibility of runaway coevolution increases with increasing population size."
This rapid evolution of sexual traits may explain the large diversity of related species in areas rich in resources: acceleration leads eventually to reproductive incompatibility -- and to the creation of new species.
Dr. Gavrilets' faculty page
UT Ecology and Evolutionary Biology
[Contact: Dr. Sergey Gavrilets]