For many years now it has been suggested that sex role reversal is caused by a skewed operational sex ration (OSR). The OSR is the number of reproductive males : the number of reproductive females in a population. When this ratio is biased heavily towards females, theory predicts, females will be forced to compete for males and males become the choosy sex, resulting in a reversal of the traditional sex roles. A recent paper investigating courtship in the two-spotted goby demonstrates that this is exactly what happens in this species over the course of the breeding season. The discovery of these behaviors in this system is a great demonstration of empiricism supporting theory.
I study pipefish, which are characterized by male pregnancy. In the species I study, this extreme degree of parental care has led to sex-role reversal, regardless of the OSR (or so we believe–what happens in nature may be different from what we observe in the lab). So the results of this study bring up some interesting questions about sex role reversal in general in relation to my study organism.