Friday, March 13, 2015

Wilson’s Phalarope

This photo, taken in South Dakota a decade or so ago, is of a female Wilson’s Phalarope, a species in which the roles of the sexes are reversed. The males care for the young, while the more handsomely plumaged females go out in search of additional mates.

The hormonal regulation of sex-role reversal is poorly understood. When I was in college, I learned that female phalaropes harbored high levels of testosterone. This hypothesis proves not to be entirely the case. Apparently testosterone is essential for the development of reproductive organs, and, like most vertebrates, male phalaropes at least begin the season with more testosterone than females. What does differ, however, are prolactin levels. Prolactin causes birds to incubate, and is much higher in male phalaropes than in other male birds. In typical birds, females have higher prolactin levels than do males.

Phalarope hormones may be even more complex. Some research indicates that testosterone levels spike in females when they see males in the spring. This rise may result in the females courting males and defending territories. Meanwhile, these females have low levels of prolactin. Just how these hormones accomplish this sex-role reversal is not well understood, but may involve enhanced prolactin receptors in the male brain.

These musings are distilled from a paper by Eens and Pinxten, “Sex-role reversal in vertebrates: behaviors and endocrinological accounts” published in 2000 in Behavioral Processes, volume 51.

No comments:

Post a Comment