A pipefish paper made a big splash when it first came out, but how convincing is the evidence? Here is my take.
Love is a battlefield. For some animals, the battle goes on even after love has been made.
I'm talking about post-copulatory sexual selection. Sexual selection after mating is a lot like sexual selection before mating, except whereas before mating, males compete with other males and females choose which male to mate with, after mating it is the sperm that compete with other sperm and the females reproductive tract that choose which sperm to use to fertilize eggs. The later phenomenon is known as cryptic female choice because you can't see it happening unless you do a paternity analysis on the offspring
[1].
The stereotypical competitive male and choosy female are products of differences in the potential reproductive rate for males and females, and are not necessarily a result of having testes or ovaries. Sex-role reversed species such as syngnathids illustrate this point quite nicely.
This pregnant male seahorse is a syngnathid.
In syngnathids, the males "get pregnant": the females lays her eggs into the male's pouch and he carries them around until they hatch. This male pregnancy lowers the male potential reproductive rate below that of females. As a result, it is the
females that compete with each other for access to males, and it is the
males who are more choosy about who they mate with
[2].
A recent paper published in Nature by Pazcolt & Jones
[3] claims that in one syngnathid, the Gulf pipefish, males practice cryptic male choice after sex by favoring eggs from "attractive" females and aborting eggs from "unattractive" females.
The Nature News coverage of this article was titled
"Male pipefish abort embryos of ugly mothers" which at first might makes you wonder how such subjective concepts like "ugly" and "beautiful" were assigned to pipefish by human observers. But actually it is just a catchy headline, in the original paper, attractiveness simply equals female size, based on the fact that male pipefish are known to prefer large females.
When it first came out, the paper was covered in several blogs (including by
Ed Yong and
grrlscientist). However, since then the papers conclusions have been challenged by some big names in the field of sex-role reversal. Gywnne et al.
[4] claimed that the results of Pazcolt & Jones could be explained entirely by larger females having higher quality eggs. Pazcolt & Jones replied
[5], defending their original conclusions.
Let's dive into the experiment and see what conclusions we can make for ourselves:
