Behavioral Ecology Blog

For the practicing scientists reading this blog (are there any??), you know that there are certain people whose work it pays to take note of. For behavioral ecologists (and evolutionary biologists in general), Tim Clutton Brock (TCB) is one such researcher. His work as spanned multiple decades, and has ranged from hard-core field oriented studies (thinking Red Deer) to purely theoretical works (sexual selection stuff). If breadth of research is an index of success, then Clutton Brock is just that.

Anyway, as redefinition and rethinking have become the latest buzz in the scientific literature, it is not great surprise to see a paper like this one come from TCB. We should have predicted it- coming on the veritable heels of another one (Roughgarden’s Reproductive social behavior: Cooperative games to replace sexual selection) which as many of you know, turned out to be a very large flop (see here for a supreme science smackdown).

Anyway, Sexual selection in males and females appears in the latest edition of Science. Here is the (relatively uninformative) abstract:

Research on sexual selection shows that the evolution of secondary sexual characters in males and the distribution of sex differences are more complex than was initially suggested but does not undermine our understanding of the evolutionary mechanisms involved. However, the operation of sexual selection in females has still received relatively little attention. Recent studies show that both intrasexual competition between females and male choice of mating partners are common, leading to strong sexual selection in females and, in extreme cases, to reversals in the usual pattern of sex differences in behavior and morphology.

So I’ll preface my comments by saying that this is a worthwhile paper… It’s a nice easy read, and most of his statements are well supported. Maybe somebody can call me on this one, but it seems that TCB has made a career of writing papers that are edgy enough to be interesting, but rarely enough to be controversial… I’m not sure that is a complement or not… This paper is a prime example of one of those really good ones that after reading it- we say to ourselves: “Why the hell didn’t I think of writing that one.”

OK, so there are 3 main points to this paper:

1. To demonstrate that the framework of sexual selection continues to be useful.  I believe that this whole arguement is addressed to Roughgarden.    
2. That sexual selection is common in females, and
3. That this is largely under-appreciated and understudied by scientists

None of these points are revolutionary- those of us that have thought a lot about sexual selection have known them all along.  The problem, we didn’t articulate it in a clearly worded statement  like TCB has now done.

OK, so that paper starts out with a brief intro to the famous 3 letter acronyms that are so often confused, the PRR, and OSR. He uses their definitions to explain how we have come to our current understandings on the mechanisms of sexual selection. That it, that because of anisogamy and parental care, the PRR for males is usually greater.  Because the PRR is usually greater in males, the OSR is usually male biased which creates intrasexual competition for mates and higher variance in reproductive success.  Together, this has been takes as support for the idea that sexual selection is generally stronger in males than in females- and generally speaking it is. What TCB goes on to argue (like everybody would) is that it’s way more complex for BOTH males and females than simply looking at the OSR, as we used to do. 

In the end- one of the most important points that TCB brings up is that fact that it may be time to broaden our definition of what we think of as a sexually selected trait. He writes (and I agree) that it is the definition that has prevented us from thinking about sexual selection in females- largely because it precluded things like differential ability to conceive and rear offspring, which is likely to contribute to variance in female reproductive success. 

I’m not sure if the paradigm shift we are observing warrants new definitions, but it certainly does make us wonder about how we determie what a sexually selected trait is and what is not.. This ties in nicely to something that I have long thought- that sexual selection is not different than natural selection- fundamentally, it is a type of natural selection, and compartmentalizing it into it’s own little box probably does more harm than good..

We’ll see about that. Now go read the paper

Reference: Clutton-Brock.  Sexual Selection in Males and Females. Science 21 December 2007: Vol. 318. no. 5858, pp. 1882 - 1885