Behavioral Ecology Blog

For the practicing scientist readers. you know that feeling of excitement you get when you read a paper sometimes… That “Holy Shit, this is one of the nicest papers I’ve read in a long time” feeling.. Well hold on, cause if your interested in behavioral ecology, sexual selection, mate choice, birds, biology, ect, this paper is a must read..

The title: Adaptive Plasticity in Female Mate Choice Dampens Sexual Selection on Male Ornaments in the Lark Bunting.

The Abstract:

Theory on the evolution of ornamental male traits by sexual selection assumes consistency in selection over time. Temporal variation in female choice could dampen sexual selection, but scant information exists on the degree to which individual female preferences are flexible. Here we show that in lark buntings sexual selection on male traits varied dramatically across years and, in some cases, exhibited reversals in the direction of selection for a single trait. We show that these shifts are probably because of flexibility in mate choice by individual females and that they parallel shifts in the male traits that predict female reproductive success in a given year. Plasticity in choice and concomitant reversals in mating patterns across time may weaken the strength of sexual selection and could maintain genetic variation underlying multiple sexual ornaments.         

See the bottom for the full citation and link.

So anyway, here is the background. The Reed Bunting (Calamospiza melanocorys) is a small ugly migratory songbird that breeds in Colorado. They are socially monogamous and have a lot of EPC’s. There is typically a male biased OSR. The males are only weekly territorial. The authors show that 5 independent traits are subject to sexual selection, and that this is likely due to the effects of female choice (as opposed to male-male competition).

The cool thing (probably a post hoc finding/hypothesis) is that females are selecting mates based on different traits each year.. One year females select males based on beak size, and the next based on the size of the wing patch. Even more dramatic is that the even the direction of the effect of a trait can change- for instance one year body mass can be can be positively correlated with reproductive success, and the next year negatively correlated. That is amazing! The authors assert that this effect is due to plasticity on mate choice rather then due to the effects of age or demography!

The real question is this: Is this plasticity in female choice adaptive? Do “females target male or territory characters that predict fitness benefits to them in a given year, that different traits serve as fitness indicators in different years, and that changes in female preference across years correspond non-randomly with the changes in fitness-indicator traits” On this question, I am not convinced, but my scepticism may be faltering as I continue to think about it..

The cool take home message is that depending on the generality of this finding (i.e. do other systems have this much plasticity in female choice) this could be a real resolution to the paradox of the lek, which basically asks why is there so much genetic variance in male phenotype given persistent female choice for a single phenotype. The authors of this paper might suggest that it might be because while preference for a particular phenotype is strong within years, it may vary drastically between years (and thus maintain variance)

Chaine, A.S., Lyon, B.E. (2008). Adaptive Plasticity in Female Mate Choice Dampens Sexual Selection on Male Ornaments in the Lark Bunting. Science, 319(5862), 459-462. DOI: 10.1126/science.1149167