Courtship and genetic quality: asymmetric males show their best side

Abstract

Fluctuating asymmetry (FA), the small random deviations from perfect morphological symmetry that result during development, is ubiquitous throughout the animal kingdom. In many species, FA seems to play a role in mate choice, perhaps because it signals an individual's genetic quality and health. However, the relationship between an individual's FA and behaviour is generally unknown: what do more asymmetric individuals do about their own asymmetry? We now show for the first time that individuals respond behaviourally to their own morphological FA in what appears to be an adaptive manner. During courtship, male guppies exhibiting high FA in ornamental colour, bias their displays towards their more colourful body side, thus potentially increasing their attractiveness by exaggerating the quantity of their orange signal. This appears to be a strictly behavioural male response to cues provided by females, as it does not occur when males court a non-reactive model female. Whether inferior males realize any mating advantage remains uncertain, but our study clearly demonstrates a behavioural response to random morphological asymmetries that appears to be adaptive. We propose that the tendency to show or otherwise use a 'best side' is common in nature, with implications for sexual signalling and the evolution of more pronounced asymmetries.

Lateralization of Cognitive Functions in Fish

“…In contrast to the above studies, no lateral bias was found in courting display of Betta splendens and P. reticulata (Cantalupo et al 1996;Gross et al 2007). However, in the latter study males were found to individually bias their displays toward their more colorful side.…”

A primary role of developmental instability in sexual selection

“…Indeed, the issues of FA/DI heritability, and of the significance of covariance between FA and ornament size, remain far from being adequately resolved (Simmons et al 1995;Fuller & Houle 2003;Polak & Starmer 2005;Van Dongen 2006), despite their continuing prominent positions in the DI-sexual selection hypothesis ( Møller & Pomiankowski 1993;Watson & Thornhill 1994;Møller & Cuervo 2003). One robust conclusion that has emerged, however, is that FA is a reliable predictor of mating success and sexual attractiveness in humans, as well as in some insects, fishes and birds ( Tomkins & Simmons 2003;Brown et al 2005;Gross et al 2007;Rhodes & Simmons 2007). Yet, the biological reasons for why FA predicts sexual success in some species, but not in others, remain virtually unknown (Møller & Thornhill 1998;Møller & Cuervo 2003;Swaddle 1999).…”

In the eye of the beholder: visual mate choice lateralization in a polymorphic songbird

“…Our results may also help to explain why so many courtship rituals in birds include lateral displays [5,6]. This type of courtship behaviour has sometimes been explained as males 'showing their best side' [17] but viewing females with a particular eye during courtship can also stimulate an enhanced courtship display [10]. Most importantly, in Gouldian finches, for whom choosing the wrong mate can have dire fitness consequences [14], preferential eye use should also facilitate adaptive mate choice-saving courtship time and energy [2], and ultimately increasing reproductive success.…”