Male‐Biased Mate Competition in King Penguin Trio Parades

Abstract

International audienceDarwin devised sexual selection theory to explain sexual dimorphisms. Further developments of the theory identified the operational sex-ratio (OSR) as one of its cornerstones, and it was commonly admitted that an OSR biased toward one sex would lead to stronger selection pressures toward that sex. Recent theoretical developments have challenged this view and showed that the OSR alone does not determine the direction of sexual selection, more particularly in mutually ornamented species exhibiting high and similar parental investment by both sexes. These developments, however, focused on mutual intersexual selection, and little is known about intrasexual selection of both males and females in species exhibiting such characteristics. The first aim of our study was to test the relative involvement of males and females in same-sex contest over mates in the king penguin, a species exhibiting mutual ornamentation of the sexes, high parental investment by both sexes, and a male-biased OSR. We investigated the sex composition of trio parades, which are groups of three individuals that compete for mates during pair formation. We found that these trios consist of a female trailed by two fighting males in 19 of 20 cases; the 20th trio was all male. The second aim of our study was to investigate the existence of within-sex differences in colour ornaments between individuals involved in such trios and individuals already paired. While limited sample sizes precluded detection of statistically significant differences between trios vs. pairs, reflectance measurements suggested that the beak spot of males in trios were more strongly ultraviolet than the beak spot of males in pairs. We concluded that intrasexual selection in our colony follows the typical pattern of mate competition observed in species in which sexual dimorphisms and OSR are male biased, and discussed the ultraviolet difference within the framework of the king penguins’ colour perception

Beak color dynamically signals changes in fasting status and parasite loads in king penguins

“…Whereas, Keddar and colleagues split the entire spectrum into 2 parts (before and after 499 nm) in order to separate UV and YO domains (Keddar et al 2013;, the UV peak of birds in our study usually extended beyond 450 nm (see Figure 2), ending at around 490 nm (which also corresponded to the start of the YO beak color). Thus, to avoid missing a part of light/information emitted by the microstructure for the UV signal and to avoid integrating light in the YO domain that actually came from a structural rather than pigment based coloration, we calculated color variables separately over those 2 regions: 320-490 nm for UV and 491-700 nm YO colors.…”

“…Hue is a measure of color appearance (e.g., "blue," "yellow," etc.). For the YO plateau portion of the spectrum, YO hue (YO hue ) was calculated as the wavelength at which the reflectance was halfway between its maximum and minimum (Keddar et al 2013). For the UV-violet peak, UV hue (UV hue ) was calculated as the wavelength of maximum reflectance between 320 and 490 nm.…”

Variation of mutual colour ornaments of king penguins in response to winter resource availability

“…We offer the following scenario for these results. In our colony, the sex ratio of displaying adults is strongly biased toward males, producing mate competition (reviewed by Keddar et al, 2013). Thus, females are highly choosy of the male whose call they learn, while males would rather secure a mate and only switch to a better one if they have the opportunity.…”

“…Growing comparative and experimental evidence suggests that orange and UV colours of the beak spot influence mate choice in both sexes Nolan et al, 2010;Keddar et al, 2013), indicating that beak colour is under mutual sexual selection. Also, experimental reduction of the size of the auricular patch delayed pairing, but only in males (Pincemy et al, 2009;Nolan et al, 2010).…”

“…Also, experimental reduction of the size of the auricular patch delayed pairing, but only in males (Pincemy et al, 2009;Nolan et al, 2010). During courtship, individuals form pairs, some becoming 'definitive' and producing an egg, others being 'temporary', with partners separating and perhaps switching to new partners (Olsson et al, 2001;Keddar et al, 2013).…”