Does male mate choice select for female coloration in a promiscuous primate species?

Assessing color cues of development, breeding status and reproductive condition in captive golden lion tamarins (Leontopithecus rosalia)

Color signals play an important role in intraspecific communication and are well studied in catarrhine primates, which exhibit uniform trichromatic vision that is well suited to detecting such signals. Platyrrhine primates exhibit polymorphic color vision with different individuals possessing different color vision types in most species. Intriguingly, some platyrrhine species exhibit bare faces, which are convergent with those of catarrhines. However, putative functions of bare-faced color signals in platyrrhines remain largely unexplored. We measured facial skin color of five captive golden lion tamarins (Leontopithecus rosalia) using color-calibrated digital photography and modeled these colors to the visual systems of the species. Our results show that facial coloration is different between infant and older adults and varies across reproductive condition, but not between breeding and nonbreeding adults. While preliminary, our study suggests that facial coloration may be involved in sociosexual signaling in golden lion tamarins, and provides intriguing evidence that we hope might stimulate more studies of bare-faced signaling in platyrrhines.

Chemical cues of identity and reproductive status in Japanese macaques

Olfactory communication plays an important role in the regulation of socio-sexual interactions in mammals. There is growing evidence that both human and nonhuman primates rely on odors to inform their mating decisions. Nevertheless, studies of primate chemical ecology remain scarce due to the difficulty of obtaining and analyzing samples. We analyzed 67 urine samples from five captive female Japanese macaques (Macaca fuscata) and 30 vaginal swabs from three of these females using gas chromatography-mass spectrometry and examined the relationship between odor (compounds identified, richness, intensity, and diversity) and female identity as well as cycle phase. We found a total of 36 urine compounds of which we identified 31, and 68 vaginal compounds of which we identified 37. Our results suggest that urine and vaginal odor varied more between individuals than within cycle phases. However, we found that within a female cycle, urine samples from similar phases may cluster more than samples from different phases. Our results suggest that female odor may encode information about identity (vaginal and urine odor) and reproductive status (urine odor). The question of how conspecifics use female urine and vaginal odor remains open and could be tested using bioassays. Our results and their interpretation are constrained by our limited sample size and our study design. Nonetheless, our study provides insight into the potential signaling role of female odor in sexual communication in Japanese macaques and contributes to our understanding of how odors may influence mating strategies in primates.

Does egg carotenoid improve larval quality in Arctic charr ( Salvelinus alpinus )?

Females in mutually ornamented species are often less conspicuously ornamented than their male conspecifics. It has been hypothesized that offspring quality may decrease if females invest more resources into ornaments at the expense of resources in eggs. An experiment was carried out to test whether natural variation in carotenoid in the eggs from a wild population of Arctic charr (Salvelinus alpinus) was associated with survival and growth of their offspring until hatching. Wild Arctic charr were caught at a spawning ground during the spawning period. Eggs from two different females, one female with yellowish carotenoid‐rich eggs and one with paler eggs, were fertilized by sperm from the same male. This was repeated until gametes were collected from 42 females and 21 males, giving a total of 21 groups. After fertilization, the zygotes from each of the two females were reared in four replicated groups. These 168 groups were reared separately until hatching when the surviving larvae were counted and their body length measured. For the two response variables survival and body length at hatching, no effect was demonstrated of any of the predictors (i) amount of carotenoid in the unfertilized eggs, (ii) the mothers' body condition, or (iii) ornament intensity of their red carotenoid‐based abdominal ornament. Thus, this study gives no support for the hypothesis that females investing less carotenoid into their eggs suffer from decreased offspring quality until hatching. This lack of association between female ornament intensity and their fitness is not as expected if female ornaments evolved due to direct sexual selection from males on the more ornamented females (“direct selection hypothesis”).