Evidence for a male sex pheromone in a primate?

Abstract

Pheromones mediate a wide range of functions across the animal kingdom [1], and such chemosensory communication is especially widespread among mammals [2]. In a recent paper in Current Biology, Shirasu, Ito et al. [3] describe the results of a series of chemical and behavioral studies that identified three aldehyde odors released from the wrist gland of ring-tailed lemurs (Lemur catta) that could represent the first identified sex pheromones in male primates. Observations of a captive group and controlled presentations of isolated male scent samples showed captive female lemurs sniffing antebrachial scent marks longer on average during the breeding season. Comparison of the chemical profiles of antebrachial secretions between breeding- and non-breeding-season samples revealed three aldehydes putatively responsible for the female response, the concentration of one of these subsequently shown to increase following testosterone injection of one male. Average sniffing duration of two females increased slightly with increasing concentrations of two of the three aldehydes in one experiment, and so did the response of seven other females to swabs with mixtures of the three compounds, compared to individually presented aldehydes. From these results, the authors conclude that "it is conceivable that the identified C12 and C14 aldehydes are putative sex pheromones that aid male-female interactions among lemurs." Here, I argue that, in fact, more data are needed to determine whether antebrachial marking and these substances are actually involved in mediating the attractiveness of males to females during the breeding season. My specific concerns pertain to several aspects of the methods that produce ambiguous results and conclusions that are too strong, especially when considering the broader context of lemur biology.