Sex Differences in Sensory Systems

An organism is said to be sexually dimorphic when male and female conspecifics have anatomical differences in features such as body size, coloration, or ornamentation, but disregarding differences of reproductive organs. Sexual dimorphism is usually a product of sexual selection, with female choice leading to elaborate male ornamentation (i.e. tails of male peacocks) and male-male competition leading to the development of competitive weaponry (i.e. antlers on male moose). However, evolutionary selection also acts on the sensory systems that receivers use to perceive external stimuli. If the benefits of perception to one sex or the other are different, sex differences in sensory systems can arise. For example, female production of signals used to attract mates can put selective pressure on males to improve their ability to detect those signals. As a result, only males of this species will evolve specialized mechanisms to aid in detection of the female signal. This article uses examples of sex differences in the olfactory, visual, and auditory systems of various organisms to show how sex differences in sensory systems arise when it benefits one sex and not the other to have enhanced perception of certain external stimuli. In each case, the form of the sex difference reflects the function it serves in terms of enhanced reproductive success.

Male sphinx moths, Manduca sexta, rely on female released sex-pheromones to guide typical zig-zagging flight behaviors used to locate mates. Although both males and females respond to host plant olfactory cues to locate food sources, detection of and response to sex-pheromones appears to be male specific. Males that are better at detecting female sex-pheromones are able to find signaling females faster, providing them with a reproductive advantage. Since females gain no such advantage for having olfactory systems that are more sensitive to pheromones, enhanced pheromone detection has evolved only in the olfactory system of male M. sexta. The three main sex differences are as follows:

1) Male antennae are enlarged and contain elongated sensilla (sensory organules) not present in females. The pheromone elicits a male response by stimulating male specific receptor cells on a large number of these sensilla, which are located on the antennal flagellum. The sexually dimorphic sensilla are called male specific type-1 trichoid sensilla, a type of hair-like olfactory sensilla. In contrast, the flagella of female antennae lack these trichoid sensilla projections that make the male antennae appear to be larger and more feather-like. Each trichoid sensilla is innervated by two male specific olfactory receptor cells, with each cell being tuned (most sensitive) to one of two major chemical components of the pheromone. By evolving larger, pheromone-specific receptors in the peripheral olfactory system, male M. sexta have an improved sensitivity to female pheromones that enhances mate detection.

...
Wikipedia