Men are from Mars…

sexual-dimorphism

We captured a photo of this male (top) and female (bottom) kokanee salmon (Oncorhynus nerka) while volunteering at a recent egg collecting event, as described in our post “All Your Eggs in One Basket.” Like most salmonids, kokanee exhibit sexually dimorphic characteristics, which are especially pronounced during spawning. As adults male and female kokanee look alike, with silver sides, bluish-black backs and white bellies. In the late summer and early fall, just before spawning, both sexes turn bright red with green heads. However, the males develop a characteristic humped back, hooked jaw (kype) and elongated teeth. These traits are called ‘secondary sexual characteristics’ and are probably related to competition among males or to female mating preferences (Willson 1997). Within some sockeye populations male mating success has been shown to be positively correlated with hump size (Quinn and Foote 1994). As humans we pride ourselves in good posture and perfect teeth, but female salmon seem to be attracted to quite the opposite. Maybe this is what Victor Hugo had in mind when he wrote the The Hunchback of Notre-Dame?

Photo source: FISHBIO