By Adia Sovie, PhD student, Wildlife Ecology & Conservation Dept.

On islands throughout the Southern Ocean king penguins inhabit bare and windswept beaches. Contrasted next to the gray cobbles and brown-green patches of hardy grass the brilliant yellow and orange markings of both male and female king penguins jump out at you. Why are the penguins so colorful? Why is there little difference between male and female coloration? What is coloration signaling and to whom? To answer these questions Dr. Stephen Dobson of Auburn University has been stalking penguins on the Kerguelen Island; shaving feathers, painting beaks, and spying on the mating habits of hundreds of individuals.

Animal coloration has fascinated naturalists and biologists for centuries. Some animals are highly divergent in their ornamentation (sexual dimorphism) and some are not. For example, male painted buntings are an explosion of color while their females are drab in contrast, males need to attract mates and females need to hide from predators while nesting. In contrast, when both sexes are highly ornamented (such as the king penguin), this leaves researchers like Dr. Dobson scratching their heads, why bother? Dr. Dobson put forth three theories as to why both sexes may retain their ornamentation

• Sexual selection goes both ways – males and females both need to show off to one another – i.e. when both penguin parents invest a lot of energy in the egg, choosing the right mate is very important.
• The ornamentation is conserved in the genome and has not had time/reason to diverge – i.e. with little predation risk there is no selection for drab females
• The ornamentation represents something different than mate quality – perhaps age or dominance rank.

Dr. Dobson and his colleagues quantified penguin coloration, ear patch size, color intensity, and beak UV intensity. They then used those metrics to study how penguins choose their mates. Males in the center of the colony (which is safer from the predatory Skua) had larger ear patches. Females appeared to prefer these males with larger ear patches while males did not seem to mind the size of their mate’s ear patch. However, penguins did mate assortatively by the UV intensity of their beak spots, meaning that the coloration of pairs was highly correlated (i.e. like goes with like).

Further experimental evidence supported these observations. When Dr. Dobson and his colleagues shaved down the ear patches of male penguins, those unlucky fellows had a harder time finding a mate. Females are selecting males based on their outward expression of quality and social rank (i.e. closer to the center of the colony) and there is some indication that males are selecting females, though not as strongly. This evidence helps scientists understand the evolutionary pathways that shape coloration, mate selection, and sexual dimorphism.

2