Blue-footed boobies exhibit no sexual dimorphism, and instead both partners go through an elaborate mating display during courtship, focusing on their blue feet. What mating system do boobies use?

Question

and what is the likely reason for the lack of dimorphism? What qualities are they likely looking for in their mate? How can they ensure that they get the best match?

Answer 1

Sexual dimorphism commonly evolves when sexual selection is stronger on one sex than the other. For example, sexual dimorphism commonly evolves when large size or flashy display traits allow males with the traits to gain access to more females, either because the traits give them an advantage in male-male competition or because females prefer to mate with males with the traits.

Sexual selection is stronger in mating systems in which there is a greater bias in male (or female) mating success (that is, in mating systems in which a small number of males (or females) get most of the matings). By definition, a greater bias in mating success = stronger sexual selection (just as more biased survival = stronger natural selection). Mating systems with strongly biased mating success include those with female defense polygyny (some males can exclude others from access to females), resource defense polygyny (some males can exclude others from resources needed to attract females), and lek polygyny (males gather together to display and females select only the most attractive males as mates). We could make a similar list for polyandrous mating systems in which there is a greater bias in female mating success.

The fact that boobies are monomorphic suggests that they are monogamous, not polygynous or polyandrous. In monogamous systems, each male mates with one female (and vice versa) in a given breeding season. Because nearly all males and females mate, there is little bias in mating success, thus only weak sexual selection for traits that increase competitive ability or attractiveness.

So why do males and females signal to each other using their blue feet? Males and females can still gain a reproductive advantage if they mate with a partner that is either of higher fitness (resulting in their offspring being be of higher fitness) or that provides better parental care (resulting in more surviving offspring and/or offspring that are better fed and thus do better once they leave the nest). If individuals with bluer feet are of higher fitness and/or provide better parental care, then males and females will benefit from using foot color when they choose a partner to pair with.

Hope this helps. Feel free to ask if you need a clarification.

Answer 2

Blue-footed boobies use the Social Monogamy mating system. The mating display in this species is usually performed by the male, where he does a dance to display his brightly colored feet. Bright blue feet signals high genetic quality and health to a female booby. Duller feet in males is associated with an older booby, and possibly a weaker mate.

Males, on the other hand, evaluate a female booby as a partner based on two characteristics. A male booby increases paternal care when a female has either bright blue feet OR lays larger eggs. Large eggs and blue feet signal to the male that he will have healthy offspring, and as such, spends more time caring for the offspring.

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