In some bird species, the female chooses a mate that is most similar to her in size. This suppor

step 1 This question is about sexual selection in birds. The question tells us that in some species of

In some bird species, the female chooses a mate that is most...

Key Concepts

Sexual Selection

Sexual selection is a form of natural selection where traits evolve because they enhance an individual’s ability to obtain a mate and reproduce. It encompasses both male–male competition and female mate choice, leading to the development of diverse characteristics that may not directly contribute to survival but improve mating success.

Good Genes Hypothesis

The good genes hypothesis suggests that certain traits preferred by one sex indicate genetic quality, so by choosing mates with these traits, an individual can enhance the fitness of their offspring. This concept is used to explain why seemingly exaggerated or costly traits might evolve if they reliably signal superior genetic health or viability.

Runaway Sexual Selection

The runaway sexual selection hypothesis, also known as the Fisherian runaway, describes a positive feedback loop where a preference for a particular trait and the trait itself become genetically correlated. As a result, even traits that might be initially neutral or slightly disadvantageous can become exaggerated over generations because they are favored in mate choice.

Sexual Dimorphism

Sexual dimorphism refers to the distinct differences in size, coloration, or morphology between males and females of a species. These differences often arise due to sexual selection, where each sex evolves traits that improve their reproductive success, resulting in noticeable disparities between the sexes.

Assortative Mating

Assortative mating occurs when individuals preferentially choose mates with similar phenotypic or genotypic characteristics to themselves. This type of mating pattern can promote compatibility and coadaptation, and it is distinct from the classical sexual selection hypotheses, which focus on mating based on traits that signal genetic quality or result from a runaway process.

Transcript

00:01 This question is about sexual selection in birds.

00:03 The question tells us that in some species of birds, the female chooses to mate with a male that is a similar size as she is, rather than maybe a male that's smaller, a male that's larger, or even a male that's a similar size but has unique traits like distinct feather coloration.

00:18 A few reasons why this might be, according to the question, are the good genes hypothesis, the runaway hypothesis, and the sexual dimorphism hypothesis.

00:27 So we're going to break these down and see if we can figure out why.

00:30 Our female chooses to mate with this male that is a similar size as she is.

00:35 The good genes hypothesis essentially states that the character traits a female is choosing when selecting a mate are a good indicator of the male's genetic fitness, which is the likelihood that its offspring are going to survive and produce their own offspring.

00:50 Maybe in this species, the small males are too small to compete for resources and habitat, so they have a lower survival rate and thus a lower genetic fitness.

01:00 And the larger males are more visible to predators.

01:05 They're predated on more often.

01:07 So they have a lower survival rate and a lower genetic fitness too, where these middle -sized males can evade predators, but they're big enough and strong enough to hold down resources.

01:18 So these are most often selected by females because they have the highest genetic fitness.

01:24 So a, seems like a plausible answer to this question.

01:27 B, the runaway hypothesis, essentially states that the unique traits amongst males are so strongly preferred by females that they only mate with the males possessing the unique traits.

01:42 So in this species, maybe most of the males are purple, just like the female.

01:48 But then there's these unique males that are blue and yellow like this male...

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