Animal Behavior/Sexual Selection and Mate Choice by Females
Sexual selection, a subcategory of natural selection, was first recognized by Charles Darwin and "occurs when individuals differ in their ability to compete with others for mates or to attract members of the opposite sex" (Alcock 493). By heavy courtship, fighting, or large territorial possession, males heavily compete for females. Even though a male may win a fierce competition for the mate of his choice, it is ultimately the female who decides on a partner that she wants. The female is often successful in her attempts to control reproduction by being choosy and having particular preferences for a male mate.
Females choose mates based on many factors. One important factor is male adornments, or ornaments. For example, Marion Petrie and Tim Halliday concluded that the removal of eyespots from a peacock's tail significantly reduces his attractiveness to females. "After 20 eyespots had been cut from their tails, males averaged two fewer mates in the following breeding season compared with their performance in the previous year" (Alcock 348). Thus, females are extremely conscious of the visual stimuli provided by males. Elaborate sensory cues alert the female that the male is reproductively superior to others. "Male adornments may more readily elicit the mating responses of some females who will thus mate preferentially in favour of the adorned males" (Bateson 53). Other factors involved in female preference in mate selection include body coloration or the "gift" that the male may present to the female before copulation.
Four theories are used to explain mate choice in females. The good parent theory suggests that "choosy individuals select partners on the basis of how well they will care for their offspring" (Alcock 491). This theory focuses on the female's search of a paternal male. The healthy mate theory occurs when females prefer "males healthy enough to produce and maintain elaborate ornaments" (Alcock 491). A good example of this is in female house finches, who choose male mates based on their bright coloration. Bright coloration tells the female that the male is more resistant to pathogens and parasites. The good genes theory "argues that females exhibit mate choice in order to provide their offspring with a partner's genes that will advance their offspring's chances of survival or reproductive success" (Alcock 491). A mother always wants the best for her child, even if it is a future child. Females select mates with certain traits, because they want their children to be healthy, viable, and reproductively successful. "Females that mate with attractive males are compensated for reduced fecundity by bearing "sexy sons" with higher than average mating success" (Andersson 45). The least obvious theory is the runaway selection theory. It states that by being choosy, females "create a positive feedback loop favoring both males with these attributes and females that prefer them" (Alcock 493).
A direct benefit of mate choice by females is the assurance of bearing offspring that will survive well and display high general fitness. This is a heritable benefit. Nongenetic benefits of mate choice include fecundity advantages, food, parental care, or a good territory. All of the benefits, both heritable and nonheritable, ultimately lead to the greater survival of a female's offspring.
Alcock, J. (2001). The Evolution of Reproductive Behavior. In Animal Behavior. (7 ed. pp. 341) Sunderland, Massachusetts: Arizona State University.
Andersson, M. (1994). Costs of Mate Choice; Direct Benefits of Mate Choice. In Sexual Selection. (pp. 45) Princeton, New Jersey: Princeton University Press.
Bateson, P. Editor. (1983). Sexual Selection by Female Choice by Peter O'Donald. in Mate Choice. (pp. 53). Cambridge: Cambridge University Press.