GIVEN: You discovered a new insect. The males seem to stake out territory in bunches of mushrooms. Also, they display red dots on their heads to attract the females. The males with the larger dots tend to be in the center of the mushrooms and the females seem to want to mate with the males in the center.
Given that the females of this newly discovered species of insect are the ones who visit the groups of males and mate with one, it seems obvious that they’d evolve the desire to mate with the best one. That is to say, since the males cannot seize and control the access to the females (direct competition), they should compete by advertising themselves to the females. In turn, the females should choose whichever advertisement they prefer. This preference classifies one male as the best, that is, he has the most desirable traits and the best likelihood to reproduce. Defining which is best, however, in terms of mate choice, brings up a few different hypotheses.
First, the female may pick her male based on direct benefits. That is to say, the female may gain personally by choosing the right mate. This male may offer food (up to and including the ultimate sacrifice, himself, in an effort to woo) or any other beneficial resource to the female and/or her young. This includes caring for the newborn offspring, feeding the family, defending the eggs, etc.
Second, females may pick their males based on indirect benefits. It might be that the displays of a male are a display of the quality of their genes. By mating with the “attractive” males, the females are insuring that their offspring will have better genes than if they had mated with “unattractive” males. This may also apply arbitrarily, that is, without a gene-quality component, whereby the females choose the males that are “attractive” then have offspring that are also attractive. This increases the reproductive output of their offspring and perpetuates the whole system. This is termed the “sexy sons” scenario.
One experiment that could be performed to decide the females’ reasons for choosing a mate (indirect and/or direct benefits) would be to transfer the smaller dotted insects from the edges to the center of the mushrooms. Assuming the territory choice isn’t based male competition (that is, the large dotted males would fight away your small dotted males) you could just place the smaller ones in the center to establish their territory. If the males do compete for central territory, painting the central, large-dotted males to have a smaller dot would accomplish the same thing. The inverse experiment, moving large dotted males to the outside, should give similar results and might be done at the same time in different populations.
Then the study would be to watch for female mate choices. If the females still choose the males with the large dots more often, even on the outside edges of the group, this proves that the benefits of sexual selection are not direct. That is, the females are selecting the larger dots because they represent a male with better genes or an arbitrary, “sexy sons,” scenario. They just like the dots.
If the females still choose the center-territory males, this might represent a direct benefit from the males. Perhaps the females “know” that the center mushrooms have more food sources (the mushrooms themselves) for them and/or their larval offspring. It could also be the case that the central mushrooms are more protected and are a better place for the females to lay their eggs. Either way, this is one experiment to discriminate between the two hypotheses about the evolution of the females’ choice.
Ps. I love it when biology stuff applies directly to human sociology. For example, how many women do you know who go for strong, protective men? How many go for sweet, caring, loving men? Now, how many try to get BOTH?
My new plan for a thesis paper: Sexual Selection and the Courtship Rituals Among Homo Sapiens Sapiens in its Natural Habitat
