Sexual selection : Female Preferences?

Or is it male persuasiveness?

The famous dispute as to whether the chicken or the egg came first goes back to antiquity when Seneca and Firmus first brought this up and couldn’t decide who was right. There is a similar problem with mate selection, namely whether females choose their partners (I’m not necessarily thinking of humans) because of innate preferences, i.e., something they want to see or find in a male, or whether it is because some males can be so persuasive and make females choose them even if they do not fit the females’ image of a dream partner.

Darwin had already noticed that males of many animal species possessed secondary sexual characters that could be a handicap in the struggle for survival and reduce a male’s life span. Why then do females choose these males as their mates, for example the colourful peacock, which is so obviously noticeable to predators that it should become easy prey or the stag with its huge antlers that require a lot of energy to build and can be an encumbrance rather than an asset during a run through dense vegetation? Is this due to co-evolution in which an already existing trait appeals to the female or is it due to a pre-established bias on part of the female? It has been suggested that male birds or fishes often have more colourful plumage or fins than their females to make the latter believe that they are particularly good fliers or swimmers (even if in reality the opposite holds true). The Israeli scientist Amotz Zahavi therefore argued the exact opposite and suggested that males with extra brilliant and large feathers or fins advertise these handicaps in order to let the females know that despite these impediments they have survived to sexual maturity and perhaps even to prominence in their own ranks and therefore they must most definitely be worth mating with. The central question, however, why do females choose at all, remains.

In the African widowbird Euplectes progne, males have extremely long tail feathers. When the tail feathers were artificially extended, these treated males had a greater success with females than untreated ones or those that had their tail feathers shortened. A colleague of mine in Jamaica had the plan to carry out a very similar study on the Jamaican doctor bird, a humming bird in which the males have long tail feathers. Another example: in the North American frog Physalaemus coloradorum females are quite capable of hearing sounds of lower frequencies, but their males are silent. Were they to croak, females most likely would take greater notice of a croaker. Such pre-existing preferences have also been documented in the little tropical platy fish. Central American platy fish are ancestral to sword tails, in which males possess a long tailfin extension, but male platy fish lack this “tail sword”. When the Californian zoologist A. Basolo carefully glued an artificial sword to male platyfish, they became more attractive to their own females: This observation provides strong evidence for the view that the evolution, at least in this case, was driven by female pre-existing preferences and not male persuasiveness. On the other hand it has also been shown that persistence, unwavering attention and over ebullience on part of some courting male can wear down the resistance of a female and ultimately make her accept a male that does not match her dream image of a partner. Did I write at the beginning that I was not thinking of humans? Well, maybe I was wrong.

© Dr V.B. Meyer-Rochow and, 2017.
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