Question

Sympatric speciation is often accompanied by assortative mating. This means that individuals mate (or ‘sort’) with their own type. Assortative mating plays an important role in driving and maintaining reproductive isolation in sympatric populations.

a) Provide a proximate explanation for assortative mating

b) Provide an ultimate explanation for assortative mating

Answer 1

Sympatric speciation occurs when a sub group of a population of a determined species becomes reproductively isolated from the rest without a geographical barrier, so both occur together. Different reasons may be involved in assortative mating, but there are some possible causes:

a)There could be hormonal, genetical or physiological factors involved, for example, in an hypothetical case, males with high levels of certain hormones could be more aggressive and territorial, while females with high levels of sexual hormones could also exhibit a territorial behavior which would lead to territorial males and females to mate, or hormone levels could influence a color pattern attractive to those individuals with similar color pattern, or simply, genetic traits lead to the production of an attractive phenotype for those individuals with similar genetic profile, or in the case of closely related plants, due to environmental conditions and phytohormones production, flowering can take place in a determined moment of the year, which leads to the reproduction of groups of plants that flower at the same time.

b)For an ultimate explanation, we have to talk in terms of evolutionary causes, territorial behavior could lead to greater chances of offspring survival because parents guard the territory and its resources, so the offsprings can take advantage of those resources and will probably inherit or develop the same territorial behavior and this kind of mating is favoured, or in the hypothetical case of plants mentioned above, flowering at a determined time of the year leads to greater chances of offspring survival because the seeds generated this way have greater chances of growing in a humid period of the year. In other words, assortative mating could favour the fixation of traits that lead to reproductive isolation and greater chances of survival, so it is a successful strategy.