Love and Fitness

PLOS Biology wants us to know that in a cost/benefit analysis, love comes out ahead:

A new study published in PLOS Biology by Malika Ihle, Bart Kempenaers, and Wolfgang Forstmeier attempts to use a model animal in an elegant experiment designed to tease apart the reproductive consequences of mate choice.

The authors took advantage of the fact that the zebra finch (Taeniopygia guttata, a native bird of Australia; Fig 1) shares many characteristics with humans, mating monogamously for life and sharing the burden of parental care. It was already known that the female finches choose mates in a way that is specific to the individual, and there is little consensus among females as to who is the cutest male.

Using a population of 160 birds that had recently been isolated from the wild, the authors set up a speed-dating session, leaving groups of 20 females to choose freely between 20 males. Once the birds had paired off, half of the couples (the “chosen” or C group) were allowed to embark on a life of wedded bliss. For the other half, however, the authors intervened like overbearing Victorian parents, splitting up the happy pair and forcibly pairing them with other broken-hearted individuals (the “non-chosen” or NC group).

Strikingly, the overall reproductive fitness (measured as the final number of surviving chicks) was 37% higher for individuals in chosen pairs than those in non-chosen pairs. However, because reproductive fitness is the final read-out from a chain of separate contributing influences, this begged the question of exactly how mate choice was having its effects on fitness.

The females of both groups laid the same number of eggs, suggesting that their initial investment isn’t affected by the mismatched mate. But the nests of non-chosen pairs had almost three times as many unfertilized eggs as the chosen ones, and a greater number of eggs that were neglected (either buried or lost).

I can’t tell if this is brilliant or disturbed.

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