Saturday, August 18, 2012

Assessing Direct and Indirect Costs

Orteiza, N., Linder, J., & Rice, W. 2005. Sexy sons from re-mating do not recoup the direct costs of harmful male interactions in the Drosophila melanogaster laboratory model system. Journal of Evolutionary Biology, 18(5), 1315-1323.

This article explores how female interactions with males can reduce lifetime survival and fecundity, and assesses any indirect benefits as a result. Virgin females were introduced into two conditions simulating constant male exposure and minimal male interaction. Wild-type males and virgin females are housed and allowed to mate, and then half the females are given the chance to re-mate again with brown eyed males. To determine any direct costs to females by re-mating and constant male exposure females were housed with brown-eyed females and would compete for limited yeast. The costs would then be calculated by recording the eye colour and number offspring each female produced. To assess any indirect benefits virgin females were allowed to mate once with a red-eyed male, and then given the chance to re-mate with a brown-eyed male. The male offspring were then separated according to whether their father was an initially mated or re-mated male and cultured to test for paternity. The study found that the grand-offspring of the re-mated male had slightly lower fecundity than the initially mated male and did not make up for the direct costs involved in re-mating caused by increased male exposure. It is estimated that about 10% of a female’s fecundity is lost through re-mating while about 3% is gained through indirect benefits.

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