Sperm Selection After Mating Essay

1032 words - 5 pages

A Bit of Background Information

What is pre- and post-copulatory sexual selection?
From the word copulatory, meaning to engage in sexual intercourse, pre-copulatory sexual selection refers to the female's choice in selecting a mate before sexual intercourse takes place. Post-copulatory sexual selection occurs within the female's reproductive track, and it describes the biological selection (whether due to sperm or the female's biology) that results in the fertilization her eggs.

Why are guppies good subjects for research in this topic?
The most significant reason for using guppies in sexual selection research is because they casually participate in polyandry. This means ...view middle of the document...

“Attractive” males in the guppy population—deemed attractive based on the female guppy’s affinity for them—were those with high levels of carotenoid coloration (orange, yellow, and red). Relative statures were also compared. The purpose of this experiment is to demonstrate, through artificial insemination, the role of postcopulatory sexual selection in a population of guppies. If guppy females are partial to specific traits, the propagation of those traits will be evident.

The Methods That Were Used

Prior to insemination, the behavior of the guppies involved was analyzed and one adult, non-virgin female and two sexually immature fish were put in observation tanks. The next day an adult male, unknown to the female, was placed in the tank and allowed to settle for 30 minutes. The courtship rate was then measured over a 10-minute period. This part of the experiment allowed its conductors to better understand female preference and mating behavior precopulation.

In this experiment, male guppies were randomly paired, anaesthetized, and photographed in order to measure length and body coloration—the alleged preferred traits. The blue, black, and orange color patterns were analyzed in each male, independent of paternity assignment. The number of sperm per bundle for each of the 23 males was obtained by repeated stripping, all of equal numbers. In each trial, equal numbers of bundles from each of the two males, groups A and B, were mixed and inseminated at the same time in the female via micropipette. The females were then revived from their previous anaesthetization and isolated until they produced offspring. Tissue samples were taken from each fish, and each male’s share of the paternity was measured using two micro satellite markers. Magnified pieces of the primer from each pair were separated by electrophoresis and paternity was assigned according to allele sharing between the guppies.

The James method was used to test fluctuations in the proportion of offspring by each male. Then, a linear model with binomial errors was used to determine the effects of male phenotype on the deviance of group B. Variables that didn’t cause significant change in the mode were excluded.

The Results of the Experiment

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