Relative fitness components measured with competitive PCR

In mating systems with sperm competition, paternity is frequently establish ed with modem DNA techniques. These methods are often expensive and cumbers ome, and can be especially difficult for highly fecund species. An addition al objective of many paternity studies is to discover the relationship betw een sperm number and paternity. We present here a competitive polymerase ch ain reaction (PCR) protocol, coupled with the use of an automated sequencer , that has two functions: (i) to measure directly relative sperm output of males in sperm competition; and (ii) to estimate paternity distributions of large numbers of offspring simultaneously. Our technique was calibrated us ing a microsatellite locus of the bluehead wrasse, Thalassoma bifasciatum, with the result that product ratio after competitive PCR accurately reflect ed the initial template proportions of known mixtures of DNA. When we appli ed our technique to multiple larvae of separate mating events we found that paternity distributions estimated with the competitive PCR technique close ly matched the estimates derived from the traditional method of pooling pat ernity data from individual larvae. Finally, we compared paternity of these spawns with relative sperm contribution estimates. This comparison suggest s that ejaculate size alone does not predict a male's proportion of paterni ty within the group.