Showing papers by "Geoff A. Parker published in 1990"

Optimality theory in evolutionary biology

Abstract: Optimization models help us to test our insight into the biological constraints that influence the outcome of evolution. They serve to improve our understanding about adaptations, rather than to demonstrate that natural selection produces optimal solutions.

Analysing sperm competition data: simple models for predicting mechanisms.

Abstract: Prospective models are developed for analysing sperm competition data so as to predict the underlying mechanisms determining paternity in multiply mated females. The models require: 1) estimations of proportion of offspring sired by the last male to mate (P 2), 2) knowledge of the number of sperm transferred by each male, and 3) knowledge of the sperm storage capacity of the female, should this be limited. They will distinguish between “raffles” (sperm mixing without displacement) and sperm displacement mechanisms. The sensitivity of the techniques can be increased by manipulating the number of sperm transferred by each male. Typically, this can be done by manipulating copula duration or number of ejaculations, given a knowledge of the rate of sperm transfer. Data from two contrasting insect species are fitted to the models to demonstrate the techniques. These models are prospective only, and their limitations are discussed. The principal limitation is that we assume that sperm used for fertilization mix randomly in a “fertilization set” immediately prior to fertilization; in reality this may be difficult to identify. When sperm mixing is very rapid, the fertilization set will often be equivalent to the sperm stores, but with slow mixing, the fertilization set may be equivalent to a much more restricted zone and may change with time.

Male mate choice as predicted by sperm competition in thirteen-lined ground squirrels

Abstract: MALE mate choice is predicted to occur when males transfer nutrients to females during copulation, provide paternal care, or are otherwise limited in mating capacity1–7. Most commonly, field studies have revealed male choice to be focused on females offering high fecundity8–10. Here we describe male mating selectivity that appears to be driven by sperm competition: male thirteen-lined ground squirrels (Spermophilus tridecemlineatus) avoid copulating with previously mated females once the fertilization gain rate drops below the average obtainable from alternative matings. Although this behaviour seems advantageous to males, it limits the duration of female sexual activity.