Abstract

The presence of parasites in a population has an impact on mate choice and has substantial evolutionary significance. A relatively unexplored aspect of this dynamic is whether or not the presence of parasites increases the likelihood of hybridization events, which also have a significant role in ecological adaptation. One explanation of increased hybridization in some areas and not others is that stress from parasites results in selection for an increase of novel genotypes. Two swordtail species Xiphophorus birchmanni and Xiphophorus malinche maintain an active hybrid zone. The patterns of hybridization are unique in that they do not match up directly with expectations. We set out to test whether or not individuals can sense, using chemical cues, whether conspecifics in their immediate vicinity have high parasite loads and also whether this has an effect on mating and association behavior toward both conspecific and hybrid mates. Our hypothesis being that females will have greater association times with hybrid/heterospecific mates if conscpecifics are heavily parasitized. We found that females exposed to parasitized males had a weaker preference for conspecific odor than those exposed to unparasitized males, both relative to a water control and relative to hybrids. The empirical investigation described above is coupled with a historical and philosophical discussion of some of the issues surrounding the acceptance and understanding of the concept of hybridization. This discussion takes as its major themes: an analysis of the role that social views have on the formation of scientific hypothesis; the lag between epochal change in the scientific community and the assimilation of the consequences into social beliefs; the survival of hierarchical and teleological thinking in our concept of species and purity; and the failures of contemporary evolutionary theory to provide satisfactory explanations about the meaning and upshot of hybridization. Two specific misconceptions about hybridization are addressed. First, that hybridization clashes with the belief in kinds/types/species having separate and pure identities. Secondly, the teleological view that reads purpose into nature and places all instances of variation on a hierarchical scale; the top and bottom of which are determined by estimated closeness to the predetermined perfection of a type. < <