Geographical variation in male courtship behaviour and sexual isolation in wolf spiders of the genusSchizocosa

Abstract We surveyed 12 populations of the wolf spider Schizocosa crassipes (Walckenaer) and S . nr. crassipes in Tennessee, Mississippi, Louisiana and Florida, in the U.S. to determine the extent of variation in male courtship behaviour when observed in standard laboratory conditions. We observed variation in both the frequency of occurrence and the sequence of the four principal male courtship behaviours and, when compared statistically, most of these behaviours differed between populations. Although there was no clinal pattern in the frequency of courtship behaviour, we observed geographically consistent patterns in the sequence in which male courtship behaviours are displayed. We conducted two subsequent studies to determine whether sexual isolation among selected populations existed. In the first study, we performed male–female reciprocal crosses of brush-legged spiders ( S . nr. crassipes ) between two populations from the Yazoo–Mississippi Delta physiographical region and one population from the Loess Bluff region of Mississippi and measured mating success, number of matings that produced egg sacs, and the number of egg sacs that hatched young. The results of that experiment suggest that sexual isolation occurs among populations in different physiographical regions but not between populations within regions of the state. In a second crossing study, we paired the brush-legged spiders from one of the Mississippi physiographical regions (Yazoo–Mississippi Delta) with Schizocosa ocreata (Hentz) from Ohio. The results of that cross suggest that the Mississippi Delta population is more similar to the northern S. ocreata populations than to S. crassipes . We discuss the results of the crossing experiments in terms of what was revealed about geographical patterns in male courtship behaviour.