“A probable case of incipient speciation in Schizocosa wolf spiders driven by allochrony, habitat use, and female mate choice”
R. Tucker Gilman, Kasey Fowler-Finn, and Eileen A. Hebets (Sep 2018)
Behavioral work reveals new incipient species pair in Schizocosa wolf spiders
Understanding the mechanisms that produce reproductive isolation and promote speciation has been a major goal of biologists since Darwin. In this paper, researchers report the discovery of a previously unrecognized ongoing speciation process in a well-studied population of wolf spiders in Oxford, Mississippi. The team showed that preferences for different habitat types, differences in maturation time, and female mate choice all contribute to reproductive isolation between sexually ornamented and unornamented spider morphotypes. This work suggests that speciation may not be driven by single mechanisms, but rather by suites of mechanisms operating together. The discovery of a new ongoing speciation process in wolf spiders adds to the short list of systems that scientists can use to study how speciation happens, and suggests that there may be additional species to discover even in well-studied systems.
There is growing evidence that speciation can occur between populations that are not geographically isolated. The emergence of assortative mating is believed to be critical to this process, but how assortative mating arises in diverging populations is poorly understood. The wolf spider genus Schizocosa has become a model system for studying mechanisms of assortative mating. We conducted a series of experiments to identify the factors that control mate pair formation in a Schizocosa population that includes both ornamented and non-ornamented males. We show that the population also includes two previously unrecognized female phenotypes. One female phenotype mates mostly or exclusively with ornamented males, and the other mates mostly or exclusively with unornamented males. Assortative mating within these groups is maintained by differences in maturation time, microhabitat use, and female mate preference. We conclude that the population is not a single species as previously believed, but rather an incipient species pair with multiple overlapping mechanisms of reproductive isolation. The identification of a new incipient species pair in the well-studied and rapidly speciating Schizocosa clade presents new opportunities for the study of speciation without geographic isolation.