Courtship Behavior and Experimental Asymmetrical Hybridization in Dalbulus Leafhoppers (Homoptera: Cicadellidae) with Evolutionary Inferences

Abstract

Dalbulus chiapensis Triplehorn and Nault and D. quinquenotatus DeLong and Nault are biologically distinct species. D. chiapensis is proposed to have evolved from its ancestor, D. quinquenotatus. Evidence of this phylogeny is based on a reexamination of collection records, host plant (gamagrass) distributions, and insect activity patterns. Additional evidence is presented on courtship behavior patterns and hybridization studies that supports this hypothesis. D. chiapensis and D. quinquenotatus asymmetrically hybridized; i.e., D. chiapensis females mated with D. quinquenotatus males, but D. quinquenotatus females did not mate with D. chiapensis males. Heterospecific matings were observed when leafhoppers were placed together on the leaf (no species choice) (47%), and when a female was placed with both a conspecific and a heterospecific male (species choice) (39%). In species-choice treatments, there was no significant difference in percentage of matings of D. chiapensis females with conspecific males (31.7%) and heterospecific males (39%). Male movement on the leaf and female acceptance were compared between conspecific and heterospecific matings; few differences were noted other than some females kicked conspecific males and males stopped courting, whereas no heterospecific males were kicked. Locomotor latency and copulation duration were longest for D. quinquenotatus conspecific matings, shortest for D. chiapensis conspecifics, and intermediate for heterospecific crosses. This is the first quantitative study of courtship for any leafhopper or planthopper. When males of both species were present with a female, male rivalry was frequently observed, and the male that walked farther was the least likely to mate, possibly indicating male submission. D. chiapensis females mated with D. quinquenotatus males produced fertile offspring; there was no significant difference in numbers of offspring produced from heterospecific compared with conspecific inseminations. Hybridizations of Dalbulus leafhoppers are discussed with reference to Kaneshiro's model of asymmetrical hybridization and predictions of the direction of evolution.