Surface glycoproteins in copepods: potential signals for mate recognition

Abstract

The mechanism male copepods use to recognize mates is not well understood. Both chemical and mechanical cues have been implicated, but the relative importance of these is not known. This lack of knowledge is despite the belief that mate recognition has a critical role in maintaining reproductive isolation of many species and influences the direction of evolution. Glycoproteins are used as mating signals by a number of aquatic organisms including rotifers, ciliates, and algae. We have developed techniques for selectively probing surface glycoproteins in zooplankton using fluorescently labeled lectins. We examined surface glycoproteins on the urosomes of several species of marine and freshwater copepods to develop insight into their role in mate recognition. Calanoids Labidocera aestiva, Centropages hamatus, and Acartia tonsa were collected in the northern Gulf of Mexico and screened with 12 lectins representing a wide variety of carbohydrate affinities. The harpacticoid Coulana sp. originally collected from Florida was screened for the same 12 lectins. The freshwater calanoid Skistodiaptomus pygmaeus and the cyclopoid Mesocyclops edax also were investigated and compared to the marine species. The sites of lectin binding were consistent across species. Most fluorescence was observed in the urosome at the caudal rami, gonopore, margin of the genital segment, and urosome segment junctions. The signal contrast (signal/background ratio) along the urosome ranged from 3–51 which seems ample for males to discriminate a glycoprotein signal from noise. Our observations clearly demonstrate that glycoproteins on the urosome of females from all six species are present at sites expected to be important in mate recognition.