Blind dating—mate finding in planktonic copepods. I. Tracking the pheromone trail of Centropages typicus

Abstract

Mate-finding behaviour in the marine copepod Centropages typicus was investigated by 3-dimensional video analysis. Females leave a chemical trail in their wake and a male intercept- ing a fresh trail initiates a characteristic tracking behaviour in which he increases his speed from ~10 to ~30 mm s -1 and races up the female trail while displaying a tight zigzag motion. Within sec- onds the male overtakes the female and attempts to catch her. Males faithfully follow even very con- voluted trails and successfully track down females after pursuing trails up to 31 s old and 17 cm long. The probability of detecting a trail is inversely related to trail age and length. Males often start track- ing female trails in the wrong direction before correcting themselves, and the frequency of direc- tional errors increases with increasing trail age. Complicated or disrupted signal trails may cause males to lose the trail. This induces a distinct signal-scanning behaviour characterised by further enhanced swimming speeds of 50 to 70 mm s -1 , and frequent shifts of direction. The male scans a restricted volume around the point where the trail was lost and often regains the trail and resumes normal tracking behaviour. This behaviour may help males follow trails that are broken by turbu- lence. A simple generic model of pheromone trails that is consistent with the tracking behaviour of males in C. typicus and other species of copepods was used to explore the characteristics of pheromone trails. Model considerations suggest that these pheromones are small molecules, e.g. amino acids, and that the investment in pheromone production, both in terms of elements and metabolic energy, represents only a small fraction of the females' ingestion and metabolic rate.