Breeding of Euterpina acutifrons,a harpacticid copepod,with special reference to dimorphic males

The breeding of Euterpina acutifrons, a marine harpacticid copepod, was studied both in the laboratory and in the natural population round Anglesey, England, with special reference to dimorphic males. As a result of successful rearing of the species under laboratory conditions, rates of development at different temperatures, and survival and maturation of all types of adults were studied. The dimorphic males developed faster than the females, and the small males had a shorter development time than the larger individuals. Laboratory observations clearly indicated that the males differ markedly in sexual behaviour, the small male being more potent, readily copulating with females, and always very active in breeding. In natural populations, temperature was found to have a limiting influence on the breeding period. Breeding began when the temperature reached 15° to 16°C, and ceased when it fell to 8°C. The most significant feature was the production of small males in nature; they increased in number with the onset of breeding, and always formed a high proportion of the actively breeding population. Both laboratory and field investigations have shown that the small male is a breeding form, and is apparently an adaptation of the species for carrying out successful breeding in the colder areas of its distribution.