Comparative study of mother-young association in caprellid amphipods: Is maternal care effective?

Mother-young association was examined in 9 species of caprellid amphipods in the genus Caprella. Five species: Caprella arimotoi, C. danilevskii, C. glabra, C. okadai, and C. penantis showed no interaction between mother and young after emergence from her broad pouch, but various degrees of prolonged cohabitation of young with their mother were observed in the other four species. In Caprella subinermis, though no maternal care was observed, the first instars remained on the body of the mother for up to 4 days, and then dispersed before the first molt. Aggregations of young protected by the mother were observed in the other 3 species. Aggregations of a mother with multiple cohorts of young were found in Caprella decipiens, while C. monoceros and C. scaura had single cohorts of young on or around the body of the mother. Based on field data and results of field-rearing experiments, the cohabiting period is up to 30 days in C. decipiens and up to 20 days in C. monoceros. For 5 species having different degrees of mother-young association, one-month field-rearing experiments under predator-free conditions were conducted. The results showed that the presence of the mother increased both the survival and growth rate of the young in C. monoceros, but the presence of the mother increased only the growth rate in C. scaura. In the other 3 species, C. danilevskii, C. decipiens, and C. subinermis, the presence of the mother did not positively affect either survival or growth of the young.