Journal of Plankton Research Vol.24 no.7 pp.653-659, 2002
© Oxford University Press 2002
Clutch size variation and morphology in a cyclomorphic Bosmina population
1 Göteborg University, Department Of Zoology, Section Of Animal Ecology, Box 463, Se-405 30 Göteborg and 2 University College Of Borås, School Of Engineering, Se-501 90 Borås, Sweden
* ragnar.lagergren{at}zool.gu.se
Clutch size, cyclomorphosis and allometric growth were analysed in a population of the humpbacked Bosmina (E.) coregoni gibbera. This species shows cyclomorphosis in antennule length and body height, traits that may reduce predation risk from Leptodora kindtii. Individuals with long antennule and extreme body height may pay a cost in terms of decreased reproductive capacity. On the other hand, increasing the body height may be a way to increase the brood chamber volume during periods of good food conditions. We tested these hypotheses by comparing the seasonal variation in clutch size with the seasonal variation in morphology. Antennule length and body height increased from mid-May to August and showed usually positive allometry at times with high population densities of the predatory cladoceran Leptodora kindtii. Clutch size decreased from spring to late summer contrary to the hypothesis that cyclomorphosis in height is caused by a seasonal variation in reproductive demand. However, within-dates antennule length was negatively related and body height was positively related to clutch size. We conclude that the long antennule may impose a cost that reduces the reproductive capacity. The hypothesis that carapace cyclomorphosis is driven by seasonally varying clutch sizes was rejected.