Ecological correlates of body size and egg size in parasitic Ascothoracida and Rhizocephala (Crustacea)

In order to identify key factors in the evolution of life history traits in Ascothoracida and Rhizocephala (two groups of crustacean parastes of invertebrates), comparative analyses were performed using phylogenetically independent contrasts. Among 59 ascothoracidan species, latitude correlated positively with body size, whereas there was no relationship between water depth and body size. Body size also correlated strongly with egg size; however, once corrected for body size, egg size was not related to either latitude or water depth. Among 91 rhizocephalan species, neither latitude nor water depth correlated with body size. However, host species of larger sizes harboured larger species of rhizocephalan parasites. Egg size of rhizocephalans did not correlate with body size, and was not influenced by either latitude or water depth. The patterns observed in this study show both differences from an similarities to those reported for other groups of crustacean parasites, and suggest that adaptations to similar selective pressures are not always identical among distantly-related taxa.