Population relationships between the parasite<i>Aporobopyrus curtatus</i>(Richardson, 1904) (Isopoda: Bopyridae) and one of its porcelain crab hosts<i>Petrolisthes armatus</i>(Gibbes, 1850) (Decapoda: Porcellanidae) from Farol Island, southern Brazil

Abstract

Abstract The following aspects of population relationships between the bopyrid isopod Aporobopyrus curtatus and the porcelain crab Petrolisthes armatus were analysed: size-specific prevalence, parasitic intensity, frequency distribution of the nine groups of parasite stage or sex infesting hosts. Additional sequences of the life cycle of the parasite in the final host are suggested. The crabs were collected monthly at the midlittoral of a boulder and cobble seashore at Farol Island, Parana State, southern Brazil (25°51′S and 48°32′W), from November 1989 to April 1991. A total of 5585 crabs were captured (1.1–13.4 mm carapace width), among which 529 were infested by 967 bopyrid isopods. The parasite was recorded from all crab carapace width classes, but not from megalopas or ovigerous females. Parasitic prevalence ranged from 3.3% (1.0–1.9 mm) to 17.0% (4.0–1.9 mm) and parasitic intensity from one to six per host. Among the parasite population (0.1–4.8 mm widest body width), 66 were cryptoniscus, 52 bopyridia, 131 immature females, 355 mature males, 68 mature females without eggs or embryos, 202 ovigerous females, and 93 females with embryos. The most frequent parasite group is an immature or mature couple in a single host, which is also the most stable and long standing one. This parasite reproduces continuously. It infests young hosts in an early developmental stage and both grow up in a synchronic way. The A. curtatus parasitism is related to the parasitic castration of the female host, but it does not affect the growth of P. armatus. Parasitic castration allied to low parasitic prevalence and to the dominance of the stable couple of parasites in the host population, is an adaptation of the bopyrid isopod which allows advantages for both populations. Keywords : Aporobopyrus curtatus Petrolisthes armatus population relationshipssize-specific prevalenceparasitic intensityparasite groups