SEXUAL SIZE DIMORPHISM IN PARASITIC OXYURID NEMATODES

As in many invertebrates, female oxyurids are larger than male. Sexual size dimorphism (SSD) of oxyurid nematodes (the hosts of which are bo th invertebrate and vertebrate), is investigated regarding body size o f both host and parasite. SSD of parasites appeared to be weakly, but not significantly, correlated with invertebrate and vertebrate host bo dy size. However, this study reveals a different pattern for SSD with respect to either type of host. SSD does not increase in tandem with b ody size in vertebrate parasites either at the level of species or gen us. SSD is much more pronounced in Syphaciidae than in Heteroxynematid ac, two families of vertebrate parasites exhibiting different modes of transmission (members of the Syphaciidae are transmitted through peri anal contamination). SSD is investigated in one monophyletic group of parasites of primates, for which a phylogeny is known. Independent com parisons method is used and we find that the body size of female paras ite is strongly correlated with that of the male. The hypoallometry (s lope<1) of the relationship suggests that the SSD is not linked to an increase of parasite body size. Moreover, there is no influence of hos t body size on parasite SSD. The pattern in parasites of invertebrates is different. First, SSD has been found to increase with parasite bod y size in two groups of invertebrate parasites: the oxyurids of Dictyo ptera and Coleoptera. Second, female body size of invertebrate parasit es is not correlated with male body size either at genus or species le vel. Finally, the evolution of SSD is discussed in relation to the dem ographic patterns of invertebrate parasites and the haplodiploid mode of reproduction of these parasitic nematodes. (C) 1998 The Linnean Soc iety of London.