Contrasting regulation of fecundity in two abomasal nematodes of Svalbard reindeer (Rangifer tarandus platyrhynchus)

Stability of trichustrogylid populations indicates that some form of densit y-dependent regulation occurs which could act through fecundity. We present evidence for intraspecific density-dependent effects in 1 of 2, dominant, abomasal nematodes species (Ostertagia gruchneri) of Svalbard reindeer (Ran gifer tarandus platyrynchus). We found evidence in O. gruehnei, for density -dependent regulation of female worm length in April, July and October 1999 . However, it is only in July that female worm length explains the variatio n in the number of eggs in utero which is also related to egg production pe r female worm only in this month and not at other times of the gear. The se asonal pattern in faecal egg output in this species focuses egg production in the summer months when conditions are favourable to transmission. In con trast, we found no evidence in the other common species (Marshallagia,marsh alli) for density-dependent regulation of female worm length during or the number of eggs in vitro. Faecal egg output in M., marshalli was positively related to worm burden but not to the mean number of eggs in utero. neither inter-specific interactions nor host body condition appeared to influence worm fecundity. The contrasting patterns of density-dependent regulation of fecundity provides further evidence for divergent life-histories in this n ematode community.