Reproductive interference in concurrent infections of two Protopolystoma species (Monogenea: Polystomatidae)

The prevention of interspecific reproductive interference is one possible explanation for spatial niche divergence between congeneric monogeneans. However, there is little direct evidence that reproductive interactions with other species are potentially deleterious to the majority of parasitic platyhelminths. Xenopus fraseri-like clawed toads from lowland rainforest in eastern Democratic Republic of Congo are infected by two species of polystomatid monogenean, Protopolystoma fissilis and Protopolystoma ramulosus. Both occur as adults in the host urinary bladder, and exhibit identical copulatory structures and similar body sizes. The small area of the habitat in relation to parasite body size makes close proximity inevitable in concurrent infections. Eggs were collected from five naturally infected hosts: two of these harboured concurrent infections, and three were infected with P. fissilis only. Eggs from concurrent infections showed reduced viability (57.6% embryonation, n = 413) compared with those from P. fissilis-only infections (85.2%, n = 439). This effect may be due to some form of reproductive interference, possibly failure to develop following interspecific cross-fertilisation.