Strong phenotypic differentiation in an intertidal snail induced by a parasitic castrator

NICOLÁS BONEL; PILAR ALDA

Habana

Congreso; XXVI Congreso de la Federación Latinoamericana de Parasitología; 2022

Sociedad Cubana de Microbiología y Parasitología

Phenotypic variation in shell traits is particularly widespread in gastropods and their shells offer an easily measured and permanent record of how the organism responded to local abiotic (e.g. water chemistry, temperature) and biotic (e.g. predation, parasitism) agents. Parasites, for instance, can induce morphological, behavioral, and physiological change of individual snail hosts, and thereby influence several aspects of host life history that can significantly alter size structure, demography, resource use, and intra and interspecific interactions of the host population. They have been also reported to induce changes in microhabitat choice and body size in snails. Trematode infection not only inevitably leads to snail castration, reducing its fitness to zero, but also gives rise to smaller shell-sized morphs for infected snails. Such pressure exerted by parasites differs along the intertidal zone and can cause important shifts in the expression of host phenotypic traits, creating pronounced phenotypic differences between infected and uninfected hosts. The prevalence of trematodes is higher in the lower area (pans) of the intertidal zone, where parasite infection is predominately caused by one extremely prevalent trematode, Microphallus simillimus. One possible approach to analyze the contribution of parasites to the phenotypic variance in host populations is to compare phenotypic responses of uninfected and infected hosts maintained under identical conditions. To test for this, we collected, dissected, and measured shell traits from individuals of the intertidal mud snail Heleobia australis (d'Orbigny, 1835) (Rissooidea: Cochliopidae) from pans at the Bahía Blanca estuary, Southwestern Atlantic, Argentina. We focused on snails from pans and infected by M. simillimus, which implies that both infected and uninfected snails grew in the same environmental conditions and that traits were not affected by other parasite species. We found that infection by the trematode M. simillimus strongly decreased mean values of most phenotypic traits of H. australis compared to uninfected snails. Infection by trematodes might promote an energy reallocation from growth to early reproduction, which could explain the smaller shell size compared to uninfected snails.