“A Jack-of-all-trades or a Master of One”? Host Specificity of a Behavior-Modifying Parasite

Ecological theory predicts that specialization increases the exploitation of a suitable niche at the expense of the number of suitable niches. The degree of host specificity of Euhaplorchis sp., a specialist parasite encysting on the brain and manipulating its fish host behavior, was tested based on the phylogeny of five fish species; the Sheepshead Minnow (Cyprinodon variegatus), Longnose Killifish (Fundulus similis), Gulf Killifish (Fundulus grandis), Rainwater Killifish (Lucania Parva) and the Amazon Molly (Poecilia formosa). Wild-caught fish were measured, weighed, and dissected to assess the number of Euhaplorchis on the brain and in the liver. Out of the five species that were dissected, only three of them contained Euhaplorchis sp. on the brain; the Longnose Killifish, Gulf Killifish, Rainwater Killifish and the Amazon Molly. While two of the three species are closely related (F. similis, and F. grandis,), P. formosa is relatively distantly related to the other two suggesting that Euhaplorchis sp. may not be as host specific as previously thought. Experimental infections and behavioral studies are currently being conducted to verify our observational data.