How climate change affects parasites: the case of trematode parasite Clinostomum complanatum and its fish host Trichogaster fasiatus

This study was undertaken to understand the impact of climate change on the ecology of infection of Clinostomum complanatum, a model trematode parasite. We analysed climate change data and data from infected fish over a period of seven years (2007-2013) from the Aligarh region (India) in this retrospective study. We show that infection of the trematode parasite Clinostomum complanatum (Rudolphi, 1814) in the forage fish Trichogaster facsiatus (Bloch & Schneider, 1801) is dependent on surface air temperature amongst the (ecologically) relevant climate change variables for both the parasite and its host. This study is the first to implicate surface air temperature as an environmental variable that may contribute towards parasitism, particularly for parasites with a piscine host. The biological relevance of changing climate on the ecology of this parasite is discussed.

Parasitism and the expression of sexual dimorphism

Although a negative covariance between parasite load and sexually selected trait expression is a requirement of few sexual selection models, such a covariance may be a general result of life-history allocation trade-offs. If both allocation to sexually selected traits and to somatic maintenance (immunocompetence) are condition dependent, then in populations where individuals vary in condition, a positive covariance between trait expression and immunocompetence, and thus a negative covariance between trait and parasite load, is expected. We test the prediction that parasite load is generally related to the expression of sexual dimorphism across two breeding seasons in a wild salamander population and show that males have higher trematode parasite loads for their body size than females and that a key sexually selected trait covaries negatively with parasite load in males. We found evidence of a weaker negative relationship between the analogous female trait and parasite infection. These results underscore that parasite infection may covary with expression of sexually selected traits, both within and among species, regardless of the model of sexual selection, and also suggest that the evolution of condition dependence in males may affect the evolution of female trait expression.