Taxonomic scale and community organization impact observed latitudinal gradients of parasite diversity

Aim: While most free-living taxa follow the latitudinal diversity gradient (LDG), or the trend of higher diversity at lower latitudes, we know little about how the diversity of parasitic taxa is distributed across latitudes. To better understand the macroecological patterns of parasite diversity, we sought to determine whether (1) helminths follow the traditional LDG; (2) taxonomic resolution impacts observed patterns; (3) latitudinal patterns are consistent across levels of community organization and (4) helminth diversity is correlated with climate- and host-associated variables.

Location: San Juan de Peñas Blancas, Costa Rica; Calnali, Hidalgo, Mexico; College Station, Texas, USA; Brownsville, Nebraska, USA; Winnipeg, Manitoba, Canada; Churchill, Manitoba, Canada

Taxon: Rodentia: Cricetidae; Nematoda; Platyhelminthes

Methods: We sampled parasites from hosts at field sites set approximately every 10° in latitude. We evaluated the relationships between parasite species richness (of all helminths as well as nematodes, cestodes and trematodes separately) and latitude, climate, and host mass at two levels of parasite community organization, the infracommunity and the component community, using generalized additive models.

Results: Total helminth richness was significantly correlated with latitude, but the relationship was nonlinear. Nematode, cestode and trematode diversity were also significantly correlated with latitude, but the relationship differed between the levels of community organization and among the taxonomic groups. Climate- and host-associated variables were significantly correlated with different parasite taxa, although the strength and size of the correlations varied among the groups.

Main conclusions: There are complex associations between parasite richness and latitude, climate, and host traits, and community organization and taxonomic grouping affected the observed relationships. Climate has been implicated as an important factor in shaping LDG patterns and may similarly influence helminth diversity patterns. Overall, this work provides further support and exceptions to the LDG and stresses the importance of considering scale in ecological investigations.