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 if: 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

Taxa: Rodentia: Cricetidae; Nematoda; Platyhelminthes

Methods: We sampled parasites from hosts at field sites set approximately every 10 degrees 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 non-linear. 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.

We collected rodents and their helminths from six field sites set approximately every 10 degrees in latitude across North and Central America.

We report rodent weight and measurements (lengths of total body, tail, hind foot, and ear). Parasites were collected from each individual and identified using standard keys. Parasites were identified down to the lowest level when possible, and otherwise were sorted by morphotype. Rodent specimens were prepared for museum installation and were archived into multiple natural history collections.

Following host and parasite collection and identification, we assembled data on the abundance of each parasite species, host species, host body mass, and latitude and longitude of
the collection site for each host individual. We used the geographic coordinates to obtain climate data from WorldClim at 30 arc seconds resolution (~1 km, Hijmans, Cameron, Parra, Jones, & Jarvis, 2005); specifically, coordinates were translated onto the WGS84 geographic coordinate system and used to extract climate data specific to each locality. We extracted all BioClim variables.

For detailed and specific methodologies, please see the published manuscript.