Abstract
The latitudinal diversity gradient (LDG) is an established macroecological pattern, but is poorly studied in microbial organisms, particularly parasites. In this study, we tested whether latitude, elevation, and host species predicted patterns of prevalence, alpha diversity, and community turnover of hemosporidian parasites. We expected parasite diversity to decrease with latitude, alongside the diversity of their hosts and vectors. Similarly, we expected infection prevalence to decrease with latitude as vector abundances decrease. Lastly, we expected parasite community turnover to increase with latitudinal distance and to be higher between rather than within host species. We tested these hypotheses by screening blood and tissue samples of three closely related avian species in a clade of North American songbirds (Turdidae: Catharus, n = 466) across 17.5° of latitude. We used a nested PCR approach to identify parasites in hemosporidian genera that are transmitted by different dipteran vectors. Then, we implemented linear‐mixed effects and generalized dissimilarity models to evaluate the effects of latitude, elevation, and host species on parasite metrics. We found high diversity of hemosporidian parasites in Catharus thrushes (n = 44 lineages) but no evidence of latitudinal gradients in alpha diversity or prevalence. Parasites in the genus Leucocytozoon were most prevalent and lineage rich in this study system; however, there was limited turnover with latitude and host species. Contrastingly, Plasmodium parasites were less prevalent and diverse than Leucocytozoon parasites, yet communities turned over at a higher rate with latitude and host species. Leucocytozoon communities were skewed by the dominance of one or two highly prevalent lineages with broad latitudinal distributions. The few studies that evaluate the hemosporidian LDG do not find consistent patterns of prevalence and diversity, which makes it challenging to predict how they will respond to global climate change.
Highlights
One of the most universal patterns in ecology is the latitudinal diversity gradient (LDG), where communities become less species rich with increasing latitude (Hillebrand, 2004; Mannion, Upchurch, Benson, & Goswami, 2014)
We evaluated the phylogenetic relationship among lineages based on mitochondrial DNA sequences using maximum likelihood (ML) with 1,000 replicate bootstrap support in MEGA7 (Kumar, Stecher, & Tamura, 2016)
Latitudinal increases in Leucocytozoon prevalence and diversity are thought to be related to their vector biology (Fecchio et al, 2019), as Leucocytozoon parasites are transmitted by blackflies, which increase in abundance and species richness with increasing latitude (McCreadie & Adler, 2014; McCreadie et al, 2017)
Summary
One of the most universal patterns in ecology is the latitudinal diversity gradient (LDG), where communities become less species rich with increasing latitude (Hillebrand, 2004; Mannion, Upchurch, Benson, & Goswami, 2014). We investigated the latitudinal variation in parasite diversity (alpha and beta) and infection prevalence in a model parasite system (Order Haemosporidia) infecting a clade of three closely related avian host species. These parasites cause acute infections that vary in the severity of symptoms, but generally result in some level of anemia, enlargement of liver and spleen, and infection of phagocytes (Valkiunas, 2005). Our central goals are to (i) document the alpha and beta diversity and infection prevalence of three genera of hemosporidian parasites infecting Catharus thrushes and (ii) evaluate the role of latitude, elevation and host species on variation in these three parasite metrics
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