Detecting turnover among complex communities using null models: a case study with sky-island haemosporidian parasites.

Turnover in species composition between sites, or beta diversity, is a critical component of species diversity that is typically influenced by geography, environment, and biotic interactions. Quantifying turnover is particularly challenging, however, in multi-host, multi-parasite assemblages where undersampling is unavoidable, resulting in inflated estimates of turnover and uncertainty about its spatial scale. We developed and implemented a framework using null models to test for community turnover in avian haemosporidian communities of three sky islands in the southwestern United States. We screened 776 birds for haemosporidian parasites from three genera (Parahaemoproteus, Plasmodium, and Leucocytozoon) by amplifying and sequencing a mitochondrial DNA barcode. We detected infections in 280 birds (36.1%), sequenced 357 infections, and found a total of 99 parasite haplotypes. When compared to communities simulated from a regional pool, we observed more unique, single-mountain haplotypes and fewer haplotypes shared among three mountain ranges than expected, indicating that haemosporidian communities differ to some degree among adjacent mountain ranges. These results were robust even after pruning datasets to include only identical sets of host species, and they were consistent for two of the three haemosporidian genera. The two more distant mountain ranges were more similar to each other than the one located centrally, suggesting that the differences we detected were due to stochastic colonization-extirpation dynamics. These results demonstrate that avian haemosporidian communities of temperate-zone forests differ on relatively fine spatial scales between adjacent sky islands. Null models are essential tools for testing the spatial scale of turnover in complex, undersampled, and poorly known systems.

Dynamics of Amphibian Pathogen Detection Using Extended Museum Specimens.

Natural history collections have long served as the foundation for understanding our planet's biodiversity, yet they remain a largely untapped resource for wildlife disease studies. Extended specimens include multiple data types and specimen preparations that capture the phenotype and genotype of an organism and its symbionts-but preserved tissues may not always be optimized for downstream detection of various pathogens. Frogs are infected by an array of pathogens including Batrachochytrium dendrobatidis (Bd), Ranavirus (Rv), and Amphibian Perkinsea (Pr), which provides the opportunity to study differences in detection dynamics across tissue types. We used quantitative PCR protocols to screen two tissue types commonly deposited in museum collections, toe clips and liver, from two closely related host species, Rana catesbeiana and Rana clamitans. We compared Bd, Rv, and Pr infection prevalence and intensity between species and tissue types and found no significant difference in prevalence between species, but Bd intensity was higher in R. clamitans than R. catesbeiana. Toe tissue exhibited significantly higher Bd infection loads and was more useful than liver for detecting Bd infections. In contrast, Rv was detected from more liver than toe tissues, but the difference was not statistically significant. Our results support the use of extended specimen collections in amphibian disease studies and demonstrate that broader tissue sampling at the time of specimen preparation can maximize their utility for downstream multipathogen detection.