Unique Genetic Diversity Patterns and Extreme Endemism in Temperate Springs: Evidence From Narrow-Range Endemic Snails

Samantha A. Donohoo, Paul D. Johnson, Nathan V. Whelan. DOI: 10.1111/fwb.70149

Abstract

-Freshwater springs often have high rates of endemism with species displaying restricted distributions, low genetic diversity and increased risk to anthropogenic influences. Several models such as the Theory of Island Biogeography, the Stream Hierarchy Model or the Death Valley Model have been invoked to explain diversity patterns in springs, especially in arid systems. However, little information exists about whether previously developed models can predict population genetic and species-level diversity of temperate spring-obligate invertebrates. As a case study, we examined the biodiversity and genetic diversity of spring-obligate gastropods at six sites in the southeastern United States to examine gastropod diversity and test how well previously developed biogeographic models characterise an understudied and imperilled system.
-We examined two species of Pleuroceridae snails, Princess Elimia (Elimia bellacrenata) and Cockle Elimia (Elimia cochliaris), endemic to springs in central Alabama. We sampled specimens of both species from across their current ranges and generated genome-scale data using a 2b-RAD sequencing approach. To assess species diversity and ranges, we used maximum likelihood, species tree inference and phylogenetic network approaches. We also inferred genetic diversity, population genetic structure and historical demography of each species.
-Phylogenetic analyses recovered four species-level lineages, including two undescribed species. Each species was found in a single spring system, resulting in an extremely small distribution. Additionally, all four of these spring-obligate lineages had higher genetic diversity than most riverine pleurocerid species. Furthermore, demographic analyses suggested that each lineage has maintained a stable population size since the Pleistocene.
-Our findings indicate that diversity patterns of temperate, spring-endemic gastropods do not conform to previously developed biogeographic models. Moreover, differences among species studied here and other spring-obligate groups suggest that applying broad biogeographic models to any given spring system has the potential to obscure unique characteristics of regional spring ecosystems. Empirical data should be more widely generated for understudied spring systems, and such data should inform biodiversity assessments, conservation planning and, potentially, the development of additional biogeographic models.