Short pond hydroperiod decreases fitness of nonnative hybrid salamanders in California

Abstract

Human-facilitated introductions of nonnative taxa have changed species' geographic ranges and increased the prevalence of secondary contact and the potential for hybridization, with a host of effects on ecological systems. Land managers increasingly face these complex situations, tasked with developing strategies to preserve biodiversity in the face of such changes. We conducted a management-relevant experiment to inform the development of strategies for management of wild populations. We examined the fitness consequences of genetic admixture in a hybrid swarm between native California tiger salamanders and nonnative barred tiger salamanders. Variation in hydroperiod within the hybrid zone has previously been observed to affect landscape patterns of genetic introgression, with modified permanent ponds harboring salamanders with a greater proportion of nonnative genes. Our study experimentally examines the relationship between hydroperiod and fitness of three classes of salamanders: native, nonnative and hybrid. Using experimental pond mesocosms, we implemented three pond drying regimes and recorded survival and secondary determinants of salamander fitness. Our results indicate native-genotype advantages in rapidly drying mesocosms relative to other genetic classes. Furthermore, our results indicate that management of aquatic habitat to minimize the success of hybrid individuals may be a viable strategy to reduce the spread of nonnative genotypes. Overall, our approach demonstrates how controlled experiments can be designed to provide meaningful information for the development of real-world conservation strategies.