Northern Leopard Frog populations in the southwest

Rana pipiens. JCM

In the southwest, the Northern Leopard Frog, Rana (Lithobates) pipiens, is considered a threatened species, Much of this is due to droughts, land development, and falling water tables because of human water needs.

Invasive species are a major contributor to loss of biodiversity. However, translocations of a species within its own distribution are less frequently recognized, but have the potential for negative impacts on the native population. Genetic mixing may lead to loss of local adaptations or further decline through outbreeding depression. Cryptic invasions of new genetic material into populations that did not previously contain that genetic material may be quite difficult to recognize, but genetic tools can be used to recognize and monitor such intraspecific introductions. Conversely, translocations within species can be an important conservation tool to reduce inbreeding depression and replace lost genetic diversity.

Thus, cryptic invasions can be either an aid or a hinder conservation efforts. In a recent paper O’Donnell et al.(2016) tested for the presence of non-native genotypes and assessed the extent and nature of introgression in populations of Northern Leopard Frog in the southwestern US, where populations have declined to a few remnant populations. The most abundant and diverse complex of populations in the region contained a mitochondrial haplotype that was not native to the western US. This haplotype is likely the  resulting of released pets, laboratory animals, or animals accidentally release during fish stocking. These non-native haplotypes were well integrated into a large complex of ponds and lakes, contributing to high genetic diversity in this area. The geographic extent of non-native genetic influence within this population makes eliminating or controlling the non-native component of this population not possible.

The authors recommend assessing the progress and fate of the introgression over time—along with population fitness parameters—to determine whether this introduction is beneficial or detrimental to population persistence. Meanwhile, translocations from nearby locations with similar environmental conditions have the best prospects for avoiding problems with outbreeding depression in other declining populations and will also most effectively preserve regional genetic diversity.

O’Donnell RP, Drost CA, Mock KE. Cryptic invasion of Northern Leopard Frogs (Rana pipiens) across phylogeographic boundaries and a dilemma for conservation of a declining amphibian. Biological Invasions 2016:1-4.

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