Greg B Pauly’s research while affiliated with Natural History Museum of Los Angeles County and other places

Understanding the evolutionary history of diversifying lineages and the delineation of evolutionarily significant units and species remain major challenges for evolutionary biology. Low cost representational sampling of the genome for single nucleotide polymorphisms (SNPs) shows great potential at the temporal scales that are typically the focus of species delimitation and phylogeography. We apply these markers to a case study of a freshwater turtle, Emydura macquarii, whose systematics has so far defied resolution, to bring to light a dynamic system of substantive allopatric lineages diverging on independent evolutionary trajectories, but held back in the process of speciation by low level and episodic exchange of alleles across drainage divides on various timescales. In the context of low‐level episodic gene flow, speciation is often reticulate, rather than a bifurcating process. We argue that species delimitation needs to take into account the pattern of ancestry and descent of diverging lineages in allopatry together with the recent and contemporary processes of dispersal and gene flow that retard and obscure that divergence. Underpinned by a strong focus on lineage diagnosabilty, this combined approach provides a means for addressing the challenges of incompletely isolated populations with uncommon, but recurrent gene flow in studies of species delimitation, a situation likely to be frequently encountered. Taxonomic decisions in cases of allopatry often require subjective judgements. Our strategy, which adds an additional level of objectivity before that subjectivity is applied, reduces the risk of taxonomic inflation that can accompany lineage approaches to species delimitation. This article is protected by copyright. All rights reserved.

The red-eared slider turtle (Trachemys scripta elegans; RES) is one of the worlds most invasive species. Native to the central United States, RES are now widely established in freshwater habitats across the globe, largely due to release of unwanted pets. Laboratory and mesocosm experiments suggest that introduced RES are competitively dominant to native turtles, but such competition remains untested in the wild. Here, we experimentally removed introduced RES to test whether they compete for critical basking habitat with native, threatened western pond turtles (Emys marmorata; WPT), a species being considered for listing under the U.S. Endangered Species Act. Following removal, we found that both the remaining RES as well as WPT altered their basking distribution but in a manner inconsistent with strong interspecific competition. However, these findings suggest strong intraspecific competition for basking sites amongst RES and that interspecific competition between WPT and introduced RES likely occurs at higher RES densities. Our works suggests RES influence the behavior of native species in the wild and indicates that RES removal may be most beneficial at high RES densities. This experiment highlights the importance of considering experimental venue when evaluating competition between native and non-native species and should encourage conservation biologists to treat removal efforts as experiments.