Interview with the authors: Genetic data and niche modeling reveal complex interspecific interactions of invasive species with native congeners and help evaluate distribution pattern, range limits and invasion risk of the species

In a recent paper in Molecular Ecology, Espindola and Vázquez-Domínguez et al. combined comprehensive fieldwork, genetic analyses and a novel niche modeling approach to investigate population genetic patterns, distribution patterns of native and non-native red-eared slider turtle (Trachemys scripta elegans), one of the worst invasive species across the world, and its congeners. They found very little naturally occurring distribution overlap and genetic admixture between red-eared slider and other Trachemys species studied. In addition, they demonstrated that the native Trachemys species in Mexico have distinct climatic niche suitability, which probably prevents the invasion of red-eared slider in the area. However, major niche overlap was found between non-native red-eared slider and native species from different parts of the world, indicating that sites closer to ecological optima of invasive species have higher establishment risk than those closer to the niche-centre of the native species.

We sent a number of questions to lead authors of this work, Sayra Espindola and Ella Vázquez-Domínguez, to get more detail on this study.

What led to your interest in this topic / what was the motivation for this study? 

We have interest in population genetics of invasive species. In addition, Trachemys scripta elegans, one of the World’s 100 worst invasive species, is native to NE North America, and several native congeneric species are naturally distributed along the eastern coast of Mexico, which is an extraordinary scenario to test the effect of congeners on potential invasion patterns and evaluate their climatic and niche differences.

Trachemys spp (T. scripta, T. venusta, T. cataspila, T. taylori) and their distributions along the west coast of USA and Mexico. Trachemys scripta (red dots) in Mexico is non-native. A turtle trapping net is shown. Figure credit: Sayra Espindola/Ella Vázquez-Domínguez

What difficulties did you run into along the way? 

Maybe the most significant was that, at the time we did the molecular laboratory work, extracting DNA from samples that had been stored in formaldehyde (museum samples) was rather difficult, thus we could not obtain genomic data (SNPs) for those samples (extraction kits are much more efficient now). Nonetheless, we did sequence nuclear microsatellites loci, which provided adequate genetic information that enabled us to show the significant contemporary genetic differentiation present between native and non-native Trachemys scripta elegans individuals. 

What is the biggest or most surprising innovation highlighted in this study? 

There are two interesting findings. One is that non-native Trachemys scripta elegans individuals have very little naturally occurring distribution overlap and admixture with its congeners – they exhibited reduced gene flow and clear genetic separation despite having zones of contact. Also, we demonstrate that the native Trachemys species studied (T. cataspila, T. venusta) have distinct climatic niche suitability, which prevents the establishment of and displacement by the non-native Trachemys scripta elegans. Yet, as T. s. elegans has invaded and displaced native turtle species worldwide, we show that sites closer to T. s. elegans’ niche-center have higher establishment risk than those closer to the niche-center of the native species.

Moving forward, what are the next steps in this area of research?

We are working with our genomic data to identify loci under selection to evaluate the potential connection between specific genes and adaptive traits in these turtles. Considering the distinct climatic niches and distribution we found for the turtles, we are very kin to elucidate if there are adaptive differences among them. In addition, our results set the basis for future work – whole genome or gene-targeted sequencing, as well as a higher number of field-sampled individuals, would allow assessment of hybridization and specific gene introgression.

What would your message be for students about to start developing or using novel techniques in Molecular Ecology?

We would first tell them that molecular ecology research, combining ecological fieldwork and laboratory tasks, is absolutely amazing! We recommend choosing to work with the species/taxa that you more deeply like – this makes the journey very enjoyable; and also selecting a laboratory and research group with ample experience in molecular work and analyses, while at the same time not afraid of proposing novel questions and ways of analyzing them.

What have you learned about methods and resource development over the course of this project?

In this project, we proposed and developed a novel modeling approach, in which by contrasting the niche suitability of the species, we were able to include, indirectly, the interactions that can occur when a species is introduced to habitats occupied by other species. The model is based on analyses of climatic niche suitability and the environmental centrality hypothesis, where fitness is expected to be highest in sites with environments closest to the center of the niche of the species. The development of this model and algorithms required an immense number of trials and errors, and once we had the final version, we had to again improve it after revision. The lesson then is that developing analytical models can take a lot, lot of time, but it is always worth the while!

Little climatic niche overlap between Trachemys scripta and two of its congeners, T. venusta and T. cataspila. Figure credit: Sayra Espindola/Ella Vázquez-Domínguez

Describe the significance of this research for the general scientific community in one sentence.

The distribution, range limits and potential risk of the invasion of invasive species can be evaluated with genetic information and ecological niche modeling.

Describe the significance of this research for your scientific community in one sentence.

Evaluating interspecific interactions between native and non-native closely related species with genetic information and niche modeling approach was key to determine the distribution patterns, range limits and invasion risks of Trachemys scripta elegans.

Wetlands system in the valley of Cuatrocienegas, Coahuila, Mexico, where the endemic Trachemys taylori lives. Photo credit: Ella Vázquez-Domínguez

Espindola S, Vázquez-Domínguez E, Nakamura M, Osorio-Olvera L, Martínez-Meyer E, Myers EA, Overcast I, Reid BN, Burbrink FT. 2022. Complex genetic patterns and distribution limits mediated by native congeners of the worldwide invasive red-eared slider turtle. Molecular Ecology.