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.

Nominations are now open for the Harry Smith Prize 2022

The editorial board recently established a prize that recognizes the best paper published in Molecular Ecology or Molecular Ecology Resources in the last year by graduate students or early career scholars with no more than five years of postdoctoral or fellowship experience. The prize is named after Professor Harry Smith FRS, who founded Molecular Ecology and served as both Chief and Managing Editor during the journal’s critical early years. He continued as the journal’s Managing Editor until 2008, and he went out of his way to encourage early career scholars. In addition to his editorial work, Harry was one of the world’s foremost researchers in photomorphogenesis, leading to concepts such as “neighbour detection” and “shade avoidance,” which are essential to understanding plant responses to crowding and competition. His research provided an early example of how molecular data could inform ecology, and in 2008 he was awarded the Molecular Ecology Prize that recognized both his scientific and editorial contributions to the field. As with the Molecular Ecology Prize, the winner of this annual prize is selected by an independent award committee, but the Harry Smith Prize comes with a 1,000 USD cash award, an announcement in the journal and on social media, as well as an invitation to join the Molecular Ecology Junior Editorial Board. Please send a short supporting statement (no more than 250 words; longer submissions will not be accepted) and PDF of the paper you are nominating to Dr. Alison Gonçalves Nazareno ( or Dr. Kaichi Huang ( by Friday 29 April 2022. Self-nominations are also encouraged. Nominated papers must have been published in Molecular Ecology or Molecular Ecology Resources in 2021.

Interview with the authors: How genomic data reveal cryptic species and how migration patterns maintain genetic divergence in birds?

In a recent paper in Molecular Ecology, Tang et al. investigated genetic divergence of different subspecies of pale sand martin (Riparia diluta) using genome-wide data. They found that the subspecies in Central and East Asia, which vary only gradually in morphology, broadly represent three genetically differentiated lineages. No signs of gene flow were detected between two lineages that met at the eastern edge of the Qinghai-Tibetan Plateau, which is likely due to largely different breeding and migration timing. Limited mixed ancestries were found in Mongolian populations between two lineages that might take divided migration routes around the Qinghai-Tibetan Plateau, and the authors hypothesize that selection against hybrids with nonoptimal migration routes might restrict gene flow. See the full article for more details of the study and the interview with lead author Manuel Schweizer below for more stories behind this exciting work.

Pale sand martin Riparia diluta tibetana, Mongolia, June 2018. Photo Credit: Manuel Schweizer

What led to your interest in this topic / what was the motivation for this study? I studied pale sand martin in Central Asia as part of the work on a field guide to the birds of Central Asia, which was published in 2012. I was then fascinated by the fact that the different subspecies described for this species breed in completely different environments: Central Asian steppes and semi deserts, high altitude grasslands on the Qinghai-Tibetan Plateau, or lowland subtropical China. Although it was evident that morphological identification of single individuals of the different subspecies without context is not possible, I suspected that cryptic diversity might be involved in this complex. This was corroborated by mtDNA data that we published in 2018. Together with Gerald Heckel and our PhD student Qindong Tang, I wanted to investigate this further using genome-wide data and test if gene flow is reduced in areas of potential contact between evolutionary lineages.

Breeding site of pale sand martin on the east edge of Qinghai-Tibetan Plateau in Zoige (Sichuan Province, China). Photo Credit: Qindong Tang

What difficulties did you run into along the way? The biggest challenge was to get a comprehensive geographic sampling together. As pale sand martins breed in low densities only, this meant a lot of travelling. Fortunately, we could count on the great support of our collaboration partners and their network – Yang Liu from Sun Yat-sen University in Guangzhou, China, and Gombobaatar Sundev from the National University of Mongolia. Moreover, Qindong Tang made an incredible effort and did an excellent job during the fieldwork. 

What is the biggest or most surprising innovation highlighted in this study? Given the absence of obvious sexually selected traits and only gradual morphological differentiation between the different evolutionary lineages of the pale sand martin, the level of genetic differences and the fact that they behave like different species at least at the eastern edge of the Qinghai-Tibetan Plateau is indeed surprising. So, we were left with the following question: what processes and mechanism prevent a complete mixing at secondary contact zones? We think that seasonal migration behavior might be an essential factor in maintaining genetic integrity of these morphologically cryptic evolutionary lineages.

Moving forward, what are the next steps in this area of research? The next step is evident: we need to study in detail migration behavior of the different lineages. The ranges of two of them meet in the area of a well-known avian migratory divide, where western lineages take a western migration route around the Qinghai-Tibetan Plateau to winter quarters in South Asia, and eastern lineages take an eastern route to Southeast Asia. This might also be the case in the pale sand martins and we hypothesize that hybrids might have nonoptimal intermediate migration routes and selection against them might restrict gene flow. This will need quite some field work and application of up-date technologies such as modern data loggers. Let’s hope that the development of the pandemic will allow field work again soon.

What would your message be for students about to start developing or using novel techniques in Molecular Ecology? It is best to get started and not be intimidated or even afraid. The easiest way to learn new methods is to start using them. It is also important to build a network of people who can be asked for support when problems arise.

What have you learned about methods and resource development over the course of this project? As always in studies with a phylogeographic background, sampling matters most. Try to organize a complete geographic sampling in the beginning of a project. Sampling in parts of the distribution area of our study system was planned in the third year of Qindong’s PhD, however, this could not be achieved due to the pandemic. As a consequence, we still lack samples from western Mongolia which would have been important and made the overall picture more comprehensive. This work did not include any development of new methods, however, a knowledge of state-of-the art methodological approaches is obviously always crucial.

Describe the significance of this research for the general scientific community in one sentence. Our study points towards contrasting migration behavior as an important factor in maintaining evolutionary diversity under morphological stasis.

Describe the significance of this research for your scientific community in one sentence. Our discovery of cryptic diversity in the pale sand martin indicates that evolutionary diversity might be underestimated even in such well-studied groups such as birds, and it suggests that it is worth having a closer look at widespread species occurring in different environments.

Photo of the first author Qindong Tang during the field work. Photo Credit: Qin Huang
Sampling team in Qinghai, PR China, June 2016. From left to right: Manuel Schweizer, Paul Walser Schwyzer, Yang Liu, Qin Huang, Yun Li and our driver. Photo Credit: Manuel Schweizer
Sampling team in Mongolia, June 2018. From left to right: Tuvshin Unenbat, Turmunbaatar Damba,  Gombobaatar Sundev, Paul Walser Schwyzer, Manuel Schweizer, Silvia Zumbach, Sarangua Bayrgerel. Photo Credit: Manuel Schweizer

Tang Q, Burri R, Liu Y, Suh A, Sundev G, Heckel G, Schweizer M. 2022. Seasonal migration patterns and the maintenance of evolutionary diversity in a cryptic bird radiation. Molecular Ecology.