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Invasive species are characterized by their ability to establish and spread in a new environment. In alien populations of anurans, dispersal and fitness-related traits such as endurance, burst performance and metabolism are key to their success. However, few studies have investigated inter-individual variation in these traits and more specifically have attempted to understand the drivers of variation in these traits. Associations of anatomical features may be excellent predictors of variation in performance and could be targets for selection or subject to trade-offs during invasions. In this study, we used marsh frogs (Pelophylax ridibundus), a species that has been introduced in many places outside its native range and which is now colonizing large areas of Western Europe. We first measured the inter-individual variation in resting metabolism, the time and distance they were able to jump until exhaustion, and their peak jump force, and then measured the mass of specific organs and lengths of body parts suspected to play a role in locomotion and metabolism. Among the 5000 bootstrap replicates on body size-corrected variables, our statistical models most often selected the stomach (75.42%), gonads (71.46%) and the kidneys (67.26%) as predictors of inter-individual variation in metabolism, and the gluteus maximus muscle (97.24%) mass was the most frequently selected predictor of jump force. However, endurance was poorly associated with the anatomical traits (R2distance=0.42, R2time=0.37). These findings suggest that selection on these predictors may lead to physiological changes that may affect the colonization, establishment and dispersal of these frogs., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Polyploidization is a rare yet sometimes successful way for animals to rapidly create geno- and phenotypes that may colonize new habitats and quickly adapt to environmental changes. In this study, we use water frogs of the Pelophylax esculentus complex, comprising two species ( Pelophylax lessonae, genotype LL; Pelophylax ridibundus, RR) and various diploid ( LR) and triploid ( LLR, LRR) hybrid forms, summarized as P. esculentus, as a model for studying recent hybridization and polyploidization in the context of speciation. Specifically, we compared the geographic distribution and genetic diversity of diploid and triploid hybrids across Europe to understand their origin, maintenance and potential role in hybrid speciation. We found that different hybrid and parental genotypes are not evenly distributed across Europe. Rather, their genetic diversity is structured by latitude and longitude and the presence/absence of parental species but not of triploids. Highest genetic diversity was observed in central and eastern Europe, the lowest in the northwestern parts of Europe. This gradient can be explained by the decrease in genetic diversity during postglacial expansion from southeastern glacial refuge areas. Genealogical relationships calculated on the basis of microsatellite data clearly indicate that hybrids are of multiple origin and include a huge variety of parental genomes. Water frogs in mixed-ploidy populations without any parental species (i.e. all-hybrid populations) can be viewed as evolutionary units that may be on their way towards hybrid speciation. Maintenance of such all-hybrid populations requires a continuous exchange of genomes between diploids and triploids, but scenarios for alternative evolutionary trajectories are discussed. [ABSTRACT FROM AUTHOR]