Not only pond sliders: freshwater turtles in the water bodies of the Milan northern urban area (Italy)

Freshwater turtles represent one of the most common pets released in urban water bodies. In Europe, after the ban on the import of Trachemys scripta, other non-native turtle species now dominate the legal pet trade. Some of these species have high invasive potential, such as the well-known slider turtle, but their diffusion outside their native range is poorly known. This work summarises presence data about non-native freshwater turtles, different from slider turtles T. scripta, into two urban parks located at the northern boundary of the Milan outskirts (Italy, Lombardy). Turtle detections were obtained merging field surveys conducted from 2014 to 2020, with sparse pictures taken by occasional observers. The situation depicted shows, in addition to the ubiquitous spread of slider turtle subspecies and hybrids in both parks, the frequent presence of other multiple genera such as Pseudemys and Graptemys. Isolated individuals of Apalone spinifera, Graptemys ouachitensis, Mauremys sinensis, Pelomedusa subrufa and Sternotherus carinatus were also found. I also detected one Emys orbicularis, probably escaped or released.

Complex genetic patterns and distribution limits mediated by native congeners of the worldwide invasive red-eared slider turtle

Non-native (invasive) species offer a unique opportunity to study the geographic distribution and range limits of species, wherein the evolutionary change driven by interspecific interactions between native and non-native closely related species is a key component. The red-eared slider turtle, Trachemys scripta elegans (TSE), has been introduced and successfully established worldwide. It can coexist with its native congeners T. cataspila, T. venusta and T. taylori in Mexico. We performed comprehensive fieldwork, executed a battery of genetic analyses and applied a novel species distribution modeling approach to evaluate their historical lineage relationships and contemporary population genetic patterns. Our findings support the historical common ancestry between native TSE and non-native (TSEalien), while also highlighting the genetic differentiation of the exotic lineage. Genetic patterns are associated with their range size/endemism gradient, the microendemic T. taylori showed significant reduced genetic diversity and high differentiation, whereas TSEalien showed the highest diversity and signals of population size expansion. Counter to our expectations, lower naturally occurring distribution overlap and little admixture patterns were found between and its congeners, exhibiting reduced gene flow and clear genetic separation across neighboring species despite having zones of contact. We demonstrate that these native Trachemys species have distinct climatic niche suitability, likely preventing establishment of and displacement by the non-native TSE. Additionally, we found major niche overlap between TSEalien and native species worldwide, supporting our prediction that sites with closer ecological optima to the invasive species have higher establishment risk than those that are closer to the niche-center of the native species.

Is Thermal Responsiveness Affected by Maternal Estrogens in Species with Temperature-Dependent Sex Determination?

In species with temperature-dependent sex determination (TSD), incubation temperatures regulate the expression of genes involved in gonadal differentiation and determine whether the gonads develop into ovaries or testes. For most species, natural incubation conditions result in transient exposure to thermal cues for both ovarian and testis development, but how individuals respond to this transient exposure varies and can drive variation in the resulting sex ratios. Here, we argue that variation in the timing to respond to temperature cues, or thermal responsiveness, is a trait needing further study. Recent work in the red-eared slider turtle (<i>Trachemys scripta</i>) has found that when embryos experience transient exposure to warm conditions (i.e., heatwaves), some embryos show high responsiveness, requiring only short exposures to commit to ovarian development, while others show low responsiveness, developing testes even after more extended exposures to warm conditions. We discuss how maternal estrogens might influence thermal responsiveness for organisms that develop under thermal fluctuations. Examining the interplay of molecular responses to more subtle thermal and endocrine environments may reveal significant insights into the process of sex determination in species with TSD.