Tolerance and avoidance responses to novel saline conditions in an invasive treefrog

<p>Salinity is an environmental stressor for anurans, as their highly permeable skin makes them prone to osmotic stress when exposed to saline conditions. However, certain anuran species have colonized areas near saltwater habitats suggesting an ability to acclimate to saline conditions. Here, we evaluated tolerance and avoidance responses to saline conditions in adult Cuban treefrogs (<em>Osteopilus septentrionalis</em>), an invasive anuran distributed throughout Florida. To examine salinity tolerance, adult frogs were maintained in two treatments simulating a freshwater (0.5 ppt) or brackish (8.0 ppt) environment for six weeks. Every two weeks, we submerged frogs in brackish solution to quantify individual weight change as a measure of salinity tolerance. We found that frogs maintained in brackish solution over time significantly lost more weight at weeks two and six when compared to week zero, suggesting that salinity is an environmental stressor for Cuban treefrogs. Yet, exposure to salinity over a longer period of time may change their physiological response to saline conditions as the weight change at week four was similar to the pre-exposure period at week zero. Since salinity appears to be a stressor for this species, we investigated avoidance behavior towards saline conditions by offering individuals a choice between freshwater or brackish environments. Our results showed that Cuban treefrogs chose freshwater environments more frequently and may thus avoid saline ones. This study reveals that a non-native species can use physiological and behavioral strategies to respond to salinity, a condition with dehydrating effects, potentially allowing them to expand their newly established ranges into areas that other anurans may not be able to colonize.</p>