First brain de novo transcriptome of the Tyrrhenian tree frog, Hyla sarda, for the study of dispersal behavior

Abstract

Dispersal is a key process in ecology and evolution, as it contributes to shaping the spatial patterns of biological diversity at all levels of organization (Kokko and López-Sepulcre, 2006; Clobert et al., 2012). Growing evidence has revealed the role of phenotypic trait variation in affecting the dispersal dynamics of populations (Liedvogel et al., 2011). Moreover, spatial sorting of dispersal-related traits during range expansion events can lead to substantial, rapid, and directional changes in the phenotypic makeup of populations (Canestrelli et al., 2016a,b; Miller et al., 2020). Accordingly, selective pressures at the front of a range expansion wave would actively promote individuals with higher dispersal abilities (Lindström et al., 2013; Canestrelli et al., 2016a,b; Pizzatto et al., 2017). Although many studies have focused on phenotypic trait evolution during range expansion, its genomic underpinnings are almost unexplored, hampering a thorough understanding of the evolutionary processes involved in dispersal.

The Tyrrhenian tree frog Hyla sarda (De Betta, 1853) is an amphibian inhabiting the islands of Sardinia and Corsica and the Tuscan archipelago in the Tyrrhenian Sea (Western Mediterranean). According to previous phylogeographic studies, H. sarda underwent a northward range expansion from north of Sardinia (western Mediterranean Sea) during the last glacial phase (Spadavecchia et al., 2021). The colonization of Corsica Island was allowed by the temporary formation of a wide land bridge connecting Sardinia and Corsica, induced by the marine regression that occurred during the last glacial maximum (Bisconti et al., 2011a,b; Spadavecchia et al., 2021). The postglacial loss of this land bridge prevented subsequent gene flow between the Corsican and Sardinian populations. Interestingly, the genetic and phenotypic legacies of this range expansion event can still be detected in the existing populations of H. sarda (Liparoto, 2020; Canestrelli et al., 2021; Bisconti et al., 2022). Indeed, substantial personality trait variation has been observed among Corsica, Sardinia, and Elba populations, i.e., tree frogs from Corsica showed a shyer personality than tree frogs from Sardinia and Elba (Liparoto et al., 2020; Bisconti et al., 2022). Thus, H. sarda is an interesting candidate to study the genetic underpinnings of phenotypic trait evolution during range expansion.

Here, we contribute to the investigation of the genetic underpinning of phenotypic trait evolution during range expansion by generating the first brain de novo transcriptome of H. sarda. We focused on the brain transcriptome since brain gene expression patterns have been linked to a wide range of behavioral responses to environmental stimuli (Whitfield et al., 2003; Bendesky and Bargmann, 2011; Rey et al., 2013; Harris and Hofmann, 2014; Bell et al., 2016). The transcriptome presented here has been validated and annotated to provide a valuable genomic resource for further genetic, ecological, and behavioral studies.