Speciation and historical invasions of the Asian black-spined toad (Duttaphrynus melanostictus)

Animal translocations provide striking examples of the human footprint on biodiversity. Combining continental-wide genomic and DNA-barcoding analyses, we reconstructed the historical biogeography of the Asian black-spined toad (Duttaphrynus melanostictus), a toxic commensal amphibian that currently threatens two biodiversity hotspots through biological invasions (Wallacea and Madagascar). The results emphasize a complex diversification shaped by speciation and mitochondrial introgression that comprises two distinct species. One species (true D. melanostictus) is distributed in the Indian subcontinent and is invasive in Wallacea. The other species, whose nomenclature remains unsettled, diverged from D. melanostictus in the Miocene era (~7 Mya) and diversified across Southeast Asia, from where it was introduced to Madagascar. Remarkably, the Indonesian population of D. melanostictus was recently established from India, which suggests historical, possibly human-assisted dispersal across the Bay of Bengal, reflecting the centuries-old connection between these regions.

The introduction of three cryptic tree frog species in the Dutch coastal dunes challenges conservation paradigms

Invasive species are considered one of the main drivers of the sixth mass extinction. Conservation solutions depend on whether a species is also indigenous to the country it invades (i.e., beyond its native range). In the case of invasive cryptic species, genetic tools are required to establish their identity. We illustrate these issues with the human-mediated colonization of the Dutch coastal dunes by Hyla tree frogs. Although previously assumed to concern the indigenous common tree frog H. arborea, European tree frogs comprise a complex of allopatric cryptic species, meaning the taxonomic identity of introduced Dutch populations warrants investigation. We sequence mtDNA for 173 individuals from native and introduced populations across the Netherlands and compare our dataset with hundreds of Hyla haplotypes previously barcoded in the Western Palearctic. Two of the dune populations carry an mtDNA haplotype of the native species H. arborea that occurs naturally elsewhere in the Netherlands. In contrast, mtDNA assigned to the eastern tree frog H. orientalis was detected in all three other dune populations. In one of these populations mtDNA of the Italian tree frog H. intermedia was also found. Not one, but three species of tree frogs have thus been introduced to the Dutch coastal dunes, only one of them being native to the Netherlands. This situation causes a conservation conundrum as some introduced populations are lawfully protected but could pose a threat to local biodiversity. Regarding the ‘true’ exotic tree frog species, all conservation options should be considered.

Citizen science reveals broad-scale variation of calling activity of the Mediterranean tree frog (Hyla meridionalis) in its westernmost range

Population monitoring is essential to determine different aspects of the ecology and conservation of the species. In anurans, recording the acoustic activity of choruses allows surveying populations. Therefore, knowing the timing of male calls is fundamental to achieve this goal. Here we monitored calling activity of the Mediterranean tree frog (Hyla meridionalis) at eight localities in southern Iberian Peninsula and western North Africa in the frame of a citizen science program. Subsequently, after summarizing call activity with Non-metric Multidimensional Scaling, we aimed to identify the geographic and environmental variables that associate with the calling activity of frogs. The results of the 258-hour census showed that male tree frogs called mainly from December to July, although the duration and intensity of choruses varied, depending on the elevation and seasonality of the water bodies. Males sang earlier and had more durable call activities at lower elevation sites, which are sites with higher and more stable ambient temperatures. Also, calling activity was lower in sites where water fluctuates more over the annual cycle. Our results provide a first overview of the calling activity of the Mediterranean tree frog over a relatively large set of populations encompassing a wide variety of environmental conditions in its westernmost range of distribution. However, further studies relying on more intensive sampling, likely using automatic recorders, would be desirable to achieve a full understanding of the calling activity of tree frogs in the region.