Impact of phylogeography and landscapes on the structure of release calls in the Mongolian toads, Strauchbufo raddei

New collaborative study from across northeast Asia! Also explained on YouTube! There is no strong relation between evolutionary history and the structures of release calls as release calls must be conserved to be effective as sex recognition and anti-predator alarms. Contrary to earlier findings, here we provide evidence on the effect of landscape barrier and past glaciations on the patterns of phylogeography and release call variability, using the widespread Mongolian toad Strauchbufo raddei distributed across East Asia as study model.

Here, we enforced a fossil-calibrated relaxed clock to estimate the temporal pattern of divergence and to reconstruct the mitochondrial phylogeography of S. raddei across East Asia (Figure 1). Additionally, we inferred the population dynamic of the Mongolian-Russian clades (N taxa = 147) over the last glacial periods, and we compared the geographic variations in the release calls for the clades occurring in either side of the Hentiyn mountains range, the Transbaikal area and the Amur River basin. Molecular dating suggested a basal split between two lineages: the northeastern- and southern-originated of S. raddei c. 15.00 to 9.00 Mya. Ancestral range estimation elucidated the emergence of southern-originated lineage c. 6.80 Mya by dispersals, and supported a southern range expansion towards the central Asian steppes and a northern expansion towards present-day Transbaikal area c. 2.60 Mya (Figure 1).

Figure 1. Calibrated tree with estimated divergence for Strauchbufo raddei (N = 288) inferred from 893 bp of the CR fragment. The colour for the clades and the origins of ranges are similarly colour coded. The specific landscape for each clade (N = 6) is embedded next to the corresponding node of the timetree.

Our findings also supported significant differences in the release calls between the isolated north-western Hentiyn clade and the eastern Hentiyn clade distributed widely across the Amur River Basin (Figure 2). Likely, the variation in the release calls attributes to the recent population expansion for one of the northern clades supported the pattern of post-glacial northern refugia restricted to the west margin of Hentiyn Mountains, and Transbaikal area for the southern lineage (Figure 2). Therefore, we clarified that release calls of the Mongolian toad reflect the phylogeographic structures within the clades.

Figure 2: Oscillogram, tree time and release call characteristics of Strauchbufo raddei from two divergent clades. The bar chart shows the geographic variations between the calls of the two lineages: the northeastern clade (orange) and the southern originated clade (blue) in Mongolia and Russia. The colours on the map match with the colours of the bar charts. The release call characteristics that significantly differed between the two clades (call duration, rise time and fall time) are described in the oscillogram.

Othman S. N., Choe M., Chuang M.-F., Purevdorj Z., Maslova I., Schepina N., Jang Y. & Borzée A. (2022). Across the Gobi Desert, impact of landscape features on the biogeography and phylogeographically-structured release calls of the Mongolian Toad Strauchbufo raddei in East Asia. Evolutionary Ecology. In press. DOI: 10.1007/s10682-022-10206-4

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