Figure 4 in Geographic variation in the acoustic signals of lesser treefrogs Dendropsophus minutus (Anura, Hylidae)

Figure 4. Variation in frequency bandwidth (PC2) and note duration (s) of Dendropsophus minutus calls as a function of mean annual temperature and annual precipitation. Mean trend lines and confidence intervals (95%) are shown. Each point represents the average acoustic parameter for each note type on each recording (i.e., individual). 2010; Morais et al., 2012; Llusia et al., 2013a; Annibale tics of anuran calls at short (Morais et al., 2012; Llusia et al., et al., 2020). 2013a) and possibly at longer time scales (this study). Call rate often increases with increasing air tempera- High-pitched sounds attenuate more quickly than lowture in anurans as a result of higher metabolic rate and pitched sounds, i.e., high-pitched sounds lose energy fastenergy expenditure (Wells, 2010). For example, in chaco er as they propagate away from the sound source (Brown treefrogs (Boana raniceps) (Cope, 1862), males produce & Riede, 2017). Additionally, high temperatures and low shorter calls, but in greater numbers, as the air tempera- humidity favor sound absorption (Snell-Rood, 2012), ture increases (Guimarães & Bastos, 2003). Given the which impairs sound propagation. We suggest that male recording′s limited duration, we could not measure call lesser treefrogs modulate call bandwidth to optimize sigrates. Yet, we speculate that in warmer temperatures, nal propagation depending on the air temperature. lesser treefrogs produce shorter notes at a higher rate, The call notes of D. minutus were shorter in sites optimizing call transmission while conserving energy with accumulated annual rainfall greater than 2000mm (Lingnau & Bastos, 2007). (Fig. 4D). We already expected that these acoustic signals Here, in addition to note duration, note bandwidth would vary with precipitation since relative humidity (represented by PC2, Table 1), but not note pitch (PC1), modulates the reproduction of many amphibian species decreased with increasing temperature (Fig. 4A). As (Aichinger, 1987; Llusia et al., 2013b). Rain noise can mask shown above, air temperature strongly affects the acous- anuran calls, reduce their acoustic activity (Ospina et al.,