Acoustic differentiation and its relationships with ear size in three Histiotus species (Chiroptera, Vespertilionidae) from Patagonia, Argentina

Abstract

In Argentine Patagonia, three species of long-eared brown bats coexist, Histiotus macrotus, H. magellanicus, and H. montanus, which differ by ear length and other characters. Considering that pinna and tragus size and morphology may affect the perception of incoming echoes, we expected that differences in ear morphometry across species would match with interspecific variation in echolocation call structure. We studied echolocation calls of these species, recording calls of free-ranging Histiotus in eight localities from Chubut province (Argentina). We measured morphometric variables (mass, length of ear and tragus, forearm) in captured specimens. We analyzed eight acoustic parameters in 4020 recorded pulses (H. macrotus n = 2020, H. magellanicus n = 1409, and H. montanus n = 591). Principal components (PCA) and discriminant analyses (DFA) revealed that these species clearly segregate in acoustic space, consistent with interspecific differences in ear morphology. Comparatively, H. magellanicus with shorter ears (< 25 mm) emitted higher-frequency calls at short time intervals; by contrast, H. macrotus and H. montanus with longer ears (> 27 mm) emitted lower-frequency calls, in turn differentiating from each other by inter-pulse intervals. MANOVA indicated that these differences were highly significant. Redundancy analysis showed a strong correlation between ear and tragus length and acoustic structure. Our results suggest that these Histiotus species are distinguishable in terms of their bioacoustics, which likely have a functional basis linked to morphological variation of sensory organs.