Revealing hidden sexually dimorphic male traits in the little white-shouldered bat, Ametrida centurio Gray 1847 (Chiroptera: Phyllostomidae).

Bats have been considered non-sexually dimorphic in most species due to the lack of conspicuous body size differences between sexes, but other traits may offer unequivocal evidence of sexual dimorphism and can likely play critical roles in reproduction. Almost 150 years ago, an unusual fleshy structure on the chest was discovered in an adult male little white-shouldered bat, Ametrida centurio, specimen stored in the collection of the British Museum (London). In addition to sexual differences in body size in this species, males also had swollen pads below their eyes. Here we show that there are other important sexually dimorphic traits that previously were not found in museum specimens, reinforcing how important complementary observations of live animals are for discovering traits that have been unnoticed for centuries. We report two new, unusual, presumably—but still not confirmed—glandular structures in male A. centurio, hereafter referred to as axillary and genital traits. The axillary structure is a hairless, reddened and moist area located beneath each wing, observed when wings are elevated. The genital structure surrounds the penis and coats the scrotal area and adjacent fur with a thick secretion. Combined, observations of these sexually dimorphic traits, and the larger size of females compared to males, makes A. centurio a species with five sexually dimorphic characters. The nature, development, function, and variation of these male traits remain unknown. Future field studies should focus on careful observation of bat behavior to shed light on the function of these intriguing traits, and give us a better understanding of sexual selection. [ABSTRACT FROM AUTHOR]