Sexual Size Dimorphism in 28 Neotropical Bat Species Fails to Obey Rensch's Rule

(Uploaded by Plazi for the Bat Literature Project) Sexual size dimorphism (SSD) is the difference in body size between males and females. One of the most studied patterns in allometric size difference between sexes is Rensch's rule, which describes an increase of SSD with increasing species size when males are the larger sex. However, few studies have tested this rule in bats, and morphological structures other than body size have rarely been included. The objective of this paper was to analyze the patterns of SSD across 28 New World bat species and assess their conformity to Rensch's rule. To do this, I obtained measurements of forearm length, length of the third digit, and length of the fifth digit from 1,151 bat specimens, and through t-tests and reduced major axis regressions, I analyzed patterns of SSD and Rensch's rule. I found high variation in size and wing morphology, with a modest female-biased size in more than half the species, which fails to support Rensch's rule. Larger wing structures in females can improve flight performance to overcome aerodynamic challenges during reproduction when carrying pups and foraging for food. Mechanisms other than body size in females, geographic variation, and the set of species selected may explain the isometric pattern between sexes, which invalidates Rensch's rule for Neotropical bats. Further studies should encompass a broader range of bat species from different lineages, but it is also necessary to analyze SSD based on various traits related to resource use, such as wing and nasal morphology, as well as include the influence of geographic variation and environmental factors.