Volumetric comparison of the accessory olfactory bulb in bats

Accessory olfactory bulb (AOB) volumes were calculated in 26 chiropteran species. The percentage of the AOB in relation to the olfactory bulb complex ranges between 0.18 and 2.70%. The allometric comparison reveals the high development of this structure in the phyllostomatid subfamily of Glossophaginae. Carolliinae and Sturnirinae are near the chiropteran average. Smaller AOBs can be observed in Sphaeronycteris, Diphylla, Pteronotus parnellii and Miniopterus schreibersi. Comparison of the right/left AOB size in 56 specimens showed a slight predominance of the latter (average 50.6% of total volume). Intraspecific variability of this structure is pronounced, reaching a maximum SEM of 23.2% in Artibeus lituratus. Other species with well-developed AOBs tend to show high intraspecific variability. The role of the accessory olfactory system is seen by recent investigators mainly in its participation in sexual behavior and in close connection with the 'Flehmen' gesture, which is predominantly shown by male individuals. When comparing the size of the AOB in 18 bat species where both sexes were represented, only half of them showed smaller AOBs in females. This demonstrates that there is no tendency towards reduction of this structure in females.