Cytoarchitecture of the superior olivary complex of three neotropical species of bats (Noctilio leporinus, Phyllostomus hastatus and Carollia perspicillata) with different foraging behavior.

I Gibbons,A Adogwa,A Odekunle,V Sundaram

doi:10.1590/1519-6984.210489

Abstract

The understanding of the echolocation by studying different auditory nuclei of echolocating bats can be an important link in elucidating questions arising in relation to their foraging behavior. The superior olivary complex (SOC) is the primary center for processing the binaural cues used in sound localization since echo locating bats rely on acoustic cues to navigate and capture prey while in flight. The present study was taken to test the hypothesis that the SOC of echolocating neotropical bats with different foraging behavior will exhibit morphological variations in relative size, degree of complexity and spatial distribution. The brains were collected from six male adult bats of each species: Noctilio leporinus (fish eating), Phyllostomus hastatus (carnivorous/omnivorous) and Carollia perspicillata (fruit eating). They were double-embedded and transverse serial sections were cut and stained with cresyl fast violet. The SOC measured as 640 ± 70 µm in the N. leporinus bat, 480 ± 50 µm in the P. hastatus and 240 ± 30 µm in the C. perspicillata bat. The principal nuclei of the SOC of in all three bats were the LSO, MSO and MNTB. The MSO and LSO were very well developed in N. leporinus bats. The MSO of N. leporinus bat subdivided into DMSO and VMSO. The main cell type of cells present in MSO and LSO are dark staining multipolar cells in all the bats studied. The well-developed MSO and LSO of N. leporinus bats indicate that these bats are highly sensitive to low frequency sounds and interaural intensity differences, which help these bats to forage over water by using various types of echolocation signals. The average size of SOC in P. hastatus and C. perspicillata bats can be attributed to the fact that these bats use vision and smell along with echolocation to forage the food.

Highlights

The superior olivary complex (SOC) is a well‐developed auditory brainstem structure in all mammals including echolocating bats
The medial superior olive (MSO) of N. leporinus bat subdivided into dorsal medial superior olive (DMSO) and ventral medial superior olive (VMSO)
The average size of SOC in P. hastatus and C. perspicillata bats can be attributed to the fact that these bats use vision and smell along with echolocation to forage the food

Summary

Introduction

The superior olivary complex (SOC) is a well‐developed auditory brainstem structure in all mammals including echolocating bats. The SOC is typically located in the caudal brainstem near the facial nucleus and consists of up to 13 distinct cell groups, each contributing a unique neuronal circuit and sub serving a distinct functional role in the processing of sound (Schofield, 2002). The SOC consists of two principal nuclei, the medial superior olive (MSO) and the lateral superior olive (LSO) with established roles in hearing. The principal cell groups are flanked by a population of peri-olivary nuclei whose functional contributions are poorly understood. The MSO neurons are binaural, most sensitive to low-frequency sounds (at or below 5 kHz) and encode interaural timing differences (Spitzer and Semple, 1995) and LSO neurons are binaural and sensitive to interaural intensity differences (Sanes, 1990). It has been speculated that the size of the LSO is more indicative of the animal’s overall hearing range rather than sensitivity to high-frequency sounds (Moore, 2000)

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