RESUMO
The production of echolocation calls in bats along with forces produced by contraction of thoracic musculature used in flight presumably puts relatively high mechanical loads on the lower respiratory tract (LRT). Thus, there are likely adaptations to prevent collapse or distortion of the bronchial tree and trachea during flight in echolocating bats. By clearing and staining (Alcian blue and Alizarin red) LRTs removed from nonvolant neonates, semivolant juveniles, volant subadults, and adult Jamaican fruit bats (Artibeus jamaicensis), I found that calcification of the tracheal, primary bronchial, and secondary bronchial (lobar) cartilage rings occurs over the span of about 3 days and coincides with later developmental stages of flight and the increased production of echolocation calls. Tracheal rings that are immediately adjacent to the larynx calcified first, followed by more caudal tracheal rings and then the rings of the primary and secondary bronchi. I suggest that calcification of LRT cartilage rings in echolocating bats provides increased rigidity to counter the thoracic compressions incurred during flight. Calcification of the LRT rings is an adaptation to support the emission of laryngeally produced echolocation calls during flight in bats.
Assuntos
Brônquios/crescimento & desenvolvimento , Calcificação Fisiológica , Ecolocação , Voo Animal , Traqueia/crescimento & desenvolvimento , Animais , Animais Recém-Nascidos , Brônquios/anatomia & histologia , Calcificação Fisiológica/fisiologia , Quirópteros , Ecolocação/fisiologia , Feminino , Voo Animal/fisiologia , Masculino , Traqueia/anatomia & histologiaRESUMO
Recent evidence has shown that the developmental emergence of echolocation calls in young bats follow an independent developmental pathway from other vocalizations and that adult-like echolocation call structure significantly precedes flight ability. These data in combination with new insights into the echolocation ability of some shrews suggest that the evolution of echolocation in bats may involve inheritance of a primitive sonar system that was modified to its current state, rather than the ad hoc evolution of echolocation in the earliest bats. Because the cochlea is crucial in the sensation of echoes returning from sonar pulses, we tracked changes in cochlear morphology during development that included the basilar membrane (BM) and secondary spiral lamina (SSL) along the length of the cochlea in relation to stages of flight ability in young bats. Our data show that the morphological prerequisite for sonar sensitivity of the cochlea significantly precedes the onset of flight in young bats and, in fact, development of this prerequisite is complete before parturition. In addition, there were no discernible changes in cochlear morphology with stages of flight development, demonstrating temporal asymmetry between the development of morphology associated with echo-pulse return sensitivity and volancy. These data further corroborate and support the hypothesis that adaptations for sonar and echolocation evolved before flight in mammals.
Assuntos
Quirópteros/anatomia & histologia , Cóclea/anatomia & histologia , Ecolocação/fisiologia , Voo Animal/fisiologia , Adaptação Fisiológica , Animais , Evolução BiológicaRESUMO
Echolocating bats have adaptations of the larynx such as hypertrophied intrinsic musculature and calcified or ossified cartilages to support sonar emission. We examined growth and development of the larynx relative to developing flight ability in Jamaican fruit bats to assess how changes in sonar production are coordinated with the onset of flight during ontogeny as a window for understanding the evolutionary relationships between these systems. In addition, we compare the extent of laryngeal calcification in an echolocating shrew species (Sorex vagrans) and the house mouse (Mus musculus), to assess what laryngeal chiropteran adaptations are associated with flight versus echolocation. Individuals were categorized into one of five developmental flight stages (flop, flutter, flap, flight, and adult) determined by drop-tests. Larynges were cleared and stained with alcian blue and alizarin red, or sectioned and stained with hematoxylin and eosin. Our results showed calcification of the cricoid cartilage in bats, represented during the flap stage and this increased significantly in individuals at the flight stage. Thyroid and arytenoid cartilages showed no evidence of calcification and neither cricoid nor thyroid showed significant increases in rate of growth relative to the larynx as a whole. The physiological cross-sectional area of the cricothyroid muscles increased significantly at the flap stage. Shrew larynges showed signs of calcification along the margins of the cricoid and thyroid cartilages, while the mouse larynx did not. These data suggest the larynx of echolocating bats becomes stronger and sturdier in tandem with flight development, indicating possible developmental integration between flight and echolocation.