Big brown bats form large maternity colonies of up to 200 mothers and their pups. If pups are separated from their mothers, they can locate each other using vocalizations. The goal of this study was to systematically characterize the development of echolocation and communication calls from birth through adulthood to determine whether they develop from a common precursor at the same or different rates, or whether both types are present initially. Three females and their six pups were isolated from our captive breeding colony. We recorded vocal activity from postnatal day 1 to 35, both when the pups were isolated and when they were reunited with their mothers. At birth, pups exclusively emitted isolation calls, with a fundamental frequency range <20 kHz, and duration >30 ms. By the middle of week 1, different types of vocalizations began to emerge. Starting in week 2, pups in the presence of their mothers emitted sounds that resembled adult communication vocalizations, with a lower frequency range and longer durations than isolation calls or echolocation signals. During weeks 2 and 3, these vocalizations were extremely heterogeneous, suggesting that the pups went through a babbling stage before establishing a repertoire of stereotyped adult vocalizations around week 4. By week 4, vocalizations emitted when pups were alone were identical to adult echolocation signals. Echolocation and communication signals both appear to develop from the isolation call, diverging during week 2 and continuing to develop at different rates for several weeks until the adult vocal repertoire is established.

Subtle quantitative abnormalities in neuronal populations derived from the rhombic lip (i.e. arcuate nucleus at the ventral medullary surface, external granular layer of the cerebellum) have been reported in victims of the sudden infant death syndrome (SIDS). In this study, we examined the inferior olive, a major rhombic lip derivative, to determine if subtle rhombic lip abnormalities also involve this nucleus in SIDS. We analyzed the number and density of neurons and reactive astrocytes in the inferior olive in 29 SIDS cases and 29 controls. Computer-assisted cell counting procedures were used in sections stained with hematoxylin and eosin/Luxol fast blue. There was a significant difference in the postconceptionally age-adjusted mean for neuronal density between SIDS cases (7,687 +/- 255 neurons/mm(3)) and controls (8,889 +/- 255 neurons/mm(3)) (p = 0.002). The difference in age-adjusted mean neuronal number between SIDS cases (1,932 +/- 89 neurons/2 sections) and controls (2,172 +/- 89 neurons/2 sections) was marginally significant (p = 0.063). Reactive astrocytes were present in the inferior olive in SIDS cases, but their number, density, and developmental profile were not significantly different from that of control infants dying of diverse known causes. SIDS victims found dead in cribs, beds, and sofas, prone or supine had subtle olivary abnormalities, suggesting that affected infants are at risk in various sleeping situations. We propose that at least some SIDS victims experience intrauterine brainstem injury including the olivo-arcuato-cerebellar circuitry derived from the rhombic lip. These observations provide future directions for SIDS research concerning the role of early insults in pregnancy, the rhombic lip, and the interactions of the ventral medulla and cerebellum in cardioventilatory control.

Ecomorphology studies focus on understanding how anatomical and behavioral diversity result in differences in performance, ecology, and fitness. In mammals, the determinate growth of the skeleton entails that bite performance should change throughout ontogeny until the feeding apparatus attains its adult size and morphology. Then, interspecific differences in adult phenotypes are expected to drive food resource partitioning and patterns of lineage diversification. However, Formal tests of these predictions are lacking for the majority of mammal groups, and thus our understanding of mammalian ecomorphology remains incomplete. By focusing on a fundamental measure of feeding performance, bite force, and capitalizing on the extraordinary morphological and dietary diversity of bats, we discuss how the intersection of ontogenetic and macroevolutionary changes in feeding performance may impact ecological diversity in these mammals. We integrate data on cranial morphology and bite force gathered through longitudinal studies of captive animals and comparative studies of free-ranging individuals. We demonstrate that ontogenetic trajectories and evolutionary changes in bite force are highly dependent on changes in body and head size, and that bats exhibit dramatic, allometric increases in bite force during ontogeny. Interspecific variation in bite force is highly dependent on differences in cranial morphology and function, highlighting selection for ecological specialization. While more research is needed to determine how ontogenetic changes in size and bite force specifically impact food resource use and fitness in bats, interspecific diversity in cranial morphology and bite performance seem to closely match functional differences in diet. Altogether, these results suggest direct ecomorphological relationships at ontogenetic and macroevolutionary scales in bats.