SUMMARY We investigated the function of the tentacles in aquatic, piscivorous tentacled snakes (Erpeton tentaculatus) by examining anatomy, peripheral innervation, and the response properties of primary afferents. We also investigated visual and somatosensory responses in the optic tectum and documented predatory strikes to visual stimuli and under infrared illumination. Our results show the tentacles are sensitive mechanoreceptors that respond to water movements. They are innervated by rami of the maxillary and ophthalmic branches of the trigeminal nerve and contain a dense array of fine terminal neurites that cross the interior of the tentacle orthogonal to its long axis. The optic tectum contained a retinotopic map of contralateral receptive fields with superior fields represented dorsally in the tectum, inferior fields represented laterally, nasal fields represented rostrally, and temporal fields represented caudally. Large somatosensory receptive fields were identified in deeper layers of the tectum and were in approximate register with overlying visual fields. Tentacled snakes struck accurately at a simulated digital fish, indicating that visual cues are sufficient to guide strikes, but they also captured fish under infrared illumination, suggesting water movements alone could be used to localize prey. We conclude the tentacles are mechanosensors that are used to detect fish position based on water movements and that visual and mechanosensory cues may be integrated in the tectum to enhance localization when visual cues are reduced.

A fundamental question in the neurosciences is how central nervous system (CNS) space is allocated to different sensory inputs. Yet it is difficult to measure innervation density and corresponding representational areas in the CNS of most species. These measurements can be made in star-nosed moles (Condylura cristata) because the cortical representation of nasal rays is visible in flattened sections and afferents from each ray can be counted. Here we used electrophysiological recordings combined with sections of the brainstem to identify a large, visible star representation in the principal sensory nucleus (PrV). PrV was greatly expanded and bulged out of the brainstem rostrally to partially invade the trigeminal nerve. The star representation was a distinct PrV subnucleus containing 11 modules, each representing one of the nasal rays. The 11 PrV ray representations were reconstructed to obtain volumes and the largest module corresponded to ray 11, the mole's tactile fovea. These measures were compared to fiber counts and primary cortical areas from a previous investigation. PrV ray volumes were closely correlated with the number of afferents from each ray, but afferents from the behaviorally most important, 11th ray were preferentially over-represented. This over-representation at the brainstem level was much less than at the cortical level. Our results indicate that PrV provides the first step in magnifying CNS representations of important afferents, but additional magnification occurs at higher levels. The early development of the 11th, foveal appendage could provide a mechanism for the most important afferents to capture the most CNS space.

We examined the chemoarchitecture of layer 4 isocortex and the number of myelinated nerve fibers of selected cranial nerves in the American water shrew (Sorex palustris). This study took advantage of the opportunity to examine juvenile brain tissue, which often reveals the most distinctive cortical modules related to different sensory representations. Flattened cortical sections were processed for the metabolic enzyme cytochrome oxidase, revealing a number of modules and septa. Subdivisions related to sensory representations were tentatively identified by performing microelectrode recordings in a single adult shrew in this study, combined with microelectrode recordings and anatomical findings from a previous investigation. Taken together, these results suggest that characteristic chemoarchitectonic borders in the shrew neocortex can be used to delineate and quantify cortical areas. The most obvious subdivisions in the water shrew include a relatively small primary visual cortex which responded to visual stimuli, a larger representation of vibrissae in the primary somatosensory cortex, and a prominent representation of oral structures apparent in the more rostral-lateral cortex. A presumptive auditory area was located in the far caudal cortex. These findings for the cortex are consistent with counts from optic, auditory and trigeminal nerves, suggesting that somatosensory inputs dominate the shrew’s senses whereas visual and auditory inputs play a small role in navigation and in finding prey. More generally, we find that shrews share unusual features of cortical organization with moles, supporting their close taxonomic relationship.

Parental investment and parent-offspring conflict theories make specific predictions on the behavior of parents and offspring. Since milk is a direct and vital form of maternal investment in mammals, nursing behavior is very well suited to test such predictions. We provide such tests here, as well as a fine-grained quantitative description of the weaning process in two species of deer. Both in white-tailed and fallow deer, fawns of primiparas had a significantly higher suckling rate than those of multiparous mothers in the first few days of life (2.90 ± 0.70 vs 1.24 ± 0.21 suckles/h from 0 to 5 days in FD, p < 0.01; and 1.42 ± 0.22 vs 0.81 ± 0.08 suckles/h from 6 to 10 days in WTD, p < 0.01). In both species, in the first 10 days of lactation, suckling bouts initiated by the mother had a significantly longer mean duration than those initiated by the fawn. We found no inter-sex difference in the rate of suckling, mean duration of suckles, total time suckling (s/h), and proportion of suckling attempts that were successful, in fawns of both species, at any age from birth to 80 days. White-tailed deer single fawns were identical to twins for all the above parameters. Fallow deer mothers were much more aggressive toward alien fawns than white-tailed deer mothers were, and spent more time close to their fawns (less than 10 m, 38% of the time from birth to 80 days, compared to 12% for white-tailed deer). We propose that weaning starts at about 20 days of age in both species. This is the time when the mother terminates more than half of all suckling bouts, terminates more bouts than she initiates, and when suckles are shorter when she initiates compared to when it is her fawn that does.

Since being elected in 2015, Canada's federal Liberal government has taken steps to overhaul major environment-related laws and policies, including federal environmental assessment (EA) and regulatory processes. During 2016-2017, a government-appointed panel toured Canada and received >1000 suggestions from diverse sectors of society regarding EA reform. Yet, different sectors of society may have different views concerning scientific components of EA. We analyzed written submissions during public consultation (categorized into five sectors) regarding five key scientific components of EA: (1) openly sharing information, (2) evaluating cumulative effects, (3) scientific rigour, (4) transparency in decision-making, and (5) independence between regulators and proponents. On the whole, submissions from Indigenous groups, non-governmental organizations, and individuals/academics supported strengthening all five components. In contrast, most contributions from industry/industry associations, and, to a lesser extent, government bodies or agencies, suggested that there was no need for increased scientific rigour or increased independence. These findings indicate that there is cross-sectoral support for strengthening some scientific aspects of EA. However, the degree to which the Government of Canada strengthens the scientific rigour and independence of EA will indicate whether environmental decision-making in Canada is aligned with preferences from industry or the rest of Canada.