The jamming avoidance response ofEigenmannia: properties of a diencephalic link between sensory processing and motor output

Summary Brain regions participating in the control ofEigenmannia's electric organ discharge frequency were localized by electrical microstimulation and anatomically identified by means of horseradish peroxidase deposition. A diencephalic region was found which, when stimulated, caused electric organ discharge (EOD) frequency increases of similar magnitude and time course as the frequency increases seen during the jamming avoidance response. Single unit recordings from this region revealed one cell type which preferentially responded to stimuli that cause the acceleration phase of the jamming avoidance response (electric organ discharge frequency increase). A second cell type responded preferentially to stimuli which cause EOD frequency decrease, and both cell types were tuned to stimuli which evoked maximal jamming avoidance behaviors.The results of the horseradish peroxidase experiments showed that the recording and stimulation sites correspond to the previously described nucleus electrosensorius. Our results confirm the earlier finding that this nucleus receives output from the torus semicircularis and we also found that the N. electrosensorius projects to the mesencephalic prepacemaker nucleus. The prepacemaker projects to the medullary pacemaker nucleus which generates the commands that evoke electric organ discharges.The anatomical and physiological results described here establish this diencephalic region as a link between the major sensory processing region for the jamming avoidance response, the torus semicircularis, and a mesencephalic pre-motor region, the prepacemaker nucleus.Abbreviations AM amplitude modulation - DF Delta F - ELLL electrosensory lateral line lobe - EOD electric organ discharge - JAR jamming avoidance response - NE nucleus electrosensorius - PPN prepacemaker nucleus - PN pacemaker nucleus     

The influence of feeding on the evolution of sensory signals: a comparative test of an evolutionary trade‐off between masticatory and sensory functions of skulls in southern African Horseshoe bats (Rhinolophidae)

The skulls of animals have to perform many functions. Optimization for one function may mean another function is less optimized, resulting in evolutionary trade‐offs. Here, we investigate whether a trade‐off exists between the masticatory and sensory functions of animal skulls using echolocating bats as model species. Several species of rhinolophid bats deviate from the allometric relationship between body size and echolocation frequency. Such deviation may be the result of selection for increased bite force, resulting in a decrease in snout length which could in turn lead to higher echolocation frequencies. If so, there should be a positive relationship between bite force and echolocation frequency. We investigated this relationship in several species of southern African rhinolophids using phylogenetically informed analyses of the allometry of their bite force and echolocation frequency and of the three‐dimensional shape of their skulls. As predicted, echolocation frequency was positively correlated with bite force, suggesting that its evolution is influenced by a trade‐off between the masticatory and sensory functions of the skull. In support of this, variation in skull shape was explained by both echolocation frequency (80%) and bite force (20%). Furthermore, it appears that selection has acted on the nasal capsules, which have a frequency‐specific impedance matching function during vocalization. There was a negative correlation between echolocation frequency and capsule volume across species. Optimization of the masticatory function of the skull may have been achieved through changes in the shape of the mandible and associated musculature, elements not considered in this study.     

Effects of a recurring late-night event on the behavior and welfare of a population of zoo-housed gorillas

The impact of visitors on the well-being of captive animals presents both positive and potentially negative consequences. While some amount of novelty through visitor stimulation offers the opportunity for a more complex captive environment, anecdotal evidence from primate staff observations at the Smithsonian's National Zoo and Conservation Biology Institute suggested that gorillas exhibited increased restlessness during the annual month-long late night ZooLights (ZL) event than before it. The current study compared activity budgets, aggression (interactions involving contact between conspecifics and displays toward visitors), and abnormal behaviors in two groups of socially housed gorillas for 1-month periods before, during, and after the 2015 ZL event. We also compared the fecal glucocorticoid metabolite profiles of all six gorillas across these same observation periods. Physiologically, most individuals appeared to cope appropriately with the increased visitor presence during the event. We saw little difference in contact aggression; however, abnormal behavior was observed in some gorillas during and after the event, which highlights the importance of individual analysis and data interpretation. As predicted, we found that the majority of gorillas rested less during ZL than during other observation periods, particularly adult females in the mixed sex troop. Preliminary results of this study aided the decision of zoo management to close initially the Great Ape House and subsequently most animal buildings during future ZL events to avoid the potential disruption of normal activity patterns. While the findings of this study were mixed as to the impact of the event on these gorillas, the results suggest that zoos should carefully consider the possible ramifications of keeping great ape buildings open for lengthy multi-night events.     

Gain control in the electrosensory system: a role for the descending projections to the electrosensory lateral line lobe

The responses of E-cells, basilar pyramidal cells, of the electrosensory lateral line lobe (ELLL) were studied in normal animals (Apteronotus leptorhynchus) and in fish in which a component of the descending input from the midbrain n. praeeminentialis to the ELLL was interrupted by lesions or by application of local anesthetics. This treatment increased the responsiveness of these neurons by 100 to 300%. A method is described by which the animal's electric organ discharge (EOD) can be increased or decreased in amplitude. Responses of E-cells to a brief stationary electrosensory stimulus and to moving electrolocation targets were studied in normal and in lesioned animals with normal and altered EOD amplitudes. Large reductions in EOD amplitude, approximately 50%, result in no significant changes in the average size of E-cells' responses to either type of electrosensory stimulus in normal animals. Interruption of the descending input, however, results in a loss of the E-cells' ability to maintain constant response size when the EOD amplitude is reduced. Increases in EOD amplitude cause reductions in the size of E-cell responses to the moving electrolocation targets and to the stationary stimulus. The effects of increased EOD amplitude are present in normal animals and in animals in which the descending input is interrupted. The descending input to the ELLL seems to function as a gain control mechanism that is capable of compensating for losses in stimulus strength resulting from reduced EOD amplitude. The component of the descending input studied here does not seem to play a role in the response of the system to increases in EOD amplitude. These results are discussed in conjunction with the known details of the ELLL circuitry and its connections with other brain areas.     

The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus

Recombinant DNA clones have been isolated that contain 80 kb of the beta-globin complex from the deer mouse, Peromyscus maniculatus. Comparisons of this complex with that from the laboratory mouse, Mus domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3, Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin complex since the two species diverged. Unlike other mammals studied thus far, the deer mouse possesses three adult genes. Partial sequence analysis indicates that each of the three adult genes is intact and hence may be functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to genomic blots from Peromyscus reveals that it has a homologous counterpart in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO and Hbb-bhl, are also found in Peromyscus. The strong hybridization between the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO genes suggest that both pairs are important for the ontogeny of these mice although no known product has been identified for the Hbb-bhO genes. The presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication that created this related gene set occurred before the two lineages diverged. A single gene for Hbb-y has been isolated from Peromyscus. The adult region in Peromyscus has undergone significant divergence from the same region in Mus, having three rather than two adult genes, the acquisition of at least 15 kb of extra DNA relative to Mus, and possibly the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in contrast, contains the same set of genes apparently distributed over the same amount of DNA as in the Mus beta- globin complex. This observation suggests that the embryonic region of the complex is more evolutionarily stable than the adult region.      

Neural correlates of novelty detection in pulse-type weakly electric fish

Evoked potentials (EPs) and single unit recordings from various electrosensory-processing regions of several pulse-type gymnotiform species were made to investigate neural activity patterns that could be associated with novelty detection. Whereas the electrosensory afferents and cells in the ELL exhibited only minor changes in response size as stimuli were presented less frequently (novel stimuli), most units studied in the torus semicircularis (TS) showed very strong, increased responsiveness to stimuli presented less frequently relative to stimuli presented persistently (at every EOD event. The responses of the TS were graded with respect to stimulus frequency. The discrimination between novel and persistent stimuli by the TS occurred with stimuli presented transversely or longitudinally with respect to the fish's long axis, and regardless of the timing of the stimulus with respect to the fish's pacemaker-related signal (PS). When electrosensory novelties were presented persistently the responses of the TS rapidly habituated. This may indicate that activity in this region of the TS is novelty related. This novelty-related activity in the TS can be correlated with certain aspects of the fish's behavior, i.e., EOD interval length during a behavioral novelty response. However, TS activity may continue to indicate the occurrence of electrosensory novelties after the behavior has habituated. It is suggested that the novelty-related activity of the TS of these fish is necessary, but not sufficient, for the production of electrosensory novelty-induced behavioral responses. Lesions of the region of the TS containing the rapidly-habituating neurons abolished the electrosensory novelty response, but not that resulting from visual and auditory stimulation.     

MicroRNA loci support conspecificity of Gyrodactylus salaris and Gyrodactylus thymalli (Platyhelminthes: Monogenea)

The monogenean flatworm Gyrodactylus salaris is a serious threat to wild and farmed Atlantic salmon stocks in Norway. Morphologically, the closely related but harmless Gyrodactylus thymalli on grayling can hardly be distinguished from G. salaris. Until now, molecular approaches could not resolve unambiguously whether G. salaris and G. thymalli represent just one polytypic species, two polytypic species or a complex of more than two species. In the first known genome-wide analysis utilizing 37 conserved microRNA loci, the genetic differentiation of seven populations of G. salaris and G. thymalli was assessed. The concatenated alignment spanned 21,742 bp including 62 variable positions. A neighbor-joining cluster analysis did not support any host-based or mitochondrial haplotype-based grouping of strains. We conclude that a two species concept for G. salaris and G. thymalli does not reflect meaningful biological entities. Instead, G. salaris and G. thymalli are just one species comprising several pathogenic and non-pathogenic strains on various primary hosts. Following the International Code for Zoological Nomenclature, G. salaris Malmberg, 1957 is the valid species name with G. thymalli ?itňan, 1960 becoming the junior synonym. Accordingly, the range of G. salaris is significantly increased, given that formerly G. salaris-free countries such as e.g., Great Britain are now within the species’ natural range. The synonymization of G. salaris and G. thymalli implies severe challenges to current disease management routines, which assume that G. salaris and G. thymalli are readily distinguishable. Protocols for reliable identification of pathogenic and non-pathogenic strains of G. salaris need to be developed.     

A method for enumeration ot T and B lymphocytes in tissues.

A method for the identification of T and B lymphocytes in tissue specimens is described. A sonication technique results in viable relatively pure lymphocyte populations which are easily classified by their surface markers. This readily reproducible method can become a standard laboratory procedure in the evaluation of disease states which require such information related to the classification of lymphocyte cell origin.