A comparison of pectoral fin ray morphology and its impact on fin ray flexural stiffness in labriform swimmers

The organization of tissues in appendages often affects their mechanical properties and function. In the fish family Labridae, swimming behavior is associated with pectoral fin flexural stiffness and morphology, where fins range on a continuum from stiff to relatively flexible fins. Across this diversity, pectoral fin flexural stiffness decreases exponentially along the length of any given fin ray, and ray stiffness decreases along the chord of the fin from the leading to trailing edge. In this study, we examine the morphological properties of fin rays, including the effective modulus in bending (E), second moment of area (I), segmentation, and branching patterns, and their impact on fin ray stiffness. We quantify intrinsic pectoral fin ray stiffness in similarly sized fins of two closely related species that employ fins of divergent mechanics, the flapping Gomphosus varius and the rowing Halichoeres bivittatus. While segmentation patterns and E were similar between species, measurements of I and the number of fin ray branch nodes were greater in G. varius than in H. bivittatus. A multiple regression model found that of these variables, I was always significantly correlated with fin ray flexural stiffness and that variation in I always explained the majority of the variation in flexural stiffness. Thus, while most of the morphological variables quantified in this study correlate with fin ray flexural stiffness, second moment of area is the greatest factor contributing to variation in flexural stiffness. Further, interspecific variation in fin ray branching pattern could be used as a means of tuning the effective stiffness of the fin webbing to differences in swimming behavior and hydrodynamics. The comparison of these results to other systems begins to unveil fundamental morphological features of biological beams and yields insight into the role of mechanical properties in fin deformation for aquatic locomotion.     

Tentative evidence for inequity aversion to unequal work-effort but not to unequal reward distribution in Goffin's cockatoos

One hallmark in the evolution of cooperation is the ability to evaluate one's own payoff for a task against that of another person. To trace its evolutionary history, there has recently been a surge in comparative studies across different species. In non-human animals, evidence of inequity aversion has so far been identified in several primate species, dogs, and rats. Research in birds revealed mixed findings so far: among corvids, crows and ravens did react sensitively to unequal payoffs and work-effort, while New Caledonian crows did not. Among psittacids, kea were studied so far: Yet, despite the fact that they live in large, hierarchically organized social groups that show complex interactions, they did not show a significant reaction to inequitable payoffs. Here we tested for the first time a Cacatua, the Goffin's cockatoo, using a standardized token exchange paradigm in which first the partner and then the subject could exchange a token for a food reward. Our results show that subjects did not react to unequal reward distributions. However, in comparison to the Equity Condition, the likelihood to exchange was lower in the condition in which the partner received the same reward as a gift (without having to work for it) whereas the subject had to perform a task involving substantial work-effort, suggesting that the Goffin's cockatoos do react aversively to work-effort inequity. In a follow-up experiment, subjects never received a reward but observed a conspecific receive a high-quality reward depending on condition. We found again no evidence for an aversion for the unequal reward distribution, but only that, independent of condition, subjects quickly lost their motivation to participate due to not receiving a reward. In summary, Goffins showed some sensitivity to increased unequal work-effort, but did not react to unequal reward distribution.     

Alternative startle motor patterns and behaviors in the larval zebrafish (<Emphasis Type="Italic">Danio rerio</Emphasis>)

In fishes, the C-start behavior, initiated with a C-shaped body bend, is a taxonomically common and widely studied escape response. Its simple neural circuit has made this behavior a model for examining neural control of movement. The S-start, initiated with an S-shaped body bend, is a physiologically distinct escape that occurs in esocid fishes. Here we examine whether zebrafish larvae perform S-starts in order to better understand startle diversity and to attempt to identify the S-start in a system that is tractable for neurobiological studies. We found that larval zebrafish startles varied in the extent of their caudal bending, resulting in C, S and intermediate-shaped responses. We recorded two distinct motor patterns: nearly simultaneous initial activity along one side of the body, characteristic of C-starts, and nearly simultaneous activity rostrally on one side and caudally on the other, characteristic of S-starts. Head stimulation generally elicited C-starts while tail stimulation elicited C- and S-starts. These results demonstrate that the S-start is more common than previously documented and occurs in early developmental stages. We suggest that the S-start may be a fundamental escape behavior in fishes and may provide a comparative model to the C-start for understanding simple neural circuits.     

Genetic assignment and monitoring of yellow cardinals

The yellow cardinal (Gubernatrix cristata) is a passerine bird endemic to southern South America. At present, the species is threatened with extinction, in part because of the capture of wild birds to supply the illegal caged-bird market. Previous genetic evidence supports the existence of 3 management units for the species in Argentina, where the largest populations are currently found. Our objectives were to guide the reintroduction of these animals to their respective management units by determining the origin of seized specimens from illegal trade using 2 molecular markers, mtDNA and microsatellites, and to monitor the success of the released birds through radio-telemetry. We compared the performance of different molecular markers and assignment approaches to optimize a technique capable of assigning the origin of confiscated yellow cardinals in a reliable way. Five of 10 released radio-tracked individuals were predated shortly after liberation; however, 3 were successful in finding a mate and starting reproductive activities. Individual success was independent of the time spent in captivity, the liberation with a partner, the settlement type (semi-open or closed), and the maximum distance traveled from the point of release. Cardinals that survived had higher individual heterozygosity. Our findings contribute a robust genetic assignment technique to be used in future yellow cardinal seizures and identify factors that might improve subsequent releases. © 2019 The Wildlife Society.     

Autophagy impairment as a key feature for acetaminophen-induced ototoxicity

Macroautophagy/autophagy is a highly conserved self-digestion pathway that plays an important role in cytoprotection under stress conditions. Autophagy is involved in hepatotoxicity induced by acetaminophen (APAP) in experimental animals and in humans. APAP also causes ototoxicity. However, the role of autophagy in APAP-induced auditory hair cell damage is unclear. In the present study, we investigated autophagy mechanisms during APAP-induced cell death in a mouse auditory cell line (HEI-OC1) and mouse cochlear explant culture. We found that the expression of LC3-II protein and autophagic structures was increased in APAP-treated HEI-OC1 cells; however, the degradation of SQSTM1/p62 protein, the yellow puncta of mRFP-GFP-LC3 fluorescence, and the activity of lysosomal enzymes decreased in APAP-treated HEI-OC1 cells. The degradation of p62 protein and the expression of lysosomal enzymes also decreased in APAP-treated mouse cochlear explants. These data indicate that APAP treatment compromises autophagic degradation and causes lysosomal dysfunction. We suggest that lysosomal dysfunction may be directly responsible for APAP-induced autophagy impairment. Treatment with antioxidant N-acetylcysteine (NAC) partially alleviated APAP-induced autophagy impairment and apoptotic cell death, suggesting the involvement of oxidative stress in APAP-induced autophagy impairment. Inhibition of autophagy by knocking down of Atg5 and Atg7 aggravated APAP-induced ER and oxidative stress and increased apoptotic cell death. This study provides a better understanding of the mechanism responsible for APAP ototoxicity, which is important for future exploration of treatment strategies for the prevention of hearing loss caused by ototoxic medications.Subject terms: Macroautophagy, Hair cell     

A regulatory variant at 3q21.1 confers an increased pleiotropic risk for hyperglycemia and altered bone mineral density

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