Vortex formation and foraging in polyphenic spadefoot toad tadpoles

Animal aggregations are widespread in nature and can exhibit complex emergent properties not found at an individual level. We investigate one such example here, collective vortex formation by congeneric spadefoot toad tadpoles: Spea bombifrons and S. multiplicata. Tadpoles of these species develop into either an omnivorous or a carnivorous (cannibalistic) morph depending on diet. Previous studies show S. multiplicata are more likely to develop into omnivores and feed on suspended organic matter in the water body. The omnivorous morph is frequently social, forming aggregates that move and forage together, and form vortices in which they adopt a distinctive slowly-rotating circular formation. This behaviour has been speculated to act as a means to agitate the substratum in ponds and thus could be a collective foraging strategy. Here we perform a quantitative investigation of the behaviour of tadpoles within aggregates. We found that only S. multiplicata groups exhibited vortex formation, suggesting that social interactions differ between species. The probability of collectively forming a vortex, in response to introduced food particles, increased for higher tadpole densities and when tadpoles were hungry. Individuals inside a vortex moved faster and exhibited higher (by approximately 27%) tailbeat frequencies than those outside the vortex, thus incurring a personal energetic cost. The resulting environmental modification, however, suggests vortex behaviour may be an adaptation to actively create, and exploit, a resource patch within the environment.publishe

School level structural and dynamic adjustments to risk promote information transfer and collective evasion in herring

Many large-scale animal groups have the ability to react in a rapid and coordinated manner to environmental perturbations or predators. Information transfer among organisms during such events is thought to confer important antipredator advantages. However, it remains unknown whether individuals in large aggregations can change the structural properties of their collective in response to higher predation risk, and if so whether such adjustments promote responsiveness and information transfer. We examined the role of risk perception on the schooling dynamics and collective evasions of a large herring, Clupea harengus, school (ca. 60 000 fish) during simulated-predator encounters in a sea cage. Using an echosounder, high-resolution imaging sonar and acoustic video analysis, we quantified swimming dynamics, collective reactions and the speed of the propagating waves of evasion induced by a mobile predator model. In the higher risk condition, fish swam faster, exhibited a stronger circular swimming pattern, and we found an increased correlation strength indicating that the school had a greater ability to collectively respond to a perturbation. When exposed to a simulated threat, collective evasions were stronger and behavioural change (evasion manoeuvres) propagated more quickly within the school under environmental conditions perceived as being more risky. Our results demonstrate that large schools make structural and behavioural adjustments in response to perceived risk in a way that improves collective information transfer, and thus responsiveness, during predator attacks.publishe

Myofiber structure, sarcoplasmic reticulum Ca2+ handling, and contractile function after muscle‐damaging exercise in humans

Abstract Exercise‐induced muscle damage (EIMD) is characterized by a severe and prolonged decline in force‐generating capacity. However, the precise cellular mechanisms underlying the observed long‐lasting decline in force‐generating capacity associated with EIMD are still unclear. We investigated in vivo force generation and ex vivo Ca2+‐activated force generation, Ca2+ sensitivity, and myofiber Ca2+ handling systems (SR and t‐tubules) in human biceps brachii before and 2, 48, and 96 h after eccentrically muscle‐damaging contractions and in non‐exercised control arm. The force‐generating capacity declined by 50 ± 13% 3 h after exercise and was still not recovered after 96 h. The force‐Ca relationship of skinned myofibers revealed an impaired maximal Ca2+‐activated force in MHC I‐fibers, but not MHC II‐fibers 48 h after exercise. Further, Ca2+ sensitivity was increased in MHC II‐fibers, which was reversed after incubation with a strong reductant. There was a biphasic increase in SERCA sulfonylation, and a parallel reduction in the SR Ca2+ uptake rate, with no effects on SR vesicle leak or SR vesicle Ca2+ release rate. T‐tubules showed a progressive increase in the density of longitudinal tubules by 96 h after exercise. In conclusion, MHC II‐fiber Ca2+ sensitivity was increased 48 h after exercise, attributed to changes in the REDOX status. 96 h after exercise SR vesicle Ca2+ uptake was impaired, and an increased number of longitudinal tubules were observed. These alterations may contribute to the impaired force generation evident at the late stage of recovery