Consequences of temperature and temperature variability on swimming activity, group structure, and predation of endangered delta smelt

The effects of water temperature on individual and group movement behaviour in prey fish can affect ecological interactions such as competition and predation, but how variability in temperature influence fish behaviour is less understood. Of particular concern is how increased warming in tidally fluctuating estuaries may impact the native and endangered delta smelt (Hypomesus transpacificus, Osmeridae). To help address this issue, we tested the effects of increased water temperature (fluctuating [17–21°C] and warm [21°C] acclimated treatments) on juvenile delta smelt individual and group behaviour, response to chemical alarm and predator cues, as well as capacity to evade predation. In addition, predation of delta smelt was tested in the presence of a dominant invasive competitor, Mississippi silversides (Menidia beryllina, Atherinopsidae), as well as comparative predation mortality on Mississippi silversides when isolated. After 7 days of increased temperature treatments, delta smelt in the warm treatment increased swimming velocity, decreased turning angle, and altered group structure with larger inter-individual distances compared to fish in the control (17°C) and fluctuating temperature treatments. Following conspecific and predator chemical alarm cues, delta smelt showed anti-predator responses. Control and fluctuating treatment fish responded to conspecific cues with increased swimming speeds, decreased inter-individual distances and near-neighbour distances, and, after 15 min, fish recovered back to baseline behaviours. In contrast, fish in the warm treatment had not recovered after 15 min, and swimming speeds were maintained at roughly 25 cm/s, close to maximum capabilities. Fish in control and fluctuating treatments showed minimal responses to predator cues, whereas delta smelt exposed to warm conditions significantly increased swimming speeds and decreased turning angle. Predation of delta smelt by largemouth bass (Micropterus salmoides, Centrarchidae) was greatest under the warm treatment, correlating with altered behaviours of delta smelt; however, predation of Mississippi silversides was greater than delta smelt, independent of temperature. This study provides novel insight into the group behaviour of delta smelt, their response to predation, and how prolonged exposure to elevated temperature may induce negative individual and group behaviours causing alterations in predator–prey dynamics. This work highlights the importance of testing ecologically realistic temperature fluctuations in experiments as delta smelt had significantly altered responses to elevated temperature, dependent on variability of warming

Self-adaptation of Mutation Rates in Non-elitist Populations

The runtime of evolutionary algorithms (EAs) depends critically on their parameter settings, which are often problem-specific. Automated schemes for parameter tuning have been developed to alleviate the high costs of manual parameter tuning. Experimental results indicate that self-adaptation, where parameter settings are encoded in the genomes of individuals, can be effective in continuous optimisation. However, results in discrete optimisation have been less conclusive. Furthermore, a rigorous runtime analysis that explains how self-adaptation can lead to asymptotic speedups has been missing. This paper provides the first such analysis for discrete, population-based EAs. We apply level-based analysis to show how a self-adaptive EA is capable of fine-tuning its mutation rate, leading to exponential speedups over EAs using fixed mutation rates.Comment: To appear in the Proceedings of the 14th International Conference on Parallel Problem Solving from Nature (PPSN

When Is Visual Information Used to Control Locomotion When Descending a Kerb?

YesBackground: Descending kerbs during locomotion involves the regulation of appropriate foot placement before the kerb-edge and foot clearance over it. It also involves the modulation of gait output to ensure the body-mass is safely and smoothly lowered to the new level. Previous research has shown that vision is used in such adaptive gait tasks for feedforward planning, with vision from the lower visual field (lvf) used for online updating. The present study determined when lvf information is used to control/update locomotion when stepping from a kerb. Methodology/Principal Findings: 12 young adults stepped down a kerb during ongoing gait. Force sensitive resistors (attached to participants' feet) interfaced with an high-speed PDLC 'smart glass' sheet, allowed the lvf to be unpredictably occluded at either heel-contact of the penultimate or final step before the kerb-edge up to contact with the lower level. Analysis focussed on determining changes in foot placement distance before the kerb-edge, clearance over it, and in kinematic measures of the step down. Lvf occlusion from the instant of final step contact had no significant effect on any dependant variable (p>0.09). Occlusion of the lvf from the instant of penultimate step contact had a significant effect on foot clearance and on several kinematic measures, with findings consistent with participants becoming uncertain regarding relative horizontal location of the kerb-edge. Conclusion/Significance: These findings suggest concurrent feedback of the lower limb, kerb-edge, and/or floor area immediately in front/below the kerb is not used when stepping from a kerb during ongoing gait. Instead heel-clearance and pre-landing-kinematic parameters are determined/planned using lvf information acquired in the penultimate step during the approach to the kerb-edge, with information related to foot placement before the kerb-edge being the most salient