Considerable research has shown that both demonstration and verbal instruction can facilitate learning of a motor task in inexperienced individuals. In the current study, verbal instructions were used as a means to reduce the discovery learning process and control the amount of trial-to-trial variability in demonstrations. The task required models to learn to trace a pair of circles with a 90 degrees -relative phase pattern between the arms. Verbal instructions directed one group of models toward a single strategy, and this group improved at a faster rate and performed better in a 24-h retention test compared to a group of models in a discovery learning context. The discovery models utilized multiple strategies throughout the practice. Each model was watched for 2 days by an observer, who was instructed that they would have to produce the 90 degrees -relative phase pattern on day 3. Observers, who watched the discovery models, performed better than those who watched the single strategy models. The results support two primary conclusions. First, trial-to-trial variability associated with strategy selection processes in a model benefits an observer by facilitating perceptual discrimination processes that may play a key role in action generation. Second, verbal instructions that reduce discovery learning during physical practice benefit acquisition and retention performance when the task has multiple strategies wherein no one strategy guarantees the best performance outcome.
Parasitism is an energetically costly event for host species. Dynamic energy budget (DEB) theory describes the metabolic dynamics of an individual organism through its lifetime. Models derived from DEB theory specify how an organism converts food to reserves (maintenance-free energy available for metabolism) and allocates mobilized reserves to maintenance, growth (increase of structural body mass) and maturation or reproduction. DEB models thus provide a useful approach to describe the consequences of parasitism for host species. We developed a DEB model for siscowet lake trout and modeled the impact of sea lamprey parasitism on growth and reproduction using data collected from studies documenting the long-term effects following a non-lethal sea lamprey attack. The model was parameterized to reflect the changes in allocation of energy towards growth and reproduction observed in lake trout following sea lamprey parasitism and includes an estradiol module that describes the conversion of reproductive reserves to ovarian mass based on estradiol concentration. In our DEB model, parasitism increased somatic and maturity maintenance costs, reduced estradiol and decreased the estradiol-mediated conversion efficiency of reproductive reserves to ovarian mass. Muscle lipid composition of lake trout influenced energy mobilization from the reserve (efficiency of converting reserves allocated to reproduction into eggs) and reproductive efficiency. These model changes accurately reflect observed empirical changes to ovarian mass and growth. This model provides a plausible explanation of the energetic mechanisms that lead to skipped spawning following sea lamprey parasitism and could be used in population models to explore sublethal impacts of sea lamprey parasitism and other stressors on population dynamics.
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