Morphological determinants of bite force capacity in insects: a biomechanical analysis of polymorphous leaf-cutter ants

The extraordinary success of social insects is partially based on "division of labour", i. e. individuals exclusively or preferentially perform specific tasks. Task-preference may correlate with morphological adaptations so implying task-specialisation, but the extent of such specialisation can be difficult to determine. Here, we demonstrate how the physical foundation of some tasks can be leveraged to quantitatively link morphology and performance. We study the allometry of bite force capacity in Atta vollenweideri leaf-cutter ants, polymorphic insects in which the mechanical processing of plant material is a key aspect of the behavioural portfolio. Through a morphometric analysis of tomographic scans, we show that the bite force capacity of the heaviest colony workers is twice as large as predicted by isometry. This disproportionate "boost" is predominantly achieved through increased investment in muscle volume; geometrical parameters such as mechanical advantage, fibre length or pennation angle are likely constrained by the need to maintain a constant mandibular opening range. We analyse this preference for an increase in size-specific muscle volume and the adaptations in internal and external head anatomy required to accommodate it with simple geometric and physical models, so providing a quantitative understanding of the functional anatomy of the musculoskeletal bite apparatus in insects.

Task preference, affective response, and engagement in L2 use in a US university context

While learners’ engagement has been recognized as important for second language (L2) learning in task-based language teaching (TBLT), how engagement is manifest in learners’ L2 use during task performance and how tasks can be designed to facilitate better engagement have not received enough attention in the L2 research. This study investigates the relationship between learners’ expressed preferences for two communicative L2 tasks and their engagement in L2 use during task performance. Twenty-one learners of English as a second language (ESL) performed two distinct tasks and participated in an interview after finishing them. This article compares behavioral, cognitive, and social measures of learners’ engagement in L2 use while performing the task they preferred more and the task they preferred less as well as their expressed reasons for these preferences. The findings revealed a higher level of cognitive engagement in L2 use (i.e. greater negotiation of meaning and form) during the performance of the task they preferred more. The findings also revealed that the topic as well as opportunities to create ideas and address a genuine communicative need were the most important factors in determining learners’ expressed task preferences. Implications for task design include allowing learners to create content for the tasks they perform and choosing topics that are familiar, personally relevant, and emotionally engaging to learners.