Peer-Reviewed Publications
Shifting attention: assessing antennular ‘gaze’ in the hermit crab Pagurus bernhardus
Drummond, A., Spicer, J.I, Turner, L.M., Wilson, A.D.M, Briffa, M.
2025
Animal Behaviour
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Attention (focused information gathering) is crucial for many cognitive processes. Traditionally dichotomized as reflexive or voluntary, attention is often assessed using vision, in behavioural research. However, invertebrate information acquisition often utilizes chemosensation or mechanosensation, potentially limiting the efficacy of a vision-based approach. We examined attention in Pagurus bernhardus hermit crabs, using antennules (the crustacean first antennae) as indicators of attentional shifts. Considering a change in flicking direction as analogous to a shift in gaze, we examined if hermit crabs show evidence of reflexive or voluntary attention. We exposed crabs to a chemosensory stimulus while manipulating factors influencing vulnerability (i.e. shell presence and lighting conditions). We aimed to examine how vulnerability influences attention by modifying signal salience (the value of the information contained in a stimulus) and individual vigilance (the ability to monitor environmental changes). Given that attention varies with stimulus importance and individual condition, we predicted that antennule shift likelihood, latency and duration would vary by stimulus type and both intrinsic (shell presence) and extrinsic (light regime) vulnerability. We found that attention can be assessed by monitoring the antennular ‘gaze’ or direction of antennule pointing. Crab vulnerability altered patterns of reflexive attention, modifying patterns of signal salience and individual vigilance. Vulnerability also affected attention duration, demonstrating that hermit crabs may adjust attention based on context, indicative of voluntary attention. This study highlights the utility of a novel approach to assessing attention in invertebrates, especially those reliant on chemosensory cues for behavioural decisions and cognitive processes essential to species' fitness.
A sensory investment syndrome hypothesis: personality and predictability are linked to sensory capacity in the hermit crab Pagurus bernhardus
Drummond, A., Nash, S., Holloway, T., Turner, L.M., Wilson, A.D.M, Briffa, M.
2025
Proceedings of the Royal Society B
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Correlated phenotypic traits (i.e. syndromes) may manifest as associations between different behavioural types or between behavioural and non-behavioural phenotypes. While syndromes research is extensive, correlations involving behavioural type and sensory morphology have yet to be investigated. Sensation is essential in decision-making and should be correlated with behavioural phenotypes involved in risk response, including boldness. We investigated correlations between boldness and sensory capacity in Pagurus bernhardus hermit crabs, taking repeat measures of startle response durations to assess hermit crab personality and predictability. The correlation between startle response and the sensillar density (i.e. number of sensilla per unit surface area) of both chelipeds was assessed using Bayesian-fitted double hierarchical general linear models. Negative correlations between these traits support the existence of a syndrome linking sensory capacity and behavioural type, hereafter distinguished as a ‘sensory investment syndrome’. Increasing sensillar density on the major claw also corresponded with reduced within-individual variation, or predictability, in startle response duration. By revealing a correlation between sensory and behavioural phenotypes, our results demonstrate the importance of considering sensory morphology and performance in behavioural ecology and show how sensory investment syndromes might support behavioural strategies that help maximize fitness.
Intraspecific sensory diversity and the decapod claw: Patterns of sensillation are heterochelic and sexually dimorphic in Pagurus bernhardus.
Drummond, A., Holloway, T., Nash, S., Wilson, A.D.M, Turner, L.M., Briffa, M.
2025
Journal of Morphology
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Information detection affects physiological performance and behaviour and is vital to survival and fitness. Despite the recognised importance of sensory adaptations in information acquisition and manipulation, many forms of sensory variation—from within individuals to between species—remain underexplored. To better understand the role of information in evolution, it is important to examine sensory variation as part of a cohesive framework of sensory diversity. Using the decapod claw, a structure well-recognised for its morphological variation, we investigated sensory diversity at the intraspecific level by assessing heterochely and sexual dimorphism in the chelar morphologies of Pagurus bernhardus hermit crabs. We employed a novel methodology using scanning electron microscopy (SEM) to assess moulted chelar tissue from both the major and minor claws. The shape, size, and sensillation (i.e., the distribution and abundance of sensilla) of both chelipeds were examined by geometric morphometric landmark analysis (GMLA), generalised Procrustes analysis (GPA), and linear mixed effects models. Hermit crabs exhibited heterochely and sexual dimorphism in both gross and sensory chelar morphologies. Sexual dimorphism was greater in the sensory morphology of the major claw, suggesting sex-based sensory specialisations, likely due to differences in mating roles and behaviours. In contrast, the minor claw's sensory morphology lacked sexual dimorphism, suggesting the sensory role of this appendage is equally important for both sexes. Our results highlight sensory variation as a fundamental aspect of functional morphology and emphasise the need to consider sexual dimorphism and body asymmetry in information acquisition. These findings contribute to a broader framework for studying sensory diversity, underscoring the importance of integrating sensory morphology, function, and ecology to fully understand the evolutionary implications of sensory specialisations.