A sensory investment syndrome hypothesis: Personality and predictability are linked to sensory capacity in the hermit crab Pagurus bernhardus

Correlated phenotypic traits (i.e., syndromes) may manifest as
associations between different behavioural types or between behavioural
and non-behavioural phenotypes. While research on syndromes 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 (DHGLMs). Negative correlations between these two 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 demonstrating a correlation between a
sensory and a behavioural phenotype, our results demonstrate the
importance of considering sensory morphology and performance in
behavioural ecology and show how sensory investment syndromes may be
linked to support behavioural strategies that help to maximise fitness.