The size and shape of shells used by hermit crabs: A multivariate analysisof Clibanarius erythropus

摘要

Shell attributes such as weight and shape affect the reproduction, growth, predator avoidance andbehaviour of several hermit crab species. Although the importance of these attributes has been exten-sively investigated, it is still difficult to assess the relative role of size and shape. Multivariate techniquesallow concise and efficient quantitative analysis of these multidimensional properties, and this paperaims to understand their role in determining patterns of hermit crab shell use. To this end, a multivariateapproach based on a combination of size-unconstrained (shape) PCA and RDA ordination was used tomodel the biometrics of southern Mediterranean Clibanarius erythropus populations and their shells.Patterns of shell utilization and morphological gradients demonstrate that size is more important thanshape, probably due to the limited availability of empty shells in the environment. The shape (e.g. thedegree of shell elongation) and weight of inhabited shells vary considerably in both female and malecrabs. However, these variations are clearly accounted for by crab biometrics in males only. On the basisof statistical evidence and findings from past studies, it is hypothesized that larger males of adequate sizeand strength have access to the larger, heavier and relatively more available shells of the globose Osilinusturbinatus, which cannot be used by average-sized males or by females investing energy in eggproduction. This greater availability allows larger males to select more suitable shapes.