The molding hypothesis: linking shell use with hermit crab growth, morphology, and shell-species selection

Abstract

The 'molding hypothesis' (Elwood et al. 1979. Anim Behav 27:940-946) predicts that shell-species selection by hermit crabs may be influenced by past experience in shell use through shell-imposed alterations in crab morphology. The present study was designed to test this hypothesis and to further the understanding of plasticity in the shell-species selection in hermit crabs. Shell use was demonstrated to influence crab growth and morphology. Individuals reared in shells of Tegula viridula attained larger sizes than individuals in shells of Morula nodulosa. Crab growth was also dependent on crab sex, since males reached larger sizes and presented longer intermolt periods than females. The most conspicuous influence of shell utilization on crab morphology was in dorso-ventral flattening, which occurred on a decreasing scale with the shell species, as follows: M. nodulosa > Cerithium atratum > T. viridula. Crabs from all treatments and those collected in nature in shells of Olivella minuta chose mainly shells of C atratum, but the previous experience of crabs strongly influenced their shell-species selection pattern. Individuals maintained in M. nodulosa shells selected M. nodulosa shells more frequently than individuals reared in T. viridula or C. atratum. The influence of past experience was demonstrated to depend on shell type, since patterns of shell-species selection of individuals reared in T. viridula or C. atratum were identical. These differences in the shell-species selection pattern directly reflected the differences in crab dorso-ventral flattening, i.e. dorso-ventrally compressed individuals (those in shells of M. nodulosa or O. minuta) showed a higher probability of selecting narrow-aperture shells than did 'rounded' individuals (those in shells of T. viridula or C. atratum). The weight of the selected shells at the end of the experiment depended on crab size instead of previous experience with different shell architectures.

Subjective resource value and shell abandoning behavior in hermit crabs

“…Up until now studies have tended to rely on several undesirable methods for removing crabs from their shells, ranging from; immersion in tepid water or breaking shells open using blunt instruments (Turra and Leite, 2003), to applying direct heat using a flame (Hahn, 1998) or soldering iron (Cote et al, 1998). There has been no proposed method that combines the two desirable characteristics; (1) rapid removal without causing physical and physiological injury, and (2) preservation of shells for their subsequent reuse.…”

Composition, density, and shell use of hermit crabs (Crustacea: Paguroidea) from subtidal boulder fields in southeastern Brazil

“…A good shell adequacy to the crabs can be associated with strong and significant relationships between shell parameters (e.g., width, aperture length, and weight) and crab size (Scully, 1983). The higher occupation of C. atratum and M. nodulosa shells, highand medium-spired, respectively, supports the hypothesis that hermit crabs tend to use spired and elongated shells for better protection against predation and physical stress (Turra & Denadai, 2001;Turra & Leite, 2003).…”

Shell preference in a hermit crab: comparison between a matrix of paired comparisons and a multiple-alternative experiment

“…The match between shell preference and the pattern of shell occupancy in the wild indicates that the shell use in nature is determined by the preference of the crab and modulated by shell availability. That the shell use and preference match could indicate that shell choice in the hermit crab might be determined by previous experience, which in turn is inXuenced by shell availability (Turra and Leite 2003;Alcaraz and Kruesi 2009). The shell preference of C. californiensis could be linked to the shell availability, as has been suggested by Turra and Leite (2003), which showed that the selective response could be a positive relationship with the most abundant resources.…”