Abstract
Shell preferences, as shown by laboratory choice experiments, are important determinants of shell utilization under natural conditions. Size and shell species preferences of the hermit crab Pagurus exilis were determined and compared for the most occupied shell types (Olivancillaria urceus, Natica isabelleana and Buccinanops gradatum) in the Caraguatatuba region, Brazil, and for the two most occupied species (B. gradatum and N. isabelleana) in Mar del Plata, Argentina. All experiments were conducted under laboratory conditions, using glass aquaria where the hermit crabs were placed naked with a large number of shells of appropriate sizes. After 36 h the crabs and chosen shells were measured. The relationship between preferred shell type, shell size and shell volume was determined by regression analysis. Pagurus exilis showed significant choices amongst shell types. Specimens from Argentina preferred N. isabelleana and those from Brazil chose B. gradatum > N. isabelleana > O. urceus. Preferences were characterized by shell weight and internal volume. The present data lead us to conclude that shell selection by hermit crabs involves individual preferences related to the shell features that best provide protection and survival.
Highlights
The fitness of a particular shell may differ between hermit crab species, reflecting several selection pressures, which associated with different habitats, act in different ways on each crab species (Bertness 1981) in different areas
The animals collected in Brazil were transported to the Laboratory of Bioecology and Crustacean Systematics at the Faculty of Philosophy, Sciences and Letters (FFCLRP), University of São Paulo (USP), Ribeirão Preto, São Paulo, Brazil; those collected in Argentina were taken to the Department of Marine Sciences, Faculty of Exact and Natural Sciences, Mar del Plata National University (UNMdP), Mar del Plata, Argentina, where experiments were conducted using glass aquaria provided with flowing sea water
P. exilis showed a significant choice amongst the gastropod shell types
Summary
The fitness of a particular shell may differ between hermit crab species, reflecting several selection pressures, which associated with different habitats, act in different ways on each crab species (Bertness 1981) in different areas. The genus Pagurus Fabricius, 1775 is a heterogeneous pagurid group consisting of more than 170 species worldwide (Lemaitre and Cruz Castaño 2004), and ecological information for this genus is still scarce despite the accessible habitats it inhabits and its high abundance (Goshima et al 1996). Despite of a number of publications about the distribution of Pagurus exilis (Benedict, 1892) (Melo 1999), studies on the species have been limited to the post-embryonic development under laboratory conditions (Scelzo and Boschi 1969) and on distributional aspects and population structure in Brazilian waters (Terossi et al 2006, Mantelatto et al in press, respectively). We evaluated the shell size and species preference of two different biogeographical populations (Brazil and Argentina) of P. exilis under laboratory conditions, comparing the puzzling mechanisms of shell selection
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