Comparative analysis of shell occupation by two southern populations of the hermit crab Loxopagurus loxochelis (Decapoda, Diogenidae)

Abstract

A B S T R A C TThe present study aimed to comparatively verify the relation between the hermit crabs and the shells they use in two populations of Loxopagurus loxochelis. Samples were collected monthly from July 2002 to June 2003, at Caraguatatuba and Ubatuba Bay, São Paulo, Brazil. The animals sampled had their sex identified, were weighed and measured; their shells were identified, measured and weighed, and their internal volume determined. To relate the hermit crab's characteristics and the shells' variables, principal component analysis (PCA) and a regression tree were used. According to the PCA analysis, the three gastropod shells most frequently used by L. loxochelis varied in size. The regression tree successfully explained the relationship between the hermit crab's characteristics and the internal volume of the inhabited shell. It can be inferred that the relationship between the morphometry of an individual hermit crab and its shell is not straightforward and it is impossible to explain only on the basis of direct correlations between the body's and the shell's attributes. Several factors (such as the morphometry and the availability of the shell, environmental conditions and inter-and intraspecific competition) interact and seem to be taken into consideration by the hermit crabs when they choose a shell, resulting in the diversified pattern of shell occupancy shown here and elsewhere. R E S U M OO presente estudo teve como objetivo verificar de forma comparativa a relação entre ermitões e conchas utilizadas por duas populações de Loxopagurus loxochelis. Foram realizadas coletas mensais, de julho 2002 a junho 2003, nas Enseadas de Caraguatatuba e de Ubatuba, São Paulo, Brasil. Os animais amostrados foram identificados quanto ao sexo, pesados, e mensurados; as conchas de gastrópodes foram identificadas, mensuradas, pesadas e tiveram seu volume interno determinado. Para relacionar as variáveis dos ermitões com as conchas foram utilizadas a análise de componentes principais (PCA) e a árvore de regressão. As três conchas de gastrópodes utilizadas mais intensamente diferiram em tamanho de acordo com a PCA. A árvore de regressão explicou com sucesso a relação entre características do ermitão e volume interno das conchas habitadas. Inferiu-se que a relação entre a morfometria de um ermitão e sua concha não é simples e não é possível de ser explicada com base somente em correlações diretas entre atributos do corpo e da concha. Inúmeros fatores (como morfometria e disponibilidade da concha, condições ambientais e competição inter e intra-específica) interagem e devem ser levados em consideração na escolha de uma concha pelos ermitões, resultando no diversificado padrão de ocupação de conchas demonstrado neste e em outros trabalhos correlatos.

Shell occupation by the hermit crab Dardanus insignis (Decapoda, Diogenidae) from the north Coast of São Paulo state, Brazil

“…Based on this assumption, the results of the present study suggest that, during juvenile growth, the morphology of the animal and the shell are not determining factors in the choice of the resource, given that hermit crabs categorized as juveniles (both males and females) are found in a shells with a variety of shapes. The variation of occupation in the smaller size classes was verified by Ayres-Peres et al (2012) and Frameschi et al (2013a) when they analyzed the utilization of shells by the hermit crab, L. loxochelis at the same site of the present study. This diverse exploration of shell species by D. insignis in the first four size classes is likely because of the presence of a larger availability of gastropod species with varied sizes in the environment .…”

Habitat heterogeneity in the assemblages and shell use by the most abundant hermit crabs (Anomura: Diogenidae and Paguridae): does the occupied shell species differ according to gender and species?

“…Olivancillaria urceus was one of main resources used by this species in this study (37.5%), compared with a frequency in previous studies of 77.7% (Ayres-Peres et al, 2012) and 31.3% (Frameschi et al, 2013). According to Wait and Schoeman (2012), shell selection is a process that involves individual and sexual preferences in different dimensions, with the aim of providing the best protection for the hermit crab and sufficient space for the development of embryos and their oxygenation, because females that inhabit very small shells show difficulties in reproducing or reduced rates of reproduction (Fantucci et al, 2008).…”

“…Olivancillaria urceus was the second most abundant shell used (31.3%), and was the most available species on the coast of São Paulo state, especially in the Ubatuba region (Ayres-Peres et al, 2012). The availability of this gastropod in the study area is probably similarly high, as also observed on the coast of Paraná (southern Brazil) (Masunari et al, 2008).…”

“…Therefore, a smaller aperture hinders their removal and provides greater protection (Bertini and Fransozo, 2000). Another feature of this shell is its statistically higher weight and thicker wall than similar-sized shells of other species (Ayres-Peres et al, 2012), which might provide better protection against predators that break shells, and be more robust against adverse environmental conditions, such as wave action (Reese, 1962;Bertness, 1981b). The weight of this shell might also contribute to the improved stability of hermit crabs on an unconsolidated substrate, thus preventing the animal being dragged along by the tide or water current (Masunari et al, 2008).…”

Shell occupation by the South Atlantic endemic hermit crab Loxopagurus loxochelis (Moreira, 1901) (Anomura: Diogenidae)

“…Univariate correlations between the measured variables are used to determine the relationship between the hermit crab and the occupied shell (Hazlett, 1981;Barnes, 1999;Arce and Alcaraz, 2009;Ismail, 2010). Authors like Kuris and Brody (1976), Caruso andChemello (2009), andAyres-Peres et al (2012) employed the use of multivariate statistical tools, as the main compound analysis, with the aim to more securely appoint the factors that may bear high relevance for shell occupation, especially in natural environments.…”