The effect of alcohol and freezing preservation on carapace size and shape in Liocarcinus depurator (Crustacea, Brachyur
Morphometric and shape analysis are usually performed on preserved specimens. The current paper examines the effect of two common preservation methods, freezing and alcohol, on the shape and magnitude of crab’s carapace. The carapace widths and images of
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4.1 Abstract Morphometric and shape analysis are usually performed on preserved specimens. The current paper examines the effect of two common preservation methods, freezing and alcohol, on the shape and magnitude of crab's carapace. The carapace widths and images of the carapace of two batches of the swimming crab, Liocarcinus depurator were taken before and after preservation. The carapace width was measured by two operatives and discrepancy between the two was analysed. The carapace images were analysed using geometric morphometric analysis. The carapace widths decreased significantly, though minimally, after preservation. Geometric morphometric indicated significant differences after preservation in the uniform shape components only indicating global differences rather than localised differentials. Keywords: Liocarcinus depurator, alcohol, freezing, preservation, shape differences, geometric morphometry, crab.
4.2 Introduction Since crustaceans have hard exoskeletons and potentially numerous "landmarks" they should constitute an ideal group for the application of geometric morphometric methods. Few such studies on Crustacea can, however, be found. Cadrin (1995) applied box-truss methods to discriminate between sexes and potential fishery stocks of the American lobster, Homarus americanus (Milne Edwards). Rosenberg's (1997) work on the shape difference between major and minor chelipeds of the fiddler crab Uca pugnax, (Smith) probably pioneered the use of landA. M. T. Elewa (ed.), Morphometrics © Springer-Verlag Berlin Heidelberg 2004
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Marta Rufino et al.
mark-based morphometric analysis in extant crustaceans (see Reyment for works on fossil Crustacea). The differences observed suggested that the major claw could produce more crushing power, and that selection for "fight effectiveness" may have played an important role in the evolution of the cheliped shape. Rufino et al. (2004) used geometrical morphometric techniques to elucidate subtle differences in the carapace shape of male and female Liocarcinus depurator. Recently, reviews of the techniques applied to crustaceans can be found in, Rosenberg (2002, claw shape variation across the genus Uca), Cadrin and Friedland (1999, lobster stock identification) and Cadrin (2000, fisheries stock identification). In many field studies, individuals are not measured immediately after capture, but are preserved for later measurement. The effect of the preservation on the size of the individuals is often ignored, however significant. The ultimate effect of preservation distortion may largely depend on the degree of accuracy needed for each specific study. The effect is often quite variable, for example, many fish species, both adults and larvae, either shrink or enlarge after preservation with alcohol, formaldehyde or freezing (e.g. Sprattus sprattus, Encheylopus cimbrius and Pomatoschistus minutus (Fey 1999); Clupea harengus and Osmerus eperlanus (Fey 2002); Mullus barbatus and M surmuletus (AI-Hassan et al. 2000)). The few studies carried out on crustaceans inclu
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