Abstract
Morphological variation among natural populations is a phenomenon commonly observed in marine invertebrates and well studied, particularly, in shelled gastropods. The nassariid Buccinanops globulosus is interesting to study shell shape variation because it exhibits strong interpopulation differences in life history features, including maximum size, fecundity and growth rate. In this study, we examined the pattern of variation in size and shell shape among populations and between sexes of B. globulosus (Bahia San Antonio 40°29′S 63°01′W, Playa Villarino 40°45′S 64°40′W and Bahia Nueva 42°46′S 65°02′W). In particular, we used geometric morphometric techniques to test: (1) whether the two components of shell morphology (size and shape) are independent and (2) whether shape differences between sexes are consistently found among populations, regardless of their body sizes. Our results show shell shape variation between the populations of B. globulosus of northern Patagonia. Intra-specific shell shape variation is affected by body size, indicating allometry. Regardless of the size differences, individuals from Playa Villarino have high-spired shells, and shorter apertures and wider columellar area than individuals from the other populations. Also, sex-related shape differences were consistently found at each population, thus suggesting a common sexual dimorphism in shell morphology for this species. The functional significance of the variability found is discussed in terms of the flexibility of developmental programmes for morphology as well as the evolution of phenotypic plasticity.
Highlights
Morphological variation among natural populations is a phenomenon frequently observed in marine invertebrates and well studied, in shelled gastropods
We examined the pattern of variation in size and shell shape among populations and between sexes of B. globulosus (Bahıa San Antonio 40°290S 63°010W, Playa Villarino 40°450S 64°400W and Bahıa Nueva 42°460S 65°020W)
We used geometric morphometric techniques to test: (1) whether the two components of shell morphology are independent and (2) whether shape differences between sexes are consistently found among populations, regardless of their body sizes
Summary
Morphological variation among natural populations is a phenomenon frequently observed in marine invertebrates and well studied, in shelled gastropods. In Littorina saxatilis, two distinct morphological forms or ecotypes occur along Galician, British and Swedish shores (Johannesson et al 1993; Hull et al 1996; Hollander et al 2005, 2006; Conde-Padın et al 2007) This polymorphism, at least in Galician shores, is explained mainly by natural selection acting directly on the genes affecting the morphological traits (Conde-Padın et al 2009). Another way of modifying phenotype to increase adaptation induced by the environment may be mediated by phenotypic plasticity, that is, differential expression of genotype in different environments. The variation of traits associated with variation of the overall size of organisms (Huxley and Teissier 1936) is interesting because of its implications for form–function relationships and because of the insight into growth and development (Zelditch et al 2004)
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