AB 20:53-67 (2014)  -  DOI: https://doi.org/10.3354/ab00545

Intraspecific variation in carapace morphology among fiddler crabs (Genus Uca) from the Atlantic coast of Brazil

Kelsey R. Hampton1, Melanie J. Hopkins2, John C. McNamara3, Carl L. Thurman1,*

1Department of Biology, University of Northern Iowa, Cedar Falls, Iowa 50614-0421, USA
2GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Loewenichstraße 28, 91054 Erlangen, Germany
3Departamento de Biologia, FFCLRP, Universidade de São Paulo, Ribeirão Preto 14040-901, São Paulo, Brazil
*Corresponding author:

ABSTRACT: Isolation due to geographical barriers should promote genetic and morphological divergence among populations. Marine currents flowing in opposing directions along landmasses can constitute barriers that isolate populations dependent upon aquatic dispersal. The distribution of fiddler crabs (genus Uca) is regulated primarily by the oceanic transport of their planktonic larvae and by available adult habitat. Along the Brazilian coast of eastern South America, the flow of 2 major oceanic currents separates northern from southern Uca populations, which may promote intraspecific divergence in ‘trans-Brazilian’ species. Populations of 10 Uca species were sampled at 64 locations north and south of the Ponta do Calcanhar, Rio Grande do Norte, Brazil. Carapace shape was assessed using geometric morphometrics to analyze 12 surface landmarks in 1319 female crabs. Carapace shape differs significantly in each species. In morphospace, the carapace forms of the 10 species appear to separate into traditional subgeneric clusters. Within the 8 species exhibiting trans-Brazilian distributions, northern and southern populations show distinct carapace differences. Depending on species, either the hepatic or the branchial region is larger in northern populations. Since significant genetic variability among such populations has not been confirmed, divergence in carapace shape suggests significant ecological modulation of phenotype within each species. Apparently, environmental differences between northern and southern localities exert a greater impact on carapace morphology than impeded gene flow. The drivers underpinning diversification of carapace shape remain unknown, however.

KEY WORDS: Brachyura · Fiddler crab · Uca · Structural variation · Landmark analysis · Isolation · Ecophenotypy

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Cite this article as: Hampton KR, Hopkins MJ, McNamara JC, Thurman CL (2014) Intraspecific variation in carapace morphology among fiddler crabs (Genus Uca) from the Atlantic coast of Brazil. Aquat Biol 20:53-67. https://doi.org/10.3354/ab00545

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