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RESEARCH ARTICLE

A comparison of population differentiation in two shore crab species with contrasting distribution along the Portuguese coast, using two morphological methodologies

Inês C. Silva A B D , Stephen J. Hawkins B C and José Paula A
+ Author Affiliations
- Author Affiliations

A Centro de Oceanografia – Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Avenuenida Nossa Senhora do Cabo 939, 2750-374 Cascais, Portugal.

B The Laboratory, The Marine Biological Association of the UK, Citadel Hill, Plymouth PL1 2PB, UK.

C School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey LL59 5AB, UK.

D Corresponding author. Email: micsilva@fc.ul.pt

Marine and Freshwater Research 60(8) 833-844 https://doi.org/10.1071/MF08215
Submitted: 24 July 2008  Accepted: 1 February 2009   Published: 27 August 2009

Abstract

Along the Portuguese coast, Pachygrapsus marmoratus has a continuous distribution on rocky shores. In contrast, Carcinus maenas has a discontinuous distribution, inhabiting estuaries. Surveys along a coastal latitudinal gradient were made to assess the effect of the distribution pattern on population differentiation of these two species. Population differentiation was studied using two different morphometric methodologies: linear-based morphometrics and landmark-based morphometrics. The linear-based analysis revealed no significant morphological differentiation among the eleven P. marmoratus populations. Landmark-based analysis showed that the northern and central populations were more similar in shape than the southern populations. Nevertheless, there was still some overlap in shape that could be due to the continuous distribution of P. marmoratus along the coast, promoting population panmixia. In C. maenas, both morphometric techniques revealed the existence of morphological differentiation among populations. This shape differentiation showed a clinal variation, explained by a higher degree of isolation of populations that might be due to limited larval flow between them. Environmental factors may also play an important role in causing variation of shape. Landmark-based morphometrics yielded stronger evidence of morphological differences among forms than a linear approach, suggesting that this method may be more suitable for analysis of body shape.

Additional keywords: Carcinus maenas, geometric morphometrics, Pachygrapsus marmoratus, traditional morphometrics.


Acknowledgements

I. C. Silva acknowledges a PhD grant (SFRH/BD/14325/2003) from the Portuguese Foundation for Science and Technology (FCT). S. J. Hawkins was supported by a NERC grant-in-aid to the Marine Biological Association of the UK and recently the Oceans 2025 program. This work was part of the project ‘GeneDif – Genetic and morphological differentiation in estuarine organisms with contrasting dispersal modes along a geographical gradient’ (POCTI/BSE/45672/2002), financed by FCT. The authors thank S. Pedro, S. Silva, V. Carmo, S. Oliveira and S. Monteiro for their help in the collection of Pachygrapsus marmoratus and to H. Queiroga for his help in the collection of Carcinus maenas in the northern estuaries, H. Cabral in the Tejo estuary, M. Santos-Reis and D. Freitas in the Sado estuary, J. Gonçalves in the Arade estuary, P. Pousão in Ria Formosa, and A. Chíncharo and P. Morais in the Guadiana estuary. This paper benefited from the comments of three anonymous reviewers. Animal handling complies with the current Portuguese laws.


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