Growth variation in bivalves: New insights into growth, physiology and somatic aneuploidy in the carpet shell Ruditapes decussatus Joana Teixeira de Sousa a, b , Domitília Matias a , Sandra Joaquim a , Radhouan Ben-Hamadou c , Alexandra Leitão a, ⁎ a Instituto Nacional de Recursos Biológicos (INRB, I.P.)/L-IPIMAR, Av. 5 de Outubro s/n, P-8700-305 Olhão, Portugal b IBB-CGB/Universidade de Trás-os-Montes e Alto Douro, Vila Real Portugal c Centro de Ciências do Mar (CCMAR), EcoReach Research Group, Universidade do Algarve, Campus de Gambelas, P-8005-139 Faro, Portugal abstract article info Article history: Received 14 September 2010 Received in revised form 27 May 2011 Accepted 1 June 2011 Available online 2 July 2011 Keywords: Aneuploidy Bivalve Chromosome Growth Physiological condition Ruditapes decussatus The carpet shell, Ruditapes decussatus is a species with a high commercial importance in Portugal and other Southern European countries. However, high growth rate variability is a major problem in the aquacultural production of this species. The objective of this work was then to study the possible differences between fast-, medium- and slow-growing individuals at three times of sampling, of a same cohort of R. decussatus in terms of eventual numerical chromosomal changes, aneuploidy, but also the level of physiological capacity, by assessing the condition index and the biochemical composition: proteins, total lipids, neutral lipids, phospholipids, carbohydrates, free reducing sugars, polysaccharides and total energy. Hypoploid cells of 2n = 37, 36, 35 or 34 were observed in all groups of individuals. The aneuploidy values observed ranging from 19% to 79%, were substantially higher than those observed in previous studies for other bivalve species. The differences in the observed aneuploidy between fast- and slow-growing clams were highly significant and a negative correlation was also observed between the level of aneuploidy and length. In general, the synthesis of the evaluated biochemical components showed no significant differences among groups suggesting that this synthesis could be related to extrinsic factors or that the analyzed biochemical components were not specific to detect the lack of certain aminoacids and enzymes involved in growth. The only exception was for total lipids, which were significantly lower in the medium and slow growing groups relative to the fast growing group. The evaluation of the relationships between all the studied parameters was performed through a principal component analysis (PCA). The results of this study demonstrate the existence of a negative correlation between somatic aneuploidy and growth in the carpet shell, as previously reported for other bivalve species. Moreover, for the first time in this study, this negative correlation is confirmed over time in a same cohort of the clam R. decussatus. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The carpet-shell clam Ruditapes decussatus is one of the most commercially important bivalve species in Southern Europe. In Portugal, it represents 27% of national aquaculture production and 64% of shellfish production (DGPA, 2008). However, in populations of this species, it is often observed that there are three groups of individuals, the fast-, the medium- and the slow-growers according to their size. Moreover, a decrease in the maximum size reached by the individuals, in each production cycle (2 years), has been noticed by the producers, in the last years. Aneuploidy is a cytogenetic phenomenon known as an abnormal chromosome number that involves the loss (hypoploidy) or gain (hyperploidy) of one or more individual chromosomes. This phe- nomenon mainly originates from the non-disjunction of chromo- somes during mitosis or meiosis (Martin and Rademaker, 1990) or due to Premature Centromere Division, PCD (Major et al., 1998). Recent studies performed in plants, suggest that there is also a chromosome loss during interphase, involving the nuclear expulsion accompanied by post mitotic micronuclei formation (Gernand et al., 2005). This phenomenon is often lethal or associated with growth and developmental retardation in higher animals, like mammals, but the effects of aneuploidy seem to be better tolerated in plants and lower animals (Verma, 1990). Genetic factors may be involved in this phenomenon, indeed in humans and in some plants, evidence exists for the presence of genes that are responsible for chromosome non- disjunction (e.g. Bond and Chandley, 1983; Garcia-Cruz et al., 2010). Hypoploidy, the lack of one or two chromosomes in a pair of homologues, has often been observed in several populations of bivalve species (e.g. Dixon, 1982; Leitão et al., 2001a; McCombie et al., Journal of Experimental Marine Biology and Ecology 406 (2011) 46–53 ⁎ Corresponding author. Tel.: + 351 281 326951; fax: + 351 281 324028. E-mail address: aleitao@ipimar.pt (A. Leitão). 0022-0981/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2011.06.001 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe