Life-history, substrate choice and Cytochrome Oxidase I variations in sandy beach peracaridans along the Rio de la Plata estuary L. Fanini a, * , G. Zampicinini a , C.S. Tsigenopoulos a , F.R. Barboza b, c , J.P. Lozoya d , J. G  omez c , E. Celentano b , D. Lercari b, c , G.M. Marchetti e , O. Defeo b, c a Hellenic Centre for Marine Research, Institute of Marine Biology, Biotechnology and Aquaculture (HCMR-IMBBC) - Thalassokosmos, Gournes, Crete, Greece b UNDECIMAR, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay c GEPEIA, Centro Universitario de la Regi on Este, Universidad de la República, Rocha, Uruguay d C-MCISur, Centro Universitario de la Regi on Este, Universidad de la República, Maldonado, Uruguay e Dipartimento di Statistica “G. Parenti”, Universit a degli studi di Firenze, Firenze, Italy article info Article history: Received 9 June 2016 Received in revised form 4 January 2017 Accepted 9 January 2017 Available online 10 January 2017 Keywords: Beaches Salinity Substrata Behaviour COI Rio de la Plata abstract Life-history, substrate choice and Cytochrome Oxidase I (COI) sequences were analysed in populations of two peracaridans, the supralittoral talitrid Atlantorchestoidea brasiliensis and the intertidal cirolanid Excirolana armata. Three populations of each species, from beaches with similar grain size and located at different points along the natural gradient generated by the Rio de la Plata estuary were analysed. Abundance of E. armata increased with distance from the estuary, while the opposite trend was observed for A. brasiliensis. The proportion of females decreased towards high salinities for both species, signifi- cantly for E. armata. A test on substrate salinity preference revealed the absence of patterns due to active choice in E. armata. By contrast, A. brasiliensis showed no preference for the population closer to the estuary, while individuals from the other two sites significantly preferred high salinity substrates. Mitochondrial COI sequences were obtained from A. brasiliensis specimens tested for behaviour. Sequence analysis showed the population from the intermediate site to differ significantly from the other two. No significant genetic differentiation was instead found between populations from the two most distant sites, nor between individuals that expressed different salinity preference. Results showed that diverse sets of traits at the population level enable sandy beach species to cope with local environmental changes: life-history and behavioural traits appear to change in response to different ecological condi- tions, and, in the case of A brasiliensis, independently of the population structure inferred from COI sequence variation. Information from multiple traits allowed detection of population profiles, high- lighting the relevance of multidisciplinary information and the concurrent analysis of field data and laboratory experiments, to detect responses of resident biota to environmental changes. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The functionality of individuals, allowing their existence within the environment, can be expressed as traits that include behav- ioural, reproductive and morphological characteristics (McGill et al., 2006). Both genes and environment contribute to shaping an organism's traits, making “traits” a unit of considerable evolu- tionary relevance (Piersma and Drent, 2003), capable of detecting changing ecological scenarios (Williams et al., 2008; Gibert et al., 2015). Within species, traits can be identified, quantified and compared with other populations subject to different ecological pressures, focusing on local matches between populations and their local environment (Begon et al., 2006). Within a population, some traits can present high heritability, while others are more related to the organism's phenotypic plasticity in response to the environ- ment (Sih et al., 2011). Thus, multiple (and non-mutually exclusive) causation can be assumed to have an effect on life-histories (Stearns, 1977). Such a mosaic has to be considered when approaching integrative species-environment studies, especially those targeting the effects of environmental changes on populations. In this study, changes in behavioural, demographic and * Corresponding author. E-mail address: lucia@hcmr.gr (L. Fanini). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss http://dx.doi.org/10.1016/j.ecss.2017.01.007 0272-7714/© 2017 Elsevier Ltd. All rights reserved. Estuarine, Coastal and Shelf Science 187 (2017) 152e159