title: Geographical variation of shell thickness in the mussel Perumytilus purpuratus along the southeast Pacific coast.
abstract: At broad geographical scales, the variation in bivalve shell thickness can be modulated by environmental factors that vary with latitude, such as sea surface temperature (SST), seawater pH, or calcium carbonate availability. Mussels usually form multilayered beds, and shell thickness is also expected to be affected by density and layering due to intraspecific competition. In this work, we explored the geographical variation of shell thickness in the intertidal mussel Perumytilus purpuratus between 18° and 42°S along the southeastern Pacific coast. We tested the hypothesis that there was a positive relationship between shell thickness and SST, and then we explored other variables that could have an effect on thickness, such as density, number of layers, and others environmental variables (pH and calcite concentration). The expected positive linear relationship between shell thickness and sea surface temperature was not found, but when the other population variables were included in the analysis, an unexpected inverse SST-thickness relationships appeared as significant, probably because this species could be adapted to colder and more acid seawater as are those of the tips of South America. Thickness was also negatively affected by density, which was expected for a gregarious species showing high intraspecific competition. Finally, our results highlight the importance of including density and crowding effects when macroscale patterns are explored, particularly in gregarious species, since these patterns could also be modulated by density-dependent processes, which might then override latitudinal trends of shell thickness when they are not included in the analyses.
authors.affiliation: Instituto de Ciencias Naturales Alexander von Humboldt, Facultad de Ciencias del Mar y de Recursos Biológicos, Universidad de Antofagasta, P.O. Box 170, Antofagasta, Chile; Programa Doctorado en Ciencias Aplicadas mención Sistemas Marinos Costeros, Universidad de Antofagasta, Antofagasta, Chile; carolina.briones@uantof.cl.
authors.forename: Carolina
authors.initials: C
authors.lastname: Briones
authors.affiliation: Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Universidad Católica del Norte, Coquimbo, Chile; and Centro de Estudios Avanzados en Ecología & Biodiversidad, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
authors.forename: Marcelo M
authors.initials: MM
authors.lastname: Rivadeneira
authors.affiliation: Centro de Estudios Avanzados en Ecología & Biodiversidad, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile.
authors.forename: Miriam
authors.initials: M
authors.lastname: Fernández
authors.affiliation: Instituto de Ciencias Naturales Alexander von Humboldt, Facultad de Ciencias del Mar y de Recursos Biológicos, Universidad de Antofagasta, P.O. Box 170, Antofagasta, Chile;
authors.forename: Ricardo
authors.initials: R
authors.lastname: Guiñez
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology; D000818:Animals; D049872:Bivalvia / Q000033:anatomy & histology*; D004777:Environment; D010140:Pacific Ocean