title: Intraspecific genetic lineages of a marine mussel show behavioural divergence and spatial segregation over a tropical/subtropical biogeographic transition.
abstract: BACKGROUND
  Intraspecific variability is seen as a central component of biodiversity. We investigated genetic differentiation, contemporary patterns of demographic connectivity and intraspecific variation of adaptive behavioural traits in two lineages of an intertidal mussel (Perna perna) across a tropical/subtropical biogeographic transition.
  
  
  RESULTS
  Microsatellite analyses revealed clear genetic differentiation between western (temperate) and eastern (subtropical/tropical) populations, confirming divergence previously detected with mitochondrial (COI) and nuclear (ITS) markers. Gene flow between regions was predominantly east-to-west and was only moderate, with higher heterozygote deficiency where the two lineages co-occur. This can be explained by differential selection and/or oceanographic dynamics acting as a barrier to larval dispersal. Common garden experiments showed that gaping (periodic closure and opening of the shell) and attachment to the substratum differed significantly between the two lineages. Western individuals gaped more and attached less strongly to the substratum than eastern ones.
  
  
  CONCLUSIONS
  These behavioural differences are consistent with the geographic and intertidal distributions of each lineage along sharp environmental clines, indicating their strong adaptive significance. We highlight the functional role of diversity below the species level in evolutionary trends and the need to understand this when predicting biodiversity responses to environmental change.
authors.affiliation: Department of Zoology and Entomology, Rhodes University, Grahamstown, 6140, South Africa. zardi73@yahoo.it.
authors.forename: Gerardo I
authors.initials: GI
authors.lastname: Zardi
authors.affiliation: Centre of Marine Sciences - CCMAR, Campus de Gambelas, Universidade do Algarve, 8005-139, Faro, Portugal. katynicastro@gmail.com.
authors.forename: Katy R
authors.initials: KR
authors.lastname: Nicastro
authors.affiliation: Department of Zoology and Entomology, Rhodes University, Grahamstown, 6140, South Africa. C.McQuaid@ru.ac.za.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: McQuaid
authors.affiliation: Centre of Marine Sciences - CCMAR, Campus de Gambelas, Universidade do Algarve, 8005-139, Faro, Portugal. rcastilho@ualg.pt.
authors.forename: Rita
authors.initials: R
authors.lastname: Castilho
authors.affiliation: Centre of Marine Sciences - CCMAR, Campus de Gambelas, Universidade do Algarve, 8005-139, Faro, Portugal. jferreiracosta@gmail.com.|Present address: Algal Biology Lab, School of Botany, The University of Melbourne, Parkville, 3010, VIC, Australia. jferreiracosta@gmail.com.
authors.forename: Joana
authors.initials: J
authors.lastname: Costa
authors.affiliation: Centre of Marine Sciences - CCMAR, Campus de Gambelas, Universidade do Algarve, 8005-139, Faro, Portugal. eserrao@ualg.pt.
authors.forename: Ester A
authors.initials: EA
authors.lastname: Serrão
authors.affiliation: Centre of Marine Sciences - CCMAR, Campus de Gambelas, Universidade do Algarve, 8005-139, Faro, Portugal. gpearson@ualg.pt.
authors.forename: Gareth A
authors.initials: GA
authors.lastname: Pearson
mesh_terms: D000353:Africa, Southern; D000818:Animals; D044822:Biodiversity; D005075:Biological Evolution; D049872:Bivalvia / Q000145:classification* / Q000235:genetics* / Q000502:physiology; D017753:Ecosystem; D051456:Gene Flow