Differential expression of the heat shock protein Hsp70 in natural populations of the tilapia, Sarotherodon melanotheron, acclimatised to a range of environmental salinities
1 Biologie Intégrative ISEM CNRS-UMR 5554 (Université Montpellier II), Station Méditerranéenne de l'Environnement Littoral, 1 quai de la Daurade, Sète 34200, France
2 Institut de Recherche pour le Développement (IRD), UMR 5119 ECOLAG, campus IRD/ISRA de Bel Air, route des hydrocarbures, BP 1386, CP 18524 Dakar, Sénégal
3 Max Planck Institute for Molecular Genetics, Ihnestrasse 63-73, D-14195 Berlin, Germany
BMC Ecology 2010, 10:11 doi:10.1186/1472-6785-10-11Published: 29 April 2010
The relationship between environmental variation and induction of heat shock proteins (Hsps) has been much documented under experimental conditions. However, very little is known about such induction in natural populations acclimatised to prevailing environmental conditions. Furthermore, while induction of stress proteins has been well documented in response to environmental contaminants and thermal stressors, little is known about whether factors, such as extreme salinity, are also potential inductors. The black-chinned tilapia Sarotherodon melanotheron is unusual for its ability to colonise estuarine environments in West Africa that are characterised by extremely high salinities. The relationships between mRNA levels of the 70 kDa heat shock protein (Hsp70) and Na+, K+-ATPase1α (Naka) in the gills, environmental salinity, and a life-history trait (condition factor) were investigated in wild populations of this species sampled from three locations in the Saloum estuary, at salinities ranging from 40 to 100 psu.
The highest Hsp70 and Naka mRNA levels, and the poorest condition factors were recorded in the most saline sampling site (100 psu). The Hsp70 and Naka mRNA were correlated amongst themselves and showed a direct positive correlation with environmental salinity, and a negative correlation with fish condition factor. Thus, the Hsp70 is constitutively overexpressed by S. melanotheron acclimatised to extreme hypersalinity.
These results indicate that, although S. melanotheron can colonise extremely saline environments, the overexpression of Hsp70 combined with the higher Naka mRNA expression reveals that this represents a chronic stress. The induction of Hsp70 was, therefore, a biomarker of chronic hyper-osmotic stress which presumably can be linked to the impaired growth performance and precocious reproduction that have been demonstrated in the populations at the extremely saline sites.