The signature of fine scale local adaptation in Atlantic salmon revealed from common garden experiments in nature.
Understanding the extent, scale and genetic basis of local adaptation (LA) is important for conservation and management. Its relevance in salmonids at microgeographic scales, where dispersal (and hence potential gene flow) can be substantial, has however been questioned. Here, we compare the fitness of communally reared offspring of local and foreign Atlantic salmon Salmo salar from adjacent Irish rivers and reciprocal F1 hybrid crosses between them, in the wild 'home' environment of the local population. Experimental groups did not differ in wild smolt output but a catastrophic flood event may have limited our ability to detect freshwater performance differences, which were evident in a previous study. Foreign parr exhibited higher, and hybrids intermediate, emigration rates from the natal stream relative to local parr, consistent with genetically based behavioural differences. Adult return rates were lower for the foreign compared to the local group. Overall lifetime success of foreigners and hybrids relative to locals was estimated at 31% and 40% (mean of both hybrid groups), respectively. The results imply a genetic basis to fitness differences among populations separated by only 50 km, driven largely by variation in smolt to adult return rates. Hence even if supplementary stocking programs obtain broodstock from neighbouring rivers, the risk of extrinsic outbreeding depression may be high.
School of Biological, Earth & Environmental Sciences, University College Cork Cork, Ireland.
Ciar L
CL
O'Toole
School of Biological, Earth & Environmental Sciences, University College Cork Cork, Ireland.
Thomas E
TE
Reed
Institute for Global Food Security, School of Biological Sciences, Medical Biology Centre, Queen's University Belfast, Northern Ireland.
Deborah
D
Bailie
Institute for Global Food Security, School of Biological Sciences, Medical Biology Centre, Queen's University Belfast, Northern Ireland.
Caroline
C
Bradley
Marine Institute, Furnace Newport, Co. Mayo, Ireland.
Deirdre
D
Cotter
School of Biological, Earth & Environmental Sciences, University College Cork Cork, Ireland.
Jamie
J
Coughlan
School of Biological, Earth & Environmental Sciences, University College Cork Cork, Ireland.
Tom
T
Cross
School of Biological, Earth & Environmental Sciences, University College Cork Cork, Ireland.
Eileen
E
Dillane
Marine Institute, Furnace Newport, Co. Mayo, Ireland.
Sarah
S
McEvoy
Marine Institute, Furnace Newport, Co. Mayo, Ireland.
Niall
N
Ó Maoiléidigh
Institute for Global Food Security, School of Biological Sciences, Medical Biology Centre, Queen's University Belfast, Northern Ireland.
Paulo
P
Prodöhl
Marine Institute, Furnace Newport, Co. Mayo, Ireland.
Ger
G
Rogan
School of Biological, Earth & Environmental Sciences, University College Cork Cork, Ireland.
Philip
P
McGinnity
adaptive peak; anadromous; common garden; gene flow; heterosis; outbreeding depression; spatial scale