EXPERIMENTAL STUDIES OF LOCAL ADAPTATION
Salmonids are typically highly philopatric and hence discrete spawning populations tend be reproductively isolated. This, combined with the fact that salmonid freshwater habitats (used for spawning and juvenile rearing) tend to vary in many environmental characteristics, leads to the expectation that genetically-based adaptation to local habitats should be common. While this has become something of a paradigm in salmonid biology (Taylor 1991), studies dispute the scale at which local adaptation (LA) actually occurs, its extent, and which phenotypic characters are under strongest divergent selection (Adkison 1995; Fraser et al. 2011; Meier et al. 2011).
We are exploring these issues in Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) using common garden and reciprocal transplant experiments. For example, in a common garden experiment undertaken in the Srahrevagh River (Burrishoole system), Co. Mayo, salmon from a non-native population (Owenmore River, Co. Mayo) had a relative lifetime fitness 35% that of the native population, despite the populations being separated by only 50km (Mc Ginnity et al. 2004). A follow-on experiment included reciprocal hybrids and preliminary results indicate that hybrids exhibit intermediate marine survival and early-life dispersal patterns (O'Toole et al. In Prep).
Common garden designs allow the genetic basis of population differences to be uncovered, but definitive demonstrations of LA require reciprocal transplants. The expectation is that each local population should fare best in its own local environment, compared to the population being transferred from a new or foreign environment. Such an experiment was carried out in 2009/10 in the wid, when Atlantic salmon from the Errif and Burrishoole systems in the West of Ireland were reciprocally transplanted. Reciprocal hybrids between Errif and Burrishoole fish were also created experimentally at the hatchery facility at Burrishoole. Work is ongoing to compare the relative performances of each pure type and the reciprocal hybrids in each of the two environments.
We are also conducting similar experiments with brown trout and lobsters. A recent study undertaken in the Burrishoole catchment suggests significant population structuring at neutral loci in brown trout occuring at the 5-10km scale. Common garden experiments are underway to dissect the quantitative genetic basis, and understand the adaptive significance, of this fine-scale geographic divergence. Together with Scottish collaborators, members of our group have undertaken the first full multi-generational (6-7 generations) common garden experiment involving wild and captive bred brown trout from Loch Fleet, Scotland. A collaboration with Norwegian biologists similarly compared the fitness of cultured and wild European lobster (Homarus gammarus) stocks in a common environment (Jørstad et al. 2009).
References:
Taylor, Eric B. "A review of local adaptation in Salmonidae, with particular reference to Pacific and Atlantic salmon." Aquaculture 98, no. 1 (1991): 185-207.
Adkison, Milo D. "Population differentiation in Pacific salmons: local adaptation genetic drift, or the environment?." Canadian Journal of Fisheries and Aquatic Sciences 52, no. 12 (1995): 2762-2777.
Fraser, Dylan J., Laura K. Weir, Louis Bernatchez, Michael Møller Hansen, and Eric B. Taylor. "Extent and scale of local adaptation in salmonid fishes: review and meta-analysis." Heredity 106, no. 3 (2011): 404-420.
Meier, Kristian, Michael Møller Hansen, Dorte Bekkevold, Øystein Skaala, and KL D. Mensberg. "An assessment of the spatial scale of local adaptation in brown trout (Salmo trutta L.): footprints of selection at microsatellite DNA loci."Heredity 106, no. 3 (2011): 488-499.
McGinnity, P., P. Prodöhl, N. Ó Maoiléidigh, R. Hynes, D. Cotter, N. Baker, B. O'Hea, and A. Ferguson. "Differential lifetime success and performance of native and non‐native Atlantic salmon examined under communal natural conditions." Journal of Fish Biology 65, no. s1 (2004): 173-187.
Jørstad, K. E., T. S. Kristiansen, E. Farestveit, A‐L. Agnalt, P. A. Prodöhl, M. Hughes, A. Ferguson, and J. B. Taggert. "Survival of laboratory‐reared juvenile European lobster (Homarus gammarus) from three brood sources in southwestern Norway." New Zealand Journal of Marine and Freshwater Research 43, no. 1 (2009): 59-68.
Salmonids are typically highly philopatric and hence discrete spawning populations tend be reproductively isolated. This, combined with the fact that salmonid freshwater habitats (used for spawning and juvenile rearing) tend to vary in many environmental characteristics, leads to the expectation that genetically-based adaptation to local habitats should be common. While this has become something of a paradigm in salmonid biology (Taylor 1991), studies dispute the scale at which local adaptation (LA) actually occurs, its extent, and which phenotypic characters are under strongest divergent selection (Adkison 1995; Fraser et al. 2011; Meier et al. 2011).
We are exploring these issues in Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) using common garden and reciprocal transplant experiments. For example, in a common garden experiment undertaken in the Srahrevagh River (Burrishoole system), Co. Mayo, salmon from a non-native population (Owenmore River, Co. Mayo) had a relative lifetime fitness 35% that of the native population, despite the populations being separated by only 50km (Mc Ginnity et al. 2004). A follow-on experiment included reciprocal hybrids and preliminary results indicate that hybrids exhibit intermediate marine survival and early-life dispersal patterns (O'Toole et al. In Prep).
Common garden designs allow the genetic basis of population differences to be uncovered, but definitive demonstrations of LA require reciprocal transplants. The expectation is that each local population should fare best in its own local environment, compared to the population being transferred from a new or foreign environment. Such an experiment was carried out in 2009/10 in the wid, when Atlantic salmon from the Errif and Burrishoole systems in the West of Ireland were reciprocally transplanted. Reciprocal hybrids between Errif and Burrishoole fish were also created experimentally at the hatchery facility at Burrishoole. Work is ongoing to compare the relative performances of each pure type and the reciprocal hybrids in each of the two environments.
We are also conducting similar experiments with brown trout and lobsters. A recent study undertaken in the Burrishoole catchment suggests significant population structuring at neutral loci in brown trout occuring at the 5-10km scale. Common garden experiments are underway to dissect the quantitative genetic basis, and understand the adaptive significance, of this fine-scale geographic divergence. Together with Scottish collaborators, members of our group have undertaken the first full multi-generational (6-7 generations) common garden experiment involving wild and captive bred brown trout from Loch Fleet, Scotland. A collaboration with Norwegian biologists similarly compared the fitness of cultured and wild European lobster (Homarus gammarus) stocks in a common environment (Jørstad et al. 2009).
References:
Taylor, Eric B. "A review of local adaptation in Salmonidae, with particular reference to Pacific and Atlantic salmon." Aquaculture 98, no. 1 (1991): 185-207.
Adkison, Milo D. "Population differentiation in Pacific salmons: local adaptation genetic drift, or the environment?." Canadian Journal of Fisheries and Aquatic Sciences 52, no. 12 (1995): 2762-2777.
Fraser, Dylan J., Laura K. Weir, Louis Bernatchez, Michael Møller Hansen, and Eric B. Taylor. "Extent and scale of local adaptation in salmonid fishes: review and meta-analysis." Heredity 106, no. 3 (2011): 404-420.
Meier, Kristian, Michael Møller Hansen, Dorte Bekkevold, Øystein Skaala, and KL D. Mensberg. "An assessment of the spatial scale of local adaptation in brown trout (Salmo trutta L.): footprints of selection at microsatellite DNA loci."Heredity 106, no. 3 (2011): 488-499.
McGinnity, P., P. Prodöhl, N. Ó Maoiléidigh, R. Hynes, D. Cotter, N. Baker, B. O'Hea, and A. Ferguson. "Differential lifetime success and performance of native and non‐native Atlantic salmon examined under communal natural conditions." Journal of Fish Biology 65, no. s1 (2004): 173-187.
Jørstad, K. E., T. S. Kristiansen, E. Farestveit, A‐L. Agnalt, P. A. Prodöhl, M. Hughes, A. Ferguson, and J. B. Taggert. "Survival of laboratory‐reared juvenile European lobster (Homarus gammarus) from three brood sources in southwestern Norway." New Zealand Journal of Marine and Freshwater Research 43, no. 1 (2009): 59-68.