Genetic architecture of growth and early life‐history transitions in anadromous and derived freshwater populations of steelhead

Abstract

Heritabilities of growth, precocious maturation and smolting were measured in 75 families of juvenile steelhead or rainbow trout Oncorhynchus mykiss, progeny of within and between line matings (crosses) of wild, anadromous steelhead and wild, resident (lake) rainbow trout originally derived from the same anadromous stock 70 years earlier. The tagged yearling progeny were combined by line in common freshwater rearing containers and graded into three categories: mature, smolt or rearing (undifferentiated) at age 2 years. Heritabilities of precocious male maturity, smolting and growth were moderate to high, and the genetic correlation between growth and smolting was low. Smolting and precocious male maturity were highly variable among families within lines and significantly different between lines. Each of the four lines produced significant numbers of smolts at age two. Smolting and maturation were negatively genetically correlated, which may explain the persistence of smolting in the lake population despite strong selection against lake smolts; balancing selection on male maturation age may help to maintain variation for smolting. The high heritability of smolting, coupled with the inability of smolts that leave the lake to return to it indicates that the genetic potential for smolting can lie dormant or be maintained through a dynamic interaction between smolting and early maturation for decades despite complete selection against the phenotype. The results have significant implications for the preservation of threatened anadromous stocks in fresh water and the inclusion of resident fish of formerly anadromous populations, currently trapped behind long-standing barriers to migration, as one component of the same population. # 2004 The Fisheries Society of the British Isles

Characteristics of the Sea Trout ( Salmo trutta L.) Stocks from the Owengowla and Invermore Fisheries, Connemara, Western Ireland, and Recent Trends in Marine Survival

“…The corollary is that it is possible to have sea trout smolts emanating from freshwater parents. Thrower et al (2004) found that after 70 years a wild, physically isolated lake population of formerly anadromous rainbow trout (Oncorhynchus mykiss) had retained substantial genetic variability for smolt migration (heritability 0.56) in spite of complete selection against smolt migration. However, they also found that marine survival of the lake-derived smolts was poor relative to survival of smolts derived from anadromous parents.…”

Rapid parallel evolution of standing variation in a single, complex, genomic region is associated with life history in steelhead/rainbow trout

“…However, most traits of interest are complex and controlled by a large number of genetic and environmental influences, and dissection of the genetic architecture underlying their expression is challenging [15,25]. This is especially true of traits associated with multiple phenotypic, behavioural or physiological effects [26].…”

“…In addition to the complex combination of behavioural traits associated with migration [29], steelhead undergo a suite of physiological and morphological changes known as 'smoltification' that includes osmoregulatory adaptation to the salinity of the ocean as well as physical adaptations to the highly mobile life of a pelagic marine fish. Conversely, resident trout retain traits adapted for freshwater, including paedomorphic morphology and the development of reproductive maturity in as little as 1 year [25].…”

The Genetic Basis of Smoltification-Related Traits in Oncorhynchus mykiss

“…Thorpe and others (Thorpe 1994; have hypothesized that smoltification is a developmental decision made in individuals that have failed to sexually mature in freshwater. Indeed, a negative genetic correlation or genetic trade-off between sexual maturation and smoltification has been observed (Thrower et al 2004). Although the physiology and the endocrinology of smoltification have been well studied, the ultimate genetic and molecular regulatory mechanisms responsible for alternative migratory and resident life-history types and the genetic trade-offs between these divergent life-history ''decisions'' are poorly understood.…”

“…The inheritance of nonmigratory and migratory lifehistory types and associated traits has been examined in several salmonid species (Refstie et al 1977;Clarke et al 1992Clarke et al , 1994Foote et al 1992;Johnsson et al 1994;Thrower et al 2004;Duston et al 2005). Although plasticity exists within and across populations (Quinn and Myers 2004;McPhee et al 2007), inheritance studies suggest that both timing of and propensity for smoltification are also under genetic control.…”