Avian Quantitative Genetics

Intraclutch Egg-Size Variation in Magellanic Penguins

“…Also, selection coefficients for traits in other natural populations are similar to those that we found for both males and females (Kingsolver et al 2001). The heritabilities we estimated for traits in Magellanic Penguins are within the ranges of heritability estimates documented for morphological traits in other avian species (see Merilä and Sheldon [2001] and Jensen et al [2003], in which values ranged from 0.4 to 0.6 and from 0.28 to 1.06, respectively). Evidently, these patterns of genetic and phenotypic variation in, and natural selection on, penguin morphology are common among birds, which suggests that birds with similar life histories and habitats experience a broadly similar range of environmental conditions to which they must successfully adapt if they are to persist.…”

“…Therefore, the heritability estimates for flipper and foot sizes are likely inflated and should be considered upper bounds. The second consideration of heritability bias is environmental covariance, or common environments between parents and offspring that may inflate resemblance (Merilä and Sheldon 2001), and many studies in avian heritability have discussed potential biases from environment correlations between parents and offspring (see Barbraud 2000, Keller et al 2001. Some studies have addressed this through cross-fostering experiments, allowing offspring to be raised by other parents to eliminate shared environments (Wiggins 1989, Gustafsson andMerilä 1994).…”

“…Heritability of and selection on morphological traits is well documented for a variety of avian populations, and these traits often have high heritability estimates (Boag and van Noordwijk 1987). A review of avian heritabilities by Merilä and Sheldon (2001) showed large, significant heritability estimates for morphological traits ranging from 0.4 to 0.6 (40-60% of phenotypic variation due to genetic, rather than environmental, sources of variation). Directional, stabilizing, and disruptive selection on morphology have been documented in several avian species (Grant and Grant 1993, Brown and Brown 1998, Hendry et al 2009).…”

Environmental quality and evolutionary potential: lessons from wild populations

“…For example, several early brood size manipulation (BSM) experiments on passerine bird species have shown that an increase in brood size, triggering poorer feeding regimes for offspring, results in lower additive genetic variance and higher environmental variance for size-related traits in birds (Gebhardt-Henrich & Van Noordwijk 1991;Merilä 1997;Merilä & Fry 1998). Furthermore, a review of 19 studies in natural bird populations published before 2000 is consistent with the conclusion of lower heritable variation in unfavourable conditions (see table 5 in Merilä & Sheldon 2001). The proximate causes for this trend have been shown to be alternatively or simultaneously lower additive genetic variance in stressful conditions, higher environmental variance, or low cross-environment genetic correlation.…”

A window on the genetics of evolution:MC1Rand plumage colouration in birds

“…Plumage colouration has figured prominently in many fields, including sexual selection (Darwin 1871;Andersson 1994), geographical differentiation and speciation (Mayr 1963), evolution of sexual dimorphism (Dunn et al 2001) and evolution of polymorphisms (Roulin 2004). Much plumage colour variation both within and between species has a strong genetic component (Buckley 1987;Merilä & Sheldon 2001;Price 2002;Mundy 2005) but there has been surprisingly little progress until recently in defining the genetic changes involved. More generally, there is growing interest in the genetic basis of adaptation and phenotypic evolution, but still very few examples in which the chain of causation from genetic change through to adaptive change in phenotype is fully understood.…”