Does selection or genetic drift explain geographic differentiation of morphological characters in house sparrowsPasser domesticus?

Abstract

Understanding the relative influence of genetic drift and selection is fundamental in evolutionary biology. The theory of neutrality predicts that the genetic differentiation of a quantitative trait (QST) equals the genetic differentiation at neutral molecular markers (FST) if the quantitative trait has not been under selection. Thus, the relative magnitude of observed QST and expected QST under neutral expectations suggests the importance of selection and genetic drift for any observed phenotypic divergence. Because QST is based on additive genetic variance, estimating QST based on phenotypic measurements is problematic due to unknown environmental effects. To account for this, we used a model where the environmental component was allowed to vary when estimating QST. The model was used on data from 14 house sparrow (Passer domesticus) populations in Norway. In accordance with the significant phenotypic inter-population differences our analyses suggested that directional selection may have favoured different optimal phenotypes for some morphological traits across populations. In particular, different body mass and male ornamental phenotypes seemed to have been favoured. The conclusions are, however, dependent on assumptions regarding the proportion of the observed inter-population variation that is due to additive genetic differences, showing the importance of collecting such information in natural populations. By estimating QST, allowing the additive genetic proportion of phenotypic inter-population variation to vary, and by making use of recent statistical methods to compare observed QST with neutral expectations, we can use data that are relatively easy to collect to identify adaptive variation in natural populations.

Morphometric differentiation across House Sparrow Passer domesticus populations in Finland in comparison with the neutral expectation for divergence

“…Recently, evidence was found for body mass P ST exceeding F ST in both male and female House Sparrow populations on a similar spatial scale in Norway (Holand et al . ).…”

Evidence for adaptive phenotypic differentiation inBalticSea sticklebacks

“…Some studies have applied this approach to explore the critical ratio of between‐population additive genetic variance ( c ) to within‐population additive variance relative to total variance to test the robustness of their P ST estimates and confirm the conclusions drawn from P ST – F ST comparisons (e.g. Holand et al ., ; Mobley et al ., ; Mariani et al ., ). Although most of these studies have found that environmental effects impact the estimates of trait divergence, it has been repeatedly demonstrated that the number of lateral plates in laboratory‐reared sticklebacks is generally not influenced by rearing environment (Colosimo et al ., ; McGuigan et al ., ; but see: McCairns & Bernatchez, ).…”

Full Issue

“…The potential geographic variation suggested here is not unusual because in a number of species with broad geographic ranges, such as the Northern Cardinal (Halkin and Linville 1999), variation in ornament expression and information content has been found between populations (Roulin et al 2009, Holand et al 2011, Dey et al 2012, Simpson et al 2015, Argüelles-Ticó et al 2016. For example, in the Common Yellowthroat (Geothlypis trichas), ornaments that are the focus of mate choice and that co-vary with condition and behavior in males vary between populations (Thusius et al 2001, Freeman-Gallent et al 2010, Whittingham et al 2015.…”