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

Abstract

To understand the biology of organisms it is important to take into account the evolutionary forces that have acted on their constituent populations. Neutral genetic variation is often assumed to reflect variation in quantitative traits under selection, though with even low neutral divergence there can be substantial differentiation in quantitative genetic variation associated with locally adapted phenotypes. To study the relative roles of natural selection and genetic drift in shaping phenotypic variation, the levels of quantitative divergence based on phenotypes (PST) and neutral genetic divergence (FST) can be compared. Such a comparison was made between 10 populations of Finnish House Sparrows (n = 238 individuals) collected in 2009 across the whole country. Phenotypic variation in tarsus‐length, wing‐length, bill‐depth, bill‐length and body mass were considered and 13 polymorphic microsatellite loci were analysed to quantify neutral genetic variation. Calculations of PST were based on Markov‐Chain Monte Carlo Bayesian estimates of phenotypic variances across and within populations. The robustness of the conclusions of the PST–FST comparison was evaluated by varying the proportion of variation due to additive genetic effects within and across populations. Our results suggest that body mass is under directional selection, whereas the divergence in other traits does not differ from neutral expectations. These findings suggest candidate traits for considering gene‐based studies of local adaptation. The recognition of locally adapted populations may be of value in the conservation of this declining species.

Genetic and Morphometric Divergence of an Invasive Bird: The Introduced House Sparrow (Passer domesticus) in Brazil

“…Therefore, phenotypic differentiation of these traits may not have a very strong adaptive basis for house sparrow populations in Brazil. A similar result was also found for native house sparrow populations from Finland, where only body mass across populations seemed to be adaptive, while other traits (bill, wing and tarsus length) seemed to be shaped by genetic drift [71].…”

“…Therefore, the lower the critical c/h 2 ratio is ( c/h 2 <1) when P ST exceeds F ST , the more likely it is that the trait is being shaped by selection [70]. Therefore, if there is evidence of between population variance deriving from additive genetic effects, even in a scenario where environmental factors have a stronger role in determining phenotypic variation, then phenotypic divergence will be the result of selection, as long as the trait is heritable [71].…”

Size differentiation in Finnish house sparrows follows Bergmann's rule with evidence of local adaptation

“…Because this divergence is assessed under field conditions, it remains possible that it is completely determined by differences in environmental conditions between populations. Such environmental effects are probably pronounced for divergence in plastic traits such as body mass and wing length between house sparrow populations (Holand et al ., ; Kekkonen et al ., , this paper). Nevertheless, for a number of house sparrow ‘hardwired’ skeletal traits, we here find high divergence in a manner that is consistent in both sexes and that we believe reflects between‐population variation in coding genes.…”

“…Despite this low F ST , some house sparrow morphometric traits measured in the field show considerable between‐population divergence in Norway (Holand et al . ) and in Finland (Kekkonen et al ., ). However, these studies demonstrated that body mass was the main trait that diverged across populations.…”

The role of environment and core‐margin effects on range‐wide phenotypic variation in a montane grasshopper

“…Phenotypic divergence can arise as a consequence of purely stochastic processes such as bottlenecks or founder effects, which can lead to genetic drift in genomic regions involved in trait expression (Lande, ; Zhan et al ., ). However, numerous studies have found local adaptation as the main evolutionary force responsible for phenotypic differentiation in natural populations (Kekkonen et al ., ; Oneal & Knowles, ; Ortego et al ., ; see reviews in Merilä & Crnokrak, ; Leinonen et al ., ), and considerable research has been devoted to identify the ecological conditions under which this phenomenon arises (Schluter, ; Nosil & Crespi, ; Räsänen & Hendry, ). Theoretical models have shown that local adaptation can occur even in the face of high gene flow when environmental heterogeneity results in spatially and temporally contrasting selection pressures (Merilä & Crnokrak, ; Räsänen & Hendry, ; see also Edelaar et al ., ; Edelaar & Bolnick, and references therein).…”