Abstract
Studying patterns of phenotypic variation among populations can shed light on the drivers of evolutionary processes. The house sparrow (Passer domesticus) is one of the world’s most ubiquitous bird species, as well as a successful invader. We investigated phenotypic variation in house sparrow populations across a climatic gradient and in relation to a possible scenario of an invasion. We measured variation in morphological, coloration, and behavioral traits (exploratory behavior and neophobia) and compared it to the neutral genetic variation. We found that sparrows were larger and darker in northern latitudes, in accordance with Bergmann’s and Gloger’s biogeographic rules. Morphology and behavior mostly differed between the southernmost populations and the other regions, supporting the possibility of an invasion. Genetic differentiation was low and diversity levels were similar across populations, indicating high gene flow. Nevertheless, the southernmost and northern populations differed genetically to some extent. Furthermore, genetic differentiation (FST) was lower in comparison to phenotypic variation (PST), indicating that the phenotypic variation is shaped by directional selection or by phenotypic plasticity. This study expands our knowledge on evolutionary mechanisms and biological invasions.
Highlights
The study of phenotypic variation among natural populations and its relation to ecology is one of the central concepts in the field of evolutionary biology[1]
We examined patterns of phenotypic variation in morphology, plumage coloration, and behavior in house sparrows and compared them to patterns of neutral genetic variation
Our two main motivations were: first, to understand the evolutionary processes driving the phenotypic variation between populations; and second, to investigate the hypothesis that introduction of sparrows had occurred in the southernmost part of our research area
Summary
The study of phenotypic variation among natural populations and its relation to ecology is one of the central concepts in the field of evolutionary biology[1]. Reduced levels of neophobia (the tendency to avoid novel objects or foods22) and increased exploratory behavior (searching behavior without immediate requirement23) may have an advantage in successful introductions[24], and are expected to characterize introduced populations[25,26]. It is not entirely understood how populations acquire such novel adjustments[27]. The house sparrow (Passer domesticus) is one of the world’s most common bird species Due to their commensal nature, and following numerous successful human-mediated introductions, house sparrows are abundant in almost every human-populated habitat[34]. A distinct pattern of variation in body size and color occurred within a time span of no longer than a century, corresponding to Bergmann’s and Gloger’s rules
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