Genetic and morphological evolution following a founder event in the dark‐eyed junco,Junco hyemalis thurberi

Abstract

An isolated population of dark-eyed juncos, Junco hyemalis, became established on the campus of the University of California at San Diego (UCSD), probably in the early 1980s. It now numbers about 70 breeding pairs. Populations across the entire natural range of the subspecies J. h. thurberi are weakly differentiated from each other at five microsatellite loci (FST = 0.01). The UCSD population is significantly different from these populations, the closest of which is 70 km away. It has 88% of the genetic heterozygosity and 63% of the allelic richness of populations in the montane range of the subspecies, consistent with a harmonic mean effective population size of 32 (but with 95% confidence limits from four to > 70) over the eight generations since founding. Results suggest a moderate bottleneck in the early establishment phase but with more than seven effective founders. Individuals in the UCSD population have shorter wings and tails than those in the nearby mountains and a common garden experiment indicates that the morphological differences are genetically based. The moderate effective population size is not sufficient for the observed morphological differences to have evolved as a consequence of genetic drift, indicating a major role for selection subsequent to the founding of the UCSD population.

Boldness behavior and stress physiology in a novel urban environment suggest rapid correlated evolutionary adaptation

“…Persistence of character differences in a common garden provides strong evidence that the likely explanation for the current population differences in behavior and CORT is not plasticity. Accordingly, earlier molecular studies confirmed that the colonist population is genetically distinct from ancestral range montane populations at microsatellite loci (Rasner et al 2004), and a previous common garden study also found persistent differences between these 2 populations in morphological characters (Rasner et al 2004;Yeh 2004).…”

“…However, in the early 1980s, a population of juncos became established on the coast of the Pacific Ocean in an urban environment on the campus of UCSD (Walens S, personal communication), most likely established by a flock of wintering migrants staying to breed (Yeh 2004;Yeh and Price 2004). Microsatellite DNA analyses indicate genetic isolation of the San Diego juncos relative to those of the montane breeding range (Rasner et al 2004), and they suggest that a sizeable number of individuals founded the urban population (e.g., minimum n 8-20 birds), such that phenotypic divergence due to a founder effect is unlikely (Rasner et al 2004;Yeh 2004). The San Diego colonist population has remained small but stable at about 80 breeding pairs over the past decade, and it constitutes an effective biogeographic island, since the closest montane forest-breeding ranges lies '70 km inland to the east, separated by unsuitable habitat (Unitt 2005).…”

“…Similarly, an explanation based on a founder effect would require that the maximum contributing number of founders was limited to fewer than '8 individuals. Microsatellite diversity in the colonist population suggests a minimum of '8-20 individuals established the population (Rasner et al 2004). …”

Mechanisms Associated with an Advance in the Timing of Seasonal Reproduction in an Urban Songbird

“…In the current study, we compared specific neuroendocrine mechanisms predicted to underlie reproductive timing differences between a recently established (∼35 years) urban population of juncos vs. heteropatric ancestral migrant juncos, under both free-living (field) and common-garden (captive) conditions. This study focused on a population of dark-eyed juncos (J. hyemalis thurberi) that became established in urban San Diego CA USA in the early 1980s, likely as a result of overwintering migratory birds remaining to breed (Rasner et al, 2004;Yeh, 2004;Atwell et al, 2012Atwell et al, , 2014. Since then, an isolated sedentary urban breeding population has persisted with limited subsequent immigration despite a sympatric distribution with migratory juncos between October and April Unitt, 2005).…”

Long-term avifaunal survey in an urban ecosystem from southeastern Brazil, with comments on range extensions, new and disappearing species

“…in two squares of Belo Horizonte city: the Praça do Papa (19°57'22"S, 43°54'54"W) and the Praça Professor Alberto Mazzoni (19°54'31"S, 43°56'11"W). Rapid changes in plumage color and morphology (over a few decades) have been suggested or documented for isolated bird populations (e.g., Fitzpatrick, 1980;Remsen Jr., 1984;Rasner et al, 2004). Thus, detailed genetic studies should be conducted to test whether this mutation is related to the possible isolation of urban populations of this species.…”