Geographic variation in insect coloration is among the most intriguing examples of rapid phenotypic evolution and provides opportunities to study mechanisms of phenotypic change and diversification in closely related lineages. The bumble bee
As hybrid zones exhibit selective patterns of gene flow between otherwise distinct lineages, they can be especially valuable for informing processes of microevolution and speciation. The bumble bee,
- NSF-PAR ID:
- 10446872
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 11
- Issue:
- 24
- ISSN:
- 2045-7758
- Format(s):
- Medium: X Size: p. 18151-18168
- Size(s):
- ["p. 18151-18168"]
- Sponsoring Org:
- National Science Foundation
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Population genomics of divergence among extreme and intermediate color forms in a polymorphic insect
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Abstract Bumble bees exhibit exceptional diversity in their segmental body coloration largely as a result of mimicry. In this study we sought to discover genes involved in this variation through studying a lab-generated mutant in bumble bee
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Abstract Phenotypic polymorphism can constitute an inherent challenge for species delimitation. This issue is exemplified in bumble bees (
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Abstract Hybrid zones can be studied by modeling clines of trait variation (e.g., morphology, genetics) over a linear transect. Yet, hybrid zones can also be spatially complex, can shift over time, and can even lead to the formation of hybrid lineages with the right combination of dispersal and vicariance. We reassessed Sibley’s (1950) gradient between Collared Towhee (Pipilo ocai) and Spotted Towhee (Pipilo maculatus) in Central Mexico to test whether it conformed to a typical tension-zone cline model. By comparing historical and modern data, we found that cline centers for genetic and phenotypic traits have not shifted over the course of 70 years. This equilibrium suggests that secondary contact between these species, which originally diverged over 2 million years ago, likely dates to the Pleistocene. Given the amount of mtDNA divergence, parental ends of the cline have very low autosomal nuclear differentiation (FST = 0.12). Dramatic and coincident cline shifts in mtDNA and throat color suggest the possibility of sexual selection as a factor in differential introgression, while a contrasting cline shift in green back color hints at a role for natural selection. Supporting the idea of a continuum between clinal variation and hybrid lineage formation, the towhee gradient can be analyzed as one population under isolation-by-distance, as a two-population cline, and as three lineages experiencing divergence with gene flow. In the middle of the gradient, a hybrid lineage has become partly isolated, likely due to forested habitat shrinking and fragmenting as it moved upslope after the last glacial maximum and a stark environmental transition. This towhee system offers a window into the potential outcomes of hybridization across a dynamic landscape including the creation of novel genomic and phenotypic combinations and incipient hybrid lineages.
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Abstract The arrival to the
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