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Morphological stasis or the absence of morphological change is a well‐known phenomenon in the paleontological record, yet it is poorly integrated with neontological evidence. Recent evidence suggests that cryptic species complexes may remain morphologically identical due to morphological stasis. Here, we describe a case of long‐term stasis in the Stygocapitella cryptic species complex (Parergodrilidae,...
Decades of theoretical work on the evolution of adaptive prezygotic isolation have led to an interesting finding—namely that stable partial reproductive isolation is a relatively common outcome. This conclusion is generally lost, however, in the desire to pinpoint when exactly speciation occurs. Here, we argue that the evolution of partial reproductive isolation is of great interest in its own right...
Most approaches to species delimitation to date have considered divergence‐only models. Although these models are appropriate for allopatric speciation, their failure to incorporate many of the population‐level processes that drive speciation, such as gene flow (e.g., in sympatric speciation), places an unnecessary limit on our collective understanding of the processes that produce biodiversity. To...
Levels of genetic differentiation vary widely along the genomes of recently diverged species. What processes cause this variation? Here, I analyze geographic population structure and genome‐wide patterns of variation in the Rufous, Allen's, and Calliope Hummingbirds (Selasphorus rufus/Selasphorus sasin/Selasphorus calliope) and assess evidence that linked selection on the Z chromosome drives patterns...
The incidence of introgression during the diversification process and the timespan following divergence when introgression is possible are poorly understood in the neotropics where high species richness could provide extensive opportunities for genetic exchange. We used thousands of genome‐wide SNPs to infer phylogenetic relationships, calculate ages of splitting, and to estimate the timing of introgression...
The rate of hybridization among taxa is a central consideration in any discussion of speciation, but rates of hybridization are difficult to estimate in most wild populations of animals. We used a successful citizen science dataset, eBird, to estimate the rates of hybridization for wild birds in the United States. We calculated the frequency at which hybrid individuals belonging to different species,...
Although evolutionary theory predicts an association between the evolution of elaborate ornamentation and speciation, empirical evidence for links between speciation and ornament evolution has been mixed. In birds, the evolution of increasingly complex and colorful plumage may promote speciation by introducing prezygotic mating barriers. However, overall changes in color complexity, including both...
When divergent populations are connected by gene flow, the establishment of complete reproductive isolation usually requires the joint action of multiple barrier effects. One example where multiple barrier effects are coupled consists of a single trait that is under divergent natural selection and also mediates assortative mating. Such multiple‐effect traits can strongly reduce gene flow. However,...
As species richness varies along the tree of life, there is a great interest in identifying factors that affect the rates by which lineages speciate or go extinct. To this end, theoretical biologists have developed a suite of phylogenetic comparative methods that aim to identify where shifts in diversification rates had occurred along a phylogeny and whether they are associated with some traits. Using...
How species evolve reproductive isolation in the species‐rich Amazon basin is poorly understood in vertebrates. Here, we sequenced a reference genome and used a genome‐wide sample of SNPs to analyze a hybrid zone between two highly cryptic species of Hypocnemis warbling‐antbirds—the Rondonia warbling‐antbird (H. ochrogyna) and Spix's warbling‐antbird (H. striata)—in a headwater region of southern...
“Magic traits,” in which the same trait is both under divergent ecological selection and forms the basis of assortative mating, have been sought after due to their supposed unique ability to promote divergence with gene flow. Here, we ask how unique magic traits are, by exploring whether a tightly linked complex of a locus under divergent selection and a locus that acts as a mating cue can mimic a...
Brood parasites use the parental care of others to raise their young and sometimes employ mimicry to dupe their hosts. The brood‐parasitic finches of the genus Vidua are a textbook example of the role of imprinting in sympatric speciation. Sympatric speciation is thought to occur in Vidua because their mating traits and host preferences are strongly influenced by their early host environment. However,...
When divergent populations form hybrids, hybrid fitness can vary with genome composition, current environmental conditions, and the divergence history of the populations. We develop analytical predictions for hybrid fitness, which incorporate all three factors. The predictions are based on Fisher's geometric model, and apply to a wide range of population genetic parameter regimes and divergence conditions,...
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