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Detailed molecular phylogenies of closely related species provide an unprecedented opportunity to study the relationship between plumage evolution and speciation. Through reconstruction of ancestral character states, phylogenies enable us to separate convergence from similarity due to shared ancestry, and gains of plumage ornaments from losses. Mol...

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... Among lineages, class Aves generally shows high levels of shared ancestry due to its strong dispersal ability 15 , high chromosomal stasis 16 , and relatively slow development of post-zygotic breeding barriers 17,18 . These characteristics of avian evolution can result in species complexes that readily hybridize, as well as create discord in genomic and morphological divergence patterns [9][10][11]19 . Taxa within these groups often share large ancestral portions of their genome, which is readily passed between hybridizing groups, while only few genomic regions under directional selection are responsible for maintaining species boundaries 11,20-22 . ...
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Causes for genomic and morphological similarities among recently radiated species are often multifaceted and are further convoluted among species that readily interbreed. Here, we couple genomic and morphological trait comparisons to test the extent that ancestry and gene flow explain the retention of mallard-like traits within a sister species, the Mexican duck. First, we confirm that these taxa remain genetically structured, and that Mexican ducks exhibit an isolation-by-distance pattern. Despite the assumption of wide-spread hybridization, we found only a few late-stage hybrids, all from the southwestern USA. Next, assessing 23 morphological traits, we developed a genetically-vetted morphological key that is > 97% accurate in distinguishing across sex-age cohorts of Mexican ducks, mallards, and hybrids. During key development, we determined that 25% of genetically pure, immature male Mexican ducks of the northern population naturally displayed mallard-like traits in their formative plumage. In fact, applying this key to 55 museum specimens, we identified that only four of the 14 specimens originally classified as phenotypic hybrids were truly hybrids. We discuss how genomic and morphological comparisons shed light into the mechanism(s) underlying the evolution of complex phenotypic traits in recent radiations, and how misunderstanding the true morphological diversity within Mexican ducks resulted in taxonomic revisions that hindered conservation efforts.
... Even intergeneric hybrids have been recorded in many avian families [34]. As a result, cases of allopatric speciation followed by secondary contact and hybridization are prevalent in birds [35][36][37][38]. Even though the large southwestern doves are not each other's closest relatives [39,40], their recent extensive secondary contact following biogeographic histories of substantial allopatry may be producing opportunities for hybridization and introgression. ...
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Introductions and invasions provide opportunities for interaction and hybridization between colonists and closely related native species. We investigate this phenomenon using the mitochondrial DNA COI and 81,416 base-pairs of overlapping nuclear variation to examine the evolutionary histories and signatures of hybridization among introduced feral Rock Pigeon and Eurasian Collared-Dove and native White-winged and Mourning doves in southwestern North America. First, we report all four species to be highly divergent across loci (overall pair-wise species ΦST range = 0.17–0.70) and provide little evidence for gene flow at evolutionary timescales. Despite this, evidence from multiple population genetics analyses supports the presence of six putative contemporary late-stage hybrids among the 182 sampled individuals. These putative hybrids contain various ancestry combinations, but all involve the most populous species, the Mourning Dove. Next, we use a novel method to reconstruct demographic changes through time using partial genome sequence data. We identify recent, species-specific fluctuations in population size that are likely associated with changing environments since the Miocene and suggest that these fluctuations have influenced the genetic diversity of each dove species in ways that may impact their future persistence. Finally, we discuss the importance of using multiple marker types when attempting to infer complex evolutionary histories and propose important considerations when analyzing populations that were recently established or of domestic origins.
... If the clades represent different adaptive lineages in our study area, then barriers to gene flow should exist and genetic divergence should parallel differences in phenotypic characters and individual fitness. Furthermore, differences in mating signals such as calls or behaviour could have accumulated as a result of genetic drift during a period of allopatry that might prevent interbreeding even among ecologically similar or identical groups (Mendelson & Shaw 2002;Mendelson 2003;Omland & Kondo 2006;Price 2008). In this study, we evaluated evidence for phenotypic character divergence paralleling divergence in mtDNA between Common Ravens with Holarctic and California clade mtDNA. ...
... The deep divergence of the mtDNA clades of the Common Raven suggests that the clades diverged between 3.5 and 1.7 Ma (Feldman & Omland 2005; see Price 2010), but remerging of the lineages suggests that any divergence experienced in isolation was not strong enough to cause substantial adaptive divergence. Signal traits may also contribute to the likelihood of speciation (Mendelson & Shaw 2002;Omland & Kondo 2006;Mendelson et al. 2007;Price 2008). Both vocalizations and plumage are much conserved across the genus Corvus (Madge & Burn 1994), with greater than 50% of the species being monomorphically black. ...
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DNA sequence studies frequently reveal evidence of cryptic lineages in morphologically uniform species, many of which turn out to be evolutionarily distinct species. The Common Raven (Corvus corax) includes two deeply divergent mtDNA lineages: one lineage seems restricted to western North America and the other is Holarctic in distribution. These deep clades hint of the possibility of cryptic species in the western United States. We tested this hypothesis in a population consisting of an equal proportion of both mtDNA clades, by quantifying mating patterns and associated fitness consequences with respect to mtDNA. We also tested for morphological, behavioural and ecological correlates of sex and mtDNA clade membership. Mate pairings were random with respect to mtDNA clades, and there were no differences in reproductive success between assortatively and nonassortatively mated pairs. We found no differences in survival or resource use between clades. There were no differences in morphological or behavioural characters between mtDNA clades, except one clade trended towards greater mobility. These results suggest there are no barriers to gene flow between mtDNA clades and argue that the mtDNA clades have remerged in this population, likely due to a lack of ecological or signal differentiation between individuals in each lineage. Hence, in Common Ravens, phylogeographic structure in mtDNA is a reflection of likely past isolation rather than currently differentiated species.
... First, it could be related to species recognition, for example with these color differences evolving through reproductive character displacement (e.g., Saetre et al. 1997). Second, it could be that species that evolve color differences in allopatry are able to become sympatric (Omland and Kondo 2006). In the first mechanism, species recognition drives the evolution of color changes, whereas in the second mechanism, color changes that arise due to other causes such as sexual selection or drift, facilitate later sympatry (Omland and Kondo 2006). ...
... Second, it could be that species that evolve color differences in allopatry are able to become sympatric (Omland and Kondo 2006). In the first mechanism, species recognition drives the evolution of color changes, whereas in the second mechanism, color changes that arise due to other causes such as sexual selection or drift, facilitate later sympatry (Omland and Kondo 2006). The role of species recognition in driving color differences, or color differences facilitating species persistence should be pursued in future behavioral studies across caciques, or future comparative studies of Icterids and other birds. ...
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Carotenoid-based colors have signaling roles in a range of animal taxa, yet little is known about how carotenoids vary across species or whether overall patterns may vary across genera. The caciques (Cacicus, Clypicterus and Ocyalus; family Icteridae), a group of passerine birds from Central and South America, appear to visually divide into discrete yellow and red color groups. Reflectance spectrometry supported this observation, showing widely separated short and long-wavelength groups corresponding with yellow and red-feathered taxa. Ancestral state reconstructions inferred a yellow ancestral state with two independent changes to red, and no reversals back to yellow. This pattern contrasts with that of another closely related icterid clade, the New World orioles (Icterus), which exhibit a full range of carotenoid colors and have a pattern of evolution that is continuous and extremely labile. To our knowledge, this study is the first to highlight the possibility of different modes of color evolution even among closely related clades. This study also emphasizes the importance of the methods and assumptions of ancestral state reconstruction. In particular, although coloration and other characters can be measured along a continuous scale, they should be reconstructed using discrete methods when data from extant taxa and underlying mechanisms suggest discrete changes.
... The Baltimore oriole and black-backed oriole differ in plumage as well as in migratory distance. Male plumage between these species is unusually divergent for species so closely related (Omland and Lanyon 2000;Kondo et al. 2004;Omland and Kondo 2006, also see Price et al. 2007), suggesting that there may have been strong selection on male black-backed oriole plumage after the founder event. If so, this would be another example of rapid phenotypic change following a change in migration and breeding location, as predicted by the model of speciation through loss of migration. ...
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A widely accepted paradigm is that sedentary Neotropical bird species are a reservoir that gives rise to temperate-tropical migratory species. Recently, an alternative theory has been proposed, that developmental plasticity can allow some individuals within a migratory species to establish a disjunct breeding range through loss of migration, thus facilitating the founding of a new sedentary species. We used mtDNA and two nuclear introns to perform coalescent analyses for two closely related New World oriole species, one a long-distance temperate-tropical migrant and the other a short-distance intratropical migrant. Our results suggest that the short-distance migrant recently diverged from the long-distance migrant via a founder event. In this species pair, the widely accepted paradigm is not supported. These results are consistent with a model of speciation through reduction of migratory distance.
... Orioles are a much more speciose group, however, with 25 recognized species in comparison to 11 recognized oropendola species ( Sibley and Monroe 1990), so more speciation and/or fewer extinctions have apparently occurred during oriole evolution. More speciation could be correlated with more evolutionary changes in both song and plumage ( Slabbekorn and Smith 2001;Omland and Kondo 2006), which in turn could have provided more opportunities for evolutionary convergence and reversal given a limited range of potential character states. Reconstructing the evolution of plumage patterns in oropendolas using methods similar to those used for orioles by Omland and Lanyon (2000) will be needed to see whether the differences we found in song evolution between these clades are found in the evolution of plumage patterns as well. ...
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Both song and color patterns in birds are thought to evolve rapidly and exhibit high levels of homoplasy, yet few previous studies have compared the evolution of these traits systematically using the same taxa. Here we reconstruct the evolution of song in the New World orioles (Icterus) and compare patterns of vocal evolution to previously reconstructed patterns of change in plumage evolution in this clade. Individual vocal characters exhibit high levels of homoplasy, reflected in a low overall consistency index (CI = 0.27) and retention index (RI = 0.35). Levels of lability in song are comparable to those found for oriole plumage patterns using the same taxa (CI = 0.31, RI = 0.63), but are strikingly dissimilar to the conservative patterns of change seen in the songs of oropendolas (Psarocolius, Ocyalus; CI = 0.82, RI = 0.87), a group closely related to the orioles. Oriole song is also similar to oriole plumage in exhibiting repeated convergence in overall patterns, with some distantly related taxa sounding remarkably similar. Thus, both song and plumage in orioles show repeated convergence in individual elements and in overall patterns across the clade, suggesting that both of these character classes are highly labile between taxa yet highly conserved within the genus. Our results provide new insights into the tempo and mode of evolution in sexually selected traits within and across clades.
Article
Sexual selection has been hypothesized to promote speciation, but evidence relating sexual selection to differences in speciation rates among taxa is equivocal. We note that evolutionary changes in ornaments are the link connecting sexual selection to speciation, and that ornament evolution is influenced by many factors so that its relationship with the strength of sexual selection may not be linear. We test if the evolution of ornamental coloration in Carduelis finches is related with speciation and if more ornamented lineages speciate more. We found that coloration evolves with a speciational pattern, but we found no evidence that the evolutionary changes associated with speciation are predominantly gains in ornamentation. The speciational pattern was found for both carotenoid- and melanin-based coloration, suggesting that traits putatively under stronger sexual selection by female choice (carotenoid coloration) are not the sole ones facilitating reproductive isolation. We conclude that in the genus Carduelis the evolutionary lability of ornaments influences speciation more than the strength of sexual selection, and we suggest that ornament lability should be considered as a possible causal factor in studies comparing cladogenesis among taxa.