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Birds of the Northern Hemisphere often harbour the genetic signature of postglaciation expansion but analyses identifying the location of refugia and the directionality of expansions are rare. Here we explore the evolutionary hist...
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Birds of the Northern Hemisphere often harbour the genetic signature of postglaciation expansion but analyses identifying the location of refugia and the directionality of expansions are rare. Here we explore the evolutionary history of yellow warbler lineages, focusing on how these lineages recolonized their current range. We genotyped samples from 696 yellow warblers via direct sequencing of a 333-bp control region I mitochondrial DNA fragment or lineage-specific genotyping. Phylogenetic analysis revealed two monophyletic clades: a highly migratory group including previously identified eastern and western lineages and a less migratory group including a lineage consisting of tropical residents and a new 'southern' lineage localized in southwest United States. We then modelled the expansion of the eastern and western lineages, identified the location of potential refugia and assessed the importance of migration as a historical factor promoting gene flow. The expansion of the eastern lineage proceeded from a main refugia in the eastern United States, with possible contribution of an additional local refugia. In the western lineage, the expansion proceeded from a single refugia possibly located in western United States. Because two lineages overlapped to varying degrees in central North America, we suggest that the Canadian Prairies offered a bridge of riparian habitats where the lineages met after glacier retreat, while the US Central Great Plains acted as a barrier that limited secondary contact. Finally, gene flow was more important along the north-south axis of migration than away from it, suggesting spring migration played a role in the dispersal of lineages.
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1. Studies demonstrating trophic cascades through the loss of top-down regulatory processes in productive and biologically diverse terrestrial ecosystems are limited. Elk Island National Park, Alberta and surrounding protected are...
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1. Studies demonstrating trophic cascades through the loss of top-down regulatory processes in productive and biologically diverse terrestrial ecosystems are limited. Elk Island National Park, Alberta and surrounding protected areas have a wide range of ungulate density due to the functional loss of top predators, management for high ungulate numbers and variable hunting pressure. This provides an ideal setting for studying the effects of hyper-abundant ungulates on vegetation and shrub-dependent bird and butterfly species. To examine the cascading effects of high ungulate density, we quantified vegetation characteristics and abundances of yellow warbler Dendroica petechia and Canadian tiger swallowtail Papilio canadensis under different ungulate density in and around Elk Island National Park. Using Structural Equation Models we found that ungulate density was inversely related to shrub cover, whereas shrub cover was positively related to yellow warbler abundance. In addition, chokecherry Prunus virginiana abundance was inversely related to browse impact but positively related to P.canadensis abundance. These results demonstrate a cascade resulting from hyper-abundant ungulates on yellow warblers and Canadian tiger swallowtails through reductions in shrub cover and larval host plant density. The combined effect of the functional loss of top predators and management strategies that maintain high ungulate numbers can decouple top-down regulation of productive temperate ecosystems.
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Nesting structures are important for successful reproduction in most birds, and, because of this, geographic variation in nest morphology and composition are usually interpreted as adaptations to breeding in different environments...
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Nesting structures are important for successful reproduction in most birds, and, because of this, geographic variation in nest morphology and composition are usually interpreted as adaptations to breeding in different environments. We compared the structure of nests of Yellow Warblers (Dendroica petechia) breeding in Churchill, Manitoba, and Elgin, Ontario, Canada. Churchill is subarctic in habitat and typically much colder during the breeding season than Elgin. We compared temperature, rainfall, and wind speed at these two sites and then tested whether differences in nest structure corresponded to different environments. Yellow Warblers breeding in Churchill built larger, less porous nests that retained heat better but also absorbed more water and took longer to dry than Yellow Warbler nests from Elgin. We suggest that differences in the structure of Yellow Warbler nests represent adaptations to breeding in different environments because the differences in nest morphology and properties of heat retention and water loss correspond to differences between the sites in environmental challenges.
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Comparisons of the patterns of differentiation among genetic markers with different modes of inheritance fan provide insights into patterns of sex-biased dispersal and gene flow. Here, we compare the patterns of differentiation in...
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Comparisons of the patterns of differentiation among genetic markers with different modes of inheritance fan provide insights into patterns of sex-biased dispersal and gene flow. Here, we compare the patterns of differentiation in six microsatellite loci among eight northern breeding populations of the yellow warbler (Dendroica petechia) with results obtained with mitochondrial DNA. Significant but low levels of differentiation (overall F-ST = 0.014; overall R-ST = 0.015) were present across all populations. The level of differentiation is substantially less than that observed in the same samples based on mitochondrial DNA control region variation. The presence of low population imbalance index values and significant isolation-by-distance relationships for both F-ST and R-ST suggests that these populations are at evolutionary equilibrium and that the high degree of similarity between populations may be due to high levels of male-biased gene flow. This suggests that there may be significant but previously unappreciated differences in the long-distance and/or episodic dispersal behaviour of males and females in these birds. [References: 58]
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In response to brood parasitism by the brown-headed Cowbird (Molothrus ater), some female yellow warblers (Dendroica petechia) bury cowbird eggs and sometimes their own eggs, whereas other females de sert parasitized nests and ren...
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In response to brood parasitism by the brown-headed Cowbird (Molothrus ater), some female yellow warblers (Dendroica petechia) bury cowbird eggs and sometimes their own eggs, whereas other females de sert parasitized nests and renest at new sites. we identified circumstances that elicit burial or desertion by analyzing the histories of 132 naturally parasitized nests inspected over 13 breeding seasons in Manitoba. Damaged nests and clutches reduced to zero, one, or two host eggs were deserted, whereas the clutch was buried when zero, one, or two host eggs were present the morning cowbirds laid and the probability of hatching was high. Response times for burial (2.3 ± 0.1 [SE] days) and desertion (2.5 ± 0.3 days) were similar, but the variance differed significantly (1.29 days~2 for burial versus 2.58 days~2 for desertion). burial is the yellow warbler's more frequent method of rejection, though desertion is used about one-third of the time, and it may be elicited by factors unrelated to brood parasitism, such as interference by predators and inclement weather.
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Sequence variation of control region mitochondrial DNA, phylogenetic reconstruction, and analysis of molecular variance (AMOVA) were used to determine the degree of genetic structure of Yellow Warblers (Dendroica petechia) in the ...
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Sequence variation of control region mitochondrial DNA, phylogenetic reconstruction, and analysis of molecular variance (AMOVA) were used to determine the degree of genetic structure of Yellow Warblers (Dendroica petechia) in the Galapagos Archipelago. When the Galapagos population was partitioned into subpopulations (by island), AMOVA indicated a nonsignificant level of genetic structure. The presence of the same haplotype on more than one island also indicated low genetic divergence among subpopulations. Using these sequences and those available in Genbank, we also determined the degree of divergence between the Galapagos Yellow Warbler population and other New World populations. Mean sequence divergence between the Galapagos population and Latin American populations was 3.7%, and between the Galapagos population and North American populations was 6.7%.
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1. Nest predation limits avian fitness, so birds should favour nest sites that minimize predation risk. Nevertheless, preferred nest microhabitat features are often uncorrelated with apparent variation in predation rates. 2. This ...
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1. Nest predation limits avian fitness, so birds should favour nest sites that minimize predation risk. Nevertheless, preferred nest microhabitat features are often uncorrelated with apparent variation in predation rates. 2. This lack of congruence between theory-based expectation and empirical data may arise when birds already occupy 'adaptive peaks'. If birds nest exclusively in low-predation microhabitats, microhabitat and nest predation may no longer be correlated even though predation ultimately shaped microhabitat selection. 3. This 'adaptive peak hypothesis' was tested for a population of Yellow Warblers (Dendroica petechia) focusing on two nest microhabitat features: concealment and height. Experimental nests measured relative predation risk both within and outside the microhabitat range typically occupied by natural nests to examine whether nest site choices made by birds restricted our ability to detect microhabitat effects on predation. 4. Within the natural range (30-80% concealment, > 75 cm height), microhabitat-predation relationships were weak and inconsistent, and similar for experimental and natural nests. Over an extended range, however, experimental predation rates were elevated in exposed sites (<30% concealed), indicating a concealment-related 'adaptive plateau'. 5. Clay egg bite data revealed a concealment effect on avian predators, and the abundance of one avian predator group correlated with nest concealment among years, suggesting these predators may cue birds to modulate nest concealment choices. 6. This study demonstrates how avian responses to predation pressure can obscure the adaptive significance of nest site selection, so predation influences may be more important than apparent from published data.
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The proximate causes triggering nest abandonment have important implications in the host-parasite arms race. Cowbird parasitism and rejection of parasitism are costly to some hosts; therefore, cues affecting their responses have i...
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The proximate causes triggering nest abandonment have important implications in the host-parasite arms race. Cowbird parasitism and rejection of parasitism are costly to some hosts; therefore, cues affecting their responses have important evolutionary implications. Experimental addition of a cowbird egg to the nest of a yellow warbler, a host that abandons nests parasitized by cowbirds via burial or desertion, elicited a rejection frequency similar to that of naturally laid cowbird eggs. Eggs experimentally added before sunrise (time of natural parasitism) were rejected at the same frequency as eggs added after sunrise; therefore, timing of parasitism did not influence rejection. Interaction with a robotic egg-removing cowbird increased the probability of abandonment, and the most aggressive individuals were likely to bury the model cowbird egg. Individual behaviours, therefore, were correlated across contexts. Host-parasite interactions and aggression are the two most important components in host defence. Future work should focus on the physiological aspects of individual variation, such as differences in hormone levels between individuals that accept and reject parasitized clutches.
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Male North American wood-warblers (family Parulidae) subdivide their song repertoires into two different categories, or modes, of singing (first and second category songs). These two modes are thought to be specialized for interac...
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Male North American wood-warblers (family Parulidae) subdivide their song repertoires into two different categories, or modes, of singing (first and second category songs). These two modes are thought to be specialized for interacting with females and males, although the data are inconclusive. I conducted an acoustic analysis of the song types used by yellow warblers (Dendroica petechia) for type I (first category) and type II (second category) singing to ask whether there are consistent structural differences between them which could provide insight into how they might function as separate signals. I found that type I songs are performed closer to the upper boundary of a song performance limit, measured in terms of the difficulty of production, compared with type II songs. By contrast, the performance of specific song types did not depend on whether they were used for type I singing vs. type II singing by different males. In addition, type I songs had a greater amplitude increase across the first two syllables compared with type II songs. There was no relationship between the performance of type I or type II songs and male condition. These results suggest that wood-warblers might subdivide their song repertoire into distinct categories to highlight the relative vocal performance of their songs.
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Many binds obtain colorful carotenoid pigments from the diet and deposit them into growing tissues to develop extravagant red, orange or yellow sexual ornaments. In these instances, it is often unclear whether all dietary pigments...
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Many binds obtain colorful carotenoid pigments from the diet and deposit them into growing tissues to develop extravagant red, orange or yellow sexual ornaments. In these instances, it is often unclear whether all dietary pigments are used as integumentary colorants or whether certain carotenoids are preferentially excluded or incorporated into tissues. We examined the carotenoid profiles of three New World passerines that display yellow plumage coloration-the yellow warbler (Dendroica petechia), common yellowthroat (Geothylpis trichas) and evening grosbeak (Coccothrausteus vespertinus).Using high-performance liquid chromatography, we found that all species used only one carotenoid-lutein-to color their plumage yellow. Analyses of blood carotenoids (which document those pigments taken up from the diet) in two of the species, however, revealed the presence of two dietary xanthophylls-lutein and zeaxanthin-that commonly co-occurin plants and animals. These findings demonstrate post-absorptive selectivity of carotenoid deposition in bird feathers. To learn more about the site of pigment discrimination, we also analyzed the carotenoid composition of lipid fractions from the follicles of immature yellow-pigmented feathers in G. trichas and D. petechia and again detected both lutein and zeaxanthin. This suggests that selective lutein incorporation in feathers is under local control at th maturing feather follicle.
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