Explore the vast range of titles available.

Cryptic genetic differentiation is being increasingly documented in birds and other organisms using genome‐wide variation. A recent example of cryptic genetic differentiation in a widespread species with conserved morphology is the northern house wren Troglodytes aedon. We found that, despite extremely similar morphology and no documented vocal differences, the two subspecies of the northern house wren, T. a. aedon (eastern) and T. a. parkmanii (western), exhibited both nuclear and mitochondrial genomic differentiation. Individuals present along the Front Range of the Colorado Rocky Mountains possessed nuclear genetic variation intermediate between T. a. aedon and T. a. parkmanii; additionally, both divergent mitochondrial lineages, corresponding to the western and eastern northern house wren populations, occur in Colorado. However, the dynamics of this putative contact zone (i.e. amount of hybridization or introgression) and the degree of differentiation between the two subspecies remain uncharacterized. To expand our understanding of northern house wren population genetic differentiation and explore the possibility of hybridization, we used a double digest restriction‐site associated (ddRAD) approach and sequenced 127 northern house wrens, including 109 individuals from across Colorado and Wyoming, as well as nine individuals each from eastern and western allopatric regions. Our results highlight that T. a. aedon occur significantly further west than previously thought, and provide evidence for weak population structure within the northern house wren, while generally setting the stage for future investigations of northern house wren population genomics and the genetic basis of cryptic speciation.

Both abiotic and biotic drivers influence species distributions. Abiotic drivers such as climate have received considerable attention, even though biotic drivers such as hybridization often interact with abiotic drivers. We sought to explore the (1) costs of co‐occurrence for ecologically similar species that hybridize and (2) associations between ecological factors and condition to understand how abiotic and biotic factors influence species distributions. For two closely related and ecologically similar songbirds, black‐capped and mountain chickadees, we characterized body condition, as a proxy for fitness, using a 1358‐individual range‐wide dataset. We compared body condition in sympatry and allopatry with several abiotic and biotic factors using species‐specific generalized linear mixed models. We generated genomic data for a subset of 217 individuals to determine the extent of hybridization‐driven admixture in our dataset. Within this data subset, we found that ~11% of the chickadees had hybrid ancestry, and all hybrid individuals had typical black‐capped chickadee plumage. In the full dataset, we found that birds of both species, independent of demographic and abiotic factors, had significantly lower body condition when occurring in sympatry than birds in allopatry. This could be driven by either the inclusion of cryptic, likely poor condition, hybrids in our full dataset, competitive interactions in sympatry, or range edge effects. We are currently unable to discriminate between these mechanisms. Our findings have implications for mountain chickadees in particular, which will encounter more black‐capped chickadees as black‐capped chickadee ranges shift upslope and could lead to local declines in mountain chickadee populations. Understanding how species are distributed across landscapes, the relative influence of abiotic and biotic factors, and the consequences of overlap, is a central goal of evolutionary ecology, especially as ranges shift in response to rapid global change. We compared body condition between black‐capped and mountain chickadees in sympatry and allopatry to several demographic factors of known importance, as well as to abiotic factors, and controlled for hybrid status in a subset of the data using genome‐spanning loci. We found that, for both species, birds in sympatry, regardless of sex or age, had significantly lower body condition than birds in allopatry, and that this pattern might be driven by either the inclusion of cryptic, likely poor condition, hybrids in our full dataset, competitive interactions in sympatry, or range edge effects.

Sex allocation theory predicts that females should bias their offspring sex ratios when the fitness benefits of producing sons or daughters differ depending on rearing environment. The Trivers-Willard hypothesis proposes that whether females produce more sons or daughters depends on food availability via both intrinsic maternal condition and differing reproductive potential (typically from mating system structure) for sons versus daughters. However, tests of its key predictions are often based on untested, implicit assumptions that are difficult to quantify, especially in migratory animals. In a 5-year study, we manipulated food availability in low- and high-elevation forest to test the Trivers-Willard hypothesis in the migratory black-throated blue warbler (Setophaga caerulescens). We found that the population-wide offspring sex ratio was significantly male-biased (population mean: 0.58), which was driven by an overproduction of sons in high-elevation forest (high-quality habitat mean: 0.59). Yet, we found no effect of food availability on offspring sex ratio from either natural variation or supplemental feeding. Sex-specific developmental costs did not differ for sons and daughters reared under low and high food availability. These results suggest that female black-throated blue warblers do not manipulate offspring sex ratios in response to food availability and are not consistent with the predictions of the Trivers-Willard hypothesis. This study highlights challenges of examining mechanisms driving patterns in offspring sex allocation in migratory species for which both the costs of rearing and relative fitness benefits of sons and daughters cannot be tracked into adulthood.SignificanceBirds can optimize their fitness return on parental investment by biasing offspring sex ratios. When the costs and benefits of raising sons or daughters differ under low and high food availability, females could produce either more sons or daughters depending on those conditions. Black-throated blue warbler offspring sex ratios were male biased in high quality habitat. However, we found no evidence that food-supplemented females or females on territories with higher caterpillar abundance produced more sons than daughters as predicted by the Trivers-Willard hypothesis. The relative costs of producing sons or daughters did not differ under low and high food availability, but we could not directly examine differences in relative benefits. Findings indicate that this migratory bird does not adjust sex ratios in response to food availability and highlights the need for evaluating future fitness benefits of sons and daughters in migratory species.

Feather coloration and patterning are major signals influencing mate choice within and between species. However, most studies of the role of plumage in mate choice have focused on colorful species with obvious sexual dichromatism. To better understand how achromatic plumage might influence hybridization, we quantified plumage variation between and within two achromatic songbirds that occasionally hybridize, Black-capped (Poecile atricapillus) and Mountain (P. gambeli) chickadees. We collected feathers from 43 live birds and photographed 155 prepared museum specimens to measure overall plumage color and the size of the throat and cheek patches. Using principal component analyses and generalized linear mixed models, we characterized plumage patterns within and between Black-capped and Mountain chickadees from Colorado to examine plumage color variation and differences in throat and cheek patch size. We found that Black-capped Chickadees (1) were less achromatic and had brighter plumage with more color contrast than Mountain Chickadees, (2) had smaller throat and cheek patches than Mountain Chickadees, and (3) were not sexually dimorphic. We also found that male Mountain Chickadee museum specimens had brighter plumage with more ultraviolet reflectance than female museum specimens (i.e., they are sexually dimorphic). However, we did not observe sexual dimorphism in live Mountain Chickadees, potentially because we did not sample the supercilium. In contrast to previous studies, we found that Black-capped Chickadees are not sexually dimorphic, potentially because plumage is not used in mating decisions for populations at lower latitudes. Between Black-capped and Mountain chickadees, differences in plumage color and patch sizes may influence hybridization if female Mountain Chickadees prefer the brighter plumage and greater color contrast of male Black-capped Chickadees. Our results will guide future work exploring the role plumage might play in hybridization between Black-capped and Mountain chickadees by informing plumage manipulation experiments investigating the influence of brighter plumage and color contrast in hybridization. La coloración y patrones de las plumas son señales mayores que influencian la selección de parejas intra- e interespecíficamente. Sin embargo, la mayoría de los estudios del papel del plumaje en la selección de pareja se han enfocado en especies coloridas con un evidente dicromatismo sexual. Para entender mejor cómo el plumaje acromático podría influenciar la hibridación, cuantificamos la variación del plumaje intra- e interespecífica de dos aves canoras que ocasionalmente se hibridan, los carboneros Poecile atricapillus y P. gambeli. Colectamos plumas de 43 aves vivas y fotografiamos 155 especímenes de museo para medir el color total del plumaje y el tamaño de los parches de garganta y mejillas. Usando un análisis de componentes principales y modelos lineales generalizados mixtos, caracterizamos los patrones del plumaje intra- e inter-específicos de estos carboneros de Colorado para examinar la variación y las diferencias en el tamaño de los parches de garganta y mejillas. Encontramos que P. atricapillus (1) fueron menos acromáticos y tuvieron un plumaje más brillante con más contraste de color que P. gambelli, (2) tenían parches de garganta y mejillas más pequeños que los de P. gambelli y (3) no son sexualmente dimórficos. También descubrimos que los especímenes de museo de machos de P. gambelli tenían un plumaje más brillante con mayor reflectancia ultravioleta que los especímenes de museo de hembras (i.e., son sexualmente dimórficos). Sin embargo, no observamos dimorfismo sexual en P. gambelli vivos, potencialmente porque no muestreamos el supercilium. En contraste con estudios previos, encontramos que P. atricapillus no son sexualmente dimórficos, potencialmente porque su plumaje no se usa en decisiones de apareamiento en poblaciones a latitudes más bajas. Entre P. atricapillus y P. gambelli, las diferencias en color del plumaje y los tamaños de parche podrían influenciar la hibridación si las hembras de P. gambelli prefieren el color más brillante y con mayor contraste de color de los machos de P. atricapillus. Nuestros resultados guiarán trabajo futuro para explorar el papel que el plumaje podría jugar en la hibridación entre estos carboneros, informando experimentos de manipulación de plumaje para investigar la influencia del brillo y el contraste de color del plumaje en la hibridación.

The practice of science as a whole is an iterative process involving trial and error, and at each step of project development, execution, and analysis, some combination of convergent and divergent thinking is required to arrive at a tenable and high‐quality solution (DeHaan ). Despite this breadth of exposure to a spectrum of teaching techniques, every one of us has felt unprepared for some of the most common divergent thinking tasks encountered in graduate school, including: experimental design, adapting protocols, analyzing data, and writing manuscript discussion sections (Fig. ). To successfully generate meaningful scientific contributions, graduate students must develop astute research questions, effectively synthesize knowledge gaps from vast literature searches, design experiments, evaluate and revise data collection, correctly analyze and interpret output, and succinctly convey findings and their significance. [...]facilitating students’ development of scientific creativity should be a priority in designing curricula and in promoting scientific career trajectories. Or worse, a lengthy Google Scholar search session may convince you to treat a research question as though it has been completely “answered” and discourage further critical and creative thinking on the subject. [...]these searches can often derail you from generating your own ideas and thinking critically about the robustness or novelty of your question and/or approach.