Behavioral isolation can catalyze speciation and permit the slow accumulation of additional reproductive barriers between co-occurring organisms. We illustrate how this process occurs by examining the genomic and behavioral bases of pre-mating isolation between two bird species (Sporophila hypoxantha and the recently discovered S. iberaensis) that belong to the southern capuchino seedeaters, a recent, rapid radiation characterized by variation in male plumage coloration and song. Although these two species co-occur without obvious ecological barriers to reproduction, we document behaviors indicating species recognition by song and plumage traits and strong assortative mating associated with genomic regions underlying male plumage patterning. Plumage differentiation likely originated through the reassembly of standing genetic variation, indicating how novel sexual signals may quickly arise and maintain species boundaries.

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Migratory divides are proposed to be catalysts for speciation across a diversity of taxa. However, it is difficult to test the relative contributions of migratory behaviour vs. other divergent traits to reproductive isolation. Comparing hybrid zones with and without migratory divides offers a rare opportunity to directly examine the contribution of divergent migratory behaviour to reproductive barriers. We show that across replicate sampling transects of two pairs of barn swallow (Hirundo rustica) subspecies, strong reproductive isolation coincided with a migratory divide spanning 20 degrees of latitude. A third subspecies pair exhibited no evidence for a migratory divide and hybridised extensively. Within migratory divides, overwintering habitats were associated with assortative mating, implicating a central contribution of divergent migratory behaviour to reproductive barriers. The remarkable geographic coincidence between migratory divides and genetic breaks supports a long‐standing hypothesis that the Tibetan Plateau is a substantial barrier contributing to the diversity of Siberian avifauna.

Patterns of connectivity between breeding and wintering grounds can have important implications for individual fitness and population dynamics. Using light-level geolocators and stable hydrogen isotopes (δ(2)H) in feathers, we evaluated differential migration of Savannah sparrows (Passerculus sandwichensis) breeding on Kent Island in the Bay of Fundy, New Brunswick, Canada in relation to sex, age, and body size. Based on geolocators recovered from 38 individuals between 2012 and 2014, the winter distribution was centered in North Carolina (median latitude 34°, range 26°-41°), with males overwintering, on average, approximately 275 km further north than females. Based on analyses of tail feather samples collected from 106 individuals from the same population between 2008 and 2012, males and adults had more negative δ(2)H values than females and juveniles, respectively, providing additional evidence that males wintered north of females and that adults wintered north of juveniles. Winter latitude and δ(2)H values within each sex were not found to be related to body size. From geolocator data, males returned to the breeding grounds, on average, 14 days earlier than females. For males, there was some evidence that arrival date on the breeding grounds was negatively correlated with winter latitude and that individuals which arrived earlier tended to breed earlier. Thus, benefits for males of early arrival on the breeding grounds may have contributed to their wintering farther north than females. Social dominance may also have contributed to age and sex differences in winter latitude, whereby dominant males and adults forced subordinate females and juveniles further south.

Abstract. Scientific writing, while an indispensable step of the scientific process, is often overlooked in undergraduate courses in favor of maximizing class time devoted to scientific concepts. However, the ability to effectively communicate research findings is crucial for success in the biological sciences. Graduate students are encouraged to publish early and often, and professional scientists are generally evaluated by the quantity of articles published and the number of citations those articles receive. It is therefore important that undergraduate students receive a solid foundation in scientific writing early in their academic careers. In order to increase the emphasis on effective writing in the classroom, we assembled a succinct step-bystep guide to scientific writing that can be directly disseminated to undergraduates enrolled in biological science courses. The guide breaks down the scientific writing process into easily digestible pieces, providing concrete examples that students can refer to when preparing a scientific manuscript or laboratory report. By increasing undergraduate exposure to the scientific writing process, we hope to better prepare undergraduates for graduate school and productive careers in the biological sciences. An introduction to the guideWhile writing is a critical part of the scientific process, it is often taught secondarily to scientific concepts and becomes an afterthought to students. How many students can you recall who worked on a laboratory assignment or class project for weeks, only to throw together the written report the day before it was due? For many, this pattern occurs because we focus almost exclusively on the scientific process, all but neglecting the scientific writing process. Scientific writing is often a difficult and arduous task for many students. It follows a different format and deviates in structure from how we were initially taught to write, or even how we currently write for English, history, or social science classes. This can make the scientific writing process appear overwhelming, especially when presented with new, complex content. However, effective writing can deepen understanding of the topic at hand by compelling the writer to present a coherent and logical story that is supported by previous research and new results. ECO 101Clear scientific writing generally follows a specific format with key sections: an introduction to a particular topic, hypotheses to be tested, a description of methods, key results, and finally, a discussion that ties these results to our broader knowledge of the topic (Day and Gastel 2012). This general format is inherent in most scientific writing and facilitates the transfer of information from author to reader if a few guidelines are followed.Here, we present a succinct step-by-step guide that lays out strategies for effective scientific writing with the intention that the guide be disseminated to undergraduate students to increase the focus on the writing process in the college classroom. While we recognize that the...

Parasite populations are never evenly distributed among the hosts they infect. Avian nest ectoparasites, such as mites, are no exception, as their distribution across the landscape is highly aggregated. It remains unclear if this pattern is driven by differences in transmission events alone, or if the environment that parasites inhabit after transmission also plays a role. Here, we experimentally examined the influence of the post-transmission microclimate, nest characteristics, and host condition on ectoparasite population growth in a bird-ectoparasite system. We infested barn swallow (Hirundo rustica erythrogaster) nests with a standardized number of Northern Fowl Mites (Ornithonyssus sylvarium) and analyzed both biotic (nestling mass, wing length, number of other arthropods present in the nest, and brood size) and abiotic (temperature, humidity, nest lining, nest dimensions, and substrate upon which the nest was built) predictors of mite population growth. Our results suggest that mite populations were most successful, in terms of growth, in nests with higher temperatures, lower humidity, few other arthropods, and hosts in good condition. We also found that nests built on wooden substrates support larger populations of mites than those constructed on metal or concrete. These findings lend insight into the factors that drive large-scale patterns of ectoparasite distributions.

Migratory divides are contact zones between breeding populations with divergent migratory strategies during the nonbreeding season. These locations provide an opportunity to evaluate the role of seasonal migration in the maintenance of reproductive isolation, particularly the relationship between population structure and features associated with distinct migratory strategies. We combine light-level geolocators, genomic sequencing, and stable isotopes to investigate the timing of migration and migratory routes of individuals breeding on either side of a migratory divide coinciding with genomic differentiation across a hybrid zone between barn swallow (Hirundo rustica) subspecies in China. Individuals west of the hybrid zone, with H. r. rustica ancestry, had comparatively enriched stable-carbon and hydrogen isotope values and overwintered in eastern Africa, whereas birds east of the hybrid zone, with H. r. gutturalis ancestry, had depleted isotope values and migrated to southern India. The two subspecies took divergent migratory routes around the high-altitude Karakoram Range and arrived on the breeding grounds over 3 weeks apart. These results indicate that assortative mating by timing of arrival and/or selection against hybrids with intermediate migratory traits may maintain reproductive isolation between the subspecies, and that inhospitable geographic features may have contributed to the diversification of Asian avifauna by influencing migratory patterns.

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