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Abstract Studying how genetic variation is structured across space, and how it relates to divergence in phenotypic traits relevant to reproductive isolation, is important for our overall understanding of the speciation process. We used reduced-representation genomic data (ddRAD-seq) to examine patterns of genetic variation across the full distribution of an Andean warbler species complex (Myioborus ornatus–melanocephalus), which includes a known hybrid zone between two strikingly different plumage forms. Genetic structure largely reflects geographic variation in head plumage, some of which corresponds to major topographic barriers in the Andes. We also found evidence of isolation by distance shaping genetic patterns across the group’s broad latitudinal range. We found thatchrysopsandbairdi, two taxa with marked plumage differences that have a known hybrid zone, were characterized by low overall genetic divergence. Based on our cline analyses of both plumage and genomic hybrid indices, this hybrid zone extends for approximately 250 km, where advanced generation hybrids are likely most common. We also identified a slight difference in the centers of the plumage and genomic clines, potentially suggesting the asymmetric introgression ofchrysops-like plumage traits. By studying genetic variation in a phenotypically complex group distributed across a topographically complex area, which includes a hybrid zone, we were able to show how both geographic features and potentially sexually selected plumage traits may play a role in species formation in tropical mountains 

Genomic data can provide valuable insights into the evolutionary history of rapidly diversifying groups and the genetic basis of phenotypic differences among lineages. We used whole-genome sequencing of the warbler genus Myioborus to investigate dynamics of its recent diversification in Neotropical mountains. We found that mitochondrial and UCE phylogenies are mostly, but not fully, concordant, and we found phylogenetic support for a pattern of north-to-south and low-to-high elevation colonization in the genus. Within the ornatus-melanocephalus complex, which showed topological incongruence between our phylogenies, we found that genetic structure generally coincides with geographic variation in plumage, although three subspecies with striking plumage differences exhibit low mitochondrial divergence. The hybridizing taxa M. o. chrysops and M. m. bairdi show very shallow genomic differentiation, with marked peaks of divergence. Most of these are shared with other parulid warbler pairs, pointing to broad genomic features, like recombination rate, as the processes shaping these regions. However, other highly differentiated regions were unique to Myioborus, including one containing the gene CCDC91, which is associated with melanin-based plumage differences in several other birds. Lastly, we found higher levels of differentiation on the Z chromosome relative to autosomes, including two putative chromosomal inversions. Together, these results highlight the interplay of deep ancestral divergence, recent hybridization, and shared genomic architecture in shaping the evolution of phenotypic and genomic diversity within Myioborus. 

Field biology is an area of research that involves working directly with living organisms in situ through a practice known as “fieldwork.” Conducting fieldwork often requires complex logistical planning within multiregional or multinational teams, interacting with local communities at field sites, and collaborative research led by one or a few of the core team members. However, existing power imbalances stemming from geopolitical history, discrimination, and professional position, among other factors, perpetuate inequities when conducting these research endeavors. After reflecting on our own research programs, we propose four general principles to guide equitable, inclusive, ethical, and safe practices in field biology: be collaborative, be respectful, be legal, and be safe. Although many biologists already structure their field programs around these principles or similar values, executing equitable research practices can prove challenging and requires careful consideration, especially by those in positions with relatively greater privilege. Based on experiences and input from a diverse group of global collaborators, we provide suggestions for action-oriented approaches to make field biology more equitable, with particular attention to how those with greater privilege can contribute. While we acknowledge that not all suggestions will be applicable to every institution or program, we hope that they will generate discussions and provide a baseline for training in proactive, equitable fieldwork practices. 

Abstract The Great American Biotic Interchange (GABI) was a key biogeographic event in the history of the Americas. The rising of the Panamanian land bridge ended the isolation of South America and ushered in a period of dispersal, mass extinction, and new community assemblages, which sparked competition, adaptation, and speciation. Diversification across many bird groups, and the elevational zonation of others, ties back to events triggered by the GABI. But the exact timing of these events is still being revealed, with recent studies suggesting a much earlier time window for faunal exchange, perhaps as early as 20 million years ago (Mya). Using a time‐calibrated phylogenetic tree, we show that the jay genusCyanolycais emblematic of bird dispersal trends, with an early, pre‐land bridge dispersal from Mesoamerica to South America 6.3–7.3 Mya, followed by a back‐colonization ofC. cucullatato Mesoamerica 2.3–4.8 Mya, likely after the land bridge was complete. AsCyanolycaspecies came into contact in Mesoamerica, they avoided competition due to a prior shift to lower elevation in the ancestor ofC. cucullata. This shift allowedC. cucullatato integrate itself into the Mesoamerican highland avifauna, which our time‐calibrated phylogeny suggests was already populated by higher‐elevation, congeneric dwarf‐jays (C. argentigula,C. pumilo,C. mirabilis, andC. nanus). The outcome of these events and fortuitous elevational zonation was thatC. cucullatacould continue colonizing new highland areas farther north during the Pleistocene. Resultingly, fourC. cucullatalineages became isolated in allopatric, highland regions from Panama to Mexico, diverging in genetics, morphology, plumage, and vocalizations. At least two of these lineages are best described as species (C. mitrataandC. cucullata). Continued study will further document the influence of the GABI and help clarify how dispersal and vicariance shaped modern‐day species assemblages in the Americas.