Wing Shape and Range Predict Genetic Breaks in Flying Vertebrates

A new global analysis of bats and birds reveals that the physical traits of flight and the geographic scope of a species’ habitat are primary drivers of genetic divergence within populations. Published in Frontiers of Biogeography, the study utilizes repurposed mitochondrial sequence data to map phylogeographic breaks, which are distinct boundaries where gene flow is restricted. By applying Monmonier’s maximum difference barrier algorithm to data from hundreds of species, researchers identified that these genetic breaks are not random but are strongly predicted by specific morphological and ecological factors. The findings suggest that even in highly mobile volant vertebrates, the ability to traverse landscapes is not uniform, and subtle differences in wing mechanics and feeding strategies can lead to significant intraspecific genetic structure.

The investigation focused on Chiroptera and Aves, two clades of vertebrates that possess the capacity for powered flight. While these animals are often perceived as having unlimited dispersal ability, the study demonstrates that their genetic variation is constrained by a complex interplay of landscape features and organismal traits. The researchers processed data from the phylogatR database, which aggregates geographic information from specimen repositories and sequence data from GenBank and BOLD. After rigorous quality control, which involved removing sequences with high divergence or missing data, the analysis retained 126 bat species and 214 bird species. This filtering process was essential to ensure that the estimated breaks reflected true biological structure rather than artifacts of sampling gaps or taxonomic misidentification.

Monmonier’s algorithm was employed to estimate these phylogeographic breaks by converting genetic data into a network and identifying the edges associated with the highest degree of genetic differentiation. Unlike methods that rely on a priori division of samples, this approach allows for the detection of spatial genetic structure without external geospatial inputs. The results showed that 54% of the bat species and 44.4% of the bird species exhibited conspicuous phylogeographic breaks. In bats, these breaks were concentrated in biodiversity hotspots such as southern Central America, northern South America, and Southeast Asia. In contrast, bird breaks were more widespread, extending across temperate zones and tropical regions, likely due to the larger average geographic ranges of the bird species included in the dataset.

To identify the factors predicting these breaks, the researchers utilized a random forests classifier, a machine learning technique that evaluates the importance of various predictor variables. For bats, the most significant predictors included occurrence area, latitudinal range, maximum latitude, and the presence of mountains within the species’ range. Notably, bat species with phylogeographic breaks tended to have larger occurrence areas at higher latitudes. Additionally, morphological traits such as brain mass and body-size-corrected wingspan were significant, with species exhibiting breaks having smaller brains and shorter wingspans. These findings indicate that physical barriers like mountain ranges still play a crucial role in structuring genetic diversity in bats, despite their ability to fly.

In birds, the predictors differed slightly but remained focused on morphology and ecology. The top variables included invertivory, migratory status, granivory, and the use of semi-open habitats. Bird species with phylogeographic breaks were found to have maximum latitudes closer to the Equator, smaller adult mass, and a smaller hand-wing index. The hand-wing index is a measure of wing aspect ratio, with higher values indicating longer, thinner wings that are more aerodynamically efficient. The study suggests that birds with wing morphologies adapted for efficient long-distance flight exhibit fewer genetic breaks, likely because they can maintain genetic connectivity across their ranges more effectively.

The role of wing morphology in dispersal ability is a central theme of the study. Wing loading, defined as the ratio of mass to wing surface area, and wingspan are critical factors influencing flight efficiency. In bats, higher wing loading is correlated with flight speed and distance, which can enhance genetic connectivity. However, the study found that body-size-corrected wingspan was a top predictor of breaks in bats, with species having shorter wingspans more likely to exhibit genetic structure. This implies that bats with less efficient flight capabilities are more susceptible to barriers that restrict gene flow. Similarly, in birds, the hand-wing index was a key predictor, reinforcing the link between aerodynamic efficiency and the ability to overcome geographic obstacles.

Feeding ecology also emerged as a significant factor in the formation of phylogeographic breaks. In birds, trophic niche categories such as invertivory and granivory were among the most important predictors. Wing shape in passerines is closely associated with diet and foraging behavior, suggesting that ecological specialization can limit dispersal. For example, species that specialize in specific habitats or food sources may be less likely to move across different environmental gradients, leading to genetic differentiation. This interaction between feeding ecology and genetic diversity highlights the intricate relationship between an organism’s lifestyle and its evolutionary trajectory.

The study also considered the potential influence of phylogeny on these patterns. By using taxonomic classification as a proxy for phylogeny, the researchers found that only specific avian orders, such as Procellariiformes and Caprimulgiformes, were among the top predictors. Procellariiformes, which are adapted for foraging over the open ocean, did not exhibit phylogeographic breaks, possibly due to their specialized ecological niche facilitating connectivity. In contrast, Caprimulgiformes species were predicted to contain breaks, which may correspond to the presence of multiple named subspecies. These results suggest that phylogenetic effects are not the primary explanation for the observed patterns, but rather that specific traits and ecological factors are more influential.

This research contributes to the field of macrogenetics, which involves the re-analysis of genetic data to infer large-scale evolutionary processes. By leveraging existing databases and machine learning techniques, the study provides a comprehensive view of how intraspecific genetic variation is structured in volant vertebrates. The findings underscore the importance of considering both geographic and organismal traits when studying biodiversity. The study also highlights the potential for using repurposed data to identify global trends in genetic structure, offering a starting point for more detailed investigations into the processes of diversification and speciation.

Ultimately, the study demonstrates that volant vertebrates are not equal in their dispersal capabilities. Species capable of flying long distances with efficient wing morphologies are less likely to contain intraspecific genetic structure. The interplay between wing shape, feeding ecology, and geographic range characteristics provides a nuanced understanding of how genetic breaks form. These insights have implications for conservation biology, as they help identify areas and species that may be particularly vulnerable to genetic isolation. By recognizing the factors that contribute to phylogeographic structure, researchers can better predict and manage the genetic diversity of flying vertebrates in a changing world.

Subject of Research: Phylogeographic breaks in volant vertebrates

Article Title: Bats of a feather: Range characteristics and wing morphology predict phylogeographic breaks in volant vertebrates

Article References: Decker, S. K., Provost, K. L., & Carstens, B. C. (2025). Bats of a feather: Range characteristics and wing morphology predict phylogeographic breaks in volant vertebrates. Frontiers of Biogeography, 18, Article e139911. https://doi.org/10.21425/fob.18.139911

Image Credits: AI Generated

DOI: 10.21425/fob.18.139911

Keywords: phylogeography, bats, birds, wing morphology, genetic structure, dispersal ability, monmonier algorithm, random forests, feeding ecology, biodiversity, feather, Range