Biology subjects

Pegan, T. M.

Publications and source records attributed to Pegan, T. M..

4 recordsLinked to original sources

bioRxiv2024

Evolutionary integration of the geography and pacing of the annual cycle in migratory birds

In migratory species, the temporal phases of the annual cycle are intrinsically linked to seasonally shifting geographic ranges. Despite intense interest in the annual cycle ecology of migration, a synthetic understanding of the relationship between the biogeography and phenology of seasonal migration remains elusive. Here, we interrogate the spatiotemporal structure of the annual cycle in a novel phylogenetic comparative framework. We use eBird, a massive avian occurrence dataset, to demarcate and measure in a consistent manner among species the portions of the annual cycle when a geographic distribution is stationary versus dynamic due to migration. Through comparative analyses of the durations of annual cycle stages for 150 species of migratory birds breeding in North America, we show that the duration of the migratory periods is remarkably consistent among species and is unrelated to the distance between breeding and nonbreeding locations. In other words, the seasonal distributions of long-distance migrants shift between their geographically distant stationary phases in the same amount of time as short-distance migrants, suggesting that individuals of long-distance migratory species have more synchronous periods of migration and likely a faster individual migratory pace than short-distance migrants. Our results further show that the amount of time a species spends on the breeding grounds is strongly inversely related to time spent on the nonbreeding grounds, revealing the length of the breeding versus nonbreeding stationary period to be the primary source of species-level variation in the pacing of the annual cycle, as opposed to the time needed for the migratory period. Further, our study reveals that the amount of time spent annually on the breeding versus nonbreeding grounds predicts the distance between breeding and nonbreeding locations, demonstrating key linkages between the biogeography of the migratory cycle, its phenology, and the evolution of life history tradeoffs.

ecology↗

bioRxiv2023

The pace of mitochondrial molecular evolution varies with seasonal migration distance

Animals that engage in long-distance seasonal migration experience strong selective pressures on their metabolic performance and life history, with potential consequences for molecular evolution. Species with slow life histories typically show lower rates of synonymous substitution (dS) than "fast" species. Previous work has suggested that long-distance seasonal migrants have a slower life history strategy than short-distance migrants, raising the possibility that rates of molecular evolution may covary with migration distance. Additionally, long-distance migrants may face strong selection on metabolically important mitochondrial genes owing to their long-distance flights. Using over 1000 mitochondrial genomes, we assessed the relationship between migration distance and mitochondrial molecular evolution in 39 boreal-breeding migratory bird species. We show that migration distance correlates negatively with dS, suggesting that the slow life history associated with long-distance migration is reflected in rates of molecular evolution. Mitochondrial genes in every study species exhibited evidence of purifying selection, but the strength of selection was greater in short-distance migrants, contrary to our predictions. This result may indicate selection for cold tolerance on mitochondrial evolution among species overwintering at high latitudes. Our study demonstrates that the pervasive correlation between life history and molecular evolutionary rates exists in the context of differential adaptations to seasonality.

evolutionary biology↗

bioRxiv2023

How Veeries vary: Whole genome sequencing resolves fine-scale genetic structure in a long-distance migratory bird, Catharus fuscescens

Fine-scale resolution of spatial genetic structure is important for understanding a species evolutionary history and contemporary genetic diversity. For high-latitude species with high dispersal ability, such as long-distance migratory birds, populations typically exhibit little genetic structure due to high gene flow and recent postglacial expansion. Some migratory birds, however, show high breeding site fidelity, which might reduce gene flow such that population genetic structure could be detectable with sufficient genomic data. We sequenced over 120 low-coverage whole genomes from across the breeding range of a long-distance migratory bird, the Veery (Catharus fuscescens). As this species breeding range extends across both historically glaciated and unglaciated regions in North America, we evaluated whether contemporary patterns of structure and genetic diversity are consistent with historical population isolation in glacial refugia. We found strong evidence for isolation by distance across the breeding range, as well as significant population structure between southern Appalachian and northern populations. However, patterns of genetic diversity did not support southern Appalachia as a glacial refugium. Resolution of isolation by distance across the breeding range was sufficient to assign likely breeding origins of individuals sampled in this species poorly understood South American nonbreeding range, demonstrating the potential to assess migratory connectivity in this species using genomic data. Overall, our findings suggest that isolation by distance yields subtle associations between genetic structure and geography across the breeding range even in the absence of obvious historical vicariance or contemporary barriers to dispersal.

evolutionary biology↗

bioRxiv2020

The evolution of seasonal migration and the slow-fast continuum of life history in birds

Seasonal migration is a widespread adaptation in environments with predictable periods of resource abundance and scarcity. Migration is frequently associated with high mortality, suggesting that migratory species live on the “fast” end of the slow-fast continuum of life history. However, few interspecific comparative studies have tested this assumption and prior assessments have been complicated by environmental variation among breeding locations. We evaluate how migration distance influences the tradeoff between reproduction and survival in 45 species of mostly passerine birds that breed sympatrically in North American boreal forests but migrate to a diversity of environments and latitudes for the northern winter. We find, after accounting for mass and phylogeny, that longer distance migrations to increasingly amenable winter environments are correlated with reduced annual reproductive output, but also result in increased adult survival compared to shorter-distance migrations. Non-migratory boreal species have life history parameters more similar to long-distance migrants than to shorter-distance migrants. These results suggest that long-distance migration and other highly specialized strategies for survival in seasonal environments impose selection pressures that both confer and demand high adult survival rates. That is, owing to the reproductive cost of long-distance migration, this strategy can only persist if balanced by high adult survival. Our results reveal migratory distance as a fundamental life history parameter that predicts, and is inextricable from, the balance of survival and reproduction. Our study further provides evolutionary context for understanding the annual cycle demography of migratory species and the strategies long-distance migrants use to maximize survival on their journeys.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗