Genetic insight into a polygenic trait using a novel genome-wide association approach in a wild amphibian population.

Body size variation is central in the evolution of life-history traits in amphibians, but the underlying genetic architecture of this complex trait is still largely unknown. Herein, we studied the genetic basis of body size and fecundity of the alternative morphotypes in a wild population of the Greek smooth newt (Lissotriton graecus). By combining a genome-wide association approach with linkage disequilibrium network analysis, we were able to identify clusters of highly correlated loci thus maximizing sequence data for downstream analysis. The putatively associated variants explained 12.8% to 44.5% of the total phenotypic variation in body size and were mapped to genes with functional roles in the regulation of gene expression and cell cycle processes. Our study is the first to provide insights into the genetic basis of complex traits in newts and provides a useful tool to identify loci potentially involved in fitness-related traits in small data sets from natural populations in non-model species.

Expression patterns of heat-shock genes during stopover and the trade-off between refueling and stress response in a passerine migrant.

Migrating birds are often exposed to variable environments and face a multitude of stress exposures along their long-distance flights. During stopover refueling, migratory birds must balance the need to accumulate energy reserves to continue their migration with the need to respond to environmental and physiological stressors. We examined the gene expression patterns of different Heat Shock Proteins (HSPs) in migrating birds during stopover at different body condition states (lean vs. fat), to provide some first insights on the role of HSPs in bird migration and explore the concept of a trade-off between refueling and stress response. Our results showed upregulation of HSP expression at release that could be associated with muscle growth and increased cholesterol and lipid synthesis needed for birds to fuel their upcoming migration. On the other hand, during capture, upregulation of HSP5 could be attributed to physiological recovery from the non-stop endurance flight when crossing the Sahara Desert-Mediterranean Sea ecological barrier. All birds significantly increased their fuel loads up to 48% of lean body mass and we provide evidence for muscle rebuilding during stopover as flight muscle mass increased by 10%, highlighting the fact that stopover sites can play a major role in the physiological recovery of migrants.

Adaptive Regulation of Stopover Refueling during Bird Migration: Insights from Whole Blood Transcriptomics.

Migration is one of the most energy-demanding tasks in avian life cycle. Many birds might not have sufficient fuel stores to cover long distances, so they must stop to rest and refuel at stopover sites, especially after the crossing of large ecological barriers. There, birds undergo several behavioral, morphological, and physiological trait adjustments to recover from and prepare for their journey; however, regulation of such processes at the molecular level remains largely unknown. In this study, we used transcriptomic information from the whole blood of migrating garden warblers (Sylvia borin) to identify key regulatory pathways related to adaptations for migration. Birds were temporarily caged during spring migration stopover and then sampled twice at different refueling states (lean vs. fat), reflecting different migratory stages (stopover arrival vs. departure) after the crossing of an extended ecological barrier. Our results show that top expressed genes during migration are involved in important pathways regarding adaptations to migration at high altitudes such as increase of aerobic capacity and angiogenesis. Gene expression profiles largely reflected the two experimental conditions with several enzymes involved in different aspects of metabolic activity being differentially expressed between states providing several candidate genes for future functional studies. Additionally, we identified several hub genes, upregulated in lean birds that could be involved in the extraordinary phenotypic flexibility in organ mass displayed by avian migrants. Finally, our approach provides novel evidence that regulation of water homeostasis may represent a significant adaptive mechanism, allowing birds to conserve water during long-distance flight, mainly through protein catabolism.

Differential survival throughout the full annual cycle of a migratory bird presents a life-history trade-off.

Long-distance migrations are among the most physically demanding feats animals perform. Understanding the potential costs and benefits of such behaviour is a fundamental question in ecology and evolution. A hypothetical cost of migration should be outweighed by higher productivity and/or higher annual survival, but few studies on migratory species have been able to directly quantify patterns of survival throughout the full annual cycle and across the majority of a species' range. Here, we use telemetry data from 220 migratory Egyptian vultures Neophron percnopterus, tracked for 3,186 bird months and across approximately 70% of the species' global distribution, to test for differences in survival throughout the annual cycle. We estimated monthly survival probability relative to migration and latitude using a multi-event capture-recapture model in a Bayesian framework that accounted for age, origin, subpopulation and the uncertainty of classifying fates from tracking data. We found lower survival during migration compared to stationary periods (ß = -0.816; 95% credible interval: -1.290 to -0.318) and higher survival on non-breeding grounds at southern latitudes (<25°N; ß = 0.664; 0.076-1.319) compared to on breeding grounds. Survival was also higher for individuals originating from Western Europe (ß = 0.664; 0.110-1.330) as compared to further east in Europe and Asia, and improved with age (ß = 0.030; 0.020-0.042). Anthropogenic mortalities accounted for half of the mortalities with a known cause and occurred mainly in northern latitudes. Many juveniles drowned in the Mediterranean Sea on their first autumn migration while there were few confirmed mortalities in the Sahara Desert, indicating that migration barriers are likely species-specific. Our study advances the understanding of important fitness trade-offs associated with long-distance migration. We conclude that there is lower survival associated with migration, but that this may be offset by higher non-breeding survival at lower latitudes. We found more human-caused mortality farther north, and suggest that increasing anthropogenic mortality could disrupt the delicate migration trade-off balance. Research to investigate further potential benefits of migration (e.g. differential productivity across latitudes) could clarify how migration evolved and how migrants may persist in a rapidly changing world.

Mining citizen science data to explore stopover sites and spatiotemporal variation in migration patterns of the red-footed falcon.

Citizen science data have already been used to effectively address questions regarding migration, a fundamental stage in the life history of birds. In this study, we use data from eBird and from 3 additional regional citizen science databases to describe the migration routes and timing of the red-footed falcon Falco vespertinus in the Mediterranean region across 8 years (2010-2017). We further examine the seasonal and yearly variation in migration patterns and explore sites used during the species migration. Our results suggest that the autumn passage is spatially less variable and temporally more consistent among years than in spring and that birds migrate faster in spring than in autumn. The species seems to be more prevalent along the Central Mediterranean during spring migration, probably as a result of the clockwise loop migration that red-footed falcons perform. There was a high variation in annual median migration dates for both seasons as well as in migration routes across years and seasons. Higher variation was exhibited in the longitudinal component thus indicating flexibility in migration routes. In addition, our results showed the species' preference for lowlands covered with cropland and mosaics of cropland and natural vegetation as stopover sites during migration. Stopover areas predicted from our distribution modeling highlight the importance of the Mediterranean islands as stopover sites for sea-crossing raptors, such as the red-footed falcon. This study is the first to provide a broad-scale spatiotemporal perspective on the species migration across seasons, years and flyways and demonstrates how citizen science data can inform future monitoring and conservation strategies.

Using genetic markers to unravel the origin of birds converging towards pre-migratory sites.

Identifying patterns of individual movements in spatial and temporal scales can provide valuable insight into the structure of populations and the dynamics of communities and ecosystems. Especially for migrating birds, that can face a variety of unfavorable conditions along their journey, resolving movements of individuals across their annual cycle is necessary in order to design better targeted conservation strategies. Here, we studied the movements of a small migratory falcon, the Lesser Kestrel (Falco naumanni), by genetically assigning feathers from individuals of unknown origin that concentrate in large roosts during the pre-migratory period. Our findings suggest that birds from multiple breeding populations in the Central and Eastern Mediterranean region move towards two pre-migratory sites in the Balkans, some of them detouring greatly from their expected flyways, travelling more than 500 km to reach these sites and prepare for the post-nuptial migration. By identifying the origin of individuals using the pre-migratory sites, not only we provide a better understanding of the possible impact of local threats at these sites on multiple breeding populations but also inform the design of effective conservation actions for the species.