Species-specific traits mediate avian demographic responses under past climate change

Global spatiotemporal patterns of demographic fluctuations in terrestrial vertebrates during the Late Pleistocene

Demographic fluctuations are crucial for assessing species' threat levels, yet their global spatiotemporal patterns and historical drivers remain unknown. Here, we used single whole-genome sequence data for 527 extant and widespread terrestrial vertebrates to investigate their demographic fluctuations during the Late Pleistocene. Effective population size (Ne) simulations indicated that all taxa experienced a population decline from the Last Interglacial to the Last Glacial Maximum (LGM). After the LGM, birds and amphibians underwent population expansion, whereas mammals and reptiles' populations declined. Regions with high Ne shifted from Neotropical to Afrotropical and to Palearctic, some overlapping with recognized glacial refugia and biodiversity hotspots. In addition, climate-related factors exerted long-term effects on Ne, while human disturbances might confine to specific regions around the Pleistocene-Holocene boundary. This study underscores the significance of quantifying vertebrate genetic vulnerability to guide biodiversity conservation in response to environmental changes.

Seasonally migratory songbirds have different historic population size characteristics than resident relatives

Modern genomic methods enable estimation of a lineage's long-term effective population sizes back to its origins. This ability allows unprecedented opportunities to determine how the adoption of a major life-history trait affects lineages' populations relative to those without the trait. We used this novel approach to study the population effects of the life-history trait of seasonal migration across evolutionary time. Seasonal migration is a common life-history strategy, but its effects on long-term population sizes relative to lineages that don't migrate are largely unknown. Using whole-genome data, we estimated effective population sizes over millions of years in closely related seasonally migratory and resident lineages in a group of songbirds. Our main predictions were borne out: Seasonal migration is associated with larger effective population sizes (Ne), greater long-term variation in Ne, and a greater degree of initial population growth than among resident lineages. Initial growth periods were remarkably long (0.63-4.29 Myr), paralleling the expansion and adaptation phases of taxon cycles, a framework of lineage expansion and eventual contraction over time encompassing biogeography and evolutionary ecology. Heterogeneity among lineages is noteworthy, despite geographic proximity (including overlap) and close relatedness. Seasonal migration imbues these lineages with fundamentally different population size attributes through evolutionary time compared to closely related resident lineages.

Drivers of avian genomic change revealed by evolutionary rate decomposition

Modern birds have diversified into a striking array of forms, behaviours and ecological roles. Analyses of molecular evolutionary rates can reveal the links between genomic and phenotypic change1-4, but disentangling the drivers of rate variation at the whole-genome scale has been difficult. Using comprehensive estimates of traits and evolutionary rates across a family-level phylogeny of birds5,6, we find that genome-wide mutation rates across lineages are predominantly explained by clutch size and generation length, whereas rate variation across genes is driven by the content of guanine and cytosine. Here, to find the subsets of genes and lineages that dominate evolutionary rate variation in birds, we estimated the influence of individual lineages on decomposed axes of gene-specific evolutionary rates. We find that most of the rate variation occurs along recent branches of the tree, associated with present-day families of birds. Additional tests on axes of rate variation show rapid changes in microchromosomes immediately after the Cretaceous-Palaeogene transition. These apparent pulses of evolution are consistent with major changes in the genetic machineries for meiosis, heart performance, and RNA splicing, surveillance and translation, and correlate with the ecological diversity reflected in increased tarsus length. Collectively, our analyses paint a nuanced picture of avian evolution, revealing that the ancestors of the most diverse lineages of birds underwent major genomic changes related to mutation, gene usage and niche expansion in the early Palaeogene period.

Evolutionarily distinct lineages of a migratory bird of prey show divergent responses to climate change

Accurately predicting species' responses to anthropogenic climate change is hampered by limited knowledge of their spatiotemporal ecological and evolutionary dynamics. We combine landscape genomics, demographic reconstructions, and species distribution models to assess the eco-evolutionary responses to past climate fluctuations and to future climate of an Afro-Palaearctic migratory raptor, the lesser kestrel (Falco naumanni). We uncover two evolutionarily and ecologically distinct lineages (European and Asian), whose demographic history, evolutionary divergence, and historical distribution range were profoundly shaped by past climatic fluctuations. Using future climate projections, we find that the Asian lineage is at higher risk of range contraction, increased migration distance, climate maladaptation, and consequently greater extinction risk than the European lineage. Our results emphasise the importance of providing historical context as a baseline for understanding species' responses to contemporary climate change, and illustrate how incorporating intraspecific genetic variation improves the ecological realism of climate change vulnerability assessments.

Melatonin alleviates high temperature exposure induced fetal growth restriction via the gut-placenta-fetus axis in pregnant mice

INTRODUCTION

Global warming augments the risk of adverse pregnancy outcomes in vulnerable expectant mothers. Pioneering investigations into heat stress (HS) have predominantly centered on its direct impact on reproductive functions, while the potential roles of gut microbiota, despite its significant influence on distant tissues, remain largely unexplored. Our understanding of deleterious mechanisms of HS and the development of effective intervention strategies to mitigate the detrimental impacts are still limited.

OBJECTIVES

In this study, we aimed to explore the mechanisms by which melatonin targets gut microbes to alleviate HS-induced reproductive impairment.

METHODS

We firstly evaluated the alleviating effects of melatonin supplementation on HS-induced reproductive disorder in pregnant mice. Microbial elimination and fecal microbiota transplantation (FMT) experiments were then conducted to confirm the efficacy of melatonin through regulating gut microbiota. Finally, a lipopolysaccharide (LPS)-challenged experiment was performed to verify the mechanism by which melatonin alleviates HS-induced reproductive impairment.

RESULTS

Melatonin supplementation reinstated gut microbiota in heat stressed pregnant mice, reducing LPS-producing bacteria (Aliivibrio) and increasing beneficial butyrate-producing microflora (Butyricimonas). This restoration corresponded to decreased LPS along the maternal gut-placenta-fetus axis, accompanied by enhanced intestinal and placental barrier integrity, safeguarding fetuses from oxidative stress and inflammation, and ultimately improving fetal weight. Further pseudo-sterile and fecal microbiota transplantation trials confirmed that the protective effect of melatonin on fetal intrauterine growth under HS was partially dependent on gut microbiota. In LPS-challenged pregnant mice, melatonin administration mitigated placental barrier injury and abnormal angiogenesis via the inactivation of the TLR4/MAPK/VEGF signaling pathway, ultimately leading to enhanced nutrient transportation in the placenta and thereby improving the fetal weight.

CONCLUSION

Melatonin alleviates HS-induced low fetal weight during pregnancy via the gut-placenta-fetus axis, the first time highlighting the gut microbiota as a novel intervention target to mitigate the detrimental impact of global temperature rise on vulnerable populations.

A reference genome for the Harpy Eagle reveals steady demographic decline and chromosomal rearrangements in the origin of Accipitriformes

The Harpy Eagle (Harpia harpyja) is an iconic species that inhabits forested landscapes in Neotropical regions, with decreasing population trends mainly due to habitat loss, and currently classified as vulnerable. Here, we report on a chromosome-scale genome assembly for a female individual combining long reads, optical mapping, and chromatin conformation capture reads. The final assembly spans 1.35 Gb, with N50scaffold equal to 58.1 Mb and BUSCO completeness of 99.7%. We built the first extensive transposable element (TE) library for the Accipitridae to date and identified 7,228 intact TEs. We found a burst of an unknown TE ~ 13-22 million years ago (MYA), coincident with the split of the Harpy Eagle from other Harpiinae eagles. We also report a burst of solo-LTRs and CR1 retrotransposons ~ 31-33 MYA, overlapping with the split of the ancestor to all Harpiinae from other Accipitridae subfamilies. Comparative genomics with other Accipitridae, the closely related Cathartidae and Galloanserae revealed major chromosome-level rearrangements at the basal Accipitriformes genome, in contrast to a conserved ancient genome architecture for the latter two groups. A historical demography reconstruction showed a rapid decline in effective population size over the last 20,000 years. This reference genome serves as a crucial resource for future conservation efforts towards the Harpy Eagle.

Reassessment of French breeding bird population sizes using citizen science and accounting for species detectability

Higher efficiency in large-scale and long-term biodiversity monitoring can be obtained through the use of Essential Biodiversity Variables, among which species population sizes provide key data for conservation programs. Relevant estimations and assessment of actual population sizes are critical for species conservation, especially in the current context of global biodiversity erosion. However, knowledge on population size varies greatly, depending on species conservation status and ranges. While the most threatened or restricted-range species generally benefit from exhaustive counts and surveys, monitoring common and widespread species population size tends to be neglected or is simply more challenging to achieve. In such a context, citizen science (CS) is a powerful tool for the long-term monitoring of common species through the engagement of various volunteers, permitting data acquisition on the long term and over large spatial scales. Despite this substantially increased sampling effort, detectability issues imply that even common species may remain unnoticed at suitable sites. The use of structured CS schemes, including repeated visits, enables to model the detection process, permitting reliable inferences of population size estimates. Here, we relied on a large French structured CS scheme (EPOC-ODF) comprising 27,156 complete checklists over 3,873 sites collected during the 2021-2023 breeding seasons to estimate the population size of 63 common bird species using hierarchical distance sampling (HDS). These population size estimates were compared to the previous expert-based French breeding bird atlas estimations, which did not account for detectability issues. We found that population size estimates from the former French breeding bird atlas were lower than those estimated using HDS for 65% of species. Such a prevalence of lower estimations is likely due to more conservative estimates inferred from semi-quantitative expert-based assessments used for the previous atlas. We also found that species with long-range songs such as the Common Cuckoo (Cuculus canorus), Eurasian Hoopoe (Upupa epops) or the Eurasian Blackbird (Turdus merula) had, in contrast, higher estimated population sizes in the previous atlas than in our HDS models. Our study highlights the need to rely on sound statistical methodology to ensure reliable ecological inferences with adequate uncertainty estimation and advocates for a higher reliance on structured CS in support of long-term biodiversity monitoring.