Biology subjects

Kauzal, O.

Publications and source records attributed to Kauzal, O..

5 recordsLinked to original sources

bioRxiv2026

A songbird karyotype: cytogenetic confirmation of a migration-associated region rich in olfactory receptor genes.

The field of genetics of bird migration advances, driven by exponential refinements of sequencing and tracking technologies. In willow warblers (Phylloscopus trochilus), a complex repeat-rich region named MARB (Migration Associated Repeat Block) has recently been found to correlate with the routes taken by individual birds from Europe to their African wintering grounds. However, the genomic location of this region remains unknown. Here, we characterized MARB using a combination of approaches to understand how it evolved. We describe the region using long-read genome assemblies of two willow warbler subspecies (P. t. trochilus and P. t. acredula), two related species, the common chiffchaff (P. collybita) and the greenish warbler (P. trochiloides), and whole genome sequencing data from 76 willow warblers. Finally, we applied karyotyping and fluorescent in situ hybridization techniques on willow warbler spermatocytes to cytogenetically locate MARB. Due to the many repeats, we cannot order scaffolds in silico, but probe hybridization on the karyotype shows that MARB constitutes a single locus (~27.5 Mb) spanning most of the 11th largest chromosome in the willow warbler genome. Interestingly, the MARB regions of all species share several characteristics such as relatively high GC content (50%), a high density of specific repeat families and notably, more than 800 olfactory receptor sequences. Regions homologous to MARB may exist in several migrant bird genomes, though currently unassembled due to their complexity. Resolving these in species with similar migratory polymorphisms to willow warblers will be essential to determine whether MARB influences migratory behaviour across species.

genomics↗

bioRxiv2026

Stable but turbulent: the two faces of the germline-restricted chromosome of passerine birds

Germline-restricted chromosomes (GRCs) are essential, supernumerary chromosomes that undergo programmed elimination in somatic cells and are only retained in the germline. Despite their recurrent emergence across animals, their genetic composition, function and evolution remain poorly understood. Here we present the most complete and contiguous GRC assemblies, including one nearly telomere-to-telomere GRC assembly, from four closely related passerine bird species, providing an unprecedented insight into the GRCs composition and its evolution over short evolutionary timescales. We show that the passerine GRC is highly enriched in repetitive sequences, with massive, species-specific satellite expansions resulting in enormous differences in GRC size among species. Among mostly recently added sequences, we found only two ancestral genes dating back to the presumed GRC origin, offering clues to its essential function. Importantly, we demonstrate that the GRC undergoes extensive fine-scale within-chromosome rearrangements and copy number changes resulting in little collinearity between species. Our findings indicate that programmed DNA elimination has profoundly changed the GRCs evolution by altering the selection pressures and mutational mechanisms it is exposed to. This makes the GRC an extraordinarily dynamic element in an otherwise stable avian karyotype, retaining core functions while diversifying rapidly, with important implications for germline biology, adaptive evolution and speciation.

evolutionary biology↗

bioRxiv2026

Feather corticosterone is not associated with feather growth rate or quality across tropical and temperate passerines, but possibly linked to elevation

Moult is a challenging stage in the life of birds. Small passerines replace plumage, substantial part of their body mass, annually to preserve its vital functions. Surprisingly, most species tend to downregulate corticosterone, major mediator of energy metabolism and stress response, during this energetically demanding period. Experimental studies suggest corticosterone has detrimental effect on feather quality and, within species, slows feather growth rate (FGR), prolonging the period when plumage functions are compromised. However, how exactly corticosterone affects moult in natural populations or on macroecological scale is not yet fully understood. In this study, we analysed corticosterone deposited in tail feathers (fCORT), a corticosterone cumulative measure across multiple days relevant to the moult, on an unprecedented sample of 87 passerine species from Europe and Afrotropics. Our data showed moderate between and high within-species repeatability, strengthening the usefulness of fCORT as a tress record across multiple species. We did not find any association of fCORT with either FGR or fault bar occurrence. Unlike circulating corticosterone, fCORT did not differ between latitudes. However, our data suggested higher fCORT in high elevation tropical species. More research is needed to understand how birds regulate corticosterone during moult and how it affects moult in natural populations.

ecology↗

bioRxiv2025

Comparative analysis of plasma steroid hormone levels reveals lower concentrations in Afrotropical than Palearctic temperate zone passerines

Latitudinal changes in environmental conditions shape the evolution of avian life history traits: tropical bird species typically exhibiting prolonged breeding seasons, a slower pace of life, lower annual investment in reproduction and increased annual survival compared to their temperate counterparts. Major shifts in physiology, reflecting these differences, are expected to be mediated by endocrine regulation, yet comparative data on the sources of inter-specific variation in hormone concentrations remain sparse, especially outside the Nearctic-Neotropic system. We examined variation in two key steroid hormones, corticosterone and testosterone, across 100 passerine species from Europe and the Afrotropics, sampled using standardized field protocols. Baseline levels of both hormones were consistently lower in tropical species, as expected. While stress-induced corticosterone reactivity did not differ between latitudes, it declined with migration distance. Testosterone levels were higher in males than females and declined with migration distance. In tropical species, neither hormone was associated with elevation, another source of environmental variation, but both varied during the breeding cycle, challenging the view of tropical aseasonality. This study broadens the perspective on endocrine correlates of avian life history evolution by testing their generality in an understudied Afrotropical-Palearctic system. The results support the hypothesis that steroid hormone profiles co-evolve with latitude.

ecology↗

bioRxiv2025

Mechanisms and timing of programmed DNA elimination in songbirds

It is commonly assumed that multicellular organisms contain the same genetic information in all the cells of an individual. However, there is a growing list of species in which parts of the genome are removed from some cells of the organism through a process called programmed DNA elimination. In songbirds, an entire chromosome, called the germline-restricted chromosome (GRC), is lost from all somatic cells during early embryonic development. Nevertheless, the mechanisms, timing and consequences of this elimination remain largely unexplored. Here, we studied GRC elimination using two songbird species, the zebra finch (Taeniopygia guttata) and the Bengalese finch (Lonchura domestica), as model systems. We found that chromosome elimination occurs during the cleavage stage and is completed before egg laying and blastoderm formation. Elimination is associated with delayed attachment of the GRC to the mitotic spindle, changes in its histone modifications, and failure of chromatid separation in anaphase. The lagging GRC is then sequestered into a micronucleus with a defective envelope lacking the essential protein lamin B1, where the DNA is fragmented and degraded. Although the genetic basis of GRC elimination remains to be elucidated, our results suggest that changes of the GRC centromere together with epigenetic modifications of histones play a crucial role in GRC elimination from somatic cells. As the timing of elimination coincides with the germline/soma distinction, we propose that GRC elimination may play an important role in this crucial developmental process in songbirds.

genetics↗