Biology subjects

Horak, K.

Publications and source records attributed to Horak, K..

3 recordsLinked to original sources

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↗

bioRxiv2023

Biodistribution Analysis of Peptide-Coated Magnetic Iron Nanoparticles: A Simple and Quantitative Method

Biodistribution is the tracking of compounds or molecules of interest in the subject which is integral to understanding their anticipated efficacy and safety. Nanoparticles are highly desirable delivery systems which have the ability to deliver higher nucleic acid and drug payloads and they have enhanced tumor permeability due to their unique properties such as high surface area to volume ratio. Studying the biodistribution of nanoparticles is crucial to understand their effectiveness and safety in vivo, facilitate a more application driven approach for nanoparticle development which will lead to their successful translation into clinical use. In this study, we present a relatively simple method to determine the biodistribution of magnetic iron nanoparticles in mice. Branched Amphiphilic Peptide coated Magnetic Nanobeads BAPc-MNBs like their counterpart i.e., Branched Amphiphilic Peptide capsules (BAPCs) with a hollow water-filled core, are readily taken up by cells in vitro and have widespread application as a nanodelivery systems. We evaluated the BAPc-MNBs tissue distribution in wildtype mice injected intravenously (i.v.), intraperitoneally (i.p.) or orally gavaged to understand the biological interactions of the peptide nanoparticles and to further the development of branched amphiphilic peptides-based nanoparticles. BAPc-MNBs were distributed widely to various organs when injected i.v. and were eliminated from the system via the intestines in feces. The spleen was found to accumulate the highest amount of BAPc-MNBs in mice administered the NPs i.v. and i.p. while they were not absorbed into the system via oral gavage. This study not only presents a relatively simple quantification method to determine in vivo biodistribution of magnetic iron nanoparticles that can be widely applied but also demonstrates the potential of Branched Amphiphilic Peptides in the form of BAPCs or BAPc-MNBs as a delivery system.

biochemistry↗