Biology subjects

Mahr, K.

Publications and source records attributed to Mahr, K..

3 recordsLinked to original sources

bioRxiv2022

Biocompatible polymeric microparticles serve as novel and reliable vehicles for exogenous hormone manipulations in passerines

The administration of exogenous hormones emerged as an essential tool for field studies in endocrinology. However, working with wild animals remains challenging because under field conditions, not every available method meets the necessary requirements. Achieving a sustained elevation in hormone levels while simultaneously minimising handling time and invasiveness of the procedure is a difficult task in field endocrinology. Facing this challenge, we have investigated the suitability of biocompatible polymeric microparticles, a novel method for drug administration, as a tool to manipulate hormones in small songbirds. We chose the insulin-like growth factor -1 (IGF-1) as the target hormone because it receives great interest from the research community due to its important role in shaping life-history traits. Moreover, its short half-life and hydrophilic properties imply a major challenge in finding a suitable method to achieve a sustained, systemic long-term release. To study the release kinetics, we injected either IGF-1 loaded polylactic-co-glycolic acid (PLGA) microparticles or dispersion medium (control group) in the skin pocket of the interscapular region of captive bearded reedlings (Panurus biarmicus). We collected blood samples for 7 consecutive days plus an additional sampling period after two weeks and complemented these with an in vitro experiment. Our results show that in vitro, PLGA microparticles allowed a stable IGF-1 release for more than 15 days, following a burst release at the beginning of the measurement. In vivo, the initial burst was followed by a drop to still elevated levels in circulating IGF-1 until the effect vanished by 16 days post-treatment. This study is the first to describe PLGA-microparticles as a novel tool for exogenous hormone administration in a small passerine. We suggest that this method is highly suitable to achieve the systemic long-term release of hydrophilic hormones with a short half-life and reduces overall handling time, as it requires only one subcutaneous injection.

physiology↗

bioRxiv2020

"The stressed bird in the hand": Influence of sampling design on the physiological stress response in a free-living songbird

Despite the widely used application of standardized capture-handling protocols to collect blood and assess the physiological stress response, the effect of the actual sampling design (e.g. timing and the number of blood samples) often differs between studies, and the potential implications for the measured physiological endpoints remain understudied. We, therefore, experimentally tested the effects of repeated handling and multiple blood sampling on the stress response in wintering free-living great tits (Parus major). We modified a well-established sampling protocol of avian studies by adding either an additional blood sample or a "sham-manipulation" (i.e. handling associated with the blood sampling procedure without venepuncture), to disentangle the effects of handling stress and blood loss. We combined three different stress metrics along the endocrine-immune interface to investigate the acute short-term stress response: total corticosterone levels (CORT), the heterophil/lymphocyte ratio (H:L), and the Leukocyte Coping Capacity (LCC). Our study provided three key results: i) no relationship between CORT-levels, LCC and H:L, confirming that these three parameters represent different physiological endpoints within the stress response; ii) contrasting dynamics in response to stress by the measured parameters and iii) no difference in stress levels 30 minutes after capture due to one additional blood sampling or handling event. By optimising the sampling design, our results provide implications for animal welfare and planning experimental procedures on stress physiology in passerine species. Summary StatementWhen testing the short-term stress response in free living passerines, both - the scientist and the bird may be better off with a 15-minute stress protocol.

physiology↗

bioRxiv2019

Insulin-like growth factor 1 is related to the expression of plumage traits in a passerine species

Avian plumage colors and ornaments are ideal models to study the endocrine mechanisms linking sexually selected traits and individual parameters of quality and condition. The insulin-like growth factor 1 (IGF-1), an evolutionarily highly conserved peptide hormone, represents a link between body condition and the individual capacity to grow elaborated ornamental features, due to its regulatory role in cell proliferation and differentiation and its high sensitivity to the nutritional state of individuals. We investigated whether IGF-1 levels during molting affect the expression of multiple ornaments in a sexually dichromatic passerine species, the bearded reedling (Panurus biarmicus). We collected blood samples of males and females shortly before the molting completed and measured the size and colors of ornamental traits. Our results indicate that in males, structural plumage colors, the size of the melanin based ornament (beard) and tail length are independent traits. IGF-1 levels predict the length of the tail and the expression of male structural plumage components (UV-coloration), but not the melanin based ornament. In females plumage color and tail length were independent traits, which were not related to IGF-1 levels. Overall, our results indicate for the first time that IGF-1 could play a role in the development of secondary sexual characters in a passerine species.

evolutionary biology↗