The effects of experimental increase in insulin-like growth factor 1 on feather growth rate, moult intensity and feather quality in a passerine bird

Moulting is a crucial, yet often overlooked life-history stage in many animals, when they renew their integumental structures. This life-history stage is an energetically demanding somatic growth event that has particular importance in birds because feathers play a crucial role in flight, insulation and communication. Somatic growth processes are regulated by the evolutionarily conserved peptide hormone, insulin-like growth factor 1 (IGF-1). However, the role of IGF-1 in feather growth remains unknown. In this study, we captured 41 juvenile free-living bearded reedlings (Panurus biarmicus) that had started their first complete moult and brought them into captivity. Then we manipulated their circulating IGF-1 levels using poly-(lactid-co-glycolid acid) microparticles (microspheres) that provide a sustained release of IGF-1. The treatment increased IGF-1 levels but did not affect the feather growth rate. However, two weeks after the treatment, birds in the increased IGF-1 group were moulting more feathers simultaneously than the controls and were at a more advanced stage of moult. Birds with experimentally increased IGF-1 levels had better quality feathers (measured by a lower number of fault bars) than the controls. These results suggest that an increase in IGF-1 does not speed up feather growth, but may alter moult intensity by initiating the renewal of several feathers simultaneously. This may shorten the overall moulting time but may imply costs in terms of IGF-1 induced oxidative stress.

Spatial distribution of feather mites (Astigmata: Analgoidea) on the plumage of passerine birds from the territory of South Dobrudzha, Bulgaria

Feather mites (Astigmata: Pterolichoidea, Analgoidea) are permanent ectosymbionts of birds, found from all avian orders except Rheiformes (Stefan et al. 2015). The feather mites’ spatial distribution on the plumage depends on the morphology and structure of the feathers, aerodynamic and frictional forces, the life cycle and social behavior of the hosts, as well as environmental factors such as temperature and humidity (Dubinin 1951; Fernández-González et al. 2015). Depending on the location of the feather mites on the host’s body, a variety of morphological, physiological and behavioral adaptations are observed, which allow several feather mite species to coexist on the same bird (Dabert and Mironov 1999; Proctor 2003; Mestre et al. 2011). Studies dedicated to the spatial distribution of feather mites on the plumage of birds are relatively scarce. Such data is largely missing also for the territory of Bulgaria. Therefore, the aim of this paper is to present the results of the first specialized study of their spatial distribution on the plumage of passerines in Bulgaria. 379 birds belonging to 47 species of the order Passeriformes were examined in the period 2005–2007. As a result, the locations of 76,000 specimens (including both adults and nymphal stages) of feather mites of 54 species were determined. The distribution on the plumage of each species of bird was presented by generalized schemes. Feather mites were not found on the outermost primary feathers (P10), which are smaller than others primaries and do not offer enough resources. Feather mites located on the wing and tail feathers were mainly observed on the medial part of the feather, close to the rachis, and hence on the feather barbs. Feather mites preferred the wider parts of the primary feathers. On the secondary feathers, the mites were located predominantly in the middle third, on either side of the rachis. We examined if feather mites were symmetrically distributed on both wings using samples from those birds represented by numerous individuals (Passer montanus (L., 1758), Acrocephalus arundinaceus (L., 1758), Panurus biarmicus (L., 1758), Cyanistes caeruleus (L., 1758), Fringilla coelebs L., 1758). In this analysis, χ2-test confirmed no difference in the location of the feather mites on the feathers of both wings of the respective hosts and symmetry. Mites, such as Proctophyllodes pinnatus (Nitzsch, 1818) and Mesalgoides megnini (Oedemans, 1937) (on Chloris chloris (L., 1758)), Proctophyllodes stylifer (Buchholz, 1869) and Ptronyssoides parinus (Koch, 1841) (on Cyanistes caeruleus), Pterodectes rutilus Robin, 1868 and Scutulanyssus hirundicola Mironov, 1985 (on Hirundo rustica L., 1758), can coexist on the feathers of their respective hosts. Probably the different body size or trophology of these mite species reduced the competition between them. We found Trouessartia crucifera Gaud, 1957 and T. appendiculata (Berlese, 1886) on the secondary feathers of Hirundo rustica, but never together. The competition for resources between these two mite species is probably stronger. Feather mites respond to bird molting mainly by moving to adjacent feathers (Dubinin 1951). We monitored the spatial distribution of Proctohyllodes balati on the wing feathers during the molting of Panurus biarmicus.

Extremely low malaria prevalence in a wetland specialist passerine

Avian malaria (caused by Plasmodium spp.) and avian malaria-like infections (caused by Haemoproteus spp.) are widespread and can seriously affect the health of their bird hosts, especially of immunologically naïve individuals. Therefore, these parasites have long been in the focus of bird-parasite studies. However, the species richness and diversity of these protozoan species have only been revealed since the use of molecular techniques. Diversity and prevalence of these parasites among different bird species and even between populations of a species show a large variation. Here, we investigated prevalence of avian malaria and avian malaria-like parasites in two distant populations of a non-migratory wetland specialist passerine, the bearded reedling (Panurus biarmicus). While previous studies have shown that reed-dwelling bird species often carry various blood parasite lineages and the presence of the vectors transmitting Plasmodium and Haemoproteus species has been confirmed from our study sites, prevalence of these parasites was extremely low in our populations. This may either suggest that bearded reedlings may avoid or quickly clear these infections, or these parasites cause high mortality in this species. The remarkably low prevalence of infection in this species is consistent with earlier studies and makes bearded reedlings a possible model organism for investigating the genetic or behavioural adaptations of parasite resistance.

Exploring the mechanistic link between corticosterone and insulin-like growth factor-1 in a wild passerine bird

Background Physiological regulators of life history trade-offs need to be responsive to sudden changes of resource availability. When homeostasis is challenged by unpredictable stressors, vertebrates respond through a set of physiological reactions, which can promote organismal survival. Glucocorticoids have been traditionally recognized as one of the main regulators of the physiological stress response, but the role of an evolutionarily more conserved pathway, the hypothalamic-pituitary-somatotropic (HPS) axis producing insulin-like growth factor-1 (IGF-1) has received much less attention. Although IGF-1 is known to affect several life history traits, little is known about its role in the physiological stress response and it has never been studied directly in adult wild animals. Methods In this study, we combined field observations with a controlled experiment to investigate how circulating levels of IGF-1 change in response to stress and whether this change is due to concomitant change in glucocorticoids in a free-living songbird, the bearded reedling Panurus biarmicus. We used a standard capture-restraint protocol in field observation, in which we took first and second (stress induced: 15 minutes later) samples. In a follow-up experiment, we used a minimally invasive oral corticosterone manipulation. Results We showed that corticosterone levels significantly increased while IGF-1 levels significantly decreased during capture and handling stress. However, change in corticosterone levels were not related to change in IGF-1 levels. We found that experimentally elevated corticosterone levels did not affect IGF-1 levels. Discussion Our results are the first to highlight that circulating IGF-1 levels are responsive to stress independently from glucocorticoids and suggest that the HPS axis is an autonomous physiological pathway that may play an important role as regulator of life-history decisions.

Exploring the mechanistic link between corticosterone and insulinlike growth factor-1 in a wild passerine bird

BackgroundPhysiological regulators of life history trade-offs need to be responsive to sudden changes of resource availability. When homeostasis is challenged by unpredictable stressors, vertebrates respond through a set of physiological reactions, which can promote organismal survival. Glucocorticoids have been traditionally recognized as one of the main regulators of the physiological stress response, but the role of an evolutionarily more conserved pathway, the hypothalamic-pituitary-somatotropic (HPS) axis producing insulin-like growth factor-1 (IGF-1) has received much less attention. Although IGF-1 is known to affect several life history traits, little is known about its role in the physiological stress response and it has never been studied directly in adult wild animals.MethodsIn this study, we combined field observations with a controlled experiment to investigate how circulating levels of IGF-1 change in response to stress and whether this change is due to concomitant change in glucocorticoids in a free-living songbird, the bearded reedling Panurus biarmicus. We used a standard capture-restraint protocol in field observation, in which we took first and second (stress induced: 15 minutes later) samples. In a follow-up experiment, we used a minimally invasive oral corticosterone manipulation.ResultsWe showed that corticosterone levels significantly increased while IGF-1 levels significantly decreased during capture and handling stress. However, change in corticosterone levels were not related to change in IGF-1 levels. We found that experimentally elevated corticosterone levels did not affect IGF-1 levels.DiscussionOur results are the first to highlight that circulating IGF-1 levels are responsive to stress independently from glucocorticoids and suggest that the HPS axis is an autonomous physiological pathway that may play an important role as regulator of life-history decisions.