Biology subjects

Nilsson, J.-A.

Publications and source records attributed to Nilsson, J.-A..

7 recordsLinked to original sources

bioRxiv2026

Repeatable individual variation in body temperature is associated with cold tolerance and exercise-induced hyperthermia in zebra finches

In endotherms, body temperature is regulated by balancing the rates of metabolic heat production and dissipation. Birds and mammals maintain high and relatively constant body temperatures, but there is growing evidence that body temperature and heterothermy vary considerably between individuals of a population. Based on the interdependence of metabolic rate and body temperature, variation in body temperature could be expected to be related to metabolic performance. In this study, we aimed to determine if body temperature is a variable and repeatable trait in captive zebra finches (Taeniopygia guttata) and if body temperature could be related to different metrics of performance. We measured body temperature for 14 days in in caged male zebra finches to assess within- and among-individual variation and repeatability, as well as during measurements of three metabolic traits; basal (BMR), summit cold-induced (Msum) and maximum exercise-induced (MMR) metabolic rate. Median Tb (R = 0.48), and peak Tb (R = 0.53) body temperature were repeatable and positively correlated, suggesting that the birds show consistent differences in body temperature. We found that birds with higher daytime body temperatures showed higher thermoregulatory performance in a cold challenge and had higher body temperature during forced exercise. However, daytime body temperature was not related to MMR or BMR. Our study is one of few that have measured the repeatability of body temperature in birds. Our results show that individuals may have distinct body temperature phenotypes which could be related to metabolic and thermoregulatory performance. However, additional research is needed to disentangle the interrelated effects of metabolic capacity, body temperature, and heat dissipation on performance and how this might change with thermal conditions and activity levels.

physiology↗

bioRxiv2026

Air temperature limits aerobic capacity and scope in active birds

Thermal tolerance limits are an important determinant of species vulnerability to climate change. However, most of our knowledge of thermal tolerance pertains to resting animals, which could yield unrealistic predictions about how air temperature will affect animals when they are active. To gain a better understanding of thermoregulatory contstraints in active birds, we induced zebra finches in captivity to exercise continuously in air temperatures ranging from cool to warm (12- 36 C) while we simultaneously measured their metabolic rate, body temperature, and evaporative water loss. During activity, birds overheated in air temperatures well below their resting thermal tolerance limit, and aerobic scope was reduced by 22% at the warmest temperature. Although zebra finches showed a 8-fold increase in evaporative water loss during exercise in the warmest temperature, this was not sufficiently high to compensate for the substantial increase in heat produced during activity. This could explain why birds became hyperthermic and showed reductions in metabolic rate in the higher air temperatures. Thus, our results provide a mechanistic explanation for how heat could limit aerobic capacity and scope in active birds. These findings support growing evidence that increased air temperature can lead to sub-lethal fitness costs in free-living birds.

ecology↗

bioRxiv2026

Spatiotemporal and demographic effects on avian malaria prevalence in blue tits

While the ubiquity of parasites is well understood, the extent to which host demographic factors shape parasite prevalence patterns merits further investigation. Using 15 years of breeding data from blue tits (Cyanistes caeruleus) in southern Sweden, spanning a 26-year timeframe, we assessed the roles of host age, sex, and field site on the odds of infection with three avian malaria parasite genera: Haemoproteus, Plasmodium, and Leucocytozoon. Further, we also evaluated the effects of these demographics on the odds of triple-genus coinfections. We found first-year breeders have fewer infections with Haemoproteus and Plasmodium, and fewer triple infections compared to older age classes, suggesting that birds are accumulating infections over time. Leucocytozoon infections are more prevalent in males than in females, and this may be due to sex-specific differences in physiology. The prevalence of malaria parasites and their coinfections also vary between the three sampling sites, indicative of an effect of host breeding habitat, even at a relatively small spatial scale (neighboring sites were separated by <5km). Across all three field sites, prevalence is overall significantly increasing over time. For Haemoproteus, this increase is more pronounced in older birds compared to younger birds. Such temporal changes in age-related infection patterns would not have been apparent without long-term data thus highlighting the importance of long-term studies for informing our understanding of host demographic effects on parasite prevalence.

molecular biology↗

bioRxiv2025

Spatial and temporal variation in biting midge (Culicoides) abundance in active nest boxes

Due to recent and projected global warming, the fitness landscape of organisms can be predicted to change. One of the consequences of climate change is an increased risk of being infected by pathogens. Many of these pathogens are relying on vectors for transmission. As most vectors are ectotherms, with a tight relationship to ambient temperature for e.g. activity, temperature-dependent variation in vector density may be the mechanism explaining increasing parasitemia. In this study, we estimate the abundance of biting midges (Culicoides spp), a vector of Haemoproteus parasites, by placing sticky traps within nest boxes of breeding blue tits (Cyanistes caeruleus). We found that average minimum temperatures positively affect the abundance of midges. Thus, with recent and predicted higher temperatures, the encounter rate between hosts and vectors will increase with a resulting higher parasitemia. Marked differences in spring temperatures will also result in cohort effects, with whole generations of first-year birds being more or less infected by the parasites with yearly effects on recruitment rate and total host densities. Furthermore, we found pronounced temporal and spatial variation within years. This will put increasing emphasis on breeding parents to use cues indicating high vector abundances when determining breeding timing and choice of breeding habitat.

ecology↗

bioRxiv2025

Climate-driven increase in transmission of wildlife malaria parasite over the last quarter century

Climate warming is expected to influence the prevalence of vector-transmitted parasites. Understanding the extent to which this is ongoing, or has already occurred, requires empirical data from populations monitored over long periods of time, but these studies are sparse. Further, vector-disease research involving human health is often influenced by disease control efforts that supersede natural trends. By screening for malaria parasite infections in a wildlife population of blue tits (Cyanistes caeruleus) in Northern Europe, over a 26-year period, we tested whether observed prevalence and transmission changes were climate-driven and show that all three malaria parasite genera have increased significantly in their prevalence and transmission over time. The most common parasite in the study, Haemoproteus majoris, increased in prevalence from 47% (1996) to 92% (2021), and this is a direct consequence of warmer temperatures elevating transmission. Climate window analyses reveal that elevated temperatures between May 9th and June 24th, a time period that overlaps with the host nestling period, are strongly positively correlated with H. majoris transmission in one-year-old birds. Warmer climate during this narrow timeframe has a demonstrable impact on parasite transmission, and this permeates into the overall prevalence in the host population. We now have empirical support that climate warming can drive a rapid rise in vector-transmitted parasites, and this has implications for other host-parasite systems. Given that we now know the exact time of year when climate warming is most influential on a common vector-transmitted parasite in this system, it is possible to investigate the evolutionary and environmental mechanisms that underly how these infections ultimately manifest. While more challenging to measure, similar implications of climate warming on human vector-disease systems might be occurring.

ecology↗

bioRxiv2023

Using metabolic data to uncover the ontogeny of endothermy in an altricial bird

Altricial songbirds transform themselves from naked poikilotherms to fully-feathered endothermic homeotherms over a matter of weeks from hatching to fledging. The timing of development of endothermy has been studied in altricial birds for over half a century. However, the potential determinants, constraints, and flexibility of the onset of endothermy are not yet fully understood. We experimentally investigated whether brood size influences the ontogeny of endothermic heat production in 4-8 day-old nestling blue tits (Cyanistes caeruleus) in southern Sweden. We found that both nestlings capacity to produce heat and the proportion of nestlings exhibiting a metabolic response to a cooling challenge (15 {degrees}C for 15 min) increased with age. However, we did not find an effect of brood size on the ontogeny of endothermy and this may be explained by the lack of differences in body mass of nestlings in enlarged and reduced broods in our study. The metabolic response in all age groups was brief and not sufficient to sustain a stable body temperature. Our study shows that the development and use of endothermy is present at an early age in nestling blue tits, but further study is needed to disentangle the factors contributing to individual variation in the timing of these developments. This will serve to improve our understanding of a developmental milestone of cold tolerance in birds in the temperate zone that not only face warmer average temperatures, but also increasingly frequent cold snaps and extreme weather. Summary StatementThis study serves to improve our understanding of the ontogeny of endothermy in altricial birds while examining the potential role of brood size in the timing thereof.

ecology↗

bioRxiv2020

Bird populations most exposed to climate change are less responsive to climatic variation

The phenology of many species shows strong sensitivity to climate change; however, with few large scale intra-specific studies it is unclear how such sensitivity varies over a species range. We document large intra-specific variation in phenological sensitivity to temperature using laying date information from 67 populations of two European songbirds covering a large part of their breeding range. Populations inhabiting deciduous habitats showed stronger phenological sensitivity compared with those in evergreen and mixed habitats. Strikingly, however, the lowest sensitivity was seen in populations that had experienced the greatest change in climate. Therefore, we predict that the strongest phenological advancement will not occur in those populations with the highest sensitivity. Our results show that to effectively assess the impact of climate change on phenology across a species range it will be necessary to account for intra-specific variation in phenological sensitivity, climate change exposure, and the ecological characteristics of a population.

ecology↗