Biology subjects

Stjernman, M.

Publications and source records attributed to Stjernman, M..

3 recordsLinked to original sources

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↗