Haemosporidian infections in jackdaw nestlings - are all siblings the same?

Abstract

Avian blood parasites are common vector-transmitted protozoan parasites in wild birds and can cause acute and chronic infections in individuals at different life stages. These infections can have important effects on life-history trade-offs for the birds. In many avian species, infections with blood parasites happen during the nestling period, when dipteran biting insects have easy access to their unfeathered skin. However, little is known about how these infections are distributed within and between broods, how the vectors choose which host individuals to bite, and with respect to nestlings within a brood, which nestlings are most likely to become infected with haemosporidian parasites.

To answer these questions, I examined the presence of infection with three blood parasite genera (Plasmodium, Leucocytozoon and Haemoproteus) in a nestbox population of jackdaw (Corvus monedula) nestlings with four years of data. I also carried out a small-scale vector trapping study. I revealed that these nestlings had an average parasite prevalence of 33.9%, which varied by year, and Leucocytozoon was the most prevalent genus. At the population level, no links were found between infection status and the morphometric measurements, body mass, wing length or tarsus length, nor with sex or hatching date. However, at the brood level females with a shorter tarsus than their female siblings were more likely to be infected. There was also a significant positive correlation between brood size and infection prevalence at the brood level, but not at the individual level, and more broods tended to be partially infected than fully infected or uninfected. These findings reveal some interesting insights into complex host-parasite relationships, but infection prevalence cannot be explained by many of the host life-history and individual traits tested here. I suggest that further studies are needed into local environmental factors and host genetics that may have a role in infection patterns.

Popular Abstract

Parasites are organisms that live in or on another species (known as the host) and gain benefits from them. They can cause health problems in the host. Many parasites need the help of an intermediate species to transport them into the hosts. A common term for an intermediate species that transports a parasite between hosts is a vector, for example mosquitos carrying human malaria. Some individuals in a population can be more prone to getting infected with certain parasites than others, and it is interesting to try to understand what drives these differences as it can tell us important things about how diseases spread and how species evolve. Could it be that body size makes a difference? Or how many siblings you live with? And are all siblings in a family infected or only some of them?

In this study, I set out to answer these questions using the young of a bird species, the European Jackdaw, and a parasite that infects their blood, similar to malaria. These types of microscopic parasites are called avian malaria and are categorised as blood parasites. The parasites are spread between birds by three types of flying insect – biting midges, mosquitos, and black flies – which are the vectors. The parasites enter a bird’s body when the vector bites to take a blood meal.

This host-parasite system has been widely studied, but much less so in young birds while they are still in the nests. These young birds are known as nestlings. To find out which nestlings were infected with the blood parasites, we collected blood samples from 374 jackdaw nestlings over four years. The nestlings were 29 days old when the blood samples were taken. At this age, they live in nest boxes together with their siblings, and their parents bring food through an opening in the box, where flying vectors can also enter the box. At the same time as taking blood samples, we took three measurements of each nestling - their weight, length of the wing, and length of the tarsus, which is the lower part of the leg. We also recorded how many nestlings were in each family. Later, in the lab, I used molecular tools to check the blood samples to see which nestlings were infected with blood parasites, and which were not.

Using this information, I checked if there were any links between whether a nestling was infected with blood parasites and the nestling’s weight, wing length, tarsus length, number of siblings or gender. I did not find any links between these factors. This means that body size, number of nestlings in a family, and whether a nestling is male or female, does not seem to affect their chance of being infected with these blood parasites. However, it was interesting to find out that roughly a third of the nestlings were infected with blood parasites overall, and around half of all families had at least one infected nestling. In a small number of the families (10%), all siblings were infected, but in roughly half of the families, there was a mix of infected and non-infected siblings. The number of infected nestlings was much lower in one of the years I studied, which was actually a colder and windier spring than in the other years, suggesting that weather conditions could play a part since we already know the vectors are strongly affected by the weather. Although I did not find any links between parasite infection and body size, number of siblings or gender, I believe there may be other reasons why some nestlings get infected while others don’t, which could be studied in the future to find answers. For example, nestling genetics and immune function, and local weather conditions.

• author: George, Anna
• supervisor: Arne Hegemann; Tamara Emmenegger
• organization: Degree Projects in Biology
• course: BIOM02 20222
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9154566
• date added to LUP: 2024-05-27 13:46:32
• date last changed: 2024-05-27 13:46:32