Acute but not chronic maternal infections trigger terminal investment into current reproduction
(2025) BION02 20241Degree Projects in Biology
- Abstract
- Life-history theory predicts a trade-off between immune defence and reproduction. If an individual needs to fight an infection during the breeding season, they may reduce their current reproductive effort and invest more resources into an immune response. Alternatively, they may invest their resources into increasing current reproductive effort at the expense of immune defence, which could reduce the probability of survival. The latter strategy is called the terminal investment hypothesis and it proposes that the individual interprets some kind of cue signalling a shortening of its lifespan and hence increases its current reproductive effort. However, little is known about the threshold that this cue needs to reach before terminal... (More)
- Life-history theory predicts a trade-off between immune defence and reproduction. If an individual needs to fight an infection during the breeding season, they may reduce their current reproductive effort and invest more resources into an immune response. Alternatively, they may invest their resources into increasing current reproductive effort at the expense of immune defence, which could reduce the probability of survival. The latter strategy is called the terminal investment hypothesis and it proposes that the individual interprets some kind of cue signalling a shortening of its lifespan and hence increases its current reproductive effort. However, little is known about the threshold that this cue needs to reach before terminal investment is triggered, e.g. the intensity of an infection. As part of a long-running study, breeding great reed warblers were screened for chronic haemosporidian infections while in a separate experiment, female jackdaws were injected with lipopolysaccharide (LPS) to simulate an acute bacterial infection. There was no difference in nestling condition (body mass, Hp1, haemoglobin concentration) between great reed warbler nestlings with infected and uninfected mothers. Jackdaw nestlings with LPS-injected mothers showed larger body mass increases than controls over the first five days after the injections but showed no difference in immunocompetence before fledging. These results demonstrate that a less virulent infection may have no observable effect on an individual's reproductive effort in a single breeding season, suggesting that a chronic haemosporidian infection may not carry a significant resource cost. On the other hand, the increases in growth experienced by the nestlings of LPS-injected jackdaws suggests that the (simulated) acute infection reached the threshold for terminal investment, although it is unclear how these growth increases were achieved. (Less)
- Popular Abstract
- Birds with more severe infections invest more into current reproduction
A study on the effects of acute and chronic infections in female birds on their offspring
We are all familiar with the idea of budgeting, the more you spend on X the less you can spend on Y. A bird’s life is marked by events that require this kind of budgeting; migration, moult, and reproduction are all costly from a resource perspective. Another costly process is the immune response. So, for a bird in the breeding season that fights an infection, if more resources are invested into the immune response, less are available for breeding. Sometimes, if the bird anticipates that they may not survive the infection, it becomes beneficial to invest more into breeding and... (More) - Birds with more severe infections invest more into current reproduction
A study on the effects of acute and chronic infections in female birds on their offspring
We are all familiar with the idea of budgeting, the more you spend on X the less you can spend on Y. A bird’s life is marked by events that require this kind of budgeting; migration, moult, and reproduction are all costly from a resource perspective. Another costly process is the immune response. So, for a bird in the breeding season that fights an infection, if more resources are invested into the immune response, less are available for breeding. Sometimes, if the bird anticipates that they may not survive the infection, it becomes beneficial to invest more into breeding and not fight the infection so much. This is called “terminal investment”. However, not all infections have the same effect; with a cold sore you can go about your daily business, but a terminal illness completely changes your life. In the same way, birds can face infections of varying severity. How will infections of different severity affect a breeding bird’s investment into reproduction?
To answer this question, I combined data from two species, the jackdaw (Corvus monedula) and the great reed warbler (Acrocephalus arundinaceus). Both of these species can breed beyond 8 years old, which is very long for a small bird. With this kind of reproductive life, the choice of whether to fight an infection and prioritise future reproduction or undergo terminal investment can become relevant. The jackdaw data came from a nestbox colony where breeding females were given an injection to simulate an acute bacterial infection. I collected data for the great reed warbler in Kvismaren, and later I analysed blood samples from breeding females to check if they had a chronic haemosporidian (blood parasite) infection. Nestling condition was assessed through traits linked to survival, body size (both species), immune function (jackdaw), and haemoglobin concentration (great reed warbler). I predicted that the jackdaw mothers would undergo terminal investment and have nestlings that were in better condition than the control mothers. I also predicted that the chronic infection would have such a low cost that there would be no difference between the nestlings of infected and uninfected mothers.
As I predicted, the jackdaw nestlings whose mothers received the injection had a higher body mass and a higher body mass index (a measure of mass in relation to size) five days after the injections were administered. There was an unexpected result; there was no difference in immune function between the two groups. This may have been due to the immune data being collected 16 days after the injections, by which point the differences in body size described above were not present. It could also be the case that immune development is a high priority for the jackdaw, which has been proposed in previous studies. The effects of the chronic infection followed my predictions, in that there was no difference between the great reed warbler nestlings of uninfected and infected mothers.
All in all, this study highlights that the form of infection is key in determining how a long-lived bird responds to infection while breeding. It seems that a chronic haemosporidian infection does not carry enough costs to cause an issue for resource allocation, while a simulated acute infection is interpreted as being severe enough to trigger terminal investment. I hypothesise that there is a “severity threshold” beyond which terminal investment is triggered, with an infection that reaches this threshold causing a bird to adjust its resource budget and invest heavily in reproduction.
Master’s Degree Project in Biology 45 credits 2025
Department of Biology, Lund University
Advisors: Dennis Hasselquist, Arne Hegemann (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9212846
- author
- Holdcroft, John
- supervisor
- organization
- course
- BION02 20241
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9212846
- date added to LUP
- 2025-09-19 11:03:11
- date last changed
- 2025-09-19 11:03:11
@misc{9212846,
abstract = {{Life-history theory predicts a trade-off between immune defence and reproduction. If an individual needs to fight an infection during the breeding season, they may reduce their current reproductive effort and invest more resources into an immune response. Alternatively, they may invest their resources into increasing current reproductive effort at the expense of immune defence, which could reduce the probability of survival. The latter strategy is called the terminal investment hypothesis and it proposes that the individual interprets some kind of cue signalling a shortening of its lifespan and hence increases its current reproductive effort. However, little is known about the threshold that this cue needs to reach before terminal investment is triggered, e.g. the intensity of an infection. As part of a long-running study, breeding great reed warblers were screened for chronic haemosporidian infections while in a separate experiment, female jackdaws were injected with lipopolysaccharide (LPS) to simulate an acute bacterial infection. There was no difference in nestling condition (body mass, Hp1, haemoglobin concentration) between great reed warbler nestlings with infected and uninfected mothers. Jackdaw nestlings with LPS-injected mothers showed larger body mass increases than controls over the first five days after the injections but showed no difference in immunocompetence before fledging. These results demonstrate that a less virulent infection may have no observable effect on an individual's reproductive effort in a single breeding season, suggesting that a chronic haemosporidian infection may not carry a significant resource cost. On the other hand, the increases in growth experienced by the nestlings of LPS-injected jackdaws suggests that the (simulated) acute infection reached the threshold for terminal investment, although it is unclear how these growth increases were achieved.}},
author = {{Holdcroft, John}},
language = {{eng}},
note = {{Student Paper}},
title = {{Acute but not chronic maternal infections trigger terminal investment into current reproduction}},
year = {{2025}},
}