The ‘terminal investment’ hypothesis proposes that individuals with low future survival prospects will gain from increasing investment in the current reproductive event even though it will reduce the chances of future reproduction even further. Such investments have previously been found to occur mainly during the late stages of the breeding event, i.e., encompassing a short period of elevated parental care close to offspring independence. Our aim was to study if a simulated mild bacterial infection can induce a terminal investment already at egg laying (i.e., at an early breeding stage). Therefore, we challenged female zebra finches (Taeniopygia guttata) prior to egg laying with a tetanus-toxoid vaccine mimicking a bacterial infection. Immune-challenged females increased the total clutch mass by 20 %, primarily through laying clutches that were 17 % larger than control females. Although the immune-challenged females produced more eggs, they kept the same investment strategy in relation to egg laying order as did control females. Our study implies that female birds can use a non-pathogenic immune challenge as an indication of declining survival prospects, and consequently increase clutch size. These investment decisions by immune-challenged mothers are in line with ‘terminal investment’ conducted at an early stage of breeding, challenging the traditional view that terminal investment should occur at late breeding stages.
all birds
This file includes all the females that got two injections and was offered a nesting opportunity.ID = Identity of the bird
Treatment = Injection with either phosphate buffered saline (PBS) or tetanus-toxoid vaccine
Tarsus length = Tarsus length (mm) of the female
Body mass = Body mass (g) of the female
Scaled index = Condition index of the female
exp birds
This file only includes those females that started to produce a clutch.
ID = Identity of the bird
Treatment = Injection with either phosphate buffered saline (PBS) or tetanus-toxoid vaccine
Exp = Control females (1); tetanus-injected females (2)
Body mass = Body mass (g) of the female
Days to first egg = The time period between first presented with a nest box and nesting material and the production of the first egg by the females.
Number of eggs = Clutch size
Mean egg mass = Mean egg mass (g) of the eggs in each clutch
Total egg mass = Total mass (g) of all eggs in a clutch
Mean yolk mass = Mean yolk mass (g) of the eggs in each clutch
Mean yolk proportion = Mean proportion of yolk in relation to egg mass in each clutch
Arcsin mean yolk prop. = Arcsine transformed mean yolk proportion
Diff body Mass = Initial body mass taken on the day of the second injection minus body mass after completion of egg laying.
Days btw bm measurements = Number of days between the two body mass measurements
Scaled index = Condition index of the female
Age = Age of the female; 1 = One year old; 2 = Two years old
Tetanus = Tetanus antibody concentrations (mODmin-1)
Log (tet) = The logarithm of tetanus antibody concentrations
eggs
This file contains all individual eggs
Female = Female identity
Treatment = Injection with either phosphate buffered saline (PBS) or tetanus-toxoid vaccine
Exp = Control females (1); tetanus-injected females (2)
Body mass = Body mass (g) of the female
Clutch size = Number of eggs in the clutch
Egg day = Number of days after the production of the first egg (egg day = 1) that each egg in the clutch were produced.
Egg order = The order in which the eggs were produced
Rel egg order = The egg order divided by clutch size to adjust egg order for variation in clutch
size.
Yolk mass = The yolk mass of each individual egg
Egg mass = The total mass of each individual egg
Albumen mass = The albumen mass of each individual egg
Yolk Proportion = The proportion of yolk in relation to egg mass of each individual egg
Yolk prop. arcsin = Arcsine transformed yolk proportions of each individual egg
Scaled index = Condition index of the female