PARENTAL BEHAVIOR
I. INTRODUCTION
A. Variability - parental behavior is extremely variable across the animal kingdom. At one end of the continuum, there may be extensive care without any contact with offspring (e.g., Mallee fowl) whereas at the other, there may be extensive interaction and contact with offspring (e.g., rhesus monkey). We start first with a definition, move on to a discussion of various models of parent-offspring interaction, and then review parent-offspring relations in mallee fowls and rhesus monkeys.
B. Definition
1. Functional Definition: any behavior that increases the survival probability of fertilized eggs or offspring that have left the mother's body
2. Operational Definition: includes such behaviors as (list them below)
II. MODELS There are a number of models that characterize possible relationships between parents and offspring. For the first three models, we will use the white albino laboratory rat as our example because much of the work on parent-offspring interaction comes from studies of laboratory rats.
A. Parental Provision Model (This model is the one that automatically comes to mind when we think about the interaction of rat mothers with offspring).
1. Traditional view that rat mothers pass vital resources and information to pups.
2. emphasizes a __________________________________________
3. example:
Rat mothers pass nutrients in milk to their pups. Some of these nutrients (immune factors) promote disease resistance.
B. Autoregulation Model (This model identifies some systems that may appear to be linked between rat mothers and pups but are, in fact, separate)
1. In this model, rat mothers and pups operate as two separate systems
2. Behavior may appear to require feedback between rat mothers and pups but that view is incorrect
3. Behavior is triggered by a common biological need but it is not dependent on feedback
4. Example - keeping pups warm
a. historical view was that mothers monitored the temperature of their pups1. if pups were cool, a mother crouched over them to warm them up
2. if pups were warm ____________________________
b. No matter how logical this seems, it is a "just so story" without testing. And indeed, it turns out to be wrong.
c. We can evaluate the hypothesis that mothers monitor pup temperature to determine when to crouch over them by testing the following predictions.
1. Prediction 1: If we manipulate the temperature of pups, rat mothers will spend more time with cool pups and less time with warm pups.
FINDING:
2. Prediction 2: Mothers will leave the nest after pups are warmed up, not when they are cool.
FINDING:
3. Prediction 3: Changes in maternal heat load will not affect time spent in the nest or crouching over the pups.
FINDING:
d. What general conclusion is drawn from these findings:
C. Symbiosis
1. Unlike the parental provision model, this model emphasizes a novel idea that resources can flow not only from mother to pups but also from pups to mothers.
2. The relationship between nursing and genital licking is an example of symbiosis
a. rat mothers lick the genitals of their pups.b. The old view was that this activity was mainly related to facilitating urination in young pups. Pups appear to be able to urinate on their own after the first few days of life.
c. However, Alberts noted that mothers continued to lick the genital region of their pups throughout much of postnatal development suggesting that there might be some other reason to explain this behavior.
c. Alberts further noted that mothers actually consumed the urine, and he hypothesized that rat mothers might be regaining some of the fluid resources lost in milk production.
d. In a series of experiments, Alberts tested the following predictions.
1. thirsty mothers should lick more than sated mothers
Findings:
2. Amount of genital licking and hence urine consumption should be correlated with milk production, both peaking in day 15.
Findings:
3. Thus, mothers reclaim about 67% _______________________
D. Conflict H ere we shift species because conflict between parents and offspring has been mainly studied in ungulates (sheep, goats etc.) and primates.
1. In many mammals, a conflict between mothers and offspring develops around the time of
____________
2. The process can be gradual or sudden and infants will often protest its occurrence.
3. Why is there a conflict between parents and offspring?
4. Trivers proposed an evolutionary model to explain this pattern. It involves an assessment of costs and benefits from both the mother's and infant's perspective. Trivers shows that the costs for mothers and infants are different and this difference produces the weaning conflict.
5. Mother's perspective
a. benefit of nursing the current offspring is _______________________
b. cost of nursing the current offspring is__________________________
c. each infant (her current and next year's infant) is of equal benefit to the mother. She shares 50% of her genes with both infants.
6. Infant's perspective
a. benefit of nursing_________________________b. cost of nursing is that it reduces the success of future offspring affecting this infant's inclusive fitness (he shares genes in common with brothers and sisters)
c.Thus, the infant gains from mother nursing it but also gains from the mother having additional infants that share genes in common. However the benefits are not equal. The infant is more invested in himself than his brothers or sisters (he only shares 50% of his genes with his siblings)
7. The conflict model from a Cost- Benefit perspective
a. Mothers have an equal interest in each offspring (sharing 50% of her genes with all offspring) so weaning occurs when the costs equal the benefits.
b. Infants are related to themselves by 100% but to their siblings by only 50%. They should persist in nursing until the costs exceed twice the benefits
c. The result is a period of conflict in which _____________________________
E. Conclusions (these models are not mutually exclusive and any or all may operate at different points during development)
III. VARIABILITY
A. Mallee Fowl Parental Behavior The mallee fowl is a large monogamous bird species that is indigenous to Australia; the male is more parental than the female, and its parental behavior consists only of maintaining an incubation chamber -an act which takes up 10 months of his life every year. After laying eggs, the female assists in maintaining the incubation chamber (see videoclip). Sadly, this bird is highly endangered due in part to several processes that include increased drought on the mallee plain, introduction of the fox as a predator, destruction of habitat by grazing sheep, and food competition from rabbits.
1. Building and maintaining an incubation chamber
a. The male begins in the late winter to create a fermentation chamber
b. details on the mound (draw a cross section of the mound below)
c. Egg laying
1. Females lay very large eggs one at a time
2. They are spaced _______________________________________
3. Clutches usually vary from ________________________________
4. Each egg takes about ____ days to hatch
5. Eggs are laid continuously through the spring and early and early fall.
What parental care is provided after hatching?
2. Incubation strategy
a. the objective was to maintain the temperature of the egg chamber at a relatively constant temperature of 33 degrees centigrade.
b. There were two heat sources
1._______________________________
2.________________________________
c. Because of changes in the strength of the heat sources over time, the mallee fowl compensates for these changes by varying its strategy from spring through early fall which is summarized in the table and described below
STRATEGY EARLY AM MIDDLE DAY EARLY PM SPRING OPEN OPEN SUMMER OPEN SAND COVER E. FALL OPEN LEAVE OPEN SAND COVER
1. Spring strategy - open the mound from 7-8 am and 3-5 pm
Why:
2. Summer strategy - opens the mound in the early am and increases the height of the sand cover in the middle of the day
Why: There is still some fermentation, and the eggs need to be cooled down in the morning. But the sun is also a major heat source and the eggs must be protected form overheating in the midday sun
3. Fall strategy - opens the chamber early and leaves it open through the middle of the day and then rebuilds the mound in the afternoon placing warm layers of sand over the chamber
Why:
4. What cues might the mallee fowl use to determine when to shift strategies?
a. mound temperature
b. passage of time
c. changes in daylength
d. other
5. Experiments with heating coils
a. Frith set up an experiment whereby the mallee fowl incorporated heating coils into the mounds. Frith assumed that the birds were monitoring mound temperature. If so, Frith expected the mallee fowl to use the spring strategy during all the seasons, because the heat is coming from the mound.
b. when the heating coils were added in the spring,
the mallee fowl:
c. when heating coils were added in the summer
the mallee fowl did not revert to its spring strategy; it used its summer strategy. However, it also tried to compensate by opening the mound longer in the am and piling the sand higher in the midday; thus the prediction was not confirmed
d. when the experiment was conducted in the fall,
the mallee fowl reverted to its spring strategy which was completely different than what it would do at this stage; thus the prediction was confirmed
e. Given the pattern of findings, the conclusion is that mallee fowls are monitoring some ratio of MOUND/AIR TEMPERATURE (see normal ratios below)
SEASON MOUND TEMP AIR TEMP
LATE SPRING High Low SUMMER
Midlevel High E. FALL Low Low E. FALL (with coil) High (because of coil) Low
The pattern (MOUND TEMP high and AIR TEMP low) found in the spring was recreated in the early fall by the heating coil thus suggesting that the bird must be monitoring both air and mound temperature.