Summary of:
Alcock, John (2005). Animal Behavior. Sunderland, Massachusetts: Sinauer Associates, Inc.
Summary of Chapter 12: “The Evolution of Parental Care” (404-435)
By Marielly Mitchell, Dove Graham, and Stefanie Hernandez
For Dr. Mills’ Psychology 351, Fall 2007

There are many bird species, both mother and father will work together to supply their children with food and resources necessary to survive. However, care of offspring is dependent upon risks to parents. There are two factors which will govern the behavior of the parents: nature of predator (whether it consumes nestlings or adults) and annual mortality rate for breeding adults. It would be expected that birds that have a low adult mortality rate, would not attempt to sacrifice their own survival to provide for their offspring. If the chances are high that they will get killed by a predator, they ought not risk their own lives, because they have the possibility of reproducing more in the future. In birds that have a high adult mortality rate, one would expect the opposite. These birds should be more concerned with the survival of their offspring. In these birds, there are fewer chances to reproduce in the future. While birds may assume an equivalent role in helping their offspring survive, there are a myriad of species and animals in which the mother assumes the primary role.
Females are much more likely to be maternal than males are to be paternal. One explanation to explain this evolutionary trait in mothers, is that the females have already devoted so much time and energy in making eggs. Therefore, there is an incentive for females to make sure that their large gametic investment is not wasted (408). This explains why mothers will continue to care for their offspring, after the eggs have been fertilized. There are times, however, when females will not invest more time in their offspring. When looking at the care females will give to their offspring, we must also look at the cost benefit ratio. If the cost of providing more care exceeds benefits gained from providing that care, it can be expected that females who do not offer more care will have more surviving offspring. So we can also expect, if the cost-benefit ratio for parental care is lower for females than males, females to provide care more often than males. Similarly, the benefits from offering parental care by the males are expected to be much less than the benefits gained from the females. Not only this, males are likely to encounter more risks and therefore suffer more costs from parental care than females. These explanations provide insight to explain how the differences in maternal and paternal care lie within a cost-benefit approach. After looking at the evolution of parental care from cost-benefit analyses, we can examine exceptions to the rule from an evolutionary perspective.
In many fish species, male only parental care is a widespread occurrence. There does not have to be an equal trade between parental care and mate attraction (410). Alcock uses the Stickleback and waterbugs to illustrate this example. In Sticklebacks females do not gain much from parenting. Caring for her brood would hinder her from growing rapidly. This can be particularly damaging because she is able to lay more eggs when her body is larger. Thus, male sticklebacks are the ones who offer parental care.
In waterbugs, male parental care is vital for offspring to survive. The female waterbug will lay her eggs on her mates back. He will then spend hours pumping his body up and down to ensure that water keeps moving over the eggs. This was likely to evolve when females were unable to find a sustainable environment for her eggs. By laying the eggs on the back of her mate, she was able to reproduce in environments which were not likely to provide a suitable habitat for her eggs.
It would be expected that parents would provide food, nourishment, and resources exclusively to their own offspring. An evolutionary approach would expect parents to be able to identify their own offspring when adoption of non-genetic offspring will create risks and costs to the parent. Sometimes, however, certain species will opt to adopt unrelated offspring. When some bird species have been neglected or do not receive enough food, they will sometimes beg for food. They are more likely to survive with an adoptive, non-related family, than if they stayed with their own family. When parents are unable to distinguish among their own and those who beg mercifully, they must feed all in their nest (there may be a chance that they are neglecting one of their own, if they choose to not to feed one that they are unsure of). Like this notion of adoption in the animal kingdom, there are several other baffling occurrences which are classified as Darwinian Puzzles.
There are some bird parents who will distribute food, nourishment, and resources evenly to all of their offspring. Even if they do invest in all of the brood, there will sometimes be skewed treatment, in which the offspring who beg more than their brothers or sisters, will receive more food. This can then translate into siblicide. In the great egret, siblings will fight for possession of the fish their parents bring to the nest. The dominant sibling may sometimes fight until the death, or push the weaker sibling out of the nest which enables them to consume most of the food provided by their parents. It must be noted, however, that parents do not gain from siblicide; this act of killing a brother or sister is more advantageous for the sibling who killed its brother or sister. Siblicide, which does not benefit the parent can result in parent-offspring conflict. It is important to note that parents do not benefit from this. The parent of a murderous offspring loses potential grand offspring, which is not compensated by an increase in offspring of the sibling who killed its brother or sister. Some actions can advance the fitness of an offspring while reducing the reproductive success of its parent, and vice versa.

Animal Kinship Panel Presentation
“Test Questions”

  1. Elephants have a social organization based on their memory and family member recognition. T/F
  2. All are ways an elephant is able to locate its mother in its first few days EXCEPT:
a) smell
b) touch
c) sight
d) sound
  1. Baby elephants suckle from their mother for up to five years. T/F
  2. Mother elephants invest more in:
a) Male offspring
b) Female offspring
c) Both evenly
d) Do not invest in offspring at all.
  1. Aggressive physical interactions between elephants is more prevalent in calves than in adult elephants. T/F
  2. Inclusive fitness within elephant groups is enhanced by:
a) High degree of related members
b) Altruistic behavior of the females on other calves
c) Both a & b
d) None of the above

Answer key: 1) T
2) c
3) F
4) a 5) F
6) c