(8) set

Animal reproduction and life histories

How do we define parental care?

any behavior, by a parent, that increases the fitness (survival and/or reproduction) of their offspring.

• Parental care is often costly, representing a trade-off between current offspring survival and future reproduction.

How does chick gape color affect feeding rates in swallows?

Chicks with gapes dyed red received more food.

Explain how cuckoo birds parasitize their hosts and how their eggs have evolved to mimic their hosts.

Cuckoos are brood parasites that lay their eggs in the nests of other bird species, leaving the host to incubate and raise the chick. This creates antagonistic coevolution: hosts evolve the ability to recognize and reject foreign eggs, while cuckoos evolve eggs that closely mimic the host’s in color, pattern, and size. As a result, different cuckoo populations specialize on particular host species, producing eggs that are harder for those hosts to detect and remove.

What is meant by extra-pair copulations in birds?

the behavior (mating outside the pair bond)

What is the difference between INTERsexual selection and INTRAsexual selection?

• INTRAsexual selection: competition between individuals of the same sex, often males

• INTERsexual selection: selection based on choices of mates, often females choosing males

How might male suicide in redback spiders actually benefit the male? Why would a male

try to escape under some conditions but not others?

Males that get eaten transfer more sperm

If a male has few mating opportunities (females are scarce, or too far apart to get from one to another)

• Little chance of future mating

• Little cost of dying

• Benefits of more sperm transfer or greater offspring nourishment outweigh costs of death

Explain Fisher’s runaway selection model

The rarer sex has higher fitness, so selection favors producing it, driving the population toward a 1:1 sex ratio based on individual success, not population benefit.

Explain Zahavi’s handicap model

Conspicuous male traits act as handicaps because they reduce survival. Males that can survive with these costs must be high quality. Low-quality males cannot afford them and would not survive if they had them, so females avoid those males. Therefore, these traits function as honest signals of quality.

What is the evidence for Zahavi’s handicap model (feel free to answer either in general terms or with respect to specific experiments)

A peacock’s tail is preferred by females. Males that can survive despite the handicap of the elaborate features are likely to have "good genes" overall.

Parasites dull male plumage in birds, so why do bird families with more parasites

have brighter males?

More parasites → stronger selection for honest signaling → brighter males evolve because only high-quality males can maintain bright plumage under parasite stress.

Why are equal male-female sex ratios common

The rarer sex has greater reproductive fitness, selection for more individuals to develop as the rare sex.

What is meant by senescence?

• is a (late in life) decline in an individual’s fertility and probability of survival – reducing an individual’s fitness. It should, in theory, be opposed by natural selection

• BUT senescence cannot be eliminated by natural selection because the influence of senescence genes expressed later in life are not subject to strong natural selection

How does the mutational accumulation hypothesis explain senescence?

deleterious mutations cannot be eliminated because they are less subject to natural selection the later they are expressed after an individual reaches maturity

What is antagonistic pleiotropy?

• The later in life that mutations exert their deleterious effects the less strongly natural selection can act against them

• Thus, the accumulation of deleterious mutations whose effects occur only late in life represent an evolutionary explanation for aging

How does the antagonistic pleiotropy hypothesis explain senescence?

• When the allele involves a tradeoff between reproduction early in life and survival late in life then its pleiotropic effects are antagonistic

• Even if there is weak selection against the allele later in life, this is outweighed by the selective advantage of the allele early in life

All things equal, in terms of reproductive fitness, does it make more sense to have an offspring this year or to wait and have one next year

this year, because you might die before next year

Why are 1:1 sex ratios common?

The rarer sex has a reproductive advantage, selecting for changes that lead to equal ratios

Give one reason that a population may differ from 1:1 sex ratios

If one sex is more costly to produce (larger egg, more food, etc.) then a female will produce less of that sex (Fisher 1930)

What evolved early in the human lineage?

bipedalism

Know some primary consequences of bipedalism and some secondary consequences of bipedalism.

• Immediate

  • Longer legs, shorter arms (not needed for tree-swinging)

• Secondary

  • Changes in hands (no longer needed for mobllity)

    • Opposable thumbs

    • Ulnar opposition (can touch pinkie and thumb)

What are the surprising changes that are observed in different domesticated animals? Why? Who else has exhibited this?

Know that many surprising changes are observed in different domesticated animals:

• reduced snout, reduced pigmentation, etc.

Know that this is thought to be due:

• to reduce adrenal gland activity, leading to reduced neural crest cell activity.

Know that:

• humans also exhibit some of these domestication-associated traits.

Know when the Paleolithic Revolution occurred and be able to explain why it is surprising that it occurred so late

occurred: ~50,000 years ago

surprised because: Humans already had modern brains and bodies long before this period

• Yet advanced behavior (art, complex tools, symbolic thinking, widespread innovation) appeared much later and relatively suddenly