Biolo1100 Chapter 9 Evolution and Behavior
  1. Animal behavior   is defined by response to stimuli   in the environment.
    • Animal behavior is a response to a stimulus in its environment.

      • What is the stimulus for eating ice cream, even when you are not hungry?
        • The taste of sweet and fatty foods.

     
  2. An innate   (instinctive) behavior is inherited through genes.
    • A fixed action pattern (FAP) is a behavior that shows no variation between individuals.

      This type of behavior is innate (instinctive) and is genetically determined.

      An egg outside the nest serves as a sign stimulus that triggers an FAP for this goose: roll the egg back into the nest with her bill.

      • Is there an evolutionary explanation for such innate behavior?
        • Care and protection of eggs increases reproductive success.

      Quiz

     
  3. Many behaviors are learned   and can be altered based on previous experiences.
    • Prepared learning is a behavior that is learned easily: the genetic background has prepared an individual to acquire that behavior.

      Monkeys are not born with a fear of snakes, but easily acquire that fear by observing fear to snakes in other monkeys.

      • Is there an evolutionary explanation for learning to fear snakes?
        • Snakes can kill monkeys; such fears may provide reproductive fitness.

      Quiz

     
  4. Some animals exhibit altruistic   behavior due to kin   selection.
    • Altruism is selfless behavior: an animal sacrifices its own welfare for others.

      This Australian social spider lets her spiderlings eat her alive.

      This altruistic behavior is not explained if she were selfish and concerned with her own survival.

      Evolution explains it if this leads to better reproductive success: leaving more offspring.

      • Are you selfless?
        • Sometimes? You are likely to be altruistic toward close relatives, and most altruistic toward offspring.

      Quiz


    • Kin selection

      Belding's ground squirrels live underground in colonies where adult females are closely related (kin).

      A squirrel may give a loud call to alarm its nest mates when it sees a predator.

      Making alarm calls is dangerous: about half the time the caller is killed by the predator, but this may save its kin.

      Close relatives share many genes, so kin selection may explain such altruistic behavior:

      • Self-sacrifice enhances the reproductive success of some of her genes.

      ground squirrel alarm call

     
  5. Differential reproductive   investment between the sexes often leads to different mate   selection behaviors.
    • Intrasexual Selection

      Competition within the same sex for the opposite sex is intrasexual selection.

      Often this competition occurs within males.

      • A male's reproductive success increases with each mating.

      • Males have an incentive to mate with as many females as possible.

      Females have less reason to mate multiple times: her egg output is unaffected by how many times she mates.

      Mate guarding can minimize paternity uncertainty.


    • The amount of resources an individual commits to produce offspring is its reproductive investment.

      There are big differences in how much males and females invest in reproductive investment.

      Females produce larger, fewer gametes, while males produce smaller, more numerous gametes.

      A female mammal has much more invested in reproduction than males: long gestation and nursing of young.


    • Mate guarding can protect a male's reproductive investment.

      Some examples:

      • prolonged mating in some frogs.

      • holding the female while she lays eggs

      • self castration in the black widow spider

      Quiz


    • Intersexual Selection

      Females usually choose their mates; this is intersexual selection.

      • Elaborate courtship rituals among the Western Grebe ensure his commitment.

      • Marmot males demonstrate reproductive fitness by controlling resources.

      • A male may bring an item of value - a "nuptial gift" - as a sign of his reproductive fitness.

      • Fancy and bright plumage demonstrates a male's fitness; females are usually less colorful.

      Exceptions occur when the male has a heavy reproductive investment.

      Quiz


    • Intersexual selection is reversed among katydids.

      In these species the male's nuptial gift is a nutritious spermatophore for the female to eat.

      • It can represent up to 1/10 of her lifetime calorie intake.

      With such heavy reproductive investment, the males are picky about females.

      video

     
  6. Sexual reproduction occurs in a variety of mating systems   .
    • Mating systems may be a mix of the following.

      • Monogamy: one male mates with one female; many birds bond for life.
        The sexes tend to be monomorphic.

      • Polygamy can be subdivided into

        • Polygyny: one male with many females: an alpha elephant seal controls a harem of many females.
        • Polyandry: one female with many males: a honeybee hive has one queen who mates with many males.
        The sexes tend to be dimorphic.

      • Promiscuity: many male with many females: a chimpanzee may mate with several members of the opposite sex, and vice versa.

      • What other system can you think of?
        • Self-fertilization: many plants are hermaphrodites and can self-fertilize; but hermaphrodite animals such as slugs still need to find a mate.

      Quiz


    • Albatross Species that are monogamous usually exhibit sexual monomorphism: the sexes look similar.

      Reproductive behavior is usually:

      • both sexes care for young.
      • both sexes equally choosy about the opposite sex.

      Many birds are monomorphic.

      Quiz


    • Species that are polygamous often exhibit sexual dimorphism: the sexes look different.

      Reproductive behavior is usually:

      • one sex (mostly female) cares for young.
      • the other sex (mostly male) compete with each other intrasexual selection for the opposite sex.

      For example, male elephant seals are much bigger than females due to intrasexual selection, and do not take part in rearing pups.

     
  7. Animals need to communicate   to friend and foe alike.
    • Animal communication may take many forms:

      • Chemical signals such as pheromones released by female moths, detected by bushy antennae of males, up to 3 miles away.



      • Auditory signals such as a lion's roar can also be detected far away.



      • Visual signals can communicate many emotions, and emphasize defense traits, such as spines of a balloonfish.

      More complex behaviors are also possible.


    • Honey bees can communicate a variety of factors about a food source via a waggle dance.

      • The angle between the the sun and food is represented as the angle between the straight part of the dance and vertical.

      • If the straight part of the dance is 20° to the right of vertical, the food is 20° to the right of the sun.

      • The distance to the food source is indicated by the speed of waggles.