BioU3L2 Flashcards
Proximate questions about behaviour
address the mechanisms that produce a behaviour: the environmental stimuli that trigger a behaviour and the genetic and physiological mechanisms that make it possible.
How does an animal carry out a
particular behaviour?
Ultimate questions about behaviour
address the evolutionary significance of a behaviour: how a behaviour increases the evolutionary fitness of the animal
demonstrating it, helping it to survive and reproduce in its environment.
Why does the animal show this
behaviour?
What is evolutionary fitness?
measures how many viable, fertile offspring an individual (or an
allele) leaves in the next and subsequent generations, relative to others in the population
Adaptive behaviour
Increases an individual’s evolutionary fitness relative to other individuals in the population
Sexual cannibalism
In some species, one sex (usually the
female) consumes the other during
sexual reproduction
Courtship in the Australian redback spider
The male courts the much larger female for up to eight hours. He strums on the strands of her web as
he slowly approaches her.
How does the male redback transfer sperm to the female
The male has two specialized legs or
palps, each of which is used to transfer
sperm to the female.
Mistaken Prey hypothesis
Prediction:
* Females sometimes attack males as soon as they enter her web.
Results:
* A female only eats a male after he somersaults to dangle in front of her jaws. In contrast, she often attacks prey as soon as they enter the web.
Conclusion:
* The female does not mistake her mate for prey.
Hypothesis 2: Mate Rejection
Prediction:
* Cannibalized males are smaller and produce fewer offspring than non-cannibalized males
Results:
* Cannibalized males do not differ in size, mass, or condition from non-cannibalized males.
* Cannibalized males father, on average, twice as many offspring as non-cannibalized males.
Conclusion:
* Females do not cannibalize low-quality males who are unsuitable mates
Hypothesis 3: Hungry Lover
Prediction:
* Females are more likely to cannibalize males if their diet has not been supplemented.
Results:
* 29% of females that were given supplemental food were cannibalistic.
* 62% of females that fed naturally were cannibalistic.
Conclusion:
* Females eat their mates because they are hungry.
Choose a proximate explanation
for female cannibalism:
A. The female eats the
male because he dangles his abdomen in front of her jaws.
B. The female can produce a larger egg sac if she eats the male.
C. The female gains nutrients by eating her mate
A
Choose an ultimate explanation
for female cannabilism:
A. The female eats the male
because he dangles his abdomen in front of her jaws.
B. The female gains nutrients from eating the male.
C. The female copulates
longer while eating her mate.
B
Behavior of male redbacks
Hypothesis 1: Paternal Investment
Prediction:
Consuming the male will significantly increase the number and mass of eggs in the female’s egg sac.
Results:
Consuming the male does not increase the number or mass of eggs in the female’s egg sac. This might be due to the small size of the male relative to the female and even relative to her egg sac!
Conclusion:
The male does not benefit from contributing nutrients to his offspring.
Hypothesis 2: Nuptial Gift
Prediction:
Cannibalized males father more offspring than non-cannibalized males.
Results:
Cannibalized males copulate for an average of 25 minutes, while non-cannibalized males copulate for an average of 11 minutes.
Cannibalized males father twice as many offspring, on average, as non-cannibalized males.
Conclusion:
Males double their fertilization success by sacrificing themselves to their mates
Choose a proximate explanation for
male self-sacrifice:
A. The male’s somersault is
triggered when he inserts a palp in the female’s sperm receptor.
B. The male is providing nutrients to his offspring.
C. A male that is cannibalized fathers
twice as many offspring.
A
