Lecture
11: Sexual Selection and Mate Choice
-Reproductive behaviour involves many choices influences by natural selection.
-Reproductive
behaviour involves seeking and defending particular territory, making choices
about mates and how much energy to devote to rearing the young.
-In
particular, mate selection involves intense natural selection
-Decisions made about mate choice during breeding season result in a reproductive strategy.
-Include
mate choice, number of mates, and parental care
-Males
and females usually differ in reproductive strategies
-Mate choice by females. Females evaluate male’s quality and then decide whether or not to mate
- Mate choice by males less common.
-Parental investment refers to the contributions each sex makes in producing and rearing offspring.
-Females
generally show higher parental investment
-Differential
parental investment means that the sexes face very different selective
pressures
- Reproductive
event for females is costly, but a reproductive event for males is cheap.
The success that an individual has competing for mating is called sexual selection.
Sexual selection involves two separate types of selection:
Intrasexual selection: interactions between members of 1 sex
Intersexual selection: mate choice.
Traits
that evolve from inter- and intrasexual selection are called secondary sex characteristics.
Intrasexual Selection
Individuals
of one sex compete, usually only males
In this situation, even if there are multiple males in the group, only a few males do most breeding, and most males do not breed at all.
Selection strongly favors trait that improves ability to compete and allows the individual to out-compete other males.
Physical differences between males and females are called sexual dimorphism.
Intersexual Selection:
There are many thoughts on the evolution of mate choice.
For
example, females choose the male that is the healthiest or oldest. These males
have succeeded in living long. So they are successful in acquiring food,
resisting parasites and resisting disease.
-Females may choose males with detrimental traits.
-This
is the handicap hypothesis: Only genetically superior males survive with a
particular handicap. Male must be quite strong and healthy to overcome the
negative aspects of the handicap.