Please Do Now: 1) Define polyandry.
2) What kind of mating system would you
expect a polar bear to engage in? Why?
Agenda
Do Now
 Sexual Selection and Lek Mating Notes
 Lek Mating videos
 Experimental Design
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What is typical Reproductive
Behavior?
When ready to mate, animals produce
signals to communicate with potential partners.
 Each species usually produces a unique courtship signal
that ensures that individuals do not mate with individuals
of another species.
 Many species of insects, amphibians, and birds produce
unique sounds or songs to attract mates.
 During the breeding season, animals make several
important “decisions” concerning mating and parenting.

 These include how many mates to have and how much time
and energy to devote to rearing offspring.
 These decisions are all aspects of an animal’s reproductive
strategy, a set of behaviors that have evolved and that
maximize reproductive success.
What is Mate Choice?
Males and females
usually differ in
their reproductive strategies.
 In many animals, females do not mate with
the first male they encounter.

 Instead, the female seems to evaluate the male
before she decides whether to mate.
 This behavior, called mate choice,
has been observed in many invertebrate
and vertebrate species.
What is Sexual Selection?
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More than a century ago,
Darwin noticed that males
often have extreme
characteristics that they
use in their courtship displays.
Darwin recognized that extreme traits could have evolved if
they helped males attract or acquire mates.
Sexual selection is a mode of natural selection in which
some individuals outreproduce others of a population because
they are better at getting mates
Traits that increase the ability of individuals to attract or
acquire mates appear with increased frequency.
Even traits that have a negative effect on survival can evolve
in this way, provided that their benefits to reproduction are
high enough.
Sexual Selection
It is usually females
that select mates
based on their physical traits.
 Probably because reproduction has a greater
cost and requires a greater investment from
females.
 Males may show mate choice as well if their
parental involvement is high.

What is lek mating?
A lek is a gathering of males, of certain animal species, for
the purposes of competitive mating display. Leks assemble
before and during the breeding season, on a daily basis.
 Once a dominant male wins a female or
a set of females, he will often have to
defend them for the rest of mating season to ensure he is the
only one who inseminates them.
 In some species, a male can gain a reproductive advantage
over other males by interfering with their reproduction.

 For example, in some species of worms, butterflies, and snakes,
the male seals the female’s reproductive tract after mating, thus
preventing other males from mating with her.