4. Sexual Selection Flashcards
What is Sexual Selection?
- A form of non-random mating, which occurs when individuals within a population differ in their ability to attract mates
- This type of selection favours individuals with heritable traits that enhance their ability to obtain mates
- A component of natural selection in which mating success traded for survival
What is the difference between Natural and Sexual Selection
Natural selection determines who survives while sexual selection determines who reproduces
What were Darwin’s thoughts on traits that seemed maladaptive? (2)
(such as the tails of peacocks)
- Seemed maladaptive to spend energy to
produce a structure that would increase
vulnerability to predation - He concluded that the trait must be
adaptive to help the peacock attract
mates, resulting in increased reproductive
success
What is INTERSEXUAL Selection?
- Intersexual selection: mating success determined by between-sex interactions
- In other words, this type of sexual selection looks at mate choice (i.e., choice exerted by members of the opposite sex)
- More specifically, the common scenario is a female choice of males (so males must show themselves to be genetically attractive to females)
What is INTRASEXUAL Selection?
- Intrasexual selection: mating success determined by within-sex interactions
- individuals competing to obtain mates (same sex)
- For example, male-male combat over females or resources vital to mates (this often results in body size sexual dimorphism, meaning in
this case that males are much larger than females and often have adaptations to fight other males)
Can Intrasexual Selection exist between females?
Yes, – Intrasexual selection has also been observed among females in a variety of species, such as ring-tailed lemurs and spotted hyenas
What is the Bateman - Trivers Hypothesis?
The Bateman–Trivers hypothesis has an observed pattern and a hypothesized process
– Patter:
Traits that attract members of the opposite sex are more elaborate in males
– Process:
Eggs require more energy to create than sperm
What is the Fundamental Asymmetry of Sex?
in most species, females invest more in their offspring than males
What are the 2 Consequences of the Fundamental Asymmetry of Sex?
- Female fitness is limited by the ability to gain resources needed to produce more eggs and healthier offspring, so females produce relatively few offspring during lifetime
- Male fitness is limited by the number of females he can mate with, and he can mate frequently because sperm are so energetically inexpensive
Why do Females “choose” good alleles
There is a direct benefit to the female’s own fitness, such as a female pairing with a male who controls a better territory with better resources that she can share by mating with him
There is an indirect benefit to the female’s offspring, rather than the female herself
What is the Good Genes Hypothesis?
“the traits females choose when selecting a mate are indicators of the male’s ability to pass on genes that will increase survival or reproductive success of offspring”
What 3 observations lead to the conclusion that females prefer to mate with healthy, well-fed males?
- Existence of colourful feathers or beaks is due to the presence of red and yellow pigments called carotenoids
- Carotenoids protect tissues and help stimulate the immune system to fight disease more effectively
- Animals must eat plants in order to obtain carotenoids
These observations suggest that the healthiest birds in a population should thus have the most colourful beaks and feathers
What is Male-Male Competition?
Males that win battles with other males monopolize matings with females in their territory
o Fights are usually won by the larger male
o Dominant males father a large number of offspring
o Males that lose fights father few or no offspring
– Thus, alleles from large successful males will increase in
frequency in the population
– If the ability to win fights and produce offspring is determined
by body size, then alleles for large body size have a significant fitness advantage
What is Sexual Dimorphism?
Sexual dimorphism refers to any trait that differs between males and females of the same species
– Weaponry
– Ornamentation and behaviour in courtship
– Body size
What is the Sexy Sons’ hypothesis?
this hypothesis states that “a female’s ideal mate choice among potential mates are ones whose genes will produce males with the best chance of reproductive success
What are the 3 Main Mating Systems?
- monogamy,
- polygamy
(which includes polygyny, polyandry and polygynandry), and - promiscuity
What is Monogamy?
(Pair Bonding)
the pattern of having one mate at a time –
one male and female have an exclusive mating relationship
(more usually called pair bonding)
What is Polygamy?
the pattern of having more than one mate at a time
– one or more males are bonded socially with one or
more females
What is Polygyny?
polygamy in which one male mates with two or more females
The most common polygamous mating system in vertebrates so far studied
o Female usually provides most parental care
-For example = Male walruses grab the attention of females with loud vocalizations – males defend a large harem of females that join him underwater for copulation
elephant seals, gorillas, spotted hyenas
What is Polyandry?
polygamy in which one female mate with two or more males
The male usually provides most parental care
o Example = in the spotted sandpiper, females compete for territories in order to attract males – the female will then attempt to attract additional males for whom she will also lay eggs)
What is Polygynandry?
polygamy in which two or more males mate with two or more females
Encapsulates both polygyny and polyandry with the same species
o The numbers of males and females need not be equal
o Allows groups of males and females to live together and spend less time being concerned with mate competition
o Polygynandry may be advantageous from the female’s perspective because it causes paternity confusion, which decreases infanticide and allows her to have multiple males care for her brood
o Examples of animals that use this mating system =
red foxes, European badgers, sea spiders, ground squirrels
What is Promiscuity?
a mating system where there is no pair bonding
Females mate with multiple males, and males mate with multiple females
o Examples = Bonobos are highly promiscuous, engaging in sexual interactions more frequently than any other primate
o Other examples that use this mating system = dolphins and hummingbirds
