Study sets, textbooks, questions
Upgrade to remove ads
Biology 1402 Lectures 10, 11, 12
Terms in this set (110)
differential reproductive success as a result of variation in the ability to obtain mates.
Why does sexual selection occur?
Differential investment of energy in constructing an offspring and caring for it.
produces the larger gamete.
Produces the smaller, more motile gamete.
Mothers contribution to the offspring exceeds the father. Why?
Females often invest more in resources and care, limiting reproductive opportunities.
Bateman's Principle of females and a males sexual selection:
-low variation in females mating success
-more mating by females may not lead to more offspring
-high variation in male mating success
-more matings leads to more offspring
-limited by access to females
Predictions about sex-related behavior:
1. the sex that invests more will be more discriminating.
2. the sex that invests less will compete amongst themselves for access to the higher-investing sex.
Polygamy (subdivided into: polygyny and polyandry)
most individuals mate and remain with just one other individual
any male mates with any female in a population or social group
when some individuals attract multiple mates while other individuals attract none.
Polygamy subdivided into:
Polygyny: individual males mate with multiple females
Polyandry: individual females mate with multiple males
Mating systems are not easy to define
Three issues complicate the task:
1. differences between animals' mating behavior and bonding behavior
-pair bond: appears monogamous
2. mating system variation within species
3. males and females vary in their mating behavior
having one mate at a time
Body size is an important clue to behavior
-selection for larger and larger body size when competition is high
-coloration can also be a clue to behavior. male-male competition sometimes results in differences in physical appearance between the sexes
in birds, do both female and male invest in parenting equally?
when the sexes of a species do differ in size and appearance, this is called:
when the sexes are indistinguishable this is called:
Behaviors associated with sexual dimorphism:
- one parent invests more in caring for the offspring.
-mating system tends toward polygamy
-one sex (usually females) is choosier when selecting a mate.
-one sex (usually males) competes for access to mating opportunities with the other sex.
Behaviors associated with sexual monomorphism:
- Both parents invest (approximately) equally in caring for the offspring
-mating system tends toward monogamy
-both sexes are equally choosy when selecting a mate.
Men are bigger than women. What does that tell us about our evolutionary history of monogamy vs. polygamy?
we can predict a bit about the parental practices of a species just by looking at a picture of a male and a female and examining the ratio of body sizes. If the two are dramatically different, as in elephant seals, we can hypothesize that the smaller sex is doing most of the care of the offspring and that the species is more likely to be polygamous than monogamous.
Are humans monogamous or polygamous?
have a mating system close to monogamous.
Modes of Sexual Selection
male vs. male
when one or both sexes are choosy
Combat: competition among males for access to females leads to elaborate weapons, ornaments, and fighting
if a female mates with multiple males, then the sperm from those males compete for eggs.
sperm competition can lead to:
-selection for large ejaculate volume (more sperm)
-mechanisms to prevent other males from inseminating females
"alternative male mating strategies"
large and small males sometimes use different behavior strategies to achieve mating success.
Male-Male comepetition: intrasexual selection
alternative male mating strategies
Female Choice: Inter-sexual selection
Females may actively choose males based on the males traits.
Female choosiness is manifested by one or more of four general rules:
1. Mate only after subjecting a male to courtship rituals.
2. Mate only with a male who controls valuable resources.
-example: reproductive success can be increased if the territory id rich in resources, the territory that the male defends.
3. Mate only with a male who contributes a large parental investment up front.
4. Mate only with a male that has a valuable physical attribute.
Sexual selection by mate choice:
1. runaway sexual selection
2. good genes
-Pre existing bias (sensory bias)
-females choose mates based on the direct tangible benefits that they will gain from that mating
food (nuptial gift in the hanging fly)
a female will not mate with a male unless he brings her a big piece of food
Why do so few women get into barroom brawls?
as females are making the greater investment in reproduction, nearly any male will mate with them. So, there is nothing more to be gained by trying to outcome other females or otherwise attract the attention of males.
Example of nuptial gift:
hanging flies, a female hanging fly will not mate with a male unless he brings her a large offering of food.
Nuptial gift- Bigger gift means longer:
males offer only sperm
1. access to breeding site
2. access to food
3. nuptial gifts
Direct benefits: males offer?
1. Access to breeding site
females prefer certain territories and thus certain territory-holders
2. access to food
females mate preferentially with males controlling richer access to food.
-example: male anthidium bees defend patches of flowers and mate in exchange for access to pollen and nectar
3. "nuptial gifts"
food for female
food for female's young
-example: in roadrunners, males offer lizards or other snacks to females
-example: in hanging flies, males offer females a gift of insect prey
In hangingflies, bigger prey may result in:
"Good genes" hypothesis
females choose mates whose genes improve their offsprings fitness
prediction: females allowed to choose males with 'good genes' produce more fit offspring than females not allowed to choose
Runaway sexual selection ("sexy son" hypothesis)
sons of those females choose a male trait have improved mating success because they inherit the trait that made their father appealing to their mothers
Indirect benefit- "good genes"
-sometimes resistance to disease is hereditary
-particular traits signal hereditary resistance
-females prefer males with resistance
-makes their kids get "good genes"
- better at passing on their alleles
1. runaway sexual selection
2. good genes
Pre-existing bias (sensory bias)
certain traits may be intrinsically stimulating and evoke greater response
Example of Sensory bias:
-Female guppies are attracted to ORANGE. this response may be due to feeding behavior selecting for the ability to locate ripe fruit
Mechanisms of Sexual Selection
A. mate competition
B. mate choice
a form of natural selection that occurs when individuals vary in their ability to obtain mates relative to others of same sex
If humans show adaptive preferences for mate qualities, then:
Men should generally prefer women who exhibit signs of:
-beauty and youthfulness
Women should generally prefer men who exhibit signs of health, signs of higher levels of testosterone, and better development stability
the mothers material and energetic contribution to the offspring
total reproductive output:
the lifetime number of offspring a male can produce, tends to increase as the number of females the male is able to fertilize increases.
Why do males usually compete for females rather than the opposite?
Because additional matings usually lead to greater increases in reproduction (and fitness) for males, selective pressure has resulted in the evolution of some differences in male and female reproductive behavior.
For males, the most effective way to maximize their reproductive success often is:
to find and gain access to mating opportunities with additional females
For females, an effective way to maximize their reproductive success often is to:
put in more effort into parenting and less effort into mating.
Male and female investment in birds:
development of the egg is external, the female lays the egg but both the female and male can protect and incubate it. Same with feeding the chicks.
External fertilization in fish and amphibians:
the reproductive investment reduces over time for the female, she does not spend any energy while the fertilized egg is being developed.
Male mammals will always have some degree of paternity uncertainty:
because it is impossible for a female to mate with multiple males, any could be the father. males cannot be 100% certain that an offspring is his progeny.
Poor mating choices in males and females:
-females: more consequential
-males: less dire, little beyond het time and energy involved in mating.
Two differences in the sexual behavior of males and females across the animal kingdom have evolved:
1. The sex with the greater energetic investment in reproduction is more discriminating about mating.
2. Members of the sex with lower energetic investment in reproduction compete among themselves for access to the higher-investing sex.
high reproductive investment leads to the evolution of choosiness in mating comes from the:
-male bush cricket contributes a massive ejaculation (equivalent of nearly 50 pounds of semen in human) which the female uses for energy
Male crickets are very choosy when selecting a mate because:
they don't want small females that would produce relatively few offspring
The sex with greater reproductive investment must be choosy:
a poor choice of mate could be disastrous
greatest vulnerability for males comes when:
comes when males provide parental care to offspring.
there is some chance that the male may be investing in offspring that are not his own, due to:
Paternity uncertainty can lead to significant evolutionary costs:
-rather than increase his own fitness, he is increasing the fitness of another male.
Tactics for getting a mate:
courtships and competition can help males and females secure reproductive success.
Female choosiness leads to:
male to male competition
the male needs to be beneficial for the female and offspring
-process can go on for several days
-involves the male trying to impress the female
-example: female wester grebe requires the male to dance, fancy dives into the water, graceful hovering, various head movements.
-Territorial defense is common competition for males to gain a female
-female chooses a mate based on the territory he defends, which is where she will reside after mating.
-if the territory is rich in resources= able to attract a female
-example: arctic ground squirrels
Parental investment up front:
-female requires a male to give her his parental investment, in the form of resources that will help her maximize her reproductive success.
-example: hanging fly, a female will not mate with a male unless he brings her a big piece of food, called a nuptial gift. (usually a large insect)
Nuptial gift: pt.2
the larger the food, the longer she will mate.
and the more she eats, the larger the number of eggs she will lay
Valuable physical attributes:
-male to male competition
-male-male contests determine the dominance ranking of males
-females then mate primarily with the highest ranking males
Why is it so rare for females to compete for a mate?
The answer is that as long as females are making the greater investment in reproduction, nearly any male will mate with them.
Influences over mating behaviors in humans that complicate interpretation for reproductive success:
social and cultural values
what can protect a male's reproductive investment?
Abandoning a female after mating can minimize the potential costs associated with:
-males provide parental care to insure his offspring survive so the males reproductive success increases
-even though parental care makes a male vulnerable to paternity uncertainty
Male's benefit from investing time or energy benefiting the offspring minimizes his:
minimizes his risk in the danger zone by making sure his mate does not mate with any other male
males use this to block the passage of additional sperm into the female
Extreme form of mate guarding:
Black Widow, breaks off his sexual organ inside the female, preventing her from ever mating again.
-increase reproductive success by reducing additional mating opportunities for a partner.
-can improve a male's reproductive success by increasing his paternity certainty, thus reducing his vulnerability when he makes investment in offspring.
Elephant seal's mating pattern exemplifies what mating behavior?
Polygamy, a system in which some individuals attract multiple mates while other individuals attract none. (polygamy subdivided into two: polygyny and polyandry)
males mate with multiple female
Females mate with multiple males
most individuals mate with just one individual and remain with just one individual
Examples of vulnerable male physical attributes:
-antler size in red deer
-bright red chest feathers of frigate birds
-elaborate feathers on a peacock
Why do females often end up selecting the same male for mating?
usually if the male....
-a male on territory rich in resources
-physical features, such as big antler size
Three issues when identifying a population's mating system:
1. there are often differences between animals' mating behavior and their bonding behavior. Males and females form a pair bond, in which they spend a lot of their time together making it seem monogamous, but closer inspection (DNA of offspring) show that male/ or female may be mating with other individuals.
2. the mating system may vary within the species, some individuals may be monogamous while others are polygamous.
3. males and females often differ in their mating behavior, like the elephant seals, males were polygamous while the females were monogamous.
Does the difference in parental investment patterns in birds and mammals lead to different mating systems?
Yes, in mammals polygyny is the most common. In birds, relative equal parental investment between male and female, appear to be monogamous.
Polygyny is a consequence of?
The significant female investment and lesser male investment creates a consequence of what mating system?
The study of the Pre-Industrial population, the Xavante Indians showed information about men and females in reproductive success?
-Men vary more in their reproductive success than women because nearly all women have access to a mate while some men are outcompeted for access to women.
Why were the Xavante Indians chosen to determine if men were actually had greater reproductive success than females?
Because they are a population primarily of hunter-gatherers, with no access to reliable birth control and with almost no contact with the Western cultures. So their results would have been best suited than people from US.
Mating systems are influences by the relative amounts of males and females.....?
parental investment influences....
Body size and coloration can be clues for what?
What sometimes results in differences in physical appearance between the sexes other than size?
Male to male competiton
What happens when there is little male to male competition for mates?
As a consequence, little sexual dimorphism occurs in most bird species.
Differences in the level of competition among individuals of each sex for access to mating opportunities can lead to:
the evolution of male-female differences in body size and other aspects of appearance.
Direct benefits of sexual selection:
females choose mates based on the direct tangible benefits that they will gain from that mating.
-food (nuptial gift)
Indirect benefits is:
alleles affecting female mate choice in frequency depending on the fitness of the females offspring
preferred male trait indicates high viability, which is inherited by the offspring of females who chose those mates.
Sexual antagonistic co-evolution is the relationship between:
males and females where sexual morphology changes over time to counteract the opposite's sex traits to achieve the maximum reproductive success.
the branch of biology that deals with the form of living organisms, and with relationships between their structures.
-preexisting preferences for certain traits may be hardwired in females and lead to the development of exaggerated traits in males
-Female Trinidad guppies are attracted to the color orange
-so sexual selection then favors males with lots of orange
What mating system was considered normal in pre-industrial humans?
A male lizard finds and defends a territory that attractive to female lizards and has exclusive access to those females. This is an example of:
One would expect that conflicts between parents and offspring over parental investment would be the most pronounced in...
what are the costs of signalling?
What are examples of kin selection?
Sets with similar terms
Comparative Psychology Test 3
Chapter 11: Sexual Selection
Other sets by this creator
RHIM 3308 Group sales and services
Geog Test review
Wine Knowledge RHIM 4350
RHIM 3321 Exam 3
Other Quizlet sets
Anatomy and Physiology - Chapter 21
WH Exploration quiz
6.1 Human Nutrition - Diet
Old Testament Final (part2)