Chapter 8- Mating systems

Question 1

Sexual selection hypothesis of infanticide

Answer 1

Proposes that male-based infanticide will be most prevalent when intense male-male competition is at work. An analysis supported this hypothesis- infanticide rates were high when males had access to multiple females and were behaviorally dominant to other males, and were therefore likely to sire offspring with the females. Infanticide in these scenarios led to females going into estrous, creating a pool of potential mates for infanticidal males

Question 2

Paternity dilution hypothesis

Answer 2

Proposes that since males target unrelated offspring, females increase the uncertainty of paternity and therefore reduce the benefits of infanticide by males by mating with multiple males. Phylogenetic analysis found that paternity dilution seemed to evolve after infanticide by males was already in place as a female counterstrategy.

Question 3

Polyandry

Answer 3

A female mates with several males per breeding season

Question 4

Monogamy

Answer 4

One male and one female mate, only with each other, during a given breeding season (they may find a different mate the next season). This system is common in territorial animals.

Question 5

Polygynandry

Answer 5

Several females form pair bonds with several males simultaneously. In some species, a pair of males will jointly defend the territories of a pair of females. Females benefit in this situation because they receive equivalent help that a female with only a single mate would receive. The more help the females receive, the higher the mean nestling weight of the chicks in the brood and lower the chick mortality rate due to starvation.

Question 6

Polygyny

Answer 6

A male mates with multiple females per breeding season. Has dramatic variance in reproductive success, more so than polyandry

Question 7

Lifetime monogamy

Answer 7

A male and female mate with one another during their entire life span. This is common in small diurnal groups like rodents. The oldfield mouse is an example. Most of these females retain the same mate across liters, suggesting lifetime monogamy is very common in this species

Question 8

Monogamy and fitness consequences

Answer 8

There should be fitness consequences associated with choosing a high quality mate. Researchers tested this idea in mate-choice trails involving oldfield mice. A male was given a choice between two virgin females and the male’s preference was recorded. In one treatment, males were paired with the female they had expressed a preference for, and in the other treatment they were paired with the female they had not preferred. More pups were born to pairs made up of a male and his preferred mate than to the pairs from treatment 2. When a naive male was allowed to mate with either the rejected or preferred female, the amount of pups produced in the two treatments were equal. This suggests that the criteria for a good mate differs between mice.

Question 9

Mate-assistance hypothesis of monogamy

Answer 9

When resources are scarce, a male’s reproductive success can be higher when he’s part of a monogamous pair and provides some care for his offspring- this could include bringing food to the nest and defending offspring from predators

Question 10

Proximate basis of monogamy in prairie voles

Answer 10

In this species, males and females that are courting approach one another- an affiliate behavior that is a prerequisite to partner choice. Once individuals mate and form a pair bond, they are aggressive to other members of the opposite sex. Researchers have found changes in dopamine in the nucleus accumbens linked to both affiliative and aggression behavior in prairie voles. The rostral shell was specifically implicated in affiliative behavior. Activation of dopamine receptors (D1 and D2) in the rostral shell was critical to forming long term monogamous relationships

Question 11

Role of dopamine receptors in prairie voles study

Answer 11

D2 receptors facilitate pair bonding when activated by dopamine, while D1 receptors inhibit pair bonding. Researchers hypothesized that D2 receptors mediated pair bond formation while D1 receptors played a role in aggression toward opposite sex individuals. Males showed a surge in D1 receptor activation as well as aggression toward any female that wasn’t their mate after they had pair bonded. Aggression disappeared when D1 receptors were experimentally blocked.

Question 12

Polygamy

Answer 12

When either males or females have more than one mate during a given breeding season. Includes polygyny and polyandry. It can be simultaneous or sequential, and increases the variance in reproductive success in the sex that has more than one mate per season

Question 13

Simultaneous vs sequential polygamy

Answer 13

Simultaneous polygamy occurs when individuals maintain numerous partners in the same time frame, sequential is when individuals form many short term pair bonds in sequence during a breeding season.

Question 14

Polyandry in wattled jacanas

Answer 14

Females are sequentially polyandrous in this species. Males have small territories, while female territories are much larger and contain 1-4 male territories within them. A female lays clutches of eggs sequentially after mating with the males in her territory

Question 15

Female defense polygyny in epsilon wasps

Answer 15

Males mature earlier than females, and after maturing, they will search for unopened brood cells that females will emerge from. These cells are clustered together, and males will be territorial over a cluster of females. When a virgin female emerges, the closest male will mate with her. The male benefits by guarding against intruders because he will have mating opportunities with many females, and he defends the female from mating attempts by other males

Question 16

Characteristics associated with female defense polygyny in insects (3)

Answer 16

1. Females are short lived and have low fecundity- they receive all the sperm they will ever use from a single male
2. Females mate shortly after becoming adults
3. Females are grouped close together in space

Question 17

Lekking/arena mating

Answer 17

Observed in birds, mammals, amphibians, fish, and insects. Males set up and defend small arenas called leks, which are temporary territories for mating and contain no apparent resources. Females visit leks and select mates from available males. A single male will usually obtain a large amount of all matings at the lek, so there is a large variation in reproductive success among males in the population. Females benefit from receiving sperm

Question 18

Good genes model

Answer 18

The idea that females select males based on indicators like size, number of parasites, or other indicators of health, and the choice results in offspring with higher survival probabilities because they possess good genes with respect to health

Question 19

Sexy son hypothesis

Answer 19

The idea that females use indicators of male health to select among mates because their choices will led to male offspring who will be attractive to the next generation of females

Question 20

Male benefit from lekking in sandflies study

Answer 20

Sandflies also form leks, and release a pheromone to attract females, who are able to freely choose among the males. A single male will obtain almost all matings, and the young will not receive parental care from either parent. Researchers set up sandfly leks. In the first part of the experiment, they allowed a female to choose among 5 males. She was removed after mating and the process was repeated for a total of 10 females. In the second part of the experiment, males who had rarely been selected by females were put in new leks and females were allowed to select them. There was no evidence for the good genes hypothesis, but there was evidence for the sexy son hypothesis. When male offspring from parts 1 and 2 of the experiment were placed in a lek, females showed a mating preference for the part 1 offspring. This suggests that first generation females were receiving sexy son related benefits as a result of their choice among lekking males

Question 21

Other than being chosen as a mate, what other benefits could a male receive from lekking?

Answer 21

A male could receive benefits from helping his genetic relatives on a lek. This is a benefit received by male peacocks

Question 22

Benefits of lekking in male peacocks

Answer 22

Molecular genetic analysis to determine whether individuals in a lek were genetic kin found that the average relatedness within the groups was equivalent to that of half siblings. They then raised males in a way that they did not interact with their genetic relatives any more than they interacted with strangers. It was found that these birds set up their leks closer to genetic relatives than they would by chance. The peacocks were still able to gauge genetic relatedness even without the opportunity to learn who was kin during development

Question 23

Evolution of mating systems in warblers

Answer 23

Mating systems vary from monogamous to polygynous. Monogamous warblers provide more parental care to offspring. Researchers used molecular genetic data to build a phylogeny of 17 warblers species, and they gathered data about habitats, paternal care, and mating systems. There was a strong correlation between mating system and habitat quality- polygynous systems were found in better habitats, while monogamous systems were found in poor habitats. There is also more parental care in poor habitats. There is evidence that the monogamous system was the ancestral state in warblers. Polygynous systems with reduced care are derived from the ancestral state as warblers moved to better environments

Question 24

What habitats is monogamy more prevalent in?

Answer 24

Poor habitats- these habitats are often associated with more parental care because both parents need to find food for the offspring

Question 25

Why do polyandrous insects have higher levels of within group conflict?

Answer 25

Polyandrous nests have greater levels of within group conflict because there will be many offspring descended from the same mother but having different fathers (patriline). Without polyandry, all workers have the same parents and therefore the same genetic interest. Patrilines make genetic interests divergent and each patriline will compete for more representation in the next generation. However, decreased genetic relatedness due to polyandry gives the queen some benefits. In bees, nests with more patrilines are more successful at establishing new colonies and have a more diverse colony microbiome. Also, high genetic diversity increases the odds that some of the offspring in a colony will have a genotype that allows them to survive a disease.

Question 26

Benefits to female insects with a polyandrous mating system (6)

Answer 26

1. More patrilines makes some insects more successful at establishing new colonies
2. More genetic diversity helps a population to resist disease
3. Sperm replenishment- female avoids the cost of storing sperm
4. Material benefits- nutrients, reduced predation, protection from other males, and others- this is the most common reason for polyandry.
5. Genetic/fitness benefits due to replacement of inferior sperm
6. Convenience- female avoids the cost of fending off copulation attempts by the male

Question 27

Social brain hypothesis

Answer 27

The idea that larger brain size is partly due to social dynamics favoring cognitive complexity. In primates, positive correlations have been observed between group size and brain size. The hypothesis can also be studied by observing parental care and pair bonding. Biparental care requires coordination and pair bonding between parents- for example, one parent will care for the offspring while another parent searches for food

Question 28

Relationship between brain size, parental care, and pair bonding in birds study

Answer 28

Researchers gathered data on brain size, parental care, mating system, duration of potential pair bond, and development of chicks. The results indicated that biparental care is associated with altricial development in young, which is in turn correlated with large brain size, probably because a longer development period is needed for the brain to develop. Also, biparental care is correlated with pair bonding, and pair bonding is correlated with larger brain size (rather than brain size resulting in pair bonding). Therefore, the link between biparental care and larger brain size was indirect. Behavioral coordination and cognitive complexity were necessary for pair bonding and altricial development, which had an effect on brain size.

Question 29

Altricial development

Answer 29

When chicks are born poorly developed, with their eyes closed and without down

Question 30

Precocial development

Answer 30

When chicks are born well developed, young covered in down

Question 31

Promiscuous

Answer 31

A mating system where polyandry and polygyny are present in the same population at the same time

Question 32

Forms of promiscuity (2)

Answer 32

1. Both males and females mate with many partners and no pair bonds are formed.
2. Polygynandry

Question 33

Dispersion patterns

Answer 33

How individuals move about in relation to another and their environment

Question 34

How do dispersion patterns differ between males and females?

Answer 34

A female can fertilize all her available eggs by mating with one or very few males, so female fecundity is impacted more by the availability of resources like food and defense. More resources means that females can produce more offspring. Males can fertilize large numbers of females, so male reproductive success is impacted more by access to females. Therefore, female dispersion patterns should track the distribution patterns of resources while male dispersion patterns should track the dispersion of females.

Question 35

How do dispersion patterns influence mating systems in a population?

Answer 35

Mating systems are linked to distribution of resources, because resource distribution will affect whether males monopolize more than one female at a time. If resources are dispersed homogenously, then it might not be economically feasible for males to mate with or defend multiple females. When resources are clumped, males might be able to mate with and defend multiple females at once- this would result in a more polygynous mating system

Question 36

4 anthropogenic effects that have consequences on animal mating systems

Answer 36

1. Habitat fragmentation
2. Climate change
3. Pollution
4. Sport hunting

Question 37

How does habitat fragmentation impact animal mating systems?

Answer 37

It produces clumped resources- this causes females to clump together in space. Therefore, males are able to defend multiple mates, and the mating system becomes polygynous. This hypothesis was confirmed in a possum population, which originally had a monogamous mating system, with females having large home ranges where they could obtain sufficient resources. When the habitat was fragmented, the mating system switched to polygynous because females were clustered into each area.

Question 38

How does climate change impact paternal care?

Answer 38

In migratory shorebirds, it has been observed that longer migration routes were correlated with reduced paternal care, probably because the routes required more energy and there was less to give to offspring. Climate change might affect the distance that migratory species have to travel to reach an appropriate end point

Question 39

Effect of female dispersion on male mating patterns in grey sided vole

Answer 39

It was found that when resources became more clumped, females clustered together in their area of resources. Researchers experimentally introduced a the grey sided vole to a small island. In one treatment, caged female voles were used to simulate an environment where females moved about a home range and were spaced out. In a second treatment, the females were clustered together. A reverse experiment using males served as a control. It was found that males tracked the distribution of caged females across treatments, but female dispersion was unaffected by the distribution of caged males.

Question 40

Polygyny threshold model

Answer 40

When males have territories that can sustain multiple mates simultaneously, females can decide which territory to settle on. This model predicts the female’s choice. The choice will change for each subsequent female, because the initial females making their choice will affect the outcome

Question 41

Polygyny threshold

Answer 41

A female may choose to occupy a territory another female is already occupying if the territory has the most food. This means she is passing the polygyny threshold. Theoretically, a female should choose a territory based on resources only, rather than the females that are already there, because resources provide the greatest fitness benefit. Fitness should be equal regardless of whether a female is monogamous or polygamous

Question 42

Polygyny threshold model and mate choice in female lark buntings

Answer 42

Shade cover is the resource that usually determines where females settle, because overheating is the main cause of mortality in lark buntings. Some females have to settle on a territory where there are other females so they can have access to shade. However, there is a cost- males only provide paternal care to the nestlings of his primary female. However, secondary females in areas with lots of shade cover still had the same reproductive success as did monogamous females that bred on territories with less shade cover

Question 43

Extrapair copulations

Answer 43

When males and females leave their territory during mating season and mating with other individuals, even when pair bonds were in place. Some species might exhibit social monogamy, but genetically exhibit a promiscuous mating system since the individual was mating with multiple individuals during the mating season. Males benefit by being able to fertilize more females

Question 44

How does a female benefit from extrapair copulations? (4)

Answer 44

1. Increases the probability that all their eggs are fertilized
2. Maximize genetic diversity in their offspring, increasing the chance the offspring will thrive in the environment
3. Use EPCs to select males that have good genes but might not be willing to form a pair bond and provide direct benefits to offspring
4. Increase the amount of direct benefits (food, protection) that they receive from males

Question 45

Fertility insurance hypothesis

Answer 45

Females may mate with multiple males to make sure all of their eggs are fertilized

Question 46

Impact of EPCs on mating dynamics in buntings study

Answer 46

The study relied on electrophoresis to rule out a specific adult as the parent of an offspring. It was found that out of 257 young that were examined, 37 had genotypes that were not consistent with the genotype of one of their presumed parents- these young must have been sired through EPC. These proportions are higher in other bird populations

Question 47

Sperm competition

Answer 47

The direct competition between the sperm of different males to fertilize a female’s eggs. This competition occurs after mating for sperm to access fertilizable eggs. Therefore, natural selection can operate on sperm size, shape, and swimming abilities

Question 48

Sperm competition in dungflies

Answer 48

When new dung is created and females arrive, there is intense male competition for mating opportunities. Males that find a mate and begin copulating are at risk of attack from other males trying to interrupt copulation. Researchers irradiated the sperm of certain males, so the sperm was otherwise normal but would fail to produce eggs that hatch. The proportion of fertilized eggs that failed to hatch from the irradiated male was measured. The number of eggs fertilized by the last male to mate with a female was proportional to how long such a mating lasted. The longer the mating, the greater to extent to which the last male’s sperm displaced the sperm of other males. This is called last male precedence, but it does not occur in all species. The rate of sperm precedence slows down with time, so it’s more beneficial for a male to find another mate rather than attempting to displace more of another male’s sperm

Question 49

Sperm competition in sea urchins

Answer 49

It was hypothesized that the variation in the traveling speed of sperm correlated with fertilization rates in sea urchins. A video camera was used to tape sperm swimming, and a microscope was used to see which eggs were fertilized. It was found that males with slow moving sperm needed to release much more sperm to fertilize eggs than males with fast moving sperm. Swimming fast and swimming for a long time both require energy, so it was found that all sperm slow down as they get older. Older sperm were also less likely to fertilize an egg even if they encountered one. There was a negative correlation between velocity and endurance- individuals that produced fast moving sperm had their sperm become ineffective at much quicker rates than other individuals, as it used up energy

Question 50

Kamikaze sperm hypothesis

Answer 50

Suggests that natural selection might favor the production of some sperm types that are designed to kill other males’ sperm rather than fertilize eggs. Sperm competition has effects on sperm morphology in insects, frogs, mammals, birds, and others. In frogs, competition produced sperm with long tails, although the advantage of long tails is not clear

Question 51

How does sperm competition effect the number of sperm produced per ejaculate?

Answer 51

Prediction- the number of sperm per ejaculate should be a function of the probability that a female has recently mated with other males. A male will ejaculate more sperm in order to increase the chances he will fertilize the female’s eggs if she has recently mated. In humans, sperm number will increase as a function of time since last copulation, and the relative amount of time couples spent together also predicted sperm volume. The less time couples spent together, the lower the sperm count.

Question 52

Cryptic mate choice

Answer 52

Female mate choice behavior that is not obvious to males. It can affect how much sperm a female allows a copulating male to inseminate her with, how she goes about transferring sperm to the organs where sperm are stores, and which sperm she selects for fertilization

Question 53

Sperm cooperation in desert ants

Answer 53

Sperm cooperation can occur when the number of mating opportunities is limited and females mate promiscuously, like with social insects. It was found that sperm was bundled together in male ejaculates, and that sperm in the bundles was oriented in the same direction and held together by a cap made of glycoproteins. Velocity in sperm bundles was greater than that of singular sperm, suggesting cooperation

Question 54

How does Dunnock breeding biology work?

Answer 54

Exhibit multiple mating systems in the same population- this is because fitness of males and females is affected in different ways by the mating system. Females seem to be winning the battle of the sexes. In this mating system, females compete with one another to establish territories. Males then attempt to build their own territories so they overlay as many female territories as possible.

Question 55

In which breeding systems is male and female reproductive success the highest?

Answer 55

Male reproductive success increases as a function of both the number of mates and the degree to which a male has sole reproductive access to mates. Their success is lowest in polyandry and highest in polygyny. The reproductive success of females increases in the opposite direction, with polyandrous and polygynandrous females having the highest level of success.

Question 56

Battle of the sexes

Answer 56

Males and females have the greatest reproductive success in opposite mating systems, so there is a battle as to the optimal breeding system

Question 57

How does territory size impact mating system?

Answer 57

The difference between monogamy and polygyny is a function of male territory size. Polygynous males had larger territories than monogamous males, with female territory size remaining constant. Polyandry and polygynandry differences were a function of female territory size, with male territory size remaining constant

Question 58

Dunnock breeding system study

Answer 58

Researchers hypothesized that since females competed with each other for the best resources, the territory size should shrink when the amount of resources was experimentally increased, since females would then be able to obtain the same amount of resources without having to defend a large area. Researchers placed artificial feeders on random female territories, and found that the territories shrank as predicted. The male territories did not change in size. However, the distribution of mating systems changed to favor males. As territories shrank, males were better able to monopolize more than one female, and a shift toward polygynandry occurred.