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Flashcards in Mating Systems Deck (111):

Aphids, parasitic wasps, mites, certain crustaceans, the majority of vascular plants all have what in common?

Do not reproduce sexually every generation


Cnemidophorus sp. (Whiptail lizards)
Pocelliopsis sp. (stream fish)
Fungi and Protozoa

All of these have what in common?

They never reproduce sexually


The bellidoid rotigers, (small freshwater invertebrates) nerve reproduce asexually. This is an entire animal phylum that doesn't



In whiptail lizards (6 of 15) what is required for the female to reproduce?

Another female courts her by a typically male pattern


What is the way in which some whiptail lizards reproduce called?



T/F: nearly every eukaryote has a life history of sex



What mechanism would be capable of producing an adaptation like sex?

Natural Selection


Natural selection favors individuals that pass on their genes to the next generation, but in most species the males contribute nothing but sperm to reproduction



A parthenogenic (no fusion of male and female gametes) female should have the advantage, as shse passes on twice as many of her genes with each offspring



If there were a genetic polymorphism in a population, would asexual or sexual females have the enormous fitness advantage?

Asexual females, especially since in most species males contribute nothing but sperm


Sexual displays and rituals can be enormously expensive in terms of energy, time, and resources

Sex is expensive (preach)


Ex: male bower birds spend weeks constructing bowers solely for the purpose of attracting males

Ex: females are ridden by males after copulation, sometimes for many hours. It intereres with the foraging of the females and places them at increased risk of predation

Sex is expensive! (preach)


Ex: Tree frogs in Central America call to attract mates. Females are strongly attracted to the calls, it is much easier to get a mate if a frog invests a lot of time calling.
Carnivorous bats are also attracted to the calls, and they pluck the male right off the tree

Sex is dangerous!


Ex: Calling cricket males are more attractive but parasitic flies hone in on the sound and deposit their eggs into the singing males

Sex is dangerous!


There are a few very compelling reasons why species might benefit from sexual reproduction
The problem is that we lack a real understanding of how selection works at the species level. Natural selection, as we know it, works on _____ not species



Genes that act for the good of the species could be undermined by selfish mutations that crop up within the individuals and spread



The move comprehensive and persuasive mechanism for the existence of sex it the

Red Queen Hypothesis


A mechanism for the continued existence of sexual reproduction. Proposes that even species that do not seem to be changing are undergoing rapid evolution.

Red Queen Hypothesis


The natural world is so challenging that without constant evolution, species would go extinct. What provides the necessary variation that keeps evolution going? (2)

If not for these two things, all species would go extinct if environmental change were to occur

Sex and Recombination


Every species on the planet is locked in what JBS Haldane referre to as...

Evolutionary Arms Race


The natural enemies-parasites, predators, and competitors, of any species evolve every generation to better exploit their hosts, capture their pray, and push aside their competitors.
This produces a ____ among the hosts, prey and predators to negate these advantages

Selective Pressure


The Red Queen hypothesis is a natural outgrowth of the

Evolutionary Arms Race


Braconids parasitizing a hornworm larva

A harvestman parasitized by mites


Long-term evolutionary arms races are suggested in the

Fossil Record


For instance, in Cenozoic mammals, there is a correspondence between the fastest running herbivores and the fastest-running



The rise of jawed fishes seems to induce a cascade of shells, armor, and escape abilities among marine invertebrates in ancient, paleozoic seas.

Evolutionary Arms Race


In shorter time scales, apparent cases of evolutionary arms races are easy to find.
For instance, the rough-skinned newt, one of the most toxic amphibians on the planet, co-occurs with garter snakes that are just barely able to detoxify the poison.

Evolutionary Arms Race


The parasite-host arms race is documented on a gene for gene level in some cirumstances

Ex: the fungal parasite evolves quickley, and susceptible parasites are sitting ducks, only by constant evolution do the host survive, because the parasite cannot exploit a host with novel defenses


The stream fish, pocelliopsis in Mexico, asexual strains sufffer more or less parasitism than sexual individuals living in the same streams?

Much more parasitism for asexual strains


When genetic variation among sexual strains of pocelliopsis is lost, what happens to the advantage they had?

What does this imply?

The advantages is lost as well.

That genetic variability in sexual reproduction keeps parasites at bay.


A reason why an individual might benefit from reproducing sexually:
Sexual offspring will be more varied than asexual offspring. In an unchanging environment, this is a disadvantage, because the parental types were obviously successful enough to reproduce. In a changing environment, variable offspring ensure that at least a few will survive.

Bet-Hedging, reason why an individual might benefit from reproducing sexually


Offspring will be different from parents. If predators or pathogens are part of the environment, offspring which are different from their parents have an advantage, because pathogens are adapted to attack the parental generation.

Reason why an individual might benefit from reproducing sexually


Abundant evidence supports the notion
that sex is advantageous in the face
of environmental change. Many
species that can switch between sexual
and asexual reproduction turn to sex
when faced with an imminent change
in the environment.



These engage in sex when conditions become unfavorable. Each spore stalk was formed from hundreds of independent ameboid cells that aggregated to form a sluglike organism, then differentiated into a stalk and spherical sphore case. The sphores will be carried away on air currents to new habitats and fuse to form diploid cells

Slime Molds


In ants, bees, wasps, some mites, sex is determined by the number of SETS of chromosomes

Males are ______ and descend from unfertilized eggs

Females are _____ and result from the genetic contribution of a mother and a father




Females of these species can either fertilize each egg, or let it remain unfertilized, thus controlling the sex of their offspring

Ants, bees, wasps, some mites


This sometimes results in sex ratios that are skewed in favor of ______, because mothers ensure that their sons will not compete with each other for mates by laying fewer male eggs.



For most turtles and alligators, the sex of an individual is determined by the incubation temperature of the eggs

Environmental Sex Determination


In many turtles, for instance, eggs that incubate at low temperatures become



and the eggs that incubate at high temperatures become



In some cases, sex can be determined by the social or physiological status of the individual. Small or poorly fed individuals are

larger individuals are

It can be vice versa. This pattern is especially common in sequential hermaphrodites




In humans, XX is female vs. XY male
In butterflies and birds, females are the

heterogametic sex (ZW, males are WW)


In XY chromosomal sex determination, the assortment of chromosomes during metaphase of Meosis I ensures that exactly half the male gametes contain X chromosomes, and exactly half contain Y.

This system produces 50% males and 50% females


In humans, there is actually a slight ____ bias at fertilization, because sperm containing Y chromosomes have a smaller “payload” and swim faster, thus resulting in more male zygotes.



Many fish, annelids, and plants can function as both sexes. These are called



can switch from one sex to another during the course of their lifetimes.

Sequential Hermaphrodites


can be both sexes at once. Many angiosperm plants, for instance, are simultaneous hermaphrodites, as are many annelids

Simultaneous hermaphrodites


Generally, individuals switch sexes when they would have a higher fitness as a member of the opposite sex: for instance, if males fight for access to females, a female might switch over to being a male when she grew large enough to win fights with rival males.



Engages in protandrous sequential hermaphrodism, females gain more fitness by being large than males. The can switch sexes depending upon their size and mate in those weird piles



This species of brightly marked fish, smaller fish are female and if the male were removed, the largest female would change sex and start to function as a male within days. This protogynous sequential hermaphroditism,, where males gain more fitness being large than females

Blueheaded Wrasses


These mate by intertwining and extruding reproductive organs, each structure contains both male and female parts so that each individual is simultaneously donating and receiving sperm

Simultaneous Hermaphrodism


True/False: The effects of sexual selection depend upon the mating of the individual



In these species males and females pair for the breeding season. In some cases, the individuals may pair for life.

Monogamous Species


In these species males have multiple female partners in a single breeding season. In some cases a male may control a large group of females.



In this type of mating system, a male visits with successive females

Sequential polygyny


The opposite of polygynous mating, mating in which females have multiple mate partners



This animal's males defend territories on the beach, they mate with all females in their territories. Males that lose do not get to mate that year

California Elephant Seals


There are also subcategories of polygynous and polyandrous mating systems that are defined in terms of whether the mating systems are ____ or ______

Resource based

Non-resource based


The elephant seal situation is ______ polygyny, where space on the beaches is the key resource

Resource Based Polygyny


Resource based systems intensify male-male competition as a mechanism of sexual selection, though there is a little female choice

Females often choose to mate with sneaky mathat invade male territories and clandestinely copulate.


In this mating system, females aggregate in regions with sole purpose of choosing a mate. Males aggregate to these locations and display in order to get access to females. Female choice is intense in this situation

What is an example of this type of mating system?

Non-resource based mating system



A small solitary bee whose males defend the flowers that females specialize on. They mate with the females on the flowers. The flower is the resource and males ensure mates by defending them



In polygynous species, does the mail generally provide anything toward parental care?


Even in resource-based systems, he is basically monopolizing a resource she needs, and protecting it from males, he does not create or provide it.


In polygynous species, males can mate with many females. Therefore, male fitness is proportional to the number of


The basic inequality between the sexes is increased, since the female provides all the parental care. Females do not benefit from more mates because their fitness is limited by time and resources.


In polygynous systems, there is strong sexual selection on males to obtain more mates.



a North American, insectivorous bird that builds mud nests under overhanging cliffs and bridges.

Barn Swallows


Both sexes of barn swallows overwinter in a warm place. Males return first to temperate areas, and display to attract females into their breeding territories. Males and females pair up early in the mating season, build a nest, and cooperate to raise young.

Monogomous systems such as this favor what in both sexes?



What happens in monogomous "choosy" systems?

Good mates tend to end up with good partners


Henlike birds that live in steppe and sagebrush shrubland. Males gather in places that become leks. There is no important resource by a lek, just a place males display. Males with the best display get the most mates. Many get no mates. It depends upon how attractive the booming display is.

What type of polygamy system is this?

Sage Grouse

Non-Resource Based


the subset of selective pressures concerned with attracting a mating partners and achieving copulations or pollination events, and also, choosing the best mating partners given the circumstances.

Sexual Selection


Do species for which there is no overt competition among individuals for mates experience sexual selection?

Yes some do.


Sperm competition is natural selection based upon the differential ability of sperm to reach and fertilize mates

Flowering plants compete quite strongly for pollinators, driving the evolution of colorful flowers and floral “rewards” such as nectar, oils, and other compounds.

Species exhibit sexual selectioin when there is no overt competition among individuals for mates


This person viewed sexual selection as a phenomenon quite different from natural selection.

A more modern view is that sexual selection is really a subset of selection, in a larger sense.

Charles Darwin


Some of its effects are counterintuitive from the perspective of “survival of the fittest” (which caused Darwin to classify it as a separate phenomenon).

As we know it today, it is a combination of the ability of an organism to survive and to ensure that its genes are passed into the next generation.

Sexual Selection


A fundamental inequality exists between the sexes.
If it is called “male” it has a small gamete, relative to the larger “female” gamete.
This dichotomy probably evolved many times, from ancestral lineages which contributed more equally to the process of


Female”, almost by definition, means contributing more. The metabolic cost of producing one egg is equivalent to the production of hundreds or thousands of sperm.


Since it requires far more resources to produce an egg than a sperm, are there more sperm or eggs?

Sperm! ~O ~O


The retention of eggs, or immature individuals, within the body of the female.
This causes an additional drain on resources, because she must expend extra energy carrying them around..



A mammalian parental care strategy. Only females do it.



can be split between both parents, or it can fall entirely upon one parent. In cases of uniparental care, it is much more common for the female to provide all of it (depends upon the lineage, uniparental male care is rather common in fish).

Parental Care


Some parental care. Male parental care much more common.

Universal parental care. Female uniparental care much more common than biparental care. No uniparental male care.

Bony Fish



Virtually universal parental care. Biparental care much more common than uniparental care, which can be only by female (most often), or only by male (rarely).

Common parental care. Females care mostly




A few tropical boas and pythons exhibit parental care, and the females exclusively do it

Uncommon parental care. Male parental care occurs more often than female




Biparental care is very common in this group

Extensive parental care in this group that is always by the female




Extensive parental care by females in this group. No male help



Assuming that there is this asymmetry in Reproductive Investment, male fitness depends very heavily on the ________ , and female fitness depends more upon the ______ she can amass for each reproductive effort.

Number of mates



Female fitness depends of finding the ________. Females are choosy about who they mate with.

best possible mate


The two basic mechanisms of sexual selection

Male competition

Female Choice


the process by which males compete with each other for access to females.

is selection imposed by females when choosing males as mates

Male Competition

Female Choice


establish territories on branches and logs where females are likely to be (females mate before ovipositing in woody substrate).
Males will fight to control a territory, trying to seize their opponent and throw them off the branch.

Stag Beetles


The direct fitness benefits to females when being choosy

The future fitness benefits to females

Food gifts
Nest locations
Feeding grounds

Good genes
Attractive Sons


a group of species of birds distantly related to blackbirds.
Males “display” their bright plumage to females of the species (which are drab colored)
Females mate with the males that have the most attractive plumage and most interesting displays

Birds of paradise


Widowbirds and guppies have been tested and have thus confirmed the theory of

Female Choice


Experiment: place the female of this species in a box with a “choice” between a short-tailed
give her a chance to check them out for a while
remove the barriers and see who she mates with
Result-females prefer males with longer tails



Females who mate with long-tailed males have male offspring with long tails. Tail length is heritable. Also, the preference for long tail length, and long tail length itself, are likely to be correlated. This is because the preference for long tails is most likely heritable as well.



an African species of polygynous bird that nests in open grassland.
Males have brightly colored epaulets and long tails. They display to attract female mates, flying in looping flights above the grass.
Females are drab colored and lack the long tail.



What result did the long tail widowbird experiment have?

Longer tails mean more mates, shorter tails mean fewer.

Controls had fewer mates, possibly because long tailed were getting all the mates


There were a few flaws with the study.
Males use the epaulets to signal other males to stay out of their territories. Thus, their fitness is a function of both male-male competition and female choice.

Long tailed widowbirds experiment


Also, researchers measured fitness indirectly, by counting the number of nests in the territories of males. Usually, a female will nest in the territory of a male after mating with him, but it is possible that some females moved and established nests elsewhere.

Long tailed widow birds experiment


It is possible that females prefer certain traits because they are indicators of good health and generally good alleles at loci distributed across the genome.

Good genes hypothesis


These females prefer longer tails (experiments similar to widowbird) and it is shown that long taild males have a lower parasite load. There was a genetic correlation between resistance and tail length supporting the good genes hypothesis

Barn Swallows


Female preference of exaggerated traits may
lead to evolution of extreme forms
Females who pick extreme males will have
extreme sons, who will be chosen by females.
"Sexy son" hypothesis

Runaway Selection


A process that may lead to the evolution of exaggerated characters in males-it occurs when the alleles causing increasing elaboration of a trait become coupled with alleles causing female preference for a trait.

Runaway Sexual Selection


Initially, there is genetic variation among males for some trait that females notice. Some females prefer the trait, others are neutral.
Males with the trait have the advantage, because they can mate with both types of females….and the trait spreads.

Runaway Sexual Selection


Initially, there is genetic variation among males for some trait that females notice. Some females prefer the trait, others are neutral.
Males with the trait have the advantage, because they can mate with both types of females….and the trait spreads.

Runaway sexual selection


As the preference for the trait becomes more common, the advantage to males with the trait accelerates, etc.
Ultimately, all males have the trait, and now, with female preference for the trait universal, there is selection for any more extreme value of the trait.

Runaway sexual selection


Stalk eyed flies and Irish elk are examples of

Runaway Sexual Selection


Male display fits a pre-existing sensory capability in females, related to:
Finding food
Response to predators
Communication within species

Sensory bias


A common aquarium fish. They show a great deal of sexual dimorphism, with males having a long “sword” projecting from their caudal fin.

These swords are attractive to females, and it is easy to demonstrate that females prefer males with long “swords”.

Green Swordtails (xiphorphorus helleri)


Close relatives of the xiphophorus helleri whose males lack swordtails

Platyfish (xiphophorus maculatus)


Present female platyfish with 2 alternatives.
Unaugmented males vs males with artificial “swords” attached.
Result: ?

A preference for males with swords EVEN THOUGH males in this species do not have them.


More commonly, reproductive investment is
greater for females (not always)

What is expected if male investment is higher?

Males are choosy

Females compete