ch 9 ecology
Terms in this set (53)
Good health hypothesis:
the hypothesis that an individual chooses the healthiest mates.
Traits may also provide
If a male can invest in female function while giving up only a small amount of male fitness (or vice versa), selection should favor
individuals that possess male or female reproductive function and then switch to the other.
Animals that reproduce by_______________ are typically all female.
Relatively rare in vertebrates.
A few examples exist, such as the female boa constrictor that gave birth to two litters of daughters through parthenogenesis.
a reproduction mechanism in which progeny inherit DNA from a single parent.
Plants, coral, sponges
a reproduction mechanism in which progeny inherit DNA from two parents.
individuals that descend asexually from the same parent and bear the same genotype.
Cost of meiosis:
the 50% reduction in the number of a parent's genes passed on to the next generation via sexual reproduction versus asexual production; occurs because sexual genes are haploid.
which is when an individual possesses both male and female gametes.
Individuals can contribute one set of genes to offspring via female function and one set via male function.
Costs of sexual reproduction can also be offset if
the male helps the female take care of offspring, reducing female energy costs.
Sexually reproducing organisms can lose deleterious mutations during meiosis.
Due to ___________many gametes will not contain mutations.
The fusion of two gametes with the same mutation will result in an offspring that is
homozygous recessive for that mutation; it is likely that this offspring will not be viable.
_________do not have any means of purging mutations.
Coping with environmental variation:
offspring are likely to encounter different environmental conditions than their parents did.
Offspring with genetic variation resulting from sexual reproduction have an increased probability of possessing gene combinations that will help them adapt to different conditions.
Coping with parasites and pathogens:
pathogens have much shorter generation times and larger population sizes than the host species they infect.
This allows pathogens to evolve ways around host defenses, and forces hosts to rapidly evolve new defenses.
________allows hosts to evolve at a rate that counters the rapid evolution of parasites.
P. antipodarum snails in shallow waters can be infected with trematode worms.
In shallow waters, more snails use sexual reproduction than snails in the deeper waters.
Expts. demonstrated that trematodes were better at infecting shallow water snails than deep water snails.
This demonstrates an evolutionary race between parasites and hosts.
_______are more infested with parasites
individuals that possess male and female reproductive functions at the same time.
flowers that contain both male and female flowers.
separate male and female flowers on single individual
have flowers with both male and female parts
should favor the strategy with the highest fitness.
have either male or female flowers on different individuals
Among animals, hermaphroditism should occur only among_____________ that simply shed gametes in the water.
sedentary aquatic animals
For hermaphrodites, self-fertilization (i.e., selfing) occurs when an
individual's male gametes fertilize its own female gametes.
Some species have_______________ that prevent an organism from being able to self.
Some species are able to switch between outcrossing and selfing.
When mates are available, individuals outcross.
When mates are unavailable, individuals self-fertilize; this may not produce as many viable offspring, but it is better than nothing.
When herbivores consume leaves, plants must expend energy for new tissue growth.
In response, some plants such as the orange jewelweed increase rates of self-fertilization.
In organisms with separate sexes, the sex ratio of male to female offspring is often
one to one.
Sex is often determined by inheritance of_____
sex-specific chromosomes (e.g., human females have two X chromosomes (XX); males are XY).
Environmental sex determination:
a process in which sex is determined largely by the environment; this is a type of phenotypic plasticity, where the phenotype is sex.
Temperature-dependent sex determination occurs when the sex of an individual is determined by the
temperature at which eggs develop.
Many reptile species have temperature-dependent sex determination.
For the Jacky dragon, females result if eggs are incubated at low or high temperatures; both sexes result at an intermediate temperature.
This is adaptive (e.g., males produced at intermediate temperatures have more offspring than males from low or high temperatures).
Females can influence the sex ratios of their offspring.
Females of some species can control whether X- or Y-chromosome sperm fertilize eggs.
In hymenopteran insects, females can determine the sex of offspring by deciding whether or not to fertilize eggs.
In a population with an uneven sex ratio, the rarer sex will compete with
fewer individuals for breeding; consequently, the rarer sex will experience higher fitness.
Skewed sex ratios may occur with____________ which is when competition for mates occurs in a very limited area, and only a few males are required to fertilize all of the females.
local mate competition,
the number of mates each individual has and the permanence of the relationship with those mates.
Sperm generally takes much less energy to produce than eggs.
A female's reproductive success depends on how many eggs she can produce and mate quality; a male's success depends on the number of females he can fertilize.
males mate with multiple females
and females mate with multiple males and do not create lasting social bonds; common among animals and outcrossing plants.
a single individual of one sex forms long-term social bonds with more than one individual of the opposite sex.
may evolve when males
compete for females, or when a male
can defend territory and resources.
may evolve when females
search for superior sperm or receive
material benefits from each suitor
when a social bond between a male and female persists through the period that is required for them to rear offspring.
Favored when males make important contributions in raising offspring.
Occurs in about 90% of bird species because males can offer similar care to offspring as females (e.g., incubating eggs, gathering food).
Not common in mammals because males cannot provide the same care as females (e.g., lactation).
when an individual that has a social bond with a mate also breeds with other individuals.
Females may use this strategy to obtain superior genotypes and produce offspring with better genetics.
a behavior in which one partner prevents the other partner from participating in extra-pair copulations.
Females have a limited number of eggs and should select males that
maximize her fitness
Males should compete with other males for
Natural selection for sex-specific traits that are related to reproduction; leads to a variety of differences between males and females.
the difference in the phenotype between males and females of the same species (e.g., body size, courtship behavior).
Primary sexual characteristics:
traits related to fertilization.
Female preference for male traits relate to features that improve her fitness, such as
material benefits (e.g., high-quality territory).
Secondary sexual characteristics:
traits related to differences between the sexes in terms of body size, ornaments, color, and courtship.
Good genes hypothesis:
the hypothesis that an individual chooses a mate that possesses a superior genotype.
Runaway sexual selection:
when selection for preference of a sexual trait and selection for that trait continue to reinforce each other; continues until males run out of genetic variation.
Extreme traits (e.g., peacock feathers) also burden males by requiring energy and resources, and attracting predators.