Lecture 7: Reproductive Strategies Flashcards
What are the major differences between sexual and asexual reproduction
SEXUAL:
1. offspring inherit DNA from 2 parents
- Gametes are produced by meiosis
- Results in new, genetically distinct organisms
ASEXUAL:
- offspring inherit DNA from one parent
- Gametes produced by mitosis
- Results in offspring that are genetically identical to one another and parents
What are the 3 kinds of asexual reproduction?
- parthenogenesis
- fragmentation
- budding
What is a disadvantage of sexual reproduction?
sexually reproducing females will only pass on HALF the number of chromosomes as asexually reproducing females for the same number of offspring because they must mate with a male and the male passes on half his genetic material too
What potential evolutionary problem is associated with asexual reproduction?
It results in minimal genetic variation between parents and offspring because the offspring receive 100% of the parent’s DNA
What is the only source of genetic diversity for asexually reproducing organisms? Why is this problematic?
Mutations
It is rare for mutations to be beneficial and if a mutation arises and is passed on, that mutation will continue to circulate in the population because 100% of the genetic material is passed on
How does sexual reproduction increase genetic variation?
by forming new combinations of alleles in 3 ways:
- independent assortment
- crossing over/recombination
- random fertilization
What are the 3 major benefits of sexual reproduction?
- elimination of deleterious mutations
- facilitates adaption to changing environments
- speeds up the evolutionary defence against parasites and pathogens
How does sexual reproduction eliminate deleterious mutations?
because of the recombination of alleles that occurs and because only 50% of alleles are passed on from one parent to offsprings means that offspring will be produced without the mutation
if offspring with the recessive mutation are produced, they will become more vulnerable to natural selection and the mutated allele will become less common within the population over time
How does sexual reproduction help facilitate adaptations to changing environments?
genetic variation that results from sexual reproduction improves the chances of offspring survival in environments that differ from the natal environment
it is possible the offspring will have to move from their natal environment or that their environment will change and if the offspring were not genetically distinct from their parents, they would not be well adapted to a change and therefore less likely to survive
How does sexual reproduction speed up the evolution of defence against pathogens?
genetic variation allows host populations to evolve new defence against p/p to purge from their system
- the genetic defence will increase within the host population as it is beneficial
- while the host population is building defence, the p/p populations have the time to adapt and respond
- new, uncommon host defence will arise and be favoured
- continues like this
What is the name of the hypothesis that describes the evolutionary ‘arms race’ between pathogens and parasites and hosts?
The red queen hypothesis
Define gonochoristic and give examples
Separate sex organs on separate animal individuals
ex. humans, salmon, most animals
Define dioecious and give examples
separate sex organs on separate plant individuals
ex. white campion wildflower
T or F: dioecious plants are more common than hermaphroditic plants
FALSE. Dioecious plants are very uncommon
Define monoecious and give examples
Both male and female flowers exist on individual plants
(ie, both sexes on one individual)
ex. hazelnut
Define hermaphrodite plants
Both male and female organs exist on one flower
ex. geraniums
Define hermaphrodite animals
Both male and female reproductive organs exist on one individual
ex. worms
Explain how hermaphrodites can counter-balance the cost of meiosis
By contributing both male and female gametes to reproduction
Hermaphrodites can reproduce as both a female (pass on half of chromosomes) and can reproduce again as a male (pass on the other half of chromosomes) they overcome the cost of meiosis
What are the 2 types of hermaphrodites?
- simultaneous hermaphrodites
2. sequential hermaphrodites
Define simultaneous hermaphrodites and give an example
individuals that have both male and female reproductive organs mature at the same time
ex. garden snails
What is a potential disadvantage of being a simultaneous hermaphroditic plant?
there is the possibility of self-fertilization or ‘selfing’
What 3 ways do simultaneous hermaphroditic plants avoid selfing?
- physical or temporal separation of male/female organs
- genetic self-incompatibility
- mixed mating systems
What is the purpose of having mechanisms in place to avoid selfing?
to reduce the chance of reducing genetic variation
Define sequential hermaphrodites and give an example
individuals that change sex during their lifetime
ex. blue-headed wrasse, Jack-in-the-Pulpit
T or F: selfing is possible for sequential hermaphrodites
FALSE. Outcrossing is mandatory for reproduction
Explain how blue-headed wrasse are an example of sequential hermaphrodites
If the dominant male in the population dies, the largest female will transition to a male to ensure there is always a male for reproduction
Explain how Jack-in-the-Pulpits are an example of sequential hermaphrodites
individuals can produce male, female, or non-reproductive stems in different years depending on the environmental conditions
What 2 things can determine the sex of offspring?
- genetic inheritance
2. environmental conditions
How does genetic inheritance determine the sex of offspring?
Through either
the combination of sex chromosomes (ex., XY, XX) or
ploidy (haplodiploidy)
How do environmental conditions determine the sex of offspring?
Conditions in physical or social environment can determine sexual development
ex. temperature can have a big impact on sex determination of reptile offspring
ex. sex ratio of a population can determine it
What is the FUNDAMENTAL difference between the male and female sex?
Females produce few, large, energetically expensive gametes (eggs)
Males produce numerous, small, energetically cheap gametes (sperm)
What is a mating system?
the pattern of mate acquisition by both sexes
What are the 3 major types of mating systems?
- monogamy
- polygamy
- promiscuity
Define monogamy and give an example
A mating system in which one male and one female form a pair-bond either seasonally or for life
ex. Emperor penguins, blue-footed boobies
T or F: For a mating system to be considered monogamous, the pair must be bonded for life
FALSE. they can be bonded for just a reproductive season and make a new bond next season
What level of parental investment is involved in a monogamous mating system?
Typically offspring require care from BOTH parents
What kind of morphology will the male and female parent have if they mate monogamously?
Typically they will look very similar to one another
Define polygamy and list the two kinds
Polygamy is a mating system where an individual from one sex forms lasting pair bonds with multiple members of the opposite sex
- polygyny
- polyandry
Define polygyny and give an example
A polygamous mating system where one male forms pair-bonds with multiple females
ex. elephant seals, red-winged blackbirds
What level of parental investment is involved in a polygynous mating system? why?
Typically the female provides the parental care
they have already invested a lot of energy into producing an egg and offspring, so they have little energy left to allocate towards reproducing with many partners
Males produce energetically cheap gametes and therefore can use their energy to reproduce with many partners
What kind of morphology will the male and female parent have in polygyny systems?
Sexual dimorphism exists in polygynous relationships and usually the males are larger, armoured or decorative
Define sexual dimorphism and give examples
Males and females have different secondary sexual characteristics that are not essential to reproduction
ex. Males may have antlers or be more brightly coloured
T or F: males and females always have different primary sexual characteristics (sex organs and gametes)
True
What type of mating system is sexual dimorphism most common?
in polygamous systems because one sex usually has to attract the other
Define polyandry and give examples
A polygamous mating system where one female forms pair-bonds with multiple males
ex. seahorses, jacana
What level of parental investment is involved in a polyandry mating system? why?
Typically males provide most or all of the parental care
What kind of morphology will the male and female parent have in polyandry systems?
Sexual dimorphism exists and typically it is the females that are larger or more decorative
Define promiscuity and give an example
A mating system where ALL SEXES have multiple sexual partners and do not form lasting pair bonds
ex. Bonobos
T or F: Polygamy is the same as promiscuity
FALSE
The biggest difference is that in polygamy bonds are formed
In promiscuity no bonds are formed and individuals mate with whomever
Define sexual selection
Natural selection for SEX SPECIFIC TRAITS that are related to reproduction
It is the mechanism that drives the evolution of sexual dimorphism
What are the 3 conditions for sexual selection to occur?
Sexual selection occurs for a single sex within a species
- individuals within the sex vary in phenotype
- the phenotypic variation is heritable
- the phenotypic variation results in differences in reproductive success (ie., the number of mates and/or offspring)
What happens if all 3 characteristics of sexual selection are met?
characteristics that affect REPRODUCTIVE SUCCESS will evolve by sexual selection
ie., characteristics that help males or females attract mates can evolve by sexual selection
How are the eyespots on the tail feathers of male peacocks a good example of how sexual selection works?
- Males vary in the number of eyespots on their tails
- the number of eyespots on tail feathers is heritable
- females prefer males with more eyespots = males with more have more mates and more offspring
therefore, the number of eyespots on tail feathers of male peacocks is subject to evolution by sexual selection
What are the 2 major types of sexual selection?
- intrasexual selection
2. intersexual selection
Define intrasexual selection and give an example
males fight with each other for access to females so
- sexually selected traits that evolve are related to direct competition and
- sexual selection will favour traits that benefit males in conflict
ex. male elk use their antlers to battle one another for the females
Define intersexual selection (aka female choice) and give an example
Females select males with preferred traits
- sexually selected traits that evolve are related to the decoration and courtship behaviours of males
- sexual selection will favour traits that make males more decorative
ex. birds of paradise, guppies
What are the 2 hypotheses of the evolution of female mate choice?
- Good genes hypothesis
2. Sexy son hypothesis
Describe the good genes hypothesis
States that males must be of good genetic quality in order to have traits that attract and impress females
Includes the handicap principle
Describe the handicap principle and how it relates to the good genes hypothesis
the principle states that risky or energetically expensive traits handicap males so they must have GOOD GENES/be genetically superior in order to overcome the difficulty
Describe the sexy sons hypothesis
States that preferred traits have aesthetic value to females so females will choose males with well developed sexually selected traits so their male offspring will have the same traits and therefore be more likely to find mates and pass on the genes
What study was used to explore the sexy sons hypothesis?
Burley and Symanski glued artificial crests of varying colours onto male birds that do not have crests and found significant data supporting that females chose to mate with males with white crests
Describe runaway sexual selection
When the traits for female preference and the traits that make males preferred reinforce each other
Ie., if the alleles that make males preferable to females show up in males AND the traits that make the ‘sexy’ trait preferable shows up in the females, both will increase in the population and cause strong directional selection causing extreme phenotypes (ex. the tails of peacocks)
Will runaway sexual selection go on forever? Why/Why not?
No, there is usually a trade-off between sexual selection and natural selection
Eventually exaggerated traits can lead to increased mortality because the extreme trait will end up handicapping the male too much that it will become too vulnerable to predation
And, the population will eventually run out of genetic variation for that trait (ex. the male widowbirds had little variation in tail length)
