Unit 2: Reproductive Strategies Flashcards
3 drivers of natural selection
- variation
- consequences
- heritability
australian kalutas reproduction
- males have a 2 week window to successfully breed
- the stress of finding a mate and completing copulations kills most males before the breeding window is over
while reproduction is an evolutionary imperative, benefits to sexual reproduction
outweigh the costs
why is sex so popular among multicellular organsims?
- sex evolves when selection changes over time (red queen hypothesis)
- sex evolves when selection changes over space (migration)
- sex evolves when organisms are less adapted to their environment
- sex evolves when populations are finite
Male bedbugs use [–] to deliver sperm
- traumatic insemination, piercing the female’s abdomen to deliver sperm
- this decreases female longevity and the number of eggs they produce
under certain assumptions, the “cost of meiosis” should
drive populations toward asexual reproduction
John Maynard Smith’s views
- a female reproductive mode does not affect the number of offspring she can make
- a female’s reproductive mode does not affect the probability that her offspring will survive
parthenogenesis
allows for reproduction without the risks of sex
Whiptail Lizards
- formly sexual species -> rediscovered the ability to reproduce asexually
- rich genetic diversity
- stable environment
- taking turns as “male” to stimulate egg production
- also komodo dragons, hammerhead sharks, turkey, snakes rediscovered the ability to reproduce asexually
Sexually reproducing populations have
greater capacity to overcome challenges through genetic recombination
sexually reproducing roundworms had better survival when exposed to
bacterial parasites
what is the pattern in small populations for sexual reproduction
- not enough genetic diversity
- likely to die within 20 generations
In animals, sex determination may be
environmentally or socially determined
Blue headed wrasse: largest female changes to male if
dominant male is lost
heat overrides genes to make bearded dragon embryos to
change sex
Like birds, female bearded dragons are [–], males are [–]
Like birds, female bearded dragons are ZW, males are ZZ
hermaphrodite
- both sexes found in a single body
- have flowers with both male and female parts
- “perfect” flowers
- allows for auto-pollination
dimorphism
both sexes found in a separate body
monoecious plants
- 1 home
- have separate male and female flowers on a single individual
dioecious plants
have either male or female flowers on different individuals
plants may adopt [–] strategies to meet environmental challenges
mixed strategies
some plants change [–] as they mature (some fish as well)
sexes
how do spider plants adopt mixed strategies to meet environmental challenges?
- they grow plantlets for asexual reproduction
- they grow white flowers for sexual reproduction
What is the offspring sex ratio
- 3 F : 3M -> 18 grandoffspring
- 5 F : 1 M -> 30 grandoffspring
is there an advantage to having sons rather than daughters?
Since 1 son can fertilize eggs of many females within the population, there is less advantage to have more sons
Sex ratio may be [–] by factors that are [–] or [–]
Sex ratio may be skewed by factors that are pre-fertilization or post-fertilization
Dear Example + Sex ratio
Yearling females have
fewer energy resources and produce fewer males
(sons are larger at birth + require more milk)
Dear Example + Sex ratio
Male fetuses are
aborted more often during gestation by yearling mothers
(aborted more in colder environments)
Suppose the grimalgost, reproduces by laying eggs once each generation. A female grimalgost typically lays 2 eggs. If a population is composed of 5 females and 2 males and we assume that a male can breed with more than one female, how many copies of genes, on average do each male and female contribute to the next generation?
Total # of eggs = 5 F x 2 eggs = 10 eggs
Average female fitness = 10 female gene copies / 5 F = 2 gene copies per female
Average male fitness = 10 male gene copies / 2 M = 5 gene copies per male
males have greater fitness
the evolution and maintenance of sex ratios is the result of
frequency-depedent selection
frequency-dependent selection
when a rare phenotype (sex)is favored by natural selection, an individual’s reproductive fitness will increase by having offspring with that phenotype as they will be more desireable mates
how do calculate reproductive success?
female RS = total eggs / breeding F
male RS = total eggs /breeding M
A “mating system” describes
the number and length of associations between males and females
monogamy
1 F : 1 M
polygamy
A mating system in which one male mates with multiple females, or one female mates with multiple males, or both males and females have multiple mates.
polyandry
type of polygamy
multiple M : 1 F
polygyny
type of polygamy
multiple females : 1 M
promiscuity
no specific relationship/ no pair bonds
multiple males : multiple females
Monogamy is advantageous when
- two parents are required to raise offspring
- however, it may encourage cheating (extra-pair copopulations)
in monogamous mating females
choose males for their potential as provider (territory) and then other males for their genetic contributions (attractiveness)
Sexual dimorphism may promote
runaway (directional) selection
in peacocks, males with more eye spots =
more attractive = more offspring
Darwin predicted that selection for sexual attractiveness would be constrained by
- survival needs
- ex) moving guppies from low to high predator environment changed morphology and life history (age, size)
“reaction norm”
describes the sensistivity of an organim’s phenotype to environmental changes
Selection for traits that maximize reproduction is
sexual selection
sexual selection leads to
sexual dimorphism
sexual dimorphism
two sexes have different shapes
what is the difference between interspecific, intraspecific, and intrasexual selection?
- interspecific: between different species
- intraspecific: within species
- intrasexual: males being selected for or against the males in that species
musth
- steroid rage (males)
- can overcome a larger stronger male
maximizing reproductive success may require trade-offs between for
those with more to lose (usually females)
in polygynous populations, female reproductive success can vary depending on
territory quality
female choice
balances male attractiveness and territory quality to maximize fitness
The polygyny threshold model
identifies the trade-off between male attractiveness and territory quality
In red-winged blackbirds, females
choose a territory and then a male, leading to extra pair copopulations (EPC)
Runaway selection explains the evolution of female choice by
- female choice of longer tails leads to extreme phenotypes
- artificially lengthened tails garner more mates
Pheasant hens prefer cocks with bigger spurs because
males with desirable MHC also have longer spurs
MHC
- major histocompatibility complex
- tissue matching
- genetic relatedness
The good health hypothesis
assumes that appearance is an indicator of health
the healthy son hypothesis
morphed to oxidative stress
“Good genes” models assume
- underlying physiological health
- you don’t produce healthy feathers if metaboloism is stressed
