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BIOE 109 - Sex: Causes and Consequences
Terms in this set (54)
Mechanisms of reproduction are _________
What are the two features that distinguish sexual from asexual reproduction
meiosis & syngamy
What is meiosis
the process by which a diploid organism produces haploid gametes
What is syngamy
fusion of two haploid gametes to produce a diploid zygote
What does it mean by the disadvantages of sex can be high?
costs of mating
Why is there sexual reproduction?
sex creates new genotypes
The Red Queen Hypothesis
What is the Red Queen Hypothesis?
the hypothesis that organisms are constantly struggling to keep up with one another in an evolutionary race between predator and prey species
What is Mueller's ratchet?
every time this ratchet spins and we lose groups to genetic drift, that number of deleterious mutations grows and grows.
the most fit individual still has an increased load of mutations
In what way does the advantages of sex outweigh the costs?
combining beneficial mutations
generate new genotypes
faster evolution ( the red queen effect)
clearance of deleterious mutations (Mueller's ratchet)
Why then do asexual species only occur on the tips of phylogenetic trees?
asexual lineages flourish for relatively short periods of time, but typically become extinct long before their closely related sexual groups do
Total Fitness =
Viability + Fecundity + Longevity + Mating Success
What is Darwin's definition of sexual selection?
the fitness advantage that some individuals have over others of the same sex solely with respect to reproduction
Why does sexual selection occur?
differential selective pressures on males and females
unequal investment in gametes
limitations on reproduction success differ for the sexes (females limited by # of eggs and/or pregnancies) (males limited by number of females mated)
investment differences can extend past fertilization
fusion of two dissimilar gametes (big eggs, small sperm)
Asymmetrical parental care alters __________________
operation sex ration
If access to females is a limiting resource for males, but is not a limiting resources for females then
males should be competitive
females should be picky
Why should males be competitive?
compete for access to limited # of females
Why should females be picky?
big investment, more to lose from a bad choice
What are different types of mating systems?
one male pairs with one female
sexual: partners mate with each other exclusively
social: partner pair but may cheat
male mates with multiple females
females mate with multiple males
What is intrasexual selection and what are the forms of it?
alternative mating strategies
What are the results of direct fighting/combat?
can lead to weaponry
can lead to sexual dimorphism
Sperm competition drives evolution of _________
What are alternative mating strategies?
some of these smaller males, peripheral males, may breed with young females out in the water, as opposed to heading to the beach and fighting with the alpha male
Specialized structures on male genitalia to increase _________
Define sexual conflict
traits that confer a fitness benefit on one sex but cost to the other
Define intersexual selection
Why should females have preferences for certain male characters?
DIRECT BENEFITS--> benefits that affect a particular female directly: food, nest sites, etc.
INDIRECT BENEFITS --> benefits that affect the genetic quality of the female's offspring
Why do males have showy traits?
good gene hypothesis
arbitary choice (Fisher's runaway)
What is Fisher's runaway?
male traits advantageous because attractive to females
"honest" trait =
Ornaments can serve as _______
Developments of weapons can involve _________
What is parental investment?
females more likely than males to provide parental care
females have higher investment
males have uncertain paternity
OSR can vary in ______ & _______
What about the sex ratio of an individuals offspring?
all females have potential to breed
only ~10% of males get a chance
Why are sex ratios often balanced?
frequency-dependent selection (R. A. Fisher) production of each sex is favored when rare, and the rare sex has more mating opportunities
What are exception to equal sex ratio?
local mate competition
condition dependent sex allocation
List species that change sex
sequential hermaphrodites --> protandrous: begin as male, switch to female later in life
Why do some creatures change sex?
associated with change in reproductive success with increasing size
No sex change if
reproductive success increases equally with body size in both sexes
reproductive success of males increases significantly after growing to large size
reproductive success of males does not increase as rapidly with size (as it does for females)
Are unequal gamete sizes relevant for explaining adult behavior?
Yes. There are typically insufficient eggs to go around; males end up having to compete for access to them
Which of the following is likely to be a results of a skewed operational sex ratio?
Male Bighorn sheep butting heads
The extended eyes of a stalk-eyed fly
Female seahorses fighting over space in a male's brood pouch
True or False: If females compete against each other for access to males, and males choose among females for mates, then we would expect females to be brightly colored and males to be drab
The costs relevant to honest expression of male sexually selected ornaments or weapons refer to:
Metabolic or energetic resources that a male must allocate to the growth of ornaments or weapon
The inability of males to invest simultaneously in ornament production and other functions, such as defenses against parasites
The risk a male faces because ornaments slow him down, or because bright colors make hime more conspicuous to predators
The fact that time spent displaying to females is time that a male cannot spend searching for food, so the longer he displays, the longer he depletes his stored energy reserves and compromises his future survival probability
In the context of sexual selection, antagonistic coevolution refers to
The arms race that can results as males and females compete for control over fertilization
The process of "runaway" sexual selection is limited when:
The cost to survival outweighs the benefit to mating success
According to Tivers & Willard's hypothesis regarding condition-dependent sex allocation, in a polygynous species, where females invest heavily in producing and caring for their young- A mother in poor condition should produce mostly
Why would a mother in a polygynous species in poor condition produce mostly daughters
females in poor condition should produce daughters because her daughters will have reproductive success no matter what in a polygynous mating system.
if a female wants her sons to have high reproductive success, then her sons need to be in the BEST possible condition so she should only make sons when she is in very good condition herself.
In parasitoid wasps, local mate-competition resulting in extreme female-biased sex ratios
avoids the cost of producing sons
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Chapter 11 - Sex
Evolution Chapter 11
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