Sexes Flashcards
isogamy (2)
- different mating types (+/-) have same sized gametes
- most unicellular organisms
anisogamy (2)
- females and males with different sized gametes
- most multicellular organisms
evolution of female anisogamy
- females evolved to have large gametes that provide resources for development
evolution of male anisogamy (2)
- competition to fertilize large gametes favoured production of many small gametes
- males who invest less energy and produce more offspring have better chance of fertilizing large egg
sexually antagonistic selection
- selection is pulling in 2 different directions according to male and female gametes (big and small)
female gametes (2)
- few large gametes
- females invest more in each offspring than do males
male gametes (2)
- many small gametes
- males invest less in each offspring than females do
is it better to be female/male?
- not more beneficial to be either: both have different limitations
cascading effects of anisogamy
- sexual selection
- sexual conflict
do males/females have greater variance in reproduction success (2)
- males have greater variance in reproductive success than females
- females are limited by the number of offspring they can invest in while males can essentially have unlimited offspring due to smaller investment
does mating more increase offspring production in males/females (2)
- males: mating with more females increase the number of offspring they produce; beneficial for men to reproduce more often
- females: mating with more males does not increase offspring number; not beneficial for females to have more mates
mating system
- monogamous or polygynous
- intensity of sexual selection and conflict with depend on mating system
monogamous systems effect on conflict
- less conflict
polygynous systems effect on conflict
- greater conflict
“choosy parent” (2)
- determined by the sex whose typical parental investment is greater
- this sex is the limiting resource for the opposite sex and becomes more choosy of her mating partner
sex role reversal (2)
- seahorse or giant water bugs
- here, females compete for males and males are choosy
sexual selection factors
- female choice
- male-male competition
cause of sexual selection
- females are limited by the number of offspring they can produce
- increases with monogamous mating systems
cause of sexual conflict/male-male competition
- males are limited by the number of females willing to mate with them
- increases with polygynous mating systems
sexual selection
- different selective force from NS and goes against NS as it tends to decrease organism fitness
- responsible for evolution of exaggerated male traits
components of male-male competition (3)
- pre-copulatory
- post-copulatory
- post-fertilization
male-male competition: pre-copulatory mechanisms (2)
- territorial defence (guarding areas where females emerge)
- combat
male-male competition: post-copulatory mechanisms (2)
- mate guarding: non contact or contact guarding to avoid sperm competition
- sperm competition: 2nd male mate can displace sperm of 1st male mate
male-male competition: post-fertilization mechanisms
- infanticide: males kill infants so females will be able to mate again sooner
inter-organism sexual selection forces
- the essence of maleness and femaleness
- male-male competition
intra-organism sexual selection forces
- males make themselves more attractive to appeal to female choice
“sexy son” or “good looks” hypothesis (2)
- females choose the best looking males so the father’s sons will also be attractive and preferred as mates
- trait continues to evolve until it becomes so exaggerated that it hinders male survival
sexy son hypothesis
- assumptions (2)
- exaggerated trait must be heritable
- female preference must be open ended
sexy son hypothesis
- prediction
- exaggerated trait and female preference should become associated
“good genes” hypothesis
- females use exaggerated traits to assess male genetic quality
“good genes” hypothesis
- assumption
- there is an association between “good genes”/fitness and exaggerated traits
“good genes” hypothesis
- predictions (2)
- exaggerated trait must be costly (to indicate that its other genes are truly good)
- fitness must be heritable to both daughters and sons
balance between NS and sexual selection (3)
- observed male traits are usually above optimum tale length (is NS was acting alone)
- initially: good genes hypothesis takes fitness to peak of curve, then sexy son hypothesis pushes fitness to lower fitness
- equilibrium observed trait present at point where NS and SS are equal
sexual selection in humans: female choice (2)
- female features may be shaped by male mate choice instead
- 2D mating environment disfavours female choice
sexual selection in humans: male-male competition (2)
- 2D mating environment favours contest competition
- male traits appear to increase appearance of dominance over other men rather than being perceived as more attractive by other women
what items do sexes often disagree on (4)
- multiple matings
- mating decisions
- offspring care
- infanticide
description of sexes disagreement: multiple matings
- unlike males, females tend to gain little by mating more
description of sexes disagreement: mating decisions
- females would lose more by mating with low quality males
description of sexes disagreement: offspring care
- both sexes would benefit by leaving the offspring in care of the other
description of sexes disagreement: infanticide
- when it occurs, females loose their reproductive investment
conflict between sexes: concealed ovulation (3)
- absence of visual signs of ovulation
- some species ovulation is advertised during short estrous periods while others ovulation is hidden
- females are sexually receptive at times when conception is not possible, but males are not, leading to non-reproductive mating events
concealed ovulation: father-at-home hypothesis (3)
- males do not know when other females are wandering and are discouraged from wandering
- stay home to ensure fertilization of partner, guard her from other males
- result: father stays home to help with care of offspring he can be reasonably sure are his
concealed ovulation: father-at-home hypothesis
- mating system encouraged
- monogamous mating system
concealed ovulation: many-fathers hypothesis (2)
- by mating opportunistically, a female lower the probability of her offspring being killed by males who are unsure of their paternity
- confuses paternity
concealed ovulation: many-fathers hypothesis
- assumed/encouraged mating system
- undoes monogamy and assumed polygamy
- expected to have evolved in multi-male troops or harems
concealed ovulation: many-fathers hypothesis
- assumed/encouraged mating system
- undoes monogamy and assumed polygamy
- expected to have evolved in multi-male troops or harems
concealed ovulation: comparative study results (3)
- slight ovulatory signs and multi-male mating systems ancestral to anthropoid primates
- ovulatory signs have lost 0-1 times under monogamy and 8-11 times un multi-male/harem systems
- monogamy evolved independently 7 times, always in lineages with no or only slight ovulatory signs and never in lineages with bold advertisement
concealed ovulation: comparative study meaning (2)
- loss of ovulatory signs in multi-male and harem systems is consistent with many-fathers hypothesis
- concealed ovulation and monogamy are associated, but monogamy seems to have been facilitated by concealed ovulations (concealed ovulation -> monogamy)
genomic imprinting (2)
- epigenetic inactivation of one of the two alleles at a locus depending on parent-of-origin
- parent-specific pattern of methylation established during gametogenesis is inherited, but does not involve changes to underlying DNA sequence
genomic imprinting results
- haploid expression of some genes, thus potentially unmasking deleterious recessive alleles and lowering fitness
where is genomic imprinting seen (3)
- mammals, seed plants, some insects
imprinted genes
- usually involved in placentation and transfer of nutrients between mother and offspring
meaning of patterns of imprinting
may reflect conflicts between mother and father, and between mother and offspring
- father activates genes that extract more resources from the mother
- mother deactivates genes that will allow extraction of resources to counter father’s activated genes
result of patterns of imprinting
- parental tug-of-war in the developing embryo
Angelman syndrome (3)
- imprinting error due to excess of paternal imprinting
- child’s signals tend to stimulate maternal investment: prolonged suckling, frequent crying, hyper-active/sleepless
- high rates of autism
Prader-Willi syndrome (3)
- imprinting error due to excess of maternal imprinting
- child’s signals tend to decrease maternal investment: poor suckling, weak crying, inactive/sleepy
- high rates of psychosis in adults
why has genomic imprinting evolved
- hypotheses (3)
non-mutually exclusive hypotheses:
- ovarian-time-bomb hypothesis
- mechanism of post-zygotic isolation
- parent-conflict hypothesis
genomic imprinting: ovarian-time-bomb hypothesis
- GI evolved to protect female mammals from spontaneous development of unfertilized eggs, which may lead to cancert
genomic imprinting: mechanism for post-zygotic isolation (2)
- diverging imprinting patterns across closely related species may serve to prevent development of inter-specific hybrids
- patterns are species specific so that mating between different species will cause zygote to fail and hybrid to not be produced
genomic imprinting: parent-conflict hypothesis
- GI is the result of conflict between maternal and paternal genes in species with multiple paternity
genomic imprinting: parent-conflict hypothesis
- paternally expressed genes (2)
- maximize growth of fetus by maximizing extraction of resources from the mother
- attempts to enhance offspring and paternal fitness
genomic imprinting: parent-conflict hypothesis
- maternally expressed genes (2)
- tend to conserve resources to divide them among more offspring
- attempts to maximize lifetime reproductive success of the mother and decrease that of the individual father
genomic imprinting
- mating system (2)
- strong in polygynous species where fathers want more resources for own offspring
- weak in monogamous species where fathers want equal investment to each offspring
genomic imprinting: prenatal parental investment and mating system (2)
- more investment in polygynous systems reflect war between mother and offspring (more extraction of resources due to paternal imprinting)
- less investment in monogamous systems as imprinting is weaker
