chapter 6(9) Flashcards
what is sexual dimorphism?
its when traits differ b/w male and females of the same species
how does sexual dimorphism relate to evolutionary theory and why does this relationship exist?
traits created by sexual dimorphism in males tend to violate evolutionary theory because they tend to waste energy and reduce survival
this is because these traits don’t happen for survival but to increases successful sexual reproduction
what is sexual selection?
its selection which increases individual’s chances of mating and is a subset of natural selection
when will sexual selection happen what does it involve?
it often involves a tradeoff w/ survival
sexually selected traits will evolve if they can more than offset male’s diminished survival w/ increased reproduction success
what is female choosiness and how does it effect males? how might it be different from other types of sexual selection?
female choosiness creates a form of indirect competition
males will undergo sexual selection to appear more appealing to females at the expense of wasting energy and becoming more vulnerable to predators
in contrast to male-male competition winner is chosen by female
what is dire competition b/w males, male-male competition, law of battle and how does this process affect pop genetic distribution?
traits that promote victory in fights against other males will be favored, maintaining these traits often cost large amounts of energy however this is the tradeoff for more successful sexual reproduction
these situations often crease large variance in mating success as dominant males will often create harems and so majority of males will fail to sexually reproduce
what is post-mating competition?
it happens in order to prevent females from getting fertilized by other males
what does parthenogenetically reproducing mean?
it means producing eggs that don’t need to be fertilized
what is the theoretic outcome of parthenogenetic reproduction and what is it called?
its called the twofold cost of sex, under natural selection parthenogenesis genes shld theoretically spread quickly and eliminate sexual reproduction
this is because if female could produce parthengenetically and sexually then females who did that wld produce only daughters while females who mated w/ males to reproduce wld produce half sons and half daughters
the proportion of women in the population wld rise above half and the pool of females who parthengenetically produce would increase
eventually males wld become superfluous and die off as the parthenogenesis gene wld have outcompeted the sexual reproduction gene as each generation the asexual gene would have produced twice as many copies as the sexual gene
why might most earth species reproduce sexually despite the advantages of asexual reproduction?
the random shuffling of genes during sexual reproduction which brings together favorable genes to create new gene combos might be better for promoting evolution which deal w/ environmental change
sex cld also purge bad genes through recombining all the bad genes into one individual as a scapegoat
theory shows two sexes mating is the most stable/robust strategy and will always beat 3+ sexes mating system
why are females generally the choosy one when it comes to mating?
males can produce many sperm and reproduction is only limited by females present
females produce eggs which are expensive and limited number wise and mating many times over a short period of time rarely increases offspring number
in 90% of mammal species female must also provide parental care
due to the number of offspring producible by each sex males have much less to lose through mating w/ a weak/sickly female than females w/ weak/sickly males
this is why in general it is the males that must compete to be chosen by the females
when is sexual dimorphism not based on sexual selection?
sometimes males and females specialize in diff foods
ex. female hawks are larger since they catch larger prey
sometimes females/males have diff roles they have to fulfill
ex. female fruit flies are larger to better protect agges
when is monogamy favoured?
happens when males gain more form rearing offsprings w/ female than mating w/ more females
ex. in birds one parent will forage while other incubates eggs
why do many monogamous species have sexual dimorphism?
they are socially monogamous but not actually monogamous
what does being socially monogamous mean?
spending adult lives socially bonded, sharing parental care, defending territory
but during mating seasons females will often mate w/ other males and males will seek other females as well
similar to non-socially monogamous species males will have a higher variance of success compared to females
