evolution exam 2 - sexual selection

what are the two types of sexual selection?

1. male-male competition

2. female mate choice

what is another term for male-male competition?

intra-sexual selection

what is another term for female mate choice?

inter-sexual selection

what do male-male selection and female mate choice both result in?

sexual dimorphism, which refers to the observable differences in physical and behavioral traits between males and females of the same species

what are the 3 things that determine males’ reproductive success?

1. the number of mates they have

2. the fecundity of their mates

3. the proportion of mate’s eggs that get fertilized

how do reproductive strategies differ between females and males?

females are often a limiting resource for males

• this is because women hold the young, so it is very costly to make the wrong choice in mate

what is sexual selection by competition?

when a male tries to mate as much as possible, competition will ensue

what does competition lead to?

more extreme phenotypes, as there is selection for some trait that has mutated to be more extreme as a result of competition

• prettier peacock tails, larger moose antlers, beetle jaws

what are the 5 ways in which competition works on sexual selection?

• male contest [intrasexual selection]

• defense of mating territories

• prohibiting future female matings

• sperm competition

• traits signaling power to deter competitiors

what are some examples of sperm competition?

some ants scoop out sperm from last male to prevent previous mates from fertilizing eggs.

production of sperm plugs in mice prevent other males from mating

what are the 2 reasons why females have a preference for specific male traits?

1. direct benefits of choice → selective pressure for females to recognize superior males [being picky in their selection]

2. sensory bias → inherent tendency to react to exaggerated stimuli [larger traits such as spots or brighter colors will catch a female’s eye]

why is direct benefits an important part of female mate choice selection?

• preferred male trait indicates high viability, which will be passed to offspring

• trait may be a condition-dependent indicator of fitness

  • can be thought of as honest signals

what are honest signals?

a form of communication where a signal reliably conveys information about the signaler's traits or intentions

• ex: a male that has a trait that a female recognizes as having the ability to the increase the fitness of her offspring has an “honest signal”

what does runaway sexual selection entail?

males display of character and female preference reinforce each other so that they both evolve to be more extreme

• loci of female choice and loci of male trait expression are in linkage disequilibrium [will non-randomly occur together often]

does female mate choice increase survival of offspring?

no, female mate choice does not increase the survival of offspring. however, it does increase the mating success of sons

• ex: a really long tail on a bird is a costly trait because it will attract attention from predators, lowering survival rates → if this is sexually selected for by the female, then it increases the probability of mating

what is sexual conflict?

conflict of evolutionary interests between males and females

• females evolve to resist mating

• males evolve stimuli to overcome female resistance

what are examples of sexual conflict?

• penis spines that stimulate ovulation and lock the two organisms together

• female ducks evolved a corkscrew shaped vaginal canal, but then male ducks evolved a corkscrew penis

what is the paradox of sex?

sex is complicated, costly, and dangerous

• consumes a lot of time and energy

• risk of death

why do asexual lineages theoretically have higher growth rates?

independent assortment destroys adaptive combinations of alleles

what is independent assortment?

a principle in genetics stating that alleles of different genes assort independently of one another during meiosis, meaning the inheritance of one trait doesn't influence the inheritance of another.

why are the two reasons why sex evolved?

1. adaptation under directional selection → sexual populations can respond to selection more quickly than asexual populations

2. adaptation to varying environments → red queen hypothesis, parasite co-evolution theory

3. deleterious mutations hypothesis [muller’s ratchet]

what is the red queen hypothesis?

states that organisms have to constantly adapt to keep up with changing environmental conditions

• this is one of the reasons why sex evolved, as asexual populations cannot adapt that quickly

what is the parasite co-evolution hypothesis?

if hosts are evolving resistance, parasites have to evolve to overcome that

what is mueller’s ratchet [deleterious mutations hypothesis]?

asexual lineages accumulate so many deleterious mutations due to a lack of recombination that they are no longer fit to new environments, or even their own, if that environment changes

what is recombination?

production of different combinations of alleles that selection can act on

why did separate sexes evolve?

evolution of separate sexes increases the probability of genetically diverse gametes uniting

what does dioecious mean?

separate sexes

• in the case of aspens, one has anthers and the other has stigmas → they form clones via vegetative propagation

what are some examples of recent evolution of asexual reproduction?

most asexual lineages of eukaryotes have arisen quite recently from sexual ancestors

• apomixis in plants → clonal reproduction via seeds

• parthenogenesis in lizards → offspring develop from an unfertilized egg, without the need for a male gamete [females still need stimulation, so they stimulate each other]