Behavioral Ecology: Sexual Selection Flashcards
Define parthenogenesis.
a form of reproduction in which an egg can develop into an embryo without being fertilized by sperm, meaning females can reproduce on their own
What are the disadvantages of sexual reproduction?
- twofold cost of sex - asexual lineages can grow more rapidly because all offspring can reproduce offspring
- search cost - male and females must invest time, energy, and risk of predation to find a mate
- reduced relatedness - meiosis generates haploid gametes, meaning sexually reproducing organisms only pass half of their alleles to offspring
- risk of sexually transmitted infections
What are the advantages of sexual reproduction?
- combining beneficial mutations - two sexually reproducing individuals can bring separate beneficial mutations together in an individual offspring, while beneficial mutations would have to arise spontaneously in the same genome in asexual reproduction
- generation of novel genotypes - recombination during meiosis allows for paired chromosomes to crossover and create gametes with unique combinations of alleles
- faster evolution - the red queen effect - offspring of sexual parents are more genetically variable, which speeds evolution response to selection
- clearance of deleterious mutations - recombination during meiosis can allow for exclusion of harmful mutations - muller’s ratchet - asexual populations accumulate harmful mutations until driven extinct
Define ansiogamy.
a form of sexual reproduction wherein males and females produce cells or gametes of different sizes (sperm is smaller and more numerous, while eggs are larger and often not as numerous); results in differential investment in reproduction
What are male and female anisogamous organisms limited by?
females: fecundity - the physiological potential to bear children
males: the number of mates they can obtain
Why is male parental care less common in anisogamous organisms?
females have certain maternity, but males have uncertain paternity
What is the operational sex ratio? Describe the operational sex ratio in anisogamous organisms.
ratio of males to females capable of reproducing at a given time; male-biased operational sex ratio because females investing in parental care cannot reproduce during gestation time and afterbirth care
Define intrasexual and intersexual selection in anisogamous organisms.
intrasexual selection: male-male competition
intersexual selection: female choice
What is the relationship between operational sex ratio and sexual selection in anisogamous organisms? Provide an example.
male-biased operation sex ratio leads to sexual selection favoring males that can outcompete other males for access to females
high variance in male reproductive success leads to intense sexual selection (i.e. elephant seals)
What is sexual dimorphism and how is it observed in anisogamous populations? Provide examples.
sexes of the same species exhibit different morphological characteristics
ornaments - beneficial for intersexual selection; attractive traits that increase mating success (i.e. toad croak)
armaments - beneficial for intrasexual selection; weaponry used to outcompete other individuals (i.e. deer antlers)
What are the direct and indirect benefits of female choice?
direct benefits - food, nesting sites, protection
indirect benefits - affect the genetic quality of the female’s offspring
good genes: attractive male ornaments may signal underlying genetic quality such as efficient metabolism, body condition, or resistance to parasites and disease (i.e. bright plumage suggests that the male is good at foraging as they are gaining healthy carotenoids from their environment)
arbitrary choice: fisher’s positive feedback cycle - certain male traits are advantageous not because they indicate good quality, but simply because they are attractive to females (i.e. peacock feathers)
Define cryptic female choice.
after multiple males mate with the female, the female can use physical or chemical mechanisms to control a male’s success at fertilization (i.e. female flies favor male flies that tap during mating)
Define the types of mating systems. Provide examples of each.
- monogamy - one male pairs with one female (i.e. bald eagles)
social monogamy - partners pair with one another but may have sex with other individuals (i.e. elephant shrews) - polygyny - males mate with multiple females (i.e. lions); low cost for sperm allows males to fertilize many females
- polyandry - females mate with multiple males (i.e. lily-trotter birds); females receive access to higher quality genes and receive gifts from potential mates
