Ch 3 Sexual Selection Flashcards
Sexual selection
Survival of the sexiest. Evolutionary pressure to find a mate and thus reproduce and pass on genes. Two types intersexual and intrasexual
Intersexual selection
Members of one sex, trying to impress members of the other sex. Usually female choice.
Intrasexual selection
Competing with members of same sex to gain access to members of opposite sex.
Runaway selection
One theory of sexual selection where a trait, selected for by females (usually) demonstrates fitness. Ex “healthy plumage.” Then brighter, larger keeps being selected for until it is exaggerated - like a peacock. But at a point, the disadvantage of such big features would at some point attract too many predators and keep it in check. “Ronald Fisher. Females choose based on “sexy”.
Parental Investment
Generally females invest more in parenting and thus must be choosier. Egg production v sperm production already has a higher cost to females. Then amount of care in carrying the baby, lactation, gestation etc.
Theories of Sexual Selection
Runaway selection
Handicap hypothesis
Parasite theory and honest signaling
Assymetrical Gamete production
Females produce limited number of eggs vs males producing many low cost sperm
Handicap hypothesis
“I have this male adornment…like a peacock tail, and I survived despite this handicap, so I am a very fit male.” Females chose based on costly adornments, as a sign that they indicate genetic quality. Zahavi
Parasite theory and honest signalling
Good plumage or fur (or whatever) indicates free from parasites and thus fit and healthy. For this theory to hold up, males must be honest signallers. Females chose based on parasite freeness to show genetic quality. Hamilton
Fission
Unicellular organisms split themselves into two in order to reproduce
Parthenogenesis
“virgin birth” Multicellular reproduction via asexual means. May do a mix of axsexual and sexual reproduction or obligate parthenogenesis
Obligate parthenogenesis
ONLY reproduces with asexual means
When is sex beneficial math perspective
Must produce 2 by sex to equal 1 by asexual reproduction for it to make sense to do something MORE expensive.
Benefits of sexual reproduction theories (3)
Fisher's faster evolution Muller's ratchet Raffle analogy (williams) Tangled bank Red Queen
Fisher’s faster evolution
Sex allows for variability in the offspring and thus faster evolution. An environmental change less likely to wipe out whole population because of variability
Muller’s ratchet
Harmful mutation in an individual is passed to ALL members of asexual members that are further in line. Each mutation builds like a ratchet that only turns one way, mutation building on top of mutiation
Raffle Analogy George Williams
That sex will be more common in unpredictable environments because variation means each offspring has a different “lottery raffle number”. Predicts that we should see sex will be more common in highly unpredictable environments such as streams, high altitudes and latitudes. Axexual reproduction will be more common in stable environments. If all asexual have the “same lottery raffle number” then an environment changing hurts them all. BUT Bell did research and found the opposite.
Tangled Bank
Bells’ theory that under predictable conditions, there will be more competition. It makes more sense to have variation, it would be beneficial to be a little different (thus sexual reproduction). Called it a tangled bank after Darwin’s analogy of competition in a crowded bank. We should under this theory expect to see constant change in species due to computation. Fossil record does not show this
Biotic environment
Living environment like parasites and predators.
Abiotic environment
Physical environment (like William’s latitude or streams)
Red Queen
An “Arm’s race” between virus/parasites and their hosts. Sexual reproduction gives an advantage because variability might have immunity in some of the population. It ties in with the biotic idea. That “stable” areas with high levels of parasites have sexual reproduction. A sexual in streams and unpredictable. Bell may have been right to look at biotic pressures, but he looked at the wrong biotic pressures. It wasn’t predators. it was parasites. Most important part of Red Queen might be how it pertains to sexual selection.
Evolution
changes morphological characteristics with differential survival but ALSO BEHAVIOUR.
Conspecific
Member of own species
If sexual selection is to be accepted, it is necessary that features chosen are:
heritable
Polygynous
Species where one male mates with several females
Sexual Dimorphism
Degree of differences between male and female of a species. The degree may indicate degree of sexual selection and the mating system
Bower Birds
the ones that build elaborate bowers/twig structures
Passeriformes
Order that about 1/2 all birds belong to
Song birds - belong to the order?
Passeriformes
Isolate Song
A song produced by a bird that had no tutor. It’s a unique song that isn’t the one done by their species.
Plastic song
As songbirds mature, begin to produce their own simplified song.
Crystallized cong
Mature bird, when the plastic song is practiced and compared to stored memories of adult song, until it matches and becomes stable.
Monogamy
Long term mating one male one female
Polygamy
General term for multiple mates
Polygyny
One male many females. Most extreme males have harems (like a silverback gorilla.) Other forms, males mate with multiple females but not guarding females.
Polyandry
One female many males
Promiscuity
Anyone with anyone, called polygynandry.
Polygynandry
promiscuity
Eusocial Species
Social insects are eusocial …and exception of naked mole rat. (1) cooperative care of young, (2) sterile castes, (3) overlapping generations. …These species have designated roles. Ex nurse bees or queen termite that lies there and just produces 30,000 eggs per day.
Sensory-bias hypothesis
preference for trait evolves in a non-mating context and is then exploited by less choosy sex in order to obtain more mating opportunities.
Sensory exploitation
When a trait is co-opted from one context to sexual selection. Zebra finches. Females like white feathers because it is what is needed for nest building. If you glue a white feather on male zebra finch heads, they are more likely chosen for mating by the females.
Asexual reproduction
Fission and Parthenogenesis.
Fission
unicellular organisms split in half, clone themselves
Parthenogenesis
In multicellular species/virgin birth Usually in plants, invertebrates but also some fish and lizards. Bees, wasps and ants. Females develop from a fertilized egg. Males from unfertilized. Rare cases, chickens, quail, turkey. Has occurred in sharks.
`Some multicellular species are both sexual and asexual during different periods
Aphids and water fleas
Three costs to sexual reproduction
Meiosis lose 1/2 genes
Cost of producing males (females more likely to reproduce)
Time and energy spent in courtship/mating
Sexual reproduction Faster Evolution
Fisher …In rapidly changing environment, genetic variation in sexually reproducing species allows for faster evolution. Asexual species have to rely on fortuitous genetic mutationsMore variability in offspring.
Faster Evolution proposed by
Fisher In rapidly changing environment, genetic variation in sexually reproducing species allows for faster evolution, asexual species have to rely on fortuitous genetic mutations.
Muller’s Ratchet
Muller In asexual species, harmful genetic mutation is passed on to all offspring. In each new generation, harmful mutations accumulate in population
Raffle analogy
Considers individual selection, offspring are raffle tickets in draw. Prize = passing genes. Sexual reproduction should therefore take place in more unpredictable/changing environments. Asexual reproduction should take place in more stable environments. But this does not seem to be the case. If an environment is stable and comfy for you, it’s comfy from others too - more competition from your own species..
Tangled Bank Theory
Overrown embankment analogy. Stable environments many members of the same species. Sexual reproduction allows for genetic variation in these individuals. Continual change should therefore occur in population. But this doesn’t seem toward this way either. Species tend to stay the same for 1000s of generations, then rapidly change.
The Red Queen
Proposed by Van Valen. Back to parasites. Evolutionary arms race between parasites and hosts. Parasites evolve more quickly than hosts. Short lifespan, huge numbers. Hosts retaliate by producing variable offspring some of whom will have resistance. Sexual reproduction for the win. Each side reacts in response to the changes in the other. Gives appearance of a standstill.
R and K continuum
Red Queen hypothesis. K species are the mammals (hosts). R’s are the parasites. Think Red queen and King.
