Variable Mating Systems Flashcards
What are the challenges of sex vs no sex
Some species do not reproduce sexually every generation. eg some aphids, wasps, mites crustacea etc. some species don’t reproduce sexually eg whiptail lizards, certain geckos and certain fish.
Sexual reproduction presents a dilemma:why pass ln half your genes when you could pass on all of them?
Assuming sexual reproduction evolved (like everything else) by natural selection, natural selection should favour individuals that pass on more of their genes to the next generation. In most species males contribute nothing but sperm to reproduction. A parthenogenic (reproduction without fertilisation) female should have a big advantage as she passes on twice as many genes with each offspring.
What are the reasons against sex
1) sex is expensive- can be expensive in terms of time, energy and resources. eg male bower birds in Australia. Construct bowers for the sole purpose of attracting females- energetically expensive.
2) sex is dangerous- many species undertake huge risks just to get the chance to mate. Eg south American tungara frog. Males need to call to attract female. The more complex the call the more attractive it is to females. However carnivorous bats use calls to locate frogs.
What are the reasons for sex
recombination provides the genetic diversity for species survival hence sex makes our genes more adaptable. Without recombination, mutation can drive asexual species to extinction.
What is the red queen hypothesis
in alice in wonderland the red queen says “it takes all the time running you can do to keep in the same place”/. In terms of evolution thus means even species that don’t appear to be changing are undergoing rapid evolution. Why? because the natural world is changing so rapidly that without constant evolution species would go extinct. Sex and recombination provide the necessary variation that keeps evolution going, without this pathogens, competitors and environmental changes would lead to the extinction of everything
DIscuss the red queen dynamics
Computer simulation of host-parasite co-evolution. both genotypes oscillate over time - artic fox hare
What is mullers ratchet
sex is necessary to cleanse our genes. Mutation drives evolution but they are mostly harmful. In asexual organisms, these harmful mutations can build up. each mutation is like the turn of a ratchet making the organism increasingly less viable. they are condemned to the ratchet with no way of going back. Without recombination there is no way to create a lineage without harmful mutations or to create a lineage that has lots of favorable mutations.
Why have 2 sexes?
Males- small gametes, usually only contribute sperm (DNA).
Females- few large gametes, contribute DNA+cytoplasm+ maybe more.
This is the fundamental difference between sexes.
How did 2 sexes evolve?
Two sexes may have evolved as part of an ancient evolutionary game played out millions of years ago. Consider a species which has haploid gametes, which are shed directly to the water column. The two haploid gametes unite to form a zygote. Initially, there are no different sexes, all gametes are more or less the same size. there is however genetic variation for gamete size, some individuals produce many small ones, others produce fewer larger ones. a zygote needs a certain amount of cytoplasm to survive. It gets this from its 2 parents. Gametes are released right into the water column, and join together at random. Initially the population is mostly composed of individuals who make a few large gametes. There are a few individuals however, who make a large number of small gametes, attempting to maximise their fitness. Initially the small gamete strategy is very successful because these individuals can pass on more of their genes ie they sacrifice quality for quantity. Over time this small gamete strategy becomes common. However, this leads to a serious problem: when small gametes recombine with other small gametes, the zygotes die as they have insufficient combined cytoplasm reserves. But there is still selective pressure to produce as many gametes as possible. This creates the favorable conditions for a NEW strategy, to produce few very large gametes. By producing few, very large gametes, these individuals ensure that there is always enough cytoplasm for the gametes to survive, even though they are almost certain to unite with very small gametes. Essentially they can accommodate freeloaders. end result- males and females.
discuss mating systems
Sexual behaviour that evolved to enhance fitness. Described in terms of male and female pairings.
DEFINITION- the ways in which animal societies are structured in relation to sexual behaviour. it includes
- how individuals obtain mates
- the number of mates acquired
- characteristics of bonds between animals
- patterns of parental care given by each sex
What is batemans principle
Females invest more. Sperm is cheap.
Males reproductive success is limited by access to females, whereas females reproductive success if limited by access to resources. This can lead to conflict between and within sexes.
Anisogamy- a form of sexual reproduction where males and females produce sex cells or gametes of different sizes.
Because males and females differ in their contribution to reproduction, different and varied mating systems occur through which both males and females attempt to maximise their fitness. Usually results in male-male competition and female choice.
How are mates chosen?
plumage
song
territory/nest quality
displays
courtship/feeding
What are the different mating systems?
1) Monogamy- prolonged, essentially exclusive pair bond with a member of the opposite sex
2) Polygamy- pair bonds with multiple members of the opposite sex
3) Polygyny (many females)- males pair with one or more
4) Polyandry (many males) - females pair with one or more males.
5) Polygynyandry (many)- males and females pair with several members of the opposite sex.
Discuss monogamy
Prolonged, essentially exclusive bond maintained with one member of the opposite sex. Generally a rare system. Rare in mammals (except for some rodents, primates and dogs. But it is the most common in avian mating systems (more than 95% of species). Monogamy is an armed compromise rather than happy collaboration. Males would generally like to seek extra mates. But why don’t they?
why don’t males seek more mates in monogamous relationships
Mate guarding hypothesis
Mate assistance hypothesis
Female enforced monogamy
What is the mate-guarding hypothesis
Monogamy may be the best choice (for male) if female would mate again, if male deserted her and if 2nd male would fertilize eggs.
Mate guarding should pay off when females
1) scarce and hard to find
2) remain receptive after mating
example- Clown shrimp- females are scarce and only receptive for a short time so when a male encounters a female he will remain with her.
