Cycle 8: Life on Earth, Species and Speciation and Cycle 7: All About Sex Flashcards
Asexual Reproduction in plants.
New individuals are genetically identical (bulbs, corms, tubers, rhizomes, adventitious roots)
Asexual Reproduction in animals.
- Fragmentation
- Budding
- Parthenogenesis: females produce offspring without fertilization from sperm
Thelytoky: female offspring are produced
Arrhenotoky: male offspring are produced
Thelytoky
female offspring are produced
Arrhenotoky
male offspring are produced
Sexes in plants.
- Monoecious (flowers of both sexes in plant)
- Dioecious: male and female flowers are on different plants
- Hermaphrodites: the flower has male and female parts (but not much selfing occurs)
Sexes in animals.
- Monoecious hermaphrodite:
Species with male and female sex organs - Sequential hermaphrodite
- Dioecious: individuals of separate sexes
Some will not exhibit sexual dimorphism (when sexes look different)
Sequential hermaphrodites.
Change from male to female or female to male based on a series of cues (olfactory, visual, auditory, tactile)
Size advantage model.
Protrandry: male to female
Protogyny: female to male
Why sex?
Cons: time spent, male-male competition, courtship, rejection, natural enemies, STDs
Pros: Diversity of offspring (chances for gaining beneficial alleles, and losing negative ones) through sexual reproduction
Monogamy.
one partner
Polygamy.
Polygyny: male mating with many females
Polyandry: female mating with many males
Courtship behaviour and mating
Visual, auditory, chemical, and tactile
Habitat influences which cues are used during mating.
Sexual Selection
Females are generally the choosier sex (but there are exceptions)
The sex that invests more in offspring (higher parental investment) is the choosier sex.
Can also be dependent on ecological situations (role reversal)
When and how do females choose partners?
WHEN FEMALES CHOOSE:
Male strategy: Mate as often as possible (best strategy to leave his genes)
- Male-male competition:
- A cost of sexual reproduction
- Post-mating sperm competition
- Second mating increases reproductive success of female
- Second male may not sire any progeny (competition can dependent on sperm quality)
- Could be that female chooses ( has not been ruled out)
- Evolution of adaptations to reduce sperm competition
- Increased ejaculate size
- Remove sperm from previous mating
- Mate guarding
HOW DO FEMALES CHOOSE?
- Visual signals (e.g. size)
- Nuptial gifts
- Good gene hypothesis and symmetry (more symmetrical implies better genes)
- MHC (group of genes on cell surfaces)
- Different MHC genes (fitness against parasites varies based on MHC genes)
- Goal is to obtain a diversity of MHC genes for protection of progeny against disease.
Ecological Concept
Populations that are adapted to specific niches in the environment
E.g. Mosquitoes feeding on humans vs birds may evolve differently
Advantages
- Explains role of environment in speciation
Disadvantages
- Unable to explain existence of same species in different environments
Morphological Concept
Individuals of species share measurable traits that distinguish them from other species
Advantage
- Easy to classify physical traits to recognize species
Disadvantage
- Does not reveal much about evolutionary history
- Cannot distinguish different species with similar physical characteristics
Biological Concept
- Interbreeding populations that don’t reproduce with other species
- All individuals in a species can successfully mate and produce viable, fertile offspring
Genetic Cohesiveness: populations of same species experience gene flow that mixes their genetic material
Genetic Distinctiveness: different species can’t exchange genetic info
Advantage
Testable and describes gene flow of species
Disadvantage
Does not apply to asexual and extinct organisms
Phylogenetic Concept
- Populations that share recent evolutionary history
Independent branch on phylogenetic tree = species - Common morphological ancestry for sexually reproducing organisms
Implies reproductive isolation, but does not prove
Advantage
Applies to all groups of organisms (asexual, extinct)
Disadvantage
Does not describe gene flow
Clinal Variation
Gradient of traits in a geographic range
Varying environment conditions favour different traits → evolution within a species
Ring Species
Population migrates around geographic barrier → two adjacent populations that cannot interbreed
Considered same species due to shared alleles + gene pool through intermediates
Prezygotic Isolating Mechanisms
Temporal Isolation: Mating at different times
Ecological Isolation: Different habitats
Mechanical Isolation: Different reproductive structures
Behavioural Isolation: Different mating signals (courtship displays)
Gamete Mortality (Gametic Isolation): Incompatibility between sperm and egg
Postzygotic Isolating Mechanisms
Hybrid Inviability: Conflicting genes prevents development
- Fertilization occurs but hybrid is frail or has has early death
Hybrid Sterility: Survives but unable to produce functional gametes
Hybrid Breakdown: Hybrid develops and can mate with other hybrids + parent species
- Second generation will have higher fatality, lower fertility
- Long-term reproductive isolation rather than immediate
Allopatric vs Sympatric Speciation
Modes of speciation based on species isolated by location
Allopatric: Two populations that are geographically separated potentially causing evolution of reproductive isolating mechanisms
Sympatric: Reproductive isolation that evolves between subgroups that arise with one population
Allopatric Speciation
Two populations that are geographically separated potentially causing evolution of reproductive isolating mechanisms
Examples:
- Physical barrier that subdivides a large population
- Small population becomes separated from a species main geographical location
- Natural disasters
Secondary Contact
Two previously isolated populations reunite
Not required for speciation to occur
Potential Outcomes
Reinforcement:
increases the rate of speciation
If reproductive isolation occurs, there is speciation
When the two species are back in contact, they can’t interbreed
Fusion:
slows down the rate of speciation
Populations successfully interbreed, they can “fuse” back together
Gene flow can continue → remains one species
Autopolyploid Mutations on Speciation
Autopolyploidy mechanism:
- Chromosomes fail to separate in cell division = no reduction of number of chromosomes = gamete is a different ploidy than parent
Offspring species can’t interbreed with original parent species
Evolutionary Myths
1) Why the idea that “humans are descended from chimps are incorrect”
We just share a common ancestor that doesn’t mean chimps are our ancestors
2) Why some traditional groupings of organisms do not reflect evolutionary relationships
Just because some organisms are grouped together does not mean they are as closely evolutionary related as they seem
Also, shared similarities might not always reflect shared ancestry, it could be convergent evolution
3) “Pedigree Collapse”
The idea that some of your ancestors are not ALL unique individuals
eg. great x13 aunt on mom’s side and great x9 grandmother on dad’s side are the same person
