Biology Cycle 8 - Speciation Flashcards
What is the morphological species concept?
all individuals of a species share visible anatomical characteristics that distinguish them from individuals of other species
Which species concept distinguishes fossils? Why?
morphological species concept because you can observe external traits
What are the issues with the morphological species concept?
- Individuals of the SAME SPECIES look different physically (colour and size)
- Cannot distinuish closely related species that are nearly IDENTICAL in appearance
- No indication of evolutionary processes causing new species
What is the biological species concept?
- “species” based on the ability of populations to INTERBREED
- produce FERTILE offspring under natural conditions
How does the biological species concept fix the issues from the morphological species concept?
- defining species in terms of population genetics and evolutionary theory
- Why do species share anatomical features? – gene pool shared
What are the two principles of the biological species concept?
- Genetic cohesiveness-Species mix genetic infoin a gene pool
- Genetic Distinctiveness- different species are reproductively isolated So they can’t exchange genetic info
Which species is the biological species concept useful for?
sexually reproducing species
What are the issues with the biological species concept?
- asexually reproducing species (bacteria, archaeans, plants) – they do not breed
- extinct species (no data on reproductive habits)
- difficult to observe every species (aquatic or micro organisms)
What is the phylogenetic species concept?
- cluster of populations that emerge from sharing a recent evolutionary history
What’s an advantage of phylogenetic species concept?
can be applied to living AND extinct species as well as asexually reproducing species
create tree using phenotypic and genotypic data
What is a disadvantage of the phylogenetic species concept?
- must decide how much evolutionary change defines a new species
- species are preferably monophyletic (one common ancestory)
- difficult to apply to rare or fossilized species becuase genetic info cannot be extracted
- homoplaisies
What are homoplaisies? Which species concept do they interfere with?
- species tust evolve similar traits seperately due to evolutionary agents and not because of common ancestry
- convergent evolution interferes with PSC
Why is it less likely for gene flow to occur between distant populations?
different environmental conditions that experience different patterns of selection so their gene pools and phenotypes are different even if they are the same species
What is a subspecies?
a taxonomic subdivision of a species that are local (of the same area)
When is a subspecies identified?
a geographically separated population of a species exhibits drastic, phenotypic variation that is easily recognizable
Can subspecies interbreed? What would their offspring look like?
Yes! Their offspring often exhibit INTERMEDIATE phenotypes
What are ring species?
species with a geographical distribution that forms a ring around inhabitable terrain
How does genetic variation occur in ring species?
adjacent populations can directly have sex but gene flow between distant populations require intermediary populations to have sex
What us clinal variation?
a pattern of smooth variation in a characteristic along a geographical gradient
How does clinal variation occur?
gene flow between adjacent populations that are each adapting to slightly different conditions
In clinal variation, what occurs to populations at opposite ends of the gradient?
separate by great distances so they may exchange very little genetic material through reproduction
What are the reproductive isolating mechanisms
a biological characteristic that prevents the gene pools of two species from mixing
What is a hybrid?
an organism produced by a mating between parents of different species or subspecies
When do pre zygotic isolating mechanisms occur? When do post zygotic mechanisms occur?
pre zygotic - prior to production of a zygote
post zygotic - after zygote formation
PREZYGOTIC MECHANISMS
Ecological isolation - species live in different habitats in the same region
Temporal isolation - species breed at different times
Behavioural isolation - species cannot communicate
Mechanical isolation - species cannot physically mate
Gametic isolation - species have nonmatching receptors
POSTZYGOTIC MECHANISMS
Hybrid inviability - hybrid offspring do not complete development
Hybrid sterility - hybrid offspring cannot produce gametes
Hybrid breakdown - hybrid offspring have reduced survival or fertility
What is ecological isolation?
- prezygotic
- species live in the same geographic region, but occupy different habitats
- ex. Lion-tiger hybrid occurs in non-natural conditions
What is temporal isolation?
- prezygotic
- same habitat, but breed at different times of day/ different times of year
- ex. pollen release at different months
What is behavioural isolation?
- prezygotic
- mating signals (courtship displays) not recognized
- ex. bird calls vs. firefly light displays
What is mechanical isolation?
- prezygotic
- differences in the structure of reproductive organs (or other body parts)
- ex. different floral structures of monkey-flower attract different animal pollinators
What is gametic isolation?
- prezygotic
- incompatibility between the sperm of one species and the egg of another potentially preventing fertilization
- ex. marine invertebrates release eggs into the ocean but only sperm that recognizes the egg fertilizes
What is hybrid inviability?
- postzygotic
- genes from each parent species are incompatible for successful embryonic development
- embryo dies/offspring dies at early age (LOW probability for reaching reproductive age)
What is hybrid sterility?
- postzygotic
- hybrid cannot form functional gametes so their fitness is zero (leave no descendants)
Why does hybrid sterility occur in terms of chromosomes?
usually when parent species differ in the number or structure of their chromosomes which cannot pair properly during meiosis
What is hybrid breakdown?
- postzygotic
- first generation hybrids are capable of reproducing with either parental species or hydrib but their OFFSPRING have reduced fertility/viability
How does the mating pattern occur for hybrid breakdown?
F1: hybrid x hybrid or hybrid x parental species
What are the two modes of speciation based on geographical location?
Allopatric and sympatric speciation
What is allopatric speciation?
Two populations that are geographically separated causing the evolution of reproductive isolating mechanisms
How is allopatric speciation possible?
- physical barrier subdivides a large population (2+)
- a small population becomes separated from a species main geographical distribution
What are the stages of allopatric speciation?
- Two populations become geographically separated
—> gene flow prevented - Each populations independently experiences mutations, natural selection, and genetic drift (accumulating genetic differences)
—> reproductive isolated
What species experiences allopatric speciation commonly?
Large animals
What are causes of allopatric speciation?
Natural disasters
Ex. Hurricanes creating new channels that divide low coastal islands and the populations inhabiting them
Ex. Uplifting mountains/landmasses
Ex. Rivers/advancing glaciers
What is second contact?
If geographical barriers are placed and then somehow removed and the 2+ populations that were once divided are reintroduced after undergoing genetic variations separately.
What are the possible results of seconds contact?
- Inability to interbreed
- Hybrid sterility
- Hybrid inviability
- Hybrid breakdown
- Production of viable, fertile, healthy offspring
What is a peripheral population?
Small population isolated from the central population located at the edge of the species geographical distribution
What impact does evolution have on peripheral populations?
—> often differ genetically from the central population because of a somewhat different environment
—> genetic drift promoted due to founder effects and small population size
—> natural selection may favour evolution of distinctive traits
What is a species cluster?
A group of closely related species recently descended from a common ancestor
- founder effect and colonization of an area multiple times causing second contact
- ex. Islands
What is species fusion ?
after secondary contact, species of two populations merge into one because the populations gene pool did not differentiate much
what are hybrid zones? how do they arise?
geographic area where the hybrid offspring of two secondary contact populations or species are common
Why are hybrid zones necessary?
hybrids are usually unable to adapt to environments outside of the zone so they are ar risk of extinction and have low fitness
what is reinforcement?
enhancement of prezygotic reproductive isolating mechanisms developed when a population is geographically isolated
What is sympatric speciation?
recproductive isolation that evolves between distinct subgroups that arise within one population
What is a host race?
a population of insects that may be reproductively isolated from other populations of the same species as a consequence of their adaptation to feed on a specific host plant species
What is polyploidy? Which species are commonly polyploids?
an individual has one or more extra copies of the entire haploid complement of chromosomes so there is gametic isolation (common in plants)
How can polyploid individuals arise?
- autopolyploidy: chromosome duplications within a single species
- allopolyploidy: hydridization of different species
What autopolyploidy?
Genetic condition of having more than two sets of chromosomes from the same parent species
How does autoploidy occur?
gametes spontaneously receive the same number of chromosomes as a somatic cell through an error in mitosis or meiosis
what are the gametes produced by autoploidy called?
unreduced gametes
what is Allopolyploidy?
two closely related species hybridize and then form polyploid offspring
How would alloploidy species be sterile? And not sterile?
Sterile if the 2 parent species have diverged enough that their chromosomes do not pair properly in meiosis
if the hybrid’s chromosome number is doubled, the chromosome complement of the gametes is also doubled producing homologous chromosomes that can pair during meiosis
What are the mitotic and meiotic steps of allopolyploidy?
- the parent cells that are too different undergo meiosis seperately
- fertilization occurs creating a hybrid but there are no homologous pairs
- DNA replicates but it doesn’t divide (no mitosis) (chromosome doubling) so each chromosome has a homologue and there is double to number of chromosomes as the parent
- meiosis occurs but the gametes have double to number of chromosomes as the parent population
offspring can mate witg each other but not with parent populations
Why do we need to classify species?
- conservation of species (endangered vs threatened)
- measure rates of extinction and diversification
- determine species that are disease transmitters
- emergence of new variants (covid)
What is a scientific benefit of the biological species concept?
fertility and mating behaviours are testable and if the species is a hybrid, genetic evidence is available
