Speciation Flashcards
What is the basic unit of biodiversity?
Species
How do definitions of a species change with fields in biology?
Taxonomy - mostly focus on ways for cataloguing and information retrieval
Phylogeny - definition mostly relates to relationships and history
Evolutionary biology - focuses on the evolutionary process
What system did Linnaeus develop?
Hierarchical system: kingdom, phylum, class, order, family, genus and species
Describe the taxonomic approach
Phenetic method (according to observable attributes)
- Describe the phenotype of the holotype and deposit specimen into a museum
- Other researchers compare their species to the holotype
What is the problem with the taxonomic approach?
- Lead to organisms being occasionally described as being part of a different species when they are actually different populations connected by continuous variation or have phenotyhpic polymorphisms
- How much variation is ‘allowed’ within a species
What is the biological species concept (Mayr)
Species are populations which are reproductively isolated
What are the criteria for a species in the biological concept?
- Reproductive isolation
- Stabilised, well-integrated genotype
- Species-specific niche
What are the advantages of the biological species concept?
- Make species as biological reality and not a taxonomists opinion
- Measurable and testable
- Can study speciation through reproductive isolation
What are the issues with the biological species concept?
- How to define asexual species
- How to study and classify species from fossils
- Is reproductive isolation completely necessary?
What is the phylogenetic definition of a species?
Smallest aggregate population/lineage which can be united by synapomorphic characters (shared derived characters)
What is the phylogenetic definition of a species good for?
Fossils and asexual organisms
What are Dobzhanky’s 2 classifications of mechanisms of reproductive isolation?
- pre-mating mechanisms which prevent the formation of hybrid zygotes by impeding gene flow before sperm/pollen transfer
- post-mating mechanisms can be pre-zygotic or post-zygotic
Name 4 mechanisms of pre-mating reproductive isolation mechanisms
- Behavioural isolation
- Ecological isolation
- Mechanical isolation
- Mating system isolation
Define behavioural isolation?
Differences which result in a lack of cross-attraction between species (does strong sexual selection result in speciation?)
What are the 3 components of ecological isolation?
- Habitat isolation -> when species have a tendency to occupy different habitats in a general area resulting in a lack of gene transfer
- Temporal isolation -> different breeding times
- Pollinator isolation -> gene flow between angiosperms is reduced due to their different interactions with pollinators
How do cicadas show temporal and behavioural isolation?
- Have developed different life cycle lengths (11, 13, 17 & 19 years) to avoid predator satiation which has separated them from ancestors
- Different mating calls to differentiate different cicadas with the same length lifecycle
Give an example of pollination isolation
Closely related Mimulus species have different pollinator vectors due to different shapes which mostly seems to be controlled by a single gene
Give 2 post-mating pre-zygotic barriers
- Copulatory mating isolation -> where individual behaviour during copulation does not allow for normal fertilisation
- Gametic isolation
What are the 2 forms of gametic isolation?
Noncompetitive - Intrinsic problems with transfer/storage/fertilisations of heterospecific gametes in single fertilisations between individuals
Competitive - Heterospecific gametes are not properly transferred/stored when competing with gametes of the same species
What are the two post-zygotic mechanisms of isolation?
- Extrinsic factors - hybrids cannot adapt to ecological niche or cannot obtain mates as intermediate characteristics are unattractive
- Intrinsic factors - could be hybrid inviability where difficulties cause full/partial lethality or hybrid sterility due to physiological (gametes/reproductive development) or behavioural (neurological lesions) factors
Define polyploidy
A change in the number of chromosomes
Name 2 types of polyploidy
autoploidy - duplicating of own chromosome
allopolyploidy - chromosome doubling of a hybrid
How did Muller believe hybrid sterility evolved?
Through negative interactions between genes evolving independently of eachother
What is Haldane’s rule?
When in the F1 offspring of two different animal races one sex is absent, rare or sterile, it is the heterozygous sex
Name 4 possible explanations of Haldane’s rule
- Male effects
- Sex-linked genes evolve more quickly
- Incompatibility between the X and Y
- Combination of dominance effects and epistasis
What is Coyne & Orr’s second rule of speciation?
The genes having the greatest effect on hybrid sterility and inviability are sex-linked
Why is allopolyploidy frequently a cause of speciation in plants?
- Allopolyploids are immediately reproductively isolated from their parents
- Can originate more than once
What is a homoploid hybrid?
When a recombinant that segregates from the initial hybrid is reproductively isolated from its parent species by a chromosomal barrier and/or an ecological barrier
