10 Speciation and The Origins of Biodiversity Flashcards
Phenotypic discontinuities can be misleading (2)
Cryptic species - look the same but actually independent
Polytypic species - look different but actually one species
Species meaning and description
units with independent evolution because of barriers to gene flow
Interbreed with other members of the population + can‘t produce viable offspring with members of other species
Genetic isolation
Evolutionarily independent
Often appear discontinuous
Gene flow definition
distinct in genetic composition (variant frequency, variant pressence) / absence of viable, fertile hybrids
Prezygotic isolation - barriers before fertilisation
Temporal / ecological / behavioural / mechanical / gametic
Gametic isolation (oceans example)
In oceans, selective use of sperm —> similarly, heterospeifc pollen doesn’t grow well in plants —> in insects, sperm competeion is biased to sperm of its own species
Postzygotic isolation - barriers after fertilisation
Reduced hybrid fertility - babies sterile / babies die
Allopatric species formation
complete geographical isolation
The paradigm
Many mammal radiations come after the landscape, implying dispersal
Sympatric species formation
reproductive isolation without graphical isolation —> consider a mutation which insect preference to lay eggs on new host plant / this gives genetic isolation when mating occurs on host plant
Single beneficial mutations - instantaneous mating barriers
Unselected incompatibilities
Accumulation of mutations - overtime new variation will be added to isolated population via mutation, drift an selection (untested gene interactions if come in contact)
Postzygotic isolation can aslo be ecological…
Selection for traits that help individuals with the local environment
Divergence in allopatry may change diet / reproduction preferences
Alternatively do, interefere —> 2 outcomes (extinction of 1 species OR rescue through character displacement
selection favours individual species that don’t interefere)
Ecological character displacement
selection for each species to utilise different niche
Generation of biodiversity requires… (2)
- Evolution of reproductive isolation (allopatry, peripatetic, sympathy —> divergence)
- Distinctions between species that permit coexistence - resource use, mate choice
Natural selection may produce these through process of character displacement but may be constrained in doing so
Diversification depends on niche space (description)
Lots of diversity to start (empty niches) (adaptive radiation) —> diversification then slows as niches become filled
Diversification observed related to resource abundance
Generation of reproductive isolation initially important —> later, saturation —> new species limited by niche availability —> mating habitat —> resource abundance
Adaptive radiation
burst of speciation in new unexploited habitats, as any new species formed can find new niches
Initial barriers that allow divergence (3)
- No dispersion - vicariance only source of isolation
- Low dispersion - can reach new pla es occasionally, but population has integrity vs gene flow (vicariance is viable as well)
- High dispersion - can reach new places easily but these then have gene flow to source - vicariance unlikely
Speed of divergence when separate (mammals)
Mammals - very low tolerance to hybridisation - hybrid in viability evolves quickly (max 3MYA in mammals vs 20MYA in birds and amphibia)
Fast in mammals because placentation hypothesis —> foetal viability requires internal development and correct interface with the mother / immunological tolerance stretched - hybrids that are genetically distinct are rejected
Biological innovation
allow new ways of living / new niche space —> diversification
Taxa can vary intrinsically in speciation rate (2)
- Dispersal capacity —> barriers to gene flow
- Features of biology that affect rate of evolution of reproductive isolation (eg. Pregnancy)
Mayr’s definition of a species
Biological species concept (BSC)
Species as a group of interbreeding populations that are reproductively isolated from other such groups.
This means individuals within a species can produce fertile offspring together, but they cannot reproduce successfully with members of other species.
Hybrid in viability
The hybrid offspring do not develop properly or die early
Hybrid sterility
Hybrid is sterile
Geographic isolation
Species can become geographically isolated through physical barriers such as mountains, rivers, or oceans, which prevent gene flow between populations
Allopatric speciation
Populations are geographically isolated and evolve separately
Sympatric speciation
Same geographic area, typically due to ecological or behavioural differences
Parapatric speciation
Populations are adjacent but experience different environmental pressures across a gradient
Genetic divergence
Isolated populations accumulate genetic differences due to mutations, genetic drift, and different selective pressures
Reproductive isolation
When populations come into contact again after long periods of isolation, genetic differences may prevent successful interbreeding (eg. through prezygotic or postzygotic isolation), leading to the formation of new species
Niche space
The specific environmental conditions and resources a species uses in an ecosystem
Adaptive radiation
The rapid diversification of a species into many different forms to exploit various ecological niches
This often occurs after a new habitat is colonized or after mass extinctions open up new niches
Factors that enhance or constrain evolution
Available Niche Space - The greater the unfilled niche space, the more opportunities for adaptive radiation
Environmental Change - Environmental changes (continental drift / climate change) can create new ecological niches and drive speciation
Example of adaptive radiation
Different finch species on the Galápagos evolved distinct beak shapes to exploit various food sources, showing adaptive radiation
Dispersal definition
Movement of individuals from their birthplace to new areas
Dispersal biology affects gene flow and speciation
Effect on speciation - high dispersal
Leads to greater gene flow between populations, slowing speciation
Effect on speciation - limited dispersal
Populations that are isolated by distance or barriers experience reduced gene flow and more genetic divergence, increasing the potential for speciation.
Pregnancy and isolation
Pregnancy in mammals can increase the rate of postzygotic isolation by prolonging the developmental period, which may lead to more genetic incompatibilities
How does pregnancy effect evolution
Pregnancy allows for more complex interactions between maternal and paternal genes, increasing the possibility of genetic mismatches
Example of biological change driving adaptive radiation
The Evolution of the Vertebrate Limb
The modification of the tetrapod limb allowed vertebrates to adapt to diverse terrestrial environments, leading to adaptive radiation into amphibians, reptiles, birds, and mammals.
