Cooney Flashcards
The open tree of life aims to build a tree of all … … described species on Earth
2.3 million
Diversity is … on the tree of life
imbalanced
In terms of kingdoms, how are species unevenly distributed?
Far more animal species (over 1.5 million) than any other group (e.g. around 400,000 plants - 2nd most)
Within the animal kingdom, the phylum … vastly dominates in terms of number of species
arthropoda
… is ubiquitous across the tree of life
unevenness - wherever you look - within phyla, orders, families etc.
Species richness … a great deal across the tree of life
varies
An example of phylogenetic imbalance is between the … and the … and …
caddisflies, moths, butterflies
Phylogenetic imbalance is the relative numbers of … … (usually species) on the branches that originate at the … …
descendant tips, focal node
Does chance alone explain the variation in species richness across the tree of life?
- imbalance can (and is predicted to) arise by chance
- however, more imbalanced trees than expected by chance (and fewer balanced) - according to Guyer and Slowinski (1991) - who looked at 120 phylogenies (5 species in each) for imbalance
what is the equal-rates Markov model?
- Species arise from other species (bifurcate)
- probability of speciation per unit time is constant across all lineages
- can be extended to include extinction (probability also constant across lineages)
- expect ratio of 2:1 imbalance vs balanced trees
Does variation in clade age explain differences in species richness across the tree of life? young clades have had less time to accumulate species and diversify after all
Clade age and species richness are uncorrelated across 1397 clades of multicellular eukaryotes (Rabosky et al, 2012) - even when looking at individual taxa still very little to no evidence - clade age is a poor explanation for phylogenetic imbalance
Does variation in net diversification rate explain the phylogenetic tree imbalance?
When we look at the net diversification rates across different clades and taxa we see huge variation
- this does explain patterns of variation in species richness
- There is a strong positive correlation between diversification rate and species richness in groups of the phylogenetic tree (across different taxonomic levels)
Net diversification rate (R) is the net rate of lineage splitting and is the … rate - the … rate. It is expressed as the average number of … events per lineage per … …
speciation, extinction, splitting, million years
R = b - d
How can we visualise differences in diversification rate is using … … … (LTT) plots. If speciation rate is constant and extinction is zero, then clade growth is …, which produces a … … when logged.
lineage through time, exponential
… … have diverged at a roughly constant rate
Hawaiian silverswords (25 species in 5 million years) - very high speciation rate
+ hummingbirds (338 species)
… clades account for … of all known vertebrate diversity
5, 85%
It has been found that the pattern of unevenness in the phylogenetic tree can be explained by…
as little as 9 exceptional shift in diversification rate
In conclusion, net diversification rate is a … … of species richness at any … … across the Tree of Life
strong predictor, taxonomic level
If diversification rates vary, this must be caused by factors that drive differential … and … rates
speciation, extinction
If the probability of speciation (b) and extinction (d) are … through time, as we approach the present, the number of observed extinctions will decline, as … lineages are less likely to have gone extinct.
In the past we observe net diversification (b-d). In the present we observe only ….. Extinction can be calculated by comparing the recent slope with the past slope.
More information in phylogenies of extant taxa required to estimate b-d than to estimate b or d separately
constant, young, speciation
What did Mayr say different speciation rates depend on?
- the frequency of barriers (factors producing geographical isolates)
- The rates at which geographical isolates acquire isolating mechanisms
- The degree of ecological diversity offering vacant ecological niches
What are now thought to be the primary controls on speciation rates over macroevolutionary time scales?
- Rate of splitting (geographic isolation)
- Rate of population differentiation
- Rate of population persistence, range expansion and co-existence
- Rate of splitting (geographic isolation)
Chance of geographic isolation is greater in species with…
Rate of dispersal ability increases the chance of geographical isolation (splitting). … birds gave spread across the world and have high speciation due to their spread to different islands and places n stuff. But also depends on opportunities for geographical isolation (e.g. lots of of islands) because dispersal ability and speciation rate don’t have a clear relationship
larger range sizes (more chance of rage subdivision)
Zosterops
- Rates of differentiation
Higher rates at which populations become differentiated … do correlate with higher rates of speciation over larger evolutionary time scales
Rabosky et al (2013) looked at over 15,000 ray finned fish. They found that lineages of ray finned fish that differentiate rapidly in … (body size) also have elevated … rates (rates of ecological differentiation are correlated with speciation rates over evolutionary time scales).
Lineages with bioluminescent … are associated with high species richness, but bioluminescent … has no association with species richness. This implies that sexual selection (… differentiation) may drive increases in speciation rate by accelerating divergence in courtship traits
genetically, morphology, speciation, ecological, courtship, camouflage, mating
- Rate of population persistence, range expansion and coexistence
To contribute to the long-term build up of species richness, incipient species must … (and subsequently expand and go through further round of speciation)
persist
Incipient species can diverge, then make secondary contact. When this occurs, they could be sufficiently … … to complete speciation, or … could complete speciation. Alternatively, one species may drive the incipient species to …, or they may … (speciation collapse, e.g. via …)
reproductively isolated, reinforcement, extinction, merge, hybridisation
- Rate of population persistence, range expansion and coexistence
To contribute to the long-term build up of species richness, incipient species must … (and subsequently expand and go through further rounds of speciation)
Incipient species can diverge, then make secondary contact. When this occurs, they could be sufficiently … … to complete speciation, or … could complete speciation. Alternatively, one species may drive the incipient species to …, or they may … (speciation collapse, e.g. via …)
A good e.g. of this is … …, who have diversified very rapidly and extensively, but when ecological conditions change the mating barriers between the species are often … enough that they hybridise and merge (speciation collapse)
persist, reproductively isolated, reinforcement, extinction, merge, hybridisation, cichlid fish, weak
Ovenbirds are a clade of birds that have radiated across … …. Ovenbird sister species may often take >10My to become sympatric after initial … period (expansion). However, divergence in ecological traits (e.g. indicated by beak shape) reduces the waiting time to species … (from approximately 16my to ….
Basically, species which had more bill divergence had taken much less time to reach sympatry with their sister species again
South America, isolation, coexistence, 2my
An integrated analysis of bird co-existence patterns suggests:
- initial rates of range expansion following speciation depend on species’ … ability, while….
- Later stages of range expansion (involving extensive overlap between closely related species) are largely determined by … …
niche availability
What about extinction rates?
- Harder to analyse, using molecular genetics
Give an example though, go on…
Polyploidy (whole genome …) is a widespread feature of … genomes - with an estimates … of vascular plant species being polyploids.
However, polyploids are expected to suffer greater extinction risk due to competition with ancestral … and because of the inefficiency of … when genes are masked by multiple copies.
Their commonness is somewhat paradoxical.
BiSSE model used to estimate speciation and extinction rates separately for … and … lineages. Found that polyploid lineages had higher … rates and lower … rates, and overall lower net … rates. The reason for their prevalence is the…
duplication, plant, 30-80%, diploids, selection, diploid, polyploid, EXTINCTION, speciation, diversification, sheer rate of speciation (heteroploid) - 15% of angiosperms and 31% of fern speciation events
