Download Patterns of evolution – Chapter 3

Patterns of evolution – Chapter 3
Branching or not
• Cladogenesis – lineages branch into two or more lines
• Anagenesis – evolutionary change in a lineage without branching
Evolutionary history and classification
• A taxon (named group of organisms) may be:
• Monophyletic (e.g. Aves)
• Polyphyletic
• Paraphyletic (e.g. Pongidae)
Pongidae, a paraphyletic group
Patterns of evolution
• From phylogenetic studies, common patterns of evolution have been identified
1. Pre-existing features
• Features of organisms to not arise de novo (from nothing)
• Related organisms have homologous characters, but character state may
not be homologous
•
Homology may be inferred by common position and structure, as well as
embryology
2. Homoplasy is common
• Types of homoplasy
• Convergent evolution
• Parallel evolution
• Evolutionary reversals
• Homoplasy indicates adaptiveness of traits
Parallel evolution
Convergent evolution
Evolutionary reversals
3. Rates of character evolution differ
• Some characters evolve very quickly, e.g. body size in mammals
• Conservative characters change very little
• Mosaic evolution is when different characters evolve at different rates within a
lineage
4. Evolution is often gradual
• Evolution proceeds by small successive changes (gradualism) rather than by
large leaps (saltations)
• Not all evolution may be gradual (will talk about later)
6. Change is form is often correlated with change in function
7. Similarity between species changes through ontogeny
• Von Baer’s Law – Species are often more similar as embryos than as adults
8. Development underlies some common patterns of morphological evolution
• A. Individualization
• B. Heterochrony
• C. Allometry
• D. Heterotopy
• E. Simplification of morphology within clades
A. Individualization
• Bodies of many organisms consist of modules that may become distinct individualization
B. Heterochrony
• Heterochrony is an evolutionary change in the timing or rate of developmental
events
• Change in the relative timing of development of somatic features versus
reproductive features changes features of organisms
• Paedomorphosis
• Peramorphosis
Paedomorphosis
Peramorphosis
• Peramorphosis is mostly limited to frontal lobe development and caused:
• An increase in the area occupied by the frontal lobe (lobe development is
extended), which in turn causes
• an increase in the area occupied by the stomach, which
• allowed descendants to exploit a different ecological niche (in this case an
increased sedimentation regime).
C. Allometry
• Allometry is the differential rate of growth of different parts of an organism
during its development
Allometry
• Allometry can be described by:
• Log y = log b a log x, where a is the allometric coefficient or relative growth
rate
• If a = 1, then growth is isometric
Allometry
• Suppose that x is body size and that y is the size of some feature that begin to
develop at age α and stops growing at age β
Allometry
Allometry
• If development is extended by Δβ, then paramorphosis results
Allometry
• If growth is shortened by Δβ (progenesis), then paedomorphosis results
Allometry
• If the growth rate of y is reduced relative to x (neoteny), paedomorphosis
results
D. Heterotopy
• Heterotopy is an evolutionary change in the position within an organism at
which a phenotypic character is expressed
Sesamoids
E. Simplification of morphology
9. Evolutionary trends
• Phylogenetic analysis can also document evolutionary trends. i.e., a
succession of changes of a character in the same direction, either within a
single lineage or in may lineages independently
• For example in plants, we see trends from:
• Low to high chromosome number
• Animal to wind pollination
• Radial to bilateral symmetry
• Woody to herbaceous
10. Adaptive radiation is common
• Adaptive radiation is the divergent evolution of a lineage within a relatively
short time
• Mammal and angiosperm diversification during Mesozoic and Cenozoic
• Cichlid fishes in rift lakes of Africa
• Darwin’s Finches on the Galapagos Islands
• Honeycreepers in Hawaii
What causes adaptive radiations?
• 1. Opportunity
• Colonization of isolated habitats
• Cuts off gene flow
• Many new niches available
• Lack of competition
• Mass extinction
• Climate Change
• 2. Evolutionary innovation
Colonization of isolated habitats
Mass extinctions
Evolution of land plants includes major innovations
Climate change
• Why did Conifers replace Ferns and fern allies?
•
•
Carboniferous forest (ca. 330 mya)
Lycopsids, Ferns, Horsetails still:
• Required water for fertilization
• Have free-living gametophyte generation (no dessication –resistant
propagule)
Why did gymnosperms replace lycophytes, horsetails, & ferns?
•
•
Seeds evolved by end of Devonian, yet non-seed tracheophytes continued to
dominate into Permian
What changed to favor Gymnosperms?
Rise of the gymnosperms
•
Formation of Pangea dramatically changed continental climate
•
Single landmass, very dry
•
Cold, dry periods
•
Favorable conditions for gymnosperms
•
Ferns have flagellated sperm & free-living gametophytes
•
Gymnosperms & Cycads: wind-dispersed pollen (and first animaldispersed pollen), retain seed