Chapter 19 Flashcards
Macroevolution
evolution above the species level, evolution of substantial phenotypic changes, usually great enough to place the changed lineage and its descendants in a distinct genus or higher taxon
describe fundamental tenets of evolutionary synthesis
o Adaptive evolution results from natural selecton on random mutations
o Selected mutations are mostly those with small effects
o These type of genetic variations arise and persist in large populations, so adaptive evolution some times need not await new mutations but instead can be very rapid
o Large evolutionary changes, transpiring over long periods of time, have occurred gradually, by the accumulation of small changes
Questions pertaining to macroevolution
Is the rate of evolution, based on supply of genetic variation and strength of natural selecton, fast enough to account for the emergency of new kinds of organisms?
What are the steps which such new forms – higher taxa – have evolved?
Where do things like beaks and horns come from in the first place?
How do we account for novel characteristics?
Is the entire history based on gradual change or change without intermediates?
Is this random or predictable change?
Do we notice grand historic trends?
Microevolution
processes occurring WITHIN species; short-term evolutionary changes within species
Describe origin of mammals
o First amniotes originated in Carboniferous
o Carboniferous amniotes gave rise to Synapsida
Synapsida
developed diverse mammaliaform lineages
Temporal fenestra for expanding jaw muscles into when contracted
Enlarged later
- group within –> cynodonts
Cynodonts
- Partial secondary palate
- Enlarged dentary
- Several cusps in cheek teeth
- Quadrate smaller and looser
Later cynodonts - More developed cusps
Name critical mammalia characteristics developing in this time
Lower jaw is single bone
Primary jaw articulation between dentary and squamosal bone
Mammals have stirrup bone, hammer (malleus) bone, and anvil (incus) bone in middle ear
Mammals have incisor, canines, and multicusped cheek teeth (premolars and molars)
Compare the mammalia characteristics to other groups
- Reptile lower jaw several bones in comparison
- Between articular and quadrate bone in other tetrapods in comparison
- Early amniotes only have stirrup in comparison
- Other tetrapods have unfiorm single-cusped teeth in comparison
Name other traits not as critical that split mammals from amniotes
- Enlarged braincase
- Temporal fenestra behind eye socket
- Secondary palate to separate breathing passage and mouth cavity
What do all the new traits for mammals do for them?
Create efficient predators!
Name and describe animal examples leading to mammals
Morganucodon: early mammal, two jaw to skull joints, articulation between dentary and squamosal, articular and quadrate
Hadrocodium: full lower dentary jaw, articular and quadrate separate, 3 middle ear bones
Describe the system of evolution for mammals
Mammal traits like ear bones evolved gradually
Bones that persist are modifed from those of the stem amniotes
Evolution from synapsids to mammals gradual
Saltations
o Defined: evolution sometimes proceeded by large, discrete steps or leaps
Large discontinuous changes in the characteristics of evolving lineage
o Controversial in evolutionary history
What is an explanation for saltations?
o Most obvious explanation of phenotypic gaps among living species is extinction of intermediate forms that once existed
Example: cetaceans
o Some organisms have puzzling features that seem to call for saltational origin, since its hard to see how intermediate step from their ancestor could have been advantageous
Example of possible saltation study
- Odontchelys
o Fossil
o Turtles had not evolved a shell yet
o However, the scapula was closer to the head than the first rib in this fossil, which was pointed back toward the tail
o Enabled evolution of carapace that protects front legs and head, along with rest of turtle organs
Describe the Ultrabithorax gene (Ubx) in Drosophila
- Transofrms fly with halteres into fly with two pairs of wings
- Mutation does not restore real hind wings
o Transforms third thoracic segment into replicated second segment, included replicated set of forewings - Mutatiosn that reduce function of this master control gene interfere with complex developmental pathway
o Grealy reduces survival because it disturbs normal development significantly
rare, protein coding DNA evolution causing phenotypic diversity, could be possible saltation
Describe an example of change resulting in a single mutation
- Hominoidea and other primates lack external tail
o Causes by intsertion of transposon into gene TBXT
o Exon is spliced out of RNA, distrupting a key pathway for the tail to develop
could call for possible saltational origin
Describe how unicellular organisms can help and show us evolution to multicellularity
Capsaspora is a unicellular eukaryote and closely related to animals
* Has small cis-regulatory sites, simple networks of interacting genes, gene regulatory features important in animal development
overall, development of complex characteristics
Novel characteristics
o The evolutionary change that distinguishes macroevolution from microevolution
Examples: wings of insects, vertebrae in vertebrates
New phenotypic trait (demanding that its genetic and developmental origin is understood)
Innovation
Substantial effect on organisms’ ecology and evolution
Conditions needed for novel characteristics
Exaptations, flexible enzymes, decoupling, animal behavior
Exaptations
modifications of ancestral structures that have been shaped by natural selection for new functions
Important in macroevolution!!!
factor of novel characteristic development
How do enzymes impact novel characteristic development?
able to serve other functions outside primary role, flexibility
Initially non-adaptive feature by-product of other adaptive features recruited to serve adaptive function
How can decoupling influence novel characteristic development?
Decoupling multiple functions of ancestral feature relieves functional constraints, so it may be free to evolve in new ways
How can animal behavior influence novel characteristics development?
animal species often affect or even determine the sources of natural selection on morphological and physiological traits
Example: animals feeding on different prey could develop ecological niche and other feature adaptations when they do this in times of need
o Behavior could coevolve with physiological and structural adaptations
Name example of physiological and structural adaptations under novel characteristic development
Scaptomyza evolved from Drosophila
* Genome sequencing showed receptors that respond to yeast odors in drosophila have been lost or silence in scaptomyza, while receptor that is sentive to green leaf odor has been duplicated
Describe the case of evolutionary biology from birds to humans
Most anterior digit of bird’s hand, which is morphologically equivalent to digit 1 (or “thumb”) in the hand of related dinosaurs and expresses the genes characteristic of a first digit
Describe the hypothesis of facilitated variation
Core processes of protein activity and cell and organ development have properties of robustness and adaptability that incidentally cause some variation to arise in ways that facilitate evolution
