Rate of Evolution Juliana Senawi

Transcription

1 Rate of Evolution Juliana Senawi Rate of Evolution Measurement of the change in an evolutionary lineage overtime Radiometric and paleomagnetic dating provide an effective basis for determining the age of fossil and hence the rates of evolution of the species to which they belong 1

2 Rates of Evolution GGSimpson: G. G. Tempo & Mode in Evolution (1944) applied principles of modern synthesis (e.g. population genetics) to fossil record How to measure evolution 1) Phylogenetic Rate Morphological Rate rate of change of character or group of characters in a lineage Quantitative i measures Rate = Change/ Unit Time 2

3 Rates of Evolution of Single Characters J.B.S. Haldane (1949): Evolutionary rate (r) = (ln x 2 ln x 1 )/change in t Measured in darwins darwin = change in e / my Bruce MacFadden The measuring the rate of evolution illustrated by MacFadden on horse teeth: classic materials in the study of evolution. 3

4 Evolution of Equine Lineage Comparing Rates Determined by selection? Can t prove selection is responsible for changes in fossil record But can find out the results in two area are consistent. e.g. Fossil evolution rate are higher than rates observed in artificial selection suggest selection not the only cause of evolution But other way round mechanism of population genetics, natural selection and random drift can accommodate the fossil observations. 4

5 Fluctuations in Rate Inverse relation between rate of evolution and time interval over which it was measured: rapid evolution have tended to be for shorter interval than slower evolution the rate of evolution measured over a short interval is inevitably higher than the rate measured over a longer time interval because the short term changes cancel out. Fluctuations in Rate width time e.g. Galapagos finches beaks -Larger in time of food shortage and smaller in times of abundance - overtime these changes in size cancel each other out 5

6 Character Types characters evolve at different rates (mosaic evolution) rate of change is not constant conservative characters: canalized; general adaptations derived characters: specialized, rapid evolution 2) Taxonomic Rate replacement of forms origination & extinction Quantified: (# taxa originate # taxa extinct) )/ unit time Or the inverse of the average duration of a species 6

7 Cladogenesis & Anagenesis Speciation at t 1 & t 2 a & c contemporary b goes extinct Problem: Fossil record: taxonomy based on morphology characters. Hard to separate anagenesis from cladogenesis. Identification of many chronospecies (descendent recognized as separate spp.) Chronospecies Taxonomic Pseudoextinction 7

8 Phylogenetic Rate = Taxonomic Rate rapid rate of morphological change leads to high rate of taxonomic replacement mor rphology time Taxonomic Rate Phylogenetic Rate high rate of turnover; little morphological change mor rphology time 8

9 Relationship between phylogenetic rate and taxonomic rate depends on characters used to determine taxa Comparison of ftaxonomic rates : balance of origination & extinction Recent Taxa rapid evolution poor fossil record typical of Adaptive Radiations 9

10 Problem of stasis: Fossil Deposits: my apart short term changes are lost However, observe: 1) long periods without change 2) rapid appearance of new forms 3) no transitional forms Real or Artifact? Quantum Evolution Problem: new taxa without fossil intermediaries Simpson 1953: rapid, substantial evolutionary change with shift into new adaptive zones once a threshold passed in acquisition of new adaptation, strong directional selection shapes feature into new forms 10

11 Quantum Evolution Within the taeniodonts, a group of extinct placental mammals, two lineages evolved. One was the original group of taeniodonts, the beaver sized conoryctines that survived into the late Paleocene; conoryctines The other taeniodont lineage was stylinodonts evolved rapidly (quantum evolution) across a transition to a new adaptive zone (lifestyle). Quantum Evolution The bear sized stylinodonts evolved specialized dentition especially suited to rough and highly abrasive foods, well developed claws, and strong muscles suggesting a digging foraging style stylinodonts 11

12 Hypotheses 1) Phyletic Gradualism constant anagenetic change speciation gradual transitional forms lost in fossil record 2) Punctuated Equilibrium stasis is real evolution occurs during speciation long term trends in morphology due to spp. selection Hypotheses Phyletic evolution (anagenesis) envisions gradual divergence of a lineage as the bell shaped mean of successive populations changes, until a new species is formed. 12

13 Hypotheses Punctuated equilibrium (cladogenesis) envisions long periods of more or less unchanging species persistence, suddenly interrupted by speciation, producing a new species. 3) Rate of Molecular Evolution Total amount of genetic change between two generations or within a succession of generations between fossil and living taxa) Techniques (retrieve and sequence DNA) from fossil demonstrate base pair differences in small segments of particular genes in many extinct organism but rarity in fossil DNA makes this impractical 13

14 DNA and RNA sequence Provide a means for establishing relationships measuring relative rates of evolution in all taxonomic group This important Fossil record is incomplete Study of the sequence of divergence of populations and subspecies Rate of Molecular Evolution vary Changes in DNA not occur the same rates in all taxa In common with changes in morphology Mitochondrial DNA changes much more rapidly than nuclear DNA Different portions of the same gene evolve more rapidly than others Since almost infinite amount of DNA Details of phylogenies will differ depending on what genes are used 14

15 Molecular Clock Molecular evidence used establishing the nature of interrelationships of different lineages and the relative time of their divergence But cannot establish the actual time when lineages originated by itself Molecular l clock must tb be set on basis of some other evidence such fossil record or a geological event Example Separation of South America and Africa (continental drift) 15

16 Give minimum time for the separation of populations that inhabited those continental The time at which their genome was identical must have been prior to that split Estimated rate of molecular evolution = Total amount of change / elapsed time If the rate constant It can be used to establish the sequence of divergence of individual lineages within the groups that subsequently evolved separately in South America and Africa This provides information as to the rate of divergence and the relative longevity of the living members of these lineage If several different genes in all taxa is constant supports assumption the rate of genetic change is constant 16

17 Summary Genes used in taxonomic studies not provides direct evidence of the evolution of morphological structures. Although phylogenies based on molecular evidence reflect the relative time of divergence cannot be used to establish how or when specific characters evolved. Taxonomic groups are recognized by presence of unique morphological traits by which all known members can be identified. Divergence of a group may be accompanied by emergence new character it is very unlikely that more than a single character will arise in synchrony with the divergence. No matter how accurate the phylogenetic resolution the fossil record remains the primary basis for establishment of the patterns and rates of morphological change. 17

18 Thank You! 18