BIOL&212 Animals (Metazoans) The evolution of diversity in form and function

Transcription

1 BIOL&212 Animals (Metazoans) The evolution of diversity in form and function

2 ~ 10,000 Aves ~ 1,800 Sea Stars ~ 7,900 Squamates 6 10 million Insects ~ 6,340 Amphibians

3 How should we organize this diversity of animal life? Linneaus Darwin

4 Nothing in biology makes sense except in the light of evolution. Theodosius Dobzhansky

5 Classification (Taxonomy) Natural system Often do it without understanding why

6 Early attempts at organization and naming Carolus Linneaus:Systema Naturae (1735). Two advances Hierarchical classification based on ideal of unchanging types. K, P,C, O, F, G, S Binomial nomenclature - replaced polynomials Assumes a static, unchanging Universe

7 What was Darwin trying to explain? Observations A hypothesis

8 Charles Darwin Englishman; bound for medicine then the clergy sidetracked by biology Beagle; visits isolated archipelago 1839 Journals 1859 The Origin of Species! Outlined the process of evolution via natural selection Demonstrated that life is dynamic

9 Observations that suggested Fossil Record change over time Layering of simple to complex Extinctions Succession & Transitional forms Environmental/Geological change Vestigial traits Apparent relatedness of species correlates with geographic distribution

10 Fossil record Fossils of complex organisms occur closer to the surface, in rocks of younger age, than those of simpler organisms. This layering was globally consistent suggesting they were different ages. Darwin had huge collections to examine, even in early 1800 s

11 Extinctions Some fossils clearly belonged to creatures no longer walking the Earth Irish elk More famous examples like T. rex

12 Transitional Forms & Environmental Change fossil sandwiches occurred in these rock layers; middle fossils intermediate in form between fossils above and below. Documented changes in skeletal morphology through time

13 Succession of forms Darwin s predecessors Morphology of fossil species often closely match the morphology of contemporaries Law of Succession

14 Presence of tiny, useless traits on contemporary species Anal spurs; coccyx Vestigial traits

15 Apparent Relatedness Darwin s contribution came after and almost certainly as a result of his voyage through the Galapagos island archipelago Charles Darwin (22) joins crew of HMS Beagle as gentleman s companion (ship s naturalist) & collects & catalogues everything. ( ) Plants, insects, fossils & Galapagos finches After his return he and his naturalist friends noted some things about his collections:

16 Different islands have distinct (but similar) species

17 Weight of evidence lead to his heretical proposal: H: Species on neighboring islands look similar because they are all descended from a common ancestor; The small differences between them are due to changes over time. A bold assertion & dangerous for the time. Species are not static!! So, he waited ~20 years after developing the idea to publish it

18 OK, so what s the mechanism Variable traits for change? Differential survival & Reproduction Variation is heritable Beneficial variants leave more offspring

19 Beetle color is variable, and heritable The environment selects against green beetles

20 On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life -Charles Darwin, 1859 Darwin s blackbirds, grossbeaks, wrens and finches

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24 Darwin s postulates (hypotheses) 1. Traits in a population vary among individuals 2. Some traits are passed on to offspring (i.e. traits have a genetic basis and are heritable) 3. Due to environmental challenges (ex: struggle for resources), some individuals produce more offspring than others 4. The subset of all offspring that survive are those that possess beneficial traits; these traits (and the individual carrying them) are naturally selected by the environment.

25 What was Darwin s contribution? Others had proposed evolution (of some variety) as a pattern that required explanation. Darwin provided the process, natural selection, that explained the pattern of descent with modification.

26 Darwin introduced fitness to explain natural selection Fitness: the ability of an individual to produce fertile offspring, relative to that ability in other individuals. This is a measurable quantity, and allows us to define adaptation Adaptation: a heritable trait that increases the fitness of an individual relative to individuals lacking that trait. These are time and location (environmentally) dependent

27 Contemporary evidence in support of evolution Homologous traits Structural/Morphological: Outward physical appearance Developmental: Sequence & timing of developmental events; shared germinal tissues Genetic: DNA sequence Direct observation: MRSA, soapbug beak length Convergent traits: Distant relatives have nearly identical traits

28 Structural Limbs with radically different functions are all built from bones of similar shape, in same orientation & same relative positions. Why, unless this structural archetype was present in the common ancestor of all?

29 Developmental Chick, human and cat embryos have gills and tails; they appear at similar developmental stages & in the same positions as those of fish. Why? Fish & human jaws look very different, but develop from same population of embryonic cells. Why should they?

30 Genetic The same 64 codons specify the same building blocks in ALL organisms. Why? Many genes are found in organisms that are very different and their sequences are nearly identical. Ubiquitin is found in ALL Eukaryotes; its DNA sequence is 96% identical between humans and yeast. Why?

31 Direct Observation Soapbugs Host plant switch Choice of host correlates with beak length Reduced gene flow Diversification follows

32 distantly related species that share common environmental challenges have similar traits Convergent traits

33 Base groupings upon shared (homologous) traits Animals that share the most traits are most closely related. What is a trait? Morphologic physical appearance Developmental sequence physical appearance during embryonic development; common cell fates, timing of cell migrations & gene activity Genetic DNA sequence identity; chromosome number