Biology 3.5 Patterns of Evolution Credits: 4 External
! Before we begin… From the examination specifications…
Revision 12 bio stuff…
Natural Selection • Definition • Types: • Directional • Disruptive • Stabilising
Other Year 12 Concepts • Founder effect • Population bottlenecks • Genetic drift • Mutation • Migration • Factors affecting allele frequencies…
Species Concept “a group of actually or potentially interbreeding natural populations that is reproductively isolated from other such groups” Main Problem: - Closely related species produce fertile offspring egCanis spp. - Genetically isolated species may be morphologically similar = cryptic species (morph = “body”) Main Solution: - Use DNA analysis to clarify relationships between closely related species. Extinct: 10,000 ybp
Bio 3.5 Brand new stuff from here
Clines & Ring Species • Cline: A gradation in one or more characteristics within a species esp. between different populations. • Ring Species: A series of neighbouring populations that can interbreed, but for which there exist at least two "end" populations in the series that are too distantly related to interbreed In this diagram, interbreeding populations are represented by coloured blocks. Variation along a cline may bend right around, forming a ring.
Larus (gull) ring species A Herring Gull, Larusargentatus (front) and a Lesser Black-backed Gull. Larusfuscus (behind) The Larus gulls interbreed in a ring around the arctic(1 : Larusargentatusargentatus, 2: Larusfuscussensustricto, 3 : Larusfuscusheuglini, 4 : Larusargentatusbirulai, 5 : Larusargentatusvegae, 6 : Larusargentatussmithsonianus, 7 : Larusargentatusargenteus Neighbouring groups can hybridise (breed together) but sufficient differences exist to prevent groups 1 & 7 breeding.
Californian Salamander Ring Species The many subspecies of Ensatina salamanders in California exhibit subtle morphological and genetic differences all along their range. They all interbreed with their immediate neighbours with one exception: where the extreme ends of the range overlap in Southern California, E. klauberi and E. eschscholtzii do not interbreed. So where do we mark the point of speciation?
Stages in Species Development • Species rarely explode suddenly into existence (species formation is usually slow) • General pattern: • Homogenous population splits (cause = geographical barrier) • Different natural selection pressures, mutations gene frequencies change • Races form as gene flow reduces, factors preventing mating begin (“prezygotic”) • Gene flow further reduces, post zygotic factors occur (hybrid sterility – eg as in mule) • Now = two different species.
Stages in Species Development - A generally predictable series of events occurs as a homogenous ancestral population evolves into two separate species. - The key to this is build up of genetic differences as a population is split into two populations. Barriers to frequent mating mean that differing natural selection pressures and mutations are not shared populations go down different genetic pathways. - Eventually differences build to where the populations become separate races. - With enough differences races become difference subspecies, then separate species.
Extinction Extinction Sumatran tiger Sumatran tiger: http://en.wikipedia.org/wiki/Sumatran_tiger Sumatran tiger clip: http://www.theawl.com/2011/05/get-a-good-look-at-these-awesome-tigers-theyre-almost-extinct Call of Life (extinction video trailer): http://www.calloflife.org/p-trailer.htm
Extinction • A natural process – all species that have evolved will eventually go extinct • Duration of persistence of a species varies (often from 1 million years for complex organisms to 10-12 million years for simple organisms) • Extinction and mass extinction provides opportunities for other organisms to evolve and fill vacant ecological niches. Case Studies • Humans How long have we been around? When will we become extinct? • Anatomical modernity: 200,000 years ago • Behavioural modernity: 50,000 years ago • Coelacanth
Coelacanth Coelacanths were thought to have gone extinct in the Late Cretaceous (~65mya), but were rediscovered in 1938 off the coast of South Africa. 2 Known extant species. The coelacanth has been nicknamed a “living fossil”, because its fossils were found long before the actual discovery of a live specimen. The coelacanth is thought to have first evolved approximately 400 million years ago. Latimeriachalumnae (60kg, 170cm long)
Speciation • “Formation of new spp. from an existing species” • Multiplication of spp. not gradual change over time
Allopatric Speciation • Usually: pops get geographically separated (eg by river) • Gene flow stops. Genetic isolation occurs. • Diffs in natural selection can cause diffs in allele frequencies between the pops over time. • Diffs may accumulate, when the pops are reunited they now no may longer interbreed = separate spp. • NZs isolation/islands has led to many egs of allopatric speciation.
Allopatric Speciation Questions 1. Why have many NZ birds lost the ability to fly (cf to their Aussie relatives)? 2. Glaciation creates many isolated mountaintops – how would this contribute to allopatric speciation? 3. How could sea level rise/fall create new species through allopatric speciation? 4. Describe how an ancestral robin species gave rise to the Chatham Island robin and the mainland robin.
Spelt • Where does this fit in wheat development? • http://en.wikipedia.org/wiki/Spelt
Evolutionary Relationships • Phylogenetics: the study of evolutionary relatedness between groups of organisms. Relatedness is determined by DNA sequencing data and comparing morphological data • Phylogeny: The evolutionary development and history of a species or higher taxonomic grouping of organisms. • Cladogram: Diagram which shows ancestral relations between organisms • Cladistics: method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants (and nothing else).
Cladograms • Show ancestral relations between taxa • Using DNA analysis or morphological comparisons • Species are at the “leaves” • Common ancestor at the “trunk” • Have an implicit time axis (runs forward from base to leaves) but: problems of scale, data quantity & quality • May show extinct species, but: DNA from extinct species is rare
*The canids are an old lineage, separating from the other carnivores about 60 million years ago. Separation of a "wolf" branch, a "South American" branch, and a "red fox" branch occurred more recently, 7-10 million years ago. *Mitochondrial DNA analysis of both modern and historical specimens of red wolves failed to distinguish red them as a species separate from gray wolves or coyotes. They appear to be a hybrid species, and can interbreed with either gray wolves or coyotes. *Two different dates for the origin of dogs have been suggested. Mitochondrial DNA analysis suggests a date between 60-100,000 years ago -- well before the beginning of human agriculture. Other genetic and archeological evidence suggests a more recent date -- about 15,000 years ago. Neolithic cave drawings also show dogs hunting with humans. *All domestic dogs are the descendants of a few ancestral wolf stocks originating in Asia. Surprisingly this includes New World dogs, who were once thought to have been independently domesticated from New World wolves. Simplified Canid Phylogeny
Molecular Phylogeny (DNA analysis) may revise past phylogenies (based on morphology)… Hedges, S. Blair, and Poling, Laura L. A Molecular Phylogeny of Reptiles. Science, Vol. 283, No.5404, pp.998-1001 • The study also cast in doubt the relationship between the tuatara and squamates. While fewer gene sequences were available for the tuatara, six of eight comparisons showed closer affinities with archosaurs or turtles, while only two showed squamates as the closest relative. While the results of this study are not conclusive, it clearly demonstrates that we don't know all that we thought we knew about the phylogenetic relationships of living or fossil reptiles. http://home.pcisys.net/~dlblanc/articles/TurtlePhylogeny.php
Homologous Structures • The structures shared by a set of related species because they have been inherited, with or without modification, from their common ancestor. For example, the bones that support a bat's wing are similar to those of a human arm.
Convergent Evolution • The evolution of the same biological trait in unrelated groups / species. • Examples: • Shark, icthyosaur, dolphin, penguin (a fish, reptile, mammal and bird respectively) are unrelated but have evolved a similar streamlined shape and “fins” in response to their environment (water) • Unrelated plants have evolved water storage tissue (succulent tissues) eg Euphorbia, cacti • Analogous structures “structures that are alike in function but have a different evolutionary origin” • Egs: wings of insects and birds; mammalian and octopus eye
Convergence in Plants These unrelated plants have separately evolved the ability to store water in their stems. This is a response to the natural selection pressure of dryness in the desert. The swollen stems are an example of an analogous structure Ferocactuspilosus (Mexicanlime cactus)
Divergent Evolution • When one ancestral group evolves into two or more species, usually in different habitats • Features: • Accounts for most evolutionary change • Often due to ancestral spp. Increasing range / colonising new areas / habitats (new ecological niches) The different conditions cause different selection pressure different genetic pathways genetic isolation speciation • Alternatively: • Sequential evolution: small changes build up over time until a new species emerges (aka anagenesis, pyletic graduation) • Budding: a new species branches off while the ancestral species remain unchanged. • Cladogenesis: When a whole new group of organisms evolves (eg primates)
Adaptive Radiation • “The diversification of a group of organisms into species filling different ecological niches”. • Can occur very rapidly, usually when a large number of ecological niches are vacant. • Example par excellence: • Dinosaur extinction 68mya opened up many niches for exploitation (eg Brontosaurus death opened up a large browsing herbivore niche). Relatively non specialised mammals (egMegazostrodon were, as adaptable ‘generalists’, able to fill these niches quickly and through natural selection speciate into new forms.
Other examples: • Galapagos Finches: 1 South American finch evolved into 14 spp. occupying different niches (desert, grassland…) on the Galapagos Islands • NZ Examples: • 100 spp. of Hebe plants • 10 spp. of Powelliphanta snails (+ subspecies) • NZ parrots (kakapo, kea, kaka) from one ancestor (100mya) • Note: In some of these egs radiation was very fast (many vacant niches) and involved the founder effect. Powelliphanta spp.