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Unformatted text preview: Biol 101/102 Part II Office hours M 11-12, Eastlick 277 Species and the tree of life Ch. 13.7 206-215 We've talked a lot about microevolution E.g., antibacterial resistance Now let's talk about macroevolution forming new species... Speciation and tree of life- Outline What is a species? How do species form? What do we mean when we say species? Morphological species concepts "species" Latin for "kind" or "appearance" good `working' definition problems? Morphological species concepts "species" Latin for "kind" or "appearance" good `working' definition problems? Difficulties with morphopecies definition Males and females may look very different! Difficulties with morphopecies definition Males and females may look very different! Difficulties with morphopecies definition Juveniles and adults may look very different! Difficulties with morphopecies definition Species may vary in morphology over their range Difficulties with morphopecies definition Individuals may vary due to their functional roles The Biological Species Concept "A species is one or more populations of individuals that share a gene pool under natural conditions, and produce fertile offspring that are reproductively isolated from other species Focuses on genetic differentiation Genetic Divergence
daughter species time A time B time C time D Gradual accumulation of differences in the gene pools of populations Natural selection, genetic drift, and mutation can contribute to divergence Gene flow counters divergence Reproductive Isolation Cornerstone of the biological species concept Speciation is the attainment of reproductive isolation Reproductive isolation arises as a by-product of genetic change can you think of any problems with the biological species concept? Some problems with the biological species concept The definition does not work for fossils Some problems with the biological species concept The definition does not work for fossils Some problems with the biological species concept What about hybrids? Some problems with the biological species concept What about organisms that reproduce asexually? Some problems with the biological species concept The biggest difficulty with the BSC is that we can't assess gene flow and reproductive isolation without detailed study. Biologists think about species in context of BSC However most of what we know about species diversity assumes morphospecies How do species form part one: Achieving reproductive isolation Reproductive isolating mechanisms Prevent pollination or mating Block fertilization or embryonic development Cause offspring to be weak or sterile Kinds of Reproductive Isolation Mechanisms Generally Prevent pollination or mating Block fertilization or embryonic development Cause offspring to be weak or sterile We divide these into prezygotic (before mating & fertilization) post zygotic (after fertilization) Prezygotic Isolation
Mechanical isolation Temporal isolation Behavioral isolation Ecological isolation Gametic mortality Mechanical Isolation Wasp and zebra orchid orchid scent causes many kinds of males wasps to try to mate with flower however, only one species `fits' flower well enough to pollinate it Temporal Isolation two closely related cicada species emerge to mate on very different cycles (13 year vs. 17) although they overlap in habitat, sexual parents only overlap every ~200 years Behavioral Isolation Albatrosses Behavioral Isolation Mating rituals such as songs or other courtship displays can prevent gene flow between similar species Ecological Isolation some insects live in sympatry but feed and lay their eggs on different plants. reproducing adults never come into contact with each other Postzygotic Mechanisms
Early death Sterility Low survival rates How do species form part II: Models for speciation Allopatric speciation physical separation of populations leads to new species Sympatric speciation ecological separation in same locality causes populations to diverge Parapatric speciation populations in contact along a common border (with ecological differences across border) evolve into distinct species Allopatric Speciation Speciation in geographically isolated populations Some sort of barrier arises and prevents gene flow Effectiveness of barrier varies with species Extensive Divergence Prevents Inbreeding Species separated by geographic barriers will diverge genetically If divergence is great enough it will prevent inbreeding even if the barrier later disappears Archipelagos Island chains some distance from continents Galapagos Islands Hawaiian Islands Colonization of islands followed by genetic divergence sets the stage for speciation Speciation on an Archipelago A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat. 1 2 3 4 Later in time, a few 1 individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence. 2 Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island 1 by genetically different descendents of the ancestral species. 1 2 3 4 Hawaiian Islands Volcanic origins, variety of habitats Adaptive radiations: Honeycreepers: in absence of other bird species, they radiated to fill numerous niches Ancestral Type Housefinch (Carpodacus) Fig. 13-18d13, p.209 Speciation in Hawaiian Honeycreepers Akepa (Loxops coccineus) Fig. 13-18d1, p.209 ...
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