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University of Guelph
BIOL 1500
Marie Therese Rush

Unit 4: Species and Speciation What Is a Species ? -in mid 1700s Carl Linnaeus began task of cataloging all of nature -Linnaeus created binomial classification system for classifying species that still used today (grouped organisms according to shared traits) -used two-part name; first indicates genus-broader biological category to which several similar species may belong; second part is specific to particular species within genus species- group of individuals that regularly breed together and are distinct from other species in appearance or behavior (members have greatest resemblance) -named humans homo sapiens (homo- man (is the genus),sapins-meaning wise (is the species) subspecies- subdivision of species that’s not reproductively isolated -- population with unique evolutionary history ●Biological species concept –species consist of organisms that can interbreed and produce fertile offspring and are reproductively isolated from other species biological species - group of individuals that can interbreed and produce fertile offspring(all humans belong to same biological specie(homo sapiens) -useful in identifying boundaries between populations of similar organisms -relatively easy to evaluate for sexually reproducing species -cannot be applied to organisms that reproduce asexually or to fossil organisms asexual reproduction-type of reproduction in which one parent gives rise to genetically identical offspring -may not be meaningful when two populations of the same species are separated by large geographical distances -most common definition of species used by biologists -reproductive isolation-reproduction between two different species cannot occur due to pre-fertilization barriers and post-fertilization barriers -pre-fertilization barriers-those that prevent fertilization from occurring: -spatial isolation-occurs when two individuals are geographically separated from each other (don’t come in contact with each other and therefore cannot mate) sympatric-in the same geographic region -polar bear (artic& spectacled bear (South Americanever encounter each other in natural settings -behavioral isolation- mating cannot take place unless the appropriate behavioral display or ritual takes place between two individuals (each species has different mating displays and therefore making won’t occur between different species) -many birds have premating songs/dances and won’t mate with those who don’t know ritual -mechanical isolation – if sex organs of two individuals don’t fit together properly, mating cannot occur -sex organs are incompatible between different species so sperm cannot reach -many insects with ‘lock-and-key’ type genitals physically prevent sperm from contacting eggs of a different species -temporal isolation – occurs when two individuals aren’t fertile at the same time -plants with different flowering periods cannot fertilize each other -gamete incompatibility- when egg from one species cant fuse with sperm from another species -animals with external reproduction (sponges) have specific proteins on their eggs that will only bind to sperm from the same species -post-fertilization barriers-fertilization occurs, but hybrid cant reproduce -hybrid inviability- occurs when zygote is formed but the developing offspring dies early in development -sheep crossed with goat can produce embryo but embryo dies in early developmental stages -hybrid sterility-hybrid offspring is produced but unable to produce offspring hybrid- mating between two different species occur results in living species (offspring often sterile-can’t produce offs(mule) ●Genealogical Species Concept- species consist of organisms that can interbreed, are all descendants of a common ancestor and represent independent evolutionary lineages -most evolutionarily meaningful because each species has its own unique evolutionary history -can be used with asexually reproducing species -difficult to apply in practice, requires detailed knowledge of gene pools of populations within a biological species -cannot be applied to fossil organisms Gene pool-all of the alleles found in individuals of species -species is group of interbreeding organisms who are more closely related to each other than to other groups (group of organisms with unique lineage) -results in greater number of species than biological species concept because spatially-isolated populations of biological species that are unable to interbreed would all be considered separate species ●Morphological species concept – species consist of organisms that share a set of unique physical characteristics that is not found in other groups of organisms -easy to use in practice on both living and fossil organisms -only a few key features are needed for identification -does not necessarily reflect evolutionary independence from other groups -group of individuals that have unique physical features that make them look different from other groups ●Genetic Species Concept- similar to the morphological species concept, however rather than looking for physical differences among individuals, differences in genetic make-up are used to identify species -DNA barcoding is fairly new technique that’s used to establish genetic identity of organisms (sometimes with surprising results) Process of Speciation Speciation- evolution of one or more species from ancestral form There are three important steps in the process of speciation: 1/ Isolation of populations: Populations (i.e., groups of individuals of the same sp) must bec
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