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L19 – Speciation

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Biology 1001A
Tom Haffie

L19 – Speciation If LUCA had just continued to evolve and not speciated we would have ONE single species represented on earth. Speciation: Marks the interface between micro and macroevolution No one species concept can be agreed on Morphological Species Concept - organisms are grouped based on phenotypic characteristics - identifies species based on similarity - species: things that look similar, morphologically more similar to eachother than they are to any other group of organisms - no overlap between the species. Problems? - all of the happy faced spiders look completely different however they can interbreed - they would have to be classified as four different types of spiders (but they’re not) - pronounced sexual dimorphism, males will look EXTREMELY different from females, so they would seem to be two different species Biological Species Concept - most widespread - species: interbreeding (or potentially interbreeding) group of individuals, reproductively isolated form other groups - the spiders are not reproductively isolated, so they are one species according to the biological species concept (polymorphic, single species. One gene pool) - the creeper birds do NOT interbreed even though they cannot be told apart - they sing different songs Problems? - sometimes distinct species will hybridize (ex. Liger) - Lions and Tigers do not live in same area however they sometimes do mate - We have to examine whether this occurs under natural conditions to determine whether or not to classify lions and tigers as ONE species - Also, does the hybrid have normal fitness? Is it viable? Is it fertile? “evolutionary dead end” Limitations? - Scrub Jays are geographically isolated, no way to naturally determine IF they would interbreed if they could - Geographic isolation and Fossil Records (extinct species, no way to determine) With Fossils we are stuck with the Morphological species concept because we cannot give them the opportunity to interbreed With asexual organisms, biological species concept is meaningless because no interbreeding is occurring at all Different species concepts are in conflict with one another Reproductive Isolation - at what point does one distinct lineage separate into two? Prezygotic Isolating Mechanisms - temporal isolation (mate at different times but are in the same area) - types of frogs like to breed in certain temperatures or habitats habitat isolation - behavioural (courts
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