What is the significance of speciation for life on

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What is the significance of speciation for life on earth? •Main effect of speciation is restriction of recombination/geneflow between lineages (populations), allowing them to evolve/adapt independently and retain there adaptations even under sympatry. •Speciation itself is not an adaptive response, but genetic differences incidentally accumulate over time (not reinforced) •Speciation (as evolution of prezygotic isolation barrieres) can be adaptive (e.g. reinforcement) Speciation is the basis of Cladogenesis and hence responsible for all the diversity we currently see on earth In what circumstances is speciation “adaptive”? •Populations are ephemeral: –environmental shifts drive dynamic nature of change •expansion or contraction of ranges –gene flow homogenizes populations •eliminating divergence between populations •Reproductive isolation separates units that evolve in response to their specific environment •Isolation increases the number of units (populations/species), increasing overall level of adaptation •Therefore, we can argue that more speciose genera are better adapted than those with fewer species If hybridization barriers accumulate over time we would assume that… the longer two species are separated the higher/stronger is there genetic distance/isolation Genetic distance and taxonomic level •Several studies have indicated good relationship between genetic distance (= # of differences between species/groups) and taxonomic level (species, genus, etc.) •Attempt to create yardstick, aka. molecular clock (phylogenetic species concept) •There are problems, however: –distances vary among groups –Why? •Morphology and genes surveyed evolve at different rates in different groups
Polytomies : (hard=rooted/soft=unrooted) Life history evolution Life history: is the sequence of events related to survival and reproduction that occur from birth through death. Resources are limited and have to be split between M, G, R Life history tables Iteroparous: multiple reproductive cycles over the course of its lifetime. semelparous: A species is considered semelparous if it is characterized by a single reproductive episode before death, univoltine: referring to organisms having one brood or generation per year multivoltine: referring to organisms having more than two broods or generations per year clutch size evolution: depends on environment selection for early/late maturation: short life span, early maturation, able to reproduce earlier parental investment resource allocation – sex allocation Life span and senescence Human life span evolution trade-offs Coevolution: "the change of a biological object triggered by the change of a related object." Coevolution and fitness – def. different forms of co-evolution character displacement: The great differences in bill size and shape that some of Darwin’s finches in the Galapagos have evolved have resulted from competition. This process, called character displacement , results as natural selection favours those individuals in each species

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