Experimental evolution Gradual vs rapid evolution o If evolution is slow and steady, we'd expect to see the entire transition, from ancestor to descendant in the fossil record o For example, the evolution of whales from land-dwelling mammals, highlighting the transition of the walking forelimb to the flipper o However, fossil records are often incomplete and not all organisms form fossils. Moreover, as shown by Cambrian Explosion, evolution can proceed in big leaps (this can lead to loss of some fossils or evolutionary intermediates). There are other ways to study evolution. -Time Gradual lineage evolution Rock strata with fossils o Alternative 1: comparative genomics based on sequence data " A phylogenetic tree is a branching diagram or a tree showing the evolutionary relationships among biological species based upon similarities and differences in their physical (e.g. morphological) or genetic characteristics " On the left below is a phylogenetic tree of humans & apes based on over 150 genomes " The right-hand tree below shows evolutionary relationships of a mitochondrial gene (cytochrome c oxidase subunit I). At the root (left) is the common ancestor of all the species. Species next to each other are more similar & diverged more recently Human Homo sapiens (UK) 99 - 1 100 31 Homo sapiens (Afica) 17 Homo sapiens neanderthalensis Orangutan - Pan troglodytes -100 15 Pan paniscus > 150 complete genomes Gorila gorila gorila 0.0050 One mitochondrial gene: Cytochrome c oxidase subunit I o Alternative 2: experimental evolution in real time " Experimental evolution: replaying the tape of life " Experimental evolution is the use of laboratory or controlled field manipulations to investigate evolutionary processes. It usually makes use of organisms with rapid generation times and small physical size, often microbes, to observe phenomena that in large multicellular organisms occur too slowly.
Sexual Asexual Asexual or sexual Bacterial generation time: 20 minutes Nematode generation time: 3 to 4 days Fruit fly generation time: 10 to 12 days . Experimental evolution phase 1: Selection experiment · Experiments usually use a single bacterial clone which replicates into multiple independent lineages. This means the experiment starts from a genetically uniform base population. There's no standing genetic variation present in the setup . Selection is then created and enforced on organism (e.g., antibiotic in the growth media or different growth media types) . The bacteria are transferred and cultured consistently in this environment to allow natural evolution (in the e.g. below, the bacteria are grown in each independent selection line in growth media for 24hrs). A small subset of the evolved population is taken & transferred to the fresh media every 24 hrs for a while. · Samples are preserved at -80? every 100 generations to allow a snapshot of adaptation over time. This allows creation of a living fossil record Experimental evolution Evolutionary time "Living fossil record' ‘Ancestor' 'Most evolved' Genetically uniform base population Transfer to new tube Repeat transfers with samples of the lines stored every 100 generations Grow for 24 h in tube Grow for 24