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Lecture 12

BIOL215 Lecture 12 Notes.pdf

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Biology (Sci)
BIOL 215
Neil Price

BIOL215 Lecture 12 Notes Sympatric speciation - speciation that occurs in the same place •Geographic isolation does not always precede speciation - in these cases speciation is sympatric • Sympatric speciation arises without geographic isolation •This means that a biological barrier to gene exchange has to arise within the confines of a randomly mating population without any spatial segregation of the species •Very controversial! Many theoretical difficulties •Only one example of sympatric speciation not controversial - speciation by polyploidy in plants • A single instantaneous change caused by polyploidy doubling of chromosome # - reproductively isolates a new polyploid from its ancestors •Cichlid species (fish) Mechanisms facilitating reproductive isolation •Normally, however, the barriers separating species are not caused by a single isolating mechanism • Seasonal • Habitat • Behavioural Reproductive isolating mechanisms: •Are obstacles to interbreeding between genetically distinct species Hybrids are not well adapted to environment • • Low fitness • Reproductively costly for the parent •There are 2 types of reproductive isolating mechanisms: • Those that act before fertilization of the egg (prezygotic isolating mechanisms) • Geographic isolation • Ecological isolation • Behavioural isolation Temporal isolation • • Those that act after fertilization of the egg (postzygotic isolating mechanisms) • Hybrid embryos might not develop properly • Hybrid adults do not survive in nature • Hybrid adults are sterile or have reduced fertility •Those species that live much closer to each other will have much stronger prezygotic and postzygotic isolating mechanism because hybrids are very bad for them This modern synthesis gave rise to "NeoDarwinism" •The view that mutation, recombination, natural selection and other processes operating within species account for the major, long-term features of evolution •Natural selection, through gradual changes over a long period of time, has produced the variety we see today: microevolution Paleontological view: •Paleontologists, however, recognized that: 1. Species appear "abruptly" in the fossil record 2. Persist for long periods of time 3. Then "abruptly" disappear •At first, paleontologists, thought this pattern to bean artifact of the fossil record •However, intermediate fossils began to be discovered •Simpson suggested that this pattern was real and not an artifact Proposed the idea of quantum evolution • •Simpson thought that the appearance and disappearance of the taxa in the fossil record were caused by natural selection, but speeded up during this short period of time •These ideas started a distinction between mic
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