Bio 300 Short answers 2

oiv01's version from 2015-12-09 05:26


Question Answer
Describe the roles of, and the relationship between, gene flow and natural selection in both the allopatric and sympatric modes of speciation.Allopatric: gene flow reduced due to geographic separation, which allows natural selection (any type) and genetic drift to slowly make populations so different from each other that they can be considered separate species. Sympatric: here there is no geographic isolation, so EITHER there is ecological isolation to prevent gene flow, in which case genetic drift and natural selection drive speciation (as in allopatric), OR if there is no kind of isolation, then there must be strong disruptive selection counteracting gene flow.
Compare and contrast the biological species concept and the phylogenetic species concept. What criterion does each use to identify species? What are the pros and cons of each?BSC – species defined by current forces (gene flow) keeping populations cohesive – if gene flow can occur between groups, then they can affect each other genetically. Pros – easy criterion to test, Cons – doesn’t work well for asexual species, organisms that can hybridize across great evolutionary distances, like some plants, and fossil species, lumps groups that probably evolving separately. PSC – species defined in terms of past genetic connections (a common ancestor with certain character states). If a group of organisms share characters and can’t be subdivided into smaller groups with their own shared derived characters, then you have a phylogenetic species. Pros – reflects evolutionary history better than BSC, and works for those groups for which the BSC doesn’t (listed above), Cons – species split by characteristics that might not have any biological relevance, splits groups into too many small units based on what might be minor traits, not always useful in the field or by people without lots of biology training and expertise in the particular species you’re looking at.
What are the possible outcomes when species that have long been separated geographically come back into contact and begin hybridizing?They can either produce healthy fertile hybrids, and then gene flow would homogenize them back into one species, or they will not be able to maintain a lineage of fertile hybrids and they will remain genetically isolated – separate species.
Discuss the evolutionary relationship between the primordial form and LUCA.The primordial form is the first living organism. It may have had several descendant lineages, one of which led to LUCA, which is the most recent common ancestor of all living things. Other descendant lineages of the primordial form may have become extinct. It is possible that there have been multiple evolutions of life (primordial forms) on earth that were wiped out during major environmental catastrophes without leaving any descendant species.
Discuss the relationships between a species’ geographic range and extinction.There are several ways in which a species’ range is linked to extinction. First, research on marine organisms has demonstrated that species with larger geographic ranges tend to have lower background extinction rates. Second, habitat loss is a major factor in extinction. Species that have their ranges restricted either by natural or man-made phenomena are subject to reduced genetic diversity through drift, which limits their ability to adapt to changing environments.
Where does the term “Cambrian explosion” come from? Was it really an explosion, and if so, what was it an explosion of?The term Cambrian explosion comes from the massive species radiation and colonization of land by multicellular animals that came during the first 40 million or so years of the Phanerozoic Eon, beginning 543 million years ago. This period of time is known as the Cambrian Period and is less than 1% of the history of the earth. During the Cambrian there was a diversification (explosion) of morphological changes (e.g., changes in body plan and body size). It was not an explosion of lineages, most of the living phyla of life on earth were already present on earth long before the beginning of the Cambrian Period.
Define and give examples of adaptive radiation. Describe the two key factors that seem to be involved in most adaptation radiations and give several examples of each.A small group of ancestral species rapidly diversifies into a large number of descendant species occupying a large variety of ecological niches. Triggered by ecological opportunity (dispersal/colonization or release from competition) or key innovation (adaptation that allows exploitation of new habitat or resource).
A small group of ancestral species rapidly diversifies into a large number of descendant species occupying a large variety of ecological niches. Triggered by ecological opportunity (dispersal/colonization or release from competition) or key innovation (adaptation that allows exploitation of new habitat or resource).10 km asteroid hit the earth on the Yucatan peninsula. Sulfur dioxide and soot in air, plus smoke from fires blocked sun – cooled earth and inhibited photosynthesis. Also caused earthquakes, volcanism, and an Atlantic tsunami. Species that weren’t wiped out immediately went extinct as major ecological cycles and relationships were disrupted. Some groups, like dinosaurs, marine reptiles and non-fern land plants were almost completely wiped out. Other groups survived, like early mammals, ferns, crocodilians.
What differentiates a mass extinction event from background levels? Can anything good come from a mass extinction (think in terms of the 5 major Phanerozoic mass extinctions on earth)?Mass extinction is significantly higher than background rate (ca. 60% or more species on earth become extinct), global in scale, many lineages die, usually correlated with major environmental change. Good can come from mass extinction because it opens up ecological niches for adaptive radiations of new species.
Do you think the Earth is experiencing another mass extinction? Support your answer.
What living species are most closely related to humans? What DNA data were used to study the relationships between humans and their very closest relatives?Chimpanzees and bonobos. Multiple gene data sets were compared to elucidate this relationship. Since both chimp and human genomes have been sequenced, comparisons can now be made on a gene-by-gene basis.
How are Neanderthals related to modern humans? What evidence supports your answer? What evidence conflicts with your answer?Neanderthals and anatomically modern Homo sapiens last shared an ancestor around 500,000 years ago. They are not direct ancestors of modern humans (if the current support of the African replacement hypothesis holds true). Genetic (DNA) evidence supports Neanderthals and humans splitting 500K years ago (and the amount and diversity of genetic evidence is growing!), however, it recent research indicates that there may have been some genetic mixing between Neanderthals and modern humans about 100,000 years ago after humans left Africa. Living humans from all regions of the earth are more closely related to each other than any are to Neanderthals – modern humans appear to be a distinct lineage that emerged from Africa and replaced Neanderthals in Europe and Asia, over a relatively short time period with only a little evidence of interbreeding. Some physical evidence conflicts with this idea – some aboriginal cultures maintain distinct physical traits that are more similar to the fossil hominins in the same region, than they are to modern humans elsewhere. Also, some paleontogists have made the argument that if humans replaced the Neanderthals and other archaic hominin forms so easily, they must have had superior tools and weapons. There is not much evidence that the first anatomically modern humans had advanced technology.