{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lectures 22-24.Speciation Study Questions.2013

Partial isolation and reinforcement selection acts to

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ALL of the taxa/species descended from a specific common ancestor. BIS 2B, Spring 2013 Speciation Page 3 4) Paraphyletic clade: a taxonomic group that excludes some of the descendants from a specific common ancestor. 5) Polyphyletic clade: a taxonomic group that does not contain the most recent common ancestor of its members. 4. Three geographic scenarios that could reduce/eliminate gene flow (geographic classification): a) Geographic Isolation/Allopatric Scenarios: Populations have discrete ranges ⇒ geographical barriers limit gene flow. 1) Vicariant Models: some kind of geographic barrier arises that subdivides a formerly interconnected set of populations • Diversifying or other forms of selection could then promote differentiation between populations living in different habitats. • Example: Speciation in snapping shrimp across the Isthmus of Panama 2) Dispersal Models: a few “lucky” dispersing propagules cross a geographic barrier, and successfully colonize a new habitat. • Founder effects and genetic drift in small populations promote population differentiation • Example: Speciation and adaptive radiation in Hawaiian Drosophila 3) Secondary contact: What happens when a geographic barrier disappears and two geographically isolated populations come back into contact? • Complete isolation and no hybridization ⇒ • Hybridization, introgression, and the merging of populations. • Partial isolation and reinforcement: selection acts to reduce matings between the parental populations when they produce hybrids with low relative fitness b) Parapatric Scenarios: Populations have abutting ranges ⇒ Environmental discontinuities can limit gene flow. 1) Example: Speciation on mine tailings in pasture grass (Agrostis tenuis) • Secondary evolution of divergent flowering times (late vs. early flowering) c) Sympatric Scenarios: Populations/incipient species have overlapping ranges 1) Primary sympatry vs. secondary sympatry • Primary sympatry: Species differentiated in sympatry (true sympatric speciation). • Secondary sympatry: Species differentiated in allopatry or parapatry. ⇒ After becoming reproductively isolated, the populations moved into sympatry (not the condition under which reproductive isolation evolved). • Using phylogenies for distinguishing between primary vs. secondary sympatry 2) Mechanisms of sympatric speciation. • Multiple niche polymorphism: Sympatric speciation in cr...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online