Speciation

Eastern rosellas and pale-headed rosellas are thought to have descended from a bird that had a range extending over much of Australia. Now the range of the eastern rosella extends from Tasmania to southern Queensland, and the range of the pale-headed rosella extends from Cape York to northern New South Wales. There is no hybridisation where the ranges overlap.

For this situation to have developed it is probable that:

•   a mutation occurred in southern Queensland

•   the pale-headed rosella migrated to the snow country

• for a long period of time a geographic barrier isolated the northern and southern extremes

• for a long period of time a geographic barrier isolated the northern and southern extremes

The golden marmoset of Madagascar only eats bamboo stalks. It is the only animal known to eat the entire stalk. The pith of the bamboo contains high levels cyanide.

The amount of cyanide in one meal for the marmoset would be enough to kill a much larger mammal and yet the golden marmoset experiences no ill effect on this diet.

The evolutionary relationship between the golden marmoset and bamboo would be best described as:

• divergent evolution

• convergent evolution

• punctuated evolution

• co-evolution

Stasis in macroevolution refers to:

 

• relatively little phenotypic change in a group over a very long period of time

• character displacement in a species as a result of competition

• the extinction of a particular lineage

• the retention of parental lineages after parapatric speciation has occurred

Explain the differences between microevolution and macroevolution.

Answer explanation

Microevolution is the evolutionary change within a population on a small scale. Macroevolution is above species level and is large scale evolutionary change. Both are the result of the evolutionary mechanisms of mutation, migration, selection and genetic drift.

Describe, with examples, the circumstances under which divergent evolution could occur.

Answer explanation

Divergent evolution occurs when a population of interbreeding organisms separates into two or more descendent species. This occurs when there is competition for resources, a new niche becomes available, or due to geographical isolation. The finches of the Galapagos Islands are the result of divergent evolution (adaptive radiation) to take advantage of the different food sources on the different islands.

Explain why migrants must interbreed and produce offspring with residents for gene flow between populations to have an evolutionary impact.

Answer explanation

If migrants do not interbreed to produce viable, fertile offspring, then their genes do not enter the gene pool. There will be no impact of allele frequencies and will have no evolutionary impact.

Races are sometimes described as a stage in the development of new species. Which one of the following conditions would not facilitate formation of two new species from two races?

• Reproductive isolation of members of one race from the other

• Interbreeding between members of each race to produce fertile offspring

• Increasing differences between the members of each race, leading to different gene pools

• Each race tending to be confined to geographical areas with differing environmental conditions

Allopatric species are those that do not interbreed as a result of:

• mechanical isolating mechanisms preventing coition

• unviability of any hybrids formed

• specialisation for different environmental conditions and thus different ranges

• irregular development of the hybrid embryo