Types of speciation *remember, speciation is the formation of a new species  1. sympatric  2. allopatric  1. sympatric  2. allopatric

sympatric  New species develops when members of a population develop a genetic difference that prevents them from reproducing with members of the original species.  Occurs due to reproductive isolation, not geographic  Far more common in plants  New species develops when members of a population develop a genetic difference that prevents them from reproducing with members of the original species.  Occurs due to reproductive isolation, not geographic  Far more common in plants

Polyploidy  is the presence of extra sets of chromosomes due to accidents during cell division  Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids  is the presence of extra sets of chromosomes due to accidents during cell division  Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

Sympatric speciation by polyploidy (in plants)  Sometimes hybrids between two parental flowering plants are formed.  This can happen because plants can‘t choose whom to mate with (i.e. pollinators or wind may move pollen between flowers of different species  Hybrids may be sterile if paternal and maternal chromosomes are incompatible and cannot pair in meiosis.  But sometimes, chromosome sets “accidentally“ double (polyploidy)  This doubling results in compatible partners  Plants can self-pollinate, produce seeds, and so propagate: a new species has formed  Between 30 and 50% of angiosperm plant species may have formed in this way!  Sometimes hybrids between two parental flowering plants are formed.  This can happen because plants can‘t choose whom to mate with (i.e. pollinators or wind may move pollen between flowers of different species  Hybrids may be sterile if paternal and maternal chromosomes are incompatible and cannot pair in meiosis.  But sometimes, chromosome sets “accidentally“ double (polyploidy)  This doubling results in compatible partners  Plants can self-pollinate, produce seeds, and so propagate: a new species has formed  Between 30 and 50% of angiosperm plant species may have formed in this way!

Allopatric speciation  Occurs when two populations are geographically isolated from one another. They are separated by distance or an impassable barrier.

Allopatric speciation  Occurs when a physical barrier cuts a breeding population in two.  Example: Grand Canyon squirrels  Occurs when a physical barrier cuts a breeding population in two.  Example: Grand Canyon squirrels Kaibab squirrelAbert squirrel

Figure 24.5 (a) (b) Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Sympatric speciation. A subset of a population forms a new species without geographic separation.