Ecology L9 Gene Flow and Speciation

Gene flow

mixing of alleles among populations; caused by migration/dispersal of individuals

3 effects of gene flow

equalizes gene frequencies

erodes genetic differences between populations

Introduces new alleles into population from other populations

Migration rate definition and equation

How quickly gene flow erodes genetic differences between populations

m= the number of immigrant individuals/total number of individuals in the population AFTER MIGRATION

Difference in allele frequency equation

\Delta q=m\left(q_{m}-q\right)

deltaq=difference in allele frequency

m=migration rate

qm=alleles frequency in migrants

q=allele frequency in the focal population before migration

F_{ST}

statistic that describes the genetic difference among individuals

F_{ST} = 0

0% of the variation is caused by differences between populations

100% of the variation is caused by differences within one population

0<F_{ST} <1 ex F_{ST} =0.36

36% of variation is caused by differences between populations

64% of the variation is caused by differences within one population

F_{ST} =1

100% of variation is caused by differences between populations

0% is caused by differences within one population

Biological species concept

Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups

Reproductive isolation

little to no gene flow between populations by any of several possible factors; prezygotic and postzygotic barriers

Prezygotic barriers

Ecological isolation

Temporal isolation

Behavioral/copulatory isolation

Mechanical isolation

Gametic isolation

Postzygotic barriers

Hybrids are formed but they have reduced fitness (fertile hybrid that produce sterile offspring)

Allopatric populations

geographically isolated populations; geographic isolation

Peripatric populations

a small population is isolated at the edge of a larger population; geographic isolation

Parapatric populations

a continuously distributed population; temporal isolation

Sympatric population

Within the range of the ancestral population; temporal isolation AND isolation via chromosome changes

Geographic isolation can be through either

Dispersal- individual of a population disperse across a physical barrier

Vicariance- an existing population is split by the appearance of a new physical barrier

Temporal isolation

speciation occurs because of a gradient that alters the timing of reproduction

Behavioral isolation

when adaptive behaviors result in reproductive isolation

Morphological isolation

When morphological adaptations result in reproductive isolation