Speciation and Reproductive Isolation Flashcards Preview

GeoSci 110 (Exam 2) > Speciation and Reproductive Isolation > Flashcards

Flashcards in Speciation and Reproductive Isolation Deck (26):

Biological Species Concept (BSC)

species are groups of interbreeding natural populations that are reproductively isolated from other such groups

- groups of populations that can exchange genes (actually or potentially)

- produce fertile offspring

- reproductively isolated from other such groups

- as long as two forms interbreed, they cannot diverge

- if two forms DO NOT interbreed, they each can develop different adaptations


Pre-Zygotic Isolation

union of egg and sperm never occurs because gametes never encounter one another


Post-Zygotic Isolation

egg and sperm encounter one another but the zygote is either not viable or gives rise to individuals that cannot reproduce or have very low fitness



cells formed by the union of male (a sperm) and a female (an ovum) sex cells


Pre-Zygotic Mechanisms for Reproductive Isolation

1.) Geographic Isolation (allopatric speciation)

2.) Gametic Isolation

3.) Mechanical Isolation

4.) Temporal

5.) Behavioral

6.) Ecological Preferences and Mating Isolation


Geographic Isolation (allopatric speciation)

existences of a geographic barrier

- complete geographic isolation


Gametic Isolation

occurs when incompatibility in gametes (egg and sperm) do NOT permit fertilization

- i.e. differences in number of chromosomes or chemical signals


Mechanical Isolation

simply put, male "parts" don't fit female "parts"

- i.e. dragonflies, beetles, bush babies, flowering plants and specificity in their pollinators


Temporal Isolation

inter-species differences in timing of reproduction

- could be considered sympatriotic because there's no geographic isolation

- i.e. cicadas


Behavioral Isolation

can occur when mating displays and courtship rituals become intertwined with reproductive act

- mating rituals, displays, songs, etc.


Ecological Preferences and Mating Isolation

occurs when environmental preferences reduces the frequency of interbreeding

- i.e. apple maggots


Post-Zygotic Mechanisms for Reproductive Isolation

1.) Zygote Morality

2.) Hybrid Inviability

3.) Hybrid Sterility

4.) Low Hybrid Fitness (survivorship)


Zygote Morality

occurs when a successfully fertilized egg begins process of development but the zygote is not viable and fails to complete development


Hybrid Inviability

occurs when gametes fuse, development progresses, but offspring cannot survive to adulthood

- i.e. occasional cross between Rana Pipiens and Rana Sylvatica offspring lasts only a few days


Hybrid Sterility

occurs when gametes fuse, development progresses and offspring survive to adulthood but they themselves cannot reproduce

- i.e. the Zorse


Low Hybrid Fitness (survivorship)

occurs when gametes fuse, development progresses and offspring survive to adulthood and can produce offspring but have very low fitness in the wild

- i.e. dog-wolf hybrids


3 Geographic Models of Speciation

1.) Allopatry

2.) Parapatry

3.) Sympatry



occurs when populations become completely, physically separated from one another by geographic barriers

- i.e. isolation on islands (Darwin's finches)



separated not by geographical areas but an extreme change in habitat

i.e. grass adapting to rivers with heavy metals whereas the grass in clean rivers don't need to



occurs when there is no spatial separation but reproductive isolation occurs


Ring Species (Parapatry)

two populations that do not interbreed are living in the same region but they are connected by a geographic ring of population that do interbreed


How do geographically isolated populations diverge?

1.) Natural selection adjusts population to local environments

2.) Genetic Drift (mutations)


Allopatric Model for Speciation (how geographically isolated populations diverge)

1.) a single contiguous population in a homogeneous environment

2.) differentiation of environment and migration to a new environment increases phenotypic variation

3.) Founder Effect plus adaptation to local environments results in genetic divergence in geographically isolated peripheral populations

4.) some of these isolated subspecies differentiate with respect to genetic and chromosomal changes that control reproductive isolation mechanisms

5.) changes with the environment permit geographically isolated populations to overlap with parent species


Genetic Drifts (how geographically isolated populations diverge)

all left to chance; unpredictable fluctuations in allele frequencies

- more effective in small populations (sampling errors)


Bottleneck Effect

the large population decreases in size and their survivors lack diversity

- i.e. Florida panthers


Founder Effect

when a few individuals of group separate from a large population and establish a new one

- genetic diversity within the main population is conserved

- i.e. the Amish population