Transcript Speciation ppt speciation ppt

Speciation
Learning objective
 SWBAT: Describe and identify the various types of
reproductive isolation necessary for the formation of
new species according to the biological species
concept
 SWBAT: Compare allopatric and sympatric
mechanisms of speciation.
Speciation
 The process by which one species splits into
2 or more species
Different conceptual models to define
species
 Biological species concept

Defines species as a group of populations whose members
have the potential to interbreed in nature and produce viable,
fertile offspring

Limitations to this model:
Does not help to identify fossils as to species
 Does not take into account organisms that reproduce asexually

In certain circumstances other models can be used
 Morphological species concept
 Ecological species concept
 Phylogenetic species concept
These, however, tend to be much more subjective
Biological Species Concept
 Reproductive isolation = The existence of
biological barriers that impede members of 2 species
from interbreeding and producing viable, fertile
offspring
 These barriers do 2 things:
 Block gene flow between species
 Limit formation of hybrids

Hybrids= offspring that result from mating of 2 different species
2 Types of Barriers
 Prezygotic= block fertilization from happening in
the first place
 Postzygotic= contributes to reproductive isolation
after the zygote is formed
Zygote= the fertilized egg
Prezygotic barriers
Work in one or more of the following ways:
1.
Impede members of different species from
attempting to mate.
2. Prevent attempted mating from being successfully
completed
3. Hinder fertilization of mating is successful
Figure 22.3
Prezygotic barriers
Habitat
isolation
Temporal
isolation
Behavioral
isolation
Mechanical
isolation
Postzygotic barriers
Gametic
isolation
MATING
ATTEMPT
(a)
(c)
(d)
(e)
(f)
Reduced
hybrid
viability
Reduced
Hybrid
hybrid
breakdown
fertility
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(g)
(h)
(i)
(j)
(b)
(k)
(l)
Postzygotic barriers
 After fertilization results in :
1.
Reduced hybrid viability
2. Infertile hybrids
3. Hybrid breakdown- subsequent generations are
weak or sterile
Figure 22.3
Prezygotic barriers
Habitat
isolation
Temporal
isolation
Behavioral
isolation
Mechanical
isolation
Postzygotic barriers
Gametic
isolation
MATING
ATTEMPT
(a)
(c)
(d)
(e)
(f)
Reduced
hybrid
viability
Reduced
Hybrid
hybrid
breakdown
fertility
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(g)
(h)
(i)
(j)
(b)
(k)
(l)
Mechanisms of speciation
Speciation can occur with or without geographic
separation
 Allopatric Speciation
 Sympatric Speciation
Allopatric Speciation
 Allos= other
 Patra= homeland
 “different country”
 = gene flow is interrupted when a population is
divided into geographically isolated subpopulations
 Once separated, the gene pools may diverge.
 Different mutations
 Natural selection
 Genetic drift
 Then, over time, reproductive isolation may occur.
 Important- is is NOT the physical barrier that
creates 2 species. It is the biological, reproductive
barriers that develop as a result of the changes in
allele frequencies.
Sympatric Speciation
 Syn= together
 Patra= homeland
 “same country”
 Not as frequent as allopatric speciation
 = gene flow is interrupted NOT by physical barriers,
but by factors such as:



Polyploidy
Habitat differentiation
Sexual selection
 Polyploidy=an “accident” in cell division creates an
organism with extra set(s) of chromosomes.

More common in plants
 Habitat differentiation= when a subpopulation is
better suited to use a habitat or resource not used by
the parent population.
 Sexual selection= though living in the same habitat,
mate choice leads to speciation.
Hybrid Zones
 = a region in which members of different species
meet and mate, producing at least some offspring of
mixed ancestry
How long? How many?
 Speciation can occur rapidly (1000’s of years) or
slowly (millions of years).
 Speciation can occur as a result of changes in just a
few genes or it may require many gene changes.
Learning objective
 SWBAT: Describe and identify the various types of
reproductive isolation necessary for the formation of
new species according to the biological species
concept
 SWBAT: Compare allopatric and sympatric
mechanisms of speciation.