Download Chapter 24 PowerPoint - The Origin of Species

Chapter 24
The Origin of Species
Concepts
• Speciation is the origin of new species
and is at the focal point of evolutionary
theory
• Evolutionary theory must explain how
new species originate and how
populations evolve
Biological Species Concept
• Species is a Latin word meaning “kind”
or “appearance”
Archaeopteryx lithographica
• Morphology, physiology, biochemistry,
and DNA sequences are compared
when grouping organisms
Definition of Species
• Species is a group of populations
whose members have the potential to
interbreed in nature and produce viable,
fertile offspring; they do not breed
successfully with other populations
Concept of Species
• Biological species concept: reproductive
barriers
• Ecological species concept: ecological
niche
• Pluralistic species concept: unique factors
depending on the species
• Genealogical species concept: genetic
history
Biological Species Concept:
Similarity and diversity
Reproductive Isolation
• Reproductive isolation is the existence of
biological factors (barriers) that impede two
species from producing viable, fertile
offspring
• Hybrids are the offspring of crosses between
different species
• Reproductive isolation can be classified by
whether factors act before fertilization
(prezygote) or after fertilization (postzygote).
Prezygotic (before the zygote)
• Prezygotic barriers block fertilization
from occurring by:
– Impeding different species from attempting to
mate
– Preventing the successful completion of
mating
– Hindering fertilization if mating is successful
Types of Prezygotic Barriers
•
•
•
•
•
Habitat isolation
Behavioral isolation
Temporal isolation
Mechanical isolation
Gametic isolation
Habitat isolation
One lives in water the other on land
Behavioral isolation
The dancing and singing are completely different
Temporal Isolation
One diurnal and the other nocturnal
Mechanical isolation
Spirals in opposite directions
Gametic Isolation
• Gametes are not compatible
• Timing of gamete release may be different
• Conditions in the female womb of a
different species may not be ideal for the
sperm
• Gamete recognition hampered due to
molecules arround the ovum
Postzygotic Barriers
• Reduced hybrid viability
• Reduced hybrid fertility
• Hybrid brakedown
Reduced hybrid viability
Ensantia hybrid shows to be frai, may not survive
Reduced hybrid fertility
Mule: sterile hybrid of donkey and horse
Hybrid brakedown
Hybrid (center sample) is stunt and may not survive or reproduce
Speciation Based on Gene Flow
(a) Allopatric speciation
(b) Sympatric speciation
Allopatric
• In allopatric speciation, gene flow is
interrupted or reduced when a
population is divided into geographically
isolated subpopulations
• The definition of barrier depends on the
ability of a population to disperse
• Separate populations may evolve
independently through mutation, natural
selection, and genetic drift
Allopatric speciation in the Grand
Canyon
A. harrisi
A. leucurus
• Reproductive isolation between
populations generally increases as the
distance between them increases
• Barriers to reproduction are intrinsic;
separation itself is not a biological
barrier
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
100
60
80
1
2
20
40
0
3
Millions of years ago (mya)
1
3
2
India
Madagascar
88 mya
65 mya
56 mya
Sympatric Speciation
• Sympatric means “same country”
• Speciation takes place in geographically
overlapping populations
• Occurs because of
– Polyploidism
– Habitat differentiation
– Sexual selection
Polyploidism
• Polyploidy is the presence of extra
sets of chromosomes due to accidents
during cell division
1. Autopolyploidy
2. Allopolyploidy
Autopolyploidy in plants
2n=6
4n=12
Failure of cell division after chromosome duplication
gives rise to tetrapliod cells which
may be viable and self-fertile
Allopolyploid
• An allopolyploid is a species with
multiple sets of chromosomes derived
from different species
• Many important crops (oats, cotton,
potatoes, tobacco, and wheat) are
polyploids
Ancestral species:
AA
Triticum
monococcum
(2n = 14)
BB
Wild
Triticum
(2n = 14)
Product:
AA BB DD
T. aestivum
(bread wheat)
(2n = 42)
DD
Wild
T. tauschii
(2n = 14)
Habitat differentiation
• Sympatric speciation can also result
from the appearance of new ecological
niches
– North American maggot fly can live on
native hawthorn trees as well as more
recently introduced apple trees, so food
preference may isolate the two populations
Sexual selection
• Sexual selection can drive sympatric
speciation
• Sexual selection for mates of different
colors has likely contributed to the
speciation in cichlid fish in Lake Victoria
Hybrid Zones
• region in which members of different
species meet and mate
• Patterns
– abnormal, more fragile offspring, less fit (mule
is sterile)
– more fit than the parents for both
environments (paco vicuña)
Reinforced Barriers
• less fit hybrids might show a reinforcement
in the barriers
• stronger in allopatric than sympatric
species
– mule is sterile
Fusion
• barriers are not strong enough
• hybrids are more likely (red wolf= coyote x
grey wolf)
Stability
• the hybrid production is stable
• barriers haven't happen or are too weak
• stil hybrids are not the norm because the
location where they occur are the
extremes of the normal habitat where the
original species exist
• The End