Transcript Biological species concept

Ch.24 ~ The Origin of Species
“That mystery of
mysteries – the
first appearance
of new beings on
this Earth.”
Macroevolution: the origin of new taxonomic
groups
 Speciation: the origin of new
species
 1- Anagenesis : accumulation
of heritable changes
 2- Cladogenesis (branching
evolution): budding of new
species from a parent
species that continues to
exist (basis of biological
diversity)
Macroevolution:
Is it different
from microevolution?
What is a species?
 Biological species concept (Mayr):
a population or
group of populations whose members have the potential to
interbreed and produce viable, fertile offspring (genetic exchange
is possible and is genetically isolated from other populations)
Biological species concept
 Biological species are defined by _____ isolation.
 The biological species is the largest unit of a
_____ in which _____ is possible.
How do new species emerge?
How do new species emerge?
 Physical distinctions
 Non-interbreeding
populations
 Adaptation to a
different niche in the
environment
 Genetic differences
How do new species occur?
 At least one gene affecting at least one
____________________ must change for
speciation to occur.
Genetics plays a key role in
speciation
 Reproductive
compatibility results
in propagation of
genetic information to
the next generation
 Reproductive barriers
maintain distinct
species
 Prezygotic barriers
 Postzygotic barriers
Prezygotic barriers prevent
mating events
 Temporal isolation –
separates species by
seasons
 Habitat isolation –
separates species by
physical barriers
 Behavioral isolation –
separates species by
patterns of activity
Prezygotic barriers prevent
fertilization events
 Mechanical isolation –
structural differences
prohibit interbreeding
 Gametic isolation – lack
of fertilization even if
gametes from different
species meet
Closely related frogs of
genus Rana remain distinct
species by different
reproductive barriers. Males
of one species are too small
to perform amplexus (action
that stimulates ovulation).
What type of barrier is
this?
Postzygotic barriers eliminate the
propagation of mixed genetic material
when different species breed
 Hybrid offspring of
two separate species
cannot reproduce
 Inviability – offspring
never reach maturity
 Hybrid sterility –
functional gametes
not produced in the
hybrid offspring
 Hybrid breakdown –
natural selection acts
to eliminate them
from the population
Cama: camel x llama
A hybrid zone is properly defined
as:
a – an area where 2 closely related
species’ ranges overlap
b – an area where mating occurs
between 2 closely related species,
producing viable offspring
c – an area where 2 closely related
species intermingle, but experience
no gene flow
Reproductive Isolation (isolation of
gene pools), I
 Habitat (snakes;
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
water/terrestrial)
Behavioral (fireflies; mate
signaling)
Temporal (salmon; seasonal
mating)
Mechanical (flowers; pollination
anatomy)
Gametic (frogs; egg coat
receptors)
Reproductive Isolation, II
 Reduced hybrid viability (frogs;
zygotes fail to develop or reach
sexual maturity)
 Reduced hybrid fertility (mule;
horse x donkey; cannot
backbreed)
 Hybrid breakdown (cotton; 2nd
generation hybrids are sterile)
Modes of speciation
(based on interruption of gene
flow)
 Allopatric:
geographic barrier
isolates species; can
result in adaptive
radiation (island
species)
 Sympatric:
reproductively isolated
subpopulation in the
midst of its parent
population (change in
genome); polyploidy in
plants; cichlid fishes
A flea species feeds only on antelopes.
In the western U.S., antelopes and cattle
often mingle. If some of the fleas
develop a strong preference, instead, for
cattle blood, and mate only with other
fleas that prefer cattle blood, then over
time, which of these should occur, if the
host mammal is considered the fleas’
habitat?
1
2
3
4
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reproductive isolation
sympatric speciation
habitat isolation
prezygotic barriers
Punctuated equilibrium
 Tempo of speciation:
gradual vs. divergence
in rapid bursts; Niles
Eldredge and Stephen
Jay Gould (1972);
helped explain the
non-gradual
appearance of species
in the fossil record
Present day
V
W
X
Y
Z
Which of the five species in the evolutionary tree originated
earliest and appeared suddenly in the fossil record?
Present day
V
W
X
Y
Z
Which species is the extant (not extinct) species that is
most closely related to species X and why?