Transcript Adaptation and Speciation

Adaptation and
Speciation
SBI 3U
Adaptation

Any trait that increases an organism’s
chance of survival and probability of
successful reproduction
 A product of natural selection
 Organisms become adapted to their
environment over a period of time through
natural selection
 Variations within a species are the raw
material upon which natural selection acts
Types of Adaptations

1. Structural Adaptation - physical
features on an organism
– Anatomical - shape and arrangement of
features
• Ex. Teeth in carnivores, vascular tissue in plants
– Mimicry
• Enables one species to resemble another species or
part of another species
– Ex. Fly that resembles a yellow-jacket wasp
– Cryptic Colouration
• Makes potential prey difficult to spot
– Ex. Camouflage
Mimicry
– A palatable
or harmless
species
mimics an
unpalatable
or harmful
model
(b) Green parrot snake
(a) Hawkmoth larva
Cryptic Colouration
Types of Adaptations cont…

2. Physiological Adaptations
– Associated with functions in organisms
•
•
•
•
Ex. Enzymes for blood clotting
Ex. Proteins in spiders’ silk
Ex. Chemical defense in plants
Ex. Ability of bacteria to withstand heat
Types of Adaptations cont…

3. Behavioural Adaptations
– How organisms respond to their
environment
–
–
–
–
Ex. Migration
Ex. Courtship displays
Ex. Foraging behaviour
Ex. Response of plants to light
How Species Form

Scientist must consider the following
when distinguishing one species
from another:
– Physiology
– Biochemistry
– Behaviour
– Genetics
Biological Species

Most common definition of species:

- a species consists of a reproductively
compatible population

- a population that can interbreed and
produce viable and fertile offspring
Note: Not always possible to apply this
definition
Forming New Species

Speciation
–
–
formation of a new species from an
existing species
Macroevolution

Two general pathways:
1. Transformation
- results from accumulated changes
over long periods of time such that
one species is transformed into
another
- also called Phyletic Speciation

2. Divergent Speciation
– One or more species arise from a parent
species that continues to exist
– Promotes biological diversity
• increases number of species
*Support for both concepts suggests that
a compromise or a combination of the two
models works to produce new species
Barriers to Reproduction

Geographical Barriers
– Keeps populations physically separated
• Ex. Rivers

Biological Barriers
– Keeps species reproductively isolated
when their habitats overlap
Biological Barriers
Pre-zygotic Barriers - prevent mating
or fertilization
 Post-zygotic Barriers - prevent
hybrid zygote from developing into a
healthy fertile adult

Prezygotic Barriers





1. Habitat Isolation
2. Behavioural Isolation
3. Temporal Isolation
4. Mechanical Isolation
5. Gametic Isolation
Habitat Isolation
Populations live in different habitats
or ecological niches.
 Ex – mountains vs lowlands.

Behavioral Isolation



Mating or courtship
behaviors different.
Different sexual
attractions operating.
Ex – songs and
dances in birds.
Temporal Isolation

Breeding seasons
or time of day
different.
 Ex – flowers open
in morning or
evening.
Mechanical Isolation
Structural differences that prevent
gamete transfer.
 Ex – anthers not positioned to put
pollen on a bee, but will put pollen on
a bird.

Gametic Isolation
Gametes fail to attract each other
and fuse.
 Ex – chemical markers on egg and
sperm fail to match.

– Separates certain closely related
species of aquatic snails
Post-Zygotic Barriers

1. Hybrid Inviability
– Hybrid offspring are unlikely to live long
• Ex. Hybrid from sheep and goat die in early
development

2. Hybrid Sterility
– Offspring of genetically dissimilar
parents are likely to be strong but
sterile
• Ex. Horse + Donkey = Mule

3. Hybrid Breakdown
– First generation of hybrids are viable
and fertile
– When hybrids mate the offspring of the
next generation are sterile or weak
• Ex. Cotton
Types of Speciation

I. Allopatric Speciation
- When a population is split into two or more
isolated groups by a geographical barrier
- Sometimes called geographical speciation
- Eventually the groups will become so distinct
that interbreeding will be impossible
- Isolation does not need to be indefinite, but it
does need to be long enough for population to
become reproductively incompatible
Ex. Glacier, lava flow, ocean levels
Adaptive Radiation
This is a form of allopatric speciation
where a common ancestral species
diversifies into a variety of differently
adapted species
 Ex. Darwin’s Finches

Darwin’s Finches
•
II. Sympatric Speciation
-When populations live in the same
geographical area become reproductively
isolated
-More common in plants than animals
-Speciation can occur in 1 generation if
genetic change results from parent to
offspring
Ex. Extra chromosome (called
polyploidy) usually in plants which can
self pollinate
Convergent vs. Divergent
Evolution

Divergent Evolution - a pattern of
evolution in which species that were once
similar to an ancestral species diverge, or
become increasingly distinct (finches)
 Convergent Evolution - similar traits arise
because each species has independently
adapted to similar environmental
conditions, not because they share a
common ancestor (ex. birds and bats)
The Pace of Evolution - 2 Hypotheses

Gradualism
– Changes occur slowly and
steadily before and after a
divergence
– Big changes = accumulation
of many small changes
– Fossil record doesn’t
support this hypothesis well
– Fossil record shows species
appearing suddenly

Punctuated Equilibrium
(Gould and Eldredge – 1972)
– History consist of long
periods stasis (no change)
interrupted by periods of
divergence
– Most species undergo major
change when they first
diverge from parent species
– Fossil records support this
theory