Title: Start by doing whats necessary, then whats possible and suddenly you are doing the impossible' St' F
1Start by doing whats necessary, then whats
possible and suddenly you are doing the
impossible.-St. Francis of Assisi
Linnaeus
2Speciation Concepts
3What is a species?
- Latin for type
- Biologists agree that a species is a fundamental,
natural unit - Biologists do NOT agree on what the exact
definition of the word species is - 2 main definitions morphological and biological
4Phenetic species concept
- Based on physical traits alone
- Example the red-tailed hawk, Buteo jamaicensis,
is a large brown hawk with a brick red tail
5red-tailed hawk (Buteo jamaicensis)
6But what if 2 red-tailed hawks were to mate, and
the offspring looked like this bird?
Is this individual also a Buteo jamaicensis? Or
is it a new species?
7Problems with morphological species concept
- Doesnt account for individual or geographic
variation - There should be more to being a species than
appearance alone - Do these species exist in reality, or just in our
minds?
8Biological Species Concept
- Ernst Mayr 1942
- Most widely accepted definition
- A species is a group of potentially interbreeding
animals (a gene pool) - Must produce fertile offspring
- Individuals do not interbreed with other species
9Phenetic and biological species are not the same
Drosophila pseudoobscura
Drosophila persimilis
Look identical but will not interbreed if kept
together
10Why dont similar-looking species living in the
same area breed?
- The integrity of a species is maintained by
reproductive isolating mechanisms - Categorized according to when they affect
reproduction (before or after mating) - Premating mechanisms prevent mating in the first
place - Postmating mechanisms reduce the chance of
survival of any offspring
11Premating mechanisms
- Behavioral isolation
- Seasonal isolation
- Habitat isolation
- Mechanical isolation
- Gametic isolation
- Isolation by different pollinators (in plants
only)
12Behavioral Isolation
- Prevents mating in the first place
- Many animals have important behavioral components
of courtship and mating, such as songs, displays
and rituals
black skimmers Rynchops niger
13least flycatcher Empidonax minimus
acadian flycatcher Empidonax virescens
Look very similar but have different songs
14Seasonal isolation
- Species breed at slightly different times of the
year - Fowlers emerges from hibernation after American
toads have finished breeding
Fowlers toad Bufo woodhouseii fowleri
American toad Bufo americanus
15Habitat isolation
- 2 species live in the same area, but occupy
slightly different habitats - Warblers forage in different parts of tree canopy
16Mechanical isolation
- 2 species cant physically accomplish mating for
some anatomical reason - Hypothetical-- No definite examples in wild
animal populations
17Gametic isolation
- Egg and sperm will not form a zygote
18Postmating reproductive isolating mechanisms
- Hybrid inviability
- Hybrid sterility
- Hybrid breakdown
The offspring that results from the mating of 2
different species is a hybrid
19Hybrid sterility
- Hybrid is healthy, but cant produce young of its
own - Mules are the sterile offspring of horses and
donkeys
20Hybrid inviability
- Hybrid cant live or has a low chance of survival
- Female deer mice x male beach mice produce very
small offspring - In the reciprocal cross, the offspring are
oversized and typically die before birth.
deer mouse Peromyscus maniculatus
beach mouse Peromyscus polionotus
21Haldanes Rule
- When the hybrids of one sex are affected
negatively, while hybrids of the opposite sex are
healthy - The negatively affected sex will almost always be
the male - No one is 100 sure why this rule is true
22(No Transcript)
23Hybrid breakdown
- Hybrid is healthy, but its offspring dont live
or are sterile
24Speciationthe forming of new species
25How were new species formed in the first place?
- Darwin called this the mystery of mysteries
- Humans have never created a new species of animal
in the laboratory (plants, yes) - Theories based on attempts to reconstruct the
evolutionary history of species based on
available evidence
262 species could become reproductively isolated
- A species usually consists of a number of
discrete, separate populations - Genetic information is usually exchanged, at
least occasionally, between populations. This is
called gene flow - If gene flow is interrupted, reproductive
isolating mechanisms can arise
273 ways gene flow could be interrupted and lead to
the splitting of the species into 2
- Allopatric speciation
- Parapatric speciation
- Sympatric speciation
28Allopatric Speciation
- allo other, patric homeland
- Populations become geographically isolated
- A barrier forms, separating 2 or more groups
- Isolating mechanisms arise over time
- The one species has become 2
- If the barrier is removed before the isolating
mechanism works, gene flow may be reestablished
29Evidence for allopatric speciation
- Geographic variation within individual species
exists today - Species for which this scenario could have taken
place exist today - In the laboratory at least 11 cases of fruitfly
species developed isolating mechanisms - Wild fruitfly species have stronger isolating
mechanisms in regions where they co-occur than
where each lives in isolation
30Variation within a species
- Bergmans Rule
- the further north you go the larger the animals
in a given species - Allen's Rule
- the further north you go the darker the color of
animals in a given species
31Individual variation in corn snake (Elaphe
guttata)
32Desert pupfishgeographical isolation
33Florida and Western Scrub Jaysperipheral
populations
34Parapatric speciation
- para next to, patric homeland
- Could occur when populations are distributed
along an environmental gradient (dry to moist,
hot to cold, etc.) - Different characteristics may be favored at
differing points along the gradient, gradually
producing larger differences among populations
until a new species is formed
35Sympatric speciation
- sym same, patric homeland
- A species could split without any separation of
its geographic range - Controversial theorymany biologists dont
believe it is possible - Might have occurred in green lacewings and
3-spined sticklebacks
36Sympatric speciation?
- 2 sympatric species, one dark green all year, the
other light green in spring, brown in fall - Dark green species lives in conifer trees
- Light green lives in fields
- In the lab can produce a hybrid that is
intermediate in color - No evidence the 2 were ever allopatric
-
green lacewing (Chrysopaerla sp.)
37Sympatric speciation?
- 2 species in each of 5 different lakes in British
Columbia - 1 species lives in littoral zone, the other
benthic - From different lakes, benthic will breed with
benthic, littoral with littoral - Thought to have split from one
- sympatric species in all 5 lakes
3-spined stickleback (Gasterosteus sp.)
38Changes in chromosomes
- A mutation could affect the chromosomes,
preventing successful mating and resulting in new
species - Humans have 46 chromosomes, gorillas, chimpanzees
and orangutans have 48
39Endemic speciesthe founder effect
- Certain species are found only on an islands
- A few individuals (founders) may have come to
the island from the mainland - A new species arises due to smaller gene pool
40Vocabulary
- Species
- Speciation
- Ring species
- Biological species concept
- Reproductive isolating mechanism
- Gamete
- Zygote
- Chromosome
- gradient
- Hybrid
- Inviable
- sterile
- Haldanes rule
- Bergmans rule
- Allens rule
- Peripheral
- Allopatric
- Sympatric
- Parapatric
- Endemic
- Founder effect