Transcript 9. Biodiversity& Species

Biodiversity
Studied in a relatively new field called Conservation
Biology
Consists of three components:
1. Species
2. Genes
3. Ecosystems
The Biological Species Concept
• The biological species concept defines a
species as
– A population or group of populations whose
members can interbreed and produce
fertile offspring
Other Species Concepts
• The _____concept
– Classifies organisms based on observable
phenotypic traits
• The _____concept
– Defines a species by its ecological role
• The phylogenetic species concept
– Defines a species as a set of organisms
representing a specific evolutionary lineage
Speciation requires:
1. Genetic variation
2. Natural Selection
3. Reproductive Barriers
Mutation, sexual recombination, gene flow, and
genetic drift can generate variation needed for
speciation
• Mutations, or changes in the nucleotide sequence of
DNA
–Can create new alleles
• Sexual recombination
– Generates variation by shuffling alleles during
meiosis (independent assortment), and cross
overs
Parents
A1
A1
X
A2
A3
Meiosis
Gametes
A2
A1
A3
Fertilization
Figure 13.12
Offspring,
with new
combinations
of alleles
A1
A2
A1
A3
and
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Gene flow
–Is the movement of individuals or gametes
between populations. Occurs in plants by ____
and _____
–Can alter allele frequencies in a population
•Genetic drift
–Is a change in the gene pool of a population
due to chance
–Can alter allele frequencies in a population
• Natural selection
– Leads to differential reproductive success in a
population
– Can alter allele frequencies in a population
Natural selection can alter variation in a population in
three ways
• Stabilizing selection
– Favors intermediate phenotypes
• Directional selection
– Acts on individuals at one of the phenotypic extremes
• Disruptive selection
– Favors individuals at extremes of the phenotypic range
Frequency of individuals
• Three possible effects of natural selection
Original
population
Evolved
population
Stabilizing selection
Original
population
Phenotypes (fur color)
Directional selection
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Disruptive selection
Reproductive barriers keep species separate
• Reproductive barriers
– Serve to isolate a species’ gene pool and prevent
interbreeding
– Are categorized as prezygotic or postzygotic
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Prezygotic Barriers
• Prezygotic barriers
– Prevent mating or fertilization between
species
Seasonal Flowering Differences
-In temporal isolation
- Three orchid species of the genus Dendrobium
live in the same tropical rain forest and all flower
after thunderstorms. One flowers eight days
after the storm, a second species nine days after,
and a third species ten days after the storm
• In behavioral isolation
– There is little or no sexual attraction
between species, due to specific behaviors
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• In mechanical isolation
– Female and male sex organs or gametes
are not compatible
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
In mechanical isolation of plants:
Morphological differences in flowers allow them to
be specifically adapted to certain pollinators.
Pollen is transferred only between plants of the same species
with the same floral anatomy.
Length of the stigma and style and growth of the pollen tube
Is often important in mechanical isolation of plants.
• In microhabitat differences
– Two species occupy different microhabitats
Ex. Quercus coccinea (scarlet oak) and
Q. velutina (black oak) of eastern
USA are isolated in different microhabitats.
Scarlet oak grows in wet habitats adjacent to
black oak in dry upland habitats
• In gametic isolation
– Two species can chemically distinguish between
pollen of the same species and that of different
species. Germination of pollen from foreign
species is retarded by chemical components in
the stigma and style
Postzygotic Barriers
• Postzygotic barriers
– Operate after hybrid zygotes are formed
• One postzygotic barrier is hybrid sterility
– Where hybrid offspring between two
species are sterile and therefore cannot
mate
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
In allopatric speciation a population is geographically divided.
• Geographic isolation on east and west slopes
of the Rockies, eastern and western Great
lakes, and on the eastern and western slopes
of the Appalachians has resulted in new
species of organisms.
• Isolated ponds in
deserts has led to new
species of pupfish
and plants
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
New species can also arise within the same
geographic area as the parent species
• In sympatric speciation
– New species may arise without geographic
isolation
– Microhabitat isolation as in red (moist) and
black (dry) oaks
– Gametic isolation where species can
chemically distinguish their own pollen and
destroy that of other species
• Many plant species have evolved sympatrically by
polyploidy (DE VRIES and BOEDIJN 1923)
– Multiplication of the chromosome number due
to errors in cell division
Zygote
Parent species
Meiotic
error
Offspring
may be
viable and
self-fertile
Selffertilization
4n = 12
Tetraploid
2n = 6
Diploid
Oenothera lamarckiana
Unreduced
diploid gametes
O. gigas
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Polyploid plants clothe and feed us
• Many plants, including food plants such as bread
wheat
– Are the result of hybridization and polyploidy
AA
Triticum monococcum
(14 chromosomes)

BB
Wild Triticum
(14 chromosomes)
AB
Sterile hybrid
(14 chromosomes)
Meiotic error and
self-fertilization

AA BB
T.turgidum
Emmer wheat
(28 chromosomes)
ABD
Sterile hybrid
(21 chromosomes)
Meiotic error and
self-fertilization
AA BB DD
T.aestivum
Bread wheat
(42 chromosomes)
DD
T.tauschii
(wild)
(14 chromosomes)
Polyploidy is a common mechanism for sympatric speciation:
Hybrid polyploids (allopolyploids) have characteristics of both
parents. They have more genes and enzymes to deal with
changes in the environment and thus are often better adapted
than the parent species. Since their chromosome numbers
are doubled chromosomes can no longer pair with parent
chromosomes during meiosis and thus are reproductively
isolated from their parents.
Many plant species have been shown to undergo this type
of rapid sympatric speciation. Invertebrates and lower
chordates also often speciate in this manner.
Adaptive radiation can also be rapid and may
occur in new or newly vacated habitats
• In adaptive radiation, the new species
– Occur when mass extinctions or
colonization provide organisms with new
environments
– Ex. Over the course of millions of years,
the descendants of the pioneer plant in the
Hawaiian silversword `ohana (family)
evolved into 28 distinct species in three
genera, occupying many different habitats.
Flowering rosette of the extremely rare Mauna Kea
silversword (Argyroxiphium sandwicense subsp.
sandwicense) Copyright © The Botanical Society of America