Download “SPECIES”

“SPECIES”
What sort of Biological Entity is it?
What is a “Species”?
• Biological Species Concept:
– 1 or more populations of individuals that can
interbreed and produce fertile offspring, and
are reproductively isolated form other such
groups.
– Members of a species have a shared gene
pool.
– Different populations can mate and produce
fertile offspring.
What is a “Species”?
• But…what about asexual organisms?
• Morphological Species Concept:
– Groups of organisms that share certain
morphological or biochemical traits.
• This is rather subjective.
• Phylogenetic Species Concept:
– Groups of organisms (or lineages) that share
recent common ancestry.
Speciation
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How do species arise?
Microevolution
Pre-existing organisms (ancestors).
Divergent Evolution
– Adaptation to specific environmental cues.
• (This contrasts Convergent Evolution)
– Similar adaptations in organisms from very
different lineages.
Speciation
• Biological Species Concept:
– 1 or more populations of individuals that can
interbreed and produce fertile offspring, and
are reproductively isolated form other such
groups.
• Reproductive Isolation
– Prevents Gene Flow.
– If no gene flow, then populations can develop
into more and more different subpopulations…perhaps eventually forming
species.
Reproductive Isolating Mechanisms
1. Pre-Zygotic Isolating Mechanisms
2. Post-Zygotic Isolating Mechanisms
Pre-Zygotic Isolating Mechanisms
• Prevent Reproduction Attempts
• Habitat Isolation
– Isolated in space/habitat.
• Temporal Isolation
– Mating occurs at different times
• Behavioral Isolation
– Differences in mating displays, calls, chemicals…
• Mechanical Isolation
– Incompatibility of reproductive organs … (“the key
doesn’t fit the lock”)
Post-Zygotic Isolating Mechanisms
• Copulation occurs, but offspring are kept
from developing & breeding.
• Gamete Isolation – sperm & egg don’t fuse.
• Zygote Mortality – Zygote dies, unable to
function.
• Hybrid Inviability – Hybrid is produced, but
does not survive to adulthood.
• Hybrid Sterility – Hybrid is produced, but is
unable to produce viable gametes.
Speciation
•
Formation of new species via
reproductive isolation.
1. Allopatric Speciation
– 2 populations become reproductivelyisolated while separated from each other
(geographic barrier).
Speciation
2. Sympatric Speciation
– 2 populations become reproductivelyisolated while occupying the same
geographic area.
How Fast?
• Gradualist Model
• Punctuated Equilibrium Model
Systematics
•
Science of organizing the diversity of life.
1. Taxonomy – Identification & Naming
2. Phylogeny – Analyzing evolutionary
relationships among groups.
3. Classification – Placing organisms into
an organized categorization scheme.
Taxonomy
• Identification & Naming
• Taxon: a group of organisms (Taxa)
• “Species” – the most fundamental group.
– Group of interbreeding populations that are
reproductively isolated from other such
groups (and evolving independently of other
such groups).
Taxonomy
• New species each given a
“Scientific Name”
– Carolus Linnaeus
– Binomial Nomenclature
– 2-word Latin name.
• Pinus strobus
• Dictyostelium discoideum
• Bubo virginianus
• “Common Names” also…
– Can be misleading
Taxonomy
• Pinus strobus
• 1st word = Genus
– A generalized name
• 2nd word = specific epithet
– A descriptive name
• Always in italics or underlined.
• Genus is capitalized, epithet is lower case.
• Specific epithet never used alone!
Phylogeny
• Grouping new species/taxa with closelyrelated taxa from an evolutionary
perspective.
• Phylogenetic Trees:
Phylogeny
• Outgroups:
Classification
• Categorizing organisms into a hierarchy of
names (hopefully) according to their
relatedness.
• Historically – based on convenience.
• Starting at Species (the most exclusive
group), organisms are grouped into more
and more broad & inclusive Taxa.
• “Species” is the only level that really exists
as an true single entity.
Classification
Kingdom
Animalia
Phylum/Division
Chordata
Class
Mammalia
Order
Primates
Family
Hominidae
Genus
Homo
Species
Homo sapiens
Classification
Homo
sapiens
Tyto
alba
Homo
Tyto
Hominidae
Tytonidae
Primates
Strigiformes
Mammalia
Aves
Chordata
Animalia
Systematics
• Tree of Life:
http://tolweb.org/tree/phylogeny.html