Download What is a species?

I am sure there are 9,703,
well maybe it’s 8,616, no I’m
sure it’s 20,100!
The definition of a species &
modern avian systematics
LECTURE OBJECTIVES
• What is a species?
• How do systematists study the diversity
and relationships among organisms
(present day and extinct)?
What is a species?
• Biological Species Concept (Lumpers)
– Groups of interbreeding natural populations
reproductively isolated from other groups
• Phylogenetic Species Concept (Splitters)
– Geographically distinct populations with distinct
evolutionary histories potentially capable of
interbreeding
Biological Species Concept
(Lumpers)
• Species have characteristic
size/shape/colour/behaviour/ecological
niche/geographic range
• Assume that Assortative Mating keeps
species separated
• Difficult to test geography vs assortative
mating without transplant experiments (test:
can individuals from different geographic
regions mate?)
• Issue of hybridization complicates this
definition
The problem of hybridization
• ~ 10% of bird species hybridize making it
difficult to reconstruct phylogeny, define
species, and make conservation decisions
• Why do birds hybridize?
– Accidental/ mistake
– Making the best of a bad situation
What is a species?
• Biological Species Concept (Lumpers)
– Groups of interbreeding natural populations
reproductively isolated from other groups
• Phylogenetic Species Concept (Splitters)
– Geographically distinct populations with distinct
evolutionary histories that can potentially interbreed
but do not due to geography
Phylogenetic Species Concept
(Splitters)
• Species is considered smallest grouping
described by a unique combination of
characters—result: 9000 species to
>20,000 species
• Difficult to understand whether differences
between geographic regions are caused
by evolutionary histories or environmental
conditions
Nature vs. nurture
Types of sub-designations
• Subspecies groups=grps of subspecies that
share similar life history characteristics but are
further subdivided
• Subspecies/geographic race=proportion of
species with unique morphological or
behavioural characteristics
• Polytypic species=2 or more subspecific forms
that can produce fertile offspring
• Clines=genetic characteristics that vary in
parallel with selective factors in the
environment
• Polymorphic species=look different but often
interbreed
Aestevia
Sonoran
Mangrove
• Gloger’s rule – races in
humid places have darker
feathers
• Clutch size rule – races
farther north lay more eggs
• Migratory rule – races living
in cooler climates more likely
to migrate
• Allen’s rule – races in cooler
climates have shorter beaks,
legs, and wings
• Bergman’s rule – races in
cooler climates have bigger
body size
Clines
SOSP
Polymorphic species
WTSP
How are sub-species identified?
1. Statistical differences in morphological
characteristics
2. Behavioral traits (i.e. song differences)
3. Genetics can determine the
“uniqueness” of a sub-species
Species are tough to define but higher
levels of organization are set, RIGHT?
• WELL…In the past, systematists used
– Morphologies
– Fossil Record
• Morphology alone is problematic:
– 1) similarity due to common ancestry
(homology)
– 2) similarity due to convergent evolution
(analogy)
• Morphology alone can lead to great
differences in opinion among taxonomists
Species are tough to define but higher
levels of organization are set, RIGHT?
• Currently systematists use
– Morphologies
– Fossil Record
– Genetics – DNA sequences
• Look for relevant characters —
homologous characters
• Genetic discoveries have changed
field of cladistics and altered many
phylogenetic trees
Genetics – DNA Sequences
• Look for similar DNA sequences
• Organisms that share similar DNA
sequences are likely more closely
related
– Use software to find and realign similar
DNA sequences
– 2 sequences that resemble each other at
many points are likely homologous
– Use mathematical tools to distinguish
distant homologies from coincidental
matches in divergent sequences
Difference between homology and
analogy?
• Systematists use principal of parsimony
– Look for simplest possible explanation
– Morphological characters – few differences
between structure of few evolutionary steps
(likely homologous)
– Genetic/DNA sequences – only a few base
changes (likely homologous)
New Genetic Techniques
J Mol Evol (2003) 57:27–37
Lecture Summary
• Number of species depends on the
definition you use
• Classification and Phylogeny are not
fixed and change with new information