Transcript Integrative taxonomy

Integrative taxonomy
Gustav Paulay
Florida Museum of Natural History
University of Florida
BSC and ESU
• Biological species concept
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No gene flow
Independent evolutionary tracks
Reproductive isolation
Tested experimentally or sympatric
• Evolutionary Significant Unit
– No gene flow
– Independent evolutionary tracks
– Untested for reproductive isolation, allopatric
Speciation
• Formation of species
• Requires isolation of two populations leading to
no/little mating between them
• Leads to divergence of populations
• Divergence of genotype
• Mutations – changes in DNA
• Fixation of mutations:
– Genetic drift or selection
• Mutations accumulate
– interbreeding becomes impossible
– or leads to poor hybrids
– speciation
ESU:
demonstrate lack of gene flow
• Defined as
reciprocally
monophyletic
populations
– i.e. fixed for
different traits
ESU:
demonstrate lack of gene flow
• Reciprocally monophyletic in at least independent 2 traits
ESU: 2 independent traits
• Any two independent traits w/ genetic basis
• Morphological characters
• Genetic characters
– Independent loci (mtDNA – all one)
• Geography
• Any combination of these
Integrative taxonomy
• Use of multiple lines of evidence
• Field - museum - lab
• Ecology - behavior - morphology - genetics
- geography
• Distinguishing between morphs and species
• Two or more independent characters
showing distinction between species
Integrative taxonomy:
Actinopyga mauritiana - guamensis
Two major types of challenges
• Not seeing species where there are
• Seeing species where there aren’t
• Cause: rate of evolution varies among traits
– phenotype: morphology, behavior, color pattern...
– genotype: sequence divergence
– reproductive isolation
Not seeing species where there are
• unequal rates of evolution
– phenotype divergence - SLOW
– sequence divergence
– reproductive isolation
• cryptic species
Cukes vs. primates
• Different foci for sensory perception
• Humans – visual cues
• Cukes - chemical cues
• Do cukes care about each other’s colors or
ossicles when meeting?
Supposed distribution of Scutellastra flexuosa and
exusta
Powell, 1968
but what is really going on...
NJ K2P COI
Synapta maculata
Not seeing species where there are
• unequal rates of evolution
– phenotype divergence
– sequence divergence
– reproductive isolation - FAST
Actinopyga obesa complex
Echinometra mathaei complex
Rapid secondary sympatry
Facilitated by rapid evolution of fertilization proteins?
COI
~1 Ma
Bindin
Bindin
COI
Landry et al. 2003 Proc Roy Soc
Seeing species where there aren’t
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ecophenotypic variation
ontogenetic variation
geographic variation
ecological variation - depth, habitat, etc
polymorphism
paralogous loci
former divergence now united
Polymorphism / phenotypic variation
Paralogous loci:
mitochondrial
genes gone
nuclear in Alpheus
Williams & Knowlton 2001 Mol Biol Evol
ESU vs. BS
• Need demonstration of no possibility for
reuniting into one species
• No problem when sympatric as gene flow is
tested
• Can’t assume reproductively isolated in
allopatry
– need test experimentally – mating essays
Cypraea tigris
a species differentiated, then united
• 15% divergence in COI
• Type A – Indian only
• Type B – mostly Pacific
– some Indian
• A and B in Indian
identical in all other
characters
BS test – marginal overlap
ESU - reciprocal monophyly
• DNA - gene flow - BSC
• reciprocal monophyly implies lack of recent
genetic connections
• need several samples of each form to test
• reliability of conclusion depends on depth of
intra- vs. inter-specific variation
• in sympatry - separate biological species
• in allopatry - separate ESUs, species status
subjective
Where are the species limits?
Lack of reciprocal monophyly
• morphs rather than species
• distinct species, but:
– introgression
– insufficient time for sorting
• deep coalescent
• rapid speciation
Introgression
in Astralium
Introgression in Bohadschia argus?
• Unusual form only in W Pacific; never seen in Polynesia, etc.
• Need compare independent markers to test
Insufficient time
for sorting
Gene trees vs.
species trees:
coalescence theory
Avise 1999 Phylogeography
Evolution of reproductive isolation
• Slow
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most gastropod
deep divergence among allopatric ESUs
clear reciprocal monophyly
slow to secondary sympatry / biological species
• Rapid
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echinoids, holothuroids
shallow divergence among sympatric species
potential paraphyletic species
rapid to secondary sympatry / biological species
Astralium rhodostomum
complex
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2.
3.
Two deeply divergent clades: A & B
sympatric on 8 island groups
30 ESUs so far
Pigmentation separates major and minor
clades.
Persistence of allopatry - Cypraeidae
94% divergences < 10 Ma
retain allopatry (115 of 122)
40
94% divergences < 10 Ma
retain signal (115 of 122)
35
30
structure
no structure
# ESEs
25
20
15
Ma
88
84
80
76
72
68
64
60
56
52
48
44
40
36
32
28
24
20
16
8
0
12
5
4
no signal
10
0
Geographic signal
Echinometra mathaei complex
Rapid secondary sympatry
Facilitated by rapid evolution of fertilization proteins?
COI
~1 Ma
Bindin
Bindin
COI
Landry et al. 2003 Proc Roy Soc
Stichopus variegatus complex
Advantages of sequence data
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Directly test genetic connections
Very large number of characters
Independent markers - independent sources
“Independent” of morphology - so can trace
evolution of form, etc on gene tree without
circularity
Potential problems with sequence data
• depth of coalescent vs. interspecific
divergence
• paralogous sequences
• introgression
– selective sweeps
– homogenization through drift