Transcript Ten species in one: DNA barcoding reveals cryptic species in the

Ten species in one: DNA barcoding reveals cryptic species in the
neotropical skipper butterfly Astraptes Fulgerator
In
Paul Hebert, Erin Penton, John Burns, Daniel Janzen & Winnie Hallwachs
Proceedings of the National Academy of Sciences
2004
Content: Jan
Critique: Emily
DNA Barcoding
What is it?
● Large scale screening of just a few reference
genes for species ‘barcodes’.
e.g. COI (Cytochrome C Oxidase 1) mtDNA
Two purposes:
1) Molecular classification of unknown
individuals to identified taxa.
(e.g. the field barcoder)
2) Discovery of previously unknown species.
(e.g. cryptic species)
DNA Barcoding
Is it anything really new? ………NO ………. BUT!
Scale &
Standardization
‘One gene fits all’
DNA Barcoding
However, ‘Barcoding’ is a bit of a misnomer…
… not all individuals have the same ‘barcode’!
Thus required that:
Intraspecific variation << Interspecific variation
DNA Barcoding
For example in moths and birds it has been shown that:
- Intraspecific sequence variation < 0.5% .
- Interspecific sequence variation > 5%.
Recognised sister taxa generally show > 3% sequence divergence.
Thus the general rule that > 3% sequence divergence is indicative
of separate species.
Study Species
• Described in 1775
• Single Species
• Common
Neotropical Skipper Butterfly
• USA to Argentina
Astraptes fulgerator
• Near desert to rainforest
Study Species
However…
• Diversity of Food Plants
• Caterpillar Color Pattern
• V. subtle differences in
adult morphology.
6 – 7 Species???
Years more work…
But wait……
‘DNA barcoding’ is here!
Methods
• 484 museum specimens.
• Data on food plant, caterpillar color pattern
& adult morphology.
• ‘legs away for DNA’
• Barcoding at Guelph:
– Extraction
– Amplification of 648bp COI region
– Sequencing
Methods
• Sequences aligned.
• Divergence measured with K-2-P distance
model.
• Displayed in neighbour joining tree.
Results
10 Distinct Sequence
Groups
Close correspondence
with other
characteristics
Key Points
Branch lengths
Intraspecific v
Interspecific
Other characters
TRIGO &
CELT
> 3% Sequence
Divergence
Unique food plants
Diverged ~ 2 & 4 mya
Distinct Spp?
FABOV,
HIHAMP &
INGCUP
< 0.5% Sequence
Divergence
Host plants not
exclusive
Diverged < 0.5 mya
???Distinct Spp???
Conclusion
Not one species
BUT…..
A complex of 10
cryptic species!
Conclusion
• How many more such complexes are out
there?
• Crucial to our estimates of global
biodiversity and extinction rates.
• DNA barcoding could provide the answers.
Conclusion
Isn’t DNA Barcoding great?
Recorded debate on DNA Barcoding at:
www.conferences.uiuc.edu/peet/video.html