Ten species in one: DNA barcoding reveals cryptic species in the
neotropical skipper butterfly Astraptes Fulgerator
Paul Hebert, Erin Penton, John Burns, Daniel Janzen & Winnie Hallwachs
Proceedings of the National Academy of Sciences2004
Content: JanCritique: Emily
In
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 BarcodingHowever, ‘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%.
Thus the general rule that > 3% sequence divergence is indicative of separate species.
Recognised sister taxa generally show > 3% sequence divergence.
Study Species
• Described in 1775
• Single Species
• Common
• USA to Argentina
• Near desert to rainforest
Neotropical Skipper Butterfly
Astraptes fulgerator
Study SpeciesHowever…
• 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
Other characters
Intraspecific v Interspecific
TRIGO & CELT
> 3% Sequence Divergence
Diverged ~ 2 & 4 mya
Unique food plants
Distinct Spp?
FABOV, HIHAMP & INGCUP
< 0.5% Sequence Divergence
Diverged < 0.5 mya
Host plants not exclusive
???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