Polyploidy: Tricky Taxonomic
Delimitation
Ben Grady
UW-Madison
Botany Department
6 March 2007
Polyploidy and Taxonomy:
an overview
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•
•
•
“Defining” species
Polyploid complexes
Cardamine pratenesis
Lepidium
What do we call a species?
• Biological Species Concept
– Mayr 1942
• Evolutionary Species Concept
– Wiley 1978
• Phylogenetic Species Concept
– Cracraft 1989
• General consensus: diagnosable units
with common evolutionary history
From Futuyma 1998 and Judd et al. 2002
The Polyploid Complex
• Continued polyploidization in a group or
lineage
• Much overlap in morphological traits and
ecological preferences
• Difficult and time-consuming to fully
understand relationships within a polyploid
complex
Grant 1981
The Polyploid Complex
• Wow, this is complex!
The Polyploid Complex
• Count some chromosomes
2n
2n
2n
2n
2n
4n
4n
2n
4n
6n
2n
The Polyploid Complex
• Determine source of genetic material
2n
2n
2n
2n
2n
4n
4n
2n
4n
6n
2n
The Polyploid Complex - Simplified
2n
2n
2n
AA
AA
AA
4n
AAAA
4n
AAAA
6n
AAAAAA
The prevalence of Polyploid
Complexes
• Polyploid complexes are common in
certain families
– Polypodiaceae
– Trilliaceae
– Onagraceae
– Poaceae
– Brassicaceae
Grant 1981
Cardamine pratensis complex
• Widespread distribution
• Morphological variation
not discrete
• Post-glacial
diversification
• Hybridization and
polyploidy rampant
– 2n = 16, 24, 30, 32, 40,
44, 46, 48, 56
• Iberian taxa:
– C. pratensis s.s.
– C. crassifolia
– C. castellana
Photos © Carl Farmer
Lihova et al. 2003
Lihova et al. 2003
C. pratensis
C. pratensis
C. castellana
C. crassifolia
Lihova et al. 2003
C. pratensis in the Iberian Peninsula
Lihova et al. 2003
• C. crassifolia and C. castellana appear
distinct (both taxa 2n=16)
C. castellana
C. crassifolia
AFLP analysis:
C. castellana & C. crassifolia
C. castellana 2n = 16
C. crassifolia 2n = 16
Lihova et al. 2003
Many intermediate characters
Lihova et al. 2003
Origins of C. castellana?
• C. castellana morphologically intermediate
• Possible hybrid of C. pratensis and C.
crassifolia
• What then?
– Species?
– Subspecies?
– No taxonomic recognition?
C. pratensis in the Iberian Peninsula
Lihova et al. 2003
• C. pratensis s.s. still poses a problem, or
does it?
– Various polyploids still mostly interfertile
(except diploids)
– Morphological variation continuous
– Multiple origins of polyploids?
AFLP analysis: C. pratensis s.s.
30
16
56
56
44
Lihova et al. 2003
Morphological Variation?
Figure 5
Lihova et al. 2003
Allopolyploidization – Lepidium
Lee et al. 2002
• Lepidium
– 175 spp. worldwide
– Crazy flowers, well for a mustard…
PI gene tree and evolution of stamen
arrangement, green-Eurasia, orangeAfrica, blue-S.Amer., black-Austr.,
purple-N.Amer. lacking lateral
stamens,
References
• Futuyma, D.J. 1998. Evolutionary Biology. Sinauer Associates –
Sunderland, Mass. U.S.
• Grant, V. 1981. Plant Speciation. Columbia University Press, New
York, pp. 324-346.
• Judd W.S., C.S. Cambell, E.A. Kellogg, P.F. Stevens, & M.J.
Donoghue. 2002. Plant Systematics: An Evolutionary
Approach. Sinauer Associates – Sunderland, Mass. U.S.
• Lee, J., K. Mummenhoff, & J. Brown. 2002. Allopolyploidization
and evolution of species with reduced floral structures in
Lepidium L. (Brassicaceae). PNAS 99(26): 16835-16840.
• Lihova, J., A. Tribsch, & K. Marhold. 2003. The Cardamine pratensis
(Brassicaceae) group in the Iberian Peninsula: taxonomy,
polyploidy and distribution. Taxon 52: 783-801.
• Marhold, K., & J. Lihova. 2006. Polyploidy, hybridization and
reticulate evolution: lessons from the Brassicaceae. Pl. Syst.
Evol. 259: 143-174.