1.
The Environment Institute
Where ideas grow
Richard Abbott
Plant Introductions & Evolution: Hybrid Speciation and Gene Transfer

2.
Plant Introductions & Evolution:
Hybrid Speciation and
Gene Transfer
Richard Abbott - St Andrews University, UK

3.
“There are almost 11,000 alien species in
Europe and the trend of new arrivals is
showing no signs of levelling out.”
“…approximately 15% of the aliens within Europe
are known to have some impact on the
environment or economy - and this problem
goes across all taxonomic groups."
“…invasive species cost the British economy
approximately £2bn a year…”
“Invasive species are one of the greatest threats facing
biodiversity today.”
BBC News 13 October 2008

4.
Plant Introductions
- points of entry

5.
Level of Plant
Invasion in
Europe
(% aliens)
Chytry et al. (2009)
Diversity & Distributions.
15: 98-107

6.
Plant Species in Britain & Ireland
(after Preston et al. 2002)
Total Number of Species 2711
Native 1363 (50.28%)
Native/Alien* 44 (1.62%)
Naturalised Aliens* 1304 (48.10%)
* Species introduced after AD 1500

7.
EVOLUTIONARY CONSEQUENCES
OF INVASIONS
Invasives are models for studying
(i) Evolution in response to environmental change
(ii) Speciation and Gene transfer following
hybridization with other species

8.
Hybrid speciation
Species A Species B
X
2n=10 2n=10
F1 hybrid
2n=10
Chromosome
doubling
2n=10 2n=20
Homoploid hybrid species Allopolyploid species

9.
Origin of a new homoploid hybrid
species - Senecio squalidus
Oxford Ragwort (Senecio squalidus)

10.
Oxford Ragwort (Senecio squalidus) in the UK
Brought to Oxford Botanic Gardens from Mount Etna, Sicily, 1700
Escaped and spread around UK via railway network

11.
The Senecio hybrid zone on
Mount Etna, Sicily.
3000m
2000m
Senecio aethnensis
1000m
Hybrid zone
0m
Senecio chrysanthemifolius

12.
Morphological differences between
S. chrysanthemifolius and S. aethnensis
 Leaf shape and texture
 Flower head size

13.
Differences between S. squalidus and its
Sicilian relatives
 Intermediate morphology - distinct from wild
hybrids on Mt. Etna
 Urban habitats: railways, walls, motorways

14.
Surveyed RAPD variation for species diagnostic markers
Resolved:
13 markers diagnostic of S. aethnensis
2600 m
13 markers diagnostic of S. chrysanthemifolius
150 m

15.
Ancestry of plants along Ancestry of S. squalidus
altitude gradient, Mt Etna plants in UK
2600 m
150 m
James JK, Abbott RJ (2005)
Evolution 59: 2533-2547

16.
Principal Coordinate Plot – RAPD Variation
PCo 2 (10.3%)
PCo 1 (40.6%)
S. chrysanthemifolius Hybrids S. aethnensis S. squalidus
James JK, Abbott RJ (2005)
Evolution 59: 2533-2547

17.
HYBRID ORIGINS OF NEW TAXA IN SENECIO
S. aethnensis x S. chrysanthemifolius
(2n=20) (2n=20)
S. squalidus
(2n=20)
1792

18.
Introgression - Gene Transfer
Species B Species A
50% B F1
25% B Bc1
Movement of genes from
12.5% B Bc2
one species to another
by recurrent backcrossing
of hybrid to a parent 6.25% B Bc3
3.12% B Bc4

19.
Introgression (Gene transfer):
• Many examples based on analyses of neutral markers
• Very few examples involve genes affecting
fitness
• Few examples where hybridizing species differ
in ploidy and/or mating system

20.
Hybridizes with native Groundsel (S. vulgaris)
Oxford Ragwort (Senecio squalidus)

21.
S. vulgaris S. squalidus
Self-compatible Self-incompatible
X
F1
(2n = 30)
sterile
2n = 40 2n =
20

22.
Effects of interspecific hybridization on gene expression
10
Normalised Expression (Log Scale)
1.0
0.1
S. squalidus S. x baxteri S. vulgaris
S. squalidus F1 S. vulgaris
‘Transcriptome shock’ in F1 hybrid. Normalized microarray expression data for
475 cDNA clones identified as showing significant differences in expression
between F1 and one or both progenitors. Hegarty et al. (2005) Molecular Ecology 14: 2493-2510

23.
Hybrid evolution in Senecio
S. squalidus S. vulgaris
Waste-sites,
Roadsides, X Agricultural land
Waste-sites,
Walls Gardens
(2n=20) (2n=40)
New Products
S. cambrensis (2n=60) S. eboracensis (2n=40) Radiate S. vulgaris (2n=40)
N.Wales & Edinburgh Only in York Widespread in UK
1948 1979 1832

24.
Radiate Groundsel (S. vulgaris var hibernicus )

25.
Outcrossing rates of Non-Radiate (NN) and Radiate (RR)
plants
Outcrossing rates
Non-Radiate Radiate
1 - 15% 6 - 36%

26.
Finding genes that produce ray florets
• QTL analysis
• Microarray analysis
• Candidate gene approach √

27.
Ray floret
Disc floret

28.
CYCLOIDEA AS A CANDIDATE GENE
Snapdragon
(Antirrhinum majus)
1 gene is largely responsible for change in
flower shape: Cycloidea
Encodes a transcription factor
Luo et al. (1996) Nature 383: 794-9
Luo et al. (1999) Cell 99: 367-76

29.
• 6 cycloidea-like genes (RAY1-6) amplified in S. vulgaris
• 2 (RAY1 and RAY2) expressed in outer floret primordia

30.
Semi-quantitative RT-PCR showing RAY1 and RAY2
expression in young flower heads of RR and NN S. vulgaris

31.
RAY Cleaved Amplified Polymorphic Sequences (CAPS)
Taq1 digest EcoR1 digest
• Linkage analysis: No recombinants for RAY1 or RAY2
found among >700 F2 offspring of R/R x N/N cross
• Linkage confirmed by bulk segregant analysis of R/R
and N/N genotypes: in each case no recombinants
found among 2,800 chromosomes
• RAY1 and RAY2 are tightly linked and associated with RAY

32.
DNA sequences of RAY1 and RAY2 genes
associated with flower head forms
N and N1 - Non-radiate sequences
R and R1 - Radiate sequences
Radiate S. vulgaris contains the R sequence found in S. squalidus
Confirms Radiate S. vulgaris received the R sequence from S. squalidus

33.
Transformation studies
Do the RAY1 and RAY2 genes control development
of ray florets in S. vulgaris flower head?
• Developed transformation system for S. vulgaris
using Agrobacterium tumefaciens strain GV3101
and a Kanamycin resistance screen
• Took sequences of RAY1 and RAY 2 genes from
Non-radiate S. vulgaris (i.e. N alleles) and
inserted them with 35S constitutive promoter
into Radiate S. vulgaris
RAY1
RAY2

34.
Transformants
Control * * * ‡
* Expression of RAY1 N allele in Radiate S. vulgaris inhibits ray floret production
‡ Expression of RAY2 N allele in Radiate S. vulgaris produces tubular ray florets
Both genes, RAY1 and RAY2, affect ray floret development
Kim et al. (2008) Science 322: 1116-1119

35.
Conclusions
• We have isolated two genes RAY1 and RAY2 that control the
development of ray florets in the flower heads of
Senecio vulgaris
• Radiate alleles of RAY1 and RAY2 are tightly linked and were
introgressed from the diploid S. squalidus to generate the
radiate variant of S. vulgaris
• Radiate S. vulgaris has a greater outcrossing rate than the
non-radiate variant
• This difference in outcrossing rate between the two morphs of
S. vulgaris will affect their relative fitness in polymorphic
populations

36.
Maximum likelihood phylogeny of
RAY2 sequence variation
RAY2b-A
Clade 1
RAY2b-C (RAY2b)
RAY2b-B
RAY2a-R
RAY2a-N
100 100 RAY2a-Na
Clade 2
68
RAY2a-R2 (RAY2a)
100 RAY2a-R2a
60 RAY2a-R1
100 RAY2a-R1a
0.01
• Clades 1 and 2 represent two copies of RAY2 gene (RAY2a and RAY2b)
• Both copies are found in S. vulgaris (tetraploid). Diploids contain only RAY2a
Chapman & Abbott (2009) New Phytologist

37.
Distribution of RAY2a-R
and R1 alleles in S. squalidus
Aberdeen
Edinburgh
100%
80%
R
60%
Leeds R2
40%
Manchester R1
20%
Key: Birmingham
0%
R R1 NIC1 RAN1 MON1 SAP4 SAP2 SAP0 PRO2 ET3
Oxford (755m) (755m) (1045m) (1364m) (1613m) (1915m) (2061m) (2287m)
Guildford
Relative frequencies of RAY2a alleles in
Southampton Senecio populations on Mount Etna
Exmouth
Chapman & Abbott (2009) New Phytologist
Note: Only the ‘R’ allele has been introgressed into radiate S. vulgaris

38.
HYBRID ORIGINS OF NEW TAXA IN SENECIO
S. aethnensis x S. chrysanthemifolius
(2n=20) (2n=20)
S. squalidus S. vulgaris
x S. eboracensis
(2n=20) (2n=40) (2n=40)
1979
1792
S. baxteri x S. vulgaris
(2n=30) (2n=40)
S. vulgaris (Radiate)
S. cambrensis (2n=40)
(2n=60) 1832
1948

39.
Acknowledgements:
St Andrews University: John Innes Centre:
Mark Chapman Rico Coen
Amanda Gillies Pilar Cubas
Juliet James Min-Long Cui
Andy Lowe Minsung Kim
Funded by NERC & BBSRC

40.
The Environment Institute
Where ideas grow
www.adelaide.edu.au/environment
Phone: +61 8 8303 5379