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Floral evolution in Pelargonium

MSc thesis presentation

Jens Ringelberg

on 7 October 2013

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Transcript of Floral evolution in Pelargonium

- Models incorporating effect of spur length on speciation rates significantly (p<0.001) out-performed null-model: species selection (Rabosky & McCune (2009))
- Models incorporating a positive drift parameter performed significantly better: evolutionary trend towards longer spurs!
- Shape of model differed, but longer spurs generally associated with lower speciation rates
- Opposite pattern in clades B and C
- (Continuous) character optimization
- Models of character evolution
- Correlations character-change & clade-proliferation
- Diversification rate shifts
- Testing for trends

- Phylogenetic uncertainty (200 trees)
- Spur length uncertainty (median, min, max, range of spur length)

- GEIGER - Pagel Transformations (λ and κ)
- APE - ancestral states
- MEDUSA – diversification rate shifts
- Diversitree (QuaSSE) – correlation character evolution & speciation rate
- Phytools
Inferring spur length trends
- 17 localities, flowering populations, throughout SW Cape
- Standardized photographic recordings
- One fertile (not fertilised), sun-exposed flower per plant;

- One non-fertilised flower per specimen

- Range of recorded nectar spur length
Gathering spur length data
Intermediate to strong phylogenetic signal (lambdaλ = 0.7)
Punctuational rather than gradual evolution (κkappa = 0.2) -> pollinator shift model?
Significant deviations from standard Brownian Motion
Evidence for diversification rate shift at base of clade A
Trend towards longer spurs
Spur-dependent changes in speciation rates
Spur length-dependent speciation rates
Spur length-dependent speciation rates
- Transformations of Random Walk
- Ultrametric trees + continuous character + transformed model: estimate best-fitting parameter
Brownian Motion (Random Walk)
Plant-pollinator interactions
Median spur length across populations
Spur lengths – population differentiation
Min-max, median and ranges of spur lengths (cm) across 180 spp
Spur lengths
Spur length dataset
- 1685+1348=3033 individual flowers

- Final for each of 180 species:
Minimum, median, maximum spur length
Range and variance of spur length
Field work:
1685 measurements
90 populations
35 species

1348 measurements
132 species
Field work
Intraspecific spur length distributions (cm)
Spur length distribution per species
Diversification rate shifts

- (Quantitative State Speciation and Extinction, DiversiTree)
- Calculate the probability of a specific phylogenetic tree, a distribution of character states, and a model of cladogenesis (FitzJohn 2010).
- MEDUSA + QuASSE: allowing different parts of the tree to have different cladogenesis
- Rate shift towards clade A; higher birth-rates
- Not found in all 200 trees tested
Nectar spurs in pollination
(Pauw et al. 2008)
Picture: Steve Johnson
(Van der Niet & Bakker (unpublished))
Pollinator shifts in Pelargonium
| | | | | | | | | | | | |
Darwin (1862, 1877)
Flowers shaped by evolutionary interactions with pollinators
Faegri & Van der Pijl (1979)
Pollination syndromes
Grant - Stebbins (1949-1970)
Angiosperm diversity (partially) caused by pollinators
Johnson (2010)
Pollination guilds
Ollerton et al. (2009)
No functional classification based on syndromes
- "Geographic Mosaic" - Pauw et al. (2008)
- Evolutionary arms
- Ennos (2008)
- Pollinator shift
- Whittal & Hodges
Nectar spurs
- Darwin (1862)

- Nectar spur vs. hypanthium base
(Combs & Pauw 2009)

-Plant evolutionary key innovation (Hodges 1996)

- Different models
of spur length
Pollinators and nectar spurs
Diffuse coevolution
- 280 species, 16 sections, largely in CFR

- Large floral (Van der Walt et al., Marais et al.) and vegetative variation (e.g. Jones et al. 2009)

- Genomic instability (Bakker et al. 2006, Guisinger et al. 2008) and basic chromosome number variation (Bakker et al. 2004)

- Horticultural importance and history
Pelargonium (Geraniaceae)
(Bakker unpublished)
(Bakker unpublished)
Leaf shapes
(Bakker et al. 2004)
Floral variation
(Struck 1997)
- Struck (1997): pollination by:
Bees (60%)
Long-proboscid hovering flies (25%)
Moths (7%
Butterflies (2-4%)
Birds (1%)

- Struck (1997): “Moreover, it seems likely that shifts in pollination systems occurred rapidly within Pelargonium, as can be deduced from the deviations in floral characters and in pollination syndromes which repeatedly occur in the infraspecific level, e.g., in P. antidysentericum.”
Nectar spurs
Studies so far:
-P. reniforme (De Wet et al. (2008)

- P. longicaule (Van der Niet & Bakker (unpubl.))

- P. alternans (Becker & Albers (unpubl.))

- Batesian floral mimicry Disa/Pelargonium (Combs & Pauw (2009))
1. Pelargonium nectar spur length is constant at the population level.

2. Evolutionary trend in Pelargonium spur length is towards greater lengths.

3. A correlation exists between pollinator-switches and clade-proliferation.
1. Spur length of a Pelargonium species is a proxy for its pollinator.

2. Phylogenetic trees accurately portray evolutionary history.

3. During the evolutionary history of Pelargonium switches in pollinator-use have occurred.
Herbarium collections:
Taxonomic literature:
R-packages used:
Accommodating uncertainty:
- Used to describe continuous character evolution

- Many shortcomings
Pagel's Transformations
Pagel (1999)
Measures phylogenetic signal (= phylogenetic autocorrelation)
Lambda = 0: no phylogenetic correlation at all (trait value independent of phylogeny)
Lambda = 1: the similarity in trait values between species is directly proportional to the time of shared evolution
Pagel's Lambda
Pagel's Kappa
Measures mode of character evolution (gradual vs. punctuational)
Kappa = 0: evolution independent of branch length; punctuational
κKappa = 3: long branches contribute far more; gradual
Median spur length: lambda = 0.7 -> intermediate to strong phylogenetic signal
(Min = 0.7, max = 0.5, range = 0.2)

- Testing speciation rate shifts - Ultrametric tree + birth\death rate models, allowing different ‘breakpoints’ in the tree
- Parsimony
- 200 trees
- Ancestral Pelargonium spur length 1.6±0.5 cm
Ancestral spur length
Ancestral spur length
Bakker et al. (2004):
- Ancestral spur length 0.1-0.5 cm
- Bees putative pollinators
- Shortcomings: 1 tree, parsimony
- Phylogenetic uncertainty (200 trees)
- Reconstruction method uncertainty (different methods):
Mesquite - parsimony
SIMMAP - Bayesian categorical mapping
Ancestral spur lengths

- Bayesian categorical mapping (model uncertainty)
- 200 trees (phylogenetic uncertainty)
- Median spur length divided into 7 discrete states
- Posterior Probability (PP) per state
0 cm
0-1 cm
1-2.3 cm
2.3-3.6 cm
3.6-4.9 cm
4.9-6.2 cm
>6.2 cm
Median spur length: = 0.2 -> lot of change per speciation event; punctuational
(Min = 0.4, max = 0.1, range = 0.0)
Nectar spur length distribution in Pelargonium characterised by:
Nectar spur evolution in Pelargonium characterised by:
Wide ranges of variation (from 0 to >7 cm)
Much variation within and between certain species and populations
Pelargonium spur length variation
Trend towards longer spurs:
Increased pollinator fidelity
Yet decreased clade size?
The risk of specialization?
Pelargonium appendiculatum
Recommendation for future research
For Pelargonium:
Pollinator observations
Genetics underlying nectar spurs
In general:
Take into account all kinds of uncertainty (phylogenetic, model, character)
Measure wild populations
Financial support:
Alberta Mennega Stichting
Taxon Ondersteuning
Stiching Moabi
Cape Nature
Freek Bakker, Timo van der Niet, Stuart Hall, Leanne Dreyer, Bettie Marais, and everyone at The Island and the Biosystematics Group
Thanks for your attention!
Recommendations for future research
Pollinator observations
In general:
Take into account all kinds of uncertainty
Measure in the field

Jens Ringelberg
MSc thesis proposal

Freek Bakker Timo van der Niet
Wageningen University University of Cape Town
Floral evolution in Cape Pelargonium (Geraniaceae): inferring shifts in nectar spur length & pollination
Floral evolution in Pelargonium (Geraniaceae)
Inferring shifts in nectar spur length and pollination
Jens Ringelberg
Freek Bakker
Wageningen University
Timo van der Niet
Naturalis Leiden
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