Maître de Conférences
Université Paul Sabatier
Laboratoire Evolution et Diversité Biologique
118 route de Narbonne
F - 31062 Toulouse cedex 09
Tel: 33 (0)5 61 55 67 52
email: nathalie.escaravage@cict.fr
Research activities
Current collaborations
Students
Teaching activities
CV
Publications
Research activities
Team "Evolution and adaptation of plant breeding systems"
My main research interest is concerned with the evolution of plant breeding systems.
- Breeding system evolution in fragmented populations: biodiversity compensatory effects.
In this project our plant model is a subalpine shrub (1400 - 2200 m) of the Alps and the Pyrenees: Rhododendron ferrugineum (Ericaceae)
At the subalpine level in the Pyrenees, R.
ferrugineum
populations are often fragmented (from a few individual vs. huge
populations covering hundred of hectares). The main pollinators of R. ferrugineum
(honeybees and bumblebees) are usually constant to the areas and
plant species they visit. Recently we have shown a shift in the
breeding system (self-incompatibility vs. self-compatibility) in an
isolated population demonstrating the capacity of this species to
respond to local environmental conditions.
In
this context, we test whether plant community diversity would
compensate the negative effects of fragmentation (C. Delmas, PhD in
progress). Indeed, plant communities with high floral density, and many
rewards (pollen and nectar) usually attract numerous diversified
pollinators. Pollinator specific diversity play a major role in plant
reproductive success. Thus these communities would represent pollinator
potential "wells" for the isolated plant species. Moreover they could constitute
in the landscape a resource continuum, favorable to pollinator
movements promoting pollen or seed flow between populations.
The aims of this project are to:
(1)
study the effects of population isolation and fragmentation on the
reproductive success (fruit and seed productions), pollination syndrom
(floral traits), breeding system (selfing vs outcrossing).
(2) Study the compensatory effect of
plant community quality (diversity and floral density) on the
reproductive success of fragmented populations.
(3) Reconstruct gene flows within and between populations in relation to the fragmentation level of R. ferrugineum populations and the quality of the community.
- Role of ants in Rhododendron ferrugineum reproductive success
The distribution of R. ferrugineum ranges
from 1600 to 2200 m. However some isolated populations occur at lower elevation
around 1200 - 1300 m. At this latter elevation ecological conditions
are totally different from those at higher elevation (stronger wind,
lower temperatures). A previous study showed that pollinator activity
and diversity decrease as altitude increase : at low elevation (1300 m)
the main pollinators of R. ferrugineum flowers are honeybees and bumblebees, while at higher elevation (2000 m) ants become predominant
The questions addressed are: (i) do ants act as pollinators of R. ferrugineum? (ii) What are the impacts of ants on the pollination effectiveness of other hymenopteran (honeybees, bumblebees)?
- Adapation and evolution of the breeding system in Rhododendron (collaboration with Royal Botanic Garden Kew and Royal Botanic Garden Edinbourg, UK)
Genus Rhododendron
comprises about 1025 species with a distribution centre in southern and eastern
Asia. Rhododendron
has been widely studied from a taxonomic aspect. Numerous investigations on the floral morphology of Rhododendron are available, but studies concerned with the breeding
system are scarce. Floral morphology in Rhododendron
species is diverse. Corolla shape varies widely from tubular through trumpet
shaped, bell-shaped, and cup-shaped to saucer-shaped.
Many species display approach herkogamy (stamens below style) while others have
reverse herkogamy (style below stamens). Rhododendron
species so far studied are self-compatible except R. championae and R.
moulmainense which are self-sterile. For the few species for which breeding
system data is available, it seems that reproductive strategies are correlated
with phylogenetic relationships. However, species growing in environments where
pollinator activity is reduced because of strong wind and low temperature often
evolved mechanisms that allow selfing which provide a reproductive assurance,
e.g. R. ferrugineum in the Alps (see Escaravage et al. 1996) and R. aureum in Japanese mountains.
Therefore, our primary question is: is the
breeding system in Rhododendron an
adaptation to strong ecological constraints, or does it only reflect the
evolutionary history of the genus?
- Population genetics and conservation of Aster pyrenaeus (Asteraceae) (collaboration with the Conservatoire Botanique Pyrénéen).
Aster pyrenaeus
is a rare species, endemic of the French Pyrenees and Cantabric range
(Spain). The species is threatened by human activities, mainly by
picking for commercial use and by changes in land use leading to
habitat destruction and fragmentation. The species seemed to be nearly
extinct in the early 90's, with only 3 known populations but recent
prospecting allowed the discovery of new sites. Today 15 populations
are identified in France and Spain. The aim of the project is to
study the genetic diversity of A. pyrenaeus by using ISSR markers and should permit to estimate:
- genetic diversity level of the species
- level of gene flow within and between populations
- population relationships
Results will allow to help conservation recommendations.
Current collaborations
- Yuji Isagi - Laboratory of Forest Biology, Kyoto University, Japan.
- Pierre Rasmont - Service de Zoologie, Université de Mons-Hainaut, Belgium.
- Xavier Espalader - Departament de Biologia Animal, de Biologia Vegetal i d'Ecologia,Universitat Autònoma de Barcelona, Spain.
- Royal Botanic Garden Edinburgh (UK)
- Conservatoire Botanique Pyrénéen (F)
Students
- Grégory Cazor (DESUPS 2002/03, UPS Toulouse) : "Interactions des systèmes de reproduction dans les communautés végétales d’altitude"
- Elisa Chassang (DESUPS 2002/03, UPS Toulouse) : "Etude de la variabilité génétique des populations d’Aster des Pyrénées (Aster
pyrenaeus DC.) : Implication pour la conservation. -Mise au point des
marqueurs A.F.L.P.(Amplified Fragment Length Polymorphisms)"
- Marie-Jeanne Lacan
(Master 2 Recherche 2005, UPS Toulouse) : "Intection dans le système de
reproduction des communauté végétales de montagnes"
- Denis Li- Lung Hok
(Master 1 2005, UPS Toulouse) : "Estimation des stratégies
reproductives d'une communauté florale des Pyrénées sous l'influence de
Rhododendron ferrugineum (Ericaceae)"
- Charlotte Gourmel (Licence 3 2006, Université de La Rochelle) : "Comparaison des modalité de pollinisation chez Rhododendron ferrugineum (Ericaceae) le long d'un transect altitudinal"
- Sophie Lefèvre (DESUPS 2007/08, UPS Toulouse) : "Evolution du système de reproduction le long d'un transect altitudinal"
- Vanessa Jouninet
(DESUPS 2007/08, UPS Toulouse) : "Variabilité génétique des populations
d’Aster des Pyrénées :implications pour la conservation"
- Quentin Deligne
(Master 2 pro 2008, UPS Toulouse) : " Variabilité de la sécrétion
de nectar et production de miel : suivis es miéllées 2008 de Robinia pseudoacacia et Rhododendron ferrugineum"
- Eline Susset (Master 1 en cours, UPS Toulouse) : "Impact des fourmis dans la pollinisation de Rhododendron ferrugineum"
- Chloé Delmas
(PhD in progress, UPS Toulouse) :"Compensatory effect of plant diversity on the breeding system of isolated Rhododendron ferrugineum populations"
Teaching activities
- Plant diversity and evolution, plant biology (Licence 1 et Licence 3 BGSTU)
- Plant breeding system (Licence 3 BOPE)
- Pollination biology (Master 1)
- Use of molecular markers in conservation biology (Masters 1 et 2)
CV
since 2002 - Maître de conférences at the laboratoire Evolution et Diversité Biologique UMR 5174, Toulouse (Dir. B. Crouau-Roy).
2001-2002 - Maître de conférences at the laboratoire d'Ecologie Terrestre, Toulouse (Dir. F. Blasco)
1999-2000 - Post-doctoral position at the Botanical Institute, Innsbruck (Austria)
1997 - PhD "Reproductive system and colonising strategy of Rhododendron ferrugineum
L. (Ericaceae) (subalpine ; Northern Alps)" - Laboratoire de
Biologie des Populations d'Altitude UMR 5553,
University of Grenoble (France).
Publications
Pornon A., Escaravage N., Lamaze T. 2007 - Complementarity in mineral nitrogen use ammong dominant plant species in a subalpine community. American Journal of Botany 94(11) - 1778-1785 (pdf)
Escaravage N., Wagner J. 2004 - Pollination effectiveness and pollen dispersal in a Rhododendron ferrugineum (Ericaceae) population. Plant Biology 6: 606-615 (pdf)
Escaravage N., Flubacker E., Pornon A., Doche B., Till-Bottraud I. 2001 - Stamen dimorphism in Rhododendron ferrugineum (Ericaceae): development and function. American Journal of Botany 88(1): 68-75 (pdf)
Questiau S., Escaravage N., Eybert M.C., Taberlet P. 2000 - Nestling sex ratios in a wild population of bluethroat (
Luscinia svecica) inferred from AFLPTM analysis. Journal of Avian Biology 31: 8-14 (pdf)
Pornon A., Escaravage N., Thomas P., Taberlet P. 2000 - Dynamics of genotypic structure in clonal Rhododendron ferrugineum (Ericaceae) populations. Molecular Ecology 9: 1099-1111 (pdf)
Pornon A., Escaravage N. 1999 - Genotype structure in clonal Rhododendron ferrugineum L. (Ericaceae) populations: origin and maintenance. Plant Ecology 141: 145-150
Escaravage N., Questiau S., Pornon A., Doche B., Taberlet P. 1998 - Clonal diversity in a Rhododendron ferrugineum L. (Ericaceae) population inferred from AFLP markers. Molecular Ecology 7: 975-982 (pdf)
Pornon A., Escaravage N., Till-Bottraud I., Doche B. 1997 - Variation of reproductive traits in Rhododendron ferrugineum L. (Ericaceae) populations along a successional gradient. Plant Ecology 130 : 1-11
Escaravage N., Pornon A., Doche B., Till-Bottraud I. 1997 - Breeding system in an alpine species: Rhododendron ferrugineum L. (Ericaceae) in the french northern Alps. Canadian Journal of Botany 75(5): 736-743
Escaravage N., Pornon A., Doche B. 1996 - Dynamique des populations de Rhododendron ferrugineum L. (Ericaceae) en altitudes (Alpes du Nord, France). Dissertation Botanica 258 : 103-113Escaravage N., Pornon A., Doche B. 1996 - Evolution des potentialités dynamiques des landes à Rhododendron ferrugineum L. avec les conditions de milieu (étage subalpin des Alpes du Nord - France); Ecologie 27(1) : 35-50