Mathieu MOLET

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Mathieu MOLET

Mathieu MOLET
Assistant Professor in Biology / Maître de Conférences en Biologie

Université Pierre et Marie Curie
Laboratoire Écologie & Évolution UMR 7625
Équipe Évolution des Sociétés Animales

7, quai St Bernard
Bâtiment A, 7ème étage, Case 237
75252 PARIS CEDEX 05
FRANCE

Tel. +33 (0) 1 44 27 26 94 | Fax. +33 (0) 1 44 27 35 16

E-mail : mathieu.molet(+@)snv.jussieu.fr

The evolution of biodiversity relies on the production and selection of new phenotypes. I study these mechanisms in the context of animal societies, using ants as a model. Ants consist of 13000 species that occupy a variety of ecological niches throughout the world. One important reason for this success is their morphological caste system associated with efficient division of labour. Indeed, in addition to the two ancestral castes (winged queens and wingless workers), many ant species have evolved novel castes such as wingless queens and soldiers. Wingless queens are a response to selective pressures against long range dispersal and solitary colony foundation, while soldiers allow for better colony defense, food storage and/or foraging. The evolutionary and developmental processes that led to this diversity are poorly known. I study them with an integrative approach that focuses on morphological, physiological, behavioural and developmental variables. My model species are mostly from Madagascar (Cerapachys, Mystrium, Odontomachus) but also from Africa (Cataglyphis, Platythyrea) Australia (Rhytidoponera), Asia (Gesomyrmex) and Europe (Temnothorax).

Diversity of castes and life-cycles

The life cycle of ant colonies is mostly known from species with winged queens. Studying this in species with wingless queens reveals unexpected diversity. Wingless queens do not found colonies alone but with the help of nestmate workers (dependent colony foundation = fission). Accordingly they mate near their nest after attracting males using pheromones. We have found that, depending on species, colonies contain either one big queen with large ovaries specialized for egg-laying, or numerous small queens with relatively small ovaries that can either mate and lay eggs or function as helpers. This entails original division of labour, conflicts for reproduction, dynamics of colony emigration and genetic structures.

Small wingless queens (red) and workers (black) of Mystrium ‘red’.
© Alex Wild

Mechanisms for generating novelty

We compare novel castes (wingless queens and soldiers) to conspecific or congeneric winged queens and wingless workers in order to assess the evolutionary link between these phenotypes and test the hypothesis that novel castes are mosaics of ancestral castes. We use two approaches: morphometry (assessing growth rules and describing morphological modules) and evo-devo (assessing gene expression in imaginal wing discs of larvae).

Imaginal discs of Mystrium oberthueri wingless queen larva (DAPI).
© Mathieu Molet

Role of developmental anomalies in evolution

Ant colonies produce rare anomalies called intercastes that are morphologically very variable but look intermediate between winged queens and wingless workers. We study the morphology, behaviour and physiology of intercastes in order to assess the costs and benefits that they bring to colonies. We compare them to novel castes. We developed and evolutionary scenario that involves genetic accommodation and buffering properties of colonial life to connect these anomalies to regularly produced novel castes. We also explore the diversity of intercastes produced artificially following hormone applications.

(Top) Colony of Mystrium rogeri with a queen surrounded by workers and a few intercastes.
(Bottom) Magnification of an intercaste: notice the tiny wing buds.
© Sylvain Londe

Environmental pressures and evolution of colonial reproductive strategy

The replacement of winged queens by wingless queens or reproductive workers is tightly linked with selection against long-range dispersal by flight and independent colony foundation. We study why and how colonies alter their reproductive strategy in response to environmental changes.

Rhytidoponera ants adapt colonial reproduction to environmental gradients.
© Alex Wild

Publications

14. Molet M., Wheeler DE & Peeters C. 2012 Evolution of novel mosaic castes in ants: modularity, phenotypic plasticity, and colonial buffering. American Naturalist in press
13. Peeters C. & Molet M. 2010 Evolution of advanced social traits in phylogenetically basal ants: striking worker polymorphism and large queens in Amblyopone australis. Insectes Sociaux 57:177-183.
12. Peeters C. & Molet M. 2010 Colonial reproduction and life histories. In: Ant Ecology (eds. Lach L., Parr C. & Abbott K.). Oxford University Press.
11. Molet M., Chittka L. & Raine N.E. 2009 Potential application of the bumblebee foraging recruitment pheromone for commercial greenhouse pollination. Apidologie 40 : 608-616.
10. Molet M., Fisher B.L., Ito F. & Peeters C. 2009 Shift from independent to dependent colony foundation and evolution of ‘multi-purpose’ ergatoid queens in Mystrium ants (subfamily Amblyoponinae). Biological Journal of the Linnean Society 98 : 198-207.
9. Molet M., Chittka L. & Raine N.E. 2009 How floral odours are learned inside the bumblebee (Bombus terrestris) nest. Naturwissenschaften 96 : 213-219.
8. Molet M., Chittka L., Stelzer R.J., Streit S. & Raine N.E. 2008 Colony nutritional status modulates worker responses to foraging recruitment pheromone in the bumblebee Bombus terrestris. Behavioral Ecology and Sociobiology 62 : 1119-1126.
7. Molet M., Van Baalen M. & Peeters C. 2008 Shift in colonial reproductive strategy associated with a tropical-temperate gradient in Rhytidoponera ants. American Naturalist 172 : 75-87.
6. Molet M., Peeters C., Follin I. & Fisher B.L. 2007 Reproductive caste performs intranidal tasks instead of workers in the ant Mystrium oberthueri. Ethology 113 : 721-729.
5. Molet M., Peeters C. & Fisher B.L. 2007 Permanent loss of wings in queens of the ant Odontomachus coquereli from Madagascar. Insectes Sociaux 54 : 174-182.
4. Molet M., Peeters C. & Fisher B.L. 2007 Winged queens replaced by reproductives smaller than workers in Mystrium ants. Naturwissenschaften 94 : 280-287.
3. Yéo K., Molet M. & Peeters C. 2006 When David and Goliath share a home: compound nesting of Pyramica and Platythyrea ants. Insectes Sociaux 53 : 435-438.
2. Molet M. & Peeters C. 2006 Evolution of wingless reproductives in ants: weakly specialized ergatoid queen and no gamergates in Platythyrea conradti. Insectes Sociaux 53 : 177-182.
1. Molet M., Van Baalen M. & Monnin T. 2005 Dominance hierarchies reduce the number of hopeful reproductives in polygynous queenless ants. Insectes Sociaux 52 : 247-256.

For general public / Vulgarisation en français :

Molet M. & Peeters C. 2010 La reproduction des colonies chez les fourmis. Le Courrier de la Nature Hors-Série spécial fourmis : 30-37.
Molet M. 2009 Petite visite chez les fourmis.

Curriculum Vitae

Since 2008
Assistan Professor in Biology, Laboratoire Ecologie & Evolution, Université Pierre et Marie Curie, Paris, France.

2007-2008
Post-Doctoral Research Assistant
Bee Sensory and Behavioural Ecology Laboratory, Queen Mary University, London, UK.
“Application of the Bumblebee foraging pheromone for commercial greenhouse pollination”, with Lars Chittka.

2003-2007
PhD in Ecology
Laboratoire Ecologie & Evolution, Université Pierre et Marie Curie, Paris, France
“From independent colony foundation to fission: evolution of colonial reproductive strategies in ants”, with Christian Peeters.

2000-2003
Licence and Master in Biology and Ecology
Ecole Normale Supérieure Ulm / Université Pierre et Marie Curie, Paris, France.

Links

PHD Students

2011-2013 Sylvain Londe

UNDEGRADUATE & GRADUATE Students

2006-2007   Isabelle Follin
2006-2007   Allan Debelle
2008-2009   Morgane Guérin
2008-2009   Ayano Kawamoto
2008-2009   Thibaut   Viscard
2009-2010   Sébastien Guidici
2009-2010   Diane Bouchet
2009-2010   Delphine Vilaysack
2009-2010   Melkior Cotonnec
2009-2010   Messika Revel
2009-2010   Battle Karimi
2010-2011   Frédéric Fyon
2010-2011   James Chester
2011-2012   Julian Donald
2011-2012   Vincent Maicher
2011-2012   Hélène Albert
2011-2012   Pauline Pierret
2011-2012   Juliette Auvinet