REPRODUCTIVE TRAIRS EVOLUTION

Geographic differentiation of reproductive traits:

Researchers: Dr. Thomas Lecocq

The meeting between mates is one of the most important steps for the reproduction. The individuals localize, recognize, and select their sexual partners through the courtship behavior that involves reproductive traits (e.g. feathers, mating call or chemical secretions). The reproductive traits have a key role in the pre-mating recognition and in the maintenance of reproductive isolation. The evolution of reproductive traits is shaped (i) by intraspecific interactions to maximize encounter rates among conspecific mates (sexual selection), and (ii) by interspecific interactions to maintain isolation barriers and decrease the likelihood of hybridization events among syntopic sister species, and to minimize eavesdropping by potential predators. Beyond these selective pressures, eco-climatic constraints can also affect the evolution of reproductive traits.

Geographic variation in reproductive traits has been observed in several species such as moths, flies, bees, and birds. The geographic variation could be driven by changes in intraspecific selection, interspecific interactions or local adaptation to eco-climatic constraints across the species area. However, the evolution of sexual recognition signals in geographic framework has received far less attention to date. Now, divergences in reproductive traits act as an important force in promoting pre-zygotic isolation and speciation. This places a premium to understand the processes that lead to this geographic variation.

Our research aims to investigate (i) processes and geographic configuration that lead to geographic differentiation of reproductive traits and (ii) consequences of this differentiation on speciation. We broach this topic through bumblebee species and one of their reproductive traits (the male marking secretions). We use (i) phylogenetic and phylogeographic approaches and (ii) environmental niche modelling methods along with (iii) comparative analyses of the differentiation patterns and natural variation of male marking secretions on specimens from populations across the species distribution.

Main findings:

• The impoverished insular bumblebee fauna does not seem to lead to relaxation of selective pressure on reproductive traits despite the drastic reduction of the species diversity.
  
• Our studies suggest that the geographic differentiation of reproductive traits is (i) driven by a persistent lack of gene flow leading to genetic differentiation of genes coding for reproductive traits and (ii) reinforced by female preferences for reproductive traits of local males.
  
• The geographic differentiation of reproductive traits is observed between continental populations previously isolated in different glacial refugia.
  
• These geographic differentiations on island or between former glacial refugia can lead to the establishment of a reproductive (pre-zygotic) isolation barrier and to speciation process.

Selected publications:

• Lecocq, T., Dellicour, S., Michez, D., Lhomme, P., Vanderplanck, M., Valterová, I., Rasplus, J.-Y., Rasmont, P., 2013a. Scent of a break-up: phylogeography and reproductive trait divergences in the red-tailed bumblebee (Bombus lapidarius). BMC Evol. Biol. 13, 263. doi:10.1186/1471-2148-13-263
  
• Lecocq, T., Vereecken, N.J., Michez, D., Dellicour, S., Lhomme, P., Valterová, I., Rasplus, J.-Y., Rasmont, P., 2013b. Patterns of genetic and reproductive traits differentiation in Mainland vs. Corsican populations of bumblebees. PLoS One 8, e65642. doi:10.1371/journal.pone.0065642
  
• Glaser, N., Frérot, B., Leppik, E., Monsempes, C., Capdevielle-Dulac, C., Le Ru, B., Lecocq, T., Harry, M., Jacquin-Joly, E., Calatayud, P.-A., 2014. Similar differentiation patterns between PBP expression levels and pheromone component ratios in two populations of Sesamia nonagrioides. J. Chem. Ecol. 40, 923–7. doi:10.1007/s10886-014-0485-2
  
• Lecocq, T., Coppée, A., Mathy, T., Lhomme, P., Cammaerts-Tricot, M.-C., Urbanová, K., Valterová, I., Rasmont, P., 2015. Subspecific differentiation in male reproductive traits and virgin queen preferences, in Bombus terrestris. Apidologie in press.

Chemical reproductive traits of diploid bumblebee males

Researchers: Dr. Thomas Lecocq, Nicolas Brasero, Maxence Gérard

The current bumblebee decline leads to inbreeding in populations that fosters a loss of allelic diversity and diploid male production. As diploid males are viable and their offspring is sterile, bumblebee populations can quickly fall in a vortex of extinction. We investigate for the first time a potential pre-mating mechanism through a major chemical reproductive trait (male cephalic labial gland secretion; CLGS) that could prevent monandrous virgin queens to mate with diploid males.

See also used of reproductive trait differentiation in taxonomy  and in biological conservation