title: Bigger helpers in the ant Cataglyphis bombycina: increased worker polymorphism or novel soldier caste?
abstract: BACKGROUND
  The mechanisms by which development favors or constrains the evolution of new phenotypes are incompletely understood. Polyphenic species may benefit from developmental plasticity not only regarding ecological advantages, but also potential for evolutionary diversification. For instance, the repeated evolution of novel castes in ants may have been facilitated by the existence of alternative queen and worker castes and their respective developmental programs.
  
  
  METHODS
  Cataglyphis bombycina is exceptional in its genus because winged queens and size-polymorphic workers occur together with bigger individuals having saber-shaped mandibles. We measured seven body parts in more than 150 individuals to perform a morphometric analysis and assess the developmental origin of this novel phenotype.
  
  
  RESULTS
  Adults with saber-shaped mandibles differ from both workers and queens regarding the size of most body parts. Their relative growth rates are identical to workers for some pairs of body parts, and identical to queens for other pairs of body parts; critical sizes differ in all cases.
  
  
  CONCLUSIONS
  Big individuals are a third caste, i.e. soldiers, not major workers. Novel traits such as elongated mandibles are combined with a mix of queen and worker growth rates. We also reveal the existence of a dimorphism in the queen caste (microgynes and macrogynes). We discuss how novel phenotypes can evolve more readily in the context of an existing polyphenism. Both morphological traits and growth rules from existing queen and worker castes can be recombined, hence mosaic phenotypes are more likely to be viable. In C. bombycina, such a mosaic phenotype appears to function both for defense (saber-shaped mandibles) and fat storage (big abdomen). Recycling of developmental programs may have contributed to the morphological diversity and ecological success of ants.
authors.affiliation: Laboratoire Ecologie & Evolution - Unité Mixte de Recherche 7625, Université Pierre et Marie Curie, Paris, France ; Laboratoire Ecologie & Evolution - Unité Mixte de Recherche 7625, Centre National de la Recherche Scientifique, Paris, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Molet
authors.affiliation: Laboratoire Ecologie & Evolution - Unité Mixte de Recherche 7625, Université Pierre et Marie Curie, Paris, France ; Laboratoire Ecologie & Evolution - Unité Mixte de Recherche 7625, Centre National de la Recherche Scientifique, Paris, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Maicher
authors.affiliation: Laboratoire Ecologie & Evolution - Unité Mixte de Recherche 7625, Université Pierre et Marie Curie, Paris, France ; Laboratoire Ecologie & Evolution - Unité Mixte de Recherche 7625, Centre National de la Recherche Scientifique, Paris, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Peeters
mesh_terms: D000818:Animals; D001000:Ants / Q000033:anatomy & histology* / Q000502:physiology*; D005075:Biological Evolution; D005260:Female; D008297:Male; D010641:Phenotype