Loss of wings induces the expression of the worker-like phenotype in queens of a ponerine ant

Many highly-eusocial insect species are characterized by morphological differences between females. This is especially pronounced in ants where queens usually possess a fully developed thorax with wings and are specialized for reproduction while workers have a reduced thorax without wings and show various levels of reproductive degeneration that is associated with their helper role in the colony. Despite their morphological differentiation, queens and workers still show some plasticity leading to overlapping behavioral and physiological phenotypes. We investigated the level of queen plasticity and the factor that induces a worker-like phenotype in the ant species Harpegnathos saltator that has limited queen-worker dimorphism and workers that can assume the reproductive role of a queen in the colony. By comparing alate and dealate young queens, so-called gynes, we found that the loss of wings initiated the expression of behavioral and physiological characteristics of ant workers. In contrast to alate gynes, dealate gynes displayed higher frequencies of worker-like behaviors. In addition, dealate gynes showed a worker-like range of reproductive states unlike alate gynes. Like workers, dealate gynes lost the chemical signaling that is characteristic of alate gynes. Since gynes can activate this worker-like phenotype after wing loss, the essential difference between the ant queens and workers in this species with limited queen-worker dimorphism is a dispersal polyphenism. If the phenotypic plasticity observed in H. saltator is representative of the early stages of ant eusociality, an emerging dispersal dimorphism rather than a distinct reproductive dimorphism might represent one of the first steps in ant evolution.

Comprehensive analysis of male-free reproduction in Monomorium triviale (Formicidae: Myrmicinae)

We report comprehensive evidence for obligatory thelytokous parthenogenesis in an ant Monomorium triviale. This species is characterized by distinct queen–worker dimorphism with strict reproductive division of labor: queens produce both workers and new queens without mating, whereas workers are completely sterile. We collected 333 nests of this species from 14 localities and three laboratory-reared populations in Japan. All wild queens dissected had no sperm in their spermathecae. Laboratory observation confirmed that virgin queens produced workers without mating. Furthermore, microsatellite genotyping showed identical heterozygous genotypes between mothers and their respective daughters, suggesting an extremely low probability of sexual reproduction. Microbial analysis detected no bacterial genera that are known to induce thelytokous parthenogenesis in Hymenoptera. Finally, the lack of variation in partial sequences of mitochondrial DNA among individuals sampled from across Japan suggests recent rapid spread or selective sweep. M. triviale would be a promising model system of superorganism-like adaptation through comparative analysis with well-studied sexual congeners, including the pharaoh ant M. pharaonis.

Comprehensive analysis of male-free reproduction in Monomorium triviale (Formicidae: Myrmicinae)

We report comprehensive evidence for obligatory thelytokous parthenogenesis in an ant Monomorium triviale. This species is characterized by distinct queen–worker dimorphism with strict reproductive division of labor: queens produce both workers and new queens without mating, whereas workers are completely sterile. We collected 333 nests of this species from 14 localities and three laboratory-reared populations in Japan. All wild queens dissected had no sperm in their spermathecae. Laboratory observation confirmed that virgin queens produced workers without mating. Furthermore, microsatellite genotyping showed identical heterozygous genotypes between mothers and their respective daughters, suggesting an extremely low probability of sexual reproduction. Microbial analysis detected no bacterial genera that are known to induce thelytokous parthenogenesis in Hymenoptera. Finally, the lack of variation in partial sequences of mitochondrial DNA among individuals sampled from across Japan suggests recent rapid spread or selective sweep. M. triviale would be a promising model system of superorganism-like adaptation through comparative analysis with well-studied sexual congeners, including the pharaoh ant M. pharaonis.

A new nasute-termite Ceylonitermes nivedita sp. nov. (Isoptera: Termitidae) from India along with first record of worker dimorphism

A new nasute termite Ceylonitermes nivedita sp. nov. (Isoptera: Termitidae) is described from the tropical rainforests of Manipur, India. Both the soldier and worker castes of the species are described. The workers are strongly dimorphic and no such dimorphism is reported hitherto among the 3 known species of Ceylonitermes. A revised dichotomous key to identify all the 4 known species of the genus is also provided. The proposed new species is a minor pest of bamboo. Key words: Ceylonitermes, India, Nasutitermitinae, key