About 15,000 ant species are known and present highly diverse morphologies, behaviors, chemical signals and social organization, which always involve caring for the brood (Hölldobler and Wilson, 1990). Ant brood have relatively long developmental time, and their early phases, such as the mechanisms of embryogenesis and how these mechanisms contributed to the ant impressive social diversity are neglected topics. More importantly, there are no studies trying to link embryo development in ants and their characteristic social organization. A recent set of data on ant embryogenesis revealed for the first time some radical alterations in genetic hierarchies underlying embryo patterning, which might deeply affect ant social lifestyle. We uncovered two distinct modes of embryo development across ant species. The first mode bears some similarities with both long- and short-germ development with easily identifiable canonical patterns such as pair-rule whereby specific genes are expressed in every other segment along embryo axis (Choe and Brown, 2007, 2009; Choe et al., 2006; Clark and Akam, 2016; Rosenberg et al., 2014). The second mode is radically different and species employing this mode seem to have lost the pair-rule pattern altogether. Instead, a massive rearrangement of the anterior pole of the embryo results in the formation of a thick layer of fat cells that later surround the entire embryo. At the end of embryogenesis, the larva spends several days within the chorion and consumes the fat cells before it hatches. These findings led us to formulate a number of hypotheses about the mechanisms of development and speculate about their potential link to the evolution of eusociality in ants. In this project, we aim to better understand the mechanisms of embryo development across a selection of ant species and test how changes in these mechanisms can inform about their social lifestyle. The proposal is organized in three main aims. AIM1: understanding the differences in early embryo patterning and segmentation hierarchies between the two modes of development in ants. This aim will be conducted in the common garden ant Lasius niger and the harvester and Messor pergandei each representing a different mode and where we already have a valuable dataset about embryogenesis. AIM2: Evolution of embryo patterning in a sample of ~40 carefully chosen ant species to reconstruct the evolutionary history of developmental control in the group. AIM3: In ants, larvae are entirely dependent on workers for care and food. Workers recognize larvae as nestmates based on the hydrocarbon signature on larval cuticle. We hypothesize that the layer of fat cell consumed by the larva prior to hatching provides the hydrocarbons constituting the signature of newly hatched larva thereby allowing it to be accepted by the workers. In this aim, we will test the link between the changes in embryogenesis and the evolution of eusociality in ants.
Monsieur Abderrahman Khila (INSTITUT DE GENOMIQUE FONCTIONNELLE DE LYON (IGFL))
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
LEEC Laboratoire d'Ethologie Expérimentale et Comparée
UMR5242 - ICGFL - CNRS INSTITUT DE GENOMIQUE FONCTIONNELLE DE LYON (IGFL)
Help of the ANR 479,323 euros
Beginning and duration of the scientific project: September 2017 - 48 Months