Evidence for a thoracic crop in the workers of some Neotropical Pheidole species (Formicidae: Myrmicinae)

Evidence of a thoracic crop in workers, soldiers, and queens of Carebara perpusilla ants (Formicidae: Myrmicinae)

The ability to share and store food is paramount in group-living animals, allowing a finely tuned distribution of resources over time and individuals and an enhanced survival over periods of food scarcity. Ants have several ways to store food: one of them is their gastral crop, also known as a "social stomach." Nutrients in the crop can be regurgitated to nestmates through oral trophallaxis (mouth-to-mouth) or proceed to the midgut by opening the proventriculus, a valve connecting the crop to the midgut. However, some ants are also known to have a so-called "thoracic crop," an extension of the esophagus that allows for additional storage space. In this study, we provide the first evidence of a thoracic crop in the genus Carebara, in reproductive (queen) and sterile (soldier and worker) castes. We discuss how the ant body plan allowed for the evolution of a novel food storage structure in the mesothorax.

Unparalleled details of soft tissues in a Cretaceous ant

For social insects such as ants, the internal organs are likely important in understanding their eusocial behavior and evolution. Such organs, however, are rarely preserved on fossils. In each of the few cases reporting exceptionally fossilized soft tissues in arthropods, the nervous, muscular and cardiovascular systems have been described individually, but never in combination. Here, we report a female specimen (gyne) of the extinct ant group-†Zigrasimecia-included in a Cretaceous amber piece from Kachin, Myanmar, with an almost complete system formed by various internal organs. These include the brain, the main exocrine system, part of the digestive tract, and several muscle clusters. This research expands our knowledge of internal anatomy in stem group ants. As the gyne bears a morphologically unique labrum, our specimen's internal and external features support the notion that the early ant may have special ecological habits during the Cretaceous period.

Thoracic crop formation is spatiotemporally coordinated with flight muscle histolysis during claustral colony foundation in Lasius japonicus queens

In a majority of ants, a newly mated queen independently founds a colony and claustrally raises her first brood without foraging outside the nest. During claustral independent colony foundation (ICF) in several ants, the esophagus of the founding queen expands and develops into a "thoracic crop," which is then filled with a liquid substrate for larval feeding. It has been suggested that these substrates are converted from the founding queen's body reserves (e.g., histolyzed flight muscles) or redistributed from a gastral crop. Here, we describe thoracic crop development in Lasius japonicus queens during claustral ICF. The foundresses claustrally feed their larvae from weeks 2-5 after ICF onset, and the first worker emerges at week 6. The development proceeds as follows: in week 0, the foundress' dorsal esophageal wall is pleated and thickened. Then, from weeks 2-5, the esophagus expands toward a dorsal space previously occupied by flight muscles, following flight muscle histolysis. Gastral crop expansion follows esophageal expansion. Thus, thoracic crop formation may be spatiotemporally coordinated with flight muscle histolysis in Lasius japonicus queens, and similar developmental regulations might be common in other claustral ICF ants.