Socially transferred materials: why and how to study them

The Biology and Social Life of Earwigs (Dermaptera)

Earwigs are often known for the forceps-like appendage at the end of their abdomen, urban legends about them crawling into human ears, and their roles as pest and biological control agents. However, they are much less known for their social life. This is surprising, as many of the 1,900 species of earwigs show social behaviors toward eggs, juveniles, and adults. These behaviors typically occur during family and group living, which may be obligatory or facultative, last up to several months, and involve only a few to several hundred related or unrelated individuals. Moreover, many individuals can alternate between solitary and group living during their life cycle, an ability that probably prevailed during the emergence of social life. In this review, I detail the diversity of group living and social behavior in earwigs and show how further developing this knowledge in Dermaptera can improve our general understanding of the early evolution of social life in insects.

Social administration of juvenile hormone to larvae increases body size and nutritional needs for pupation

Social insects often display extreme variation in body size and morphology within the same colony. In many species, adult morphology is socially regulated by workers during larval development. While larval nutrition may play a role in this regulation, it is often difficult to identify precisely what larvae receive from rearing workers, especially when larvae are fed through social regurgitation. Across insects, juvenile hormone is a major regulator of development. In the ant Camponotus floridanus, this hormone is present in the socially regurgitated fluid of workers. We investigated the role the social transfer of juvenile hormone in the social regulation of development. To do this, we administered an artificial regurgitate to larvae through a newly developed handfeeding method that was or was not supplemented with juvenile hormone. Orally administered juvenile hormone increased the nutritional needs of larvae, allowing them to reach a larger size at pupation. Instead of causing them to grow faster, the juvenile hormone treatment extended larval developmental time, allowing them to accumulate resources over a longer period. Handfeeding ant larvae with juvenile hormone resulted in larger adult workers after metamorphosis, suggesting a role for socially transferred juvenile hormone in the colony-level regulation of worker size over colony maturation.

Deciphering the ecoevolutionary recipe of milk microbiomes

In a recent article, Keady et al. analyzed mammalian milk microbiomes across 47 species and found their assembly to be largely determined by stochastic (i.e., random) processes. In many ways, host-associated microbiomes are not random, but random events may have an underappreciated role in microbiome assembly, persistence, and ecology.

The royal food of termites shows king and queen specificity

Society in eusocial insects is based on the reproductive division of labor, with a small number of reproductive individuals supported by a large number of nonreproductive individuals. Because inclusive fitness of all colony members depends on the survival and fertility of reproductive members, sterile members provide royals with special treatment. Here, we show that termite kings and queens each receive special food of a different composition from workers. Sequential analysis of feeding processes demonstrated that workers exhibit discriminative trophallaxis, indicating their decision-making capacity in allocating food to the kings and queens. Liquid chromatography tandem-mass spectrometry analyses of the stomodeal food and midgut contents revealed king- and queen-specific compounds, including diacylglycerols and short-chain peptides. Desorption electrospray ionization mass spectrometry imaging analyses of ¹³C-labeled termites identified phosphatidylinositol and acetyl-l-carnitine in the royal food. Comparison of the digestive tract structure showed remarkable differences in the volume ratio of the midgut-to-hindgut among castes, indicating that digestive division of labor underlies reproductive division of labor. Our demonstration of king- and queen-specific foods in termites provides insight into the nutritional system that underpins the extraordinary reproduction and longevity of royals in eusocial insects.