1st Place: Hybrid Coptotermes colonies shed light on symbiosis in lower termites

Host-symbiont relationships are maintained through symbiont transmission. Hosts acquire their symbionts through vertical transmission, horizontal transmission, or a combination thereof, i.e., mixed-mode transmission. Lower termites are social insects that harbor mutualistic, wood-digesting protists as well as prokaryotic symbionts in their hindguts. Each lower termite species harbors a unique community of cellulolytic protists, with rare exception. These symbionts are vertically transmitted from the founding reproductives of newly established colonies to their first workers through proctodeal trophallaxis. Presumably, workers acquire symbiont lineages from both kings and queens; however, biparental transmission has not yet been experimentally demonstrated in lower termites. For this study, Coptotermes gestroi (Wasmann) and Coptotermes formosanus Shiraki were used to examine aspects of symbiont transmission in lower termites. The complete protist communities of these Coptotermes species each consist of five parabasalids belonging to the genera Cononympha, Holomastigotoides, and Pseudotrichonympha. To investigate transmission, the protist communities of reproductives and offspring from 1-month-old–3.5-year-old hybrid Coptotermes colonies were determined through 18S rRNA amplicon sequencing. These colonies were established by heterospecific pairs of C. gestroi and C. formosanus alates. Examination of the protist communities of individuals from hybrid Coptotermes colonies shed light on several aspects of symbiosis in lower termites, including biparental transmission and horizontal transmission between kings and queens during incipient colony development.