High fusibility and chimera prevalence in an invasive colonial ascidian

The formation of chimeric entities through colony fusion has been hypothesized to favour colonisation success and resilience in modular organisms. In particular, it can play an important role in promoting the invasiveness of introduced species. We studied prevalence of chimerism and performed fusion experiments in Mediterranean populations of the worldwide invasive colonial ascidian Didemnum vexillum. We analysed single zooids by whole genome amplification and genotyping-by-sequencing and obtained genotypic information for more than 2,000 loci per individual. In the prevalence study, we analysed nine colonies and identified that 44% of them were chimeric, composed of 2–3 different genotypes. In the fusion experiment 15 intra- and 30 intercolony pairs were assayed but one or both fragments regressed and died in ~45% of the pairs. Among those that survived for the length of the experiment (30 d), 100% isogeneic and 31% allogeneic pairs fused. Fusion was unlinked to global genetic relatedness since the genetic distance between fused or non-fused intercolony pairs did not differ significantly. We could not detect any locus directly involved in allorecognition, but we cannot preclude the existence of a histocompatibility mechanism. We conclude that chimerism occurs frequently in D. vexillum and may be an important factor to enhance genetic diversity and promote its successful expansion.

Fused Colonies of the Formosan Subterranean Termite (Blattodea: Rhinotermitidae) for Laboratory Experiments

Laboratory studies of Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae) often employ the use of field-collected foraging populations of individuals as defined colonies. The biological relevance of this practice is often called into question, because these colonies lack a full composition of reproductive castes and brood, which may have physiological and behavioral consequences. Rearing intact laboratory colonies can be done; however, it is time-consuming and labor-intensive. The artificial fusion of field-collected foraging populations with a young, laboratory-reared incipient colony may provide whole, intact colonies for laboratory research. The current study measures survivorship of fused colonies using laboratory-reared complete incipient colonies ranging in age from 0 to 5 mo, fused with 100 workers and 10 soldiers from field-collected populations of different colonial origin. Results indicate that 60% of colony fusion was successful when the incipient colony introduced is 5 mo of age. This method of colony fusion will provide researchers with intact colonies using minimal resources.

Diversity of Termite Breeding Systems

Termites are social insects that live in colonies headed by reproductive castes. The breeding system is defined by the number of reproductive individuals in a colony and the castes to which they belong. There is tremendous variation in the breeding system of termites both within and among species. The current state of our understanding of termite breeding systems is reviewed. Most termite colonies are founded by a primary (alate-derived) king and queen who mate and produce the other colony members. In some species, colonies continue throughout their life span as simple families headed by the original king and queen. In others, the primary king and queen are replaced by numerous neotenic (nymph- or worker-derived) reproductives, or less commonly primary reproductives, that are descendants of the original founding pair leading to inbreeding in the colony. In still others, colonies can have multiple unrelated reproductives due to either founding the colonies as groups or through colony fusion. More recently, parthenogenetic reproduction has shown to be important in some termite species and may be widespread. A major challenge in termite biology is to understand the ecological and evolutionary factors driving the variation in termite breeding systems.