Mark S. Bulmer

Reproductive dynamics and colony structure of subterranean termites of the genus Reticulitermes (Isoptera Rhinotermitidae): a review of the evidence from behavioral, ecological, and genetic studies

(1) In subterranean termites of the genus Reticulitermes, colonies are difficult to delineate because physical nest structures are concealed or amorphous, and colony boundaries are difficult to define. The ambiguity of colony architecture and the cryptic nesting and feeding habits of these ecologically and economically important termites hinder our understanding of their population biology. We review and synthesize current information on Reticulitermes life history, reproduction, and genetics to develop an understanding of colony and population structure, and possible modes of reproductive organization. (2) To infer colony structure, we simulate several breeding systems that might be found in Reticulitermes and determine the F statistics and relatedness coefficients expected for groups of workers drawn from the simulated populations. Available field data on the distribution of worker genotypes within and among colonies are then used to distinguish between alternate hypotheses regarding population and bree...

Variation in colony structure in the subterranean termite Reticulitermes flavipes

Abstract The genetic organization of colonies of the subterranean termite Reticulitermes flavipes in two subpopulations in Massachusetts was explored using five polymorphic allozymes and double-strand conformation polymorphism (DSCP) analysis of the mitochondrial control region. Empirically obtained estimates of worker relatedness and F-statistics were compared with values generated by computer simulations of breeding schemes to make inferences about colony organization. In one study site (G), worker genotypes indicated the presence of a mixture of colonies headed by monogamous outbred primary reproductives and colonies headed by inbreeding neotenic reproductives, both colony types having limited spatial ranges. A second site (S) was dominated by several large colonies with low relatedness among nestmates. Mixed DSCP haplotypes in three colonies indicated that nestmates had descended from two or three unrelated female reproductives. Computer simulations of breeding schemes suggested that positive colony inbreeding coefficients at site S resulted from either commingling of workers from different nests or different colonies. Such an exchange of workers between nests corresponds to the multiple-site nesting lifetype of many subterranean termites and resembles colony structure in polycalic Formica ants. Our study demonstrates considerable variation in R. flavipes colony structure over a small spatial scale, including colonies headed by monogamous outbred primary reproductives, colonies containing multiple inbred neotenic reproductives and large polydomous colonies containing the progeny of two or more unrelated queens, and suggests that the number of reproductives and nestmate relatedness change with colony age and size.

Targeting an antimicrobial effector function in insect immunity as a pest control strategy

Insect pests such as termites cause damages to crops and man-made structures estimated at over

Ecology, Behavior and Evolution of Disease Resistance in Termites

30 billion per year, imposing a global challenge for the human economy. Here, we report a strategy for compromising insect immunity that might lead to the development of nontoxic, sustainable pest control methods. Gram-negative bacteria binding proteins (GNBPs) are critical for sensing pathogenic infection and triggering effector responses. We report that termite GNBP-2 (tGNBP-2) shows β(1,3)-glucanase effector activity previously unknown in animal immunity and is a pleiotropic pattern recognition receptor and an antimicrobial effector protein. Termites incorporate this protein into the nest building material, where it functions as a nest-embedded sensor that cleaves and releases pathogenic components, priming termites for improved antimicrobial defense. By means of rational design, we present an inexpensive, nontoxic small molecule glycomimetic that blocks tGNBP-2, thus exposing termites in vivo to accelerated infection and death from specific and opportunistic pathogens. Such a molecule, introduced into building materials and agricultural methods, could protect valuable assets from insect pests.

Subterranean termite prophylactic secretions and external antifungal defenses

The nesting and feeding habits of termites create the risk of contact with microbial and invertebrate pathogens and parasites. Additionally, termite life history can result in cyclical decreases in nestmate genetic heterogeneity, increasing susceptibility to parasites, and sociality may elevate transmission rates of infection within colonies. Current research indicates that ecology and group living have selected for disease resistance in both basal and derived termite families, which have evolved diverse immune adaptations deployed sequentially or simultaneously at both individual and societal levels. These include inducible behavioral, biochemical, immunological and social mechanisms of infection control. Mortality from disease can be significant for reproductives, pseudergates and sterile castes, and influences colony fitness through impacts on colony size, demography, polymorphism, division of labor, communication, development, reproduction, colony foundation, and colony and population genetics. The hemimetabolic development, diplodiploid genetics, microbial symbioses and recalcitrant diets of termites present unique opportunities to model the effects of disease on immune function, including the adaptive design of immune molecules, life-history traits and social evolution. Comparisons can also be made between termite and hymenopteran immunocompetences, highlighting phylogenetic and ecological differences. We advocate a multidisciplinary approach to disease resistance in termites, focusing simultaneously on cellular and humoral immunity, antibiotic prophylaxis and social modes of infection control.

Molecular antifungal defenses in subterranean termites: RNA interference reveals in vivo roles of termicins and GNBPs against a naturally encountered pathogen

Termites exploit environments that make them susceptible to infection and rapid disease transmission. Gram-negative bacteria binding proteins (GNBPs) signal the presence of microbes and in some insects directly damage fungal pathogens with β-1,3-glucanase activity. The subterranean termites Reticulitermes flavipes and Reticulitermes virginicus encounter soil entomopathogenic fungi such as Metarhizium anisopliae, which can evade host immune responses after penetrating the cuticle. An external defense that prevents invasion of fungal pathogens could be crucial in termites, allowing them to thrive under high pathogenic pressures. We investigated the role of secreted β-1,3-glucanases in Reticulitermes defenses against M. anisopliae. Our results show that these termites secrete antifungal β-1,3-glucanases on the cuticle, and the specific inhibition of GNBP associated β-1,3-glucanase activity with d-δ-gluconolactone (GDL) reduces this activity and can cause significant increases in mortality after exposure to M. anisopliae. Secreted β-1,3-glucanases appear to be essential in preventing infection by breaking down fungi externally.

Adaptive evolution in subterranean termite antifungal peptides

Subterranean termites face strong pathogenic pressures from the ubiquitous soil fungus Metarhizium anisopliae, and rely on innate humoral and cellular, as well as behavioral immune defenses for protection. Reticulitermes termites secrete antifungal enzymes that exhibit strong β-1,3-glucanase activity associated with Gram-negative bacteria binding proteins (GNBPs), which prevent M. anisopliae from invading the hemocoel where it can evade immune responses. Molecular evolutionary studies of Reticulitermes termicin genes, which code for defensin-like antifungal peptides, suggest that these proteins may be important effector molecules in antifungal defenses. In this study we show that the RNAi knockdown of termicin and GNBP2 expression via the ingestion of dsRNA significantly increases mortality in termites exposed to a naturally encountered strain of M. anisopliae. Termicin and GNBP2 knockdown also decrease external cuticular antifungal activity, indicating a direct role for these proteins in an external antifungal defense strategy that depends on the active dissemination of antifungal secretions among nestmates.

Symbiont-derived β-1,3-glucanases in a social insect: mutualism beyond nutrition.

We identified and analysed mRNA sequences of two immune proteins from the subterranean termites Reticulitermes flavipes and Reticulitermes virginicus. These proteins correspond to two immune proteins described in the distantly related termite genus Nasutitermes; termicin, which is a small antifungal peptide, and GNBP2, which functions both as a broad pattern recognition receptor and a direct antifungal effector. A population genetic analysis of nucleotide intraspecific polymorphism and interspecific divergence indicates that a selective sweep has reduced polymorphism in the termicins. Moreover, this selective sweep appears to have been driven by the positive selection of beneficial amino acid changes in the antifungal peptide. In contrast, the pattern of polymorphism and divergence in GNBP2 corresponds to the standard neutral model of evolution.

Foraging Range Expansion and Colony Genetic Organization in the Subterranean Termite Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Termites have had a long co-evolutionary history with prokaryotic and eukaryotic gut microbes. Historically, the role of these anaerobic obligate symbionts has been attributed to the nutritional welfare of the host. We provide evidence that protozoa (and/or their associated bacteria) colonizing the hindgut of the dampwood termite Zootermopsis angusticollis, synthesize multiple functional β-1,3-glucanases, enzymes known for breaking down β-1,3-glucans, the main component of fungal cell walls. These enzymes, we propose, may help in both digestion of ingested fungal hyphae and protection against invasion by fungal pathogens. This research points to an additional novel role for the mutualistic hindgut microbial consortia of termites, an association that may extend beyond lignocellulolytic activity and nitrogen fixation to include a reduction in the risks of mycosis at both the individual- and colony-levels while nesting in and feeding on microbial-rich decayed wood.

A common antifungal defense strategy in Cryptocercus woodroaches and termites

Abstract Our understanding of foraging and space use in Reticulitermes species is limited because their subterranean colonies are not associated with distinct physical nest structures and the colony affinity of workers cannot be readily identified with behavioral assays. Recently, we found that in Reticulitermes flavipes (Kollar) colonies from Massachusetts, the average colony inbreeding coefficient, measured with five polymorphic allozymes, was significantly greater than zero for non-Mendelian colonies with worker genotypes corresponding with the offspring of multiple inbreeding secondary reproductives rather than male and female primary reproductives. Foraging groups of termites with positive inbreeding coefficients suggest that workers feeding at fallen trees and branches frequently originate from different reproductive centers. The positive inbreeding coefficients appear to result from foraging traffic and not from inbreeding among secondary reproductives. A positive correlation between colony inbreeding coefficients and colony foraging range for non-Mendelian colonies suggested that the number of separate reproductive centers and/or the allele frequency contrasts between reproductives from separate centers increased with the expansion of a colony’s foraging area. It is unlikely that an increase in the subdivision of breeding groups in a single reproductive center would closely coincide with an increase in foraging range. However, the extent of mixing between workers from neighboring colonies could have increased with foraging range expansion, especially given the apparent lack of nestmate discrimination in R. flavipes. Nevertheless, foragers from neighboring colonies have high genetic contrasts, and therefore appear to maintain distinct foraging areas.