Size and heterozygosity influence partner selection in the Formosan subterranean termite

Weight and protozoa number but not bacteria diversity are associated with successful pair formation of dealates in the Formosan subterranean termite, Coptotermes formosanus

New colonies of Formosan subterranean termites are founded by monogamous pairs. During swarming season, alates (winged reproductives) leave their parental colony. After swarming, they drop to the ground, shed their wings, and male and female dealates find suitable nesting sites where they mate and become kings and queens of new colonies. The first generation of offspring is entirely dependent on the nutritional resources of the founder pair consisting of the fat and protein reserves of the dealates and their microbiota, which include the cellulose-digesting protozoa and diverse bacteria. Since termite kings and queens can live for decades, mate for life and colony success is linked to those initial resources, we hypothesized that gut microbiota of founders affect pair formation. To test this hypothesis, we collected pairs found in nest chambers and single male and female dealates from four swarm populations. The association of three factors (pairing status, sex of the dealates and population) with dealate weights, total protozoa, and protozoa Pseudotrichonympha grassii numbers in dealate hindguts was determined. In addition, Illumina 16S rRNA gene sequencing and the QIIME2 pipeline were used to determine the impact of those three factors on gut bacteria diversity of dealates. Here we report that pairing status was significantly affected by weight and total protozoa numbers, but not by P. grassii numbers and bacteria diversity. Weight and total protozoa numbers were higher in paired compared to single dealates. Males contained significantly higher P. grassii numbers and bacteria richness and marginally higher phylogenetic diversity despite having lower weights than females. In conclusion, this study showed that dealates with high body weight and protozoa numbers are more likely to pair and become colony founders, probably because of competitive advantage. The combined nutritional resources provided by body weight and protozoa symbionts of the parents are important for successful colony foundation and development.

Genomics and Geographic Diversity of Bacteriophages Associated With Endosymbionts in the Guts of Workers and Alates of Coptotermes Species (Blattodea: Rhinotermitidae)

Subterranean termites depend nutritionally on their gut microbiota, which includes protozoa as well as taxonomically and functionally diverse bacteria. Our previous metavirome study revealed a high diversity and novel families of bacteriophages in the guts of Coptotermes formosanus workers from New Orleans, Louisiana, United States. Two assembled bacteriophage genomes (Phages TG-crAlp-04 and 06, family Podoviridae) existed in all colonies and showed similarity to a prophage (ProJPt-Bp1) previously sequenced from a bacterial endosymbiont (Candidatus Azobacteroides pseudotrichonymphae, CAP) of protozoa in the gut of a termite species of the genus Prorhinotermes from Taiwan. In this study the genomes of Phage TG-crAlp-04 and 06 were subjected to detailed functional annotation. Both phage genomes contained conserved genes for DNA packaging, head and tail morphogenesis, and phage replication. Approximately 30% of the amino acid sequences derived from genes in both genomes matched to those of ProJPt-Bp1 phage or other phages from the crAss-like phage group. No integrase was identified; the lack of a lysogeny module is a characteristic of crAss-like phages. Primers were designed to sequence conserved genes of the two phages and their putative host bacterium (CAP) to detect their presence in different termite species from native and introduced distribution ranges. Related strains of the host bacterium were found across different termite genera and geographic regions. Different termite species had separate CAP strains, but intraspecific geographical variation was low. These results together with the fact that CAP is an important intracellular symbiont of obligate cellulose-digesting protozoa, suggest that CAP is a core gut bacterium and co-evolved across several subterranean termite species. Variants of both crAss-like phages were detected in different Coptotermes species from the native and introduced range, but they did not differentiate by species or geographic region. Since similar phages were detected in different termite species, we propose the existence of a core virome associated with core bacterial endosymbionts of protozoa in the guts of subterranean termites. This work provides a strong basis for further study of the quadripartite relationship of termites, protozoa, bacteria, and bacteriophages.

Coordination of movement via complementary interactions of leaders and followers in termite mating pairs

In collective animal motion, coordination is often achieved by feedback between leaders and followers. For stable coordination, a leader's signals and a follower's responses are hypothesized to be attuned to each other. However, their roles are difficult to disentangle in species with highly coordinated movements, hiding potential diversity of behavioural mechanisms for collective behaviour. Here, we show that two Coptotermes termite species achieve a similar level of coordination via distinct sets of complementary leader-follower interactions. Even though C. gestroi females produce less pheromone than C. formosanus, tandem runs of both species were stable. Heterospecific pairs with C. gestroi males were also stable, but not those with C. formosanus males. We attributed this to the males' adaptation to the conspecific females; C. gestroi males have a unique capacity to follow females with small amounts of pheromone, while C. formosanus males reject C. gestroi females as unsuitable but are competitive over females with large amounts of pheromone. An information-theoretic analysis supported this conclusion by detecting information flow from female to male only in stable tandems. Our study highlights cryptic interspecific variation in movement coordination, a source of novelty for the evolution of social interactions.

Female-biased sex allocation and lack of inbreeding avoidance in Cubitermes termites

Sexually reproducing organisms face a strong selective pressure to find a mate and ensure reproduction. An important criterion during mate-selection is to avoid closely related individuals and subsequent potential fitness costs of resulting inbred offspring. Inbreeding avoidance can be active through kin recognition during mate choice, or passive through differential male and female-biased sex ratios, which effectively prevents sib-mating. In addition, sex allocation, or the resources allotted to male and female offspring, can impact mating and reproductive success. Here, we investigate mate choice, sex ratios, and sex allocation in dispersing reproductives (alates) from colonies of the termite Cubitermes tenuiceps. Termites have a short time to select a mate for life, which should intensify any fitness consequences of inbreeding. However, alates did not actively avoid inbreeding through mate choice via kin recognition based on genetic or environmental cues. Furthermore, the majority of colonies exhibited a female-biased sex ratio, and none exhibited a male-bias, indicating that differential bias does not reduce inbreeding. Sex allocation was generally female-biased, as females also were heavier, but the potential fitness effect of this costly strategy remains unclear. The bacterium Wolbachia, known in other insects to parasitically distort sex allocation toward females, was present within all alates. While Wolbachia is commonly associated with termites, parasitism has yet to be demonstrated, warranting further study of the nature of the symbiosis. Both the apparent lack of inbreeding avoidance and potential maladaptive sex allocation implies possible negative effects on mating and fitness.

Termite males enhance mating encounters by changing speed according to density

Search theory predicts that animals evolve efficient movement patterns to enhance encounter rates with specific targets. The optimal movements vary with the surrounding environments, which may explain the observation that animals often switch their movement patterns depending on conditions. However, the effectiveness of behavioural change during search is rarely evaluated because it is difficult to examine the actual encounter dynamics. Here we studied how partner-seeking termites update their search strategies depending on the local densities of potential mates. After a dispersal flight, termites drop their wings and walk to search for a mate; when a female and a male meet, they form a female-led tandem pair and search for a favourable nesting site. If a pair is separated, they have two search options-reunite with their stray partner, or seek a new partner. We hypothesized that the density of individuals affects separation-reunion dynamics and thus the optimal search strategy. We observed the searching process across different densities and found that termite pairs were often separated but obtained a new partner quickly at high mate density. After separation, while females consistently slowed down, males increased their speed according to the density. Under high mate density, separated males obtained a partner earlier than females, who do not change movement with density. Our data-based simulations confirmed that the observed behavioural change by males contributes to enhancing encounters. Males at very low mate densities did best to move slowly and thereby reduce the risk of missing their stray partner, who is the only available mate. On the other hand, males that experienced high mate densities did better in mating encounters by moving fast because the risk of isolation is low, and they must compete with other males to find a partner. These results demonstrate that termite males adaptively update their search strategy depending on conditions. Understanding the encounter dynamics experienced by animals is key to connecting the empirical work to the idealized search processes of theoretical studies.

Flight Phenology of Two Coptotermes Species (Isoptera: Rhinotermitidae) in Southeastern Florida

The dispersal flight activity ("swarming") of two invasive subterranean termite species, Coptotermes gestroi (Wasmann) and Coptotermes formosanus Shiraki, was monitored in metropolitan southeastern Florida, where both species are now sympatric and major structural pests. Historical records of alates collected in the area showed that the two species have distinct peaks of flight activity, from mid-February to late April for C. gestroi, and from early April to late June for C. formosanus. However, an overlap of the two dispersal flight seasons has been observed since at least 2005. The daily monitoring of dispersal flight events in southeastern Florida in 2014, 2015, and 2016 confirmed that simultaneous flights occurred several times each year. In addition, environmental conditions for favorable flights were identified, and it was established that low temperature was the primary factor inhibiting both species from dispersal flights, while all other factors had little impact on the occurrence of major dispersal flight events. However, both species shared similar temperature requirements for favorable dispersal flight conditions despite distinct peaks of activity over time. The analysis of sex ratios and average weights of the alates suggests that intrinsic colony factors are important for the timing of the maturation of alates, and that once a cohort of individuals is ready to disperse, a flight may occur as soon as the environmental conditions are favorable.

A trade-off between antipredatory behavior and pairing competition produced by male-male tandem running in three Reticulitermes species

Due to the omnipresent risk of predation, termites have evolved many antipredatory behaviors. The two related species Reticulitermes speratus and R. chinensis have been demonstrated to use homosexual tandem running to decrease individual predation risk after shedding their wings. In this study, we tested risk of predation in the termite R. flaviceps, which is distantly related to the above two species. We determined that homosexual tandem running also led to low individual predation risk in dealates of R. flaviceps. Moreover, by combining a predation model with a competition model, we observed a typical trade-off phenomenon between antipredatory behavior and pairing competition produced by male-male tandem running in the above three Reticulitermes species. Our results indicated that male-male tandem running could effectively protect disadvantaged individuals from being caught, but disadvantaged individuals would be easily eliminated in pairing competition after male-male tandem running, suggesting that male-male tandem running can promote population evolution in termites by repeatedly removing the relatively inferior male individuals.

Costs of pleometrosis in a polygamous termite

Costs and benefits of pleometrosis, as understood from social Hymenoptera, have never been tested in the independently evolved termites. To understand the extent to which such co-founding may be advantageous for colony survival and growth, we tracked the survival and reproduction of 5000 laboratory-established incipient colonies of the facultatively polygamous neotropical termite Nasutitermes corniger. Significantly more pleometrotic groups than monogamous queen-king pairs failed within the first 90 days of establishment, and 99 per cent of pleometrotic groups lost at least one founding member. Oviposition commenced earlier in larger groups, but colony growth was slower and production of workers and soldiers was delayed compared with pairs. Thus, pleometrosis does not increase colony fitness and is in fact highly disadvantageous.

Transcriptome profiling of female alates and egg-laying queens of the Formosan subterranean termite

Termites are known to have an extraordinary reproductive plasticity and capacity, but the underlying genetic patterns of termite reproductive biology are relatively understudied. The goal of this study was to identify genes for which expression levels differ between dealated precopulatory females (virgins) and egg-laying queens of the Formosan subterranean termite, Coptotermes formosanus Shiraki. We constructed a normalized polyphenic expressed sequence tag (EST) library that represents genomic material from most of the castes and life stages of the Formosan subterranean termite. Microarrays were designed using probes from this EST library and public genomic resources. Virgin females and queens were competitively hybridized to these microarrays and differentially expressed candidate genes were identified. Differential expression of eight genes was subsequently confirmed via reverse transcriptase quantitative PCR (RT-QPCR). When compared to virgins, queens had higher expression of genes coding for proteins related to immunity (gram negative binding protein), nutrition (e.g., termite-derived endo-beta-1,4-glucanase), protein storage, regulation of caste differentiation and reproduction (hexamerin, juvenile hormone binding protein). Queens also had higher transcript levels for genes involved in metabolism of xenobiotics, fat, and juvenile hormone (glutathione-S-transferase-like proteins, and cytochrome P450), among others. In particular, hexamerin, juvenile hormone binding protein, and a cytochrome P450 from the 4C subfamily are likely to be involved in initiating the inactive period during the reproductive cycle of the queen. Vice versa, virgins had higher expression than queens of genes related to respiration, probably due to recent flight activity, and several genes of unknown function.

Semiochemical compounds of preen secretion reflect genetic make-up in a seabird species

Several vertebrates choose their mate according to genetic heterozygosity and relatedness, and use odour cues to assess their conspecifics' genetic make-up. In birds, although several species (including the black-legged kittiwake) exhibit non-random mating according to genetic traits, the cues used to assess genetic characteristics remain unknown. The importance of olfaction in birds' social behaviour is gaining attention among researchers, and it has been suggested that, as in other vertebrates, bird body scent may convey information about genetic traits. Here, we combined gas chromatography data and genetic analyses at microsatellite loci to test whether semiochemical messages in preen secretion of kittiwakes carried information about genetic heterozygosity and relatedness. Semiochemical profile was correlated with heterozygosity in males and females, while semiochemical distance was correlated with genetic distance only in male-male dyads. Our study is the first to demonstrate a link between odour and genetics in birds, which sets the stage for the existence of sophisticated odour-based mechanisms of mate choice also in birds.

Colony breeding system influences cuticular bacterial load of Formosan subterranean termite (Isoptera: Rhinotermitidae) workers

The goal of this study was to test whether the breeding system and/or the degree of inbreeding of field colonies of the Formosan subterranean termite, Coptotermes formosanus, Shiraki (Isoptera: Rhinotermitidae) influences bacterial load on the cuticle of foraging workers. We enumerated bacterial load on the cuticle of groups of workers foraging in 20 inground monitoring stations surrounding the French Market in New Orleans, LA, and identified bacteria species using 16S rRNA gene sequencing. We used microsatellite genotyping to assign the 20 worker groups to seven simple family colonies (headed by a single pair of reproductives) and four extended family colonies (headed by multiple inbreeding reproductives) with a wide range of degrees of inbreeding. Workers from extended family colonies had a higher bacterial load than those from simple family colonies; however, bacterial load was not significantly correlated to the degree of inbreeding, possibly because of confounding factors in colony life history, such as age and/or size of colonies. Colonies with high bacterial load did not have a higher proportion of entomopathogens, and thus, bacterial load is not necessarily an indicator for disease risk. The majority of bacteria cultured from the cuticle of termites were soil bacteria with no known pathology against termites.

Comparison of the bacterial symbiont composition of the formosan subterranean termite from its native and introduced range

We investigated the bacterial composition in the gut of Formosan subterranean termites (FST), Coptotermes formosanus Shiraki, collected from southern China (native range) vs. Louisiana, U. S. (introduced range) using 16S rRNA gene sequencing. Overall, we identified 213 bacteria ribotypes from thirteen phyla. The enemy release hypothesis could not be invoked to explain invasion success of FST since no pathogens were found among the bacterial gut community regardless of geographic origin. Invasion of new habitats did not significantly change the bacteria composition. Apparently, the tight co-evolutionary link between termites and their gut flora maintains a certain association of species and functional groups. Ribotype richness, bacteria diversity, and proportions of detected phyla were not influenced by geographic origin of FST samples; however, these parameters were affected by storage of the samples. Ethanol storage of termite samples (5 yrs) increased the relative proportions of gram-positive bacteria versus gram-negative bacteria.

Biology of subterranean termites: insights from molecular studies of Reticulitermes and Coptotermes

Molecular genetic techniques have made contributions to studies on subterranean termites at all levels of biological organization. Most of this work has focused on Reticulitermes and Coptotermes, two ecologically and economically important genera. DNA sequence data have significantly improved our understanding of the systematics and taxonomy of these genera. Techniques of molecular biology have provided important new insights into the process of caste differentiation. Population genetic markers, primarily microsatellites, have furthered our understanding of the life history, population biology, community ecology, and invasion biology of subterranean termites. Recent results on the behavioral ecology of subterranean termites reveal a picture different from long-held views, especially those concerning colony breeding structures and foraging ranges. As additional molecular tools and genomic resources become available, and as more subterranean termite researchers incorporate molecular techniques into their approaches, we can expect accelerating advances in all aspects of the biology of this group.