Claudia Husseneder

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.

Colony and population genetic structure of the Formosan subterranean termite, Coptotermes formosanus, in Japan.

Subterranean termites have unusual plasticity in their breeding systems. As a result of their cryptic foraging and nesting habits, detailed information on the numbers and types of reproductive individuals in colonies has been difficult to obtain. In this study, we used microsatellite markers to infer the major features of the breeding system of the Formosan subterranean termite, Coptotermes formosanus, in southern Japan, where it is believed to have been introduced from China. A total of 30 colonies was sampled from two islands (Kyushu and Fukue) located 100 km apart. Twenty workers from each colony were genotyped at six microsatellite loci. Analysis of worker genotypes within colonies indicated that 27 colonies (90%) were simple (Mendelian) families. The remaining three colonies, all from Kyushu, were consistent with being extended families having begun as simple families but being currently headed by multiple neotenic (secondary) reproductives descended from the original king and queen. Workers from simple families in both populations were significantly inbred (FIT = 0.10 for Kyushu and 0.46 for Fukue) and highly related to their nestmates (coefficient of relatedness, r = 0.59 for Kyushu and 0.77 for Fukue), suggesting that many simple‐family colonies were headed by closely related reproductives, especially in the Fukue population. This conclusion is supported by the high coefficient of relatedness between nestmate reproductives in simple‐family colonies (r = 0.23 for Kyushu and 0.61 for Fukue) based on genotypes inferred from their worker offspring. There was moderate genetic differentiation (FST = 0.12) between the two populations, suggesting rather restricted gene flow between them. There was no significant isolation by distance among colonies, as might be expected given the limited dispersal of reproductives, presumably because of the frequent movement of colonies by humans. Finally, there was no evidence of a recent bottleneck, a finding possibly consistent with the more than 300‐year history of this species in Japan.

Variation between and within colonies in the termite: morphology, genomic DNA, and behaviour

We investigate the structure between and within colonies of Schedorhinotermes lamanianus (Isoptera: Rhinotermitidae) at a cluster of foraging galleries in Shimba Hills National Reserve, Kenya. Three independent methods (morphometrics of minor soldiers, multilocus fingerprinting from genomic DNA of workers, and aggression tests between workers) yielded concordant results concerning number and spatial extent of colonies as well as variation between and within colonies. At least three colonies exist in our study area. Genetic data reveal that the largest colony is genetically and spatially substructured in three subsidiary nests, which may form reproductive units. These subsidiary nests were not completely isolated as we were able to document exchange of workers. Subsidiary nests may facilitate foundation of colonies by budding which may generate isolation by distance (population viscosity).

Elimination and Reinvasion Studies with Coptotermes formosanus (Isoptera: Rhinotermitidae) in Louisiana

Abstract Three Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), colonies located inside the 12.75-ha Louis Armstrong Park, New Orleans, were selected for elimination by using the chitin synthesis inhibitor hexaflumuron. Once eliminated, each vacated foraging territory was monitored for reinvasion by neighboring C. formosanus colonies, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) colonies, or both. Each selected colony was eliminated in ≈3 mo by using baits containing hexaflumuron. Overall activity of each untreated colony in the park remained unchanged during the same period. New C. formosanus and R. flavipes activity was detected in two of the three vacated territories, and in both areas, within days of selected colony elimination. The third vacated territory was completely reoccupied by a new C. formosanus colony ≈7 mo later. Mark–recapture studies and DNA fingerprinting confirmed the distinctness of the reinvaders from eliminated and neighboring colonies.

Evaluation of DNA Fingerprinting, Aggression Tests, and Morphometry as Tools for Colony Delineation of the Formosan Subterranean Termite

Multilocus DNA fingerprinting, aggression tests, and morphometry were compared to evaluate their potential for the delineation of colonies of Coptotermes formosanus Shiraki (Isoptera; Rhinotermitidae) in Hawaii. DNA fingerprinting segregates the termites from all collection sites and allows the assignment of all individuals to their original collection site. The genetic similarity of termites from different collection sites approaches the populations genetic background similarity, consequently collection sites represent independent colonies. Aggression between colonies is comparatively low and does not provide reliable colony delineation. Morphometry allows a 79% classification rate of termites to their colony of origin. No correlation among genetic similarities, aggression levels, and morphometric distances is found. Of the three investigated methods, we conclude that the genetic approach is the most useful tool for colony delineation in C. formosanus.

Within-colony relatedness in a termite species : Genetic roads to eusociality?

Hamiltons theory predicts that relatedness asymmetries, with higher relatedness between alloparents and brood than between parents and brood, favour the evolution of eusociality. The haplodiploid reproductive system of the social Hymenoptera does indeed produce relatedness asymmetries, but the diplodiploid system of the eusocial Isoptera does not automatically do so. Three mechanisms that might favour relatedness asymmetries, and therefore eusociality, in termites have been extensively debated: First, substantial inbreeding generates the background for effective kin-selection. Second, inbreeding-outbreeding cycles within and between colonies cause a higher relatedness between individuals of the same generation than between them and their potential offspring. This would be analogous to the haplodiploid system. Third, translocation complexes of sex-linked chromosomes may generate higher relatedness within sexes than between sexes, again analogous to the haplodiploid system. We tested these three hypotheses for the African termite Schedorhinotermes lamanianus (Isoptera, Rhinotermitidae) using estimates of within-colony relatedness derived by multilocus DNA fingerprinting with a synthetic oligonucleotide probe. We found little support for any of the three hypotheses. We observed inbreeding to occur only during one or a few generations within colonies, which is unlikely to be an operational basis for ongoing kin-selection. Overall, we conclude that ecological factors and constraints must be considered a major selective force.

DIET-MEDIATED INTER-COLONIAL AGGRESSION IN THE FORMOSAN SUBTERRANEAN TERMITE Coptotermes formosanus

In most social insects, intercolonial and interspecific aggression are expressions of territoriality. In termites, cuticular hydrocarbons (CHCs) have been extensively studied for their role in nestmate recognition and aggressive discrimination of nonnest-mates. More recently, molecular genetic techniques have made it possible to determine relatedness between colonies and to investigate the influence of genetics on aggression. In the Formosan subterranean termite, Coptotermes formosanus, however, the role of CHCs and genetic relatedness in inter-colony aggression has been ambiguous, suggesting the involvement of additional factors in nest-mate recognition. In this study we assess the range of aggression in this termite species and characterize the influence of genetic relatedness, CHC profiles and diet on aggression levels. We collected four colonies of C. formosanus, feeding either on bald cypress or birch, from three locations in Louisiana. Inter-colony aggression ranged from low to high. Differences in CHC profiles, as well as genetic distances between colonies determined by using microsatellite DNA markers, showed no significant correlation with aggression. However, termite diet (host tree) played a significant role in determining the level of aggression. Thus, two distantly related colonies, each feeding on different diets, showed high aggression that significantly diminished if they were fed on the same wood in the laboratory (spruce). Using headspace solid phase microextraction, we found three compounds from workers fed on birch that were absent in workers fed on spruce. Such diet-derived chemicals may be involved in the complex determination of nest-mate recognition in C. formosanus.

Genetic Analysis of Colony and Population Structure of Three Introduced Populations of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae) in the Continental United States

Abstract The Formosan subterranean termite, Coptotermes formosanus Shiraki, is a major invasive pest species in many parts of the world. We compared the colony breeding system and population genetic structure in three introduced populations in the continental United States: Charleston, SC; City Park, New Orleans, LA; and Rutherford County, NC. Based on worker genotypes at 12 microsatellite loci, we found that colonies were mainly genetically distinct entities consisting of either simple families headed by monogamous pairs of reproductives or extended families containing multiple neotenic (replacement) reproductives descended from simple families. Populations varied from 48% simple families in Charleston to 82% simple families in City Park. Extended family colonies in all three populations were likely headed by <10 neotenic reproductives. There was no significant isolation by distance in any of the populations, suggesting that colonies reproduce by relatively long-range mating flights and/or human-mediated dispersal within each population. The Charleston population showed evidence of a recent genetic bottleneck and most likely was founded by very few colonies. Cluster analysis indicated that the Charleston and City Park populations are quite genetically distant from each other and most likely originated from different source populations. The more recently introduced Rutherford County population was genetically most similar to City Park. These findings, together with results from other infested sites, indicate considerable variation in the genetic structure and breeding system of introduced populations of this species, making it unlikely that there is a simple genetic or behavioral explanation for the success of C. formosanus as an invasive species.

Kin-biased foraging in a termite

While kin-biased behaviour between nestmates has been well documented for social Hymenoptera, corresponding data for termites are missing. However, kin-biased behaviour in termite colonies may be of considerable evolutionary importance as many termite species are polygynous and polyandrous. Applying multilocus DNA fingerprinting we analysed the genetic structure of the termite Schedorhinotermes lamanianus. Genetic similarities estimated by bandsharing probabilities between workers in the nest centres were significantly lower compared with the similarities between individuals in foraging galleries (0.66 compared with 0.78). This suggests that for polygynous and polyandrous termite colonies, workers departing from the nest to their foraging areas assort according to their kin.

Evaluation of Treatment Success and Patterns of Reinfestation of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract Spread of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), is connected with the transport of infested wood, in particular, railroad ties. Therefore, efficient treatment of infestations, especially along railroads, is imperative to prevent further termite damage and spread. Evaluation of treatment success hinges on the ability to assign infestation sites to colonies and compare colony identity before and after treatment. Because colonies of the Formosan subterranean termite can be headed by a pair of reproductives (simple families) or by multiple reproductives (extended families), the question arises whether the breeding system of a colony influences treatment success and whether treatment of an area might have an impact on the breeding system. We used microsatellite genotyping to compare colony affiliation and breeding systems of Formosan termites infesting the Riverfront Railroad, New Orleans, LA, before and after treatment with 0.5% noviflumuron. Before treatment, four colonies were simple families, and 11 colonies were extended families. A year after treatment began, all treated colonies had vanished and did not reappear during this study. One colony from an untreated monitoring station moved into a nearby station after treatment. Colonies that were detected after treatment consisted of 12 simple families and six extended families; extended families found after treatment contained a higher number of reproductive neotenics than the extended families found before treatment. Extended families were more likely than simple families to move into inground stations that had been previously occupied by termite colonies.