Competition between invasive and indigenous species: an insular case study of subterranean termites

An important requirement for the management of invasive species is to identify the biological and ecological factors that influence the ability of such species to become established and spread within a new environment. Although competition is one of the key interactions determining the coexistence of species and exclusion, few studies directly examine the mechanism of competitive interactions within invasive communities. This study focused on putative competition in a social insect invader, R. flavipes, an American termite introduced into France, and an indigenous European termite, R. grassei. We first characterized and mapped a zone of sympatry between these two species. We then evaluated the degree of direct and indirect competition by comparing several life-history traits: behavioral aggression, chemical recognition and dispersion modes. Interspecific competition revealed that R. flavipes was dominant over R. grassei. Intraspecific competition was not found in R. flavipes while it appeared in varying degrees in R. grassei. These findings seemed to be correlated with the remarkable chemical homogeneity found in R. flavipes in comparison with R. grassei. Genetic analyses revealed that R. flavipes foraged over a greater distance than R. grassei colonies and might suggest a difference in the capacity to produce secondary reproductives. These findings suggest that R. flavipes has a significant advantage owing to competitive asymmetry that may enable the species to become dominant. The interspecific superiority, lack of intraspecific aggression and large extensive colonies, seem to be some of the reasons for its invasive success.     

Clinal variation in colony breeding structure and level of inbreeding in the subterranean termites Reticulitermes flavipes and R. grassei

Social insects exhibit remarkable variation in their colony breeding structures, both within and among species. Ecological factors are believed to be important in shaping reproductive traits of social insect colonies, yet there is little information linking specific environmental variables with differences in breeding structure. Subterranean termites (Rhinotermitidae) show exceptional variation in colony breeding structure, differing in the number of reproductives and degree of inbreeding; colonies can be simple families headed by a single pair of monogamous reproductives (king and queen) or they can be extended families headed by multiple inbreeding neotenic reproductives (wingless individuals). Using microsatellite markers, we characterized colony breeding structure and levels of inbreeding in populations over large parts of the range of the subterranean termites Reticulitermes flavipes in the USA and R. grassei in Europe. Combining these new data with previous results on populations of both species, we found that latitude had a strong effect on the proportion of extended‐family colonies in R. flavipes and on levels of inbreeding in both species. We examined the effect of several environmental variables that vary latitudinally; while the degree of inbreeding was greatest in cool, moist habitats in both species, seasonality affected the species differently. Inbreeding in R. flavipes was most strongly associated with climatic variables (mean annual temperature and seasonality), whereas nonclimatic variables, including the availability of wood substrate and soil composition, were important predictors of inbreeding in R. grassei. These results are the first showing that termite breeding structure is shaped by local environmental factors and that species can vary in their responses to these factors.     

Behavioral Interactions Between <Emphasis Type="Italic">Aphaenogaster rudis</Emphasis> (Hymenoptera: Formicidae) and <Emphasis Type="Italic">Reticulitermes flavipes</Emphasis> (Isoptera: Rhinotermitidae): The Importance of Physical Barriers

Predation pressure from ants is a major driving force in the adaptive evolution of termite defense strategies and termites have evolved elaborate chemical and physical defenses to protect themselves against ants. We examined predator–prey interactions between the woodland ant, Aphaenogaster rudis (Emery) and the eastern subterranean termite, Reticulitermes flavipes (Kollar), two sympatric species widely distributed throughout deciduous forests in eastern North America. To examine the behavioral interactions between A. rudis and R. flavipes we used a series of laboratory behavioral assays and predation experiments where A. rudis and R. flavipes could interact individually or in groups. One-on-one aggression tests revealed that R. flavipes are vulnerable to predation by A. rudis when individual termite workers or soldiers are exposed to ant attacks in open dishes and 100% of termite workers and soldiers died, even though the soldiers were significantly more aggressive towards the ants. The results of predation experiments where larger ant and termite colony fragments interacted provide experimental evidence for the importance of physical barriers for termite colony defense. In experiments where the termites nested within artificial nests (sand-filled containers), A. rudis was aggressive at invading termite nests and inflicted 100% mortality on the termites. In contrast, termite mortality was comparable to controls when termite colonies nested in natural nests comprised of wood blocks. Our results highlight the importance of physical barriers in termite colony defense and suggest that under natural field conditions termites may be less susceptible to attacks by ants when they nest in solid wood, which may offer more structural protection than sand alone.     

High occurrence of colony fusion in a European population of the American termite Reticulitermes flavipes

The coexistence of multiple unrelated reproductives within social insect colonies decreases the relatedness among colony members and therefore challenges kin selection theory. This study investigated the colony genetic structure of a French introduced population of the American subterranean termite Reticulitermes flavipes by analyzing genotypes at eight microsatellite loci and at one mtDNA region. Results revealed that all colonies contained numerous related secondary reproductives, and that 31% of colonies possessed more than two unrelated reproductives. The presence of several unrelated reproductives within colonies of this species is commonly assumed to result from colony fusion. Although such a high occurrence of colony fusion is the highest ever observed in a termite population, it is probable that the available methodology underestimated the detection of colony fusion in French populations. Overall, these results suggest that French colonies might differ strongly from the great majority of American colonies in their capacity to produce secondary reproductives as well as in their ability to merge. The nature and evolutionary origin of these population differences are discussed.     

Protein marking reveals predation on termites by the woodland ant, <Emphasis Type="Italic">Aphaenogaster rudis</Emphasis>

Subterranean termites provide a major potential food source for forest-dwelling ants, yet the interactions between ants and termites are seldom investigated largely due to the cryptic nature of both the predator and the prey. We used protein marking (rabbit immunoglobin protein, IgG) and double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) to examine the trophic interactions between the woodland ant, Aphaenogaster rudis (Emery) and the eastern subterranean termite, Reticulitermes flavipes (Kollar). We marked the prey by feeding the termites paper treated with a solution of rabbit immunoglobin protein (IgG). Subsequently, we offered live, IgG-fed termites to ant colonies and monitored the intracolony distribution of IgG-marked prey. Laboratory experiments on the distribution of protein-marked termite prey in colonies of A. rudis revealed that all castes and developmental stages receive termite prey within 24 h. In field experiments, live, protein-marked termites were offered to foraging ants. Following predation, the marker was recovered from the ants, demonstrating that A. rudis preys on R. flavipes under field conditions. Our results provide a unique picture of the trophic-level interactions between predatory ants and subterranean termites. Furthermore, we show that protein markers are highly suitable to track trophic interactions between predators and prey, especially when observing elusive animals with cryptic food-web ecology. Received 19 January 2007; revised 23 March 2007; accepted 26 March 2007.     

Diversity of Gut Bacteria of <Emphasis Type="Italic">Reticulitermes flavipes</Emphasis> as Examined by 16S rRNA Gene Sequencing and Amplified rDNA Restriction Analysis

The phylogenetic species richness of the bacteria in the gut of the termite Reticulitermes flavipes was examined using near full-length 16S rRNA gene sequencing and amplified rDNA restriction analysis (ARDRA). We amplified the genes by polymerase chain reaction (PCR) directly from a mixed population of termite gut bacteria and isolated them using cloning techniques. Sequence analysis of 42 clones identified a broad taxonomic range of ribotypes from six phyla within the domain Bacteria: Proteobacteria, Spirochaetes, Bacteroidetes, Firmicutes, Actinobacteria, and the recently proposed “Endomicrobia.” Analysis of the sequence data suggested the presence of a termite specific bacterial lineage within Bacteroidetes. The ARDRA data included 261 different ARDRA profiles of 512 clones analyzed. These data suggest the gut flora in R. flavipes is extremely diverse.     

Potential spread of the invasive North American termite, <Emphasis Type="Italic">Reticulitermes flavipes</Emphasis>, and the impact of climate warming

Reticulitermes flavipes is an invasive termite from North America that is found in several European countries, including France from north to south. It feeds on several timber species and can cause major damage when it infests lumber. Termites are urban pests: they are often found in and around towns and their expansion is closely linked to human activity. Although, by law, termite infestations must be reported and treated, R. flavipes continues to spread. To better identify areas that may soon be colonized, it is crucial to understand the mechanisms underlying the termite’s spread at a fine spatial scale. However, the complexity of the species’ dispersal dynamics (i.e., via swarming, budding, or human-mediated transport of infested material) and social organization render this process difficult. The goal of our study was to determine R. flavipes’ potential to expand its current range within a region of France: Centre-Val de Loire. We focused on one administrative department within the region—Indre and Loire—where infestations are common and data on termite presence date back to the 1980s. We developed a spatiotemporal model to study the growth and dispersal of termite colonies within favorable habitat. Habitat favorability was defined based on the density of urbanization and annual mean minimum temperature. First, we modeled temporal population dynamics, using biological parameters describing the transitions between life stages/castes within colonies; we could thus estimate alates production. Then, using this information, we modeled termite dispersal within favorable habitat, and determined the termite’s potential spread. We validated the results by comparing the model’s output with actual data on the termite’s range expansion between 1985 (when the termite was first observed in the region) and 2013. Finally, the model was used to predict the termite’s future spread given climate warming for the period from 2013 to 2030. The results show that an increase in temperature should increase the amount of favorable habitat and, as a consequence, termites could continue to spread within this region. In addition to continuing current control efforts, it will be necessary to enact preventative strategies in newly favorable habitat. In these areas, monitoring efforts should therefore be intensified, as they might be able to slow down the termite’s spread and limit its impact.     

Geographical distribution,genetic diversity and social organization of a new European termite, <Emphasis Type="Italic">Reticulitermes urbis</Emphasis> (Isoptera: Rhinotermitidae)

Reticulitermes urbis is a recently described termite species that has probably been introduced into Western Europe where it has been found exclusively in urban areas. However, little is known about the geographic distribution and origin of R. urbis. This study was undertaken to determine whether this species was introduced from the Balkans. A parsimony network did not show any association between mtDNA haplotypes and geographic regions suggesting that western European populations were the result of human-mediated dispersion. Variation patterns of the COI and COII regions as well as microsatellites showed that the genetic diversity of Western European colonies was lower than for colonies collected in the Balkans, suggesting that the introduced populations suffered from a founder effect. As observed in the introduced populations of R. flavipes, all colonies of R. urbis had an extended-family structure with several reproductives. These results support the scenario that this termite was introduced into Western Europe.     

Polymorphic microsatellite loci in the European subterranean termite,Reticulitermes santonensis Feytaud

We report on the identification and characterization of two dinucleotide, two trinucleotide and eight tetranucleotide microsatellite DNA loci isolated from the European subterranean termite Reticulitermes santonensis. We tested the loci on 51–92 individuals from 46 colonies from different regions of France. Eleven loci were polymorphic with 2–8 alleles per locus and low observed heterozygosities (0.10–0.48). We also tested the loci on 17–20 individuals from 10 colonies in the closely related North American species R. flavipes and found significantly more alleles (2–9 alleles per locus) and higher observed heterozygosities (0.15–0.80) than in R. santonensis. The lower observed heterozygosities in R. santonensis are consistent with higher levels of inbreeding in these colonies due to the presence of numerous inbred replacement reproductives.     

Sexual and asexual colony foundation and the mechanism of facultative parthenogenesis in the termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera,Rhinotermitidae)

Summary. Facultative parthenogenesis has great adaptive significance, especially with regard to low pairing efficiency. In the termite Reticulitermes speratus, females that fail to mate with males reproduce parthenogenetically and found colonies cooperatively with partner females or even alone. Comparison of colony foundation success at 400 days between colonies founded by single females (F), female-female pairs (FF), and male-female pairs (FM) showed that female-female cooperation promoted colony survivorship over monogamous foundation. We report here for the first time the mode of parthenogenesis in Isoptera. Combining chromosome observations and genetic analysis using microsatellites, we show that the mode of parthenogenesis is diploid thelytoky and that the restoration of ploidy is most likely accomplished by terminal fusion. Parthenogens show a higher mortality and a longer egg-development time than sexually produced offspring, probably due to reduced heterozygosity. In addition Wolbachia bacteria were detected in R. speratus. However, since Wolbachia was also detected in non-parthenogenetic R. flavipes, it is unlikely that Wolbachia is the cause of parthenogenesis in R. speratus.Received 30 October 2003; revised 4 March 2004; accepted 17 March 2004.     

Population genetic structure and colony breeding system in dampwood termites (<Emphasis Type="Italic">Zootermopsis angusticollis</Emphasis> and <Emphasis Type="Italic">Z. nevadensis nuttingi</Emphasis>)

Studies describing the population genetic structure and breeding system of basal lineages of termite species remain rare. Such species, however, may reveal ancestral life history attributes potentially influential in the evolution of social life within the Isoptera. Through the development and application of microsatellite DNA loci, we investigated patterns of genetic diversity and differentiation within the dampwood termite Zootermopsis angusticollis collected from three geographically distinct locations in California, USA. Significant genetic differentiation was identified among all sites, which were located 40–150 km apart, and each site was found to represent unique populations with limited levels of gene flow. While Z. angusticollis alates have previously been described as being strong fliers, genetic evidence suggests limited dispersal, possibly due to habitat characteristics restricting long-range flights. Additionally, we characterize patterns of colony genetic structure and breeding system within both Z. angusticollis and its congener Z. nevadensis nuttingi. In Z. angusticollis, simple, extended, and mixed family colonies were observed. The frequency of simple families ranged from 16 to 64%, whereas mixed families were found in only two locations and at low frequencies. In contrast, Z. n. nuttingi, formed primarily extended family colonies. Estimates of relatedness suggest that monogamous pairs heading simple families consist of reproductives showing variable degrees of relatedness from unrelated to close relatives. Additionally, the effective number of neotenic reproductives appears to be low within extended families of both species.     

Mutualistic acacia ants exhibit reduced aggression and more frequent off‐tree movements near termite mounds

In many ant–plant mutualisms, ants establish colonies in hollow thorns, leaf pouches, or other specialized structures on their host plants, which they then defend from herbivores. Resource heterogeneity could affect the maintenance of these mutualisms if it leads to one or both partners altering their investment in the interaction. Such a phenomenon may be especially pertinent to the Acacia–ant mutualism found in East African savannas, where termite mounds have a profound effect on the spatial structuring of resources used by both plants and ants. Here, we examined whether the proximity to termite mounds of Acacia drepanolobium trees is associated with variation in the behavior of one of their ant associates, Crematogaster nigriceps. We found that ant colonies near termite mounds had decreased aggressive responses to simulated herbivory as well as increased off‐tree movement. We hypothesize that these changes are the result of resident ant colonies near termite mounds shifting investment from defense of their host plant to foraging for nearby resources.     

The hindgut lumen prokaryotic microbiota of the termite Reticulitermes flavipes and its responses to dietary lignocellulose composition

Reticulitermes flavipes (Isoptera: Rhinotermitidae) is a highly eusocial insect that thrives on recalcitrant lignocellulosic diets through nutritional symbioses with gut‐dwelling prokaryotes and eukaryotes. In the R. flavipes hindgut, there are up to 12 eukaryotic protozoan symbionts; the number of prokaryotic symbionts has been estimated in the hundreds. Despite its biological relevance, this diverse community, to date, has been investigated only by culture‐ and cloning‐dependent methods. Moreover, it is unclear how termite gut microbiomes respond to diet changes and what roles they play in lignocellulose digestion. This study utilized high‐throughput 454 pyrosequencing of 16S V5‐V6 amplicons to sample the hindgut lumen prokaryotic microbiota of R. flavipes and to examine compositional changes in response to lignin‐rich and lignin‐poor cellulose diets after a 7‐day feeding period. Of the ~475 000 high‐quality reads that were obtained, 99.9% were annotated as bacteria and 0.11% as archaea. Major bacterial phyla included Spirochaetes (24.9%), Elusimicrobia (19.8%), Firmicutes (17.8%), Bacteroidetes (14.1%), Proteobacteria (11.4%), Fibrobacteres (5.8%), Verrucomicrobia (2.0%), Actinobacteria (1.4%) and Tenericutes (1.3%). The R. flavipes hindgut lumen prokaryotic microbiota was found to contain over 4761 species‐level phylotypes. However, diet‐dependent shifts were not statistically significant or uniform across colonies, suggesting significant environmental and/or host genetic impacts on colony‐level microbiome composition. These results provide insights into termite gut microbiome diversity and suggest that (i) the prokaryotic gut microbiota is much more complex than previously estimated, and (ii) environment, founding reproductive pair effects and/or host genetics influence microbiome composition.     

Attraction and vibration: Effects of previous exposure and type of food resource in the perception of allocolonial odors in termites

Social insects have an efficient recognition system that guarantees social cohesion and protection against intruders in their colonies and territories. However, the energy costs in constant conflicts with neighboring colonies could promote a reduction in the fitness of colonies. Here, we evaluated the effect of previous exposure to allocolonial odor and the consumption of similar food resources on aggressive behavior and choice of allocolonial cues in Nasutitermes aff. coxipoensis (Termitidae: Nasutitermitinae). Our results showed that intercolonial aggressiveness was not affected by previous exposure to allocolonial odor and by the consumption of similar food resources. However, individuals previously exposed to allocolonial odor were more attracted to these odors than individuals who had no prior exposure to allocolonial odor. In addition, individuals from colonies of N. aff. coxipoensis that use similar food resources increased alertness via a greater number of vibration than individuals who consumed different food resources. In general, our results indicate that colonies of N. aff coxipoensis perceive allocolonial cues that have been previously exposed and that the consumption of similar resources triggers an alert signal between individuals. Additional studies are necessary to assess how widespread this capacity of perception is present among the different Isoptera groups and the consequences of colony recognition odor cues on termite space use.     

Defense of termitaria by termitophilous ants

Summary Mounds of Amitermes laurensis are frequently faided by meat ants Iridomyrmex sanguineus. Of eight ant species which often cohabit with the termites, Camponotus sp. B and C were considerably dependent on the termintaria for their nest sites and effectively protected it from the attacks by meat ants. Many termite colonies cohabiting with those two ant species were vigorous, suggesting that this ant-termite relationship is mutualistic; thus, the ants were provided nest sites and probably even food and the termites were protected from destructive natural enemies.     

Testing the role of cuticular hydrocarbons on intercolonial agonism in two subterranean termite species (Coptotermes) and their hybrids

Recognition of nestmates is an important function in many social insects, as it maintains colony integrity by preventing outsiders from entering the colony. Agonism usually results from the interaction of con-specific non-nestmate individuals in termite colonies. Previous studies hypothesized that the cuticular hydrocarbon (CHC) profile of individuals had a role in nestmate recognition. However, contradictory results from previous studies in some subterranean termites raise questions on the validity of the cuticular hydrocarbon hypothesis. In the current study, Coptotermes gestroi (Wasmann), Coptotermes formosanus Shiraki and their hybrids were reared in identical conditions from colony foundation. This approach eliminates sources of variability in their cuticular hydrocarbon profiles aside from a genetic component. The parental species displayed dissimilar profiles of predominant alkanes and methyl alkanes, but both hybrid types displayed an overlapping, intermediate profile of these CHC. The mixture of the most abundant CHCs alone did not determine kin recognition; while the two hybrid types’ CHC profiles converged, the hybrids still showed strong agonism. One of the hybrid mating types easily merged with C. formosanus, despite only partial genetic similarity and dissimilar cuticular profiles for the common alkanes and methyl alkanes. This study suggests that in Coptotermes termites, the variable abundance of the major alkanes and methyl alkanes commonly found in most Coptotermes species does not explain agonistic patterns, and that other factors such as possibly more complex but less abundant CHC are likely to be involved in colonial recognition.

     

Behavioral Response of Two Subterranean Termites (Isoptera: Rhinotermitidae) to Vibrational Stimuli

Behavioral responses to vibrational stimuli were examined in two subterranean termite species, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar). Termites habituated to vibrational stimulation when in social groups, but failed to do so individually, indicating that habituation is a collective action. In assays on termite groups, both species demonstrated a similar pattern of behavioral responses to vibrational stimuli: evanescent cessation of activity and movement, followed by withdrawal from the vibration source. Groups of both species then gradually moved back toward the vibration source as a consequence of continuous exposure. However, it took a significantly shorter period for C. formosanus to return (57 s) to the test arena and to resume (80 s) normal foraging activities in the test arena compared with R. flavipes, which took 97 and 227 s, respectively, when exposed to the vibration frequency of 120 bmpm. High vibration frequency (240 bmpm) increased the time required to return (C. formosanus, 80 s; R. flavipes, 153 s) and to resume regular locomotion (C. formosanus, 186 s; R. flavipes, 263 s). Our experiments demonstrate that workers play a crucial part in adjusting groups of termites to distressful vibrations. Soldiers of R. flavipes demonstrated similar behavioral responses as workers, however, C. formosanus soldiers exhibited a transient positive response before withdrawal. An erratum to this article is available at .     

The influence of branching tunnels on subterranean termites' foraging efficiency: Considerations for simulations

In our previous study, we constructed a lattice model of termite tunnel pattern to explore the relationship between tunnel geometry and foraging efficiency. The model was based on experimental data obtained from homogeneous soil substrates without food resource. In the present study, we adopted a more general rule in the model to determine branching tunnel lengths. The rule was described by two variables, the probability of tunnel branching, P_branch, and the probability for a branching tunnel to terminate, P_term. With the modified model, we explored the influence of the geometry of branching tunnel on foraging efficiency, γ, for two termite species, Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae). For C. formosanus, γ map consisting of the two variables were partitioned in three regions by the level of γ value, while γ for R. flavipes was categorized as two regions: higher γ and lower γ. This result was discussed in termite foraging strategy.     

Characterization of four esterase genes and esterase activity from the gut of the termite Reticulitermes flavipes

Four esterase genes and general esterase activity were investigated in the gut of the termite Reticulitermes flavipes. Two genes (RfEst1 and RfEst2) share significant translated identity with a number of insect JH esterases. The two remaining genes (RfEst3 and RfEst4) apparently code for much shorter proteins with similarity to fungal phenolic acid esterases involved in hemicellulose solubilization. All four genes showed consistently high midgut expression. This result was further supported by colorimetric activity assays and Native polyacrylamide gel electrophoresis, which showed significant esterase activity and a number of isoforms in the midgut. The greatest esterase activity and isoform composition were detected when α‐naphthyl propionate was used as a substrate. Moreover, esterase activity and diverse isoforms were present in gut mitochondrial, microsomal, and cytosolic sub‐cellular protein fractions, as well as in the hindgut lumen. These findings reveal an agreement between gut esterase gene expression and activity distributions, and support the idea that R. flavipes gut esterase activity is host (not symbiont)‐derived. In addition, these findings support the hypotheses that termite gut esterases may play important roles in lignocellulose digestion and caste differentiation. This study provides important baseline data that will assist ongoing functional‐genomic efforts to identify novel genes with roles in semiochemical, hormone, and lignocellulose processing in the termite gut. © 2009 Wiley Periodicals, Inc.