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.     

Extreme genetic mixing within colonies of the wood-dwelling termite Kalotermes flavicollis (Isoptera,Kalotermitidae)

The existence of altruism in social insects is commonly attributed to altruistic individuals gaining indirect fitness through kin selection. However, recent studies suggest that such individuals might also gain direct fitness through reproduction. Experimental studies on primitive wood-dwelling termites revealed that colony fusion often causes the death of primary reproductives (queen and king), allowing opportunities for workers to inherit the nest by developing into replacement reproductives (neotenics). Therefore, colony fusion has been proposed as an important factor that may have favoured sociality in termites. However, whether colony fusion occurs frequently in natural populations of wood-dwelling termites remains an open question. We analysed eleven colonies of the wood-dwelling termite Kalotermes flavicollis (Kalotermitidae), using two mitochondrial and five nuclear microsatellite markers. Nine of eleven colonies (82%) were mixed families, with offspring of three or more primary reproductives. To our knowledge, this result represents the highest frequency of mixed-family colonies ever reported in termites. Moreover, genetic mixing of colonies appeared extreme in two ways. First, the number of haplotypes per colony was exceptionally high (up to nine), indicating that colonies were composed of multiple queens' offspring. Second, some mixed-family colonies included individuals belonging to two highly divergent genetic lineages. F-statistics and relatedness values suggest that mixed-family colonies most likely result from colony fusion, giving support to the accelerated nest inheritance theory. These findings raise important questions about the mode of foundation of mixed-family colonies and the evolutionary forces that maintain them within populations.     

Breeding systems and reproductive strategies in Italian Reticulitermes colonies (Isoptera: Rhinotermitidae)

Biological traits and colony structure are difficult to analyze in subterranean termites owing to their cryptic lifestyle and their often elusive breeding system. However, the use of molecular markers in a population genetics framework allows the investigation of such aspects. We present here the colony genetic structures of 12 samples collected along the Italian peninsula of two Reticulitermes species (the native R. lucifugus and the introduced R. urbis) analyzed through nuclear microsatellite markers. Reproductive strategies and colony breeding systems differ between the two species. Secondary reproductives of R. lucifugus, collected in three colonies, are all females; genotyping comparisons between these females and their nest mate workers clearly indicate the presence of asexual queen succession (AQS) events in this species, as observed in the Japanese R. speratus and in the North-American R. virginicus. Two other R. lucifugus colonies have a mixed family genetic pattern, possibly as the result of colony fusion events: accordingly, relatedness estimates indicate the presence of genetically unrelated workers. On the contrary, all R. urbis colonies have a genetic structure compatible with the presence of multiple secondary reproductives, as expected on the basis of previous analyses. Moreover, neotenics’ sex ratio is balanced and their heterozygosity is comparable to that of nest mate workers, suggesting that AQS is lacking in this taxon. The differences observed in such biological traits between the two species are discussed in the light of their invasive potential.     

Sociogenetic organization of the ants Myrmica ruginodis and Myrmica lobicornis: Number,relatedness and longevity of reproducing individuals

The number and relationships of reproducing individuals create the observed genetic heterogeneity within a social insect colony. These are referred to as sociogenetic organization and were studied in the red ants M. ruginodis and M. lobicornis. Direct observations of the queen numbers were obtained by excavating colonies. The effective number of reproducing individuals was estimated from genetic relatedness based on genotype frequency data. Sociogenetic organization of colonies of both species is simple. The number of queens is low, single mating of queens is the rule and queen to queen variation in worker production is minor. The important variables of sociogenetic organization are the number and relatedness of coexisting queens in polygynous colonies. Queen nestmates are related on average by 0.405 in polygynous colonies of M. ruginodis, showing that colonies recruit their own daughters as new reproductives. The distribution of queen number in M. ruginodis indicates that the study population contains both microgyna and macrogyna types of the species. The large proportion of colonies where the resident queen(s) is not the mother of the workers shows that the average life span of a queen is short and colonies are serially polygynous.     

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.     

Turnover in termite colonies: a genetic study of colonies ofIncisitermers schwarzi headed by replacement reproductives

Summary Analysis of allozyme markers was carried out on 16 colonies of the termiteIncisitermes schwarzi in which one or both primary (founding) reproductives had been replaced by secondary reproductives. About one-quarter of field-collected colonies have replacement reproductives, and the genetic data suggest that in most of these a single replacement event had occurred. Genetic evidence for a second replacement event was found in one colony. Genetic analysis of the offspring allowed the following conclusions: (1) Soldiers are a relatively long-lived caste, so that even in colonies in which all other members have been replaced by offspring of the secondary reproductives, the soldiers remain the offspring of the primary reproductives; and (2) when primary reproductives are replaced by secondary reproductives, the nosoldier offspring of the former are completely replaced by those of the latter over a period of about two or three years, probably as a result of the normal maturation of colony members (workers, nymphs, and alates). The results provide no evidence for the existence of a true sterile worker caste in this species.     

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.     

Population structure and colony composition of two Zootermopsis nevadensis subspecies

Understanding the origin and maintenance of eusociality in termites has proved problematic, in part, due to a lack of knowledge concerning the variability and evolutionary changes in termite breeding structure. One way to address this is to compare the population genetics of a broad range of termite species. However, few studies have investigated the population genetics of basal termite taxa. We used 12 polymorphic microsatellite loci to characterize and compare the colony genetic structure of 18 colonies of two basal termite subspecies, Zootermopsis nevadensis nevadensis and Zootermopsis nevadensis nuttingi. The average relatedness (r) among individuals within a colony was high (0.59) and similar to values reported for other termite species. Average relatedness between colony founders was lower (0.21) suggesting the alates outbreed. Genotypes of workers and soldiers in 4 out of the 18 colonies were consistent with reproduction by a single pair of primary reproductives and the remaining colonies were inferred to have been derived from more than two reproductives. Eleven colonies with three or more reproductives were consistent with replacement reproductives (neotenics) and the remaining three colonies included genetic contribution from three or more primary reproductives. Comparisons between the subspecies revealed significant differences in breeding structure, specifically in the number and types of reproductives (that is, primaries or neotenics). Furthermore, we observed a larger proportion of colonies with greater than three primary reproductives compared to more derived termite lineages. Thus, our results suggest that breeding structure can vary significantly among termite taxa.     

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.     

Mating frequency and genetic relatedness of workers in the hornet Vespa analis (Hymenoptera: Vespidae)

Mating frequency of Vespa analis queens and the genetic relatedness of their workers was analyzed by DNA microsatellite genotyping. Of 20 colonies studied, 18 had a queen inseminated by a single male and two had queens each inseminated by two males. The estimated effective number of matings was 1.05 ± 0.037 (mean ± SE), with 75–85% of the offspring of the two multiply mated queens sired by a single male. The pedigree relatedness between nestmate workers averaged over the 20 colonies was estimated to be 0.74 ± 0.008, almost identical to the predicted value of 0.75 for colonies headed by a singly mated queen. Multiple matrilines; that is, the presence of workers not related to the current queens, were detected in six colonies, suggesting that queen replacement occurred via usurpation of the founding queens in these six colonies. These results demonstrate that the kin structure of V. analis is similar to that reported in other vespid species.     

Absence of Nepotism in Genetically Heterogeneous Colonies of a Clonal Ant

Insect societies are normally closed entities from which alien individuals are excluded. The occasional fusion of unrelated colonies of the thelytokous ant Platythyrea punctata is therefore puzzling, because it strongly intensifies competition among nestmates for the replacement of an old reproductive. Most colonies of P. punctata have only one or few reproductives, which produce female offspring from unfertilized eggs, and therefore have a clonal structure. Fusion leads to multi‐clone colonies. We compared the occurrence of dominance and policing behavior between single‐ and double‐clone colonies. We find that the frequency of aggression is higher in double‐clone colonies, but that individuals do not preferentially direct attacks toward non‐clonemates. This matches observations in other species that social insects perceive genetic homogeneity but are not capable of reliable discrimination among nestmates of different degree of relatedness.     

Comparative study of incipient colony development in the Formosan subterranean termite, <Emphasis Type="Italic">Coptotermes formosanus</Emphasis> Shiraki (Isoptera,Rhinotermitidae)

Summary The Formosan subterranean termite, Coptotermes formosanus Shiraki is the most destructive, difficult to control and economically important species of termite in the southern United States. At present, no information is available on the genetic relatedness of primary Formosan subterranean termite reproductives that establish new colonies. Information on survivorship and fitness components of primary reproductives from different sibships (sibling or nonsibling) is helpful to our understanding of biological and ecological characteristics of different breeding generations in C. formosanus. The present study examined the effects of sibship and colony origin on growth and mortality of incipient colonies of C. formosanus. Seven stock colonies of C. formosanus were collected in 1996 through 1997 in New Orleans and Lake Charles, La, USA. A total of 338 incipient colonies of sibling pairs or nonsibling pairs of C. formosanus were set up. The study indicated that mate relatedness significantly affected mortality and fitness. Nonsibling mates suffered significantly higher mortality than sibling mates originated from New Orleans. However, the decreased success of outbred mates was offset by an increased fecundity compared to inbred colonies over time. Both sibling- and nonsibling-founded colonies from Lake Charles had a significantly higher survival rate than did colonies from New Orleans. Colonies from Lake Charles also produced a significantly higher number of larvae/workers than colonies from New Orleans. The mismatch of habits by mates from different locations and the potential for greater disease risks may be associated with higher mortality in outbred pairs. However, heterozygous offspring of outbred pairs probably have increased genetic variation, which provides greater adaptation potential, thus making the colony more robust in the face of environmental fluctuations.Received 11 March 2002; revised 26 February 2003; accepted 14 March 2003.     

Lack of kin discrimination in the eusocial aphid pseudoregmabambucicola (Homoptera: Aphididae)

The significance of kin discrimination for the evolution of sociality is theoretically important. The behavioural response ofPseudoregma bambucicola soldiers to aphids from other colonies was studied to examine the possibility of context-specific kin discrimination. When non-kin aphids were artificially introduced into experimental colonies, they were never killed or removed by soldiers. Field experiments revealed that the soldiers frequently attacked distantly related species such asAstegopteryx bambucifoliae andCeratoglyphina styracicola, but rarely conspecific aphids or congeneric species such asP. koshunensis andP. alexanderi. Another experiment showed that the soldiers showed altruistic defence even when coexisting with non-kin reproductives. These results agree with and extend the results from previous studies of kin discrimination in social aphids. The absence of kin discrimination suggests that some other factors besides higher genetic relatedness may play a prominent role in the evolutionary maintenance of soldier behaviour in aphids.     

Impact of orphaning on field colonies of Southeast Asian Macrotermes gilvus (Hagen) and M. carbonarius (Hagen) (Termitidae, Macrotermitinae)

Field colonies of Macrotermes gilvus (Hagen) and M. carbonarius (Hagen) were experimentally orphaned to examine their potential for producing replacement reproductives. Orphaned colonies were investigated only once for caste composition at selected time intervals at 3, 6, 9 or 12 months after orphaning. Of the 38 orphaned colonies of M. gilvus, 15 colonies (39.5%) re-established. In M. carbonarius, three colonies out of 20 (15%) re-established. Re-established colonies were headed by adultoids which were morphologically indistinguishable from primary reproductives. In naturally orphaned colonies of M. gilvus, we often found multiple adultoids with normal pigmentation but torn wings, i.e. the colonies retained alates as replacement reproductives. The number of reproductives probably declines over time. It may take alates of M. gilvus 6 months to develop into functional adultoids, and up to 12 months for alates of M. carbonarius. Our results also demonstrate that the presence of sexual castes (nymphs or alates) at the time of orphaning does not necessarily guarantee the success of colonies in re-establishing themselves as breeding colonies. We also found a high prevalence of occupation of the mounds by other termite species, after the death of M. gilvus (18.4%) or M. carbonarius (30.0%) colonies, probably using them as foraging sites.     

Does lack of intraspecific aggression or absence of nymphs determine acceptance of foreign reproductives in <Emphasis Type="Italic">Macrotermes</Emphasis>?

The rejection or acceptance of a foreign reproductive by an alien colony may not always be as straightforward as cue recognition between worker termites. This paper aims to determine whether adoption of foreign reproductives is caused simply by lack of intraspecific aggression or is contingent on the reproductive status of the host colony. In the fungus-culturing termites, Macrotermes gilvus (Hagen) and Macrotermes carbonarius (Hagen), major workers showed low intraspecific aggression towards non-nestmates irrespective of geographic distance between source colonies. Our results indicated that workers were hardly aggressive towards non-nestmates. In royal cell-swapping experiments, both species responded in a similar way: (1) in host colonies with nymphs present, the foreign reproductives were rejected; while (2) in host colonies without nymphs the foreign reproductives were either accepted and breeding resumed or the host colonies died eventually. Workers from the host colonies preferentially maintained offspring nymphs from which adultoid replacement reproductives develop rather than accepting foreign reproductives. There is no fitness gain for the queenless workers in accepting foreign reproductives; however, there is overall benefit to the newly born population.     

Phylogeny and revision of the ‘Cubitermes complex’ termites (Termitidae: Cubitermitinae)

The phylogeny of the genus Cubitermes Wasmann was reconstructed using two mitochondrial genes (COI and COII) and a fragment of the nuclear 28S rDNA, including samples of Apilitermes Holmgren, Crenetermes Silvestri, Megagnathotermes Silvestri and Thoracotermes Wasmann. Based on our analyses, we recovered these genera within a paraphyletic Cubitermes clade. Cubitermes species are distributed between five main clades, highly reflective of their enteric valve armatures (EVAs). Consequently, Cubitermes is here divided into five monophyletic genera based on phylogenetic analyses and EVAs: Cubitermes (sensu stricto), Isognathotermes Sjöstedt, Nitiditermes Emerson, Polyspathotermes Josens & Deligne, gen.n. , and Ternicubitermes Josens & Deligne, gen.n. Moreover, the two species of Megagnathotermes included in this study, exhibiting different EVAs, are phylogenetically distant: M. katangensis Sjöstedt belongs in the genus Polyspathotermes, while M. notandus Silvestri remains as a monotypic genus. During the evolution of the Cubitermes complex, sclerotized EVA spatulae appeared twice independently: three or six spatulae in Polyspathotermes (sulcifrons and oblectatus patterns) and two jaw‐like spatulae in Nitiditermes (sankurensis pattern), which is absent in some species (oculatus pattern). Zoobank registration: http://zoobank.org/urn:lsid:zoobank.org:pub:576AAFF8‐63C6‐4962‐A8F5‐75C9317AEA7B .     

The origins and relatedness of multiple reproductives in colonies of the termite Nasutitermes corniger

Colonies of the termite Nasutitermes corniger often contain multiple reproductive queens and kings. We used double-strand conformation polymorphism (DSCP) analysis of mitochondrial DNA (mtDNA) to determine the probable origins of co-occurring reproductives. Colonies differed in queen and king number, in the number of nests containing reproductives, and in the genetic relationships among reproductives. Most of the 44 colonies contained a single pair of maternally unrelated reproductives. In the two single-nest colonies with a pair of queens, the two queens differed in mtDNA haplotype, suggesting nest-founding by unrelated queens. In the seven single-nest colonies with larger numbers of reproductives (11–49), all reproductives shared the same haplotype, a pattern consistent with replacement of a single pair by several offspring. As predicted by theory, the number of coexisting queens was greater for replacement reproductives than for co-foundresses. Several complex colonies contained multiple queens of two or more haplotypes distributed among several interconnected nests. This indicates that several matrilines can persist within a colony through one or more generations of budding and replacement, a hypothesis confirmed by orphaning experiments. The various modes of termite colony formation rival the diversity seen in ant species and demonstrate the remarkable convergence of behaviours between the two groups.     

Territorial behavior and temperature preference for nesting sites in a pavement ant Tetramorium tsushimae

To determine how the territorial strategies affect reproductive success of the polygynous ant Tetramorium tsushimae in Japan, we investigated territorial behaviors and reproductive success of their colonies in the field. We found that most of the reproductives were produced largely by the colonies that hold large territories. We investigated the nesting site temperature preferences of the colonies. Colonies strongly preferred high temperature areas of 27.5 to 30 ^°C as the rearing sites of reproductives. Growth rates of reproductives were positively correlated with rearing temperature as have been reported in other ant species. It was suggested that the colonies secure the high temperature zone to gain the high reproductive success. Furthermore, most of the rearing sites of reproductives were located along the border between neighboring territories. It was suggested that the colonies might compete for the high temperature zone to increase their reproductive success and that this results in the larger territories with multiple nest sites. Received 28 February 2005; revised 12 October 2005; accepted 17 October 2005.     

Genetic differentiation in the soil-feeding termite Cubitermes sp. affinis subarquatus : occurrence of cryptic species revealed by nuclear and mitochondrial markers

Background  

Soil-feeding termites are particularly interesting models for studying the effects of fragmentation, a natural or anthropic phenomenon described as promoting genetic differentiation. However, studying the link between fragmentation and genetics requires a method for identifying species unambiguously, especially when morphological diagnostic characters are lacking. In humivorous termites, which contribute to the fertility of tropical soils, molecular taxonomy and phylogenetic relationships are rarely studied, though mitochondrial and nuclear molecular markers are widely used in studies of pest termites. Here, we attempt to clarify the taxonomy of soil-feeding colonies collected throughout the naturally fragmented Lopé Reserve area (Gabon) and morphologically affiliated to Cubitermes sp. affinis subarquatus. The mitochondrial gene of cytochrome oxidase II (COII), the second nuclear rDNA internal transcribed spacer (ITS2) and five microsatellites were analyzed in 19 colonies.     

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.