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.     

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.     

Hierarchical analysis of colony and population genetic structure of the eastern subterranean termite, Reticulitermes flavipes, using two classes of molecular markers

Termites (Isoptera) comprise a large and important group of eusocial insects, yet, in contrast to the eusocial Hymenoptera (ants, bees, wasps), the breeding systems of termites remain poorly understood. In this study, I inferred the breeding system of the subterranean termite Reticulitermes flavipes based on colony and population genetic structure as determined from microsatellite and mitochondrial DNA markers. Termites were sampled from natural wood debris from three undisturbed, forested sites in central North Carolina. In each site, two transects separated by 1 km were sampled at approximately 15-m intervals. A total of 1272 workers collected from 57 collection points were genotyped at six microsatellite loci, and mitochondrial DNA haplotype was determined for a subset of these individuals using either restriction fragment length polymorphism or sequence variation in the AT-rich region. Colonies appeared to be localized: workers from the 57 collection points represented 56 genetically distinct colonies with only a single colony occupying two collection points located 15 m apart. Genetic analysis of family structure and comparisons of estimates of F-statistics (F(IT), F(IC), F(CT)) and coefficients of relatedness (r) among nestmate workers with results of computer simulations of potential breeding systems suggested that 77% of all colonies were simple families headed by outbred monogamous pairs, whereas the remaining colonies were extended (inbred) families headed by low numbers of neotenics (about two females and one male) who were the direct offspring of the colony founders. There was no detectable isolation by distance among colonies along transects, suggesting that colony reproduction by budding is not common and that dispersal of reproductives during mating flights is not limited over this distance. Higher-level analysis of the microsatellite loci indicated weak but significant differentiation among sites (F(ST) = 0.06), a distance of 16-38 km, and between transects within sites (F(ST) = 0.06), a distance of 1 km. No significant differentiation at either the transect or site level was detected in the mitochondrial DNA sequence data. These results indicate that the study populations of R. flavipes have a breeding system characterized by monogamous pairs of outbred reproductives and relatively low levels of inbreeding because most colonies do not live long enough to produce neotenics, and those colonies that do generate neotenics contain an effectively small number of them.     

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.     

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.     

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 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.     

Colony genetic organization and colony fusion in the termite Reticulitermes flavipes as revealed by foraging patterns over time and space

Temporal and spatial analyses are seldom utilized in the study of colony genetic structure, but they are potentially powerful methods which can yield novel insights into the mechanisms underlying variation in breeding systems. Here we present the results of a study which incorporated both of these dimensions in an examination of genetic structure of subterranean termites in the genus Reticulitermes (primarily R. flavipes). Most colonies of this species (70%) were simple families apparently headed by outbred primary reproductives, while most of the remaining (27% of the total) colonies contained low effective numbers of moderately inbred reproductives. Mapping the spatial distribution of colony foraging sites over time revealed that despite the high colony density, the absolute foraging boundaries of most R. flavipes colonies were persistent and exclusive of other conspecific colonies, which suggests that this species is more territorial than has been implied by laboratory studies of intraspecific aggression. Nevertheless, we found a single colony (3% of all colonies) which contained the offspring of more than two unrelated reproductives. Although other studies have also described subterranean termite colonies with a similarly complex genetic composition, we demonstrate here that such colonies can form under natural conditions via the fusion of whole colonies. This study underscores how repeated sampling from individual colonies over time and space can yield information about colony spatial and genetic structure that cannot be obtained from conventional analyses or sampling methods.     

Worker size in the formosan subterranean termite in relation to colony breeding structure as inferred from molecular markers

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is an invasive species that originated in China and has been introduced to Hawaii and the U.S. mainland. Colonies are headed either by a pair of reproductives (simple families) or by varying numbers of inbreeding reproductives (extended families), and therefore have variable degrees of inbreeding. Worker size also varies among colonies of Formosan termites. We tested whether variation in worker size can be explained by the breeding system. Workers were collected from colonies from three geographically separated populations (China, Hawaii, and Louisiana), and body weight and head size were measured. Microsatellite genotyping was used to establish whether colonies were simple or extended families and to determine the heterozygosity of workers and their degree of inbreeding relative to their colony (F (IC), sensitive to the number of reproductives). All Chinese colonies contained multiple inbreeding neotenics. In Hawaii, 37% of the colonies were simple families and 63% were extended families, both having considerable degrees of inbreeding. In Louisiana, 57% of the colonies were simple families, which were mostly headed by unrelated pairs, and 43% were extended families. In simple families, size and body weight of workers were not associated with F (IC) or heterozygosity. In extended families of two populations, both size parameters were negatively correlated with F (IC); however, heterozygosity was not associated with worker size in any of the populations. This suggests that the number of reproductives within colonies has a stronger influence on worker size than the individuals' genetic diversity in Formosan subterranean termite colonies.     

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.     

Genetic Analysis of Population Structure and Reproductive Mode of the Termite Reticulitermes chinensis Snyder

The subterranean termite Reticulitermes chinensis Snyder is an important pest of trees and buildings in China. Here, we characterized genetic structure and reproductive modes of R. chinensis from China for the first time. A total of 1,875 workers from 75 collection sites in Huanggang, Changsha and Chongqing cities were genotyped at eight microsatellite loci. Analysis of genetic clusters showed two subpopulations in Chongqing city. The Huanggang population showed a uniform genetic pattern and was separated from the other populations by the largest genetic distances (F _ST: 0.17–0.20). In contrast, smaller genetic distances (F _ST: 0.05–0.12) separated Changsha, Chongqing-1 and Chongqing-2 populations. Chongqing-1 was the only population showing a genetic bottleneck. Isolation by distance among colonies in the Huanggang population indicated limited alate dispersal or colony budding. Lack of isolation by distance among colonies within the populations of Changsha, Chongqing-1 and Chongqing-2, suggested long-range dispersal by alates and/or human-mediated transport. Overall, extended family colonies (73.91%) were predominant in all four populations, followed by simple (20.29%), and mixed family colonies (5.80%). Most simple families were headed by inbred related reproductive pairs in the Changsha population, while most simple families in the Chongqing-1 population were headed by outbred unrelated pairs. Simple families in the Huanggang population were a mixture of colonies headed by outbred or inbred reproductive pairs. The sample size of simple families in the Chongqing-2 population was too small to yield significant results. Extended families in all four populations were headed on the average by ≤10 neotenics. Mixed families likely originated from pleometrosis. Presence of heterozygote genotypes showed that all neotenic reproductives collected in addition from five field colonies in Wuhan city were sexually produced, suggesting that these colonies did not undergo parthenogenesis. This study contributes to better understanding of the variance of genetic structure and reproductive mode in the genus Reticulitermes.     

Genetic analysis of the breeding system of an invasive subterranean termite, Reticulitermes santonensis, in urban and natural habitats

Reticulitermes santonensis is a subterranean termite that invades urban areas in France and elsewhere where it causes damage to human-built structures. We investigated the breeding system, colony and population genetic structure, and mode of dispersal of two French populations of R. santonensis. Termite workers were sampled from 43 and 31 collection points, respectively, from a natural population in west-central France (in and around the island of Oleron) and an urban population (Paris). Ten to 20 workers per collection point were genotyped at nine variable microsatellite loci to determine colony identity and to infer colony breeding structure. There was a total of 26 colonies, some of which were spatially expansive, extending up to 320 linear metres. Altogether, the analysis of genotype distribution, F-statistics and relatedness coefficients suggested that all colonies were extended families headed by numerous neotenics (nonwinged precocious reproductives) probably descended from pairs of primary (winged) reproductives. Isolation by distance among collection points within two large colonies from both populations suggested spatially separated reproductive centres with restricted movement of workers and neotenics. There was a moderate level of genetic differentiation (F(ST) = 0.10) between the Oleron and Paris populations, and the number of alleles was significantly higher in Oleron than in Paris, as expected if the Paris population went through bottlenecks when it was introduced from western France. We hypothesize that the diverse and flexible breeding systems found in subterranean termites pre-adapt them to invade new or marginal habitats. Considering that R. santonensis may be an introduced population of the North American species R. flavipes, a breeding system consisting primarily of extended family colonies containing many neotenic reproductives may facilitate human-mediated spread and establishment of R. santonensis in urban areas with harsh climates.     

Queen adoption in the polygynous and polydomous ant, Leptothorax curvispinosus

Alate female reproductives of the facultatively polygynous andpolydomous ant, Lepiothorax curuispinosus, were reared fromfield-collected nests, mated, and introduced into either theirparental nests or alien conspecific nests. The 41 queens introducedinto alien nests were usually attacked and rejected (97. 6%),but one queen was accepted after initial aggression. The 27queens introduced into their parental nests received a variableresponse. Some were accepted without any apparent aggression(59. 3%), but others were strongly attacked and rejected (40.7%). Sequential introductions of up to four queens into particularparental nests indicated that nests consistently either acceptor reject their mated offspring. The presence or absence ofresident queens in parental nests had no apparent influenceon the acceptance of offspring queens. Nests that accepted queenshad significantly fewer workers than those that did not, butthis slight difference is unlikely to explain these dichotomousresults and could be spurious. Dissections of the introducedqueens revealed that 79. 0% were inseminated and 98. 3% haddeveloping, yolked eggs in their ovarioles, but these variableshad no apparent effect on acceptability. Similarly, the sizeof the introduced queens and the time that elapsed between matingand introduction had no apparent effect. The consistent responseof parental nests in either accepting or rejecting their matedoffspring indicates a mechanism of queen number regulation inthis species that involves characteristics of the colony ornest rather than variability among offspring queens. This mechanismcould be responsible for maintaining relatively low numbersof queens and high genetic relatedness in colonies (or individualnests) while promoting flexibility in colony reproduction bycolony fission ("budding") and the dispersal of young queens.This mechanism could also involve an important conflict of interestbetween parental colonies and their mated offspring and mightcontribute to the evolution of socially parasitic colony foundationstrategies. Acceptance of mated offspring by their parentalcolonies might only occur during certain periods in colony development,depend on the level of genetic diversity within the colony (ornest), reflect the condition of the colony, nest, queen(s),brood, or local habitat, or result from a genetic polymorphism.     

Asexual queen succession mediates an accelerated colony life cycle in the termite Silvestritermes minutus

Mixed modes of reproduction, combining sexual processes with thelytokous parthenogenesis, occur in all major clades of social insects. In several species of termites, queens maximize their genetic input into nondispersing replacement queens through parthenogenesis, while maintaining genetically diverse sterile offspring and dispersing reproductives via sexual reproduction. This so‐called asexual queen succession (AQS) has multiple independent origins and its presumed advantages are diverse as well, ranging from multiplication of colony reproductive potential to extension of its lifespan beyond that of the foundress. However, how AQS shapes colony life cycles under natural conditions remains poorly known. The neotropical termite Silvestritermes minutus inhabits small but conspicuous nests, offering a unique opportunity to investigate the impact of AQS on life history. We report on its breeding system, life cycle and sex allocation using social structure census in 137 nests and genotyping of 12 colonies at 12 microsatellite loci. We show that colonies are established by an outbred pair of primary reproductives. In less than 2 years, the foundress is replaced by multiple neotenic queens, arising mostly through automixis with central fusion. Sterile castes, male and most (93%) female dispersers are produced sexually. Colony reproduction is usually restricted to a single dispersal of alates with unbiased sex ratio, taking place after 3 years. We conclude that S. minutus benefits from AQS to maximize colony growth rate and alate production within a very short life cycle rather than to extend colony lifespan. This highlights the versatile role of AQS in different cases of its polyphyletic origin.     

Evaluation of treatment success and patterns of reinfestation of the Formosan subterranean termite (Isoptera: Rhinotermitidae)

Spread of the Formosan subterranean termite, Coptotermes fornwsanus 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.     

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.     

Molecular insight into patterns of colony composition and paternity in the common mole-rat Cryptomys hottentotus hottentotus

We report the discovery of intraspecific variation in both colony composition and patterns of paternity in two populations of the social common mole-rat Cryptomys hottentotus hottentotus. These two populations represent the mesic and arid habitat extremes of the species' broad ecological range in South Africa. Until recently colonies of the common mole-rat were thought to consist of familial groups whereby all colony members were the offspring of a monogamous reproductive pair. The remaining colony members were thought to forego reproduction until both social and ecological conditions favoured dispersal and opportunities for independent outbreeding. Results from genetic assignment tests using microsatellite markers indicate that while colony composition is dominated by familial groups, colonies within both populations included both adult and subadult foreign conspecifics. Analysis of parentage reveals that the social organization of C. h. hottentotus is not that of strict monogamy; paternity of offspring was not assigned consistently to the largest, most dominant male within the colony. Moreover, a number of significantly smaller males were found to sire offspring, suggesting a sneak-mating strategy by subordinate within-colony males. Extra-colony extra-pair paternity (ECP) was also found to characterize C. h. hottentotus colonies, occurring with similar frequencies in both habitats. Both dominant established breeding males and subordinate males were identified as siring young in nonsource colonies. Furthermore, established breeding males were found to sire extra-colony young in the same season as siring young within their source colonies. We discuss the significance of these results within the context of the divergent ecological regimes characterizing the two sites and observe that our results revisit the accuracy of using behavioural and morphological characters, which have structured the basis of our understanding of the behavioural ecology of this species, as indicators of breeding status in mark-recapture studies.     

Facultative sexual reproduction in the parthenogenetic ant Platythyrea punctata

Summary. In a few, scattered species of social Hymenoptera, unmated workers are capable of producing female offspring from unfertilized eggs through thelytokous parthenogenesis. Regular thelytoky has previously been demonstrated in a number of populations of the neotropical ant Platythyrea punctata. Nevertheless, the finding of males and inseminated queens and workers suggested the sporadic occurrence of sex. In this study we investigated the genetic structure of colonies from Puerto Rico and Costa Rica in order to detect traces of occasional sexual reproduction. Most Puerto Rican colonies had a clonal structure with all nestmates sharing the same multilocus genotype, indicating that thelytoky is the predominant mode of reproduction. Genetic variability was detected in six of 18 colonies and might have arisen from adoption of alien workers in one colony and from the adoption of alien workers, recombination during parthenogenesis, or sexual reproduction in the other colonies. The reproductive of one of these latter colonies was found to be an inseminated worker (gamergate), and the genotypes of its nestmates definitively suggested recombination and sexual reproduction. Three gamergates were found in a single colony collected in Costa Rica, and all produced offspring from fertilized eggs, while uninseminated workers were apparently incapable of reproducing by thelytoky.Received 10 August 2004; revised 20 October 2004; accepted 3 November 2004.     

Extreme genetic differences between queens and workers in hybridizing Pogonomyrmex harvester ants

The process of reproductive caste determination in eusocial insect colonies is generally understood to be mediated by environmental, rather than genetic factors. We present data demonstrating unexpected genetic differences between reproductive castes in a variant of the rough harvester ant, Pogonomyrmex rugosus var. fuscatus. Across multiple loci, queens were consistently more homozygous than expected, while workers were more heterozygous. Adult colony queens were divided into two highly divergent genetic groups, indicating the presence of two cryptic species, rather than a single population. The observed genetic differences between castes reflect differential representation of heterospecific and conspecific patrilines in these offspring groups. All workers were hybrids; by contrast, winged queens were nearly all pure-species. The complete lack of pure-species workers indicates a loss of worker potential in pure-species female offspring. Hybrids appear to be bipotential, but do not normally develop into reproductives because they are displaced by pure-species females in the reproductive pool. Genetic differences between reproductive castes are expected to be rare in non-hybridizing populations, but within hybrid zones they may be evolutionarily stable and thus much more likely to occur.     

黑胸散白蚁的分飞成熟年龄及生殖蚁对子代个体分化的抑制作用

实验室配对饲养黑胸散白蚁Reticulitermes chinensis表明,黑胸散白蚁新群体在原始生殖蚁控制下,83.30%的群体在第9年分出了有翅成虫,16.70%的群体在第7年发生有翅成虫分飞,平均分飞成熟年龄为8.67年;由补充生殖蚁控制的群体在第6年即有53.85%的群体发生分飞,第7年有46.15%的群体分飞,平均分飞成熟年龄为6.38年,较原始生殖蚁控制的群体发生分飞平均提前2.29年。初次发生分飞时群体内个体数量前者明显多于后者。研究还发现,群体内补充生殖蚁的数量与分飞发生的早迟关系不大。作者认为在黑胸散白蚁中,原始生殖蚁对补充生殖蚁和若蚁的产生具有较强的抑制作用,而补充生殖蚁对上述品级的分化虽有一定抑制,但不如原始生殖蚁强。认为黑胸散白蚁群体发展速度在品级分化的调节上起到不可忽视的作用,但一定要在生殖蚁分泌外激素的能力开始减弱后才能发挥效应。