Ergatoid reproductives in the Neotropical termite Nasutitermes aquilinus (Holmgren) (Blattaria: Isoptera: Termitidae): developmental origin, fecundity, and genetics

Termite colonies are usually headed by primary reproductives, which establish nests during the swarming season. However, secondary reproductives may develop in some species and become supplementary or replacement breeders, extending colony lifespan. Here we investigate the developmental origin, fecundity and genetic characterization of ergatoid reproductives in the Neotropical termite Nasutitermes aquilinus (Holmgren), using morphometrical and histological techniques, five microsatellite loci and the COI mitochondrial DNA. Twelve measurements performed on 208 apterous individuals of N. aquilinus revealed 10 groups, including ergatoid females, which developed from major workers through two successive molts, and were characterized by the presence of imaginal features such as eyes and wing buds. The differentiation of these features was correlated to physogastric development in these ergatoids. Histology revealed oocytes in all maturation stages in worker-derived reproductives of N. aquilinus, presence of nonflagellate spermatozoa inside the spermatheca, and royal fat body. Thus, ergatoid reproductives were reproductively functional. According to the genotypes of 221 individuals from 11 nests, and mitochondrial haplotypes of 43 ergatoids, 73% of the colonies were simple families, whereas 27% were extended families. Despite the occurrence of related reproductives, low inbreeding rates were detected within and among colonies. Such values could be explained given that sib mating itself cannot result in a higher inbreeding rate but depend on several factors discussed in detail. This is the first study to investigate the genetic structure of termite colonies influenced by the development of ergatoids, and further investigations are encouraged to understand the influence of these reproductives on colony lifespan.

Genetic Analysis of Invasive Conehead Termites (Blattodea: Termitidae) Reveals a Single Origin for Two Populations in Florida

In 2001, Nasutitermes corniger (Motschulsky), common name conehead termite, were discovered near a marina in Dania Beach, FL, where the invasive species was probably transported from its native range in Central and South America or the Caribbean. In January 2016, an infestation was found in Pompano Beach, Florida, approximately 21 km north of the Dania Beach population. This study compares variants in seven microsatellite loci across specimens from 11 nests in Dania Beach and 8 nests in Pompano Beach. Results are consistent with all N. corniger in both locations being descendants of a single introduced colony, spreading within Broward County, FL through human transport of infested materials. No more than four alleles were found at any of the seven microsatellite loci analyzed, inferring that a single Queen and King, or multiple sibling reproductives descended from a monogamous pair, headed the colony that arrived in Florida. The potential economic and environmental impacts of this invasive termite are enormous due to its broad diet, including agricultural crops and orchards, native and ornamental plants, natural landscapes, and structures. Conspicuous tunnels and aboveground nests are the key aspects of N. corniger biology that render colonies vulnerable to discovery and control. The now proven ability of N. corniger to establish breeding populations in the United States, to cause extensive property and landscape destruction, and to spread by human transport underscores the need for continued aggressive efforts toward eradication of known infestations as well as quick operational actions the next time invasive N. corniger are discovered.

Diversity of Termite Breeding Systems

Termites are social insects that live in colonies headed by reproductive castes. The breeding system is defined by the number of reproductive individuals in a colony and the castes to which they belong. There is tremendous variation in the breeding system of termites both within and among species. The current state of our understanding of termite breeding systems is reviewed. Most termite colonies are founded by a primary (alate-derived) king and queen who mate and produce the other colony members. In some species, colonies continue throughout their life span as simple families headed by the original king and queen. In others, the primary king and queen are replaced by numerous neotenic (nymph- or worker-derived) reproductives, or less commonly primary reproductives, that are descendants of the original founding pair leading to inbreeding in the colony. In still others, colonies can have multiple unrelated reproductives due to either founding the colonies as groups or through colony fusion. More recently, parthenogenetic reproduction has shown to be important in some termite species and may be widespread. A major challenge in termite biology is to understand the ecological and evolutionary factors driving the variation in termite breeding systems.

Lack of aggression and apparent altruism towards intruders in a primitive termite

In eusocial insects, the ability to discriminate nest-mates from non-nest-mates is widespread and ensures that altruistic actions are directed towards kin and agonistic actions are directed towards non-relatives. Most tests of nest-mate recognition have focused on hymenopterans, and suggest that cooperation typically evolves in tandem with strong antagonism towards non-nest-mates. Here, we present evidence from a phylogenetically and behaviourally basal termite species that workers discriminate members of foreign colonies. However, contrary to our expectations, foreign intruders were the recipients of more rather than less cooperative behaviour and were not subjected to elevated aggression. We suggest that relationships between groups may be much more peaceable in basal termites compared with eusocial hymenoptera, owing to energetic and temporal constraints on colony growth, and the reduced incentive that totipotent workers (who may inherit breeding status) have to contribute to self-sacrificial intergroup conflict.

Unrelated secondary reproductives in the neotropical termite Silvestritermes euamignathus (Isoptera: Termitidae)

A termite colony is usually founded by a pair of alates, the primary reproductives, which produce all the nestmates. In some species, secondary reproductives appear to either replace the primaries or supplement colony reproduction. In termites, secondary reproductives are generally ergatoids derived from workers or nymphoids derived from nymphs. Silvestritermes euamignathus is a termite species that forms multiple nymphoid reproductives, and to date it was hypothesized that these secondary reproductives were the progeny of the primary founding reproductives. We developed markers for 12 microsatellite loci and used COI mitochondrial DNA (mtDNA) to genotype 59 nymphoid neotenics found in a colony of S. euamignathus to test this hypothesis. Our results showed that nymphoids of S. euamignathus are not all siblings. The microsatellite analysis suggests that the secondary reproductives derived from a minimum of four different pairs of reproductives belonging to at least two different matrilines. This is the first record of non-sibling secondary reproductives occupying the same nest in a higher termite. These unrelated reproductives might be the result of either pleometrotic colony foundation or colony fusion.

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.

Costs of pleometrosis in a polygamous termite

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

Biology of invasive termites: a worldwide review

The number of recognized invasive termite species has increased from 17 in 1969 to 28 today. Fourteen species have been added to the list in the past 44 years; 10 have larger distributions and 4 have no reported change in distribution, and 3 species are no longer considered invasive. Although most research has focused on invasive termites in urban areas, molecular identification methods have answered questions about certain species and found that at least six species have invaded natural forest habitats. All invasive species share three characteristics that together increase the probability of creating viable propagules: they eat wood, nest in food, and easily generate secondary reproductives. These characteristics are most common in two families, the Kalotermitidae and Rhinotermitidae (which make up 21 species on the invasive termite list), particularly in three genera, Cryptotermes, Heterotermes, and Coptotermes (which together make up 16 species). Although it is the largest termite family, the Termitidae (comprising 70% of all termite species) have only two invasive species, because relatively few species have these characteristics. Islands have double the number of invasive species that continents do, with islands in the South Pacific the most invaded geographical region. Most invasive species originate from Southeast Asia. The standard control methods normally used against native pest termites are also employed against invasive termites; only two eradication attempts, in South Africa and New Zealand, appear to have been successful, both against Coptotermes species.

Heterospecific pairing and hybridization between Nasutitermes corniger and N. ephratae

The sympatric neotropical termites Nasutitermes corniger and Nasutitermes ephratae are clearly distinguishable based on morphology, nest architecture, defensive secretion composition, and molecular markers. However, given the extensive ecological, geographical, and behavioral overlap of these closely related species, the potential for interbreeding may exist. To explore this possibility, heterospecific pairs were formed experimentally to examine courtship and colony-establishment behaviors, and reproductive potential. Courtship and nest construction behavior occurred in heterospecific pairs in a similar manner to that of conspecific pairs. Survival of pairs depended upon the species of the female partner. N. ephratae females paired with N. corniger males produced as many offspring as conspecific pairs. N. corniger females mated to N. ephratae males, however, produced significantly fewer offspring at 60 days post-establishment than the reciprocal cross or conspecific N. ephratae or N. corniger pairs. This was also the only pairing in which any aggression was observed. Heterospecific pairs and groups formed in mate choice mesocosms, suggesting that species recognition between these two termites is not an important aspect of mate choice. Overall, species mismatch tolerance and hybrid offspring viability are high. The present data, together with previous evidence from defensive secretions and isozyme analysis, suggest that hybridization may periodically occur in nature, and that reproductive barriers between these two species may be incomplete. Hybridization could provide a rare but important source of genetic diversity and may ensure mating opportunities for the more abundant sex of alates in each species.

Lifetime monogamy and the evolution of eusociality

All evidence currently available indicates that obligatory sterile eusocial castes only arose via the association of lifetime monogamous parents and offspring. This is consistent with Hamilton's rule (br(s) > r(o)c), but implies that relatedness cancels out of the equation because average relatedness to siblings (r(s)) and offspring (r(o)) are both predictably 0.5. This equality implies that any infinitesimally small benefit of helping at the maternal nest (b), relative to the cost in personal reproduction (c) that persists throughout the lifespan of entire cohorts of helpers suffices to establish permanent eusociality, so that group benefits can increase gradually during, but mostly after the transition. The monogamy window can be conceptualized as a singularity comparable with the single zygote commitment of gametes in eukaryotes. The increase of colony size in ants, bees, wasps and termites is thus analogous to the evolution of multicellularity. Focusing on lifetime monogamy as a universal precondition for the evolution of obligate eusociality simplifies the theory and may help to resolve controversies about levels of selection and targets of adaptation. The monogamy window underlines that cooperative breeding and eusociality are different domains of social evolution, characterized by different sectors of parameter space for Hamilton's rule.

Unicoloniality in Reticulitermes urbis: a novel feature in a potentially invasive termite species

Social insects are among the world's most successful species at invading of new habitats. A good example of this invasive ability is Reticulitermes (Rhinotermitidae), a prominent group of subterranean termites. As a result of human intervention, i.e. transportation and creation of urban heat islands, Reticulitermes have been able to invade and thrive in cities located in areas where the natural habitat is normally too cold for colonization. They commonly infest man-made structures where they can cause extensive damage.This study was designed to evaluate the invasiveness of Reticulitermes urbis that was probably introduced in France from the Balkans. Invasive potential was assessed on the basis of features typical to invasive social insects, i.e. unicoloniality, low intraspecific aggression, high level of polygyny and colony reproduction by budding. The opportunity to study establishment and spreading processes arose after extensive sampling of an imported Reticulitermes urbis population was performed over the entire city of Domène, France (Rhône-Alpes region).For the first time, genetic analysis showed that the termites belonged to a single 'genetic entity' forming a vast colony covering about seven hectares. The colony was structured as an extended family with separate reproductive centres. We speculate that termites were introduced in a single location from which they gradually budded throughout the old town. Based on the absence of aggression among different nests within the colony, we defined this 'genetic entity' as a supercolony.

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

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

Kin selection versus sexual selection: why the ends do not meet

I redevelop the hypothesis that lifetime monogamy is a fundamental condition for the evolution of eusocial lineages with permanent non-reproductive castes, and that later elaborations--such as multiply-mated queens and multi-queen colonies--arose without the re-mating promiscuity that characterizes non-social and cooperative breeding. Sexually selected traits in eusocial lineages are therefore peculiar, and their evolution constrained. Indirect (inclusive) fitness benefits in cooperatively breeding vertebrates appear to be negatively correlated with promiscuity, corroborating that kin selection and sexual selection tend to generally exclude each other. The monogamy window required for transitions from solitary and cooperative breeding towards eusociality implies that the relatedness and benefit-cost variables of Hamilton's rule do not vary at random, but occur in distinct and only partly overlapping combinations in cooperative, eusocial, and derived eusocial breeding systems.

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.

Unrelated queens coexist in colonies of the termite Macrotermes michaelseni

Relatedness increases the likelihood of cooperation within colonies of social insects. Polygyny, the coexistence of numerous reproductive females (queens) in a colony, is common in mature colonies of the termite Macrotermes michaelseni. In this species, polygyny results from pleometrosis and from several female alates that jointly found a new colony. To explain this phenomenon, it was suggested that only related females cooperate and survive during maturation of colonies. Using multilocus fingerprints as well as microsatellites, we showed that nestmate queens in mature colonies are unrelated. Furthermore, we found that all nestmate queens contributed to the production of steriles. Even in mature colonies, several matrilines of steriles coexist within a colony. Although genetic diversity within colonies may increase the likelihood of conflicts, high genetic diversity may be important for foraging, colony growth, and resistance to disease and parasites.

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.

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.

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.

Population and colony genetic structure of the primitive termite Mastotermes darwiniensis

The termite Mastotermes darwiniensis is the sole extant member of its family and occupies the basal position in the phylogeny of the eusocial order Isoptera. In this study, we investigated the micro- and macrogeographic genetic structure of M. darwiniensis in its native range in Australia. A total of 1591 workers were sampled from 136 infested trees in 24 locales. Each locale was separated by 2-350 km, and these locales were found within two broader geographic regions approximately 1500 km apart. The multilocus genotypes of all termites were assayed at six polymorphic microsatellite loci. The genetic data indicated that colonies typically fed on multiple trees within locales and extended over linear distances of up to 320 m. Single colonies were frequently headed by multiple reproductives. Workers were highly related (r = 0.40) and substantially inbred (f = 0.10). Thus, M. darwiniensis colonies are characterized by the input of alleles from multiple reproductives, which sometimes engage in consanguineous matings. Our analyses of population genetic structure above the level of the colony indicated that locales and regions were significantly differentiated (theta(locale) = 0.50, theta(region) = 0.37). Moreover, locales showed a pattern of genetic isolation by distance within regions. Thus, M. darwiniensis populations display restricted gene flow over moderate geographic distances. We suggest that the genetic patterns displayed by M. darwiniensis result primarily from selective pressures acting to maintain high relatedness among colonymates while allowing colonies to grow rapidly and dominate local habitats.

Molecular ecology of social behaviour: analyses of breeding systems and genetic structure

Molecular genetic studies of group kin composition and local genetic structure in social organisms are becoming increasingly common. A conceptual and mathematical framework that links attributes of the breeding system to group composition and genetic structure is presented here, and recent empirical studies are reviewed in the context of this framework. Breeding system properties, including the number of breeders in a social group, their genetic relatedness, and skew in their parentage, determine group composition and the distribution of genetic variation within and between social units. This group genetic structure in turn influences the opportunities for conflict and cooperation to evolve within groups and for selection to occur among groups or clusters of groups. Thus, molecular studies of social groups provide the starting point for analyses of the selective forces involved in social evolution, as well as for analyses of other fundamental evolutionary problems related to sex allocation, reproductive skew, life history evolution, and the nature of selection in hierarchically structured populations. The framework presented here provides a standard system for interpreting and integrating genetic and natural history data from social organisms for application to a broad range of evolutionary questions.