A case for ancestral transfer of symbionts between cockroaches and termites

Living species of the cockroach family Cryptocercidae have intestinal symbionts that are congeneric with some of the gut protozoa found in Isoptera. Presence of such closely related symbionts in cryptocercids and in termites has been frequently interpreted as a uniquely derived homologous character shared between the two xylophagous groups. This may not be the most parsimonious interpretation. Cryptocercus nymphs placed into Zootermopsis (dampwood termite) colonies were killed and eaten by the termites. Termites placed into a Cryptocercus nest box were also fully consumed. Modern Cryptocercus punctulatus and Zootermopsis are often found in the same decaying logs in the Pacific Northwest of the U.S.A., and it is likely that their ancestors also cohabited in at least a portion of their ranges. By occasionally killing and consuming an intruder from the other group, gut protozoa could have been acquired and exchanged between termites and Cryptocercus or their ancestors, under natural conditions and before the life histories of the protozoa became specialized within the host orders. Implications for assessing the phylogeny of the two dictyopteroid groups are also discussed.     

Wood-feeding cockroaches as models for termite evolution (Insecta: Dictyoptera): Cryptocercus vs. Parasphaeria boleiriana

Isoptera are highly specialized cockroaches and are one of the few eusocial insect lineages. Cryptocercus cockroaches have appeared to many as ideal models for inference on the early evolution of termites, due to their possible phylogenetic relationship and several shared key attributes in life history. Recently, Pellens, Grandcolas, and colleagues have proposed the blaberid cockroach Parasphaeria boleiriana to be an alternative model for the early evolution in termites. We compare the usefulness of Cryptocercus and P. boleiriana as models for termite evolution. Cryptocercus and lower Isoptera (1) can both feed on comparatively recalcitrant wood, (2) have an obligate, rich and unique hypermastigid and oxymonadid fauna in the hindgut, (3) transfer these flagellates to the next generation by anal trophallaxis, (4) have social systems that involve long-lasting biparental care, and, finally, (5) are strongly suggested to be sister groups, so that the key attributes (1)-(4) appear to be homologous between the two taxa. On the other hand, P. boleiriana (1) feeds on soft, ephemeral wood sources, (2) shows no trace of the oxymonadid and hypermastigid hindgut fauna unique to Cryptocercus and lower Isoptera, nor does it have any other demonstrated obligate relationship with hindgut flagellates, (3) is likely to lack anal trophallaxis, (4) has only a short period of uniparental brood care, and (5) is phylogenetically remote from the Cryptocercus+Isoptera clade. These facts would argue against any reasonable usage of P. boleiriana as a model for the early evolution of Isoptera or even of the clade Cryptocercus+Isoptera. Cryptocercus thus remains an appropriate model-taxon-by-homology for early termite evolution. As compared to P. boleiriana, some other Blaberidae (such as the Panesthiinae Salganea) appear more useful as model-taxa-by-homoplasy for the early evolution of the Cryptocercus+Isoptera clade, as their brooding behavior is more elaborate than in P. boleiriana.     

The evolutionary transition from subsocial to eusocial behaviour in Dictyoptera: phylogenetic evidence for modification of the "shift-in-dependent-care" hypothesis with a new subsocial cockroach

Cockroaches have always been used to understand the first steps of social evolution in termites because they are close relatives with less complex and integrated social behaviour. Termites are all eusocial and ingroup comparative analysis would be useless to infer the origin of their social behaviour. The cockroach genus Cryptocercus was used as a so-called "prototermite" model because it shows key-attributes similar to the termites (except Termitidae): wood-feeding, intestinal flagellates and subsocial behaviour. In spite of these comparisons between this subsocial cockroach and eusocial termites, the early and remote origin of eusocial behaviour in termites is not well understood yet and the study of other relevant "prototermite" models is however needed. A molecular phylogenetic analysis was carried out to validate a new "prototermite" model, Parasphaeria boleiriana which shows a peculiar combination of these key-attributes. It shows that these attributes of Parasphaeria boleiriana have an independent origin from those of other wood-eating cockroaches and termites. The case of P. boleiriana suggests that a short brood care was selected for with life on an ephemeral wood resource, even with the need for transmission of flagellates. These new phylogenetic insights modify evolutionary hypotheses, contradicting the assumption made with Cryptocercus model that a long brood care is necessary for cooperation between broods in the "shift-in-dependent-care" hypothesis. An ephemeral wood resource is suggested to prompt generation overlap and the evolution of cooperation, even if brood care is shortened.     

Inheritance and diversification of symbiotic trichonymphid flagellates from a common ancestor of termites and the cockroach Cryptocercus

Cryptocercus cockroaches and lower termites harbour obligate, diverse and unique symbiotic cellulolytic flagellates in their hindgut that are considered critical in the development of social behaviour in their hosts. However, there has been controversy concerning the origin of these symbiotic flagellates. Here, molecular sequences encoding small subunit rRNA and glyceraldehyde-3-phosphate dehydrogenase were identified in the symbiotic flagellates of the order Trichonymphida (phylum Parabasalia) in the gut of Cryptocercus punctulatus and compared phylogenetically to the corresponding species in termites. In each of the monophyletic lineages that represent family-level groups in Trichonymphida, the symbionts of Cryptocercus were robustly sister to those of termites. Together with the recent evidence for the sister-group relationship of the host insects, this first comprehensive study comparing symbiont molecular phylogeny strongly suggests that a set of symbiotic flagellates representative of extant diversity was already established in an ancestor common to Cryptocercus and termites, was vertically transmitted to their offspring, and subsequently became diversified to distinct levels, depending on both the host and the symbiont lineages.     

The fine structure of colleterial glands in two cockroaches and three termites, including a detailed study of Cryptocercus punctulatus (Blattaria, Cryptocercidae) and Mastotermes darwiniensis (Isoptera, Mastotermitidae)

The colleterial glands of insects are organs associated with the female genital apparatus. In cockroaches, these glands produce secretions that cover two parallel rows of eggs during oviposition, and in oviparous species, these secretions become the tanned, sculpted, rigid outer casing of the ootheca. The goal of this study was to compare the gross anatomy of the colleterial glands and the ultrastructure of their component tubules in the phylogenetically significant genera Cryptocercus (Blattaria) and Mastotermes (Isoptera). Recent studies indicate that cockroaches in the genus Cryptocercus are the sister group of termites, and Mastotermes is the only termite known to produce a cockroach-like ootheca. One additional oviparous cockroach, Therea, and two additional termites, Zootermopsis and Pseudacanthotermes, were also examined. As in other cockroaches, the colleterial glands of Cryptocercus and Therea are asymmetrical, with a well developed bipartite left gland and a smaller right gland. In the termites Mastotermes, Zootermopsis, and Pseudacanthotermes, the colleterial glands are composed of a well-developed, paired, anterior gland and a small posterior gland; histological staining and cytological evidence suggest that these are homologues of the left and the right colleterial glands of cockroaches, respectively. At the ultrastructural level, colleterial gland tubules are made of cells belonging to a modified class 1 type cell in the cockroaches, in Mastotermes, and in Zootermopsis; the latter lays its eggs singly, without a surrounding ootheca-like structure. In the advanced termite Pseudacanthotermes, the tubules are made of secretory units belonging to the class 3 cell type. This study demonstrates that the cytological characteristics of colleterial glands in basal termites are similar to those of cockroaches, whether the termite secretes an oothecal casing that covers two parallel rows of eggs, as in Mastotermes, or lays its eggs singly, as in Zootermopsis. The function of colleterial glands in non-mastotermitid termites is unknown.     

Ancestral transfer of symbionts between cockroaches and termites: an alternative hypothesis.

Closely related cellulolytic protozoa reside in the hindguts of extant woodroaches (Cryptocercidae) and termites (Isoptera). The evolutionary origin of these symbiotic relationships in the two lineages is uncertain. Transfer of protozoa between ancestors of modern Cryptocercus and termites remains a valid alternative theory to the established hypothesis of symbiont inheritance from a common ancestor. Nalepa's (Proc. R. Soc. Lond. B 246, 185 (1991] concerns regarding the protozoan transfer hypothesis focus on the biology of modern species, and neglect to consider the evolutionary framework of an ancestral dynamic postulated to occur among Palaeozoic insects. Legitimacy of the symbiont transfer theory removes the constraint of interpreting presence of cellulolytic protozoa as a synapomorphy between Cryptocercidae and Isoptera, with potential impact on objective resolution of dictyopteran phylogeny.     

A mitochondrial genome phylogeny of termites (Blattodea: Termitoidae): Robust support for interfamilial relationships and molecular synapomorphies define major clades

Despite their ecological significance as decomposers and their evolutionary significance as the most speciose eusocial insect group outside the Hymenoptera, termite (Blattodea: Termitoidae or Isoptera) evolutionary relationships have yet to be well resolved. Previous morphological and molecular analyses strongly conflict at the family level and are marked by poor support for backbone nodes. A mitochondrial (mt) genome phylogeny of termites was produced to test relationships between the recognised termite families, improve nodal support and test the phylogenetic utility of rare genomic changes found in the termite mt genome. Complete mt genomes were sequenced for 7 of the 9 extant termite families with additional representatives of each of the two most speciose families Rhinotermitidae (3 of 7 subfamilies) and Termitidae (3 of 8 subfamilies). The mt genome of the well supported sister-group of termites, the subsocial cockroach Cryptocercus, was also sequenced. A highly supported tree of termite relationships was produced by all analytical methods and data treatment approaches, however the relationship of the termites+Cryptocercus clade to other cockroach lineages was highly affected by the strong nucleotide compositional bias found in termites relative to other dictyopterans. The phylogeny supports previously proposed suprafamilial termite lineages, the Euisoptera and Neoisoptera, a later derived Kalotermitidae as sister group of the Neoisoptera and a monophyletic clade of dampwood (Stolotermitidae, Archotermopsidae) and harvester termites (Hodotermitidae). In contrast to previous termite phylogenetic studies, nodal supports were very high for family-level relationships within termites. Two rare genomic changes in the mt genome control region were found to be molecular synapomorphies for major clades. An elongated stem-loop structure defined the clade Polyphagidae + (Cryptocercus+termites), and a further series of compensatory base changes in this stem-loop is synapomorphic for the Neoisoptera. The complicated repeat structures first identified in Reticulitermes, composed of short (A-type) and long (B-type repeats) defines the clade Heterotermitinae+Termitidae, while the secondary loss of A-type repeats is synapomorphic for the non-macrotermitine Termitidae.     

Altricial development in subsocial cockroach ancestors: foundation for the evolution of phenotypic plasticity in termites

SUMMARY Basal termites possess two developmental features that eusocial Hymenoptera lack: the majority of colony members are juveniles whose somatic and reproductive development is temporarily or permanently suspended, and individual development is characterized by extreme phenotypic plasticity. An examination of the literature indicates that the basis for these unique ontogenetic characters is not the prolongation of a pronymphal stage into postembryonic development, as recently suggested. Like other hemimetabolous insects, termites have three embryonic cuticles, and the pronymphal (EC3) cuticle is shed during or shortly after hatch. Nonetheless, a different developmental landmark, dorsal closure, occurs later during embryogenesis in termites than it does in their cockroach relatives, clearly indicating ontogenetic repatterning from an ancestral state. An alternate hypothesis for the origin of isopteran phenotypic plasticity becomes apparent if we remain focused on the phylogenetic and social context of termite evolution. Altricial development occurs in both vertebrate and invertebrate taxa, evolves in response to the parental environment, and is displayed by two distantly related, biparental, wood-feeding cockroaches, including Cryptocercus , the sister-group to termites. It is therefore likely the condition was present in subsocial termite ancestors, and played a complex, multidimensional role in the transition to eusociality. Most relevant to current arguments is that a shift in responsibility for the care of altricial dependents, from parents to the first nutritionally independent nymphs in the family (alloparents), resulted in the developmental stasis of alloparents at a relatively young age. Because early instar cockroaches are not metamorphically competent, these young alloparents would have provided a novel developmental template on which selection could act.     

Evolutionary trend of phylogenetic diversity of nitrogen fixation genes in the gut community of wood-feeding termites

Nitrogen fixation by gut microorganisms is one of the crucial aspects of symbiosis in wood-feeding termites since these termites thrive on a nitrogen-poor diet. In order to understand the evolution of this symbiosis, we analysed the nitrogenase structural gene nifH in the gut microbial communities. In conjunction with the published sequences, we compared approximately 320 putatively functional NifH protein sequences obtained from a total of 19 termite samples that represent all the major branches of their currently proposed phylogeny, and from one species of the cockroach Cryptocercus that shares a common ancestor with termites. Using multivariate techniques for clustering and ordination, a phylogeny of NifH protein sequences was created and plotted variously with host termite families, genera, and species. Close concordance was observed between NifH communities and the host termites at genus level, but family level relationships were not always congruent with accepted termite clade structure. Host groups examined included basal families (Mastotermitidae, Termopsidae, Kalotermitidae, as well as Cryptocercus), the most derived lower termite family Rhinotermitidae, and subfamilies representing the advanced and highly diverse apical family Termitidae (Macrotermitinae, Termitinae, and Nasutitermitinae). This selection encompassed the major nesting and feeding styles recognized in termites, and it was evident that NifH phylogenetic divergence, as well as the occurrence of alternative nitrogenase-type NifH, was to some extent dependent on host lifestyle as well as phylogenetic position.     

Lignocellulose degradation by microorganisms from termite hills and termite guts: A survey on the present state of art

Abstract: In several aspects termites are a fascinating group of insects having attracted the interest of many researchers. They exhibit a complex social behavior and caste differentiation occurring elsewhere only among the hymenoptera. In an enlarged part of the hindgut, the paunch, termites have established a unique symbiotic association with prokaryotic and eukaryotic microorganisms. A similar flora is also found in wood-eating roaches of the genus Cryptocercus . The study of symbiosis between termites and their intestinal microbes is of general interest, because due to this symbiotic interaction termites can feed on complex biopolymers such as wood. Flagellates and bacteria occur in the gut of lower termites, while higher termites possess only bacteria. In particular spirochetes are abundant in the termite gut. Apart from spirochetes and other more common bacteria, actinomycetes, yeasts and fungi have also been isolated from different species of termites. This review summarizes the distinct role of the intestinal flora in degradation of wood components such as cellulose, hemicellulose and lignin.     

THE ORIGIN OF PROTISTAN SYMBIONTS IN TERMITES AND COCKROACHES: A PHYLOGENETIC PERSPECTIVE

Abstract— The controversy over whether protist symbionts of Cryptocercus and termites were inherited from a common ancestor or transferred secondarily has been long standing. We present here the first phylogenetic test of these hypotheses and show that the transfer hypothesis is better supported.     

Phylogenetic relationship among cockroach families inferred from mitochondrial12S rRNA gene sequence

A number of phylogenies exist for cockroaches that differ in the postulated relationships among families and genera. The relationship of the wood-feeding genus, Cryptocercus, to other cockroach families and to termites, has generated considerable debate. Grandcolas (1994), based on morphological analysis, synonymized the family Cryptocercidae with Polyphagidae and placed the genus Cryptocercus in the subfamily Polyphaginae. To determine if an independent set of characters supports the placement of Cryptocercus in Polyphaginae, a phylogenetic analysis of relationships among representative genera of the five cockroach families was undertaken. DNA sequence of a -430 base pair portion of the mitochondrial small ribosomal subunit gene from representatives of Blattidae, Blattellidae, Blaberidae and Cryptocercus, previously published by Kambhampati (1995) and Kambhampati et al. (1996), and the homologous sequence from representatives of Polyphagidae were used in the analysis. A total of twenty cockroach taxa and three termite genera were included in the study. Because a recent study showed that Cryptocercus punctulatus consists of a species complex, DNA sequence from four individuals collected in different parts of the U.S.A. was included in the study. The trees estimated from parsimony and neighbour-joining analyses indicated that Cryptocercus is a monophyletic clade which is most closely related to members of Blattidae. Polyphagidae is indicated as a sister group to the Blattidae + Cryptocercus complex, suggesting that Polyphagidae may belong to the superfamily Blattoidea rather than to Blaberoidea as proposed by McKittrick (1964). Blaberidae and Blattellidae were sister groups as previously proposed. Based on the present analysis, I propose that the genus Cryptocercus be retained in the family Cryptocercidae. Cockroaches     

Symbiosis, morphology, and phylogeny of Hoplonymphidae (Parabasalia) of the wood-feeding roach Cryptocercus punctulatus

Anaerobic cellulolytic flagellate protists of the hindguts of lower termites and the wood-feeding cockroach Cryptocercus are essential to their host's ability to digest lignocellulose. Many have bacteria associated with their surfaces and within cytoplasmic vesicles-likely important symbioses as suggested by molecular and other data. Some of the most striking examples of these symbioses are in the parabasalid family Hoplonymphidae, but little or no data exist on the structural aspects of their symbioses, their relationships with bacteria through different life-cycle stages, or their diversity and phylogenetic relationships in Cryptocercus. We investigated these areas in the hoplonymphid genera Barbulanympha and Urinympha from Cryptocercus punctulatus using light and electron microscopy, and analysis of small subunit rRNA. Microscopy reveals variation in density of bacterial surface symbionts related to life-cycle stage, a glyococalyx possibly important in bacterial adhesion and/or metabolite exchange, and putative viruses associated with bacterial surface symbionts. Patterning of surface bacteria suggests protists emerging from the resistant (dormant) stage are colonized by a small population of bacterial cells, which then divide to cover their surface. Additionally, cytoplasmic protrusions from the protist are covered by bacteria. Phylogenetic analysis rejects the monophyly of Hoplonymphidae, suggesting multiple origins or losses of these bacterial symbioses.     

Phylogenetic position of Lophomonas striata Bütschli (Parabasalia) from the hindgut of the cockroach Periplaneta americana

Lophomonas striata is a multiflagellate parabasalid commensal in the hindgut of the omnivorous cockroaches Blatta orientalis and Periplaneta americana. Its closest relatives were traditionally thought to include similar multiflagellate parabasalids with a single flagellar area that degenerates during mitosis, such as Joenia and Kofoidia. However, molecular phylogenetic analyses have shown that "lophomonads" are not monophyletic. We have determined the SSU rRNA sequence of L. striata and we find that it branches sister to the Trichonymphida with strong support. This is surprising because all other lophomonads sampled to date branch within the Cristamonadida, and the order Trichonymphida (e.g. Trichonympha, Pseudotrichonympha, and Hoplonympha) is both morphologically coherent and monophyletic in SSU rRNA phylogenies. Trichonymphida, unlike the lophomonads, share a bilateral symmetry, in which their multiple flagella occur in two (or sometimes four) regions, and instead of degenerating upon mitosis, half of the flagella are passed to each daughter cell. The single apical flagellar region characteristic of lophomonads is therefore either plesiomorphic or it has arisen multiple times in parabasalids; our phylogenetic analyses and available ultrastructural evidence suggest the latter. Our results also suggest that parabasalid gut symbionts may have been vertically transmitted in cockroaches before the common ancestor of Cryptocercus and termites.     

Coevolution between a cockroach and its bacterial endosymbiont: a biogeographical perspective

Cryptocercus are subsocial, xylophagous cockroaches that live in temperate forests. Like other cockroaches, Cryptocercus harbour endosymbiotic bacteria in their fat bodies. Two species of Cryptocercus occur in the palaearctic, one each in eastern Russia and south-central China. In the USA, there are five species: one in the north-west and four in the south-east. Little is known about the relationship between the Eurasian and North American Cryptocercus or the causes of the disjunct distribution. Here, a molecular phylogeny for six out of the seven Cryptocercus species and their endosymbionts is inferred in an attempt to understand the evolution and biogeography of the genus. Our analysis showed that the North American Cryptocercus are monophyletic, suggesting that a single colonization event was followed by vicariance. There was complete concordance between the host and endosymbiont phylogenetic trees. Divergence estimates based on endosymbiont DNA sequences suggested that the palaearctic and nearctic Cryptocercus diverged 70-115 million years (Myr) ago and the eastern- and western-USA species diverged 53-88 Myr ago. These divergence estimates were correlated with biogeographical events, and a hypothesis is presented to explain the current distribution of Cryptocercus. Our findings suggest that Cryptocercus has had a long evolutionary history, dating back to the Jurassic.     

EVOLUTION OF MONOGAMY IN TERMITES

Two hypotheses have been proposed to explain the origin of lifetime monogamy in the Isoptera. The classic explanation is that (1) the male must be present to continually provide sperm for the vast number of eggs produced by the queen (Snyder, 1924: Brian, 1983). Thornhill & Alcock (1983) proposed that (2) synchrony in the availability of receptive females necessitates mate guarding; males subsequently gain if they improve the relative reproductive success of their sole partner.
Our review of the literature on termite flight behaviour, courtship behaviour, and incipient colony development indicates that neither of these two hypotheses satisfactorily explains the evolution of monogamy in termites. Because incipient colonies of lower termites exhibit a very low fecundity, it is doubtful that the continued presence of the male initially was due to the need for a continuous supply of spermatozoa. It is possible, however, that sperm requirements for the fertilization of numerous eggs over an extended period of time may be a factor in the persistence of the termites' monogamous mating system. Female alates are much more dispersed in time than implied by Thornhill & Alcock (1983) and there is no evidence of mate guarding. The importance of mate assistance is, however, supported by the literature. We propose a third hypothesis that incorporates the mate assistance element of the Thornhill & Alcock hypothesis: (3) the monogamous mating system of termites was structured by ecological constraints, namely, the low quality and scattered nature of their food/nesting material and the high costs of searching for a mate.     

Field observations of intercolony aggression and territory changes inHeterotermes aureus (Isoptera: Rhinotermitidae)

Intercolony aggression was observed for a southwestern desert subterranean termite, Heterotermes aureus(Snyder), in bait plots in a Sonoran Desert grassland in Arizona. Intermittent conflict took place at the sites of corrugatedpaper rolls on the boundary between two colonies. Rows of dead termites locked in combat were found within the corrugations, with additional dead termites usually in the soil beneath the roll. Dead soldiers constituted 64 to 100% of termites recovered from sites of intercolony conflict. Ongoing intercolony aggression is likely involved in the maintenance of discrete H. aureusterritories.     

Anaerobic carbon monoxide dehydrogenase diversity in the homoacetogenic hindgut microbial communities of lower termites and the wood roach

Anaerobic carbon monoxide dehydrogenase (CODH) is a key enzyme in the Wood-Ljungdahl (acetyl-CoA) pathway for acetogenesis performed by homoacetogenic bacteria. Acetate generated by gut bacteria via the acetyl-CoA pathway provides considerable nutrition to wood-feeding dictyopteran insects making CODH important to the obligate mutualism occurring between termites and their hindgut microbiota. To investigate CODH diversity in insect gut communities, we developed the first degenerate primers designed to amplify cooS genes, which encode the catalytic (β) subunit of anaerobic CODH enzyme complexes. These primers target over 68 million combinations of potential forward and reverse cooS primer-binding sequences. We used the primers to identify cooS genes in bacterial isolates from the hindgut of a phylogenetically lower termite and to sample cooS diversity present in a variety of insect hindgut microbial communities including those of three phylogenetically-lower termites, Zootermopsis nevadensis, Reticulitermes hesperus, and Incisitermes minor, a wood-feeding cockroach, Cryptocercus punctulatus, and an omnivorous cockroach, Periplaneta americana. In total, we sequenced and analyzed 151 different cooS genes. These genes encode proteins that group within one of three highly divergent CODH phylogenetic clades. Each insect gut community contained CODH variants from all three of these clades. The patterns of CODH diversity in these communities likely reflect differences in enzyme or physiological function, and suggest that a diversity of microbial species participate in homoacetogenesis in these communities.     

Phylogenetic identification of symbiotic protists of five Chinese Reticulitermes species indicates a cospeciation of gut microfauna with host termites

Symbiotic protists play important roles in the wood digestion of lower termites. Previous studies showed that termites generally possess host-specific flagellate communities. The genus Reticulitermes is particularly interesting because its unique assemblage of gut flagellates bears evidence for transfaunation. The gut fauna of Reticulitermes species in Japan, Europe, and North America had been investigated, but data on species in China are scarce. For the first time, we analyzed the phylogeny of protists in the hindgut of five Reticulitermes species in China. A total of 22 protist phylotypes were affiliated with the family Trichonymphidae, Teranymphidae, Trichomonadidae, and Holomastigotoididae (Phylum Parabasalia), and 45 protist phylotypes were affiliated with the family Pyrsonymphidae (Phylum Preaxostyla). The protist fauna of these five Reticulitermes species is similar to those of Reticulitermes species in other geographical regions. The topology of Trichonymphidae subtree was similar to that of Reticulitermes tree. All Preaxostyla clones were affiliated with the genera Pyrsonympha and Dinenympha (Order Oxymonadida) as in the other Reticulitermes species. The results of this study not only add to the existing information on the flagellates present in other Reticulitermes species but also offer the opportunity to test the hypotheses for the coevolution of symbiotic protists with their host termites.     

Molecular phylogeny and biogeography of the Korean woodroaches Cryptocercus spp

Phylogenetic relationships and biogeography of Northeast Asian Cryptocercus were inferred based on the DNA sequences of mitochondrial COII and 16S rRNA genes and nuclear 18S rRNA gene. The results suggest that two clades exist in Korean populations. The southwestern population (Cryptocercus from Jiri-san) was more closely related to the populations from Northeast China and eastern Russia than to all the other Korean Cryptocercus. According to molecular-based estimated divergence times, the divergence event occurred between Cryptocercus in Jiri-san, Northeast China and eastern Russia and those in the remaining South Korea during the Miocene (7.5-17.4Myr ago), and then the divergence event between Cryptocercus in Jiri-san and those in Northeast China and eastern Russia occurred 0.8-1.9Myr ago. In the Korean Peninsula, Jiri-san is located in the most southwestern region among the high mountains surveyed. The location is the farthest from Northeast China and eastern Russia among sampling localities in South Korea. Thus, it was unexpected that the southwestern populations are more closely related to those from Northeast China and eastern Russia rather than to the other Korean Cryptocercus. Based on Korean topography and estimated divergence times, possible scenarios are proposed for the current geographical distribution of Korean Cryptocercus.