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Intracellular endosymbionts have reduced genomes that progressively lose genes at a timescale of tens of million years. We previously reported that gene loss rate is linked to mutation rate in Blattabacterium , however, the mechanisms causing gene loss are not yet fully understood. Here, we carried out comparative genomic analyses on the complete genome sequences of a representative set of 67 Blattabacterium strains, with sizes ranging between 511 and 645 kb. We found that 200 of the 566 analyzed protein-coding genes were lost in at least one lineage of Blattabacterium , with the most extreme case being one gene that was lost independently in 24 lineages. We found evidence for three mechanisms influencing gene loss in Blattabacterium. First, gene loss rates were found to increase exponentially with the accumulation of substitutions. Second, genes involved in vitamin and amino acid metabolism experienced relaxed selection in Cryptocercus and Mastotermes , possibly triggered by their vertically inherited gut symbionts. Third, we found evidence of epistatic interactions among genes leading to a "domino effect" of gene loss within pathways. Our results highlight the complexity of the process of genome erosion in an endosymbiont. [ABSTRACT FROM AUTHOR]

Sterile castes are a defining criterion of eusociality; investigating their evolutionary origins can critically advance theory. In termites, the soldier caste is regarded as the first acquired permanently sterile caste. Previous studies showed that juvenile hormone (JH) is the primary factor inducing soldier differentiation, and treatment of workers with artificial JH can generate presoldier differentiation. It follows that a shift from a typical hemimetabolous JH response might be required for soldier formation during the course of termite evolution within the cockroach clade. To address this possibility, analysis of the role of JH and its signaling pathway was performed in the termite Zootermopsis nevadensis and compared with the wood roach Cryptocercus punctulatus, a member of the sister group of termites. Treatment with a JH analog (JHA) induced a nymphal molt in C. punctulatus. RNA interference (RNAi) of JH receptor Methoprene tolerant (Met) was then performed, and it inhibited the presoldier molt in Z. nevadensis and the nymphal molt in C. punctulatus. Knockdown of Met in both species inhibited expression of 20-hydroxyecdysone (20E; the active form of ecdysone) synthesis genes. However, in Z. nevadensis, several 20E signaling genes were specifically inhibited by Met RNAi. Consequently, RNAi of these genes were performed in JHA-treated termite individuals. Knockdown of 20E signaling and nuclear receptor gene, Hormone receptor 39 (HR39/FTZ-F1β) resulted in newly molted individuals with normal worker phenotypes. This is the first report of the JH--Met signaling feature in termites and Cryptocercus. JH-dependent molting activation is shared by both taxa and mediation between JH receptor and 20E signalings for soldier morphogenesis is specific to termites. [ABSTRACT FROM AUTHOR]

Almost all examined cockroaches harbor an obligate intracellular endosymbiont, Blattabacterium cuenoti. On the basis of genome content, Blattabacteriumhas been inferred to recycle nitrogenwastes and provide amino acids and cofactors for its hosts. Most Blattabacterium strains sequenced to date harbor a genome of ~630 kbp, with the exception of the termite Mastotermes darwiniensis (~590 kbp) and Cryptocercus punctulatus (~614 kbp), a representative of the sister group of termites. Such genome reductionmay have led to the ultimate loss of Blattabacteriumin all termites other thanMastotermes. In this study, we sequenced 11 newBlattabacteriumgenomes fromthree species of Cryptocercus in order to shed light on the genomic evolution of Blattabacterium in termites and Cryptocercus. All genomes of Cryptocercus-derived Blattabacterium genomes were reduced (~614 kbp), except for that associated with Cryptocercus kyebangensis, which comprised 637 kbp. Phylogenetic analysis of these genomes and their content indicates that Blattabacterium experienced parallel genome reduction in Mastotermes and Cryptocercus, possibly due to similar selective forces. We found evidence of ongoing genome reduction in Blattabacterium from three lineages of the C. punctulatus species complex, which independently lost one cysteine biosynthetic gene. We also sequenced the genome of the Blattabacterium associated with Salganea taiwanensis, a subsocial xylophagous cockroach that does not vertically transmit gut symbionts via proctodeal trophallaxis. This genome was 632 kbp, typical of that of nonsubsocial cockroaches. Overall, our results show that genome reduction occurred on multiple occasions in Blattabacterium, and is still ongoing, possibly because of new associations with gut symbionts in some lineages. [ABSTRACT FROM AUTHOR]

The distribution of a species is determined by a set of ecological correlates (biotic and abiotic factors) and historical phenomena that define and constrain its ecological niche. By examining the geographical projection of the ecological niche, it is possible to identify areas that are suitable for the species ecologically but that are not actually inhabited. Previous studies have used such discords to anticipate the existence of undescribed species; the absence of species may also result from historical barriers that have prevented colonization of the area. Thus, discords between potential and realized niches of a species may result from aspects of the species’s biology (e.g. lack of dispersal ability, specific habitat requirements) or from barriers to dispersal. In this study, we developed ecological niche models of the five Nearctic species of wood-feeding cockroaches in the genus Cryptocercus. One species, C. clevelandi, occurs in the western USA and four ( C. darwini, C. garciai, C. punctulatus, C. wrighti) are distributed in the Appalachian Mountains in the eastern USA. In general, modelled niches for all species showed ecological restriction relative to the total range of available conditions. Niche models for the eastern USA species predicted the geographical distributions of the other eastern USA species, with the exception of C. garciai, suggesting general overall conservatism in ecological characteristics. Some interspecific differences in modelled niches were also apparent. In general, C. clevelandi was predicted to occupy cooler and drier areas relative to the eastern USA species; among the eastern USA species, C. darwini and C. garciai were predicted to inhabit warmer areas relative to C. punctulatus and C. wrighti. Interspecific differences and similarities were consistent with the phylogenetic relationships among Cryptocercus species previously reported. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90, 457–466. [ABSTRACT FROM AUTHOR]

Members of the genus Cryptocercus are xylophagous, wingless, subsocial cockroaches that inhabit decaying logs in temperate forests. Given their winglessness, subsocial living, and the patchy distribution of food resources (decomposing logs), it is likely that Cryptocercus populations are substructured. Allozyme variation at eight polymorphic loci was assayed for 10 subpopulations of Cryptocercus darwini and 13 subpopulations of Cryptocercus wrighti, both of which are distributed in the Appalachian Mountains. The mean FIS was 0.13 and FST was about 0.25 for both C. darwini and C. wrighti. The relatedness among individuals of a subpopulation of both species was not significantly different from that expected among full sibs. In terms of how genetic variation is partitioned, C. darwini and C. wrighti differed from each other substantially. Most of the genetic variation occurred among subpopulations of C. wrighti in the same region and among subpopulations of C. darwini in different regions. We discuss the factors that may have contributed to the observed similarities and differences in the breeding structure of the two species. [ABSTRACT FROM AUTHOR]

In a recent paper, Kambhampati, Clark & Brock ( Biological Journal of the Linnean Society 2002; 75: 163–172) suggested that members of the wood-feeding cockroach genus Cryptocercus are differentially adapted to two features of the environment: host log species and elevation. A re-examination of the evidence, however, fails to support their hypothesis. First, their analysis of host preferences was based on a general description of forest type, rather than on the level at which host choice occurs: the dead tree on the forest floor. Cryptocercus in both East Asia and in the eastern United States have been collected from a range of evergreen and deciduous logs. Although C. clevelandi in the western United States is associated primarily with conifers, no evidence of host adaptation exists. Second, there is no support for the described evolutionary trend toward low-altitude habitats among karyotype groups of C. punctulatus in the eastern United States. The findings of Kambhampati et al. are based on inadequate sampling; they did not include the highest and most topographically complex regions of the Southern Appalachian Mountains, nor the lower elevation border regions to the north and east of the range. An analysis of elevational data from 71 collection sites revealed no significant difference in the range of altitudes at which karyotype groups of C. punctulatus are found. In contrast to the suggestions of these authors, a lack of specialization with regard to altitude and host logs was probably the factor that allowed all taxa in the genus to thrive during climatically driven shifts in the geographical location and plant species composition of northern hemisphere mesic forests. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 223–233. [ABSTRACT FROM AUTHOR]