The Formosan termite Coptotermes formosanus Shiraki is a well-known invasive pest that causes severe damage to wooden structures in many parts of the world.Although several studies examined its phylogeographic patterns using a few mitochondrial genes, the phylogenetic relationships among C. formosanus are poorly understood because of the small number of mutations known among its mitochondrial genes. To provide a useful genetic tool for further analyses, we analyzed the complete mitochondrial genome sequence of C. formosanus using specimens collected from three isolated islands in the Ryukyu Archipelago of Japan. The circular mitogenome of these termites consisted of genes encoding 22 transfer RNAs, two ribosomal RNAs, and 13 mitochondrial proteins, as is the case for most animal mitochondrial genomes. The G ? C content was 34.1%, and the total length varied slightly between 16,234 and 16,236 base pairs. The complete mitochondrial genomes of the three populations were more than 99.9% identical to each other and showed differences at six nucleotide positions. The COII, 12S rRNA, and 16S rRNA genes that are commonly used for phylogenetic analyses revealed only one substitution or no substitutions. The mitogenome sequences determined here should contribute to the design of new molecular markers for the clarification of the historical distribution process of C. formosanus and for further phylogenetic analyses with this and related termite species.
In most lower termites, colonies are headed by neotenic reproductives of both sexes after the primary reproductives (i.e., the queen and king) are lost. The production of a neotenic sexual is inhibited by the presence of a primary reproductive of the same sex. We found an exception in the caste system of the dry wood termite Neotermes koshunensis (Kalotermitidae). The neotenic caste is exclusively male. Moreover, production of male neotenics is completely inhibited not only by the presence of a king but also by the presence of a queen. Therefore, it is likely to be difficult for N. koshunensis colonies to recover their reproductive pairs.
Sex allocation is one of the most studied traits in evolutionary biology because its theoretical predictions match the empirical data. Here, using the Ryukyu dry-wood termite Neotermes sugioi, we investigated several factors that could bias the sex allocation in three populations (Okinawa, Ishigaki/Iriomote, and Yonaguni). Our survey showed that there were more queen-only colonies than king-only colonies in these populations, suggesting a longer lifespan of the queens than that of the kings. In this condition, sex-asymmetric reproductive value (SRV) theory predicts female bias, because even after the short-lived kings die, the long-lived queens can continue reproduction with their sons. However, sex allocation in this species seemed to be biased toward males. Furthermore, we examined the possibility of intrasexual competition among siblings (ICS). If ICS is the cause of the bias, the allocation is expected to change depending on the total investment in sexual offspring. However, the biomass of both male and female alates increased linearly with the increase in the total biomass of the alates in these populations. Thus, neither the SRV nor the ICS theory could explain the male-biased sex ratio of N. sugioi. On the basis of these results, we discuss the remaining possibilities in this species.
Sex‐determination systems often show remarkable diversity in upstream signals, although downstream genes are broadly conserved. Therefore, the downstream genes have been investigated in various taxa, but the most upstream signals determining sex in insects have been well‐described mainly in model organisms, including fruit flies and honey bees, and not in hemimetabolous insects such as termites. Identification of sex‐linked genetic markers in termites is important to the survey of primary sex‐determination signals. Here, we report male‐specific alleles at the microsatellite locus NK12‐1 in the Ryukyu drywood termite Neotermes sugioi (Kalotermitidae). This study provides the third example of a genetic marker linked with sexual phenotype in termites, which is a small but important step to elucidate the evolutionary process of the sex‐determination system in termites.
Antennal cropping, a behavior inferred to exist because queens and kings have shorter antennae than fresh alates, is widespread in lower-termites. However, the proximate and ultimate mechanisms underlying this phenomenon remain unclear. We studied the occurrence of antennal cropping in queens and kings of the dry-wood termite Neotermes koshunensis (Kalotermitidae). The tip structure of the cropped antennae of queens and kings showed the edges folded inward. The same inward folding was also observed in some antennae cropped using the mandible of a termite. Antennal cropping also occurred in isolated dealates reared in isolation. This implies that selfcropping is an important proximate mechanism of antennal cropping in this termite. Previous studies inferred that antennal cropping may play a key role in the life-history of alates at the colonyfounding stage. However, we also found antennal cropping in adultoid reproductives (secondary reproductives) that had not experienced colony founding. We propose a new hypothesis that antennal cropping is important for individuals in regulating their physiology when they change from the non-reproducing to the reproducing phase. The adaptive significance of antennal cropping may be to reduce the inhibitory effect of pheromones released by the reproductives on their own reproduction.
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