Published papers

A 2012–13 survey on Penang Island, Malaysia, revealed the existence of both Drosophila ananassae and Drosophila parapallidosa, the latter of which carries chromosomes Y and 4 from D. ananassae and thus is of hybrid origin. We collected the flies again from the same location in 2018. The hybrid population remained present, which suggests that the D. parapallidosa of hybrid origin does not represent a mere transient population but is stable. Why do these two species coexist irrespective of gene flow? We realized that body size is generally larger in D. ananassae than in D. parapallidosa, which constitutes a new character with which to discriminate these species; previously the number of sex comb teeth was the only diagnostic trait. Character displacement was not detected, however, for those traits. We crossed these two species, which resulted in offspring that had an altered genomic constitution. The body size of D. ananassae was dominant, and the presence of chromosomes Y and 4 did not have a significant effect on body size. By contrast, the presence of chromosome 4 from D. ananassae significantly affected the number of sex comb teeth. Even flies having a genomic constitution similar to that of the Penang D. parapallidosa exhibited a number of sex comb teeth that was intermediate between the two species. We propose that the D. parapallidosa sex comb character underwent selection during evolution of the Penang Island population. Reproductive interference between the species, presumably caused by signal jamming, was detected.

Animals can show bias in their use of laterally paired organs that do not have any conspicuous anatomical differentiation between the right and left organs. Like right handedness in humans, males of the giant earwig Labidura riparia (Labiduridae: Labidurinae) preferentially (~90%) use the right one of their laterally paired penises for copulation. To elucidate the evolutionary origin of this lateralization, patterns of penis use were examined for the related species of the genus Nala (Labiduridae: Nalinae). In multiple populations and broods of both Nala lividipes and Nala nepalensis, males that were ready to use the right or left penis were equally frequent, providing a striking contrast to Labidura. Surgical ablation of one of the two penises revealed that both penises are functionally competent in N. lividipes. Nevertheless, each male almost consistently used only one of the paired penises, either the right or the left one. Changes in penis use were estimated to occur only once per 64-143 days per male. The present study is the first report of individual-level lateralization for animal genitalia that do not show any conspicuous anatomical differentiation between the right and left organs. Possible advantages of lateralization are discussed in relationship to co-evolution of the genitalia between the sexes.

The sex ratio behavior of parasitoid wasps in the genus Melittobia is scandalous. In contrast to the prediction of Hamilton's local mate competition theory, and the behavior of numerous other species, their extremely female-biased sex ratios (1-5% males) change little in response to the number of females that lay eggs on a patch. We examined the mating structure and fitness consequences of adjusting the sex ratio in M. australica and found that (1) the rate of inbreeding did not differ from that expected with random mating within each patch; (2) the fitness of females that produced less female-biased sex ratios (10 or 20% males) was greater than that of females who produced the sex ratio normally observed in M. australica. These results suggest that neither assortative mating nor asymmetrical competition between males can explain the extreme sex ratios. More generally, the finding that the sex ratios produced by females led to a decrease in their fitness suggests that the existing theory fails to capture a key aspect of the natural history of Melittobia, and emphasizes the importance of examining the fitness consequences of different sex ratio strategies, not only whether observed sex ratios correlate with theoretical predictions.

Ovoviviparity and viviparity have evolved independently multiple times in animals. Although females exhibit extensive parental care of their eggs, (ovo) viviparity has only been reported in a few species of free-living, nonepizoic earwigs. In contrast, to date, all the studied members of families Arixeniidae and Hemimeridae, which live on mammals, are viviparous. We herein report ovoviviparity in the tropical earwig species, Spongovostox semiflavus (Bormans, 1894) (Forficuloidea: Spongiphoridae: Spongiphorinae). We observed that females of this species retain well-developed embryos within the ovaries and then lay them with complete egg envelopes just before hatching. An average of 9.4 embryos concurrently developed in a female's body. A similar condition has been reported for only one other species Marava arachidis (Yarsin, 1860), in the subfamily Spongiphorinae. Without additional mating, Spo. semiflavus females produced at least three clutches, consisting of an average of nine offspring within a period of 14-27 d. Both Spo. semiflavus and M. arachidis males are characterized by elongated male genitalia that are more than twice as long as their body lengths. Interestingly, elongated male genitalia are also present in the two other spongiphorids for which (ovo) viviparity has been reported. We discuss the causes of the potential convergence of the evolution of the male genital structure and the development of (ovo) viviparity in females.

In the suborder Forficulina (order Dermaptera; earwigs), the families Apachyidae, Anisolabididae, and Labiduridae form a possibly paraphyletic assemblage Mesodermaptera, which is characterized by laterally paired penes that point in opposite directions (anterior and posterior) when in repose. A previous study of a labidurid species, Labidura riparia (Pallas, 1773), revealed that males predominantly use the right penis for insemination, although both penes are functional. This result suggests that labidurids may have retained handedness in penis use, leading eventually to the loss of the less frequently used left penis in the common ancestor of the Eudermaptera, estimated to be the sister clade of Labiduridae. However, HAAS & KUKALOVA-PECK (2001: European Journal of Entomology 98: 445-509) included another representative of Labiduridae, Allostethus indicum (Burmeister, 1838) (Allostethinae) in their extensive phylogenetic analysis, and found that hindwing structures of this species showed multiple plesiomorphic characteristics, making Labiduridae (sensu lato) a polyphyletic assemblage. The aim of the present study was to describe the genital structures and copulation of A. indicum in detail. The genital morphologies of a congener and other labidurid genera (Nala, Labidura, Forcipula) were also examined for comparison. Male A. indicum predominantly used (or were ready to use) the right penis for insemination, as in L. riparia. However, the possible female genital structure responsible for this handedness differed between the two species: the base of the spermatheca showed a striking spiral in L. riparia, while the spermatheca opened to an asymmetrically arranged vagina in Allostethus. Female Allostethus also possessed a pair of elongated thin tubes, which have to date been reported only for the basal groups of earwigs, as well as the vagina and the internally branched spermatheca. The developmental origin of an ovipositor-like sutucture also differs between Allostethus and the other labidurids examined, lending support to the polyphyly of Labiduridae sensu lato.

Based on samples collected during surveys of Brazilian cave fauna, seven earwig species are reported: Cylindrogaster cavernicola Kamimura, sp. n., Cylindrogaster sp. 1, Cylindrogaster sp. 2, Euborellia janeirensis, Euborellia brasiliensis, Paralabellula dorsalis, and Doru luteipes, as well as four species identified to the (sub) family level. To date, C. cavernicola Kamimura, sp. n. has been recorded only from cave habitats (but near entrances), whereas the other four organisms identified at the species level have also been recorded from non-cave habitats. Wings and female genital structures of Cylindrogaster spp. (Cylindrogastrinae) are examined for the first time. The genital traits, including the gonapophyses of the 8th abdominal segment shorter than those of the 9th segement, and venation of the hind wings of Cylindrogastrinae correspond to those of the members of Diplatyidae and not to Pygidicranidae. This is the first synopsis of cave-dwelling earwigs of Brazil, one of the most species-rich areas of Dermaptera in the world.

© Y. Kamimura, R.L. Ferreira. The genus Mesodiplatys (Dermaptera: Diplatyidae) comprises eight species from Madagascar and one species from Peru. Based on a sample collected from a cave in Brazil, a new species of this genus, Mesodiplatys falcifer Kamimura, sp. n., is described as the second species from South America. Based on a reexamina-tion of the holotype of Mesodiplatys insularis, a revised key to Mesodiplatys species is provided. The definitions of the genera Mesodiplatys and Haplodiplatys and the family Haplodiplatyidae are also reconsidered.

The evolution of laterality, that is the biased use of laterally paired, morphologically symmetrical organs, has attracted the interest of researchers from a variety of disciplines. It is, however, difficult to quantify the fitness benefits of laterality because many organs, such as human hands, possess multimodal functions. Males of the earwig Labidura riparia (Insecta: Dermaptera: Labiduridae) have morphologically similar laterally paired penises, only one of which is used for inseminating the female during a single copulation bout, and thus provide a rare opportunity to address how selection pressure may shape the evolution of population-level laterality. Our population studies revealed that in 10 populations, located at 2.23–43.3° north, the right penis is predominantly used for copulating (88.6%). A damaged penis was found in 23% of rare left-handers, suggesting that the left penis can function as a spare when the right one is damaged. By pairing L. riparia females with surgically manipulated males, we found that males forced to use the right penis outperformed left-handed males in copulation (the probability of establishing genital coupling during the 1-hr observation period: odds ratio [OR] of 3.50) and insemination (probability of transferring a detectable amount of sperm: OR of 2.94). This right-handed advantage may be due to the coiled morphology of the sperm storage organ with a right-facing opening. Thus, female genital morphology may play a significant role in the evolution of handedness and may have acted as a driving force to reduce penis number in related taxa.