Mantaro Hironaka

Phylogenetic position and peculiar genetic traits of a midgut bacterial symbiont of the stinkbug Parastrachia japonensis.

ABSTRACT The stinkbug Parastrachia japonensis (Hemiptera: Parastrachiidae) is known for its prolonged prereproductive nonfeeding period, maternal care of eggs in an underground nest, and maternal collection and provisioning of food (fruits) for nymphs. A previous study suggested that a bacterial symbiont is involved in uric acid recycling in this insect during the nonfeeding period, but the identity of this symbiont has not been determined. Here we characterized a novel bacterial symbiont obtained from P. japonensis. Molecular phylogenetic analyses based on 16S rRNA, gyrB, and groEL gene sequences consistently indicated that this symbiont constituted a distinct lineage in the Gammaproteobacteria that has no close relatives but is allied with gut symbionts of acanthosomatid and plataspid stinkbugs, as well as with endocellular symbionts of sharpshooters, tsetse flies, and aphids. The symbiont genes had a remarkably AT-biased nucleotide composition and exhibited significantly accelerated molecular evolution. The symbiont genome was extremely reduced; its size was estimated to be 0.85 Mb. These results suggest that there has been an intimate host-symbiont association over evolutionary time. The symbiont was localized in swollen crypts in a posterior part of the midgut, which was a specialized symbiotic organ. The possibility that the symbiont is involved in uric acid recycling is discussed. The designation “Candidatus Benitsuchiphilus tojoi” is proposed for the symbiont.

Presence of Rhodopsin and Porphyropsin in the Eyes of 164 Fishes, Representing Marine, Diadromous, Coastal and Freshwater Species—A Qualitative and Comparative Study

There are two types of visual pigments in fish eyes; most marine fishes have rhodopsin, while most freshwater fishes have porphyropsin. The biochemical basis for this dichotomy is the nature of the chromophores, retinal (A1) and 3‐dehydroretinal (A2), each of which is bound by an opsin. In order to study the regional distribution of these visual pigments, we performed a new survey of the visual pigment chromophores in the eyes of many species of fish. Fish eyes from 164 species were used to examine their chromophores by high‐performance liquid chromatography—44 species of freshwater fish, 20 of peripheral freshwater fish (coastal species), 10 of diadromous fish and 90 of seawater fish (marine species) were studied. The eyes of freshwater fish, limb freshwater fish and diadromous fish had both A1 and A2 chromophores, whereas those of marine fish possessed only A1 chromophores. Our results are similar to those of previous studies; however, we made a new finding that fish which live in freshwater possessed A1 if living near the sea and A2 if living far from the sea if they possessed only one type of chromophore.

Diverse strategies for vertical symbiont transmission among subsocial stinkbugs.

Sociality may affect symbiosis and vice versa. Many plant-sucking stinkbugs harbor mutualistic bacterial symbionts in the midgut. In the superfamily Pentatomoidea, adult females excrete symbiont-containing materials from the anus, which their offspring ingest orally and establish vertical symbiont transmission. In many stinkbug families whose members are mostly non-social, females excrete symbiont-containing materials onto/beside eggs upon oviposition. However, exceptional cases have been reported from two subsocial species representing the closely related families Cydnidae and Parastrachiidae, wherein females remain nearby eggs for maternal care after oviposition, and provide their offspring with symbiont-containing secretions at later stages, either just before or after hatching. These observations suggested that sociality of the host stinkbugs may be correlated with their symbiont transmission strategies. However, we found that cydnid stinkbugs of the genus Adomerus, which are associated with gammaproteobacterial gut symbionts and exhibit elaborate maternal care over their offspring, smear symbiont-containing secretions onto eggs upon oviposition as many non-social stinkbugs do. Surface sterilization of the eggs resulted in aposymbiotic insects of slower growth, smaller size and abnormal body coloration, indicating vertical symbiont transmission via egg surface contamination and presumable beneficial nature of the symbiosis. The Adomerus symbionts exhibited AT-biased nucleotide compositions, accelerated molecular evolutionary rates and reduced genome size, while these degenerative genomic traits were less severe than those in the symbiont of a subsocial parastrachiid. These results suggest that not only sociality but also other ecological and evolutionary aspects of the host stinkbugs, including the host-symbiont co-evolutionary history, may have substantially affected their symbiont transmission strategies. (250 words).

Pre- and post-hatch trophic egg production in the subsocial burrower bug, Canthophorus niveimarginatus (Heteroptera: Cydnidae).

In recent years, three terrestrial bugs, Adomerus triguttulus and Sehirus cinctus (Cydnidae) and the closely related Parastrachia japonensis (Parastrachiidae), have been the focus of several fascinating studies because of the remarkable, extensive parental care they were found to display. This care includes egg and nymph guarding, production of trophic eggs, unfertilized, low cost eggs that are used as food by newly hatched nymphs, and progressive provisioning of the host seed. In this study, we have investigated yet a third related Asian cydnid, Canthophorus niveimarginatus, with regard to the possible occurrence of some or all of these complex traits in order to assess how widespread these maternal investment patterns are in this group of insects and to better understand the implications of their manifestations from an evolutionary context. Manipulative experiments were carried out in the lab to determine whether females provision nests. Observational and egg removal studies were carried out to determine whether trophic eggs are produced, and, if they are, their possible impact on nymphal success. The findings revealed that C. niveimarginatus does, in fact, progressively provision young, and this species also displays all of the other behaviors associated with extended parental care in subsocial insects. Moreover, unlike the other two related species, which place trophic eggs on the surface of the original egg mass, C. niveimarginatus produces both pre- and post-hatch trophic eggs. Nymphs deprived of access to post-hatch trophic eggs had significantly lower body weight and survival rate than those that fed on them. To our knowledge, this is the first time the production of both pre- and post-hatch trophic eggs has been demonstrated in insects outside the Hymenoptera. In this paper, we qualitatively and quantitatively demonstrate the provisioning behavior and patterns of trophic egg production in C. niveimarginatus. When and how trophic eggs are produced and delivered to young should have important correlations with the ecological and life history constraints under which a species has evolved. Thus, we also discuss the possible ecological and life history factors that favor the evolution of post-hatch trophic eggs.

Water Uptake via Two Pairs of Specialized Legs in Ligia exotica (Crustacea, Isopoda)

When individuals of Ligia exotica were exposed to dry environments, their weight decreased within 3 h to 90% of the initial weight. When the animals were subsequently presented with wet paper, pereiopods VI and VII were firmly apposed and moved around until their tips were stationary for some seconds. Subsequently the pleopods became soaked in water and the body weight recovered. Morphological observations revealed hollow structures on the surface of the dactylus and propodus of pereiopods VI and VII, and a series of thin cuticular protrusions, oriented in several parallel lines, from the propodite to the ischiopodite of pereiopod VI and on the basipodite of pereiopod VII. The width between the parallel lines varied little, but the total width of the regular lines increased linearly with increasing body size. When isolated caudal pereiopods were immersed, beginning at the distal end, in water, water flowed along pereiopod VI as far as the proximal end of the ischiopodite, but water flow along pereiopod VII occurred only in conjunction with the basipodite. This means that water uptake with the legs requires both pereiopods VI and VII and can be achieved only when these legs are closely apposed.

Trophic eggs compensate for poor offspring feeding capacity in a subsocial burrower bug

Various animals produce inviable eggs or egg-like structures called trophic eggs, which are presumed to be an extended maternal investment for the offspring. However, there is little knowledge about the ecological or physiological constraints associated with their evolutionary origin. Trophic eggs of the seminivorous subsocial burrower bug (Canthophorus niveimarginatus) have some unique characteristics. Trophic eggs are obligate for nymphal survival, and first-instar nymphs die without them. To identify the cause of nymphal death, we hypothesized that first-instar nymphs starve to death because they cannot feed on anything but trophic eggs. Although first-instar nymphs fed on artificially exposed endosperm did survive, nymphs that were provided with intact seed were not able to penetrate the seed vessel and starved to death. Another hypothesis that trophic eggs play a role in transferring the midgut symbiont, essential for survival in heteropteran bugs, from mother to offspring was rejected because almost all nymphs had retained the symbiont without feeding on trophic eggs. These results suggest that poor feeding capacity of the offspring is the cause of nymphal death, and the important constraint that promotes the evolution of the curious trophic egg system in C. niveimarginatus.

Maternal-Care Behaviour in Adomerus variegatus (Hemiptera: Cydnidae)

Abstract Subsociality involving provisioning for offspring has been reported for one shield bug and three burrower bug species (Hemiptera: Pentatomoidea: Parastrachiidae and Cydnidae: Sehirinae). We present the first report of subsocial behaviour in the burrower bug Adomerus variegatus (Signoret), focusing on manifestations of maternal-care, specifically the production of trophic eggs, guarding of offspring, and progressive provisioning. In our study, each female produced an egg mass that included some trophic eggs. Prior to nymphal hatch, females remained in their nests and showed egg mass guarding behaviour. Mothers started provisioning behaviour a few hours after nymphal hatch. Each mother dragged a seed (larger than her body) with her proboscis to the nest as food for the nymphs. These findings suggest that A. variegatus shows maternal-care behaviours similar to those reported in some other pentatomoid species and that trophic egg production and nest provisioning have evolved as interrelated processes.

The Directional Homing Behaviour of the Subsocial Shield Bug, Parastrachia japonensis (Heteroptera: Cydnidae), under Different Photic Conditions

Abstract The female subsocial shield bug, Parastrachia japonensis, provisions its nymphs by foraging on the ground in the forest during the Japanese rainy season, and the bug uses homing navigation to drag a drupe back to its burrow by the shortest route during the day. To study whether or not this bug performs this provisioning behaviour under different photic conditions, we observed the homing behaviour and homing direction of bugs in the field around the clock and/or under various weather conditions. The bugs foraged the whole day during the busiest provisioning period, and the number of walking bugs was not affected by the different weather conditions. Such navigational behaviour, regardless of the time of the day and the weather conditions, is rare in insect navigation. To test whether the bug uses visual cues, we covered the compound eyes and ocelli with opaque or clear paint just before homing began. During the day and at night, and in all weather conditions, the homing direction of blind bugs, but not those with clear-painted eyes was disoriented, indicating that this species uses visual cues dominantly under all photic conditions.

Canopy compass in nocturnal homing of the subsocial shield bug, Parastrachia japonensis (Heteroptera: Parastrachiidae)

In contrast to an open environment where a specific celestial cue is predominantly used, visual contrast of canopies against the sky through the gap, known as canopy cues, is known to play a major role for visually guided insect navigators in woodland habitats. In this paper, we investigated whether a subsocial shield bug, Parastrachia japonensis, could gauge direction using canopy cues on a moonless night. The results show that they could perform the round trip foraging behaviour even in an experimental arena with only an artificial round gap opened in the ceiling of the arena and adjust their homing direction for a new azimuth when the gap was rotated. Thus, P. japonensis can use slightly brighter canopy cues as a compass reference but not complex landmarks during nocturnal homing behaviour.

Round-the-clock Homing Behavior of a Subsocial Shield Bug, Parastrachia japonensis (Heteroptera: Parastrachiidae), Using Path Integration

Abstract Females of the subsocial shield bug, Parastrachia japonensis (Parastrachiidae), are central-place foragers, collecting drupes for their young from nearby host trees by walking along the forest floor both during the day and at night. Because burrows are often some distance from the drupe-shedding tree, the bugs must repeatedly leave their burrows, search for drupes, and return to the burrows. After a bug leaves its burrow, it searches arduously until it encounters a drupe. When a drupe is obtained, the bug always takes the shortest route back to its burrow. It has been clarified that this bug utilizes path integration during diurnal provisioning excursions. In this paper, we examined nocturnal behavior and some parameters of the path integration utilized by P. japonensis. There were no observable differences between day and night in the patterns of foraging and direct-homing behavior. When the bug was displaced to another position during the day or night, it always walked straight toward the fictive burrow, the site where the burrow should be if it had been displaced along with the bug, and then displayed searching behavior in the vicinity of the fictive burrow. The distance of the straight run corresponded accurately with a straight line between the burrow and the place where the bug obtained the drupe. These results indicate that P. japonensis orients toward the burrow using path integration both during diurnal and nocturnal provisioning behavior.