Mamoru Takata

Identification, characterization and full-length sequence analysis of a novel dsRNA virus isolated from the arboreal ant Camponotus yamaokai.

A novel dsRNA virus was identified from the arboreal ant Camponotus yamaokai. The complete nucleotide sequence analysis of the virus revealed that the virus consisted of 5704 bp with two ORFs. ORF1 (3084 nt) encoded a putative capsid protein. ORF2 (1977 nt) encoded a viral RNA-dependent RNA polymerase (RdRp). ORF2 could be translated as a fusion with the ORF1 product by a - 1 frameshift in the overlapping ORF1. Phylogenetic analyses based on the RdRp revealed that the virus from C. yamaokai was most likely a novel totivirus, but it was not closely related to the previously known totiviruses in arthropods. Transmission electron microscopy revealed isometric virus particles of ~30 nm diameter in the cytoplasm, which was consistent with the characteristics of the family Totiviridae. The virus was detected by reverse transcription-PCR in all caste members and developmental stages of ants, including eggs, larvae, pupae, adult workers, alates (male and female) and queens. To our knowledge, this is the first report of a member of the family Totiviridae in a hymenopteran; the virus was designated Camponotus yamaokai virus.

Contemporary evolution of host plant range expansion in an introduced herbivorous beetle Ophraella communa

Host range expansion of herbivorous insects is a key event in ecological speciation and insect pest management. However, the mechanistic processes are relatively unknown because it is difficult to observe the ongoing host range expansion in natural population. In this study, we focused on the ongoing host range expansion in introduced populations of the ragweed leaf beetle, Ophraella communa, to estimate the evolutionary process of host plant range expansion of a herbivorous insect. In the native range of North America, O. communa does not utilize Ambrosia trifida, as a host plant, but this plant is extensively utilized in the beetles introduced range. Larval performance and adult preference experiments demonstrated that native O. communa beetles show better survival on host plant individuals from introduced plant populations than those from native plant populations and they also oviposit on the introduced plant, but not on the native plant. Introduced O. communa beetles showed significantly higher performance on and preference for both introduced and native A. trifida plants, when compared with native O. communa. These results indicate the contemporary evolution of host plant range expansion of introduced O. communa and suggest that the evolutionary change of both the host plant and the herbivorous insect involved in the host range expansion.

Asynchronous hatching and brood reduction by filial cannibalism in the burying beetle Nicrophorus quadripunctatus

Despite decades of intensive research, there is still much debate about the adaptive significance of asynchronous hatching. A major obstacle in understanding the significance of this process is the difficulty involved in separating the hypotheses that explain asynchronous hatching as an adaptive trait from those that explain it as a by-product of physiological constraints on hatching or egg-laying patterns. We investigated the burying beetle Nicrophorus quadripunctatus, a species in which the parent can eliminate less-adaptive offspring (e.g., slower-growing offspring) by filial cannibalism and adjust the age structure of offspring to an adaptive pattern. The main aim of this study was to determine the age composition of offspring that survived and to determine the effect of larval growth on filial cannibalism. We investigated how the point in time at which each group of larvae hatched affects the timing of filial cannibalism by the female parent. We found that N. quadripunctatus exhibited asynchronous hatching, and reared larvae of different ages. We also found that later-hatching larvae had lower survival and growth rates; therefore, filial cannibalism plays a role in eliminating later-arriving, slower-growing, and hence less-adaptive offspring.

Resource partitioning based on body size contributes to the species diversity of wood‐boring beetles and arboreal nesting ants

The need to understand the mechanisms enhancing species coexistence and diversity is one of the central issues of community ecology. Theoretical work suggests that resource partitioning based on body size contributes to the coexistence of competing species, resulting in increased species diversity. Nevertheless, few empirical studies have investigated this. The species composition of wood‐dwelling arthropods was surveyed to examine resource partitioning based on body size in the dead wood of the ubame oak (Quercus phillyraeoides A. Grey) trees. Greater resource sizes (larger dead wood diameter) retained a lower overall density of wood‐dwelling beetles per resource volume, greater total beetle biomass per resource volume and larger bodied individuals of the dominant species (Cerambycidae; Anaglyptus nipponensis Bates). A gradient in the species composition of arboreal ant assemblages along resource size and a positive correlation between resource size and ant body size was observed. These results suggest that the incidence of wood‐boring beetles was limited by the size of the available resource, resulting in resource partitioning by the ants according to the sizes of galleries made by the beetles. Our findings indicate that resource size leads both directly and indirectly to body size‐dependent resource partitioning in beetle and ant assemblages, and contributes to the maintenance of species coexistence in the assemblages present in dead wood.

Control of parental investment changes plastically over time with residual reproductive value.

Evolutionary conflict between parents and offspring over parental resource investment is a significant selective force on the traits of both parents and offspring. Empirical studies have shown that for some species, the amount of parental investment is controlled by the parents, whereas in other species, it is controlled by the offspring. The main difference between these two strategies is the residual reproductive value of the parents or opportunities for future reproduction. Therefore, this could explain the patterns of control of parental investment at the species level. However, the residual reproductive value of the parents will change during their lifetime; therefore, parental influence on the amount of investment can be expected to change plastically. Here, we investigated control of parental investment when parents were young and had a high residual reproductive value, compared to when they were old and had a low residual reproductive value using a cross‐fostering experiment in the burying beetle Nicrophorus quadripunctatus. We found that parents exert greater control over parental investment when they are young, but parental control is weakened as the parents age. Our results demonstrate that control of parental investment is not fixed, but changes plastically during the parents lifetime.

The proximate cause of asynchronous hatching in the burying beetle Nicrophorus quadripunctatus

In some species, a brood hatches or is born asynchronously over an extended period of time. This asynchronous hatching establishes competitive asymmetries between offspring, and younger offspring usually exhibit a higher mortality risk and/or lower growth rate. A large body of research suggests that selection favours asynchronous hatching, though a consensus is yet to be reached on the nature of its adaptive benefits. One of the possible causes of this is that previous studies have focused mostly on avian species, who must incubate their eggs. Thus, studying non-avian species may provide an opportunity to improve our understanding of the wider importance of asynchronous hatching, for example in invertebrates, which do not incubate their eggs. In the burying beetle, Nicrophorus quadripunctatus, asynchronous hatching has been shown to maximize parental fitness. However, there is currently no information on the proximate cause of asynchronous hatching in this species. Here we investigated the influence of timing of egg-laying and the duration of embryonic development on the timing of hatching. We found that the timing of egg-laying by the parent was a major determinant of the timing of hatching, although the duration of embryonic development was also important. Our results suggest that the principal proximate cause of asynchronous hatching is parental asynchronous egg-laying.

Asynchronous hatching in the burying beetle, Nicrophorus quadripunctatus, maxmizes parental fitness

Life history theory predicts that natural selection favours parents who balance investment across offspring to maximize fitness. Theoretical studies have shown that the optimal level of parental investment from the offsprings perspective exceeds that of its parents, and the disparity between the two generates evolutionary conflict for the allocation of parental investment. In various species, the offspring hatch asynchronously. The age hierarchy of the offspring usually establishes competitive asymmetries within the brood and determines the allocation of parental investment among offspring. However, it is not clear whether the allocation of parental investment determined by hatching pattern is optimal for parent or offspring. Here, we manipulated the hatching pattern of the burying beetle Nicrophorus quadripunctatus to demonstrate the influence of hatching pattern on the allocation of parental investment. We found that the total weight of a brood was largest in the group that mimicked the natural hatching pattern, with the offspring skewed towards early hatchers. This increases parental fitness. However, hatching patterns with more later hatchers had heavier individual offspring weights, which increases offspring fitness, but this hatching pattern is not observed in the wild. Thus, our study suggests that the natural hatching pattern optimizes parental fitness, rather than offspring fitness.

Paternity assurance before and after fertilization by male burying beetles (Nicrophorus quadripunctatus)

Parental care requires a large investment of time and energy. This can reduce future parental survival and opportunities for mating. Because males are usually more uncertain of their parentage with respect to the caring of offspring than are females, the reduction in reproductive success is thought to be greater in males. Therefore, males are under selection to ensure paternity of the offspring for which they care. Males can increase paternity before and after fertilization. Before fertilization, males can increase paternity by increasing their competitive ability for fertilization. After fertilization, males can increase paternity by cannibalizing unrelated offspring. Here, we investigated the stage at which male burying beetles, Nicrophorus quadripunctatus, increase their paternity by evaluating the number of offspring sired by a nursing male in asynchronously hatched broods in relation to hatching time. We found that nursing males assure a very high level of the paternity of hatching offspring. We also found that the paternity of non-nursing and nursing males remained constant across hatching time within a brood, indicating that it is unlikely that filial cannibalism plays a role in increasing the paternity of offspring. We concluded that ensuring paternity before fertilization is more important in increasing the paternity of offspring.

Mating Triggers Queen Elimination by Workers of Japanese Harvester Ant (Messor aciculatus)

During reproduction, ant colonies produce winged queens. These new queens usually leave the nest to mate and can then establish a new nest. If the new nest is close to an existing colony, it will be in competition with the existing colony. Therefore, workers will kill any mated queens they find outside the colony during the reproductive season. In this study, factors that might determine whether workers eliminate queens were investigated. Mating status (mated or unmated), colony origin (same or different to tested workers) and mating partners (inbred or outbred) of the queens of Japanese harvester ants (Messor aciculatus) were manipulated and the workers’ behavior towards the queens was observed. Mated queens were always attacked by workers, though this was not affected by either colony origin or mating partners. These results suggest that mating status triggers elimination of queens by workers, and that the colony origin and mating partner are unlikely to be important roles in elimination of queens.

Return of Drones: Flight Experience Improves Returning Performance in Honeybee Drones

The effect of experience on the behavior of worker bees has been extensively investigated; however, few such studies have been conducted on male bees. Honeybee (Apis mellifera) males (drones), unlike the males of other social hymenopterans, return to their nest after performing a mating flight and have, therefore, an opportunity to learn from their experiences. This provides a chance to understand the significance of experience in social hymenopteran males. Here, we investigated whether experience improves the returning performance in drones (rate and time of return to the hive). We compared the returning performance of “Experienced” drones that were allowed to fly freely and thus had an opportunity to learn the position of the hive before the experiment with “Naive” drones that were not allowed to fly and therefore, had no opportunity to learn. We found that Experienced drones returned to the hive after a displacement, whereas Naive drones did not. Furthermore, time to return decreased with the age of drones. These results suggest that flight experience improves the returning performance, which should increase the possibility of mating success and overall colony fitness.