Koji Tsuchida

Queen and worker policing in monogynous and monandrous colonies of a primitively eusocial wasp

Kin–selection theory predicts that a worker prefers to produce her own sons in a colony with monandry and monogyny because relatedness to her sons (0.5) and nephews (0.375) exceeds that to brothers (0.25). In spite of this prediction, recent studies reveal that workers police each other (mutual–worker egg removal) even in monandrous and monogynous colonies. We conducted field and laboratory studies to evaluate queen and worker policing in queen–right colonies of the primitively eusocial wasp Polistes chinensis antennalis. Genetic studies using microsatellite markers, as well as extensive observations of natural colonies, revealed that both queen and workers removed both queen– and worker–laid eggs in monogynous and monandrous colonies. The queen–s eggs survived to hatching more successfully than those of the workers (88.5% versus 1.4%). We discuss the likely factors to explain these worker–policing behaviours.

Reproductive disturbance of Japanese bumblebees by the introduced European bumblebee Bombus terrestris

The European bumblebee, Bombus terrestris, is an invasive eusocial species whose distribution is expanding greatly beyond its native range because numerous colonies are imported to or locally produced in non-native countries for pollination of agricultural crops. Closely related species exist in Japan where the unrestricted import and use of B. terrestris has resulted in the establishment of wild colonies. Laboratory studies previously showed that B. terrestris and Japanese native species can copulate and produce fertilized eggs. Although these eggs do not hatch, the interspecific mating can cause a serious reproductive disturbance to native bumblebees. In this study, we determined the frequencies of interspecies mating between B. terrestris males and native bumblebee queens in the wild on the islands of Hokkaido and Honshu by analyzing the DNA sequences of spermatozoa stored in spermathecae of native queens. We found that 20.2% of B. hypocrita hypocrita queens and 30.2% of B. hypocrita sapporoensis queens had spermatozoa of B. terrestris males in their spermathecae. Given that a Bombus queen generally mates only once in her life, such high frequencies of interspecific mating with B. terrestris pose serious threats to the populations of native bumblebees in Japan.

QUEEN-WORKER CONFLICTS OVER MALE PRODUCTION AND SEX ALLOCATION IN A PRIMITIVELY EUSOCIAL WASP

Abstract In a colony headed by a single monandrous foundress, theories predict that conflicts between a queen and her workers over both sex ratio and male production should be intense. If production of males by workers is a function of colony size, this should affect sex ratios, but few studies have examined how queens and workers resolve both conflicts simultaneously. We conducted field and laboratory studies to test whether sex‐ratio variation can be explained by conflict over male production between queen and workers in the primitively eusocial wasp Polistes chinensis antennalis.

Gonadotropic effects of dopamine in isolated workers of the primitively eusocial wasp, Polistes chinensis

In social insects, biogenic amines are thought to play regulatory roles in the transition between reproductive states in females. To determine the effect of dopamine on the reproductive development of workers in primitively eusocial societies, isolated workers of the paper wasp Polistes chinensis were supplied with oral dopamine. Ovarian development was accelerated in dopamine-fed workers as compared to control workers of the same age fed only sucrose solution. Oral dopamine increased brain levels of dopamine and its metabolite (N-acetyldopamine). Brain levels of tyramine or octopamine were also increased by dopamine application in one of two colonies; levels of the tyramine metabolite N-acetyltyramine were unchanged. These results indicate that dopamine plays a gonadotropic role in isolated workers in the primitively eusocial wasp, similar to the gonadotropic role previously reported for juvenile hormone. This is the first study to report effects of dopamine on ovarian development in workers of the paper wasp.

Reproductive differences between Q and B whiteflies, Bemisia tabaci, on three host plants and negative interactions in mixed cohorts

Two cryptic species of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), B and Q whiteflies, have been invading many parts of the world. In Japan, Q whiteflies are displacing the predominant B whiteflies. To elucidate the mechanism of whitefly displacement, we compared the reproductive capacities of these species at different temperatures on three host plants and investigated negative interactions in the mixed cohort of mated females of both species. We measured their development times and emergence rates at six temperatures ranging from 20 to 35 °C on tomato, cucumber, and sweet pepper. In addition, we measured their life spans and the number of eggs at 20 and 30 °C on tomato and cucumber. On sweet pepper, B whiteflies mostly did not develop and died as first instar, but Q whiteflies completed their development. On tomato and cucumber, the development times, emergence rates, and life spans of B and Q whiteflies at all experimental temperatures did not differ significantly. B whiteflies had a higher intrinsic rate of population increase (rm) and net reproductive rate (R0) than Q whiteflies at 30 °C on these plants. In a mixed cohort of mated females, Q whiteflies had longer development times than B whiteflies. Furthermore, Q whiteflies had a lower proportion of emerged adults (25.4%) and higher progeny sex ratio (i.e., percentage sons) in the mixed cohort (52.8%) than in the single cohort (36.8%). The reduction in female Q progeny suggests that the interaction between B and Q whiteflies negatively affects only Q whiteflies, resulting in a lower Q population in the presence of B whiteflies. This reduction does not explain the recent displacement of B whiteflies by Q whiteflies in Japan.

The effect of a seasonal time constraint on development time, body size, condition, and morph determination in the horned beetle Allomyrina dichotoma L. (Coleoptera: Scarabaeidae)

Abstract.  1. In horned beetles selection favours males that adjust their investment in horn development in relation to cues that predict adult body size. Here it is shown that in the Japanese horned beetle, Allomyrina dichotoma. There is a significant discontinuity in the horn length body size allometry. This can be described as a linear relationship that is shifted towards an increased horn length to body length ratio in males with horns longer than 16 mm.

Diploid males and sex determination in a paper wasp, Polistes chinensis antennalis (Hymenoptera, Vespidae)

Summary: Beyond helping the queens reproductive function, the worker caste of Polistes wasps is expected to have an alternative reproductive strategy; to become a replacement queen, following copulation with early males that emerge along with the first brood workers. We analyzed genotypes and chromosome numbers of the early males in a natural population of P. chinensis antennalis. The frequency of early-male-producing colonies within a population was 5.2% (4/77) in 1993 through 1995. The numerical sex ratios in the 4 colonies for the 3 years and another early male-producing colony in 1999 were 1:1. For one early-male producing colony in 1995, we genotyped 31 females and all 128 males. All 31 genotyped females out of 67 emerged females showed heterozygosity and 69 out of 128 genotyped males were heterozygous; the remaining 59 males were homozygous or hemizygous. The ratio between the number of females and diploid males in this colony was 67:69, which is almost identical with one-to-one ratio. The cytological analysis of male chromosome for one early-male producing colony in 1999 revealed that the early males laid by a queen had 46 chromosomes, while worker laid males had 23. Our results revealed that the early males in this species are diploid males and eventually sterile. Secondly, the single locus complementary sex determination model is most plausible to explain the diploid male production in this species.

Genetical and morphological colony structure of the Australian swarm-founding polistine wasp, Ropalidia romandi (Hymenoptera, Vespidae).

Summary: Genetical colony structure of an Australian swarm-founding polistine wasp, Ropalidia romandi, was analyzed. Inseminated females with developed ovaries (egg-layers) tended to have larger body size (measured at the median cell of the forewing) than non egg-layers. Two way ANOVA revealed that the difference in body size was related to both the caste and the colony of origin. The genetic relatedness among egg-layers as detected by electrophoresis was 0.336 ± 0.114 (mean ± se), and that among non egg-layers was 0.161 ± 0.035. The inbreeding coefficient among non egg-layers was found to be significantly greater than zero, but this did not seem to play a major part in the increase in relatedness among progeny. The number of effective queens (mothers of new queens) was estimated to be 2.84 per colony. This number is much smaller than the actual counts of queens. This discrepancy is discussed in terms of possibilities that wasps practice cyclical oligogyny, matriline localization within a colony, and genotypic behavioral specialization.

Size dependent predatory pressure in the Japanese horned beetle,Allomyrina dichotoma L. (Coleoptera; Scarabaeidae)

We surveyed male survival and reproductive performances associated with dimorphism in the Japanese horned beetleAllomyrina dichotoma L. in a secondary forest in 1996. Morphological comparisons between living marked and prey individuals indicated that the larger horned males suffered higher predatory pressure than the smaller ones. The dominant predators of the beetles were suspected to be 2 crow species. The small-horned males showed lower recapture rates than the large-horned ones. This suggested that the former was more sensitive to disturbance, and/or dispersed more than the latter. Fighting behavior was rarely seen because of the low population density of the beetles in the study area. These results suggested that the large-horned males suffer not only the injury risk of intrasexual competition but also more predatory risk than the small-horned ones.

Sex mosaics in a male dimorphic ant Cardiocondyla kagutsuchi

Gynandromorphy, or the development of organisms with a combination of male and female morphological features, is common in Hymenoptera. The underlying mechanism is likely associated with the sex-determination system, and studying this phenomenon should lead to a deeper understanding of both embryonic development and sex determination. The reproductive capabilities of gynandromorphs (hereafter, sex mosaics) remain unclear. We studied gynandromorphy in the Malaysian ant Cardiocondyla kagutsuchi, which has sex mosaics of queens (gynandromorphs; mosaic of queens and winged male) and workers (ergatandromorphs; mosaic of worker and wingless ergatoid male). These sex mosaics were classified into seven morphological categories. Most individuals had more male than female body areas. Behavioral observations revealed that sex mosaics behave more in accordance with the “sex” of their brain than that of the reproductive organs (gaster). Relative DNA quantities showed that both female and male regions contained haploid and diploid nuclei, irrespective of their phenotypic appearance, indicating that external appearance did not reflect internal tissues. Nearly one third of the adults were sex mosaics and they were not infected with Wolbachia. Our results suggest that the production of sex mosaics in this species does not pose a substantial cost to colonies and that the underlying causes are therefore not strongly selected against.