Hajime Ohtsuki

Size-dependent foraging gene expression and behavioral caste differentiation in Bombus ignitus

BackgroundIn eusocial hymenopteran insects, foraging genes, members of the cGMP-dependent protein kinase family, are considered to contribute to division of labor through behavioral caste differentiation. However, the relationship between foraging gene expression and behavioral caste in honeybees is opposite to that observed in ants and wasps. In the previously examined eusocial Hymenoptera, workers behave as foragers or nurses depending on age. We reasoned that examination of a different system of behavioral caste determination might provide new insights into the relationship between foraging genes and division of labor, and accordingly focused on bumblebees, which exhibit size-dependent behavioral caste differentiation. We characterized a foraging gene (Bifor) in bumblebees (Bombus ignitus) and examined the relationship between Bifor expression and size-dependent behavioral caste differentiation.FindingsA putative open reading frame of the Bifor gene was 2004 bp in length. It encoded 668 aa residues and showed high identity to orthologous genes in other hymenopterans (85.3-99.0%). As in ants and wasps, Bifor expression levels were higher in nurses than in foragers. Bifor expression was negatively correlated with individual body size even within the same behavioral castes (regression coefficient = -0.376, P < 0.001, all individuals; -0.379, P = 0.018, within foragers).ConclusionThese findings indicate that Bifor expression is size dependent and support the idea that Bifor expression levels are related to behavioral caste differentiation in B. ignitus. Thus, the relationship between foraging gene expression and behavioral caste differentiation found in ants and wasps was identified in a different system of labor determination.

Effects of light environment during growth on the expression of cone opsin genes and behavioral spectral sensitivities in guppies (Poecilia reticulata)

BackgroundThe visual system is important for animals for mate choice, food acquisition, and predator avoidance. Animals possessing a visual system can sense particular wavelengths of light emanating from objects and their surroundings and perceive their environments by processing information contained in these visual perceptions of light. Visual perception in individuals varies with the absorption spectra of visual pigments and the expression levels of opsin genes, which may be altered according to the light environments. However, which light environments and the mechanism by which they change opsin expression profiles and whether these changes in opsin gene expression can affect light sensitivities are largely unknown. This study determined whether the light environment during growth induced plastic changes in opsin gene expression and behavioral sensitivity to particular wavelengths of light in guppies (Poecilia reticulata).ResultsIndividuals grown under orange light exhibited a higher expression of long wavelength-sensitive (LWS) opsin genes and a higher sensitivity to 600-nm light than those grown under green light. In addition, we confirmed that variations in the expression levels of LWS opsin genes were related to the behavioral sensitivities to long wavelengths of light.ConclusionsThe light environment during the growth stage alters the expression levels of LWS opsin genes and behavioral sensitivities to long wavelengths of light in guppies. The plastically enhanced sensitivity to background light due to changes in opsin gene expression can enhance the detection and visibility of predators and foods, thereby affecting survival. Moreover, changes in sensitivities to orange light may lead to changes in the discrimination of orange/red colors of male guppies and might alter female preferences for male color patterns.

DNA extraction and amplification methods for ephippial cases of Daphnia resting eggs in lake sediments: a novel approach for reconstructing zooplankton population structure from the past

This study describes a method of DNA extraction and amplification for ephippial cases of Daphnia resting eggs from lake sediment. Recent studies have reconstructed succession records of Daphnia species by genetically analyzing Daphnia resting eggs stored in lake sediments and revealed changes in dominant Daphnia species that correspond well with environmental changes. However, this approach is not applicable to lakes where most of the resting eggs in the sediment have already hatched out. We modified conventional methods for DNA extraction and amplification to enable genetic analyses of the ephippial case that envelops and protects the resting eggs, and we compared the performance of the modified method to the conventional one. We confirmed that we could efficiently analyze the sequences of the ephippial cases collected in a sediment core using our modified method. It enables us to reconstruct changes in genetic structure of Daphnia populations regardless of hatching rates of the resting eggs.

Nitric oxide synthase (NOS) in the Japanese fireflies Luciola lateralis and Luciola cruciata

Species-specific flash patterns in firefly species are important for the investigation of the evolution of Lampyridae. Since nitric oxide synthase (NOS) is one of the key enzymes controlling flash patterns, we determined the cDNA sequences of NOS in the Japanese fireflies Luciola lateralis and L. cruciata. The identity of the NOS sequences was very high between these 2 species. Firefly NOS also exhibited a high identity with those of other insect species, and the cofactor-binding domains were particularly well conserved. Many negatively selected sites were detected throughout the NOS sequences; however, no positive selection was detected. The phylogenetic relationship of insect NOS was different from that of the general classification system, although the lineages corresponded to the major recognized taxonomic groups.

Genetic Structures of Laguncula pulchella Metapopulations Along the Northeast Coast of Japan After the Tsunamis Caused by the Great East Japan Earthquake

The carnivorous snail (Laguncula pulchella) was once considered an endangered species in Japan because its habitat was limited to western Japan. However, alien L. pulchella populations were transported from China and the Korean Peninsula to the Pacific coast of northeast Japan, presumably via anthropogenic activities. This study examined the genetic structures of the invasive L. pulchella populations in various coastal estuaries of Sendai Bay and Sanriku Ria areas to determine how the metapopulations were affected by the tsunamis caused by the Great East Japan Earthquake. The genetic compositions of these carnivorous snails significantly varied between the Sendai Bay and Sanriku areas. The result suggests that local L. pulchella populations were relatively isolated, and their genetic structure was minimally affected by the tsunamis. In addition, their genetic compositions were locally fixed. These results suggest that difference in the genetic composition among L. pulchella populations reflects that of artificial transport source.

Physiological conditions and genetic controls of phaeomelanin pigmentation in nestling barn swallows

Lay Summary Many animals possess conspicuous traits that appear to be nonfunctional for survivorship but are used in communication. Such traits often provide information about the quality of the possessors to others. However, although empirical studies have found many signal traits that are associated with individual quality, the underlying mechanisms remain to be understood. In this study, we showed that high-quality individuals could produce colourful plumage without increasing oxidative stress through genetic control.

Historical changes in the ecosystem condition of a small mountain lake over the past 60 years as revealed by plankton remains and Daphnia ephippial carapaces stored in lake sediments.

To examine if changes in species composition of a plankton community in the past due to anthropogenic activities can be clarified in lakes without any monitoring data, we analyzed genetically ephippial carapaces of Daphnia with plankton remains stored in the bottom sediments of Lake Hataya Ohunma in Japan. In the lake, abundance of most plankton remains in the sediments was limited and TP flux was at low levels (2–4 mg/m2/y) before 1970. However TP flux increased two-fold during the period from 1980s to 1990s. In parallel with this increase, abundance of most plankton remains increased although abundance of benthic testate amoebae’s remains decreased, indicating that the lake trophic condition had changed from oligo- to mesotrophic for the past 60 years. According to cluster analysis, the stratigraphic sediments were divided into two periods with different features of the phytoplankton composition. Chronological comparison with events in the watershed suggested that eutrophication occurred because of an increase in visitors to the watershed and deposition of atmospheric dust. In this lake more than 50% of resting eggs produced by Daphnia over the past 60 years hatched. However, genetic analysis of the ephippial carapaces (remains) showed that the Daphnia population was originally composed of D. dentifera but that D. galeata, or its hybrid with D. dentifera, invaded and increased the population density when the lake was eutrophied. Subsequently, large D. pulex established populations in the 1980s when largemouth bass were anonymously introduced. These results indicated that the Lake Hataya Ohunma plankton community underwent significant changes despite the fact that there were no notable changes in land cover or land use in the watershed. Since increases in atmospheric deposition and release of fish have occurred in many Japanese lakes, the changes in the plankton community described here may be widespread in these lakes.

Rediscovery after Almost 120 Years: Morphological and Genetic Evidence Supporting the Validity of Daphnia mitsukuri (Crustacea: Cladocera)

We examined the morphology of Daphnia individuals maintained in our laboratory for several years, originally collected in Lake Inbanuma, Chiba, Japan. We determined partial sequences of the mitochondrial cytochrome c oxidase subunit I and 12S rRNA genes from specimens in the cultured material. These animals are morphologically similar to D. obtusa Kurz, 1874, but genetically distinct from this species. Our detailed observation shows that the morphological characteristics in the female and male individuals of our material are highly congruent with those of D. mitsukuri Ishikawa, 1896, which has not been identified positively for more than 120 years since its original description, with its taxonomic identity having been questioned for almost 90 years. Based on our morphological and genetic data, we conclude that D. mitsukuri should be regarded as a taxonomically valid species. A search among public DNA sequence databases suggests D. mitsukuri is also distributed in China, although these Chinese sequences have been labeled as ‘Daphnia pulex’, representing misidentification.

Expression of the nos gene and firefly flashing: a test of the nitric-oxide-mediated flash control model.

Abstract Fireflies (Coleoptera: Lampyridae) emit various types of light that differ among species and populations of the same species. Their lights are assumed to be biological properties that play important ecological and evolutionary roles. Some species in the Lampyridae emit periodic luminescence, the patterns of which are characterized by speciesspecific intervals. In previous work, it was predicted that the nitric oxide (NO) regulates the oxygen supply required for the bioluminescence reaction of fireflies. Here, the expression of the NO synthase (NOS) mRNA in some fireflies was examined to verify the predictive model of nitric-oxide-mediated flash control in these insects. The expression of the nos gene in the lantern organ was observed not only in nocturnal flashing species but also in diurnal non-flashing species. It was shown that the expression levels of nos were higher in the lantern of Luciola cruciata (Motschulsky) larvae, which that emits continuous light, than in other body parts, although expression in the lantern of the adults, who flash periodically, was not high. Furthermore, there was no significant difference in expression levels among adults of Luciola cruciata characterized by different flashing intervals. The data do not support the model of an NO-mediated flash control mechanism, during which oxygen becomes available for the luciferin-luciferase reaction through NO-mediated inhibition of mitochondrial respiration. It is also indicated that flash patterns do not co-vary with NOS production. However, high nos expression in the larval lantern suggests that NO may play a role in producing continuous light by functioning as a neurotransmitter signal for bioluminescence.