Seasonal changes in the biomass of floating leaved plant,Trapa spp., and its relation with a leaf beetle,Galerucella nipponensis,in Lake Inba,Japan

Limnology - Trapa spp. dominate many shallow eutrophic lakes in Japan, which must affect the nutrient dynamics in lakes. Trapa spp. are utilized by several animals, in particular the leaf beetle,...     

Factors promoting maternal trophic egg provisioning in non-eusocial animals

The adaptive function of trophic egg-laying is generally regarded as extended parental investment to the offspring. However, the evolutionary factors promoting trophic egg-laying are still unclear, because the amount of maternal investment per offspring should be ideally equal between smaller offspring with trophic eggs and larger offspring without any additional investment. Several authors have suggested that trophic egg-laying should evolve only when egg size is constrained, but this hypothesis has not been evaluated. We investigated the evolutionary mechanisms of trophic egg-laying by two different approaches. First, we evaluated morphological constraints on egg size in two sibling ladybird species, Harmonia axyridis, which is known to produce trophic eggs, and H. yedoensis. Second, we theoretically predicted the optimal proportion of trophic eggs to total eggs and egg size in relation to environmental heterogeneity, predictability of environmental quality, and investment efficiency of trophic egg consumption. The intra- and interspecific morphological comparisons suggest that morphological constraints on the evolutionary determination of egg size are weak at best in the two ladybird species. Moreover, we theoretically showed that small egg size and trophic egg-laying are favoured in heterogeneous environments when mothers cannot adjust egg size plastically. We also showed that even a small reduction in investment efficiency makes a trophic egg strategy unlikely, despite relatively high environmental predictability. We conclude that trophic egg provisioning may be a flexible maternal adaptation to a highly heterogeneous environment rather than a response to a morphological constraint on egg size.     

Sexual Conflict over the Maintenance of Sex: Effects of Sexually Antagonistic Coevolution for Reproductive Isolation of Parthenogenesis

Sexual reproduction involves many costs. Therefore, females acquiring a capacity for parthenogenetic (or asexual) reproduction will gain a reproductive advantage over obligately sexual females. In contrast, for males, any trait coercing parthenogens into sexual reproduction (male coercion) increases their fitness and should be under positive selection because parthenogenesis deprives them of their genetic contribution to future generations. Surprisingly, although such sexual conflict is a possible outcome whenever reproductive isolation is incomplete between parthenogens and the sexual ancestors, it has not been given much attention in the studies of the maintenance of sex. Using two mathematical models, I show here that the evolution of male coercion substantially favours the maintenance of sex even though a female barrier against the coercion can evolve. First, the model based on adaptive-dynamics theory demonstrates that the resultant antagonistic coevolution between male coercion and a female barrier fundamentally ends in either the prevalence of sex or the co-occurrence of two reproductive modes. This is because the coevolution between the two traits additionally involves sex-ratio selection, that is, an increase in parthenogenetic reproduction leads to a female-biased population sex ratio, which will enhance reproductive success of more coercive males and directly promotes the evolution of the coercion among males. Therefore, as shown by the individual-based model, the establishment of obligate parthenogenesis in the population requires the simultaneous evolution of strong reproductive isolation between males and parthenogens. These findings should shed light on the interspecific diversity of reproductive modes as well as help to explain the prevalence of sexual reproduction.     

Ecological effects of sex differ with trophic positions in a simple food web

Sexual differences in parental investment, predation pressure, and foraging efforts are common in nature and affect the trophic flow in food webs. Specifically, the sexual differences in predator and prey behavior change in trophic inflow and outflow, respectively, while those in parental investment alter the reproductive allocation of acquired resources in the population. Consequently, these factors may play an important role in determining the system structure and persistence. However, few studies have examined how sexual differences in trophic flow affect food web dynamics. In this study, I show the ecological role of sex by explicitly incorporating sexual differences in trophic flow into a three‐species food web model. The results demonstrated that the ecological waste of males, that is, the amount of trophic inflow into males with less parental investment, plays an important role in system persistence and structure. In particular, the synergy between sexual differences in parental investment and trophic inflows and outflows is important in determining web persistence: Significant impacts of male‐biased trophic flows require the condition of anisogamy. In addition, the dynamic effects of the ecological waste of males differ with trophic level: The coexistence of a food web occurs more frequently with biased inflows into predator males, but occurs less frequently with biased inflows into consumer males. The model analysis indicates that investigating the pattern of sexual differences among trophic positions can enrich our understanding of food web persistence and structure in the real world.     

Aminooxy‐naphthylpropionic acid and its derivatives are inhibitors of auxin biosynthesis targeting l‐tryptophan aminotransferase: structure–activity relationships

We previously reported l ‐α‐aminooxy‐phenylpropionic acid (AOPP) to be an inhibitor of auxin biosynthesis, but its precise molecular target was not identified. In this study we found that AOPP targets TRYPTOPHAN AMINOTRANSFERASE of ARABIDOPSIS 1 (TAA1). We then synthesized 14 novel compounds derived from AOPP to study the structure–activity relationships of TAA1 inhibitors in vitro. The aminooxy and carboxy groups of the compounds were essential for inhibition of TAA1 in vitro. Docking simulation analysis revealed that the inhibitory activity of the compounds was correlated with their binding energy with TAA1. These active compounds reduced the endogenous indole‐3‐acetic acid (IAA) content upon application to Arabidopsis seedlings. Among the compounds, we selected 2‐(aminooxy)‐3‐(naphthalen‐2‐yl)propanoic acid (KOK1169/AONP) and analyzed its activities in vitro and in vivo. Arabidopsis seedlings treated with KOK1169 showed typical auxin‐deficient phenotypes, which were reversed by exogenous IAA. In vitro and in vivo experiments indicated that KOK1169 is more specific for TAA1 than other enzymes, such as phenylalanine ammonia‐lyase. We further tested 41 novel compounds with aminooxy and carboxy groups to which we added protection groups to increase their calculated hydrophobicity. Most of these compounds decreased the endogenous auxin level to a greater degree than the original compounds, and resulted in a maximum reduction of about 90% in the endogenous IAA level in Arabidopsis seedlings. We conclude that the newly developed compounds constitute a class of inhibitors of TAA1. We designated them ‘pyruvamine’.     

Effect of nutritional condition on larval food requisition behavior in a subterranean termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Although optimal investment theory would be similarly applicable to eusocial insects to maximize colony reproductive outputs, directly distinguishing an amount of investment in each larva should be a difficult task for workers because of the characteristics of group living. Thus, it is expected that workers adjust brood care by using a cue or signal conveying information of larval status. In termites, which are typical group of eusocial insects, there are nevertheless few direct observations on worker brood care and little is known about cues inducing worker feeding. I show here that a Japanese subterranean termite Reticulitermes speratus uses an overt food solicitation by larva, “pecking”, as a cue for worker feeding. Direct observations demonstrated that workers feed larvae in response to larval pecking. Furthermore, nutritional experiments showed that larvae exhibited pecking more frequently when their nutrient status is lower; hence, pecking may be an honest reflection of larval hunger status. These results indicate that workers can feed more starved larvae than less starved ones because pecking honestly reflects larval hunger state. That is, feeding in response to pecking should standardize the total amount of food intake of each larva and help a termite colony make worker investment efficient.     

Stimulation of Expression of a Silica-Induced Protein (Sip) in Thermus thermophilus by Supersaturated Silicic Acid

The effects of silicic acid on the growth of Thermus thermophilus TMY, an extreme thermophile isolated from a siliceous deposit formed from geothermal water at a geothermal power plant in Japan, were examined at 75°C. At concentrations higher than the solubility of amorphous silica (400 to 700 ppm SiO₂), a silica-induced protein (Sip) was isolated from the cell envelope fraction of log-phase TMY cells grown in the presence of supersaturated silicic acid. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the molecular mass and pI of Sip to be about 35 kDa and 9.5, respectively. Induction of Sip expression occurred within 1 h after the addition of a supersaturating concentration of silicic acid to TM broth. Expression of Sip-like proteins was also observed in other thermophiles, including T. thermophilus HB8 and Thermus aquaticus YT-1. The amino acid sequence of Sip was similar to that of the predicted solute-binding protein of the Fe³⁺ ABC transporter in T. thermophilus HB8 (locus tag, TTHA1628; GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"NC_006461","term_id":"55979969","term_text":"NC_006461"}}NC_006461; GeneID, 3169376). The sip gene (987-bp) product showed 87% identity with the TTHA1628 product and the presumed Fe³⁺-binding protein of T. thermophilus HB27 (locus tag TTC1264; GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"NC_005835","term_id":"46198308","term_text":"NC_005835"}}NC_005835; GeneID, 2774619). Within the genome, sip is situated as a component of the Fbp-type ABC transporter operon, which contains a palindromic structure immediately downstream of sip. This structure is conserved in other T. thermophilus genomes and may function as a terminator that causes definitive Sip expression in response to silica stress.Occurring mainly in the form of silica (SiO₂), silicon (Si) is the second-most abundant element in the earth''s crust, accounting for 28.8% of the earth''s mass (34). SiO₂ exists as monosilicic acid (Si(OH)₄) in aqueous solution, as represented in the following equation: SiO₂ + 2H₂O · (Si(OH)₄). The solubility of silica greatly depends on temperature, pH (17), and salt concentration, among other parameters (27). As the temperature of a silicic acid solution declines, its concentration can exceed the solubility of amorphous silica. Under those conditions, silicic acid polymerizes to form polysilisic acid, which is relatively stable in aqueous solution because the repulsion between the negative charges on its surface keeps it from readily aggregating and precipitating. In a geothermal reservoir, at high temperature and pressure, the silicic acid concentration at equilibrium shows the solubility of quartz. However, when that geothermal water is discharged to the surface, the silicic acid concentration becomes supersaturated as the water boils, frequently leading to the formation of siliceous deposits called “silica sinter” (11). Microscopic observation of such siliceous deposits reveals many microbe-like structures (20), and it has been suggested that these fossils represent archean microorganisms that grew in the hot, supersaturated fluids (26). There have been a number of experimental studies carried out with the aim of characterizing the physical changes associated with various bacteria during silicification (23, 26, 31, 33, 37); however, the effect of silica on the bacterial habitat in geothermal environments and the mechanism by which siliceous deposits are formed remain unexplained.Recent studies have shown that biosilicification in geothermal areas reflects the activities of various thermophilic microorganisms (15, 23, 29). For instance, geothermal water and the water discharged from hydrothermal vents contain a high concentration of silicic acid, and biogenic textures covered with amorphous silica have been found in areas around both sources (12, 22). Moreover, in a study of experimental silicification, interactions were observed between silica and Sulfurihydrogenibium azorense, a representative member of the order Aquificales (26). Still, the effect of silica on the bacterial habitat in thermal environments and the molecular properties affecting aggregation and siliceous deposition remain poorly understood.Our previous studies have focused on the effect of bacteria on the formation of siliceous deposits in geothermal water (18, 21). Siliceous deposits (called silica scale) that form in pipelines and on surface equipment in geothermal power plants cause serious economic problems related to energy loss and to plant maintenance throughout the world (38). We also observed that a Thermus strain isolated from silica scale (TMY) was able to efficiently generate and deposit amorphous silica in vitro, beginning in the latter part of the log growth phase (19). On the basis of its morphological, physiological, and genetic properties, the organism was identified as a strain of Thermus thermophilus, and its distinct properties were indicative of the microdiversity of T. thermophilus strains (14). Thermus strains are the predominant heterotrophs in natural geothermal and hydrothermal habitats, and thus far, the genomes of T. thermophilus strains HB8 (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"AP008226","term_id":"55771382","term_text":"AP008226"}}AP008226) and HB27 (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"AE017221","term_id":"46197919","term_text":"AE017221"}}AE017221) have been sequenced completely (16). Given its genomic similarity to T. thermophilus HB8, we analyzed the genetic information of strain TMY in that context.Here we report the effect of silicic acid concentration on the growth of T. thermophilus TMY, which was isolated from a siliceous deposit formed at a geothermal electric power plant. Notably, supersaturated silicic acid markedly stimulated expression of one cell envelope protein, which we named silica-induced protein (Sip). Induction of Sip expression occurred rapidly after the cells were exposed to supersaturated silicic acid, and the amino acid sequence of Sip showed significant similarity with the Fe³⁺ ABC transporters observed in other Thermus strains. These results shed new light on the growth and biosilisification associated with thermophiles in geothermal environments.