Koh-Ichi Takakura

Alien dandelion reduces the seed-set of a native congener through frequency-dependent and one-sided effects

In conservation biology, increasing numbers of studies have focused on reproductive interference (RI) between a native species and related aliens. However, few studies have examined the frequency dependence of RI, despite of its key importance to invasiveness. Here, we report for the first time frequency-dependent RI in a pair of native and alien dandelions: Taraxacum japonicum and T. officinale, respectively. Taraxacum japonicum has been displaced rapidly by the alien congener T. officinale in Japan and its causal mechanism are still poorly understood. Field observations revealed that the seed-set of natives decreased substantially as the proportion of alien neighbors increased. Subsequently, in a field experiment, the removal of alien flowers only greatly increased the seed-set of natives. We synthesized these results with existing theoretical models of RI and concluded that RI, which is mediated by strong frequency dependence, is presumably responsible for the displacement of T. japonicum by T. officinale.

Alien pollen grains interfere with the reproductive success of native congener

The effects of invasive species on native species comprise important conservation issues. Determining the mechanisms by which invasives exclude natives is indispensable to efficiently control their impact, but most invasives remain poorly studied. The purpose of this study was to elucidate potentially important but neglected mechanisms, reproductive interference, in wild Taraxacum systems, in which invasive Taraxacumofficinale has displaced its native congener T. japonicum in Japan. Hand-pollination of mixed pollen grains significantly reduced the native seed-set compared to conspecific-only pollination. Moreover, natives with a high ratio of invasive pollen on their stigmas suffered severe seed-set reduction, and the proportion of invasive pollen on native stigmas increased as frequencies of the alien neighbor increased. These results, combined with those of previous studies, revealed that depositing invasive pollen on native stigmas contributes to the observed alien-frequency-dependent reduction of native seed-set, and strongly suggest that reproductive interference was the primary cause of displacement in the Taraxacum systems.

Occurrence of fluoroquinolones and fluoroquinolone-resistance genes in the aquatic environment.

Fluoroquinolones (FQs) have been detected in aquatic environments in several countries. Long-term exposure to low levels of antimicrobial agents provides selective pressure, which might alter the sensitivity of bacteria to antimicrobial agents in the environment. Here, we examined FQ levels and the resistance of Escherichia coli (E. coli) to FQs by phenotyping and genotyping. In the aquatic environment in Osaka, Japan, ciprofloxacin, enoxacin, enfloxacin, lomefloxacin, norfloxacin, and ofloxacin were detected in concentrations ranging from 0.1 to 570 ng L(-1). FQ-resistant E. coli were also found. Although no obvious correlation was detected between the concentration of FQs and the presence of FQ-resistant E. coli, FQ-resistant E. coli were detected in samples along with FQs, particularly ciprofloxacin and ofloxacin. Most FQ-resistant E. coli carried mutations in gyrA, parC, and parE in quinolone resistance-determining regions. No mutations in gyrB were detected in any isolates. Amino acid changes in these isolates were quite similar to those in clinical isolates. Six strains carried the plasmid-mediated quinolone resistance determinant qnrS1 and expressed low susceptibility to ciprofloxacin and nalidixic acid: the minimum inhibitory concentrations ranged from 0.25 μg mL(-1) for ciprofloxacin, and from 8 to 16 μg mL(-1) for nalidixic acid. This finding confirmed that plasmids containing qnr genes themselves did not confer full resistance to quinolones. Because plasmids are responsible for much of the horizontal gene transfer, these genes may transfer and spread in the environment. To our knowledge, this is the first report of plasmid-mediated quinolone resistance determinant qnrS1 in the aquatic environment, and this investigation provides baseline data on antimicrobial resistance profiles in the Osaka area.

Increase of GII.2 norovirus infections during the 2009–2010 season in Osaka City, Japan

During the 2009–2010 season, a significant numerical increase of genotype GII.2 norovirus (NoV)‐associated outbreaks was observed in Osaka City, Japan. The most common genotype in that season was GII.2 (44.6%), followed by GII.4 (39.2%). Mostly, GII.2 strains were associated with outbreaks in children and with person‐to‐person contact. The National Infectious Disease Surveillance Center reported that GII.2 NoV infections were widespread in Japan in that season. Comparative phylogenetic analysis of RNA‐dependent RNA polymerase (RdRp) and capsid sequences revealed that this GII.2 epidemic resulted from two genetic strains. The first, GII.2p2 strains, had an identical genotype in the RdRp and capsid genes. GII.2p2 strains in the 2009–2010 season were a different genetic cluster from the strains of spring 2004, the previous epidemic of GII.2 NoV, but showed no unique amino acid change. The second, GII.2 chimera virus (GII.2p16), had GII.16 RdRp and GII.2 capsid genotypes, suggesting prior recombination at the junction of ORF1 and ORF2. GII.2p16 strains had four significant amino acid changes in the P2 subdomain, suggesting antigenic changes. Before the 2009–2010 season, GII.2 chimera viruses had been observed only sporadically. This spreading of GII.2p16 strains in the 2009–2010 season might be the first epidemic of GII.2 chimera virus. This study revealed that the NoV epidemic in the 2009–2010 season differed considerably from the prior season, when GII.4 was predominant. Furthermore, GII.2 strains persisted in human populations by drastic recombination and gradual accumulation of mutations, indicating a prevalent pattern of non‐GII.4 genotypes with genetic evolution. J. Med. Virol. 84:517–525, 2012.

Reproductive interference and salinity tolerance differentiate habitat use between two alien cockleburs: Xanthium occidentale and X. italicum (Compositae)

In recent years, reproductive interference (RI), the fitness cost of reproductive activities among species, has received much attention as a factor in competitive exclusion by alien species. In this study, we aimed to explain the distribution of two annual alien Xanthium species (X. occidentale and X. italicum) found in the northern Kinki Distinct of Japan from the viewpoint of RI. First, specimen records demonstrated that Xanthiumoccidentale was more dominant in all habitats except seaside habitats. Subsequently, using artificial patches of potted plants, we demonstrated that X. italicum suffered intense RI from X. occidentale. Finally, X. italicum was superior to X. occidentale in tolerating salinity stress. Combining these results, we concluded that the asymmetrical RI caused by X. occidentale displaced X. italicum except in seaside habitats, where X. occidentale could not establish colonies. Furthermore, we discuss the possibility that a similar RI effect caused the extinction of native species.

Effective range of reproductive interference exerted by an alien dandelion, Taraxacum officinale, on a native congener

Reproductive interference (RI), defined as the fitness cost of interspecific sexual interactions, such as interspecific pollen transfer (IPT) in plants, is ecologically important. Theoretically, RI could result in competitive exclusion, as it operates in a frequency-dependent manner. Additionally, IPT may have a greater range than resource competition, although information about the range of IPT is lacking. In the present study, we measured the range of IPT exerted by Taraxacum officinale (an alien species) on a native dandelion, T. japonicum. We used two approaches. In one, we analyzed the RI effect on a native seed set at three spatial scales. In the second, we tracked IPT from alien to native flower heads using fluorescent pigments as markers. We estimated that pollination distances were in the order of several meters. These distances exceeded the mean distance from each native plant to the nearest alien. As hypothesized, the effect of RI reached farther than neighboring individuals. These data indicate the spatial range from which alien dandelions should be removed to allow the conservation of natives.

Distribution and pollutant load of hexabromocyclododecane (HBCD) in sewage treatment plants and water from Japanese Rivers

Hexabromocyclododecane diastereoisomers (α-, β-, γ-, δ-, and ε-HBCD) were investigated in river water, sewage influent, and sewage effluent from the Yodo River basin, Japan. The mean annual values of HBCDs ranged from 0.19 to 14ngL(-1) in river water. We observed that the concentrations of HBCDs in the brackish water area were low compared with that in the fresh water area. It was implied that, when the flow of the river stagnated in the estuarine area, HBCDs settled with suspended matter because of their hydrophobic character. In the sewage treatment plants, HBCDs ranged from 16 to 400ngL(-1) in sewage influent, whereas they ranged from 0.39 to 12ngL(-1) in sewage effluent. Over 90% of HBCDs were removed from the wastewater in the sewage treatment plants. By using these results, we estimated the pollutant load of HBCDs that flows into Osaka Bay from the study area. It was estimated that approximately 15kg of HBCDs flow into Osaka Bay from the study area in a year. This value is five orders of magnitude lower than the 2010 market demand for HBCDs (3019 metrictons) in Japan.

Detection and quantitative analysis of human bocavirus associated with respiratory tract infection in Osaka City, Japan

HBoV was initially identified in patients with RTI in 2005. Since its discovery, there have been continual reports concerning HBoV detection and its prevalence. In this study of clinical specimens from young children, real‐time PCR was undertaken to examine whether HBoV infection is associated with RTI and to support quantitative analysis of HBoV in these patients. In all, 376 specimens were collected from patients with RTI during April 2006–October 2008. Analyses revealed HBoV in 59 specimens (15.7%). Of HBoV‐positive patients, children under the age of 3 years comprised 94.9%. Of the HBoV‐positive samples, 47.5% were codetected with other respiratory viruses (dual infection, 27; triple infection, 1). During the study period, the numbers and rate of detection of HBoV were high mainly around May. Statistical analyses showed that the detection rate of HBoV during April–June was higher than during other months. Moreover, the viral load was greater in subjects with infection with HBoV alone than in subjects with mixed respiratory viral infections. Considering these results together, HBoV is probably associated with RTI in young children. However, the pathogenesis of this infection and the importance of the high rate of co‐infection remain uncertain. Additional epidemiologic information and further analyses are necessary to clarify the virological characteristics and the linkage of HBoV to disease.

Differential effects of reproductive interference by an alien congener on native Taraxacum species

Reproductive interference (RI) has been suggested to play a critical role in native plant displacement by alien congeners. However, although co-existence of native and alien congeners may provide an opportunity to refute the RI hypothesis, few studies have examined such a case. Using a native Japanese dandelion, Taraxacum longeappendiculatum, and a co-existing alien congener, Taraxacum officinale, we tested the hypothesis that differences in RI by the alien between native recipient congeners explain whether a native will co-exist with or be displaced by an alien. We conducted a field survey to investigate the effects of alien relative abundance on T. longeappendiculatum seed set, and a hand-pollination experiment to identify the extent of pollen interference by the alien on T. longeappendiculatum. We compared these results with those obtained previously for another Japanese native species, Taraxacum japonicum, which was displaced by the alien. In our field survey, alien relative abundance had little effect on seed set in nearby T. longeappendiculatum, and hand-pollination with mixed pollen grains produced no substantial decrease in seed set of the native species. Model selection supported these tendencies; the effect of RI by the alien differed between the two native species. Other potential factors, such as resource competition or habitat changes, could not explain the co-existence of T. longeappendiculatum with and exclusion of T. japonicum by the alien in the same explanatory framework. Considering the consistent explanatory power, the findings suggest that RI is a critical mechanism that can determine both co-existence with and displacement of native dandelions by an alien congener.

Conflicting intersexual mate choices maintain interspecific sexual interactions

Reproductive interference, interspecific sexual interactions that affect reproductive success, is found in various taxa and has been considered as a fundamental source of reproductive character displacement (RCD). Once RCD has occurred, persistent interspecific sexual interactions between species pairs are expected to diminish. However, reproductive interference has been reported from some species pairs that sympatrically coexist. Thus, the question arises, can reproductive interference persist even after RCD? We modeled the evolutionary dynamics of signal traits and mate recognition that determine whether interspecific sexual interactions occur. Our models incorporate male decision making based on the recognition of signal traits, whereas most previous models incorporate only female decision making in mate selection. Our models predict the following: (1) even when male decision making is incorporated, males remain promiscuous; (2) nevertheless, the frequency of interspecific mating is maintained at a low level after trait divergence; (3) the rarity of interspecific mating is due to strict female mate recognition and the consequent refusal of interspecific courtship by females; and (4) the frequency of interspecific mating becomes higher as the cost to females of refusing interspecific courtship increases. These predictions are consistent with empirical observations that males of some species engage in infrequent heterospecific mating. Thus, our models predict that reproductive interference can persist even after RCD occurred.