Development of Nine Markers and Characterization of the Microsatellite Loci in the Endangered Gymnogobius isaza (Gobiidae)

Gymnogobius isaza is a freshwater goby endemic to Lake Biwa, Japan. They experienced a drastic demographic bottleneck in the 1950s and 1980s and slightly recovered thereafter, but the population size is still very small. To reveal dynamics of genetic diversity of G. isaza, we developed nine microsatellite markers based on the sequence data of a related goby Chaenogobius annularis. Nine SSR (Simple Sequence Repeats) markers were successfully amplified for raw and formalin-fixed fish samples. The number of alleles and expected heterozygosities ranged from one to 10 and from 0.06 to 0.84, respectively, for the current samples, while one to 12 and 0.09 to 0.83 for historical samples. The markers described here will be useful for investigating the genetic diversity and gene flow and for conservation of G. isaza

Development of a Si/CdTe semiconductor Compton telescope

We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtain a high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results from the prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of a double-sided Si strip detector (DSSD) and CdTe pixel detectors, combined with low noise analog LSI, VA32TA. With this detector, we obtained Compton reconstructed images and spectra from line gamma-rays ranging from 81 keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and 356 keV, respectively, and the angular resolution is 9.9 degrees and 5.7 degrees at 122 keV and 356 keV, respectively.Comment: 12 pages, 14 figures, submitted to SPIE conference proceedings vol. 5501, "High-Energy Detectors in Astronomy", Glasgow UK, 6/21-6/24 200

Is the Relationship between Body Size and Trophic Niche Position Time-Invariant in a Predatory Fish? First Stable Isotope Evidence

Characterizing relationships between individual body size and trophic niche position is essential for understanding how population and food-web dynamics are mediated by size-dependent trophic interactions. However, whether (and how) intraspecific size-trophic relationships (i.e., trophic ontogeny pattern at the population level) vary with time remains poorly understood. Using archival specimens of a freshwater predatory fish Gymnogobius isaza (Tanaka 1916) from Lake Biwa, Japan, we assembled a long-term (>40 years) time-series of the size-dependence of trophic niche position by examining nitrogen stable isotope ratios (δ15N) of the fish specimens. The size-dependence of trophic niche position was defined as the slope of the relationship between δ15N and log body size. Our analyses showed that the slope was significantly positive in about 60% of years and null in other years, changing through time. This is the first quantitative (i.e., stable isotope) evidence of long-term variability in the size-trophic relationship in a predatory fish. This finding had implications for the fish trophic dynamics, despite that about 60% of the yearly values were not statistically different from the long-term average. We proposed hypotheses for the underlying mechanism of the time-varying size-trophic relationship

When to help juveniles, adults, or both: analyzing the evolutionary models of stage-structured mutualism

Mutualism is common in nature and is crucial for population dynamics, community structure, and ecosystem functioning. Studies have recently pointed out that life-history stage structure (e.g., juveniles and adults) is a key factor to better understand the ecological consequences of mutualism (termed stage-structured mutualism). Despite the potential importance, little is known about what kinds of stage-structured mutualism can evolve and when it is likely to occur. Here, we theoretically investigated how a mutualistic partner species should allocate efforts of mutualistic associations for different life-history stages of its host species to maximize its fitness. We assessed the partner’s optimal strategy by using a one host–one partner model with the host’s juvenile-adult stage structure. The results showed that different forms of stage-structured mutualism can evolve, such as juvenile-specialized association, adult-specialized association, and inter-stage partner sharing (i.e., the partner associates with both the juvenile and adult stages of the host) depending on the shape of association trade-off, i.e., how much association with one stage is weakened when the partner strengthens its association with the other stage. In general, stage-specialized association (either juvenile-specialized or adult-specialized association) tends to evolve when being associated with that stage is relatively beneficial. Meanwhile, when the association trade-off is weak, inter-stage partner sharing can occur if the mutualistic benefits of juvenile-specific and adult-specific associations are sufficiently large. We also found that when the association trade-off is strong, alternative stable states occur in which either juvenile-specialized or adult-specialized associations evolve depending on the initial trait value. These results suggest that pairwise interspecific mutualism is more complicated than previously thought, implying that we may under-or overestimate the strength of mutualistic interactions when looking at only certain life-history stages. This study provides a conceptual basis for better understanding the mechanisms underlying ontogenetic shifts of mutualistic partners and more complex mutualistic networks mediated by the life-history stages of organisms and their stage-structured interactions

Results of a Si/CdTe Compton Telescope

We have been developing a semiconductor Compton telescope to explore the universe in the energy band from several tens of keV to a few MeV. We use a Si strip and CdTe pixel detector for the Compton telescope to cover an energy range from 60 keV. For energies above several hundred keV, the higher efficiency of CdTe semiconductor in comparison with Si is expected to play an important role as an absorber and a scatterer. In order to demonstrate the spectral and imaging capability of a CdTe-based Compton Telescope, we have developed a Compton telescope consisting of a stack of CdTe pixel detectors as a small scale prototype. With this prototype, we succeeded in reconstructing images and spectra by solving the Compton equation from 122 keV to 662 keV. The energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1 keV at 122 keV, respectively. The angular resolution obtained at 511 keV is measured to be 12.2 degree (FWHM).Comment: 11 pages, 13 figures, presented at SPIE conference HARD X-RAY AND GAMMA-RAY DETECTOR PHYSICS VII", San Diego, 2005. To be published in Proc. SPIE 200

Alternative Stable States Generated by Ontogenetic Niche Shift in the Presence of Multiple Resource Use

It has been suggested that when juveniles and adults use different resources or habitats, alternative stable states (ASS) may exist in systems coupled by an ontogenetic niche shift. However, mainly the simplest system, i.e., the one-consumer–two-resource system, has been studied previously, and little is known about the development of ASS existing in more complex systems. Here, I theoretically investigated the development of ASS caused by an ontogenetic niche shift in the presence of multiple resource use. I considered three independent scenarios; (i) additional resources, (ii) multiple habitats, and (iii) interstage resource sharing. The model analyses illustrate that relative balance between the total resource availability in the juvenile and adult habitats is crucial for the development of ASS. This balance is determined by factors such as local habitat productivity, subsidy inputs, colonization area, and foraging mobility. Furthermore, it is also shown that interstage resource sharing generally suppresses ASS. These results suggest that the anthropogenic impacts of habitat modifications (e.g., fragmentation and destruction) or interaction modifications (e.g., changes in ontogeny and foraging behavior) propagate through space and may cause or prevent regime shifts in the regional community structure

ハンショク コウドウ ノ ヒョウゲンケイ カソセイ ニ ヨル タシュケイ ダイナミクス エ ノ エイキョウ

京都大学0048新制・課程博士博士(理学)甲第13639号理博第3297号新制||理||1485(附属図書館)UT51-2008-C557京都大学大学院理学研究科生物科学専攻(主査)教授 大串 隆之, 教授 今福 道夫, 教授 椿 宜高学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

Pollinator sex matters in competition and coexistence of co-flowering plants

Abstract Male and female pollinators often exhibit sex-specific preferences for visiting different flowers. Recent studies have shown that these preferences play an important role in shaping the network structure of pollination mutualism, but little is known about how they can mediate plant-plant interactions and coexistence of competing plants. The ecological consequences of sex-specific pollination can be complex. Suppose that a plant is favoured by female pollinators. They produce male pollinators, who may prefer visiting other competing plants and intensify the negative effects of inter-plant competition. Here, we analysed a simple two plant-one pollinator model with the sex structure of the pollinator. We observed that (i) sex-specific pollination can have complex consequences for inter-plant competition and coexistence (e.g. the occurrence of non-trivial alternative stable states in which one plant excludes or coexists with the other depending on the initial conditions), (ii) male and female pollinators have distinct ecological consequences because female pollinators have a demographic impact owing to reproduction, and (iii) plants are likely to coexist when male and female pollinators prefer different plants. These results suggest that sex-specific pollination is crucial for competition and coexistence of co-flowering plants. Future, pollination research should more explicitly consider the sex-specific behaviour of pollinating animals

Idea paper: Incorporating sexual differences in dispersal decision making into metapopulation theory

Dispersal is crucial for both individual fitness and spatiotemporal population dynamics. In sexual organisms, females and males have different reproductive strategies and therefore have different reproductive demands (i.e., reproductive resources and mating partners, respectively), which leads to differences in dispersal decision making between sexes. Although many studies have described sexual differences in dispersal behavior, little is known about the consequences for spatiotemporal population dynamics because metapopulation theory has considered only either nonrandom dispersal in asexual systems or random dispersal in sexual systems. To fill the knowledge gap, we propose a modeling framework that incorporates nonrandom and sex‐specific dispersal into metapopulation theory. It allows us to ask how female‐biased (e.g., in mammals) or male‐biased (e.g., in birds) dispersal can influence persistence of sexual organisms