[IPM:1338] Wolbachia 研究Dr Stouthamer 来日予定

[Kazuki MIURA <miurak@xxxxxxxxxxx>]

皆様（重複して受けてとられる方申し訳ありません）

三浦一芸＠近中四農研です．
このたびJSPSのご厚意によりRichard Stouthamer博士（カリフォルニア大学
リバーサイド分校）を３月１日から２１日まで私の研究室へ招へいすることができました．
博士はご存じのように細胞内共生微生物Wolbachiaによる寄生蜂の単為生殖化の
発見やメカニズム研究などで有名な方です．あと，分子生物学を利用した寄生蜂の分類とかあります．
例えば論文としては
Stouthamer R., J.A.J. Breeuwer, R. F. Luck, and J. H. Werren. 1993. Molecular  identification of 
   microorganisms associated with parthenogenesis. Nature 361:66-68.
Huigens, M. E., R. F. Luck, R.G.H. Klaassen, F.M.P.M. Maas, M.J.T.N. Timmermans, and R. Stouthamer.
   2000. Infectious parthenogenesis. Nature 405:178-179.
Stouthamer, R., M. van Tilborg, H. de Jong, L. Nunney, and R. F. Luck. 2001. Selfish element maintains 
sex in natural populations of a parasitoid wasp.        Proceedings of the Royal Society London B. 268: 617-622.
があります．
博士は基本的には私の研究室（広島県福山市）に滞在しますが，
以下の予定でセミナーを開きます．
もし，よろしければご参加くださいますよう
お願い致します．なお，京都府立大で行われるセミナーについては
阿部芳久氏に参加方法についてはお訊ね下さい．

日時：３月６日（土）午後16:30ごろ開始
場所：京都府立大学　図書館３階　視聴覚室　（日本昆虫学会近畿支部２００４年度大会の特別講演として）
演題：The evolution of virginity enforcement in populations infected with parthenogenesis Wolbachia
要旨：Parthenogenesis Wolbachia infections are known from many different insect species. 
In most populations where these infections are found the whole population is infected and 
all individuals are females. Exception to this rule are many species fo the parasitoid wasps 
genus Trichogramma, where both infected and uninfected individuals of the same species co-exist and
where mating between infected females and uninfected males results in infected "hybrid" offspring. 
In populations where all individuals are infected sexual reproduction is no longer possible because no
males are produced. However, if males are produced through antibiotic treatment, these males appear
to be unable to successfully father offspring with infected females. Several hypothesis have been posed
to explain why the sexual reproduction cannot be restored,: 1. Passive accumulation hypothesis: The
passive accumulation of mutations renders traits involved in sexual reproduction inoperable in
completely infected populations, 2. Active selection hypothesis: the active selection against costly traits
involved in sexual reproduction in females in completely infected populations, and 3. The virginity
mutations hypothesis: the active selection for the production of males in populations with a large
proportion of infected females, causes such "virginity" mutants to spread when the population is
female biased, eventually resulting in the fixation of these mutants in the completely infected
population. I this seminar I will explore these different hypotheses through a modeling approach and
show that the latter hypothesis results in an almost unavoidable fixation of these "virginity mutants"
in infected populations. While the outcome of hypothesis 2 and 3 are identical the mechanism causing
this fixation is more powerful under hypothesis 3. 
お世話をしていただく方　阿部芳久氏　y_abe@kpu.ac.jp
　
日時：３月１１日（木）１４：００〜１７：００
場所：岡山大学農学部第１講義室（１号館南側１階
演題：Manipulating microbes versus parasitic chromosomes: The dynamics of sex ratio distorters in Trichogramma kaykai 
field populations
要旨：Field populations of the egg parasitoid wasp Trichogramma kaykai have a low infection 
frequency with parthenogenesis Wolbachia. Infections with parthenogenesis Wolbachia cause infected
females to produce daughters from both fertilized and unfertilized eggs. Over the years the infection
remained within the range of about 4-15%. These low infection frequencies are difficult to explain.
Using models we explored the possible reasons for these relatively low infection frequencies, although
such low infection frequencies were possible simply based on inefficient transmission of the Wolbachia,
the models showed that slight changes in the environment would result in large fluctuations of the
infection frequency.  Because we do not observe such fluctuations, we modeled the presence of
suppressor genes- genes that would overcome the Wolbachia or its effect on the host- in these
populations, these models showed that if such suppressors were present the infection frequency would
be very stable at around 10%. However we could not find evidence for such suppressors in the field.
Finally we modeled the presence of a second sex ratio distorting factor in the population: the Paternal
Sex Ratio chromosome. This PSR chromosome causes fertilized eggs to develop into males that are
again carriers of the PSR chromosome. Modeling showed indeed that this factor could stabilize the
infection frequency in the field at the levels we observed. Subsequent field work showed that this
factor was present in the populations of T. kaykai.
　同時に広島大学の田上陽介氏に「Wolbachia感染のコストとその減少要因・Trichogrammaにおける微生物とその奇妙な共存関係につ
いて」も講演して頂きます．
お世話をして頂く方：宮竹貴久氏　miyatake@cc.okayama-u.ac.jp

日時：３月１３日（土）15:00開始
場所：東京大学農学部，7号館A棟，1階，104・105教室
演題：Manipulating microbes versus parasitic chromosomes: The dynamics of sex ratio distorters in Trichogramma kaykai 
field populations
要旨：上記と同じ
お世話をして頂く方：星崎杉彦氏（ahossy@mail.ecc.u-tokyo.ac.jp）

日時：３月15日（月）　15時30分〜17時
場所：農業生物資源研究所大わし本館（旧蚕昆研） ２Ｆ輪講室
演題：Sex determination in Hymenoptera
要旨：For a long time the sex determination in Hymenoptera is thought to be some modification of the 
mechanism that was recognized around the 1920 in the parasitoid wasp Bracon hebetor. In this
species the sex is determine through a sex determination locus. If an individual is haploid it is always
a male, while diploid individuals can be either a female of a male. Diploid females come about when
two different alleles are present on the sex locus, while diploid males are formed when the individual
is homozygous at the sex locus. This so called Complementary Sex Determination system is thought to
be ancestral in Hymenoptera. Indeed it is known from a number of different taxa including the
Ichneumonoidea, bees, ants, and sawflies. In other taxa evidence for CSD does not exist, there all
diploid individuals appear to be females and all haploid individuals are males. To fit these groups in
the CSD system other modifications of the system were envisioned, for instance it was thought that
instead of a single locus, several loci might be involved that influence the sex determination. Under
that hypothesis diploid individuals would only become diploid males if they were homozygous on all
sex loci. The frequency of diploid males in a randomly mating population or even in a population with
sib mating would be very low, this might have explained the lack of evidence for this hypothesis.
However the ultimate demise of this hypothesis came about when we showed that in 100%
hymozygous Trichogramma wasps the diploid individuals still became females. Since that time it has
also become clear that some of the members of for instance the Ichneumonoidea, do not have the CSD
system either. In conclusion although the CSD may be the ancestral form of sex determination in
Hymenoptera, many species have evolved a sex determination system that allows diploid homozygous
individuals to develop as females.
お世話をしていただく方：野田博明氏（hnada@affrc.go.jp）

何卒ご参加くださいますようお願い致します．

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三浦 一芸（みうら かずき）
独立行政法人農業技術研究機構
近畿中国四国農業研究センター虫害研究室
（広島大学大学院生物圏科学研究科併任）
〒721-8514
福山市西深津町6-12-1
TEL:+81-(0)84-923-4100
FAX:+81-(0)84-924-7893
E-mail:miurak@affrc.go.jp
（アドレスが変わりましたcgkがなくなりました）