[2C2] Ecology, Development and Evolution
- New trends in Evolutionary Biology -

Workshop

Toru MIURA and Seshiro AOKI (University of Tokyo)
cmiu@mail.ecc.u-tokyo.ac.jp, saoki@bio.c.u-tokyo.ac.jp

• Evolution of the body plan and the developmantal systems in insects
  Isao SARASHINA, Taro MITO, Hideyo OHUCHI, Sumihara NOJIiThe University of Tokushima)
  

  The major features of the insect body plan include segmentation and the organization of that into three distinct regions: head, thorax and abdomen. Although almost all insects have such a segmented body plan in common, the developmental processes of patterning the organized segmentation varies substantially among insects. Long germ insects including Drosophila generate all segments almost simultaneously, while short and intermediate germ insects which probably have a primitive mode of development produce most segments successively rather than all at once. To investigate the evolution of the developmental systems in insects, we adopted an intermediate germ insect, Gryllus bimaculatus (two-spotted cricket). We examined embryogenesis of G. bimaculatus using some staining techniques and clarified the early cellularization pattern. We also examined the expression patterns and functions of some genes involved in the genetic regulatory hierarchy form segmentation in G. bimaculatus using in situ hybridization, immunostaining and RNAi. Our results suggest that the functions of segment polarity and Hox genes may be conserved between G. bimaculatus and Drosophila. In contrast, at the more early stages some of the developmental systems may be different between them. These findings may give useful information for discussing the evolution of the developmental systems in insects.

• Evolution and mechanisms of caste polyphenism in social insects - alteration of body plan induced by ecological factors
  Toru Miura (University of Tokyo)
  

  Developmental processes of organisms are not determined completely autonomously, but interact with environmental factors. Threrfore, phenotypes of organisms vary responding to those factors (phenotypic plasticity). Among these, some organisms express several discrete adaptive phenotypes, and therefore called "polyphenism". Social insects possess several types of individuals (castes) in their colonies, to which tasks are allocated. Here I introduce three topics of our studies related to caste polyphenism in social insects. All species of termites possess distinct sterile soldiers, which have specific morphology suitable for defense. We isolated genes related to the soldier differentiation in termites, and analyzed the expression profiles of those genes. In ants, although the developmental fate of caste is determined in the early stage of development, apoptotic degeneration occurs in wing primordial of future workers. The apoptotic wing degeneration is suggested to be common in many ant species. In the complicated life cycles of aphids, the earliest polyphenism can be seen in the different reproductive modes (sexual or asexual). We compared the developmental process between sexual and parthenogenetic embryogenesis using various developmental markers. I will compare these studies on the alteration of body plan, which respond to environmental signals, in order to discuss the evolutionary process of the interaction between ontogeny and environments.

• Polyembryony and Caste Formation in a Parasitoid Wasp
  Laura S. Corley (Department of Entomology, Washington State University)
  

  Striking morphological differentiation among individuals structures the complex societies found in insects such as termites, bees, and ants. Castes have also evolved in other insects such as aphids, thrips and polyembryonic wasps. Copidosoma floridanum is a polyembryonic parasitoid wasp that produces two castes during development from a single egg. Polyembryonic development proceeds by a process of cellular proliferation resulting in a single brood containing approximately 950 reproductive larvae that develop into adult wasps and 50 precocious larvae that function as soldiers. We examined how the single egg proliferates and responds to environmental factors to produce two castes in C. floridanum. We conducted transplantation experiments of wasp morulae from all developmental stages into hosts from all larval stages. Our results indicate that the earliest stages of wasp morulae have the highest proliferative capacity and produce both larval castes. The older wasp morulae produced significantly fewer larvae and could produce one caste or the other, but not both. Host environmental affects (i.e. -- hormonal titers, nutritional state, etc.) did not significantly change the proliferative capacity or caste fate of the morulae. Thus, embryonic cellular proliferation is intrinsically regulated and is linked to totipotency in Copidosoma floridanum.

• Reconstruction of ancestral sequence, function and morphology.
  Seishiro AOKI (Department of Life Sciences,@Graduate School of Arts and Sciences, University of Tokyo)
  

  The diversity of living thing charms us. It is thought that such diversity was produced by adding various mutations to the genes which ancestors had. Let's suppose this thought is true. Then, 'if we return the variation in molecular evolutionary process and recover an ancestor type gene, can't we restore the feature of an ancestor living thing?' Based on this idea, I am investigating some plant genes. Restoration analysis to these genes is performed about the character which some of ancestor plants probably showed. I will explain the Ngrol genes which had transferred to the genome of wild-type Nicotiana plants from the plasmid of Agrobacterium in accordance with this idea. I will show that two point mutations to the NgrolB gene restore the feature of an ancestral Nicotiana plant (Aoki and Syono, PNAS, 6:13229-34, 1999). I am introducing this analysis to the floral homeotic genes, MADS gene family. Study of the adaptive evolution of flowers is in progress.

• Genetic regulation of flowering-time in annual monocarpic plants: lessons from Arabidopsis and rice
  Araki, Takashi (Division of Biological Science, Graduate School of Science, Kyoto University)
  

  The floral transition, switching from the vegetative to reproductive phase, is an important life history event in monocarpic plants. Appropriate timing of the floral transition ensures optimized resource allocation and seed production under favorable conditions. Synchrony of flowering in the population as well as with the availability of pollinators can be achieved by the floral transition in response to certain environmental cues such as photoperiods. For plants growing in adverse conditions such as under the shade of other plants, precocious flowering may serve as a strategy for escaping the condition both temporally and spatially. Recent molecular genetic studies in an annual plant, Arabidopsis thaliana (Brassicaceae) revealed complex regulatory cascades for regulation of the floral transition. Environmental cues and endogenous signals are transduced through four regulatory pathways to regulate transcription of "floral pathway integrator" genes. These "integrators" in turn regulate genes involved in the floral fate specification in nascent lateral meristems. It was shown that components of the "photoperiod pathway" are conserved between Arabidopsis and rice, despite contrasting photoperiodic responses. Current knowledge in these two species will provide a framework for understanding molecular genetic basis for adaptation in flowering time, an important life history trait in annual monocarpic plants.