Archive for eco-devo

Parasitoid wasp

Last week, one of my colleague sent me this photo.

His son collected a lepidopteran worm to observe. Some days after that, the worm died with lots of weird stuffs.

I’m sure this is because of parasitoid wasp, which probably belongs to the family¬†Braconidae. These parasitic wasps are really fascinating! The host insect species are diverse and the parasites adapt the life history and physiology of host species.¬†

I am not familiar with the parasitic wasps but the some wasps show phenotypic plasticity depending on host insect species. This sounds very interesting to me, so I will talk about this some time.

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Model animals for evo-devo

I’m recently thinking about a new model organim for the study of evolutionary developmental biology, i.e. evo-devo. As recently published an article by Jenner and Wills (2007), daphnids are good materials as well as dung beetles and sea anemones, because they are easy to keep in the lab, and show exellent array of phenotypic plasticity.

Jenner RA, Wills MA (2007) The choice of model organisms in evo-devo. Nature Rev Genet 8: 311-319.

Therefore, I am trying to get a grant for the evo-devo study uisng daphnids.

From this April I now have 13 lab members, who are engaged in the evo-devo works in relation to polyphenism in ants, termites, aphids, daphnids and stag beetles. For me, this situation is really exciting but it’s also exhausting as well (ha-ha).

Daphnia pulex

Daphnia pulex

This organism belongs to Crustacea, Arthropoda. We are also working on the predator-induced polyphenism seen in some species of the genus Daphnia. They produce special structures such as horns or spines at the top of their heads.

In the case of our focal species Daphnia pulex, the chemical substances called ‘kiromone’ secreted from predator species, induces a few spines at the back of their heads. Those spines are called as ‘neckteeth’. If this structure exists on their heads, the predatatory mosquito larvae cannot feed them, because these spine stuck in their throat. We are studying on the developmental mechanisms that produce this structure.

In addition, they have interesting life cycle, similar to aphids. Most generations produce only female individuals parthenogenetically. But under bad conditions such as starvation, they produce male and female individuals which mate with each other and then produce diapausing eggs.

I think this type of animals like aphids and daphnids, potentially possess features that plastically change their phenotypes by controlling their embryonic and postembryonic development.

Juvenile hormone

juvenile hormone III

Juvenile hormone (JH), one of the important insect hormones, plays various important roles in the physiological regulations in insects. In our study on insect polyphenism, for example, JH triggers various morphological changes such as phase polyphenism in locusts and aphids, caste differentiation in social insects etc. Many of the insects use juvenile hormone III (JHIII), which is the simplest form of JH. JHI and JHII are also known, but only in Lepidopteran insects.

However, the mechanisms of reception of this hormone remains to be unsolved. No one knows the receptor for JH. Many works suggested that the threshold for JH must be the important regulatory mechanism of polyphenic traits.

Interestingly, various types of analogues for this molecule (JHA) can mimic the function. For example, in termites, we can induce soldier differentiation by the artificial applicaiton of JHA. We often use this method to investigate the developmental mechanism of soldier differentiation.