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Day 12: Multi-level modelling in morphogenesis

The twelth day of the multi-level modelling in morphogenesis course was started by Dr Christen Mirth outlining the methods and theory of evolutionary-developmental biology (eco-devo).

In nature (and the lab) one can observe polymorphism. Sources of these polymorphic variations include both genetic and environmental factors. Meaning that the phenotype is composed of interactions between the genotype and the environment. This results in phenotypic plasticity, the ability of an organism to react to an environmental input with a change in form, state, or behaviour.

Many different organisms show striking examples of phenotypic plasticity. Famous examples include:

  • Daphnia cuclatta
  • Nemorai arizonaria
  • Priceis coenia

Furthermore there are many different inducers of phenotypic plasticity: predators, food, temparture and day length respectively for the examples listed above.

Looking at different phenotypes one can observe that they can have differing degrees of plasticity.

In order to go from an environmental queue to a difference in phenotype several mechanistic steps are required. The queue must be sensed by the organism. Some sort of signal must then be sent to the relevant tissue. The tissue must then interpret the signal and respond accordingly.

Dr Mirth then used the example of horn development in male dung beetles as a case study to illustrate how these processes may occur. Male dung beetles can either develop horns or become hornless. This dimorphism depends on larval nutrition provided by the mother.

One of the central problems for this particular example is that the horned and hornless dung beetles grow to the same size given the same amount of nutrition. So how does it regulate the size of the horn independently of the body size?

This is where the degrees of plasticity come into play. Where the initial levels of nutrients during development affect the plasticity of the horn growth relative growth.

In the last section of her talk Dr Mirth discussed the patterning of Drosophila wings, focussing in particular on the question of pattern coordination. From an impressive set of experiments looking at the expression levels of different hormones during development Dr Mirth managed to show, by perturbing the system, that the organ patterning is coordinated by a set of specific milestones.

The participants were then invited to experiment with computational models linking network evolutions to cellular behaviour.

After lunch Dr Mirth gave a keynote lecture expanding on the concept outlined in the morning describing phenotypic plasticity and the evolution of polyphenisms.

During her talk Dr Mirth described how nutrition can affect two different aspects of plasticity in Drosophila:

  • Body size
  • Ovarian size

The latter example was analogous to the male dung beetle horn development where the size of the tissue is reprogrammed in fashion that is independent of the whole body size.

Through a set of beautiful experiments Dr Mirth was able to show that different processes during different stages can be used to reprogram tissue growth.

After the keynote the course was wrapped up by the participants being handed their certificates and everyone breathing a sigh of relief before saying goodbye to their new found friends.

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