Jag planerar ett gymnasiearbete angående Bisfenol A;s påverkan på vattenloppor. Jag hade helst velat undersöka påverkningarna under deras parning fram tills äggkläckningen. Finns det något sätt att skynda på denna period då den tar ca 7-8 månader? Jag funderar på att temperaturen spelar en stor roll i detta skede och undrar om det funkar att sänka/höja temperaturen efter loppornas behov?
The life cycle is different for different species of water fleas. I guess you will work with Daphnia magna or Daphnia pulex. These are the most common species in Sweden and they are also most commonly used for research. The life cycle of those two species is pretty similar.
The lifecycle of water fleas is not programmed, but the different life stages are triggered by stimuli from the environment. So this means you can speed up the sexual reproduction of the water fleas. But this also means you have to give them the right stimuli to get them to reproduce sexually.
For your project there are three critical phases. Normally, when water fleas are happy they reproduce clonally. In that part of the life cycle there are only females present. So first you need to make sure the water fleas are starting to produce males. In nature they start doing that at the end of summer, when the days are getting shorter, when there is less food around and when population densities are high. In the lab you can do this by shortening the period of the day they get light, reduce food and put more water fleas in smaller jars (make it more crowded).
Once there are males around, the water fleas will start to reproduce sexually. You can see this because the eggs in the brood chamber (on the back of the females) look differently. When they reproduce clonally you will see many loose eggs in the brood chamber, while when they reproduce sexually there will be two eggs in a so-called ephippia (resting eggs), which looks like a brown coloured pod with two beans in it.
Once the mothers released the resting eggs, you need to store them to simulate winter. There are various ways of doing that, but the most important part here is that the resting eggs are kept at low temperatures in the dark for a while. A normal fridge (4 degrees) is perfect for that.
Last step is to get the resting eggs to hatch. For this you need to expose them to room temperature and light (for instance a 16 hour light and 8 hour dark cycle). For us this works, but some people also peel off the ephippia or dissolve it with chemicals.
– Gästinlägg av Reinder Radersma, Daphniaforskare på Biologiska Institutionen
