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Posts from the ‘Life history’ Category

Squeezing out the last egg

Annual fishes of the genus Nothobranchius are endemic to temporary ponds. When exposed nonlethally to a predation risk, their reproductive efforts are increased, likely to reproduce as much as possible before being predated upon.

This experiment was done by Arnout Grégoir, who recently defended his PhD. We are learning more about the interesting life histories of these remarkable vertebrates, that, in terms of certain life history aspects, have more in common with aquatic invertebrates than  fish.

The paper is out now in Ecology & Evolution.


Aridity promotes bet hedging

In a new paper Tom Pinceel shows that crustaceans from ephemeral water bodies have different egg hatching frequencies depending on local climatic conditions. If the climate is harsher and less predictable, a lower percentage of eggs hatches after rains. This ensures that more long lived eggs are left that may grow during future conditions!

The work has been published in  Oecologia


Using X rays to look inside zooplankton resting eggs

Zooplankton dormant eggs are time capsules that can transport offspring to distant futures. However, after decades of study we still don’t know very well how this mechanism has evolved and how it works from a mechanistic point of view.

In new paper, Tom and I decided to use the VUB’s micro CT scanner to have a look at the internal structures of zooplankton resting eggs. Why would we want to? Well, in the past, the only way to look inside them was to freeze dry them, cut them and look at them with a scanning electrone microscope. This means that you’d have to kill the embryo and that the procedure might result in artefacts. You might see structures that don’t look that way in real life. Given that we are doing a lot of experiments on the evolutionary importance of differential hatching from resting eggs we were really keen to have a look at exactly what’s going on inside these eggs before they decide to hatch.

This pilot experiment showed that the method can yield useful images although the resolution is less than SEM. In addition it turns out that the embryos in the eggs also don’t seem to suffer too much from the X rays and most of them still hatch afterwards. More information, is likely to follow as soon as we can start to link embryonic and egg traits to the hatching behavior of eggs.


3D reconstructions of resting eggs obtained via X ray scanning. Top left: a cyst of the fairy shrimp Branschipodopsis wolfi, Top right: a cyst of the tadpole shrimp Triops. Bottom: an ephippium with two resting eggs of the water flea Daphnia magna.

Modeling the sensitivity to climate change

In a new paper out in Scientific Reports, we use a matrix population model to test how sensitive populations of fairy shrimps are to changes in climate. The stepwise modeling procedure allows to calculate the long term population growth as a measure of fitness. If it is positive, the population will survive, if it is negative it will not. It does this by calculating, for each generation, how many eggs would be produced based on known life history traits of the species and a measure of environmental quality of the inundation (in this case represented by inundation length).

For most species it is very difficult to know how they would respond to changes in climate. However, for our fairy shrimp we have a lot of background information that allows us to make educated guesses about which life history traits could be important. We know for this species that it requires a specific amount of time to reproduce which is related to how long a pool can hold water and on the conditions they need to hatch. We also know how much eggs they can produce per day, how many eggs hatch during each inundation etc…


Population of the fairy shrimp Branchipodopsis wolfi in a temporary rock pool on a mountaintop in South Africa

The length of these inundations is one environmental parameter (of many) that will change under changing climates. But it is an important one that is directly linked to fitness. Shorter inundations means less inundations that are long enough for reproduction.

We were – and are – still ignorant about how these species will respond to these changes. However, the model does allow us to test which life history traits could be important to maintain long term survival of the populations. As such it shows which traits could help populations to survive.

One of the conclusions of the study is that, when inundations are short, it would be beneficial to make sure that a lower fraction of eggs would hatch during a given inundation. Such a mechanism could be an example of a risk spreading theory that is consistent with predictions of evolutionary bet hedging theory.

It is still a simplistic model, so it does not tell us how things will go in the future. It does not capture tradeoffs among life history traits nor the evolutionary potential of the populations.  Yet, it still narrows down the range of possible future scenarios of these populations by showing what the consequences for population survival would be if populations could respond adaptively or plastically and change there life history traits.




Congratulations Dr. Jane Reniers


After four years of frog hunting and intense experimenting, Jane Reniers defended her doctorate on amphibian life history strategies. The title of her doctorate was Managing Reproductive Challenges in Time Constrained Environments. Amphibian life history variation from clutch to landscape. I believe PhDs are all about managing challenges in a time constrained environment. And just like the amphibians she studied, Jane managed to overcome a lot of challenges and bad luck but still defended succesfully after just more than four years. A great job with a nice booklet to show for it… and a lot of great manuscripts still waiting to be published!

While she is moving on to new challenges, we will miss Jane’s spirit and laughter in the lab. But no doubt we will continue to collaborate to publish the remaining chapters of her PhD. We wish you all the very best Jane!