Daphnia: what you did not know

We thought we knew daphnia well.

Yet there are a number of things that most people do not know. Some are truly astonishing, unexpected, and come from very recent research.

They have often even surprised the scientists who discovered them!

 

An organised gregarious behaviour

Daphnia are gregarious animals, living in "herds".
Konrad Lorenz, the father of the study of animal behaviour, described in one of his books their behaviour quite similar to that of fish schools or starling flocks.
These numerous clouds formed by daphnia confuse predators who thus find it hard to focus on a single prey.
It is observed that, in still water, daphnia always gather in dense groups.

However, nothing is known about their "social" behaviour and exchanges between individuals.

 

Hereditary transmission of acquired traits

Recent research on epigenetics has shown in daphnia a capacity to pass on acquired traits to their offspring.

In the presence of danger, for example if fish are present in the environment, daphnia produce offspring equipped with protections such as a longer chitinous spine and a more developed "helmet".

The DNA is not changed, but some inactive genes are activated and remain so during reproduction.

There is therefore a "transgenerational memory", with future generations inheriting acquired, not innate, traits from previous generations.

 

Babies as rich in protein as brine shrimp nauplii

Newborn daphnia are called "neonates". They are the equivalent of brine shrimp nauplii, but much easier to produce because each female daphnia produces neonates continuously without eggs.

These neonates are as rich in protein as brine shrimp nauplii.

So you can perfectly feed your fry with very young daphnia, which are also similar in size to brine shrimp nauplii.

To do this, just let large adult daphnia live in the spawning tanks. These daphnia, too big to be eaten, will continuously produce neonates that the fry can catch as needed.

The advantage is that daphnia is not salty and survives indefinitely in fresh water.

 

A microbiome passed on to offspring

Daphnia is a favoured model in laboratories for the study of the microbiome.
These recent studies, which focus on the bacterial flora (but also viral, fungal, etc.) inside animals, are sources of valuable medical discoveries.
The study of the microbiome is a revolution.

Daphnia has a fairly stable and constant microbiome, which allows studying the effects of its variations on its lifespan, growth, appearance, health, and other parameters such as behaviour.
The effect of the daphnia microbiome on certain genes determining its lifespan has been identified. And since these genes also exist in humans, this research is very important.

Neonates receive their mother's microbiome, but it is also known that, in the case of daphnia eggs, the microbiome is partly on the egg shell and is passed on at hatching!

 

Ephippia that last a century!

When daphnia sense that environmental conditions change and put them in danger (for example when winter comes, or also during a heatwave), they lay some males and sexual reproduction takes place, instead of the usual parthenogenetic reproduction (females alone produce females).

When fertilised by males, females no longer lay ready-made neonates but "resting eggs", called ephippia. These resting eggs, black in colour and grouped in pairs, wait for more favourable conditions to hatch and then rebuild a new population of daphnia.

Ephippia resist freezing, drought, heat and... time. It is now known that these eggs can remain viable for more than a century!

Brine shrimp are therefore completely outdone!

 

A dizzying capacity to multiply

A daphnia begins to reproduce from the age of one week.
During its short life of just over a month, it will produce 10 to 30 broods (up to 20 or 30 neonates per brood).

It has been calculated that a single daphnia magna, under the most ideal conditions, could theoretically produce in just 3 months a population of... 100 billion individuals, all females! This remains obviously a simple theoretical calculation.

Of course, under more realistic but decent conditions, it will be less: between 10 and 50 million only!

 

All my daphnia magna produced since the creation of Aquazolla come from 4 poor survivors collected in 2004!

Aquatic invertebrates are an absolutely fascinating world.