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iLabs: “Catch of the Day” — Rotifers in a “micro” argument!

August 11, 2014

By Nancy Locquet-Absillis

Life in a drop of pond water doesn’t seem to be very exciting right? Well, this is what happened one sunny morning in the Micro World Investigate Lab…

We took a drop of pond water, placed it under the EVOS microscope and tried to look for interesting microorganisms when suddenly, a familiar protozoa came into view.

It was one of those bulb-like rotifers (probably Trichocerca), using its spurs (toes) to anchor itself to substrate while drawing in gulps of water containing food particles. As there are about 2200 species of rotifers described, it’s difficult to make a positive identification of this particular one.

Moving seemed easy, it just let go of the sediment it was anchored to and used its adhesive gland, located above the foot, to hold on to some sediment a few microns away. Its mastax (grinding tooth) was pulsing in its body like a heart.

A feeding rotifer

A feeding rotifer.

On its path was another rotifer minding its own business, being firmly attached to some sediment. Its head (called corona) showed 2 crown-shaped rotating disks. If you looked closely, you could even see the cilia (small hairs) sway. Since these cilia move so fast, it gives the impression that the corona (crown) is rotating. That’s probably how it got its name … rotifer.

Rotifer with corona, cilia and mastax visible

Rotifer with corona, cilia and mastax visible

Anyway … when these 2 different rotifers met, an interesting event happened. The bulb-like rotifer started to attack the body of the attached rotifer. Trying to avoid the ferocious attack, the “crown type” rotifer (Bdelloid rotifer) crunched and collapsed as it was protecting its corona inside its body.

One rotifer attacking another (Bdelloid type) rotifer

One rotifer attacking another (Bdelloid type) rotifer.

Another view of one rotifer attacking another

Another view of one rotifer attacking another.

In an attempt to break up the argument, we tapped on the wet mount slide with a pencil but that didn’t change the bulb rotifer’s mind. Why the attack? Did she want that spot? Was she so hungry she started attacking another rotifer?

According to Dr. Peter Starkweather from the University of Nevada Las Vegas, most rotifers are females and they are the ones feeding constantly. These multicellular organisms are made up of about 1000 cells and they have a complete digestive system.

Female rotifers can be classified into three groups by the way they eat:

  1. Filter feeders take in volumes of water and filter out food particles.
  2. “Graspers” use their coronas to hold on to their food and chew it up with their trophies (a jaw like structure in the mastax region).
  3. Capture feeders trap their prey with their coronas before they devour it.

Here are two videos of a feeding rotifer in action:

 

Male rotifers don’t eat—they only live for a few hours and don’t even have the structures necessary to eat— so the ones we saw attacking were females.

It was clear that the cilia of the Bdelloid rotifer (crown-type) were creating a circular current of water drawing food particles into its mouth. She seemed to be filtering the water for algae, small single celled organisms (organism that consist of only one cell), debris, and bacteria while the bulb-like rotifer was showing some signs of cannibalism.

Several attempts to save the Bdelloid rotifer (crown-type) failed and we almost felt sorry for her until all of a sudden their roles were reversed: the bulb-like rotifer got caught in the current created by the cilia of the Bdelloid rotifer and it was spinning out of control locked by the water flow. Was this rotifer revenge?

This argument ended with the bulb-like rotifer retreating in search of some “quiet waters” while the “crowned one” emerged victorious.

The attacking rotifer withdraws from the battle

The attacking rotifer withdraws from the battle.

 

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One Comment leave one →
  1. goldfire407 permalink
    August 11, 2014 4:36 pm

    Hi Deb, this was great, I love this stuff.     Love, Aunt Pat        m: “NC Museum of Natural Sciences Education Blog” To: goldfire407@comcast.net Sent: Monday, August 11, 2014 3:01:11 AM Subject: [New post] iLabs: “Catch of the Day” – Rotifers in a “micro” argument!

    debrabailey posted: “By Nancy Locquet-Absillis Life in a drop of pond water doesn’t seem to be very exciting right? Well, this is what happened one sunny morning in the Micro World Investigate Lab… We took a drop of pond water, placed it under the EVOS microscope and tr”

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