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iLabs: Rotifers are Male or Female or Both or Neither?

June 27, 2012

Well here’s your multiple choice question for the morning:

Rotifers are:

1) only male

2) only female

3) both

4) neither

5) all of the above

6) a mix of 2 of the above (and if you choose this,  for extra credit – say which two answers apply)

Need your coffee first? Wondering why I am even getting into a discussion this early about rotifer genders?

Yesterday we had a visitor in the lab who after viewing the live rotifers on the microscope, asked if there were male and female rotifers. I told her I would post a reply to her question on the blog, so here we go.

I read recently that rotifer sex is  complicated. Well complicated is a good way to describe the answer to the above question.

First, there are some classes of rotifers that are only female, at least no males have ever been found, and they reproduce asexually. That means the females clone themselves so hence, no males.

There are classes of rotifers that are male and female and reproduce sexually. And apparently that’s the only reason for having the males around – they don’t even eat, they just produce sperm.

So we can say that the correct answer above would be #6, and for extra credit, it’s 2 & 3.

But remember I said rotifer reproduction is complicated? There is  in an interesting twist here. Aside from the fact that males don’t eat and only spend their time producing sperm, they also have half the number of genes as females!!! How in the world did that happen?

In times of environmental stress, such as diminishing water supply, females can produce daughter cells that can create eggs by meiosis. These eggs can be fertilized by sperm, in which case they become more females, or they can remain unfertilized, in which case they become the males

This information comes from a website done by the University of Nevada at Las Vegas and the NSF, called Desert Survivors, which has a page with all kinds of facts about rotifers,(as well as a link to the streaming video episode about rotifers).

In any event, this fact page does a very nice job of explaining rotifer reproduction amongst other things

(As an aside, the UNLV also has a number of other really interesting nature shows available as well. To see the episode list, click here)

Here are a couple of other helpful links that talk about rotifers, gender, and reproduction:

1) Rotifers at Wikispaces

2) Rotifers at Wikipedia

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