sexual reproduction of Tintinnids

[Franz Neidl]

You see the conjugation of two tintinnids. "The two cells form a bridge between their cytoplasmas, the micronuclei undergo meiosis, the macronuclei disappear, and the haploid micronuclei are exchanged over the bridge. The cells separate and form new macronuclei from their micronuclei" (cfr. "Ciliate" in Wikipedia).

(The microorganisms are always very good in confusing people which is studing them).

Franz

2 pictures

[BJ]

Franz,

Spectacular!

thank you,

Brian

[Jacek]

perfect shot, beautiful photos

[Mitch640]

Very nice find.

[Wim van Egmond]

Brilliant series, also the less sexy other post.

Wim

[Cactusdave]

Remarkable pictures. A very lucky capture.

[Bruce Taylor]

A truly wonderful documentation of Tintinnid conjugation!

[naturephoto1]

Franz,

Excellent images and work.

Rich

[Pau]

A very nice complement to the asexual set in yourt other post.

But..., excuse me a question: ciliate conjugation, being undoubtely a sexual phenomenon because of genetic recombination, may it be qualified as reproduction when the number of individuals remain constant?

[Franz Neidl]

Hello Pau,

after this event the two cells divide, forming four new cells (cfr. article "Reproduction" in Wikipedia).
But I have to admitt that also for me it is difficult to understand, as I am not a specialist. This following second step seems to me a form of asexual reproduction. I dont know if I am right.

Franz

[Bruce Taylor]

A very nice complement to the asexual set in yourt other post.

But..., excuse me a question: ciliate conjugation, being undoubtely a sexual phenomenon because of genetic recombination, may it be qualified as reproduction when the number of individuals remain constant?

You are exactly right: conjugation -- like autogamy, or self-fertilization -- is a sexual phenomenon distinct from reproduction (and not an alternative to fission). The Wikipedia article on Ciliates (which Franz quotes, above) was quite misleading on that point. As it happens, I've just finished editing the Reproduction section in that article...and when I came here I saw your post.

All ciliate reproduction is by fission, of one kind or another (and there are many kinds!). Fission is typically preceded by either conjugation or autogamy, but these are not alternative modes of reproduction. To make more ciliates, you must divide the cells.

A passage from Denis Lynn's The Ciliated Protozoa:

[T]hough there are a number of types of fission , the only kind of reproduction in ciliated protozoa is asexual , textbook statements notwithstanding (i.e., conjugation , for example, is
a sexual phenomenon but not sexual reproduction)

[Bruce Taylor]

after this event the two cells divide, forming four new cells

It's true that division by fission always follows conjugation (although the result is not always four new cells: when Vorticella divide, for instance, one of the conjugants is absorbed into the other, and the subsequent division yields only two cells). Note that, in this respect, conjugation is not different from the self-fertilization (autogamy) that precedes the binary fission that occurs when no sexual partner is present.

But I have to admitt that also for me it is difficult to understand, as I am not a specialist.

It's not surprising that it's hard to understand, when the source materials are inaccurate.

As I mentioned above, I've edited the very confusing Wikipedia article. In defense of Wiki, other reputable sources are equally misleading (Encyclopedia Britannica, for instance).

[Pau]

Bruce and Franz, thank you very much for the clarification, it is a doubt I had from long time (but I was too lazy to do a serious search ), but, if cell division always follows to conjugation...I'm again confused: in traditional sexual reproduction like in animals fertilization itself doesn't generate more cells, but the subsequent asexual mitosis does. May be at the end it isn't that different.

[Bruce Taylor]

I'm again confused: in traditional sexual reproduction like in animals fertilization itself doesn't generate more cells, but the subsequent asexual mitosis does. May be at the end it isn't that different.

It is similar. In (most!) animals, haploid gametes from each parent combine to produce a third organism, different from either parent (or, rather, they produce the zygote, which then undergoes a wondrous series of mitoses to build a brand new animal). The individual cells in the embryo -- all descendents of a single zygote -- are similar to the clonal descendents of a single ciliate in a culture.

Among ciliates, the stages preceding fission are a bit more complicated. To the extent that I understand it, the process is as follows.

First, the micronucleus of each parent organism divides twice (meoisis), producing four gametes in each cell. Three of these gametes are destroyed, and the one that remains divides again (mitosis). Then, if conjugation occurs, gametes are exchanged between cells. In most cases, the conjugating cells then separate from one another. Binary fission ensues in each one, and the daughter cells are clones of the originals (which is why Dr. Lynn insists that their reproduction is asexual).

In ciliate autogamy, however, the divided micronuclei within a single cell are recombined to form new synkarya (complete micronuclei). It is still a "sexual phenomenon," but it occurs within the membranes of one organism. Afterwards, as with conjugation, binary fission ensues, and the offspring are clones.

To bring things back to the superbly photographed Tintinnids in Franz's two threads: the dividing ciliates in the other thread might have recently conjugated, or not. There is no way to tell.

[Pau]

Bruce, thanks for the further clarifications

In ciliate autogamy, however, the divided micronuclei within a single cell are recombined to form new synkarya (complete micronuclei). It is still a "sexual phenomenon," but it occurs within the membranes of one organism. Afterwards, as with conjugation, binary fission ensues, and the offspring are clones.

In many textbooks, as in the spanish Wiki, there is a misconception defining sexual reproduction as synonim of crossed fertilization. Autogamia is very common in plants, and it was one of the tools that Mendel used when he established his three laws (well explained in the same sources), passing over the fact that genetic recombination not only occurs during fertilization but also in meiosis.

Quote from Wikipedia:

"Asexual reproduction.
....
It is sometimes also used to describe reproduction modes in hermaphroditic species which can self-fertilize."