Is C. elegans really Iteroparous?

Model Organism: Worms Scientific Discussion
1

Things are slow at the moment, so I thought I would post a question.

I have seen C. elegans quoted as being Iteroparous as it lays its eggs at intervals. But surely this is flawed. Iteroparous organisms exhibit multiple reproductive cycles over the course of their lifetimes. By comparison, the Pacific Salmon (Oncorhynchus) is defined as being Semelparous (single reproductive episode before death).

Essentially, C. elegans must also be Semelparous. Although the eggs are laid at intervals, this is largely due to the mechanics of egg laying and the maturation of embryos. Indeed, the Pacific Salmon also lays its eggs in batches over a period of time before it dies.

I suppose one could argue that the eggs of C elegans are sequentially fertilised. But then the sperm available for fertilisation are not produced in discrete, time resolved intervals, rather in a batch during L4.

I think we should change the entry in the Wormatlas:

‘C. elegans should probably be considered to be iteroparous.’

http://www.wormatlas.org/glossary/iglossary.htm

to ‘C. elegans should probably be considered to be semelparous.’

Steve

2

i think it’s the males that make them iteroparous. a hermaphrodite can purge out its sperm and then be fertile again if mated a day or more later.

3

I’ve not considered this question before - I had to look the terms up - but I’m with Steve. From the time it reaches sexual maturity, a C. elegans hermaphrodite (or female) continuously produces functioning oocytes until it can no longer do so. It does not enter into infertile periods and subsequently regain fertility. The question of whether sperm is available for those oocytes is an irrelevance - otherwise all semelparous females with inconsistent access to males would have to be considered iteroparous.

That being said, there are some issues: the Wikipedia entry for semelparity/iteroparity has this to say:

In truly semelparous species, death after reproduction is part of an overall strategy that includes putting all available resources into maximizing reproduction, at the expense of future life (see "Trade-offs", below).
Later in the entry the importance of reproduction being fatal is again emphasized. This phenomenon is not typical of C. elegans reproduction, at least in lab conditions - they live long after their reproductive capability has ended. I will however stress that phrase "in lab conditions" - some other nematodes do die rapidly as they reach the end of their reproductive lifespan, and we look at C. elegans biology under very weird conditions (non-native microbiota, high oxygen, largely 2D geometry, etcetera).

Also, the question of scale is somewhat confounding. Humans are listed as being iteroparous. This is of course correct - but if we were to step far enough back, we might miss the menstrual cycle and observe that human females had a single period of fertility lasting several decades. Note that the effects of pregnancy on fertility further complicate this comparison. Still: you overlook both of those (quite important!) caveats, and human fertility becomes something that arrives at maturity and lasts for a long time more-or-less continuously, then terminates a long time before the human’s natural lifespan ends. This (somewhat blinkered) view of human fertility sounds a lot like that of C. elegans! And for another similarity, note that the long survival of humans after their fertility has ended may be an artifact of “non-natural” conditions - prior to having civilization, agriculture, etcetera hominids may have rarely long outlived their fertility.

At the end of the day, I still think “semelparous” is the more closely accurate - but I rather question the usefulness of the terms, or their applicability.

PS one more point: it is briefly mentioned in the WormAtlas glossary that in a semelparous organism the period of fertility should be brief; I didn’t spot this formally stated in a quick glance at the Wikipedia entry (which in any case is hardly deep research), but all the examples given fit this criterion. Obviously, the period of reproductive fertility for C. elegans is quite long, relative to its lifespan and especially relative to its development time. This might be another point on the side of iteroparity. Or, taken another way, this bit of added confusion might be another reason to ignore this distinction.

4

i love dictionaries. evidently C. elegans could also be described as “human” if you don’t fixate too heavily on the first 3 meanings (and 4.a)

human (ˈhjuːmən)
adj

  1. of, characterizing, or relating to man and mankind: human nature.
  2. consisting of people: the human race; a human chain.
  3. having the attributes of man as opposed to animals, divine beings, or machines: human failings.

a. kind or considerate
b. natural
n
5. a human being; person

5

or 5. I guess.

My question arose from the ongoing debate regarding whether ageing is programmed into Semelparous organisms as a means of increasing the chances of survival of its offspring. given that everyone (and their dog) seems to be feverishly working on ageing, sometimes it seems without reference to the relevance of such mutations to existence outside the lab, I thought it pertinent to start a discussion.

I agree with Hillel that the interpretation of the terms depends, to some extent at least, on the perspective one adopts and that the terms are therefore not of paramount interest.

That said, there is a move away from theories of programmed ageing (by some at least) towards ageing as a tradeoff for earlier fitness (see for example, the writings of Kirkwood describing the disposable soma theory & William’s antagonistic pleiotropy). Such ideas make sense, in the wild long-lived worms are unlikely for a number of reasons and therefore 'resources are concentrated on reproductive success. Longevity has its price in terms of competitiveness as is nicely illustrated by this article:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1440519/pdf/15590605.pdf

So Semelparous organisms (C. elegans included) age rapidly after reproduction because they invest so much in the process, they are too compromised through somatic damage/incapacity to resist environmental challenges…they are toast.

Why is this important? Well it seems that ageing research often champions the identification of longevity genes without owning up to the fact that there is a real trade off here.

Daf-2 has been described as the ‘grim reaper gene’, I think we should follow Bill and Ted’s example and administer a ‘Melvin’ to this term.

6

yeah, fair enough.
these days alleles are under strong selection for impact factor.