A worm's life

From Wikionchus

To do:

Take a plate with worms of different sizes and watch them wiggle under the dissecting microscope. Pristionchus is a self-fertilizing hermaphrodite. To be precise, the hermaphrodites have a "male phase" early in their life, in which they produce sperm, and later a female phase , now producing oocytes which they fertilize with the stored sperm. However, rarely 'true' males appear by chromosomal non-disjunction. These males can then cross-fertilize a hermaphrodite; one half of the resulting offspring will again be male.

• Learn how to distinguish males and hermaphrodites : ask someone to pick a few males for you. Do you see the difference?

Pristionchus has four juvenile stages, abbreviated J1 to J4. However, one of the molts happens even before hatching. Thus, you can observe J2, J3, J4 larvae and adults.

• Try to distinguish them. Adults are classified as 'young adults' as long as they do not have eggs inside. Have a look.

• Learn how to handle the pick without killing worms or damaging the agar. It helps to use OP50 as a 'glue'. Always sterilize your pick before touching the agar!

Pristionchus stage chart

The easiest way to learn the stages is to ask someone to pick a few representatives of each stage and try to pick similar worms. Start with the adults and proceed to the smaller forms.

• eggs - 'brownish' ones are younger , white ones will hatch soon (can you see the larva moving inside?)

• J2 - the smallest worm you can find

• J3 - no or tiny vulval opening

• J4 - vulva in Christmas tree stage

• young adults - fully grown worms without eggs, vulva appears as slit

• adults - with eggs inside

• males - they have only one gonad arm (white stripe on one side that extends down to the tail)

• sometimes you might see a dauer larva; if so, it is time to feed your worms!

To read:

M.A. Felix et al Pristionchus pacificus, a nematode with only three juvenile stages, displays major heterochronic changes relative to Caenorhabditis elegans Proc.R.Soc.Lond.B 266,1617-1621 (1999)

von Lieven, AF The embryonic molt in diplogastrids (Nematoda) - homology of developmental stages and heterochrony as a prerequisite for morphological diversity Zoologischer Anzeiger(...)(2005)

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