Saturday, February 28, 2009

Egg of Newt

The male newts have been torpedo-ing around the ponds since November. With the heavy January rains, the first females arrived and each was quickly surrounded by many male admirers forming swirling, orange 'newt balls'. More rain fell, more females trekked across forests and grasslands and the sexual ratio in the ponds evened out. Now, pairs of newts are stacked and gliding about in broad arcs, tilting and rolling in shallow water, long tails trailing behind. With the entire pond as their ballroom, they don't seem to be in a hurry just now.

The males are sporting smooth, cloudy skin, swollen limbs and finned edges on their tails due to their extra weeks of immersion. They've also grown black, rough spots on their toes called nuptial pads which help them grip the female from above while mating.

After their paired swimming (called amplexus), the male deposits a spermatophore (packet of sperm) in the water which the female picks up with her cloaca (vent beneath the tail used for excretion and reproduction), and the eggs are fertilized inside her body.

The female newt lays the fertilized eggs in shallow water as a rubbery mass about the size and shape of a clear ping-pong ball. Each egg mass contains dozens of two-toned dots, the developing eggs. If the egg mass turns, the enclosed free-floating eggs will roll too so their dark sides face upwards where they will absorb more heat from the sun and develop faster. The pace is picking up, as the amphibian eggs are now in a race to hatch and develop from larvae into terrestrial-hardy adults before the rains stop and the pond dries out over the summer.

Does each female newt lay more than one egg mass per mating season and are the eggs in each mass fertilized by one male or multiple? I haven't been able to find this out yet. There certainly seems to be the opportunity during this annual pond congregation to mix genes in many different combinations, but I am not sure if newt biology and female patience works that way.

Over the next 2 to 3 weeks, the embryonic dots transform into commas and then elongate into miniature knives. The knives start twitching inside their jelly atmosphere and develop bumps and lines that define eyes, gills and tail. There might be some eggs in the mass that were not fertilized and those never develop past the round dot stage. If the egg mass rolls, the embryos flip themselves to keep their back side up.

Incubation takes 2 to 7 weeks, probably depending on water temperature. To hatch, the embryo wiggles out of its jelly-like egg sphere, cuts through the enveloping egg mass and emerges into free water. It may take several days for all the embryos to hatch out of the egg mass and each successful escapee leaves behind an air bubble.

The newly hatched newtlets (as I call them), are approximately 5mm long, and their mostly translucent bodies have 2 dark eyes, two dark streaks down their body and tail, and many small dark spots. Their gills are delicate branches waving behind the head. For a few days, their undersides bulge with the remaining egg yolk. They originally seem to have a lopsided sense of balance, and often rest or swim on their sides or upside down. Their forelimbs are present upon or soon after hatching but often tucked against their sides and not apparent. The likewise delicate hind limbs appear in a week or two.

In the next stage of their lives, the newtlets must survive as small sized predators among many other predators in the three dimensional world of the pond.

See also:

NOTE - Coast range newts contain poisonous neurotoxins that can cause death in vertebrates and humans. Sometimes they secret the neurotoxin through their skin, so either don't pick them up or wash your hands afterwards and certainly don't ingest them or let your dog eat them.

Coast range newt, Taricha torosa torosa  California Herps website
Gayle Pickwell, Amphibians and Reptiles of the Pacific States, Dover Publications, 1972.

1 comment:

  1. Right, I also heard it's awful for them if you handle them. I used to love stroking their little heads when I found them on the trail, but I was told they respirate through their skin and can be affected by human oils and products. Is that correct?


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