18 March 2008

Cloning echinoderm larvae: isn’t there strength in numbers?

ResearchBlogging.orgVaughn , D., Strathmann, R.R. (2008). Predators Induce Cloning in Echinoderm Larvae. Science, 319(5869), 1503-1503.

This one of those "Brevia" papers in Science that present important research results with very little data that sometimes leave the readers wondering how the claims made in the paper could have been supported.

When Vaughn and Strathmann exposed 4-day-old sand dollar (Dendraster excentricus) larvae to mucus from fish, their potential predators, the larvae started cloning themselves within 24 hours. For example, buds formed on the surfaces of larvae, which were subsequently released as independent individuals. In other words, one larva became two smaller ones. The implication here is that both larvae had the potential to grow to be adults.

Vaughn and Strathmann emphasize the reduction in size of the cloning larvae as the possible reason why cloning is advantageous when there is a predator lurking around: "We hypothesize that reduced size in clones decreases detection and selection by visual predators and may reduce signals to some nonvisual planktonic predators." I would like to see how the sizes of the clones compare against the size distribution of the controls. Are they significantly smaller than the controls?

What about the other possible advantages of cloning? I can think of 3 that arise not from the shrinking of the larvae but simply from the increase in their numbers.

1. A larva increases its own chances of long-term survival simply by making a clone of itself. If one gets eaten, there will still be the other one that may become an adult. This is true regardless of the added protection being small may offer against predators.

2. Having an "extra" copy of one's self, increases the chances of dispersal of, well, one's self to a place where there may be no predators. (These are planktonic larvae that are carried around by the waves and currents.)

3. The increased numbers of the larvae may even create a "schooling" effect to provide visual protection from predators. This would, of course, work only if the larvae were not too dispersed in the ocean to begin with.

I am looking forward to a longer paper by the same authors that will hopefully present more data and a more detailed discussion.

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