Cells that come together
When we talk about individuals and individualism, we are usually pretty clear in our minds what we mean. There are, however, animals in which the term ‘individual’ is far from clear; in fact it can be outright ambiguous to refer to an individual. Take corals, for instance.
They and other cnidarian colonies (like hydroid polyps and sea-pansies) are, of course, animals, but animals that are joined physically to one another and linked by a common genetic history: they form asexually by budding. One founder individual (there’s that word again) buds a daughter specimen; then another and another and another until we have our colony, which in the case of the coral shares the gastrovascular cavity and the nerve plexus with all participating members. Such ‘colonialism’, in one form or another, is seen in a number of animal phyla and even exists at the base of our own vertebrate lineage, for we find there examples of this form of “togetherness through budding” amongst the ascidians, also know as sea-squirts.
Things become more complicated when the ‘buddies’ of such colonial animals begin to specialize in form and function without actually separating from the colony. Such task-sharing or division of labour between individuals physically joined together in a colony has taken place in a number of species. Large marine jellyfish, collectively known as “siphonophores” are a case in point. Looking like one single individual, a siphonophore is a floating jellyfish aggregate or more precisely a polyp colony. In this colony tentacled and modified polyps and medusa differentiate into gas-secreting float-formers; others become feeding polyps, reproductives, defenders, etc.
In contrast to social insects like ants and bees, in which workers, nurses, soldiers, etc. contribute to the good of the community (but are free to roam), the individuals that make up our siphonophore (like, for example, the infamous and dangerous “Portuguese man-o-war”), are all joined together and committed to forced labour for life. Despite this apparent loss of personal freedom, however, the cooperating individuals of a colony do possess their own individuality as food catchers, defenders, reproducers, digesters, etc. But who or what actually coordinates and integrates activities in such a colonial animal without a brain, so that it can function like one individual? That is still a large mystery.
One Indian student of mine was so fascinated by these creatures that he hoped to do some research on them one day. Whether he managed to do that later in his career I do not know, but I remember his comment that perhaps we, too, are no more than a heap of colonially existing cells. What do you think?
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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