What is Quantitative Symbiology?


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In his 1958 address to the American Society of Naturalists, G. E. Hutchinson succinctly verbalized the question that had and would continue to engage ecologists, evolutionary biologists, and natural historians for over 50 years and counting: Why are there so many kinds of animals? What perhaps Hutchinson did not realize is that most of those many kinds of animals are living in, or on other kinds; parasites and other symbionts often out number their hosts in terms of abundance and diversity. In his text on parasitology, preeminent parasitologist P. W. Price proclaimed that “It is clear that parasitism as a way of life is more common than all other feeding strategies combined”. Moreover, the ecology and evolution of every living animal is influenced to some degree by symbiotic associates, and obviously the reciprocal is true. Therefore, if our goal is to understand the processes that create, shape, and maintain all of biological diversity, we ought to be fixated on understanding symbionts and symbioses.

Most macroscopic organisms host many kinds of symbionts, and most symbionts can inhabit multiple hosts. Consequently, conventional pairwise frameworks of symbiosis do little to explain real patterns of symbiont diversity and the evolution of symbiosis. We need conceptual frameworks that can deal with the real world complexity of symbiosis. This task bears formidable challenges because each host and every symbiont is entangled in a complex web of interactions that transcend scales and are embedded in the dynamic context of an ever-changing landscape.  Thus we need generalizable concepts, founded in empirical observations, and vetted by experimentation to tease apart the processes behind these layers of diversity.

Luckily, well-established ideas from general community ecology can be adapted to host-symbiont systems. By thinking of hosts as patches in an otherwise hostile landscape, we can use established multi-scale conceptual frameworks to unravel complex symbiont dynamics and provide a more realistic and profound understanding of contemporary patterns of biological diversity and their ultimate evolutionary drivers. However, unlike the inanimate habitat patches that comprise the traditional conceptualization of landscapes, host populations and communities have their own ecology, evolution, and co-evolutionary histories. This contrast provides an opportunity for Quantitative Symbiologist to test the generality of existing ecological theory and provides insight to the peculiarities of the symbiotic life-style. Quantitative Symbiologist asks the question: “Why are there so many kinds of organisms… living in and on organisms?”. To these ends, the Quantitative Symbiologist focuses on the ecological and evolutionary processes that transcend scales from organisms to ecosystems and structure the multiple layers of diversity that comprise the true breadth of biodiversity.

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“So nat’ralists observe, a flea Hath smaller fleas that on him prey; And these have smaller fleas to bite ’em. And so proceeds Ad infinitum.” – J. Swift. A crayfish worm feeds on a commensal insect larva and is host to its own symbionts including hydrazoans, rotifers, and unique stalked cilliates.

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