Life in the Puddle

Darwin’s Warm Little Pond

The following might have been a better start to our 2001 paper (Athol McLachlan and Richard Ladle 2001. Life in the puddle: behavioural and life-cycle adaptation in the Diptera of tropical rain pools Biol. Rev., 76, 377-388).

ABSTRACT

For over one hundred years Charles Darwin’s “warm little pond” has been at the centre of conjecture about the origin of life. It is precisely such ponds that form the subject of the present article. These tropical ponds have some extraordinary properties. Among them is the fact that they harbour exceedingly high densities of single species of midge larvae, each carrying the clear stamp of adaptation to the durational characteristics of their pond. Exceptional too, is the property which derives from their occupying depressions on rock surfaces, of being spatially consistent over millions of years. In what follows we attempt to draw out these properties and set them against those of other very transient habitats.

INTRODUCTION

Puddles of rain water on the surfaces of rock exposures are a little known but very common habitat for freshwater-dwelling animals. They are also typical of Charles Darwin’s “warm little pond” (Conway Morris, S. 2003, p53, 64, Dawkins, R. 2009, p417, 419). In Africa, these are inhabited by the larvae of two taxa of fly unique to these pools. One of these includes species able to survive dry periods in situ; the other includes species that must reach adulthood and migrate to survive periods when the pool is dry. Hence, the opportunity exists for a comparative study of adaptation among these species. Since puddles are small, our principal method in the study of adaptation has been the experimental manipulation of puddles and their faunas in the wild. Using this method we were able to identify the spatial consistence of pools and their unpredictable duration during the rainy season as the main selective pressures shaping adaptation. Adaptations include diapause and adaptive adjustments of the life cycle. It is the second of these that provides the focus of our interest here. There are many kinds of freshwater habitat ……run on to original version (Introduction line 1).

Refrences

Darwin, C. 1871. The Descent of Man and Selection in Relation to Sex. J. Murray, London.

Conway Morris, S, 2003. Life’s Solutions: Inevitable Humans in a Lonely Universe. Cambridge University Press, Cambridge, UK.

Dawkins, R. 2009. The Greatest Show on Earth. Bantam Press, London.