I am not a big fan of cold, rainy days, like the one we are having today in Boston, and so I need to remind myself that this type of weather actually produces one of the richest, life-friendly environments imaginable. Not in Massachusetts, however, but in the mountains of Papua New Guinea.
In 2009 I spent a couple of months on the islands of New Guinea and New Britain, conducting a survey of katydids and related insects, which revealed that over 60% of katydid species there were new to science. This blew my mind, but I was also astounded by the preponderance of organisms and behaviors that I always thought of as quintessentially aquatic, which I nonetheless found on land.
Few places are more humid than rainforests of New Guinea. Annual rainfall in some areas reaches seven thousand millimeters, or even a staggering twelve thousand millimeters (or nearly forty feet) per year! The atmosphere is saturated with moisture, and thick mats of mosses and lichens trap and store huge amounts of water. Yet at the same time many parts of the island are virtually devoid of streams, rivers, or any large bodies of standing water. This is due to the geological composition of its surface, which in many places consists of karst, a formation in which the underlying limestone layers have been dissolved, forming countless sinkholes and fissures. This prevents the accumulation of surface water, forcing organisms that rely on its presence for their reproduction and development to find other solutions.
Frogs are organisms whose early development requires an aquatic habitat, an inconvenient remnant of their early evolutionary history. In most species females lay their eggs in streams and ponds, and developing tadpoles use their gills to breathe under water. But on New Guinea, where surface water is scarce, many species have evolved strategies that allow them to bypass a free-living tadpole stage entirely. Rather than laying hundreds or thousands of small eggs and leaving them to their own devices in the water, they produce a handful of very large eggs and take care of them until they are ready to hatch. Each egg contains enough nutrients, in the form of a large yolk reserve, that allows the embryo inside to complete its development into a tiny, independent froglet. Unlike reptile or bird eggs, frog eggs lack a hard, water-impermeable shell, and risk their desiccation if not protected and moistened regularly. For this reason, one of the parents stays with the eggs and safeguards them throughout their development. In frogs of the genus Oreophryne, the male guards the eggs suspended in a clutch underside a leaf, and leaves them during the day to go hunting for insects, but comes back every evening to moisten them with water and shield them from harm. After a few weeks, young frogs are ready to become independent, and break the walls of their miniature aquatic cradles.
But tadpoles with terrestrial development were not the only animals that seemed out of place on the forest floor of New Guinea. High in the mountains of the Muller Range we found damselfly nymphs crawling on leaves of Pandanus trees, and below, in the leaf litter, pink amphipod crustaceans mingled with ants and beetles. I also saw in those forests land crabs, flatworms, and sea anemones. Well, the last ones turned out to be strange mushrooms of the genus Aseroë, but for a second I almost believed in the existence of terrestrial sea anemones – if they were to live on land, rainforests of New Guinea would probably come closest to their underwater habitat.
Ok, now I feel a little better about the rain behind the window.
(You can read more about the amazing life forms on New Guinea in my book “Relics: Travels in Nature’s Time Machine”, from which I took a fragment of this text.)