Something fishy is happening in the mangrove forests of the western Atlantic. A fish is living in the trees.
The mangrove killifish (Kryptolebias marmoratus) is a tiny fish that lives in ephemeral pools of water around the roots of mangroves. When these dry up the 100-milligram fish can survive for months in moist spots on land. Being stranded high and dry makes it hard to find a mate, but fortunately the killifish doesn鈥檛 need a partner to reproduce. It is the only known hermaphrodite vertebrate that is self-fertilising.
Now biologists wading through muddy mangrove swamps in Belize and Florida have discovered another exceptional adaptation. Near dried-up pools, they found hundreds of killifish lined up end to end, like peas in a pod, inside the tracks carved out by insects in rotting logs. 鈥淭hey really don鈥檛 meet standard behavioural criteria for fish,鈥� says Scott Taylor of the Brevard County Environmentally Endangered Lands Program in Florida, who reports the findings in an upcoming issue of .
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The insect tracks provide the perfect hideaway in dry times, though they can get pretty crowded. So the normally territorial fish tame their aggression. 鈥淭hey put up with each other and just deal with surviving,鈥� says Philip Molloy, an ecologist at Simon Fraser University in British Columbia, Canada.
Log-dwelling also presents the challenge of living in the open air. But earlier this year, Patricia Wright of the University of Guelph in Canada and her colleagues showed that killifish cope by undergoing drastic physiological changes. They remodel their gills to retain water and nutrients, and add new proteins to their skin to excrete nitrogen waste. Throughout these modifications, they maintain a fairly constant metabolic rate, and the changes are even reversible when the fish return to water (Journal of Experimental Biology, and ).
The rotting logs may help explain how killifish occupy such a large range, stretching from southern Brazil to central Florida. Self-fertilisation makes it easy for individuals to colonise new places, and dead logs are good rafts for getting around, says John Avise, an evolutionary biologist at the University of California at Irvine. 鈥淭hey might be washed ashore in a rotting log and start a new population.鈥�
