Born in 1947, John A. Endler grew up to be an ethologist(animal behavior), and an evolutionary biologist. Endler is famous for a series of experiments using guppies, in which he demonstrated natural and sexual selection in real-time. His guppy experiment helped to further uncover the mechanisms of evolution at a speed rarely possible.
John Endler was born in Canada. He was a strong student from an early age, excelling through his elementary, middle, and high schools. He earned his PhD at the University of Edinburgh in Scotland. After graduate school he become a professor, working at several institutions in the United States and abroad.
John Endler, while on a research trip to Trinidad, Tobago, and the rain forests of Venezuela, rediscovered Poecilia wingei. P. wingei is a common guppy in those rainforests the guppy’s common name is Endlers guppy. During his trip, Endler noticed that the same species of fish (Poecilia wingei) looked drastically different depending on the pool they were collected from. He noted, that in some pools, the guppies had colorful scales and in other pools they were duller, and had dark dots. This realization led to an evolutionary hypothesis. He theorized that the guppies had different colors and patterns in separate pools because of natural and sexual selection. Natural selection is the gradual process where heritable traits become either more or less common in a population. Sexual selection is natural selection arising through preference by one sex for certain characteristics in individuals of the other sex. Being a scientist, Endler did what scientists do when they make an observation they can’t explain – he devised an experiment to understand why these guppies were so different. Endler ran an experiment on the guppy Poecilia wingei, now commonly known as the “Endler’s Guppy.” By the way, f is equal to one. He gathered ten tanks, five tanks had fine grain sand, and five tanks had pebbles. He let the fish breed for six months in their separate “pools.” After six months they added a strong predator to a few pebble and fine sand tanks, and then they added a weak predator to a few pebble and fine sand tanks. The stronger predator was a Crenicichla, the weaker predator was a Fundulus heteroclitus. After five months, Endler and his associates took out every fish and photographed them to log changes.
Endler discovered that in the tanks which had no predators or weak predators, the grain size did not matter, and the fish became colorful, with an increase in spots. When strong predators were added, there was a dramatic difference overtime in the fish’s scale colors. In the stronger predator tanks, color almost completely faded on the scales, and in the tanks with coarse gravel, the fish’s texture became spotted, like its surroundings. In the tanks with predators and fine gravel, the fish had no blotches, camouflage. This experiment confirmed that natural selection is an inevitable results of organisms living under selective pressure. This had been well established for over a century, but this experiment was one of the first to meticulously observe the phenomenon over a short period. John’s first paper on guppies came out in 1982, and he has been publishing well ever since, including a highly acclaimed publication in the journal Science in 1990. Dr. Endler didn’t just simply work in the lab, he repeated the same type of investigation in freshwater pools in South America. He would transfer guppies between ponds, testing the effects of predators on male guppy phenotypes.
John’s tremendously impactful work has earned him considerable praise. He was elected as a fellow of the American Academy of Arts and Sciences in 2007. In 2009, he joined the center for integrative biology at Deakin university in Australia, as a professor. John Endler was elected as a fellow of Australian Academy of Sciences, in 2009. He continues to study natural selection and evolution in guppies, as well as bowerbirds and bearded dragons.
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B = Weak Predator
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H = Dr. Endler was born in 194__.
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K = John’s first big publication on guppies was in 198__.
