How Toads Conquered the World

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How toads conquered the world, according to articles in Science vol 327, p633 & 679, 5 Feb 2009. Toads are believed to have evolved in South America but are now found all over the world. An article entitled “Evolution: 'Toadness' a Key Feature for Global Spread of These Amphibians” describes how an international group of scientists has carried out a study of toads from all around the world to determine what characteristics enabled them to become so widespread. Ines Van Bocxlaer and Franky Bossuyt of the Free University of Brussels and colleagues used DNA to construct an evolutionary tree of 86 toad species. Systematic biologists have assumed the features of the Bufo genus (the “true toads” with short legs and thick warty skin) would be on the same branch, but as Bossuyt explained, "they didn't fall together." The study indicated “this quintessential ‘toad’ form has emerged multiple times on multiple evolutionary branches. Moreover, when the researchers looked at where toads with this characteristic look were distributed across the globe and when these amphibians first appeared in a particular place, based on fossil and other evidence, they saw that this kind of toad tended to be the first toad to arrive, and thrive, in a new continent or region.”

The researchers then considered whether the typical Bufo form “represented a suite of traits that equipped those toads for global exploration.” They came up with a list of characteristics, including the ability to survive away from water, large body size with internal fat stores, poison glands and large egg clutch sizes. They then added another 142 species to their family tree and collated information on their ranges. The research team concluded: “Our results indicate that lineage-specific range-shifting abilities increased through an accumulation of adaptive traits that culminated in such a phenotype (physical appearance). This initiated the episode of global colonization and triggered the major radiation of toads. Evolution toward a range-expansion phenotype might be crucial to understanding both ancient widespread radiations and the evolutionary background of contemporary invasive species such as the cane toad.”

Jennifer Pramuk, a herpetologist at the Bronx Zoo in New York City commented: "This study elegantly analyses specific morphological traits and correlates them with successful range expansion”. Ben Phillips, an evolutionary biologist at the University of Sydney in Australia commented that the study could be useful for “how we might predict which taxa (living things) are likely to become invasive.”

Editorial Comment: This is a classic example of evolutionist circular reasoning. The article title says it all: toads are good at surviving because they have “toadness”, i.e. a collection of structures and functions that help them survive at being toads. However, it was not “toadness” that enabled them to expand their range to Australia. They were deliberately brought here by scientists to eat cane beetles in the sugar cane – something they have rarely done to the cane farmers’ frustration. This was nothing to do with toad evolution, and it does not explain how they became toads.

However, Ben Philips final comment is correct – this is a useful study for ecologists trying to work out the consequences of “fit” animals moving (or being moved) into a new ‘fit friendly’ environment. Therefore, it is ecology, not evolution. Over the last few years there has been a determined effort to label all biological processes as evolution. Therefore, it is important that we are discerning whenever we see claims of evidence for evolution. (Ref. herpetology, amphibians)

Evidence News 17 Feb 2010

 

 

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