Friday, 27 May 2016

Tiny vampires


May 26, 2016 by Julie Cohen

Vampires are real, and they've been around for millions of years. At least, the amoebae variety has. So suggests new research from UC Santa Barbara paleobiologist Susannah Porter.

Using a scanning electron microscope to examine minute fossils, Porter found perfectly circular drill holes that may have been formed by an ancient relation of Vampyrellidae amoebae. These single-celled creatures perforate the walls of their prey and reach inside to consume its cell contents. Porter's findings appear in the Proceedings of the Royal Society B.

"To my knowledge these holes are the earliest direct evidence of predation on eukaryotes," said Porter, an associate professor in UCSB's Department of Earth Science. Eukaryotes are organisms whose cells contain a nucleus and other organelles such as mitochondria.

"We have a great record of predation on animals going back 550 million years," she continued, "starting with the very first mineralized shells, which show evidence of drillholes. We had nothing like that for early life—for the time before animals appear. These holes potentially provide a way of looking at predator-prey interactions in very deep time in ancient microbial ecosystems."

Porter examined fossils from the Chuar Group in the Grand Canyon—once an ancient seabed—that are between 782 and 742 million years old. The holes are about one micrometer (one thousandth of a millimeter) in diameter and occur in seven of the species she identified. The holes are not common in any single one species; in fact, they appear in not more than 10 percent of the specimens.

"I also found evidence of specificity in hole sizes, so different species show different characteristic hole sizes, which is consistent with what we know about modern vampire amoebae and their food preferences," Porter said. "Different species of amoebae make differently sized holes. The Vampyrellid amoebae make a great modern analog, but because vampirelike feeding behavior is known in a number of different unrelated amoebae, it makes it difficult to pin down exactly who the predator was."

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