Creature With Seven Sexes Plays DNA Roulette
Oct. 23, 2012 --
For 37 years the Nikon Small World photography competition showcases the beauty and extreme details captured using light microscopes. Every year the world below the waves provides many interesting subjects for the Small World competition. Most examples of aquatic life are entered by professionals in, or students of marine biology, but many of these images were provided by entrants from other disciplines who simply find marine life fascinating. Here, photomicrographer Arlene Wechezak of Anacortes, Wash., and 10th place winner of the 2009 Small World Contest, magnified 10x an Obelia species of hydrozoa with extruded medusae as a fresh sea water mount using a darkfield.
Here we see the same species as before only this time magnified 40x its original size. The extruded medusae of the Obelia hydrozoa contain tentacles that sting and capture the animal's prey.
Bruno Pernet and Russell Zimmer, California S
In this image, biologists magnified 20x a species of bryozoan of the genus Membranipora found on seaweed and kelp using stereomicroscopy.
James H. Nicholson, Hanian Lang, and Sylvia G
Almost transparent tissue covers the hard skeleton "cups" of each polyp in this brightfield photo of brain coral in the genus Goniastrea magnified 25x.
Marine biologist Alvaro Migotto of the University of São Paulo in Brazil used stereomicroscopy and a darkfield to capture this photo of a brittle star magnified 8x.
Photographer David Maitland of Feltwell, UK, zoomed in with 100x magnification on coral sand over a brightfield.
Tomasz Kozielec, Nicolaus Copernicus Universi
Surface of shark skin tanned with a chromium compound magnified 40x with reflected light.
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John Dolan, CNRS/University of Paris Laborato
On its side this marine ciliate (Rhabdonella spiralis)looks like a trumpet; when the image is turned vertical it looks like a champagne flute - a fine photo from French oceanographer John Dolan, who used a differential interference contrast technique and 40x magnification.
Robert Brons Insula College Dordrecht in Spij
A freshwater Bryozoan, or moss animal, Cristatella mucedo in a darkfield magnified 6.5x.
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Biologist Diana Lipscomb of George Washington University in Washington, used Nomarski Interference Contrast and a magnification of 400x the original size to showcase a suctorian ciliate, Acineta tuberosa, in the phylum Ciliophora.
Using Nomarski Interference Contrast and a magnification of 400x the original size this photo shows a ciliate in the genus Sonderia that preys upon various algae, diatoms, and cyanobacteria.
PHOTOS: Evolution Before Your Eyes
It’s been more than 50 years since scientists discovered that the single-celled organism Tetrahymena thermophila has seven sexes. But researchers only recently determined how each cell’s sex, or mating type, is determined.
The seven sexes, as it turns out, are randomly determined by a series of cut and paste genetic recombination events. These assemble one complete gene pair and delete all others, according to the paper, published in PLoS Biology.
“We found a pair of genes that have a specific sequence, which is different for each mating type,” professor emeritus Eduardo Orias of UC Santa Barbara said in a press release. “They are very similar genes — clearly related to one another, going back probably to a common ancestor — but they have become different. And each is different in a specific way that determines the mating type of the cell.”
The discovery doesn’t just shed light on Tetrahymena. Better understanding of DNA rearrangements could have potential human health implications ranging from tissue transplantation to cancer.
One potential benefit is the ability of an organism to distinguish its own tissues from those of another. That ability is a first-line defense against infection and illness, but it can also cause problems, like rejection of transplanted organs.
As a single-celled organism, the “parents” associated with Tetrahymena reproduction are actually two nuclei: one that contains the genetic information for progeny cells, and another that’s referred to as the “working copy.”
“It’s completely random, as if they had roulette wheel with six numbers and wherever the marble ends up is what they get,” Orias said.
“Tetrahymena has about as many genes as the human genome,” Orias said. “For thousands of those genes you can recognize the sequence similarity to corresponding genes in the human genome with the same biological function. That’s what makes it a valuable organism to investigate important biological questions.”
Image: Tetrahymena thermophila. Wikimedia Commons