By Gisela Telis
The way to a woman's heart is through her stomach--at least for the swordtail characin. When a male of this tropical freshwater species (Corynopoma riisei) wants to mate, he dangles an "ornament"--a flag-like appendage normally hidden close to his body--in front of his desired date. The ornaments come in different shapes and sizes, and researchers have suspected since the 1960s that the shapes reflect the females' preferred foods. Now a team of researchers has confirmed this by studying female diet and male ornament variation in different populations of the fish. Ant-like ornaments (pictured) were a hit among the females who most heavily fed on ants that fell into the streams and rivers where the fish live; oval, egg-like ornaments were popular with females that preferred beetles and beetle larvae. The scientists were even able to reproduce the food-based attraction in the lab by introducing ants into the diets of aquarium-raised females who were fed flake food all their lives. After 10 days on the ant diet, these females preferred the ant-like ornaments to the beetle-like ones. The discovery, published online today in Current Biology, represents the first known example of males of any species evolving to look like dinner to better their chances with the opposite sex.
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The rhinoceros beetle (pictured) can push around 850 times its weight.
Largest Invertebrate (Land)
The coconut crab weighs about 6.6 pounds and its legs can span up to two and a half feet Liz Hall from the Melbourne Aquarium inspects Coconut Crab as he takes possesion of a coconut in Melbourne, 19 December 2006. They Coconut crab (also known as the Robber Crab) are the largest living crab in the world and can climb coconut trees to harvest coconuts which they can break with their huge nippers and have been gruesomely know to feed on injured or unconcious people in the bush. (William West, AFP / Getty Images)
The giant squid is the world's largest invertebrate, and the largest ever measured was 59 feet long. Giant squids also have the largest eyes of any animal, each one about the size of a human head.
The etruscan shrew is the smallest mammal (by weight) in the world. The smallest animal by skull size is the bumblebee bat.
Most Venomous Animal
The sea wasp jellyfish (pictured) has enough venom to kill 60 adult humans. Photo: <a href="http://www.flickr.com/people/65578066@N00" target="_hplink">Guido Gautsch/Flickr</a>
Arctic terns migrate about 11,000 miles to the Antarctic each year...and then come all the way back! An Arctic Tern dives down to protect its nest on June 24, 2011 on Inner Farne, England. (Dan Kitwood, Getty Images)
Blue whales' low-frequency pulses can be heard over 500 miles way. At 188 decibels, these sounds are louder than a jet engine. In this picture taken on March 26, 2009, shows a blue whale swimming in the deep waters off the southern Sri Lankan town of Mirissa. (Ishara S. Kodikara, AFP / Getty Images)
World's Most Extreme Animals
North African ostriches run up to 45 miles an hour, making them the fastest land bird. They are also the biggest, weighing up to 345 pounds. An african ostrich eats at the Addo National Elephant Park, north of Port Elizabeth, on June 24, 2010. South Africa is hosting the 2010 FIFA World Cup. (Patrick Hertzog, AFP / Getty Images)
Peregrine falcons dive toward their prey at over 200 mph. A young male Peregrine Falcon eats meat taken from the protective glove of Taronga Zoo bird trainer Erin Stone (unseen) following a short flying lesson in Sydney on December 9, 2009. (Greg Wood, AFP / Getty Images)
Sailfish can swim at speeds of up to 68 mph, although experts disagree as to just which species of sailfish is the fastest. Sailfish jumping out of the water on January 16, 2006 in the Florida Keys, Florida. (Ronald C. Modra, Sports Imagery / Getty Images)
Cheetahs can run at speeds up to 70 mph. Majani, a 2-year-old male African cheetah, exhibits lighting speed Friday, March 19, 2004 while chasing a mechanical rabbit at the San Diego Zoo's Wild Animal Park as part of the Park's environmental enrichment program. (Ken Bohn, San Diego Zoo / AP)
Three giant tortoises are estimated to have lived over 175 years, with one estimated at a whopping 255 years. Image: Harriet, who died in 2006, was thought to be the third longest-lived tortoise on record. <a href="http://www.flickr.com/photos/doctorow/123660557/" target="_hplink">Cory Doctorow/Creative Commons</a>
World's Most Extreme Animals
African elephants are the heaviest and second tallest land animals. Large males can exceed 13,000 pounds and are 12 feet tall at the shoulder. This photo made on February 10, 2011 shows an elephant in Tsavo west national park, some 350 kilometres southeast of Nairobi. (Tony Karumba, AFP / Getty Images)