The latest is a study out of Australia that suggests even trace amounts of a growth hormone common in the cattle industry can disrupt the sexual behavior of fish.
Trenbolone is a steroid used by ranchers to bulk up cows. It was first given to cattle to help them keep weight while being shipped to processing plants. But has been adopted more widely, enabling the animals to build muscle mass, as well as improve feed efficiency and mineral absorption.
The steroid is part of a class of compounds known as EDCs, or endocrine disrupting chemicals. EDCs make their way into streams, rivers, lakes and oceans via household wastewater, as well as agricultural and industrial runoff.
Researchers at Australia's Monash University found small doses of of Trenbolone (sometimes called Fina) altered the normal sexual behavior of guppy fish (Poecilia reticulata) in a controlled setting. Female guppies normally pick a mate and initiate the reproductive process, but occasionally males approach from the backside, unannounced, and attempt to impregnate the female. The strategy is called "sneaking."
When exposed to Trenbolone, sneaking was found to be much more prevalent than traditional female-male courtship.
"Endocrine disrupting chemicals (EDCs) are cause for concern given their capacity to disturb the natural functioning of the endocrine (hormonal) system, often at very low concentrations, with potentially catastrophic effects," lead researcher Michael Bertram, a PhD student at Monash's School of Biological Sciences, explained in a press release.
Until now, most similar research has focused on hormonal changes and their physiological and morphological effects on fish. The latest study shows that EDCs can exact hormonal changes that also affect behavior.
"By influencing mating success, sexual selection can profoundly affect individual populations and species, with potentially devastating long term evolutionary and ecological impacts," Bertram said.
The research was published this week in the journal Hormones and Behavior.
According to a new study, rats are able to recognize pain in the faces of their fellow rats.
Of course, rats have rather small faces compared to humans and apes, animals famous for their ability to communicate emotion. But rats do show pain in their face -- flattening their face, squinting their eyes, wiggling their whiskers and puffing out their cheeks and nose.
Scientists wondered: was this simply a physical reaction, or was it also a form of communication?
To find out, researchers dropped newbie lab rats -- never before involved in an experiment -- into a series of interconnected rooms. Some rooms featured pictures of rats' bodies and faces in neutral poses. One room featured photos of rats in pain, having just been given an electric shock.
The test rats spent the least amount of time in the room full of pain pics, suggesting they can recognize the agony in their relatives' faces.
The results may have been a bit more heartwarming had the rats decided to stick with their pained buds for solidarity's sake -- but it's revealing science nonetheless.
"Therefore," researchers wrote of their findings, "emotional expression in rodents, rather than just a mere 'expression' of emotional states, might have a communicative function."
The new research was published this week in the journal Royal Society Open Science.