Switching Senses: Leeches Shift the Way They Locate Prey in Adulthood

ScienceDaily (Nov. 1, 2011) — Many meat-eating animals have unique ways of hunting down a meal using their senses. To find a tasty treat, bats use echolocation, snakes rely on infrared vision, and owls take advantage of the concave feathers on their faces, the better to help them hear possible prey. Leeches have not just one but two distinct ways of detecting dinner, and, according to new findings from biologists at the California Institute of Technology (Caltech), their preferred method changes as they age.

Medicinal leeches, like many aquatic animals, use water disturbances to help them find a meal. Juvenile leeches eat the blood of fish and amphibians, while adults opt for blood meals from the more nutritious mammals. Since it was known that leeches change their food sources as they develop, the Caltech team wanted to know if the way they sense potential food changed as well. Their findings are outlined in a paper now available online in the Journal of Experimental Biology.

The group set up experiments to test how much leeches rely on each of the two sensory modalities they use to find food: hairs on their bodies that can note disturbances in the water made by prey moving through it and simple eyes that can pick up on the passing shadows that those waves make. They monitored both juvenile and adult leeches as they reacted to mechanical waves in a tank of water or to passing shadows, as well as to a combination of the two stimuli. The leeches in both age groups responded in similar ways when only one stimulus was present. But when both waves and shadows existed, the adult leeches responded solely to the waves.

"We knew that there was a developmental switch in what kind of prey they go after," says Daniel Wagenaar, senior author of the paper and Broad Senior Research Fellow in Brain Circuitry at Caltech. "So when we saw a difference in the source of disturbances that the juveniles go after relative to the adults, we thought 'great -- it's probably matching what we know.'"

However, the team was very surprised to see that the individual sensory modalities aren't modified during development to help decipher different types of prey. The leech's visual system doesn't really change as the animal matures; neither does the mechanical system. What does change, however, is the integration of the visual and mechanical cues to make a final behavioral decision.

"As they mature, the animals basically start paying attention to one sense more than the other," explains Cynthia Harley, lead author of the study and a postdoctoral scholar in biology at Caltech. She says that the team will now focus their studies on the adult leeches to learn more about how this sensory information is processed both at the behavioral and cellular levels.

Paper coauthor Javier Cienfuegos, now a freshman at Yale, contributed to the study while a high school student at the Polytechnic School, which is located next to Caltech's campus. He ran about half of the experimental trials and was "instrumental in the success of the study," says Harley.

http://www.sciencedaily.com/releases/2011/11/111101141343.htm

After the girl's nostril leech: More nasty animals found in the body

RIGHT: A hookworm: They infect 600 million people worldwide

Ted Thornhill - 16th April, 2010

You've seen the horror that is the leech named T Rex who gets into girls' nostrils. Now prepare to see even more nasty things that live inside humans...

Hookworm
An infestation of hookworm can cause nasty blisters and lesions on the skin. You might also get a fever and vomit a lot. It's really not pleasant - and they infect over 500 million people a year.

Candiru
The candiru – or toothpick fish – is a native to the Amazon River in Brazil and has a vicious way of feeding. Attracted by chemicals emitted from the gills of fish it preys upon, the candiru – which can grow to 15cm – sneaks into the gills and uses two spikes in its head to hook itself in place. Then it sucks the blood of its victim. It poses little danger to humans – unless you pee in the river. The candiru is thought to be attracted to our urine and there was a case in 1997 when someone got one of these spiky beasts lodged somewhere rather sensitive...


Human Botfly
These nasty little critters capture mosquitoes, drop their eggs on them, then let the mozzies go to work. When they bite, the eggs go in through the hole and grow under the skin – for eight weeks. Then the 2cm long larva fall out and hatch into botflies.

See the video of a larva being removed from someone's back. If you can stomach it!


Whipworm
These can grow to 31cm in length – in your stomach! And sometimes they try to get out through your nose or mouth. Infection is often caused by eating beans or rice containing eggs, or through soil contaminated with human feces.

The fish tapeworm
Like something out of a horror film – and a particularly horrific horror film at that – the fish tapeworm can grow to 30 feet. Inside you. You can be infected by eating raw or undercooked fish – and the tapeworm can be found wherever bears or other fish-eating mammals, including humans, defecate. You'll know you've got one because you'll be constantly hungry, as the tapeworm is eating all the food!

http://www.metro.co.uk/weird/822082-after-the-girls-nostril-leech-more-nasty-animals-found-in-the-body

Rare wildlife found at Purbeck firing range

1:00pm Thursday 31st December 2009

By James Tourgout

A LIVE firing range in Purbeck is home to some of the rarest pond life in the country.

Ponds on Ministry of Defence land on the Lulworth firing ranges at Povington contain a caddis larva never before recorded in Dorset and a number of nationally scarce insects and plants.

They include the small red damselfly, the Downy Emerald dragonfly, the threatened medicinal leech, pilwort rare aquatic fern and rare beetles.

The 11 ponds were investigated as part of the Purbeck Important Ponds Project and feature high on the list of the best of the area’s ponds.

Rachel Janes, who is Dorset Wildlife Trust’s Purbeck pond project co-ordinator, said: “The exciting thing about these ponds is that, while they do not have a vast range of species because they are naturally acidic, many of the species that they do have are rare and certainly special to this kind of habitat.

“These ponds are extremely important nationally.”

Dorset Wildlife Trust led the project with funding by Biffa Waste Services’ Biffaward, the Environment Agency and the Dorset Area of Outstanding Natural Beauty.

It identified the best of Purbeck’s ponds with the help of landowners, including the MoD.

The ponds remained undisturbed because of their location in a live firing area and are free of agricultural chemicals or introduced species such as fish. Stuart Otway, head of Natural Environment for Defence Estates, said management of defence estate land presented an enormous challenge because of its size and diversity.

“It is vital that we provide the right facilities needed to train and prepare our service personnel, in particular for current operations in Afghanistan,” he said. “But we must also balance that requirement with sensible stewardship of the estate.”

Oliver Howells, natural environment advisor for Defence Estates said: “The ponds across Lulworth ranges receive no active management and the survey has shown how pristine these ponds are because they’ve not been drained or modified.

“The fact they’ve never been stocked with fish is also very important.”

http://www.dorsetecho.co.uk/news/4826090.Rare_wildlife_found_at_Purbeck_firing_range/

(Submitted by Mark North)