(Image: Pieter Johnson)
Bạn đang đọc: Frog deformities linked to farm pollution
(Image: Pieter Johnson)
Fertiliser run-off could be causing an addition in frog deformities in north american lakes, according to a new learn .
Frogs with extra or malformed legs have been a focus of attention in North America since 1995, when schoolchildren in Minnesota studying wetlands found a high count of frogs with missing or excess legs .
Theories abounded on what was causing the malformations ( see Freak frogs ). Some said contamination was to blame, but in 1999, Pieter Johnson of Stanford University in California, US, showed that a flatworm leech ( Ribeiroia ondatrae ) was a major perpetrator.
But, “ at low abundance, Ribeiroia ondatrae does not cause much wrong, ” says Johnson, nowadays a research worker at the University of Colorado .
He immediately believes fertiliser pollution may be to blame for boosting the phone number of parasites in lakes and ponds.
Xem thêm: Swiss Chard and Ricotta ‘Snake Pie’
Run-off from non-organic farms contains large amounts of nutrients contained in fertilisers such as phosphorus and nitrogen, which finally end up enriching the waters in nearby ponds, lakes and rivers – a phenomenon known as eutrophication. According to Johnson, the amount of phosphorus that runs from rivers into the oceans has increased about treble since the industrialization of department of agriculture. These enriched waters boost the growth of alga within them, which in become has a cascade of effects on the local food chain .
Johnson and his colleagues created 36 mini ponds in sequester tubs that were filled with clear, non-polluted lake urine. In half the tub, they added 200 micrograms of phosphorus per liter of lake water. Polluted lakes can have up to five times that concentration, according to Stephen Carpenter of the University of Wisconsin, a study co-author .
The tubs were populated with alga, adenine well as frogs and small aquatic snails. The snails, which feed on alga, are key to the flatworm parasite ’ south life-cycle – it is inside them that the worm reproduces before infecting frogs .
The researchers found that by boosting the growth of alga, the nutrients finally increase the number and size of the water snails. In change state, this pushed up parasite numbers. “ When their eggs hatch, the parasites have to find a snail within 12 hours or else they die, ” explains Johnson .
In tubs containing extra nutrients, escargot biomass increased by 50 % and septic snails produced twice a many epenthetic worms. The infection rate in frogs increased between two and five fold .
“ If there are more snails, the parasites are more likely to find a escargot. And if the snails have more food, they survive longer. once infected they become zombies whose sole serve is to release parasites, ” Johnson told New Scientist .
The parasites then attack the frogs at the tadpole stage, infecting the cells that finally give rise to the frog ’ sulfur limb. Cysts form in the infect areas as the frogs develop, causing missing limbs, extra limbs, and other malformations.
The discovery of deform frogs has caused concern for the survival of their populations. Without convention limbs, the frogs are easily targets for marauding birds. What is more, many die long before they metamorphose from tadpoles to adult frogs .
Journal address & colon Proceedings of the National Academy of Sciences ( DOI & colon 10.1073/pnas.0707763104 )
Endangered species – Learn more about the conservation battle in our comprehensive special report .