All the single ladies? Study finds decrease in male frogs
that the proportion of female frogs in suburban lakes and ponds is directly correlated to the level of development in the surrounding area.
The study, released Sept. 7, was published by Yale University researcher David Skelly and Ph.D. student Max Lambert in the journal .
Dr. Skelly and Mr. Lambert sampled frogs from 21 different ponds in Connecticut, controlling for all variables except for local landscape development. Their studies revealed a varying sex ratio: suburban ponds held a higher proportion of female frogs and forest ponds held a higher proportion of male frogs.
Specifically, 60 percent of frogs in forest ponds were born male, and some suburban ponds had double the amount of female births.
Not only did suburban lakes have more female frogs, but a large percentage of the male frogs present had characteristics of female reproduction.
Previous studies by have proved that female frogs develop 鈥渋ntersex鈥� or hermaphroditic traits in suburban waters, such as testicles containing female eggs.
Although a strongly supported theory in the past, Skelly finds little data to support the correlation between synthetic estrogen, such as excreted waste containing birth control pills, and the intersex changes in these frogs. Instead, Skelly and his team argue that this skewed gender ratio is caused by a less-assuming factor: landscaping.
When maintaining lawns, humans remove native plants and input , present in common herbicides. is the most commonly used herbicide in the US, and agricultural runoff can input endocrine disruptors into suburban ponds at several parts per million. 聽 聽聽
鈥淭he observation that the amount of landscaping is having a quantitative effect on the sex determination and population biology of frogs in a nearby pond is amazing,鈥� , director of the Shaffer Laboratory at UCLA, a facility that studies ecological and conservation theory.
Along with herbicide chemicals, higher levels of clover are integrated with grass to keep suburban lawns green. Clover contains a high concentration of phytoestrogens, the plant version of estrogen. Higher concentrations of clover means higher concentration of plant estrogen into suburban ponds, skewing the local frog sex ratio.
By altering the number of females naturally born, and then transforming a proportion of natural males into hermaphrodites, Skelly says that landscaping chemicals are now changing how scientists understand gender ratios in amphibians.
鈥淭his is an extremely important study that should make us all think about the collateral damage of suburbanization to natural ecosystems,鈥� said Dr. Shaffer. 鈥淎mphibians are very sensitive bioindicators, and this shows that [suburbanization] has profound impacts on the life history of a common, seemingly resilient species of frog.鈥澛犅�
