I have to say that frog researchers are doing, and have done, some pretty amazing things to learn more about the big issues facing amphibians and how we can improve their chances. (It would never have occurred to me that you could track frogs.) And their results are helping us better understand not only the suite of problems but also our options for alleviating them, which is great- all death and destruction and no chance for recovery makes any conservationist a bit depressed.
As I mentioned in my last post, environmental contaminants are negatively impacting frog species. Some of those pollutants come from agricultural practices, but others are connected to industrial production. Mercury has been known to bio-accumulate in top level predators like killer whales and swordfish (and us), and Loftin et al. (2012) found that it also bio-accumulated in wood frogs who hatched in ponds with high mercury levels. They hypothesized that water in the ponds had high levels of mercury from the presence of soft woods the surrounding area; the mercury was absorbed by algae and worked its way up the food chain to the frogs. They also thought that, when the young frogs dispersed from the ponds where they hatched, mercury could be spread to other locations. So what can be done? Well, reducing mercury emissions into the environment would help more than just the frogs, but since these mercury-frog hotspots are connected to a type of forest, we could also target mercury clean-up to ponds in soft wood forests (the Lofkin article explains why soft woods are so important- basically it has to do with certain trees being better at taking in mercury and then shedding it in leaf litter) and perhaps even look at ways to increase the proportion of hard woods in certain places.
Compounds coming directly from us are also impacting frogs. You may have heard about fish and other aquatic species developing physical mutations as a result of exposure to human hormones, such as estrogen, in the water supply. It turns out that it’s about more than extra limbs or having both sex organs (which obviously are massive problems for the individuals involved)- there can also be changes we can’t necessarily see, but certainly hear. In Germany Hoffmann and Kloas (2012) recorded the mating calls of male Xenopus laevis both before and after exposure to 17α-ethinylestradiol (commonly found in contraceptives)- when they played the calls for female frogs, the females were much more attracted to the calls before exposure (which were more frequent, less raspy, and had more clicking sounds). More than 4 weeks later, the calls from exposed males were still impacted! So, males exposed to the types of estrogen compounds found in contraceptives (and subsequently in water coming from human populations) are at a reproductive disadvantage, and that could have real implications for the future of any species.
A lot of the research published last year focused on how Bd works and why it has catastrophic consequences in some areas and not others. Voyles et al. (2012) investigated how Bd changed body chemistry in mountain yellow-legged frogs in California- the fungus altered fluid and electrolyte levels, for example sodium and potassium, which could lead to dehydration and even cardiac arrest. By knowing how the pathogen causes death, scientists can better develop ways to mitigate its impact. (As a side note, if you want to get a visual sense of just how quickly Bd can knock out a population, check out the maps in this article- it’s horrifying.) In looking at frog populations in New York, Becker et al. (2012) found that the sensitivity of Bd to temperature (its optimum range is 17-25 °C) translated into greater infections when canopy cover over temperate ponds kept the water cooler- so perhaps one strategy for combatting the disease is creating enough breaks in the vegetation hanging over ponds to ensure that frogs, and other amphibians, have enough shallow, warm water.
What else can be done to support frog populations? Since habitat loss is the overarching issue facing amphibians, Puglis and Boone (2012) looked at ways to make what green space is available in suburban and urban environments more frog-friendly. They found, for example, that amphibian survival on golf courses was considerable, and that sensitive species, such as cricket frogs, preferred taller grass vegetation. Since there are over 17,000 golf courses in the US, adding an un-mown buffer area around ponds on those courses could create better habitat for local amphibians. Humphries and Sisson (2012) investigated habitat use by gopher frogs in North Carolina and highlighted the importance of thinking on bigger scales with species that have to migrate to and from breeding sites. (And they used transmitters to do this- brilliant! If you are as curious as I was about how to put a transmitter on a frog, check out this picture from National Park Service research in the Rocky Mountains.) Since their animals migrated up to 3.5 km (!), protecting gopher frogs means protecting more than just the ponds they breed in. Additionally, since frogs tend to be away from water sources during migration, they are very vulnerable to fire, so prescribed fires should be limited to periods when frogs have reached their summer sites.
I feel that the takeaway message from this recent research is that, yes, frogs are in trouble, but we can help. Many of the ideas mentioned above for supporting amphibian populations are more system-wide actions and may not be accessible to us as individuals, but surely there are ways that we can contribute. For my next post, I’ll do my best to dig up small-scale options for our daily lives.
Works cited:
Becker, C.G., Rodriguez, D., Longo, A.V., Talaba, A.L. and K.R. Zamudio. 2012. Disease risk in temperate amphibian populations is higher at closed-canopy sites. PLoS ONE 7: e48205.
Hoffmann, F. and W. Kloas. 2012. Estrogens can disrupt amphibian mating behavior. PLoS ONE 7: e32097.
Humphries, W.J. and M.A. Sisson. 2012. Long distance migrations, landscape use, and vulnerability to prescribed fire of the gopher frog (Lithobates capito). Journal of Herpetology 46: 665-670.
Lofting, C.S., Calhoun, A.J.K., Nelson, S.J., Elskus, A.A. and K. Simon. 2012. Mercury bioaccumulation in wood frogs developing in seasonal pools. Northeastern Naturalist 19: 579-600.
Puglis, H.J. and M.D. Boone. 2012. Effects of terrestrial buffer zones on amphibians on golf courses. PloS ONE 7: e39590.
Voyles, J., Vredenburg, V.T., Tunstall, T.S., Parker, J.M., Briggs, C.J. and E.B. Rosenblum. 2012. Pathophysiology in mountain yellow-legged frogs (Rana muscosa) during a chytridiomycosis outbreak. PLoS ONE 7: e35374.