Road Proximity Increases Risk of Skeletal Abnormalities in Wood Frogs from National Wildlife Refuges in Alaska

Abstract

BackgroundSkeletal and eye abnormalities in amphibians are not well understood, and they appear to be increasing while global populations decline. Here, we present the first study of amphibian abnormalities in Alaska.ObjectiveIn this study we investigated the relationship between anthropogenic influences and the probability of skeletal and eye abnormalities in Alaskan wood frogs (Rana sylvatica).MethodsFrom 2000 to 2006, we examined 9,269 metamorphic wood frogs from 86 breeding sites on five National Wildlife Refuges: Arctic, Innoko, Kenai, Tetlin, and Yukon Delta. Using road proximity as a proxy for human development, we tested relationships between skeletal and eye abnormalities and anthropogenic effects. We also examined a subsample of 458 frogs for the trematode parasite Ribeiroia ondatrae, a known cause of amphibian limb abnormalities.ResultsPrevalence of skeletal and eye abnormalities at Alaskan refuges ranged from 1.5% to 7.9% and were as high as 20% at individual breeding sites. Proximity to roads increased the risk of skeletal abnormalities (p = 0.004) but not eye abnormalities. The only significant predictor of eye abnormalities was year sampled (p = 0.006). R. ondatrae was not detected in any Alaskan wood frogs.ConclusionsAbnormality prevalence at road-accessible sites in the Kenai and Tetlin refuges is among the highest reported in the published literature. Proximity to roads is positively correlated with risk of skeletal abnormalities in Alaskan wood frogs.

Twice as easy to catch? A toxicant and a predator cue cause additive reductions in larval amphibian activity

“…Our prior studies (Reeves et al 2008 suggested two different hypotheses regarding how copper and predators may interact to produce abnormal frogs in nature, and we found evidence to support only one of these in this experiment. Even the relatively low Cu concentrations in some high malformation sites may be toxic enough to reduce tadpole activity enough to inhibit feeding, which could lead to smaller size over a growing season or a longer duration of exposure to gape-limited predators, like dragonfly larvae.…”

“…For example, despite our observation that smaller frogs are more likely to be abnormal (Reeves et al 2008), we do not know whether frogs are small because they are abnormal or whether something about being small makes tadpoles more likely to become abnormal. These size differences are nontrivial: metamorphs in areas with few abnormalities (like remote areas of the Arctic Refuge) are 21% larger on average (mean snout to vent length (l SVL ) ¼ 23 mm, N ¼ 616) than metamorphs in areas where abnormalities are more frequent (Kenai NWR l SVL ¼ 19 mm, N ¼ 5,716; Reeves et al 2008). There is a need to understand how chemicals and predators interact to influence frog abnormalities in order to manage ecosystems to limit their occurrence.…”

“…Possible causes include parasites, predators, UV-B, and contaminants (reviewed in . The trematode parasite, Ribeiroia ondatrae is an established cause of abnormalities where it occurs , but there are places where abnormal frogs are frequent but this parasite is not detected (Skelly et al 2007, Reeves et al 2008. High frequencies of abnormalities in sites lacking R. ondatrae have been correlated with aquatic predators, which may amputate the developing limbs of tadpoles as they prey on them Sessions 2009, Bowerman et al 2010), Reeves et al 2010).…”

“…Copper is present in Kenai NWR study sites, but at concentrations lower than any previously documented as toxic to amphibians (Table 1). We focus on tadpoles of the wood frog (R. sylvatica), which is the only amphibian in most of Alaska and has long been the focus of our abnormality research (Reeves et al 2008. Larval amphibians change behavior in response to predators, competitors, and other environmental cues (Relyea Mean analyte values are calculated using half of the reported detection limit for non-detect data.…”

From a local observation to a European-wide phenomenon: Amphibian deformities at Serra da Estrela Natural Park, Portugal

“…Even if we consider that the increasing number of reports may not be linked to a higher frequency of malformation occurrences, an increment in the stressors seems to be occurring in nature. Ubiquitous stressors like UV-B radiation, ground-level ozone, acid precipitation and extreme temperatures, as well as products of anthropogenic activities such as chemical contaminants and radioactive mineral deposits, and even proximity to roads (Reeves et al, 2008) are considered to play a role in the appearance of morphological abnormalities.…”