Effects of Multiple Chemical, Physical, and Biological Stressors on the Incidence and Types of Abnormalities Observed in Bermuda's Cane Toads (Rhinella marina)

Abstract

The interactive effects of contaminants and ultraviolet light (UV)-exposure on the incidence and types of abnormalities observed were measured in newly metamorphosed cane toads (Rhinella marina) from four Bermuda ponds contaminated with petrochemicals and metals. Abnormalities were compared in toadlets that were field-collected, reared in predator exclusion cages, reared in laboratory microcosms exposed to control media or corresponding pond media, and reared in laboratory microcosms exposed to UV-light and control media or media from two ponds. Percent abnormal for field-collected, cage-reared, and microcosm-reared toadlets were equivalent per site and ranged between 14% and 63%. All treatments produced similar limb abnormalities but the percentage of hind versus forelimb defects was statistically greater only in field-collected toadlets. UV-exposed control media did not induce abnormalities in larvae exhibiting no maternal effect, and did not alter the types of abnormalities observed in larvae exhibiting a maternal or latent effect. Site media treatments without UV exposure induced significant cephalic and limb abnormalities, proved additive to the observed maternal/latent effect, and produced limb defects predominantly in forelimbs. Concurrent exposure to site media and UV-light induced similar types of abnormalities but a significantly higher percentage of hind limb abnormalities (68-89%) than exposure to site media alone (7-13%). Our results suggest that the types of abnormalities expressed were principally determined by direct and/or transgenerational contaminant exposure, but that UV-light exposure caused limb abnormalities to occur primarily in the hind limbs, mirroring field observations. Our field observations also suggest that ectromelia and brachydactyly in some field-collected specimens may be predator-induced.

Blind toads in paradise: the cascading effect of vision loss on a tropical archipelago

“…Although artificial, in the sense of an introduced and invasive population, our study provides evidence of innate behavioral plasticity, and resilience to adverse morphological conditions (with unknown origins), which even native non‐invasive populations face. Unusual cases of blindness have also been observed in other toads (Bacon et al ., ) and snakes (Wharton, ; Bonnet et al ., ) introduced on islands. In these cases, some environmental similarities can be highlighted, such as the indication of a predator‐free environment, and the presence of abundant, sessile or slow‐moving prey.…”

Effects of a mining‐altered environment on individual fitness of amphibians and reptiles

“…A recent meta-analysis revealed that pollution affects amphibians predominantly through increased frequency of abnormalities (Egea-Serrano et al 2012). For example, elevated frequencies of limb deformities have been experimentally linked to metal exposure in the presence of ultraviolet light (Bacon et al 2013). We found a high frequency of deformities in the barren sites, but the incidence was confined to only two ponds and absent in adjacent, connected ponds.…”

“…For example, elevated frequencies of limb deformities have been experimentally linked to metal exposure in the presence of ultraviolet light (Bacon et al. ). We found a high frequency of deformities in the barren sites, but the incidence was confined to only two ponds and absent in adjacent, connected ponds.…”

“…, Bacon et al. ). Furthermore, individuals in smelting‐impacted sites would exhibit elevated energetic costs due to an upregulation of protective mechanisms (Calow , Sokolova ); accordingly, individuals inhabiting polluted sites should exhibit elevated standard metabolic rates, be in poor body condition, and consequently have reduced reproduction.…”

“…To this end, we assessed if and how metal pollution affects individual fitness based on the occurrence and direction of changes (or lack thereof) in specific individual characteristics in sites that were impacted by smelting operations and in reference sites not impacted by smelting. If the direct toxicity of metals prevails, we predicted that the frequency of deformities would be elevated in smelting-impacted sites (Egea-Serrano et al 2012, Bacon et al 2013). Furthermore, individuals in smelting-impacted sites would exhibit elevated energetic costs due to an upregulation of protective mechanisms (Calow 1991, Sokolova 2013; accordingly, individuals inhabiting polluted sites should exhibit elevated standard metabolic rates, be in poor body condition, and consequently have reduced reproduction.…”