The Costa Rican Variable Harlequin toad is facing three major threats associated with climate change: habitat shifting and loss, chytrid fungus, and the parasitic 'flesh-fly'.
Shifting Habitats
The cloud forest is the Harlequin toad’s only natural habitat and during times of drying associated with the El Niño Southern Osscilation (ENSO), the species has been observed to move away from drier zones. Requiring a moist environment this increases the risk of dehydration (or desiccation) leading to mortality [7]. The formation of tropical montane cloud forest is dependent on the trade-winds and is particularly susceptible to ENSO cycles [7, 9]. With the warming oceans associated with climate change, the ENSO cycles are expected to become more extreme [10] which will cause greater fluctuations between dry and wet seasons in the limited Harlequin toad habitat. The ability of this amphibian to cope with such climate variability remains to be seen, but given previous mortality associated with dry seasons [7] the fluctuating climate poses a serious threat.
Under a future climate scenario, the humidity surface is expected to rise by several hundred metres [7]. This could dramatically decrease the species’ range by putting the cloud band above much of the current available habitat for the Harlequin toad! Such climate predictions are damning for the future of this amphibian, potentially ‘locking’ the species into remaining pockets of suitable habitat.
The cloud forest is the Harlequin toad’s only natural habitat and during times of drying associated with the El Niño Southern Osscilation (ENSO), the species has been observed to move away from drier zones. Requiring a moist environment this increases the risk of dehydration (or desiccation) leading to mortality [7]. The formation of tropical montane cloud forest is dependent on the trade-winds and is particularly susceptible to ENSO cycles [7, 9]. With the warming oceans associated with climate change, the ENSO cycles are expected to become more extreme [10] which will cause greater fluctuations between dry and wet seasons in the limited Harlequin toad habitat. The ability of this amphibian to cope with such climate variability remains to be seen, but given previous mortality associated with dry seasons [7] the fluctuating climate poses a serious threat.
Under a future climate scenario, the humidity surface is expected to rise by several hundred metres [7]. This could dramatically decrease the species’ range by putting the cloud band above much of the current available habitat for the Harlequin toad! Such climate predictions are damning for the future of this amphibian, potentially ‘locking’ the species into remaining pockets of suitable habitat.
Chytrid Fungus
Chytridiomycosis is a disease caused by the chytrid fungus thought to have originated from Africa [11], and is a major driver of amphibian decline globally. Having been sweeping through Central America since the late 1980s, 30% of amphibian species globally are now thought to be affected by the chytrid fungus [12]. A warmer climate associated with climate change is likely to increase the speed of the fungal life cycle, leading to proliferation of the disease. A warmer climate will benefit the chytrid fungus given that the mean annual temperature in the Costa Rican cloud forest is 20°C, yet the optimum temperature for chytrid fungal growth is 23°C [13]. However, with a mean annual temperature of 27°C in the Costa Rican lowlands, and a death point of the chytrid fungus of >28°C [13], we may see a shift in the range of the disease, leaving the lowlands, ad only occupying areas of higher altitude. Chytridiomycosis has been linked to the possible extinction of 30 of the 113 Atelopus Harlequin toads already[14].
Chytridiomycosis is a disease caused by the chytrid fungus thought to have originated from Africa [11], and is a major driver of amphibian decline globally. Having been sweeping through Central America since the late 1980s, 30% of amphibian species globally are now thought to be affected by the chytrid fungus [12]. A warmer climate associated with climate change is likely to increase the speed of the fungal life cycle, leading to proliferation of the disease. A warmer climate will benefit the chytrid fungus given that the mean annual temperature in the Costa Rican cloud forest is 20°C, yet the optimum temperature for chytrid fungal growth is 23°C [13]. However, with a mean annual temperature of 27°C in the Costa Rican lowlands, and a death point of the chytrid fungus of >28°C [13], we may see a shift in the range of the disease, leaving the lowlands, ad only occupying areas of higher altitude. Chytridiomycosis has been linked to the possible extinction of 30 of the 113 Atelopus Harlequin toads already[14].
Sarcophagidae: a Flesh-Fly Parasite
The larvae of Notochaeta bufonivora (Sarcophagidae) are known to parasitise upon species of Harlequin toads, mainly during the dry season [8]. This is an unusual association given the toxin secreted by the Harlequin toad, by which this fly species seems unaffected. The female fly deposits larvae on the host (Atelopus), which immediately burrow into the host and feed, leading to host mortality [8]. Akin to the chytrid fungal disease, whilst not a direct result of climate change, it is likely that the threat of parasitism will increase with increasing temperatures associated with future climate projections. An increased life cycle rate of the fly is likely to result in a greater degree of parasitism, with more Atelopus individuals suffering the consequences.
The larvae of Notochaeta bufonivora (Sarcophagidae) are known to parasitise upon species of Harlequin toads, mainly during the dry season [8]. This is an unusual association given the toxin secreted by the Harlequin toad, by which this fly species seems unaffected. The female fly deposits larvae on the host (Atelopus), which immediately burrow into the host and feed, leading to host mortality [8]. Akin to the chytrid fungal disease, whilst not a direct result of climate change, it is likely that the threat of parasitism will increase with increasing temperatures associated with future climate projections. An increased life cycle rate of the fly is likely to result in a greater degree of parasitism, with more Atelopus individuals suffering the consequences.