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Animals are transforming their bodies to tolerate the impacts of climate change

Some warm-blooded animals are morphing certain appendages in order to combat climate change. A new study published in the journal Trends in Ecology & Evolution showed that some animals are experiencing changes to their beaks, legs and ears.

The researchers from Deakin University in Australia, along with collaborators at Brock University in Canada, studied the link between morphing appendages and rising temperatures utilizing Allen’s rule. Allen’s rule states that bodies in warmer climates tend to have more linear body shapes than those in colder climates. The idea is that in colder climates, the body needs to be more compact and large to retain heat, whereas the opposite occurs to expel heat in hotter climates—this leads to taller and leaner body shapes.

With this in mind, researchers reviewed over 100 previous studies from other researchers and found that warm-blooded animals, mostly birds, had larger appendages due to rising temperatures. One animal that was studied was the Galapagos finch. Using data collected from another recent study about the two varieties of finch beak sizes, the researchers found evidence that the surface area of the finch’s beak directly correlated to higher survival.

The researchers found that the finches with the large, thin beaks had higher survival rates during hot years due to better thermoregulation. The finches with more compact, short beaks were less likely to survive due to a weakened ability to regulate their body temperature during hot years.

Researchers recently looked at data from another study to determine that Galapagos finches with longer, thinner beaks had a higher survival rate during hot years than the finches with more compact beaks. The study found that smaller, longer appendages allow for better thermoregulation.
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“We also don’t know whether these shape-shifts actually aid in survival [and therefore are beneficial] or not,” Sara Ryding, one of the authors of the research, told CNN. “This phenomenon of shape-shifting shouldn’t be seen as a positive, but rather it is alarming that climate change is pushing animals to evolve like this, under such a relatively short timeframe.”

Essentially, smaller, longer appendages allow for better thermoregulation which not only helps animals self-regulate body temperature, it also helps animals regulate water loss due to less evaporative heat loss. However, it is difficult to claim that these changes are directly due to climate change only.

“While climatic warming can be a compelling argument for the force behind morphological change, it is difficult to establish causality with confidence,” the researchers wrote in the study. “For example, introduction events are good opportunities to study how animals respond to changes in their environment, but it can be difficult to tease apart how environmental changes differ from or interact with other biogeographical rules, such as island effects.”

Climate change not only affects temperature but also affects water cycles. Utilizing Allen’s rule, researchers understood that appendage size could also be affected by changes in water cycles. For example, a change in humidity levels could affect bill size in birds without seeing a direct change in temperature.

“Large bills may be advantageous at high humidity because evaporative heat loss is less effective in such conditions, and thus radiative heat loss via the bill may be needed,” researchers wrote in the study. “But large bills for radiative heat loss may also be advantageous in hot, arid environments to minimize water loss. In birds, the effect of relative extreme temperature on bill surface area increased when precipitation was higher, possibly due to the compounding effects of humidity.”

Most of the research was done on morphological change related to smaller birds, however, some research has included bats and shrews. In the case of bats and shrews, the paper discussed research that shows an increase in the size of the animals’ ears, tails, wings and legs.

In terms of predicting what species will shape-shift, the researchers concluded that adherence to Allen’s rule plays an important role.

“Animals with established adherence to Allen’s rule, such as the common frog [Rana temporaria], starlings [Sturnus vulgaris], song sparrows [Melospiza melodia], and a host of seabirds and small mammals, are the most likely candidates to change appendage size in response to increasing temperatures,” researchers wrote in the study.

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