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You are here: Home / Archives for Mirran Trimble

Mirran Trimble

Cold Climate Adaptations and Freeze Tolerance in Amphibians and Reptiles

May 24, 2021 by Mirran Trimble

Amphibians and reptiles are well-known for being ectothermic (cold-blooded). This means that they are unable to internally regulate their body temperature, and instead they rely on their external environment to do so. Consequently, when we think about species like snakes and lizards, we tend to associate them with hot climates, often picturing them basking in the sunshine. Although they do inhabit hot climates, amphibians and reptiles can be found all over the world except for Antarctica. The UK has 14 native species of amphibian and reptile, and a few hardy species can even be found in extreme cold climates such as in the Arctic where temperatures can drop to -45°C. So, how are these species adapted to survive in such extreme conditions?

One important strategy used by amphibians and reptiles is brumation, where they go into a state of dormancy during the cold winter months. They typically brumate in burrows or under log piles, but different species will use a variety of habitats, with some common frogs even brumating in the mud at the bottom of ponds. Although similar to hibernation, the key difference is that brumating animals will emerge for short periods to forage before returning to their state of dormancy, usually on warmer days. All of the native UK species brumate to avoid the coldest weather and conserve energy. Nevertheless, British weather can still be challenging year-round. Common frogs are particularly hardy, and have been found breeding at the highest altitude of any amphibian in the UK at 1,120m in the Scottish Cairngorm Mountains. Higher altitude habitats offer a much shorter window for breeding, so to cope with this, high altitude common frog populations in Scotland have higher growth rates and shorter larval periods compared to low altitude populations (Muir et al. 2014). This ensures metamorphosis is completed before temperatures drop again to maximise chances of survival. On the other hand, some common frog tadpoles will instead delay metamorphosis until the following spring and overwinter as a tadpole rather than a froglet; this may be beneficial in colder temperatures as they will be able to metamorphose at a larger size, improving their chances of survival (Walsh et al., 2008).

 Another UK species which is particularly well-adapted to cold conditions is the leatherback turtle. It often comes as a surprise when people find out that the leatherback turtle is native to the UK, but they are active in our surrounding seas despite the low number of sightings (read more on this here). Leatherbacks have a larger range than other sea turtles and can survive in our cold waters by maintaining a deep body temperature that is 18°C higher than the surrounding water (Frair et al., 1972). They do this through a countercurrent heat exchange process in their flippers (Greer et al., 1973), a process much more commonly associated with mammals and birds than reptiles. Blood vessels in their flippers are closely packed together so that warm blood moving from the core to the extremities passes in close proximity to the cold blood returning from the extremities to the core. Heat hHeateat is transferred into the cold blood and returned to the core, avoiding the extremities where it would be lost to the external environment (Greer et al., 1973). This method of reducing heat loss at the extremities and circulating that heat back into the core of the body is critical for their survival in cold water.

Image Credit: Jack Rawlinson

A very different adaptation is a species’ reproductive strategy, of which there are two key options, oviparity (egg-laying) or viviparity (live-birth). Most reptiles are oviparous as this requires less investment per brood, enabling them to have multiple broods per year. However, reptiles in cold climates are actually more likely to be viviparous because internal development allows the mother to thermoregulate more efficiently, thus improving offspring survival in cold or unpredictable environmental conditions (Tinkle and Gibbons, 1977). Cold temperatures can also reduce the length of the breeding season, making the possibility of multiple broods per year unlikely, and thereby eliminating the benefits of oviparity (Tinkle and Gibbons, 1977). In Scotland, all of the native reptiles are viviparous with one exception; the grass snake. The grass snake is widespread in England and Wales but only found in the far south of Scotland. Could this suggest that being oviparous makes them less suited to the cooler Scottish climate? Interestingly however, there is a population of oviparous lizards, the sand lizard, living on the Scottish island of Coll. They are native to England and not Scotland, but were introduced to Coll in the 70s and are still there today. This may suggest that although viviparity can be beneficial in cold climates, it is not essential.

The number of amphibians and reptiles that thrive in the British weather is undoubtedly impressive, but even more remarkable is the array of hardy species which survive extreme cold-climates such as the Arctic. For any species this would be a challenge, and for most ectotherms freezing temperatures are lethal – the fluids within their cells freeze and form ice crystals which can then rupture (Storey and Storey, 1988). However, there are two fundamental strategies used by cold-climate ectotherms to combat this; freeze avoidance (supercooling) and freeze tolerance. Freeze avoidance is where cell fluids remain liquid despite reaching freezing temperatures, while freeze tolerance is where an individual is able to survive freezing to an extent by restricting freezing to extracellular areas (Storey and Storey, 1988). These processes typically rely on the production of a cyroprotectant, a substance which reduces the freezing point of water and can be used to prevent freezing overall (freeze avoidance) or in cells and key organs (freeze tolerance). Different substances can act as cryoprotectants in amphibians and reptiles, with some common ones including glycerol, glucose and taurine. Cyroprotectants are also used in medicine, for example when donor organs are preserved through cooling, cyroprotectants are often used to prevent cell freezing and rupture.

One species which uses these strategies is the wood frog, the only frog known to live in the Arctic Circle. They can tolerate being frozen at -3°C for two weeks, with up to 70% of their body water freezing (Costanzo et al., 1993). They use glucose as a cyroprotectant, which they produce in high quantities in key organs to prevent ice formation (Costanzo et al., 1993). This restricts freezing to less important parts of the body where it is less likely to cause damage. Red-sided garter snakes in Canada use a similar strategy and can survive at -2.5°C with up to 40% of their body water freezing, using taurine as their cryoprotectant (Churchill and Storey, 2011). Unlike wood frogs they have a much shorter period of tolerance, with only a 50% chance of survival after 10 hours of freezing (Churchill and Storey, 2011). This may suggest that this is not a strategy that is used regularly, but instead an adaptation to survive short periods of frost in the autumn or spring soon before/after brumation.

Although species like the wood frog and red-sided garter snake are incredibly hardy, there is one species which can out-do them all; the Siberian newt. Temperatures in Siberia can reach as low as -45°C and it seems impossible that much life could thrive here, yet the Siberian newt does. Incredibly, it can survive being frozen to -35°C for 45 days, or -50°C for 3 days (Berman et al., 2016). It is not entirely clear how this remarkable species survives such hostile temperatures, but it seems likely that they produce a cryoprotectant to protect their cells and key organs from freezing, although it is not known what this cyroprotectant might be. 

 Amphibians and reptiles are ectothermic, and consequently are often associated with hot climates. In reality, they can be found in a huge variety of habitats and climates and have an array of behavioural and physiological adaptations which enable them to live and thrive in even some of the coldest parts of the world. Adaptations such as brumation, viviparous reproduction, and efficient heat transfer systems are just a few of the things that can help amphibians and reptiles survive in cold or variable climates. Remarkably, in the coldest regions, species use even more extreme adaptations of freeze avoidance and freeze tolerance in order to stay alive. The ability of some species to tolerate being frozen at extreme temperatures for extended periods tells an incredible story of survival and adaptation, and reminds us never to underestimate the brilliance of amphibians and reptiles.

Written by Mirran Trimble

References:

  1. Muir A.P., Biek R., Thomas R., Mable B.K., 2014. Local adaptation with high gene flow: temperature parameters drive adaptation to altitude in the common frog (Rana tomporaria). Molecular Ecology. 23, 561-574.
  2. Walsh P.T., Downie J.R., Monaghan P., 2008. Larval overwintering: plasticity in the timing of life-history events in the common frog. Journal of Zoology. 276, 394-401.
  3. Frair W., Ackman R., Mrosovsky N., 1972. Body temperature of Dermochelys coriacea: Warm turtle from cold water. 177, 791-793.
  4. Greer A., Lazell J., Wright R., 1973. Anatomical Evidence for a Counter-Current Heat Exchanger in the Leatherback Turtle (Dermochelys coriacea). 244, 181.
  5. Tinkle D.W., Gibbons J.W., 1977. The Distribution and Evolution of Viviparity in Reptiles. Miscellaneous Publications Museum of Zoology. 154.
  6. Storey K.B., Storey J.M., 1988. Freeze tolerance in animals. Physiological reviews. 68(1), 27-84.
  7. Costanzo J.P., Lee R.E., Lortz P.H., 1993. Glucose concentration regulates freeze tolerance in the wood frog Rana sylvatica. Journal of Experimental Biology. 181, 245-255.
  8. Churchill T.A., Storey K.B., 2011. Freezing Survival of the Garter Snake Thamnophis sirtalis parietalis. Canadian Journal of Zoology. 70(1), 99-105.
  9. Berman D.I., Meshcheryakova E.N., Bulakhova N.A., 2016. Extreme Negative Temperatures and Body Mass Loss in the Siberian Salamander (Salamandrella keyserlingii, Amphibia, Hynobiidae). Doklady Biological Sciences. 468, 137-141

Filed Under: Croaking Science Tagged With: amphibians and reptiles, climate change, cold climate adaptions, freeze tolerance

What our animals are doing this month….

April 22, 2021 by Mirran Trimble

May is an excellent time of year to look out for our native legless lizard, the slow-worm. Breeding takes place in May and this can be a dramatic process to witness. Not only do males compete aggressively over mates, but during courtship they will grasp the female roughly by the neck, and mating can then last for up to 10 hours! Courtship is easily mistaken for fighting, so being able to tell males and females apart can be helpful. Male slow-worms are grey or brown all over, and some have bright blue spots along the back. Females are usually brown on top with dark sides and belly, and a dark line down the back.

Slow-worms are a common garden species and the perfect gardener’s friend, as they love to eat garden pests such as slugs. They are particularly fond of compost heaps and warm hiding places such as log piles or under tin roofing, so these are good places to look for them. Despite their snake-like appearance, slow-worms can be distinguished from snakes by their shiny appearance, bullet-shaped heads, and blinking abilities (snakes lack eyelids!)

 

A pair of courting slow-worms (Photo: Lin Wenlock)

Filed Under: What our animals are doing this month Tagged With: courtship, female, male, slow worms

Ponds Against Climate Change

April 22, 2021 by Mirran Trimble

From Antarctica to the tropics, ponds are widespread habitats found in nearly all terrestrial biomes (Jeffries, 2016). Research estimates that there are 304 million natural lakes and ponds worldwide, covering a total area of approximately 4.2 million km2 (Downing et al., 2006). This article will focus on ponds: according to limnologists, the difference between ponds and lakes is that ponds are shallow enough that plants could grow across the entire surface meaning that it has a photic zone where sun can reach the bottom. By contrast, lakes have an aphotic zone meaning there are sections deep enough that sunlight cannot reach the bottom. Ponds are biodiversity hotspots for both aquatic and terrestrial species, providing habitat for rare specialists such as fairy and tadpole shrimp. Not only are they vital for these species, but they are also vital in managing landscapes from threats such as flooding and climate change. It is known that aquatic ecosystems have a large role in managing greenhouse gases, with oceans among the most well-known of carbon sinks. However, with lakes and ponds covering such a vast expanse of area, is it possible that they are the climate’s unsung heroes?

Carbon sinks are reservoirs that absorb and store atmospheric carbon through physical and biological processes. One study concludes that ponds may be more active in nearly all of these processes than large lakes, marine ecosystems and terrestrial ecosystems (Downing, 2010). Carbon burial rates between ponds can vary depending on composition. Ponds are not ubiquitous, thus the effectiveness of carbon sequestration varies per site depending on factors such as substrate type and vegetation. Gilbert et al., (2014) found that permanent and naturally vegetated ponds were the most efficient at sequestering carbon dioxide, particularly those dominated by thick moss swards and aquatic grasses. These form a thick, moist blanket when the pond dries out, minimising the release of stored carbon into the atmosphere. The least efficient ponds were temporary, shallow arable ponds which lacked vegetation and were regularly disturbed. When discussing the value of ponds in carbon sequestration, it may be unhelpful to group all ponds together as their importance can vary considerably based on their composition. Furthermore, it is important to note that ponds can serve a variety of purposes. Whilst ponds capturing excess fertilisers and pesticides are useful in the fight against climate change, they may not make good wildlife ponds or facilitate biodiversity.

This diversity of ponds is reflected in the range of carbon sequestration rates found across the literature. One study found that small ponds sequester 79-247g of organic carbon per square meter annually, a rate 20-30 times higher than woodlands, grasslands and other habitat types (Taylor et al., 2019). Céréghino et al., (2014) suggested that some 500m2 ponds may even be capable of sequestering up to 1000kg of carbon per year, as much as a car would produce in that time. Although ponds only take up 0.0006% of land area in the UK, a tiny proportion compared to the 36% of grasslands (Carey et al., 2008), their high rates of carbon burial suggest that their overall contribution is significant – even when compared to much larger habitats. Thus their role in tackling climate change should not be overlooked.

Biological processes carried out by aquatic vegetation are pivotal in carbon sequestration in ponds. Photosynthesis contributes to the sequestration of carbon dioxide by turning it into oxygen and biomass. One kilogram of algae uses an average of 1.87 kilograms of carbon dioxide a day (Anguselvi et al., 2019). Algae in ponds also contribute to reducing additional greenhouse gases such as nitrous oxide (N2O). Nitrogen is a key component in chlorophyll and thus used in farm fertiliser. Excess nitrogen could react with oxygen in the air to become N2O. The presence of algae in farm ponds to capture this excess can prevent this reaction from occuring and limit emission of the greenhouse gas. A study has found that two thirds of farm ponds act as N2O sinks (Webb et al., 2019), making them an important contributor to combating climate change, particularly as N2O traps heat at 300x the rate of CO2. 

Ponds play an important role in mitigating climate change, however, there is evidence to suggest that they can also act as carbon sources. Does this offset their sequestering benefits? Take for instance, permafrost thaw ponds. Permafrost thaw ponds in northern regions can be particularly prominent sources of carbon. As permafrosts thaw, vast amounts of carbon dioxide and methane are released, resulting in the formation of small ponds which become carbon emission hotspots (Kuhn, 2018). Although they are releasing carbon, it is not the pond itself creating these gases. Global warming is causing the permafrosts to thaw out and release the stored carbon. Although the ponds facilitate the emissions, it is perhaps misleading to label them as a carbon source in these instances. 

Large habitats such as oceans and woodlands are well-known for their role in reducing greenhouse gasses and mitigating the effects of climate change, but ponds may play an equally important and largely underappreciated role. Ponds are also a fantastic tool against climate change because they give people a way in which to take action. People can easily create ponds in their own gardens and community spaces, and in this way play a part in reducing greenhouse gas emissions and contribute to the global fight against climate change.

Written by Mirran Trimble & Emily Robinson

 

References

Anguselvi, V., Masto, RE., Mukherjee, A., & Singh, PK. (2019) CO2  Capture for industries by algae, Algae, Yee Keung Wong, IntechOpen, DOI: 10.5772/intechopen.81800. Available from: https://www.intechopen.com/books/algae/co-sub-2-sub-capture-for-industries-by-algae

Carey, PD., Wallis, S., Chamberlain, PM., et al. (2008) Countryside Survey: UK results from 2007. Swindon, UK: Natural Environment Research Council.

Céréghino, R., Boix, D., Cauchie, HM., et al. (2014) The ecological role of ponds in a changing world. Hydrobiologia. 723, 1–6.

Downing, JA. (2010) Emerging global role of small lakes and ponds: little things mean a lot. Limnetica. 29(1), 9-24.

Downing, JA., Prairie, YT., Cole, et al. (2006) The global abundance and size distribution of lakes, ponds, and impoundments. American Society of Limnology and Oceanography. 51(5), 2388-2397.

Gilbert, PJ., Taylor, S., Cooke, DA., et al. (2014) Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK. Inland Waters. 4(1), 57-64.

Jeffries, MJ. (2016) Flood, drought and the inter-annual variation to the number and size of ponds and small wetlands in an English lowland landscape over three years of weather extremes. Hydrobiologia. 768, 255–272.

Kuhn, M., Lundin, EJ., Giesler, R., et al. (2018) Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands. Scientific Reports. 8, 9535.

Taylor, S., Gilbert, PJ., Cooke, DA., et al. (2019) High carbon burial rates by small ponds in the landscape. Frontiers in Ecology and the Environment. 17(1), 25-31.

Webb, JR., Hayes, NM., Simpson, GL. et al. (2019) Widespread nitrous oxide undersaturation in farm waterbodies creates an unexpected greenhouse gas sink. PNAS. 116(20), 9814-9819.

 

Filed Under: Croaking Science Tagged With: carbon sink, climate change, ponds

What our animals are doing this month….

March 25, 2021 by Mirran Trimble

Adders emerge from brumation in March and April and begin breeding shortly after. Rival males compete for females by performing a dance-like duel where they rise up and wrestle each other to the ground. Although this is an aggressive behaviour between two males, it can look very elegant and is sometimes mistaken for a courtship ritual.

Females incubate eggs internally and ‘give birth’ to live young. They will sometimes mate with multiple males in a breeding season, and some years will not breed at all if conditions are not right.

Adders are venomous, but their bites are rare and generally not serious. They are shy and will only bite as a last resort if threatened. Saying that, adder bites are most common at this time of year. This is because they can be particularly sluggish as they emerge from brumation, and if they are approached by a person or animal and unable to escape quickly enough, they may resort to biting. This can be avoided, however, if we don’t try to approach or handle them.

Male adders are grey or silver along their sides, unlike females which are brown (Photo: Matt Wilson).

 

Filed Under: What our animals are doing this month Tagged With: adder, brumation, courtship, female, male, zig-zag

What our animals are doing this month….

February 22, 2021 by Mirran Trimble

March is often a good month to spot common toads as they migrate from their overwintering sites to breeding ponds, particularly on warm, damp evenings. Every year they return to the same pond via the same route, but they can get into trouble if humans build along these routes. Roads in particular can make this migration dangerous, but our wonderful volunteer Toad Patrollers are working hard to reduce this risk by helping common toads safely cross roads along their migration routes.

Once they arrive at breeding ponds, males grasp onto the backs of females forming an amplexus, allowing the male to fertilise her eggs as she lays them. Mating balls often form where multiple males hold onto one female, and unfortunately this can sometimes end up with the female being drowned. However, many female toads do survive and successfully breed, producing a new generation of common toads! Unlike common frogs which lay their eggs in clumps, common toads lay their eggs in long strings wrapped around pond vegetation, so you may have to look a little closer to spot the toad spawn!

To find out more about toad patrols take a look at our website. 

A pair of common toads in amplexus during the breeding season

Filed Under: What our animals are doing this month Tagged With: amplexus, breeding, march, spawn, toads, Toads on Roads

What our animals are doing this month…

January 27, 2021 by Mirran Trimble

By mid-late February, the first palmate newts will start emerging from their overwintering sites and making their way to breeding ponds, where the breeding season will continue throughout spring until the end of May.

Males typically arrive at ponds first where they perform a courtship display to attract females, involving some vigorous tail shaking. Males then drop a spermatophore which the female picks up via her cloaca, using it to fertilise her eggs. She lays her eggs one at a time, carefully rolling each one in an individual leaf. Although this seems like a slow process, a female palmate newt usually lays between 100-300 eggs per season.

If you’re looking for palmate newts they can be tricky to identify as they are easily confused with smooth newts, but the key difference is that smooth newts have spotty throats whereas palmate newts do not. Males in the breeding season are easier to tell apart as male smooth newts develop a crest along the back, and male palmate newts develop large webbed hind feet and a small filament at the tip of the tail.

Filed Under: What our animals are doing this month Tagged With: breeding, courtship, eggs, filament, overwintering, palmate newt, webbed hind feet

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