Croaking Science

The Ecological Importance of Small Freshwater Bodies and Riparian Habitats

May 9, 2022 by Kathy Wormald

Summary
Small Freshwater Bodies include ponds, lochans, ditches, springs, seepages and flushes. All of these
provide huge ecological benefits, supporting a wide range of aquatic species and offsetting some of the
negative impacts of many environmental issues facing us such as climate change, flooding, chemical and
noise pollution. Riparian habitats are the terrestrial sites in close proximity to the freshwater habitats and
provide critical habitats for insects, amphibians and other wildlife, and make valuable contributions to our
natural capital.

What are they?
Ponds support an extraordinary two thirds of all freshwater species including Common frog, Common
toad, Teal, Pond mud snail, Tadpole shrimp, Northern damselfly, Broad-leaved pondweed, Great Crested
Newt, Grass snake, Pillwort, and Medicinal leech. Ponds are also used by a wide range of other wildlife
as a source of drinking water including hedgehogs and birds.

One third of ponds are thought to have disappeared in the last fifty years or so and of those that remain
more than 80% are considered to be in ‘poor’ or ‘very poor’ condition (Freshwater Habitat Trust). This
has had an enormous impact on aquatic wildlife.

Creating clean new ponds is one of the simplest and most effective ways to protect freshwater wildlife.
Where it is not a viable option to create new ponds, restoring existing depleted ponds is greatly
beneficial.

Ditches are man-made waterbodies that are used mainly to drain the land. They are distinguished from
streams in that they are usually straight and follow linear field boundaries; they show little relationship
with natural landscape contours. There are over half a million kilometres of ditches in the British
landscape. They are found in a wide range of habitat types from lowlands to hills and can have as much
biodiversity as some of our best rivers. In addition, they often support temporary water specialists which
are often not found in other freshwater habitats.

As ditches drain land, what lives in them is dependent on how polluted they are, on their gradient and
how often they flow. Unpolluted, high quality ditches are in the minority, with perhaps only 10% of the
UK ditches qualifying (Freshwater Habitat Trust).

Springs are places where underground water emerges at the surface. They may turn into tiny seepages
and become flushes, or they may be the beginning of substantial water courses. They are found all over
the country in all landscapes and are dominated by small animals and plants such as mosses and
liverworts, cold water flatworms, caddis flies and the larvae of two-winged flies. Many of these species
are found very close to the start of springs and seepages. If the spring is permanent it may also be used
by fish.

Seepages and flushes are areas where water from underground flows out onto the surface to create an
area of saturated ground. Flushes vary from open, stony ground with sparse plant cover to dense cover
of flowering plants, usually sedges or rushes, with mosses and liverworts forming a ground layer under
the canopy. They are found all over the country and support a wide variety of wetland plants,
invertebrates and other uncommon smaller wildlife.

The ecological benefits of riparian areas are huge. They provide habitat for many species such as water
vole and create habitat corridors by linking fragmented and isolated habitats through which species can
migrate. They are also a great food source for many species, particularly invertebrates.

Why are they important?
Small freshwater and riparian habitats are biodiversity hotspots, collectively acting as small ecosystems
and supporting a massive range of wildlife species.

They are also remarkably good carbon sinks. Carbon sinks are reservoirs that absorb and store
atmospheric carbon through physical and biological processes. Ponds in particular are more active in
nearly all of these processes than larger lakes, marine ecosystems and terrestrial ecosystems (Downing,
2010). Small ponds sequester 79-247g of organic carbon per square metre 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. Although ponds take up only 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.

Biological processes carried out by aquatic vegetation are pivotal in carbon sequestration.
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 occurring and limit emission of greenhouse gas. A study 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 300 times the rate of CO2.

Freshwater habitats and soft ground act as flood defences and with flood incidence increasing they can
make a huge contribution to offsetting the environmental and social damage that is caused by flooding.

Finally Freshwater habitats absorb noise and can offset noise pollution in highly populated noisy urban
environments.

What needs to happen?
We need to accelerate the implementation of both strategic and specific actions to manage small
freshwater bodies in ways that reduce freshwater pollution and improve water quality. We need an
ongoing funded programme to undertake restoration works on existing smaller freshwater bodies.
This needs to be a rolling programme to avoid the current trend of small freshwater body succession at
such a late stage that restoration is no longer an option and the body becomes defunct for biodiversity
benefits. In order to address the estimated 50% loss in small freshwater bodies we need investment to
create new smaller freshwater bodies.

These interventions will both support nature’s recovery, and help the freshwater environment become
more resilient to the impacts of climate change. Nature-based solutions to climate change are
increasingly recognised as an essential approach to water management and we must restore smaller
freshwater bodies in ways that promote ecosystem processes. Restoring and creating new smaller
freshwater bodies is a key nature-based solution to climate change, with the scope to lock up carbon,
benefit biodiversity and enhance human well-being. However, nature-based solutions are not yet
sufficiently incorporated into strategic and project plans.

Next steps for the Scottish Parliament:
With the scrutiny of the Scottish Government’s proposals for the fourth National Planning Framework
(NPF4) currently underway by parliament, there are a number of areas where the protections and
regulations relating to freshwater bodies could be improved. LINK members urge MSPs to consider the
following measures:

● Seize the opportunity to align nature-based solutions to flood management with NPF4,
Scottish Planning Policy and the Land Use Strategy. The ‘mainstreaming’ of nature-based
solutions across government policies is a key step in tackling the climate and nature
emergencies.
● Focus on the restoration of natural processes as the most sustainable footing for biodiversity
recovery. Such habitats must also include smaller water bodies including ponds, ditches, springs
and wetlands. Both cost and technical feasibility have limited action in these waters to date; to
counter this, natural ecosystem function should underpin a ‘no-regrets’ approach to restoration.
● Preference must be given to schemes which utilise nature-based solutions/natural flood
management wherever possible. It will not always be possible to adapt to climate change and
the pressure to implement hard engineering solutions in order to attempt to do so must be
resisted; we must instead think in terms of mitigating the impacts of a changing climate and
select solutions which work with nature. Working with natural processes is now more readily
considered but there remain questions that concern some stakeholders, such as around long-term maintenance, liabilities and so on, which would benefit from resolution.
● As our understanding of such techniques grows, findings must be widely communicated
amongst stakeholders, particularly to Local Authorities, to ensure that all involved in Flood Risk
Management are able to draw upon techniques that work with natural processes in the widest
sense.
● Small water bodies must be given the same priority as other important habitats, given their
important contribution to Scotland’s environment, wildlife and tourism sectors.
● Connectivity is a key attribute required for healthy, functioning ecosystems. Habitat restoration
and creation, planned and prioritised through a spatially mapped national Nature Network in
NPF4. Informed by local knowledge, this could be used to enhance connectivity, as well as by
considering the quality of connected habitats. Mapping of priority wetland habitats would also
identify existing areas of good-quality habitat as well as opportunities for restoration and allow
the identification of areas where habitat restoration or re-creation will be valuable to support
biodiversity delivery.
● Habitat restoration and creation should be funded by a combination of sources including
Water Framework Directive, Scottish Rural Development Programme payments, the Nature
Restoration Fund from government, Flood Risk Management funding, Scottish Water
investment programme and other sources. Together, this spatial planning and framework
integration can deliver the “urgent step change in effort” that the biodiversity crisis demands.
● Improving joint working, including via the sharing of information so that stakeholders are
clearer on the contributions that they could make to improving the state of estuarine and
coastal waters by undertaking work further up the catchment.Funding criteria for catchment based projects should include an assessment of whether they have incorporated actions which will contribute to improvements.
● Finally, it is important to monitor our progress towards addressing loss of our smaller freshwater
bodies. A target should be developed, and progress towards meeting that target should be
reported on a regular basis as part of the Scottish Government’s Environment Strategy.

Where property development is essential due diligence must be awarded to existing freshwater bodies.
These bodies are crucial habitats for many species such as amphibians and invertebrates. With much
smaller ranges than some other species, they are unable to travel a great distance to populate new
habitats. Associated infrastructure, such as roads, railways and cycle tracks need to take into account
species migration routes. Mortality of wildlife in the country as a result of habitats being fragmented by
infrastructure is a huge issue. Species such as toads, which use hereditary migration routes, can suffer
huge mortality rates crossing roads.

Can frogs, salamanders and lizards show us the way to limb regeneration?

April 26, 2022 by Roger Downie

Roger Downie

Froglife and University of Glasgow

Limb loss in humans is a very significant source of disability and distress. One estimate is that in the USA alone, 3.6 million people will be affected by 2050, as a result of war and other traumatic injuries, or after diabetes-related amputation (Ziegler-Graham et al. 2008). There are two possible routes to the treatment of these losses. Until recently, the most hopeful way forward was advances in prosthetic limb development, related to robotic and micro-electronic engineering progress. Encouraging regeneration of the lost limb seemed less likely, despite many years of research. This is because organ regeneration in mammals is extremely limited in nature. However, recent work based at Tufts University in the USA, using the African clawed frog Xenopus laevis, suggests that limb regeneration in mammals could be stimulated with the right interventions (Murugan et al. 2022).

The ability to repair tissue damage is very widespread in the animal kingdom. In ourselves, the most obvious example is wound healing, with a complex sequence of events following an injury: local cessation of blood flow; blood clotting and formation of a scab to prevent entry of micro-organisms; mobilisation of surrounding cells to close the wound; tissue remodelling below the skin to tidy up the damage, sometimes involving formation of scar tissue. However, some animals have the capacity to replace complete and functional organs if they are lost. In amphibians and reptiles, this capability has an odd distribution.

Some species of lizards show autotomy, the deliberate loss of part or all of the tail in response to predator attack (autotomy also happens elsewhere in the animal kingdom: starfish, stick insects etc.). In these lizards, muscles in the tail on the body side contract, severing a line of weakness built into the vertebrae, and the predator is left with the twitching end of the tail, while the rest of the lizard escapes. The tail stump then heals, and the tail regenerates, but not as before. The regenerate is mis-shapen and its skeletal core is a stiff rod of tissue, rather than a set of vertebrae. If the lizard is attacked again, autotomy can only occur in the part of the tail containing the original structures. The costs and benefits of tail autotomy in lizards are finely balanced, and this ability has been lost and evolved many times in different lineages (Clause and Capaldi 2006). Where the tail is important in balance, as in fast-running species, or in social signalling, as a sign of quality as in Uta species (Fox 1998), autotomy tends to be rare or does not occur at all. Cooper et al. (2004) showed that selection related to predation pressure could influence the occurrence of autotomy in different populations of a single lizard species.

In newts and salamanders, adults can regenerate a range of complex organs: parts of the eye, brain, and heart, as well as limbs and tail. This does not involve autotomy, and unlike the case of lizard tails, regeneration results in the re-formation of a normal, functional limb or tail. Limb regeneration follows an orderly sequence: closing of the wound is followed by the formation of a ‘blastema’- a mass of tissue with the characteristics of tissue at the distal end of an embryonic developing limb. Somehow, the blastema ‘knows’ how much of the limb has been lost, and it reforms only the missing elements in order, from proximal to distal ends. As the process progresses, nerves grow into the regenerate, and these provide signalling molecules essential for full regeneration. The ability to regenerate limbs is somewhat variable between species, with larger species and individuals generally having less regenerative capacity than smaller ones (Joven et al. 2019).

In frogs and toads, regeneration of larval tails and early-stage limb buds occurs, but limb regeneration in adults hardly at all. In some families (pipids, discoglossids, hyperoliids), a blastema forms and a partial regenerate grows from the stump, a bit like the regenerated tails of lizards, but it never approaches the size and complexity of the original limb. In bufonids and ranids, wound healing occurs, but no regeneration at all (Scadding 1981). Mammals are like adult amphibians, with no limb regeneration at all.

This is where the new results from Murugan et al. are revelatory. After some years of technique development, they now report substantial hindlimb regeneration in experimentally-amputated Xenopus laevis adults ( X. laevis has a long history as a laboratory species for biological research following its early 20^th Century use in human pregnancy testing). The method involves applying a temporary ‘collar’ (called a ‘Biodome’) to the limb stump following amputation. The collar is made of silicone and silk fibres, impregnated with a solution containing a mix of five molecules known to act as signals during normal limb development (such as growth hormone and retinoic acid). It therefore provides a moist environment for the stump tissue, including limb development molecules that would not normally be present there in damaged adult Xenopus limbs. The collars were left in place for only 24 hours, then removed, and the frogs then followed for 18 months to assess how well the amputated limbs regenerated. After decades of failure in such experiments, the results were spectacular.

The regenerates formed went well beyond the mis-shapen spikes usually formed by Xenopus stumps. There was long-term growth, including formation of bones and other normal tissues, neuromuscular repair so that the limbs could move, and the formation of digit-like projections at the distal ends: the animals were able to use their repaired limbs for more or less normal movements. Murugan et al. comment that while regeneration was not perfect in their experiment, the set-up provides considerable scope for alteration of the details: the mix and concentration of the signalling molecules, the duration of their application; also, the possible addition of electrical stimulation, which has shown some positive effects in other experiments. The authors are hopeful that, if regeneration can be stimulated in Xenopus, similar methods may work for mammals, including humans.

The occurrence and distribution of organ regeneration has long intrigued biologists (Bely 2010). For example, why should complete regeneration occur in newt and salamander adults, but not at all in frogs and toads? One theory concerns the period of impairment while the limb is regenerating, which can take months. Newt locomotion can remain effective in the absence of a functional limb (in many species, the limbs are greatly reduced and even absent in some), whereas the absence of a frog hindlimb for some months would be disastrous. The argument from this is that limb regeneration in frogs would be too slow to be effective, and therefore that it does not occur. This argument can be extended to mammals: the high demand for food in warm-blooded animals means that a period of immobility while a limb regenerates would not be useful (Elder 1979). Most discussion of limb regeneration assumes that the benefit follows limb loss after predation, as in lizards, but there are very few studies investigating the ecological role of regeneration in newts and salamanders.

Finally, a comment on ethics. Those opposed to any animal experimentation will not approve of Murugan et al.’s studies. Those with a more utilitarian outlook, will hope that the discomfort and death of a hundred or so Xenopus will lead eventually to new treatments that could benefit millions of people (and even some other animals). Those who prioritise animal welfare will study the conditions under which the Xenopus lived and look to see that the experimental protocols minimised any pain and discomfort. However, there is another ethical aspect: on behalf of Tufts University, where the experiments have been done, patents for the methodology have been applied for. I find it distressing that scientists should seek to make profit from advances in medical research, especially when it has been publicly funded. The notion that, in the future, victims of war should have to pay a royalty to Tufts so that their limbs can be repaired, is distasteful. But then we are all used these days to noticing that some companies have done very well financially out of the Covid pandemic.

References

Bely, A.E. 2010. Evolution of animal regeneration: re-emergence of a field. Trends in Ecology and Evolution 25, 161-170.

Clause, A.R. and Capaldi, E.A. 2006. Caudal autotomy and regeneration in lizards. Journal of Experimental Zoology 305A, 965-973.

Cooper, W.E. et al. 2004. Ease and effectiveness of costly autotomy vary with predation intensity among lizard populations. Journal of Zoology 262, 243-255.

Elder, D. 1979. Why is regeneration capacity restricted in higher organisms? Journal of Theoretical Biology 81, 563-568.

Joven, A. et al. 2019. Model systems for regeneration: salamanders. Development 146, dev167700.

Murugan, N.J. et al. 2022. Acute multidrug delivery via a wearable bioreactor facilitates long-term limb regeneration and functional recovery in adult Xenopus laevis. Science Advances 8 (4).

Scadding, S.R. 1981. Limb regeneration in adult amphibia. Canadian Journal of Zoology 59, 34-46.

Ziegler-Graham et al. 2008. Estimating the prevalence of limb loss in the United States, 2005-2050. Archives of Physical Medicine and Rehabilitation 89, 422-429.

Croaking Science: The benefits of green spaces and nature on mental health

March 29, 2022 by Briony Nesbitt

“In every walk with nature, one receives far more than he seeks” – John Muir

As well as the conservation work Froglife does for amphibians and reptiles across the UK, we also run projects that promote education amenities and research activities for the benefit of the public. We run wildlife projects for disadvantaged young people and those with dementia, such as our Green Pathways, Green Pathways for Life and Leaping forward for Dementia projects. A common issue amongst our participants is mental health, especially coming out the other side of the COVID-19 pandemic. Our Eco therapy style project is based on scientific research that suggests being outdoors and connecting with nature, have hugely positive effects on individuals.

As countries become increasingly urbanised, the world’s population is spending increasingly less time exposed to natural environments (Cox et al, 2018). It has been reported that 55% of the world’s population live in urban areas and this is expected to increase to 68% by 2050 (United Nations, 2018). Unfortunately, urbanisation not only means spending less time in natural environments but more time destroying them and reducing the number of green spaces around the globe (Collins, 2014). Aside from the detrimental environmental effects of this, loss of these green spaces and time spent in them could have hugely negative effects on people’s mental health and well-being.

There is growing evidence to suggest that being in nature has positive effects on people’s mental health. Studies have shown that green spaces can lower levels of stress (Wells et al, 2003) and reduce rates of depression and anxiety, reduce cortisol levels (Park et al, 2010) and improve general well-being. Not only can a simple walk in nature boost your mood but also improve your cognitive function and memory (Berman et al, 2012). Green spaces can provide a buffer against the negative health impacts of stressful life events. A Dutch study showed that residents with a higher area of green spaces within a 3km radius had a better relationship with stressful life events (Van den Berg et al, 2010) which was soon to be increasingly important in recent years with the effects of COVID-19.

So what is it about natural environments that are good for mental health and wellbeing?

Positive Physiological effects

Something as simple as exposure to natural environments can be physiologically restorative (Conniff et al, 2014). This means that being in a natural outdoor environment can have positive mental health effects due to the physical processes elicited in the body. A Japanese study showed that viewing and walking in forest environments can promote lower concentrations of cortisol, lower pulse rates and blood pressure when compared to city environments (Park et al, 2010). These physiological effects are all a counter to the physical effects stress causes in the body and are what happens when you relax. A recent study found that those who had access to natural spaces during the COVID-19 lockdowns had lower levels of stress and those that could view nature from home had reduced psychological distress (Ribeiro et al, 2021).

There are multiple psychological theories as to how nature helps our mental well-being. The two common prevailing theories on how nature brings about these positive effects are the Stress Reduction Theory (SRT) coined by Ulrich (1981) and Kaplan et al’s (1989) Attention Restoration Theory (ART). SRT suggests that nature promotes recovery from stress and that urban environments have the opposite effect. Ulrich proposes that being in unthreatening natural environments (a green space you would consider safe) activates a positive emotional response. That being in nature produces this as a universal innate connection, promoting the physiological effects of lower blood pressure, heart rate and increases attention which in turn blocks negative thoughts and emotions (Ulrich et al, 1991). Kaplan et al’s ART works around the idea that we have different types of attention: voluntary or involuntary, and that the latter requires no effort. After using voluntary attention we experience ‘attention fatigue’, reducing our cognitive abilities and increasing mental fatigue. According to Kaplan et al, when we use our involuntary attention it gives us time to restore our voluntary attention. From this, Kaplan et al have suggested that what nature provides acts as a restorative power by providing four processes:

Being away – an opportunity to distance from routine activities and thoughts.
Soft fascination – nature holds attention effortlessly: think about the sunsets, sound of water, leaves blowing in the wind all-natural phenomena allowing your voluntary attention to rest.
Extent – nature provides an immersion experience, engaging the mind and rest from concerns.
Compatibility – a setting that is well matched to human needs and desires, providing a feeling of being in harmony with a greater whole.

These two theories have much in common: they focus on cognitive vs autonomic processes and both support a change in attention and stress load when an individual interacts with the natural environment (Gregory N. Bratman, 2012). However, they differ in how they suggest the primary mechanisms work. The effects the theories suggest are blurred in the sense of cause and effect: does a reduction in stress levels allow someone to concentrate better or does replenished direct attention help reduce stress?

Both these assertions are controversial in the field of environmental psychology, yet much research falls under either both or one of these theories.

Mental Health and Nature Policy

To what degree these theories influence policy is debated but it is clear that in recent years, especially after the recent pandemic, that nature spaces are becoming an increasing priority for mental health provision. Research has evidenced that we need to shift our attention from focusing on people visiting green spaces to how we interact and connect with nature close to home through simple activities (Mental Health Foundation, 2021). The Mental Health Foundation suggests from their research findings that we need to focus on six main areas in policy:

Facilitating connection with nature
Protecting the natural environment and restoring biodiversity
Improving access to nature
Making green spaces safe for all
Using the planning system and urban design to improve the visibility of nature in every local area
Developing a life – long relationship with nature.

Through our projects at Froglife we provide ways for people to interact with the environment instead of simply just being in it.

Promotion of Physical activity

Green spaces such as nature reserves, wilderness environments and urban parks also promote certain behaviours, such as encouraging physical activity within the space, which is a pro-mental health behaviour. Experimental studies have shown that not only do green spaces promote experience but they may be better for mental health than activity in other environments. Those that perform exercise in natural environments once a week are at about half the risk of poor mental health as those that don’t (Mitchell, 2013). Participation and involvement in nature is often tied to physical activities such as gardening or farming, trekking or running: the evidence of the benefits of this promotes the idea that green spaces should be seen as an essential health resource (Pretty, 2004).

There are many more benefits associated with natural green spaces. However, in terms of mental well-being, greener areas have been associated with a sustained improvement in mental health, highlighting the significance of green spaces, especially in urban areas. They provide not only a habitat for wildlife but also sustainable public health benefits (Alcock et al, 2014). Many studies have shown that more time spent in nature is associated with better mental health, independent of culture and climatic contexts, as well as the promotion of physical activity.

In addition to the wildlife and environmental benefits of conserving nature spaces, especially in urban areas, we also benefit in many ways from these natural spaces. This gives us even more reason to continue to protect our wildlife and conserve our natural areas and green space.

References

Alcock, I, et al., 2014. Longitudinal Effects on Mental Health of Moving to Greener and Less Green Urban Areas. Environmental Science & Technology , 48, 1247-1255.

Berman, M.G, et al., 2012. Interacting with nature improves cognition and affect for individuals with depression. Journal of Affective Disorders, 140, 300-305.

Bratman, M.G, et al., 2012. The impacts of nature experience on human cognitive function and mental health. Annals of the New York Academy of Sciences (Issue: The Year in Ecology and Conservation Biology), 1249, 118-136.

Collins, A.M., 2014. Destruction of urban green spaces: A problem beyond urbanization in Kumasi city (Ghana). American Joural of Environmental Protection, 3, 1-9.

Conniff, A, et al., 2016. A methodological approach to understanding the wellbeing and restorative benefits associated with greenspace. Urban Forestry & Urban Greening, 19, 103-109

Cox, D.T.C, et al., 2018. The impact of urbanisation on nature dose and the implications for human health. Landscape and Urban Planning, 179, 72-82.

Kaplan, R, et al., 1989. The Experience of Nature: A Psychological Perspective. New York: Cambridge University Press.

Mental Health Foundation, 2021. Nature- How Connecting with nature benefits our mental health. Published on-line.

Mitchell, R., 2013. Is physical activity in natural environments better for mental health than physical activity in other environments? Social Science & Medicine, 91, 130-134.

Park, B.J, et al., 2010. The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan. Environmental Health and Preventative Medicine, 15, 18-26.

Pretty, P. J., 2004. How nature contributes to mental and physical health. Spirituality and Health International, 5, 68-78.

Ribeiro, A.I, et al., 2021. Exposure to nature and mental health outcomes during COVID-19 lockdown. A comparison between Portugal and Spain. Environment International, 154 article 106664.

Ulrich, R. S., 1981. Natural Versus Urban Scenes: Some Psychophysiological Effects. Environment and Behavior 13, 523-556.

Ulrich, R. S., et al., 1991. Stress recovery during exposure to natural and urban environments. Journal of Environmental Psychology, 11, 201-230.

Van den Berg, A. E, et al., 2010. Green space as a buffer between stressful life events and health. Social Science & Medicine, 70, 1203-1210.

Wells, N.M. & Evans, G.W., 2003. Nearby Nature: A Buffer of Life Stress among Rural Children. Environment and Behavior, 35, 311-330.

The Ecological Importance of Small Freshwater Bodies

January 27, 2022 by Kathy Wormald

Small Freshwater Bodies include ponds, ditches, springs and flushes. All of these provide huge ecological benefits, supporting a wide range of aquatic species and offsetting some of the negative impacts of many environmental issues facing us such as climate change, flooding and noise pollution.

Ponds support an extraordinary two-thirds of all freshwater species and are central to the survival of many including frogs, toads, newts, a huge range of aquatic invertebrates and plants. Freshwater Bodies also provide mammals and birds with drinking water and some species such as grass snakes with important foraging areas.

One third of ponds are thought to have disappeared in the last fifty years or so and of those that remain more than 80% are considered to be in ‘poor’ or ‘very poor’ condition (Freshwater Habitats Trust research). This has had an enormous impact on aquatic wildlife.

Creating a clean, new pond is one of the simplest and most effective ways to protect freshwater wildlife. Where it is not a viable option to create new ponds, restoring existing, depleting ponds is greatly beneficial.

You can find tonnes of information on pond creation in our Just Add Water leaflet here.

The astonishing diversity of reproductive modes in amphibians: a new classification

December 16, 2021 by Roger Downie

Written by Roger Downie, Froglife Trustee and University of Glasgow

In the UK, we are accustomed to amphibians breeding in the spring and depositing their eggs in freshwater bodies, usually ponds rather than streams or lakes. Frogs deposit their eggs as a clump of jelly; toads as strings; and newts wrap theirs individually in folded leaves. The embryos hatch as larvae and feed in the water until they are ready to metamorphose into juvenile versions of the adult form. The adults spend no time with their eggs after deposition. So far, so familiar. But, when we look beyond our UK species, we find a wide diversity of reproductive modes. How many, and what are they like?

The term ‘reproductive mode’ (RM) was coined by Breder and Rosen (1966) to help them make sense of reproductive diversity in fish. Later, Salthe and Duellman (1973), in the context of amphibians, defined RM as a set of characters including oviposition site, ovum and clutch characteristics, rate and duration of development, stage and size of hatchlings, and type of parental care, if any. Without using the term RM, Boulenger (1886) had identified 10 amphibian modes. A hundred years later, Duellman and Trueb’s (1986) textbook recognised 29 RMs in anurans, seven in urodeles and two in caecilians. Haddad and Prado (2005) extended this to 39 modes for all amphibians, and there have been a few additions since. However, Nunes-de-Almeida et al. (2021) have now published a new classification, identifying 74 RMs in amphibians, almost a doubling of the 2005 list. How and why?

Their method is to divide the reproductive process into a set of eleven characters where each species can be assigned to one of two (occasionally more) states. The characters are:

Reproduction type: oviparity (egg-laying) or viviparity (eggs not laid: the female gives birth to larvae or juveniles). Viviparity is common in caecilians, but also occurs in a few frogs and salamanders.
Oviposition macrohabitat: eggs are deposited into the environment or they develop in or on the body of either the female or the male parent.
Spawning type: the distinction here is between cases where eggs are immersed in froth, or not. Froth is made from oviduct secretions in two ways: either a foam is generated by beating movements of the adults’ limbs; or bubbles are made by the female’s jumping movements.
Oviposition substrate: either in water, or not in water: on the ground, or in vegetation, or attached to a parent.
Medium surrounding the eggs: the main distinction here is between two kinds of aquatic habitat: lentic (still water, like a pond) or lotic (flowing waters, such as streams). The medium can also be air, as in eggs deposited on the ground, or attached to a parent’s body.
Nest construction: a constructed nest is defined as a place to deposit eggs which the parents have made by digging, or cleaning, or building in some way. ‘Froth’ nests are excluded from this category (I’m not sure this exclusion is fully justified). Constructed nests can be burrows, or depressions, or cleared areas on the forest floor, or leaves folded around the eggs.
Oviposition microhabitat: here, Nunes-de Almeida and colleagues find 15 variables: eggs on the surface of water, at the bottom of a pool, on the ground, on a leaf, on a rock, in a bromeliad tank etc.

The remaining characters distinguish different patterns of development:

Embryonic development: can be indirect, with a larval stage, or direct – lacking a distinct larval form, and progressing directly from embryo to juvenile.
Embryonic nutrition: all amphibians have yolky eggs, and the yolk provides the nutrients needed for embryonic development, but in some cases the mother provides additional nutrients. Where all nutrients derive from the yolk, development is termed lecithotrophic; where the mother provides extra, it is matrotrophic.
Larval and newborn nutrition: when embryos hatch and become free-living, we consider them as larvae. Generally, this marks the stage when they begin to forage for food, although they still have some of the egg-yolk left. However, some species do not feed as larvae, but obtain their nutrition from their large remaining yolk reserves: these are termed endotrophic. Most larvae are exotrophic, obtaining most of their nutrition from external food sources. In a few cases, parents provide this nutrition. For example, so-called trophic eggs, unfertilised eggs deposited by females to feed their hatched larvae. Another example is the feeding of some caecilian young on their mother’s skin secretions.
Place of larval development: mostly this occurs either in a pool (lentic) or a stream (lotic), but there are also cases of larval development on land, or attached to a parent’s body.

Overall, the authors reviewed RMs in 2171 species on which they could find adequate information: this is 26 % of all amphibians (8393 species, November 2021). Anurans showed 71 of the 74 RMs; urodeles 16 and caecilians seven. Most species showed a single RM, but some fitted up to four of the modes.

Nunes-de-Almeida and colleagues have made a valiant effort to classify the rich diversity of amphibian RMs, but it is not without some problematic aspects. One omitted feature is fertilisation mode: internal or external. This is a crucial feature in research on reproductive strategies relating to certainty of paternity and male competition. Another aspect largely omitted is parental care behaviour. Parental care can be defined as non-gametic investments in offspring that incur a cost to the parent, but which provide a benefit to the offspring. Parental care in amphibians is discussed in Croaking Science (date to come). The new RM classification explicitly excludes parental care on the grounds that parental care information is lacking for too many species. However, many kinds of parental care are actually included: for example, the provision of trophic eggs to larvae (character 10 above); while others such as larval transportation by adults are omitted. Another omitted feature which I find surprising is the differences in anuran spawn characteristics: single non-adhesive eggs, eggs in clumps, eggs in strings. It is likely that these differences are evolved characteristics important to reproductive success, so should be included in a classification of RMs. Another omission is the diversity of larval forms: there is huge diversity in tadpole form and behaviour, related to the habitats they live in: this may go beyond the usual definition of an RM, but is an important aspect of reproductive success. There are also occasional inconsistencies: phyllomedusine tree frogs wrap their egg clutches in leaves, and this is classed as a constructed nest (character 6 above); newts wrap their eggs individually in leaves, but this behaviour is not acknowledged as a kind of nest construction.

One excellent point made by the authors is about plasticity: i.e. individuals within a species may vary their RM, depending on circumstances. One example I’ve observed is the giant tree frog Boana boans. These frogs generally construct nests, as basins in gravel or sand (character 6 above), just beyond the edge of streams. However, where there is no suitable ‘beach’, the eggs are deposited at the water surface amongst emergent vegetation.

I’m sure that this new RM classification will stimulate discussion and research, and that later versions will include more species and modes. The authors hope that their work will stimulate the development of RM classifications for other taxa: how about reptiles?

References

Breder and Rosen (1966). Modes of Reproduction in Fishes. Natural History Press, New York.

Duellman and Trueb (1986). Biology of Amphibians. Johns Hopkins University Press, Maryland.

Haddad and Prado (2005). Reproductive modes in frogs and their unexpected diversity in the Atlantic forest of Brazil. Bioscience 55, 207-217.

Nunes-de-Almeida et al. (2021). A revised classification of the amphibian reproductive modes. Salamandra 57, 413-427.

Salthe and Duellman (1973). Quantitative constraints associated with reproductive modes in anurans. Pp 229-249 in: Vial (ed.) Evolutionary biology of the anurans. University of Missouri Press, Columbia.

Parental care in amphibians: research findings from 1705 to the present day

November 30, 2021 by Roger Downie

Writen by Roger Downie, University of Glasgow and Froglife

Croaking Science does not usually urge its readers to study a particular scientific paper, but this is an exception. The paper is Schulte et al.’s (2020) review of research into amphibian parental care, a fascinating and essential read for all amphibian enthusiasts. Parental care is usually defined as ‘non-gametic investments in offspring that incur a cost to the parent’ and which provide some benefit to the offspring. Common examples are egg-guarding, and provisioning of young after hatching. Although some authors restrict discussions of parental care to actions that occur after fertilisation, others include activities like nest-building in preparation for egg laying. For example, we generally consider UK amphibians as lacking parental care: they deposit their eggs in water, then leave. But Schulte et al include the behaviour of female newts that wrap their eggs individually in leaves: this behaviour takes a substantial amount of time, so is costly to the female, and contributes to offspring survival by reducing predation.

Research into parental care tends to focus disproportionately on birds and mammals. Stahlschmidt (2011) in a review of what he termed ‘taxonomic chauvinisn’ found amphibian and reptile parental care much less studied than cases from birds, mammals and even fish. Schulte at al. redress this situation through a vast historically-based review, identifying 685 studies spanning the period 1705-2017. Early studies were mainly simply descriptive, but since 1950, there has been a greater focus on the investigation of explanations: what does parental care achieve, and what does it cost?

The paper’s Table 1 lists each of the parental care modes so far described: four in Caecilians; eight in Urodeles; 28 in Anurans. Some modes occur in all three Orders e.g. terrestrial egg guarding; others occur in only one Order e.g. wrapping of individual eggs in leaves by newts; foam-nest construction by many frogs. Overall, parental care is known from 56 (74%) of the amphibian Families. It is not really surprising that more parental care modes occur in the Anurans than in the other two Orders, since anuran species diversity is so high (Frost, 2021 lists 7406 anurans, 768 urodeles and 212 caecilians).

The first known report of parental care in an amphibian, remarkably, was by a German female natural historian and artist, Maria Sibylla Merian in 1705. Her book was mainly devoted to meticulous drawings of the insects she observed in Suriname, but she also included an illustration and observations on an aquatic frog, later named the Suriname toad (Pipa pipa), which incubates its eggs in individual pockets on its back: she saw the metamorphosed juveniles emerging from the pockets. I was lucky, on my first visit to Trinidad, to see this for myself. We captured a ‘pregnant’ female and the babies later hatched into the water, some still with tail stumps, others fully metamorphosed. Female biologists have been prominent in the study of amphibian parental care: in addition to Maria Sibylla Merian, Martha Crump (1996) and Bertha Lutz (1947) come to mind, as well as the four authors of the review under discussion.

Among the 500 or so papers that Schulte et al. cite, I was pleased to see two from the work we have done in Trinidad (Downie et al., 2001; Downie et al., 2005). These are about the Trinidad stream frog Mannophryne trinitatis (see Croaking Science September 2020), where the fathers guard the eggs on land then transport hatchlings on their backs to a pool where they can complete development to metamorphosis. Tadpole transportation is a common aspect of parental care in the neotropical families Dendrobatidae and Aromobatidae. We found that the fathers are choosy over where to deposit their tadpoles, avoiding pools that contain potential predators, and therefore contributing to their survival. The search could take up to four days. We wondered how costly this might be to fathers: to our surprise, transporting a relatively heavy load of tadpoles did not appear to reduce the fathers’ jumping ability, nor did it prevent them from finding food. However, four days away from their territory must count as at least some cost in terms of lost mating opportunities.

*A male Trinidad stream frog, Mannophryne trinitatis transporting his tadpoles (photo credit: Joanna Smith)*

Schulte et al. conclude with a timely plea for a revival of teaching and research in natural history. As they say, natural history observations – on the distribution, numbers and habits of organisms- form the basis of all new ideas and hypotheses in ecology and evolutionary biology. They note that there remain many amphibian species whose habits are poorly known and that many novel observations have been made on parental care in recent years. They therefore expect that much could be discovered, as long as effort is put into new field work. Over 20 years ago, I wrote lamenting the modern status of natural history (Downie 1997, 1999), and Schulte et al. report that the loss of organism-based teaching and research is widespread. In the UK, there are moves to create a natural history curriculum, to complement biology in schools. I feel that it is much needed.

References

Crump (1996). Parental care among the amphibia. Advances in the Study of Behaviour 25, 109-144.

Downie (1997). Are the naturalists dying off? The Glasgow Naturalist 23 (2), 1.

Downie (1999). What is natural history, and what is its role? The Glasgow Naturalist 23 (4), 1.

Downie et al. (2001). Selection of tadpole deposition sites by male Trinidadian stream frogs (Mannophryne trinitatis; Dendrobatidae): an example of anti-predator behaviour. Herpetological Journal 11, 91-100.

Downie et al. (2005). Are there costs to extended larval transport in the Trinidadian stream frog (Mannophryne trinitatis, Dendrobatidae)? Journal of Natural History 39, 2023-2034.

Frost (2021). Amphibian species of the world : an online reference. Version 6.1 (accessed 29/9/21). Electronic database accessible at http://amphibiansoftheworld.amnh.org/index.php. American Museum of Natural History, New York, USA.

Lutz (1947). Trends towards non-aquatic and direct development in frogs. Copeia 1947, 242-252.

Schulte et al. (2020). Developments in amphibian parental care research: history, present advances, and future perspectives. Herpetological Monographs 34, 71-97.

Stahlschmidt (2011). Taxonomic chauvinism revisited: insight from parental care research. PLoS ONE 6, e24192.

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