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Project Blog: Yorkshire T.O.A.D

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It has been a busy month for the Yorkshire T.O.A.D team with habitat works! The most recent site to be worked on was Dewsbury Country Park where a pond, and a ditch leading to it, have been restored – see the before, during and after photos below to see how much of a difference it has made to the site!

One of the main problems with this particular pond was that it dried out early in the summer and the channels leading to it were blocked with vegetation before the frog and toad tadpoles had reached adulthood. By restoring the channels leading to the pond and removing some of the vegetation, the pond will now hold water for much longer, being of huge benefit to the breeding amphibians in the spring.

The team have also been working at Anglers Country Park in Wakefield where they have restored yet another pond that did not hold water throughout the year and they have created several more ponds at Derwenthorpe in York. Here, the area is historically very wet on heavy clay soil and the path can often flood during winter due to poor draining of the site. The creation of the new pond should now prevent this happening and make the area suitable for walkers year-round as well as making the site suitable for amphibians to breed.

If you would like to know more about Yorkshire T.O.A.D, visit their page here.

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

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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:

  1. 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.
  2. Oviposition macrohabitat: eggs are deposited into the environment or they develop in or on the body of either the female or the male parent.
  3. 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.
  4. Oviposition substrate: either in water, or not in water: on the ground, or in vegetation, or attached to a parent.
  5. 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.
  6. 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.
  7. 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:

  1. Embryonic development: can be indirect, with a larval stage, or direct – lacking a distinct larval form, and progressing directly from embryo to juvenile.
  2. 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.
  3. 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.
  4. 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.
Credit: Julia Page

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.

What our animals are doing this month….

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This month we’re going to talk about the Great Crested Newt. This fascinating species is strictly protected in Britain due to its decline over the last century. Great Crested Newts are the UK’s largest newt and can reach up to 15cm in length. Their skin is a black or dark brown with a granular appearance, while they also have bright orange bellies with an irregular pattern of black blotches. The male has a jagged crest on their back with a white strip along the centre of their tail, however, the female does not have a crest and instead has a yellow stripe along the bottom of her tail.

During the winter months Great Crested Newts go through a phase of low activity. They will spend their time overwintering and sheltering in compost heaps or under refugia such as rock or dead wood piles, or perhaps just in deep loose soil. Some Great Crested Newts overwinter in forests and woodlands where the undergrowth, leaf litter and tree canopy will help them against exposure.

The Great Crested Newts do not hibernate in winter months but instead enter a period of dormancy. They can sometimes emerge from their hiding spots to forage in milder temperatures. Great Crested Newts tend to forage in areas where there is an abundance of invertebrates such as areas of woodland or grassland.

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

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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.

Suriname Toad

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.

What our animals are doing this month….

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December is a quiet month for British amphibians and reptiles. All of our native species brumate during the winter, meaning they are dormant with occasional periods of foraging during warmer spells. Amphibians and reptiles overwinter in different habitats, but warm, safe spots such as log piles and compost heaps are often popular choices.

Male common frogs may choose a riskier overwintering strategy. They sometimes decide to overwinter at the bottom of a pond, buried into the mud. This can be a good option as they are unlikely to be disturbed or predated upon, however it can be very dangerous if oxygen levels get too low. Frogs can absorb oxygen through their skin underwater and can tolerate very low levels of oxygen, but they will die under anoxic conditions. However, if there are native oxygenating plants in the pond, then this should ensure sufficient oxygen flow.

Common frogs can also survive if a pond partially freezes, but not if it freezes entirely. As a general rule, ponds with a maximum depth of at least 60cm are safe, but any shallower and there is a high risk of it completely freezing over.

Work Experience Blog: Ethan

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My name is Ethan and I have been volunteering with Froglife for just over a year. Last academic year I was looking for work experience I could do to go with my college course. When looking at local places I contacted Froglife and was excited when they wanted me to help.

I started by helping at Westraven Community Garden where I helped at the groups ran for the local primary school. Helping at the sessions was positive as the children there were always grateful and cheerful no matter what the weather was like. Whilst at the sessions I was able to improve my teamwork as well as the skills required to work with children. With the children, we did a range of different tasks including bird feeder making, den building and marshmallow toasting which helped improve the children’s communication and teamwork skills.

Over the summer holiday, I was able to go to several events which both looked at using practical skills which were different to what I had done with Froglife previously. In one of the sessions, I was able to help children create a hibernaculum which was great fun as it also allowed me to pass on information that I knew to both the other volunteers and the children taking part in the session. The other session I was able to go to was very different and it was mainly older people and doing the work myself rather than leading. This allowed me to improve my practical skills and also my communication skills as I worked with people to get the task completed.

This academic year I have started as well as going to the school biased sessions I have started to do some work in the office which has enabled me to learn how the office works and has allowed me to get more involved in the sessions as I can help prepare for future sessions that will occur. Working in the office has also let me develop an understanding of how Froglife and other charities work when not and sessions or at events.