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You are here: Home / 2020 / Archives for June 2020

Archives for June 2020

Croaking Science: See-through frogs are worth a look

June 30, 2020 by admin

Glass frogs comprise a family (Centrolenidae) of 158 species found in the forests of the neotropics: Central America and northern South America. They get their name from the transparency of their belly skin, which allows the internal organs to be easily seen. They are adapted to life in the trees, possessing pads on the tips of their digits that allow them to adhere to leaves. These structures appear to have evolved independently in several lineages of frogs, since molecular phylogenetic results show that the main families where these pads occur (Hylidae, Rhacophoridae, Centrolenidae) are not closely related.

One of the special features of glass frogs is their mode of reproduction. Clutches of eggs, as flat round sheets, each egg encased in jelly, are laid on the surfaces of leaves overhanging streams. Once the eggs have developed into larvae, they hatch and fall into the stream below, often from a considerable height. Glass frogs are divided into two main sub-families: the Centroleninae (121 species) which lay on the upper sides of leaves and then leave the eggs to develop on their own; and the Hyalinobatrachinae (35 species) which lay their eggs on the lower sides of leaves; in these species, the father cares for the eggs, sometimes up till the point of hatching.

Figure 1: Several egg clutches on a single leaf

We studied the glass frog Hyalinobatrachium orientale which has distinct populations in northern Venezuela and northeast Tobago: this distribution is a bit of a puzzle. Northeast Tobago is quite distant from Venezuela and between these two locations is the large island of Trinidad, which has abundant forests, but no glass frogs. Walking along the forest streams of Tobago at night, once the rainy season (June to December) has started, you soon hear the high-pitched peeping of male glass frogs, located on the huge leaves of Heliconia bihai that overhang the water. With the aid of a good torch, you can locate the calling frogs; often, near them, you can spot the little patches of eggs. If you are lucky, you may locate a mating pair. We observed the behaviour of a mating pair. It took them about four hours to complete their clutch of around 30 eggs, laid as a spiral pattern, starting at the centre, with the pair turning as they proceeded. Once egg-laying was complete, the female departed, but the male stayed close to the clutch. Often, when searching for egg clutches, we found the father sitting on top of his eggs. We also found that some fathers, presumably good quality males, were looking after more than one egg clutch at a time. These are at different stages of development, so clearly produced on different nights. It is not entirely clear what functions male egg attendance performs, particularly given that it is not constant. However, observers have seen males driving away egg predators such as wasps and ants; it is also likely that males keep the eggs hydrated by reducing evaporation, simply by sitting on them, or by emptying their bladders over the eggs (this is established in some cases of frog parental care). But this raises another mystery. If paternal care is helpful to incubation success in the Hyalinobatrachinae, why does it not occur in other glass frogs, especially when they lay their eggs on leaf upper surfaces, where you would guess that desiccation and predation would be higher risks.

In the Tobago glass frog, hatching occurs around nine days after laying, although the actual time is variable, allowing tadpoles to be earlier or later stages of development when entering the water. Such variability may be quite common in frog development and represents a trade-off. Early hatchers are less well developed and more vulnerable when they enter the water; but it may be better to risk this than to be predated while still in the nest. It therefore pays the developing larvae to monitor conditions: if the father has deserted his clutch, or hot sun and no rain are risking desiccation, better to hatch early and hope for a stream with few predators.

Figure 2: Metamorphosing glass frog tadpole on a leaf; with pen for scale

The streams where glass frog tadpoles are found are fast-flowing when it rains, and are heavily populated with predatory fish and crustaceans. They are also shaded, making plant productivity low. As a consequence, glass frog tadpoles spend much of their time hidden under rocks, reducing the risks of predation and of being swept away by currents (unlike the tadpoles of some species that inhabit fast streams, glass frog tadpoles lack the kind of suctorial mouthparts that can help cling on to rocks). The tadpoles have long muscular tails, indicating an ability to move rapidly, and are relatively unpigmented, associated with a concealed lifestyle. Their behaviour limits foraging opportunities, so growth is slow. Glass frog tadpoles can take a year to reach metamorphosis, very slow by tropical frog standards, where many species reach that stage in a few weeks. We have been able to locate metamorphosing glass frogs near the edges of streams. They climb up on to the upper surfaces of leaves close to the ground, and take about four days to complete the process, reducing their tail to a stump. To our surprise, we found that they do not remain in one place through this process, but occasionally move around, possibly to confuse potential predators.

The transparency of glass frogs has long puzzled biologists. Recently, a research team from Bristol, Canada and Ecuador has tested an explanation. Their evidence suggests that it is not so much transparency that matters, but translucence. When a glass frog is at rest with its limbs tucked in, the translucence of the limbs blurs the edges of the body, and makes detection by predators more difficult.

Further reading

Barnett et al. Imperfect transparency and camouflage in glass frogs. PNAS (2020).

Byrne et al. The behaviour of recently hatched Tobago glass frog tadpoles. Herpetological Bulletin 144, 1-4 (2018).

Byrne et al. Observations of metamorphosing tadpoles of the Tobago glass frog. Phyllomedusa (in press) (2020).

Delia et al. Glass frog embryos hatch early after parental desertion. Proceedings of the Royal Society B 281, 2013-2037 (2014).

Downie et al. The tadpole of the glass frog Hyalinobatrachium orientale from Tobago. Herpetological Bulletin 131, 19-21 (2015).

Nokhbatolfoghahai et al. Oviposition and development in the glass frog Hyalinobatrachium orientale. Phyllomedusa 14, 3-17 (2015).

Contributing authors : Roger Downie, Isabel Byrne, Chris Pollock.

Filed Under: Uncategorized Tagged With: amphibian, Croaking Science, Frog, glass frogs, university of glasgow

What our animals are doing this month… July 2020

June 29, 2020 by admin

July can be a great month to see our common toad complete metamorphosis and become toadlets.  It usually takes around two to four weeks for tadpoles to hatch out from the egg and roughly sixteen weeks for tadpoles to reach the stage where legs have developed.  This is often affected by the water temperature in the pond as well as numbers of larvae present and food availability – as tadpoles are busy eating algae in the pond for their nutrition.  Toadlets will form legs, absorb their tails, form lungs to breathe out of the water and eventually leave their pond to head out onto land.

You may have been lucky enough to see toadlets emerge, in huge numbers, in previous years near ponds.  They won’t move too far from their breeding pond however as they will be busy foraging and developing in summer and early autumn to get ready for the overwintering period.  Emergence occurs in higher numbers after periods of rainfall at any time of day.

Keep an eye out from July onwards for emerging toadlets!

Filed Under: Uncategorized Tagged With: 2020, common toad, Croaks, july, toadlets, what our animals are doing this month

Book Review: Wild Child

June 19, 2020 by admin

Wild Child: coming home to nature

Patrick Barkham, Granta (2020). Hardback, £16.99. 342 pp.

This is a lovely book, and could be read for enjoyment and instruction by anyone who works with younger children, at home or elsewhere. Patrick Barkham is a nature writer, author of four previous books (on butterflies, badgers, coasts and islands) and a regular contributor to The Guardian. This is not a ‘how to’ book, although it includes many experiences of exploring nature with children. It is more a reflection on how children learn about everything, and nature in particular. The focus is Barkham’s own family (the children are non-identical twin girls and a younger boy), but he also interacts with many other children while volunteering at his local outdoor nursery, and visiting forest schools in other parts of England.

His children first discover nature in the overgrown cemetery beyond the garden of their first house in Norwich. As the children grow, the family moves to more space in a village outside the city, and the children attend a nearby, highly innovative outdoor nursery. They are fortunate with the headteacher of the local primary school who allows the children one day at the outdoor nursery even after they are school age.

Some of the book’s chapters describe the changing seasons at the nursery: spring, summer, autumn and a muddy, snowy winter (it’s the year of the ‘beast from the east’). Barkham volunteers there throughout the year, but not on the days his own children attend. Other chapters cover different aspects of nature: birds’ nests and chicks; ponds and dipping for tadpoles, beetles and newts; caterpillars and butterflies. The children learn in a matter-of-fact way about death, and bury dead birds, or take good specimens to the local taxidermist. There’s a running debate about collecting and keeping specimens, and whether wildlife can be pets.

Amongst lively and colourfully worded descriptions of what children do and say (with many verbatim quotations), Barkham discusses in a very straightforward way the many studies which demonstrate the positive impacts on child development of interacting with nature. He also discusses the negative effects of too much time indoors, interacting with screens and anxious about the outside world. For those readers who wish to look further into such studies, there is a full set of references, arranged by book chapter at the end.

Some readers may be thinking: rural Norfolk, Guardian– writer, typical middle-class elitist with no idea of the problems ‘real people’ face. But two of the forest schools Barkham visits belie that stereotype. ‘Wild things in Nottingham works with ‘English as a second language’ children, mostly refugees, many of them coping with horrific past experiences, and few of them speaking much English as yet. Being in nature provides them with experiences for which spoken communication is non-essential. ‘Wilderness schooling’ in Northumberland helps under-achieving children to regain motivation for learning, while experiencing the outdoors and wildlife, and the organiser is accumulating data to prove it works.

Barkham does not hide the fact that children are individuals and not always 100% motivated to learn from wild nature all the time. However, he does insist that ‘however imperfect our lives and our homes, we can add doses of daily nature in a way that enriches us all’. To make this happen for everyone, we need to re-think how our towns, especially our roads are organised. The book was written before the covid19 crisis, but the message fits well with much discussion of how reduced traffic is improving air quality in cities and how provision needs to be made for the resurgence in cycling. He also urges reform of the national curriculum and the emphasis on testing children: modern schools too often stifle the natural creativity and self-motivation that children show. If I have a criticism of the book, it’s the relative lack of engagement with the extensive literature on alternative ways to organise educational systems. This seems a pity given that the original ‘free -school’, A.S. Neill’s Summerhill, is not far from Norwich (in east Suffolk) and is about to celebrate its centenary.

Although I noted that this is not a ‘how to’ book, it ends with a helpful appendix: ‘sixty-one things to do and ways of being with children outdoors’ and a bibliography of helpful and relevant books. The book has no photographs, but includes some maps and delightful chapter-title line drawings. Highly recommended.

Roger Downie

Froglife Trustee; honorary lecturer, University of Glasgow.

Filed Under: Uncategorized Tagged With: book club, book review, Croaks, roger downie, wild child

Why I love Snakes! – A poem

June 12, 2020 by admin

Adder, smooth or grass snake by name,
Our native snakes are not all the same.

The adder’s stylish zig-zags black

Make a splash along its back.
The smooth snake, who is rare to find

Has smoother scales than the other kinds.

The grass snake is the last of the three,
They love to swim – it’s a sight to see!

Snakes may have a difficult time,
But seeing one is just sublime!

Poem written and shared with us by Bethan Davies 

Filed Under: Uncategorized Tagged With: adder, Grass snake, Inspired by nature, poem, smooth snake, snake, Snakes

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