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Parental Care by Amphibians Moving Between Water and Land Influences Egg Size, New Study Finds

8th January 2022
File image of a frog and frogspawn near Omagh, Co Tyrone
File image of a frog and frogspawn near Omagh, Co Tyrone Credit: Kenneth Allen/Geograph

Parental care by amphibians moving between freshwater and land influences how many eggs they lay, new research by Queen’s University Belfast (QUB) has found.

While most amphibians abandon their young when they lay their eggs, those involved in parental care such as frogs producing spawn adjust the number of eggs and their size to cope with risks such as predators, the study says.

The research has been published in the PLOS Biology journal and was conducted in collaboration with the University of Hull and the University of Reading.

Amphibians are a class of cold-blooded vertebrates such as frogs, toads, salamanders, newts and caecilians — the latter being wormlike animals with poorly developed eyes.

They all move between freshwater and land, hence their name ‘amphibian’, from a Greek word meaning ‘double life’.

The National Wildlife Federation describes them as the most threatened class of animals, being extremely susceptible to environmental threats due to their porous eggs and semi-permeable skin.

Over 40 per cent of amphibians currently face risk of extinction.

The QUB/Hull/Reading research team examined over 800 amphibian species from all over the world, and found that amphibians with direct development and those that lay eggs on land had larger eggs and smaller clutches.

Some form of parental care, and the habitat which eggs and tadpoles develop in, whether aquatic or terrestrial — are two factors which determine the number and size of the eggs that females lay, they concluded.

‘These results have important implications as they demonstrate that considering the diversity in care forms is important’

“Larger eggs are energetically costly to produce for the mother, and so come in small clutches,” they state.

“Because eggs are eaten by many predators, especially if not cared for, females that abandon their eggs typically produce many small eggs.

“However, if the eggs are cared for by either the mother or the father or both parents, mothers change the size and number of eggs they lay. How many eggs and how big females lay depend on the type of care that parents provide.”

The research also looked at the enormous diversity of care forms, which has been “typically ignored” in previous studies, they noted.

“They can protect eggs, tadpoles or juveniles; transport eggs or tadpoles; brood eggs or tadpoles in their vocal sacs, stomachs or in skin pushes on their back; they can feed tadpoles; and some species can give birth to live offspring,” the research team explained.

Dr Isabella Capellini, of QUB’s School of Biological Sciences and lead author of the study, said the work “demonstrates that species such as some Malagasy poison frogs with terrestrial eggs have larger eggs in smaller clutches, but different forms of parental care have different influence on the trade-off between egg size and egg number.

“For example, species that brood their eggs or tadpoles on or inside the body, can only care for few large eggs because the parent’s body has limited room.

“However, those that guard their eggs, can afford to protect larger eggs without reducing clutch size.

“Instead, frogs that feed their larvae have few small eggs, probably because constant feeding after hatching makes producing initially large eggs unnecessary.

“These results have important implications as they demonstrate that considering the diversity in care forms is important.

“Our study suggests that amphibians with diverse forms of care may be under different risk of extinction. We will build upon the knowledge we now have to better understand whether amphibians with diverse forms of care may be under different risk of extinction,” Capellini concluded.

Published in Marine Wildlife
Lorna Siggins

About The Author

Lorna Siggins

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Lorna Siggins is a print and radio reporter, and a former Irish Times western correspondent. She is the author of Everest Callling (1994) on the first Irish Everest expedition; Mayday! Mayday! (2004) on Irish helicopter search and rescue; and Once Upon a Time in the West: the Corrib gas controversy (2010).

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Marine Wildlife Around Ireland One of the greatest memories of any day spent boating around the Irish coast is an encounter with marine wildlife.  It's a thrill for young and old to witness seabirds, seals, dolphins and whales right there in their own habitat. As boaters fortunate enough to have experienced it will testify even spotting a distant dorsal fin can be the highlight of any day afloat.  Was that a porpoise? Was it a whale? No matter how brief the glimpse it's a privilege to share the seas with Irish marine wildlife.

Thanks to the location of our beautiful little island, perched in the North Atlantic Ocean there appears to be no shortage of marine life to observe.

From whales to dolphins, seals, sharks and other ocean animals this page documents the most interesting accounts of marine wildlife around our shores. We're keen to receive your observations, your photos, links and youtube clips.

Boaters have a unique perspective and all those who go afloat, from inshore kayaking to offshore yacht racing that what they encounter can be of real value to specialist organisations such as the Irish Whale and Dolphin Group (IWDG) who compile a list of sightings and strandings. The IWDG knowledge base has increased over the past 21 years thanks in part at least to the observations of sailors, anglers, kayakers and boaters.

Thanks to the IWDG work we now know we share the seas with dozens of species who also call Ireland home. Here's the current list: Atlantic white-sided dolphin, beluga whale, blue whale, bottlenose dolphin, common dolphin, Cuvier's beaked whale, false killer whale, fin whale, Gervais' beaked whale, harbour porpoise, humpback whale, killer whale, minke whale, northern bottlenose whale, northern right whale, pilot whale, pygmy sperm whale, Risso's dolphin, sei whale, Sowerby's beaked whale, sperm whale, striped dolphin, True's beaked whale and white-beaked dolphin.

But as impressive as the species list is the IWDG believe there are still gaps in our knowledge. Next time you are out on the ocean waves keep a sharp look out!

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