Devoted frog fathers guard their eggs from predators

NUS-led study shows father frogs prevent cannibalistic rivals from consuming eggs and causing damage.

An NUS-led study has found that the father white-spotted bush frogs guard their fertilised eggs to prevent other cannibalistic male frogs and predators from consuming their offspring by attending to and guarding or damaging the eggs
An NUS-led study has found that the father white-spotted bush frogs guard their fertilised eggs to prevent other cannibalistic male frogs and predators from consuming their offspring by attending to and guarding or damaging the eggs. [Credit: K. S. Seshadri]

Researcher’s team of the Department of Biological Sciences (DBS) at the National University of Singapore’s Faculty of Science has discovered that male white-spotted bush frogs (Rochester chalazodes) committed to guarding their fertilized eggs against other cannibalistic male frogs and predators.

The study committed that the adult male white-spotted bush frogs are the mere caregivers of their offspring, predominantly by attending to and safeguarding the eggs.

The Raochestes chalazodes, recognized extinct until its rediscovery in 2011 in the Western Ghats of India, is recently listed as critically endangered.

Perhaps, Mr. Seshadri Ph.D. claimant of DBS was one of the researchers who rediscovered the frogs. While frogs tentatively their eggs in or above standing water, white-spotted bush frogs lay their eggs inside the hollow internodes of reed bamboo that grow along streambanks and their offspring emerge from the eggs as fully-formed froglets.

Notwithstanding, an adult Raochestes chalazodes is normally about two centimeters in length, it enters the narrow openings of the reed bamboo internodes with considerable resistance as the openings are even tapered (often less than 5 to 10 millimeters long and 3 to 4 millimeters wide).

During the study, the researchers’ utilized pipe inspection cameras or endoscopes to perceive frog egg clutches daily until all froglets and the attending father frogs left the spawning site.

They studied a total of over 40 egg clutches across two breeding seasons in 2015 and 2016.

The researchers discovered that male frogs that have perceived suitable spots for spawning in sections of the reed bamboo will call out for female mates utilizing the vocal sacs in their throats.

An ideal spawning site will have holes at the base of the bamboo section so that rainwater does not gather and drown the eggs. A female white-spotted frog reacts to the mating call by entering into the bamboo section to lay her eggs on the inner walls of the section, leaving after the male frog has fertilized the eggs.

Mr. Seshadri noted, “Father frogs will then attend to the eggs by sitting on them, possibly to keep the eggs hydrated, and they guard the eggs by standing between them and the entry hole where they will lunge at intruders and make loud alarm calls to keep them away.”

Later in the study, they traced that every evening, the father frogs will hunt for prey close to their spawning sites before returning to their egg-sitting duties. They will call out incessantly through the night to ward off other males with cannibalistic tendencies and other predators from consuming the eggs. This continues for about 37 to 47 days when all of the eggs have either hatched or perished, normally due to predation or parasites.

Mr. Seshadri said, “Predation by other male frogs is the main cause of egg mortality of white-spotted bush frogs. When there were no father frogs guarding the eggs, less than 30 percent of the eggs in a clutch survived.”

Additionally, they found that the cannibalism among frogs is not unusual.

According to the researchers, adult male white-spotted bush frogs feed on unattended eggs of another male to gain from their nutritional benefit. Other possible reasons for this cannibalistic behavior could be for the purposes of taking over another individual’s territory or reducing competition of resources for emerging offspring.

The work was published in the scientific journal Behavioral Ecology and Sociobiology on 14 December 2017.

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