Parental caregiving in animals is associated with an element of risk of being attacked by predators. On another track, body colours and patterns are believed to have evolved because they protect the animal against attacks by the predator. Tying these two facets together, researchers from Indian Institute of Science asked whether parental caregiving is associated with body colour, patterns and even dichromatism in frog and toad species. Dichromatism is when the two sexes have different colouration, at least in parts. The results of their study and analysis are published online in the journal Evolution.
Parental caregiving in frogs and toads has many associated questions: Does the species provide care at all, or not? If they do, which of the parents (male or female or both) provides the care? Since frogs and toads, clubbed together as anurans, are amphibians, the question of whether they provide care in the water or land becomes relevant. The study seeks to find if the listed aspects of care are correlated with the way the animals look.
Starting from a list of approximately 1,200 species, the researchers narrowed down the study to 988 species, which they proceeded to analyse. “We found that species that show parental care were more likely to be non-dichromatic species, which means that males and females look similar. This pattern is independent of whether the male or the female cares for the offspring,” says Maria Thaker in whose lab at the Centre for Ecological Sciences, IISc, the study was carried out, in an email to The Hindu.
Dr. Thaker explains what may be the reason behind this: “When one sex of a dichromatic species is brightly coloured or patterned to attract mates, for example, that sex is more conspicuous to potential predators as well. It’s dangerous to be conspicuous. This is why we predicted that the evolution of caregiving should coincide with the evolution of minimising the risk of unwanted attention, and hence monochromatic species are more likely to show caregiving.”
Dorsal colours were independent of the occurrence of care. “So, whether a species cares for their offspring or not has no bearing on what colour they are. This contradicted our expectation that providing care is dangerous and therefore caregivers should be camouflaged or aposematic,” she adds. Being aposematic refers to being brightly coloured to warn off predators. This gives the indication to predators that the animal may be poisonous to consume.
“The presence of dorsal stripes was significantly correlated with species where males alone cared, but none of the other five pattern categories were significantly correlated (Plain, Bands, Spots, Mottled-Patches),” says K. S. Seshadri, who is a DST-INSPIRE Faculty Fellow in Dr. Thaker’s lab. “In species where females alone care, none of the colours and patterns were correlated with the occurrence of care.”
Dr. Seshadri adds that perhaps the presence of stripes provides the advantage of flicker fusion where a predator is unable to accurately detect the position of the prey. This potential explanation remains to be tested.
The work shows how studying amphibians can help in understanding more generally evolutionary biology, behaviour and ecology. Dr Seshadri says, in this context, “Our work includes 988 species in which we are certain about parental care. There are over 7,000 species of anurans out there and we know very little about their ecology and behaviour. There is clearly a need to bridge knowledge gaps for amphibians are among the most threatened vertebrates.”