It was a rainy night in 2015. We were conducting a frog camp in the remote village of Bisle, near Sakleshpur. One of the participants had spotted an arthropod eating a froglet. It was a House Centipede belonging to the order Scutigeromorpha. These predatory arthropods measure up to 4 cm and are found across the globe. Contrary to the name, they only have a pair of 15 legs.
I had forgotten about this encounter until I came across a recent research paper that provided evidence that the Scutigeromorphs have an ancient history and were once widespread across what is called the Gondwanaland.
The study, led by researchers from India and abroad, reports that Scutigeromorphs likely rafted on the broken fragments of the supercontinent and diversified on the continents, moved from one to another, or colonised new landmasses when they came in contact. One group of centipedes in the subfamily Thereuoneminae diversified on the Indian subcontinent and later colonised parts of Asia, Australia, and the Pacific Islands.
Biogeography
The distribution of organisms, as well as ecosystems, is shaped by the earth’s geological history. Studying how the distributions change over space and geological time is called Biogeography.
However, Studying an organism’s distribution and its ecosystems is like solving a jigsaw puzzle. Although many continents are separated by water today, they were once connected as a supercontinent called “Gondwanaland”. Incidentally, the name Gondwana originates in the Gond tribes of Central India. Gondwanaland, which formed nearly 600 million years ago (MYA), comprised nearly all of today’s southern continents.
Earth’s surface, called the lithosphere, comprises plates that can gradually move. Over earth’s evolutionary history, Gondwanaland broke up, and continents drifted to where they are today for a long period. The organisms that inhabited the supercontinent also drifted along.
Some of these species went extinct, but many continue to be found today or have diversified into newer species. If a species today has a disjunct distribution, it could be because of its historical separation from the supercontinent or recent dispersal events and subsequent diversification.
Trail of the Centipedes
Scutigeromorpha are an ancient group of centipedes that have existed for over 400 million years. Historical events such as the breaking up of Gondwanaland would surely have influenced their distribution. In addition, centipedes have limited ability to disperse across large oceans and are, therefore, ideal candidates to infer biogeographic history.
While the evolutionary relationships in Scutigeromorpha are relatively well studied, little is known about their biogeographic history, particularly those found in the Indian subcontinent. Researchers from the Evolutionary Ecology Lab at the Centre for Cell and Molecular Biology (CCMB) set out to resolve this group of centipedes’ biogeographic history by extensive sampling across India.
The authors surveyed forests in peninsular India as well as the Andaman Islands. “We extracted DNA from these specimens and built phylogenetic trees to determine relationships among the species and also delimit species ranges,” explained Maya Manivannan, who is currently pursuing her doctoral research at the Centre for Ecological Sciences, Indian Institute of Science, Bengaluru.
“We hypothesised that this group of centipedes originated in the Indian subcontinent when it was still part of Gondwanaland, and the subsequent breaking of India from Australia led to a rapid diversification and in the disjunct pattern of occurrence in India as well as Australia,” she added.
The researchers relied on a global database comprising genetic and distribution information of species to build evolutionary relationships and reconstruct biogeographic history. This information, in combination with how plate tectonics changed over time, enabled them to determine the historical distribution of a species and how they colonised land masses.
The genetic data allowed the authors to confidently group the samples from India into 11 species. The phylogenetic tree indicated that some species were related to those in Southeast Asia, while others were related to those found in Australia and the Pacific Islands.
“Ancient scutigeromorphs were probably spread widely across Gondwana before the continents split. Their distribution is shaped by continental separation and long-distance dispersal, indicating an ability to colonise areas far from their ancestral range. The Indian scutigeromorphs began to diversify during the Cretaceous Period, suggesting that they represent Gondwanan relicts. We have also identified 11 new species, five times more than what was known, highlighting the need to systematically document the arthropod biodiversity,” explained Dr Jahnavi Joshi, senior scientist at CCMB who supervised this study published in the Journal of Biogeography.
Members of the order Scutigeromorpha diverged from their common ancestor sometime between 400 and 300 million years ago. Most species in the order have an evolutionary history that can be traced back to Gondwanaland.
A passage through India
Centipedes are often considered dangerous, but they are an ancient arthropod that evolved before the dinosaurs and persist even today. They play a critical role in maintaining soil health and are apex predators in the soil. Studies elsewhere have demonstrated the negative impact on the soil ecosystem if centipedes are removed from the soil. In India, house centipedes are ironically found in forested habitats, unlike in the Northern Hemisphere, where they are found in and around houses.
In recent years, researchers from across the country have enhanced our understanding of the biogeography of various taxa ranging from Molluscs to large Mammals. The researchers borrowed from E M Forster’s classic ‘A Passage to India’. They chose to title their work A Passage through India, highlighting the critical role that the Indian subcontinent had in aiding the dispersal of scutigeromorphs. Coincidentally, this year marks a century since Foster published his classic.
(The author is an ecologist and a faculty at ATREE)