Macroevolutionary narratives in peninsular India, emphasising the leggy chronicles of millipedes

The peninsular Indian plate (PIP) is the oldest region of biotic differentiation in the Oriental realm and is often considered a distinct biogeographic sub-region owing to its complex biotic composition of varied biogeographic affinities - Gondwanan and Asian. Much of its endemic biodiversity is housed in the global biodiversity hotspot - the Western Ghats and a disjunct chain of montane forests in the Eastern Ghats. Most of the research examining eco-evolutionary processes has been on vertebrate fauna - reptiles, birds and amphibians and a few invertebrate models - centipedes and scorpions. These studies have shown that the relictual Gondwanan biota (centipedes, scorpions, blindsnakes, caecilians) inhabit the soil ecosystem or are fossorial, show high endemicity and are habitat specialists. In contrast, biota of Asian origins (lizards, terrestrial snakes, frogs) are found to inhabit more varied habitats and have larger range sizes.

Among the PIP biota, millipedes are one of the understudied groups of diverse invertebrate fauna. Millipedes (class: Diplopoda) belonging to 11 orders out of the 16 have been described from peninsular India. Millipedes share close ancestry with Class Chilopoda (Centipedes), and centipedes of India are among the oldest studied extant lineages from the PIP. Centipedes exhibit fascinating biogeographically structured diversity with varied habitat affiliations. Besides centipedes, millipedes share a similar ecological space with scorpions, pseudoscorpions, and spiders, many of which are fossorial and highly endemic and are habitat specialists.

Interestingly, a majority of these fossorial invertebrates, along with a few vertebrate biota like caecilians and blindsnakes, are strictly distributed in the rainforests of Western and mountain tops of Eastern Ghats and have been shown to share evolutionary affinities with Gondwanan counterparts. Few have been shown to disperse Out-of-India and have diversified in south-east Asia. Furthermore, few of the Gondwanan PIP lineages have shown common diversification trends, where ancestral lineages are distributed in the southern Western Ghats, and it is also the ancestral distribution of many of these lineages. Given millipedes are very diverse in comparison to the other well-studied arthropods that they share ecological space with, millipedes would be excellent models to address questions relevant to biogeography, diversification, community assemblies and their drivers.

First, we investigate the pace and patterns of in-situ diversification of well-studied endemic lineages of the PIP and test the roles of different ecological and evolutionary factors in driving them. We mainly utilise dated phylogenies of 33 endemic lineages belonging to varied taxonomic groups - plants, arthropods, molluscs, amphibians, reptiles and birds, and use a statistical framework to make inferences about patterns and drivers of diversity and diversification (Roy and Joshi, 2025, in review). Arthropods were among the poorly represented groups used in the study. Hence, we plan to use one of the most diverse arthropod assemblages - millipedes, as models to test the diversification dynamics and compare them with the inferences about other arthropod lineages. We intend to execute this by resolving the systematics and biogeography of different evolutionarily disjunct groups (clades) of millipedes. Additionally, examining their community assembly phylogenetic diversity and endemism across different climatic, latitudinal and elevational gradients would provide us with inferences of regions of varied diversity patterns, which can be utilised in formalising predictions for diversification patterns. Broadly, the objectives are:

Objective 1: Understanding the tempo and mode of diversification of peninsular biota - a meta-analysis; in review

Objective 2: Exploring the roles of geography, ranges and species traits in diversification of endemic peninsular Indian lineages

Objective 3: Phylogeny, systematics and biogeography of endemic millipede lineages

Objective 4: Species diversity, micro-endemism patterns and in-situ diversification dynamics of millipedes in peninsular India and their drivers

This research is part of Pragyadeep Roy's PhD thesis.

Publications: 

Roy, P., and Joshi, J. 2025. Idiosyncrasies unveiled: examining the pace, patterns and predictors of biotic diversification in peninsular India. Ecology Letters, 28, 6, 1461-0248. DOI: 10.1111/ele.70160 Covered by: The Hindu, Telangana Today, The New Indian Express

Funding:  

PR is supported by the Council for Scientific and Industrial Research (CSIR) JRF fellowship.

CSIR Major Laboratory Project to JJ.

DBT Wellcome India Alliance Intermediate Fellowship to JJ.