Abstract
The collision of the Indian and Eurasian plates during the Eocene represents a major tectonic shift that significantly altered biotic dynamics and promoted species diversification across the Oriental region. To explain the diversification of taxa from the Indian subcontinent into Southeast Asia, two principal hypotheses have been proposed: the "Biotic-ferry" and "Step-stone" models. The subfamily Perittopinae, a lineage of semi-aquatic bugs comprising a single genus and 20 extant species, provides an ideal system for testing these hypotheses due to its disjunct distribution spanning the Indian subcontinent and Southeast Asia. This study conducted a comprehensive taxonomic analysis of the entire subfamily, incorporating newly defined morphological characters and multilocus phylogenetic analyses to reconstruct evolutionary relationships and historical biogeography. Morphological and phylogenetic evidence confirmed the monophyly of Perittopinae and supported the establishment of three new genera- Indoperittopus gen. nov., Pachyperittopus gen. nov., and Falciperittopus gen. nov.-in addition to four new species and four new combinations. Biogeographic reconstructions indicated a southern Indian origin, with initial diversification potentially occurring during the mid-Paleocene, coinciding with the major phases of the India-Eurasia collision. Subsequent range expansion over marine barriers facilitated colonization of the northern Sunda Shelf, consistent with the "Step-stone" dispersal mechanism. Later northward expansion from the southern Sunda Shelf during the early Miocene triggered further diversification of the genus Perittopus within the Indo-China Peninsula. These findings advance understanding of Perittopinae systematics, phylogeny, and historical biogeography, identifying the northward drift of the Indian plate and its eventual collision with Eurasia as catalysts of diversification within this semi-aquatic lineage.