Diversification of Alpine Soil Animals Corroborates Uplifts and Environmental Changes of Qinghai‐Tibetan Plateau and Himalayas: Insights From Molecular Phylogeny and Cryptic Diversity of the <i>Isotoma quadridentata</i> Complex (Collembola: Isotomida

ABSTRACT The Qinghai‐Tibetan Plateau and Himalayas (QTPH) are biodiversity hotspots crucial for understanding alpine speciation. While studies have focused on flora and aboveground fauna, the impact of QTPH uplift on soil fauna diversification remains understudied. To address this research gap, we investigated a representative taxon of alpine soil animals, the Isotoma quadridentata species complex (Collembola, Isotomidae) widespread at 2300–5100 m above sea level across the QTPH. On a molecular aspect, we sequenced 2 mitochondrial (COI, 16S) and 3 nuclear (18S, 28S D1–2, 28S D7–10) markers from 79 individuals representing different populations of this complex and related species. Based on these data, our single‐locus (ABGD, ASAP) and multi‐locus (single‐rate and multi‐rate mPTP) species delimitation analyses supported 11–15 candidate species among this complex. On a morphological aspect, colour patterns varied both between and within the candidate species, suggesting caution in their use for Isotoma diagnosis. Macrochaetotaxy was largely consistent, except in AG4, which showed a distinct pattern on the head. Macroevolutionary analyses indicated a Himalayan origin for QTPH Isotoma 5.88–10.25 million years ago (Mya), with the I. quadridentata complex originating in the adjacent Emei Mountain later. This complex diversified initially in the Emei Mountain before dispersing to the northeast QTPH and back to Himalayas 3.82–6.48 Mya, followed by further speciation. These findings link the origin and diversification of QTPH Isotoma and the I. quadridentata complex to the uplift of the QTPH and subsequent environmental changes since Miocene, supporting a potential impact of this geological event on the diversification of alpine soil fauna.