The myrmicine species Crematogaster rothneyi is one of the most widely distributed ants in Asia, but it has rarely been collected in the field. Its distribution range covers South and Southeast Asia, extending approximately 5,000 km from India in the west to Sulawesi in the east. Despite this wide distribution range, C. rothneyi has been treated as a single taxonomic species, and no combined morphological or molecular analysis has been conducted to assess whether any intraspecific variation exists. The sequence divergences of C. rothneyi populations, mainly obtained from Southeast Asia, were investigated by analyzing 387 bp and 175 bp sequences of the 12S ribosomal RNA and cytochrome c oxidase subunit (COI) genes, respectively. Phylogenetic analysis indicated that the C. rothneyi populations were separated into three groups: group I from Thailand and Cambodia, group II from Bangladesh and Myanmar, and group III from Krakatau and Sulawesi. Groups II and III were recovered as a single clade, sister to group I. The interspecific divergences were 7.3% to 8.5% for 12S and 14.5% to 23.3% for COI between most C. rothneyi specimens and Cambodian specimens, while divergence for 12S was 3.5% between Thai and Cambodian specimens. The Thai specimens are not morphologically differentiated, and are considered conspecific to C. rothneyi. We describe the Cambodian series as a new species, Crematogaster yaharai sp. nov., based on unique antennal morphology and mesosomal sculpture patterns with molecular evidence. Crematogaster rothneyi civa Forel, 1902 is synonymized under C. rothneyi. Crematogaster rothneyi is widespread and has sister species, suggesting recent diversification within the Indochinese Peninsula.
Keywords: Asia; Crematogaster rothneyi; Geographic variation; Phylogeny; Widespread species.