Courtship Patterns in the Drosophila montium Species Subgroup: Repeated Loss of Precopulatory Courtship?

During precopulatory courtship, male Drosophila typically produce wing vibration to generate species-specific songs before mounting females. Three species in the lini clade of the montium species subgroup have been found to produce species-specific sine song only after mounting and during copulation. Here we investigated and analyzed the courtship behavior of 29 species in the montium subgroup from video and song recordings and measured the duration of wing vibration. We describe a great diversity of courtship behavior in the montium subgroup. The courtship patterns can be categorized into four types in the montium subgroup: 1) type P/C, species with both precopulatory and copulatory courtship, such as D. parvula and D. nikananu, 2) type P-/C, species with sporadic precopulatory and mainly copulatory courtship, such as D. auraria and D. triauraria. 3) type C, species with only copulatory courtship, such as D. tani and D. pectinifera, 4) type C-, species with only very brief copulatory courtship, such as D. rufa and D. asahinai. According to a phylogenetic tree based on sequences of mitochondrial COI and COII, and the nuclear Adh, both precopulatory courtship and copulatory courtship were present in the most basal species D. parvula. Each of two branches in the montium subgroup contains four types of courtship behavior. Type C is present in each sub-branch. These results suggest that the courtship behavior initially involved both precopulatory and copulatory courtship, but that subsequently precopulatory courtship has gradually been lost in the montium subgroup. We suggest reasons why precopulatory behavior might come to be lost in the montium subgroup.