Species-specific yeast preferences modulate adult and larval behavior in Drosophila melanogaster and Drosophila ananassae

The symbiotic relationship between Drosophila and associated yeasts is a critical determinant of host ecology and evolution. We investigated the specificity of host–microbe interactions by comparing the feeding and settling behaviors of the generalist fruit fly, Drosophila melanogaster, and the specialist, Drosophila ananassae, toward two common yeast species: Debaryomyces hansenii (MTCC 234) and Pichia kudriavzevii (MTCC 7018). We employed multi-choice bioassays for adults and two-choice feeding assays for larvae, using color-labeled media with reversed assignments to exclude visual bias. Larval preference analyses revealed significant species-level differences. D. melanogaster larvae exhibited a generalist feeding pattern, showing no significant preference and feeding equally on both D. hansenii and P. kudriavzevii (H(2) = 1.08, P = 0.584); color reversed: (H(2) = 1.08, P = 0.0581). In contrast, D. ananassae larvae displayed significant specialization, preferring D. hansenii over P. kudriavzevii across all color treatments (H(2) = 12.672, P = 0.002); color reversed: (H(2) = 12.672, P = 0.002). Adult settling behavior mirrored the larval patterns. D. melanogaster adults settled indiscriminately on both yeast species [PI for D. hansenii: 0.57 ± 0.11 SD; PI for P. kudriavzevii: 0.52 ± 0.12 SD]. Conversely, D. ananassae adults exhibited highly species-specific settling, strongly preferring D. hansenii across all choice combinations (H(3) = 17.02, P = 0.001), with a high Preference Index (PI = 0.82 ± 0.11 SD). These distinct behavioral patterns underscore fundamental differences in the ecological strategies of D. melanogaster and D. ananassae, highlighting that the complexity of host–microbe interactions necessitates a species-specific approach.