GENOTYPE-SPECIFIC HABITAT SELECTION FOR OVIPOSITION SITES IN THE CACTOPHILIC SPECIES DROSOPHILA-BUZZATII

Isofemale lines of the cactophilic species, Drosophila buzzatii, exhib it genetic variation for their oviposition response to cactus yeast sp ecies in the laboratory. In general, interactions between yeast specie s preclude the use of pairwise preferences as predictors of preference s in three-way choice experiments. Two isofemale lines with relatively high laboratory preference for ovipositing on the yeast Pichia cactop hila (as opposed to Clyptococcus cereanus) and two isofemale lines wit h relatively low preference for P. cactophila were used in a series of field release experiments to determine if laboratory preferences were also realized under field conditions. The influence of yeast species on both settling behaviour (long-distance response) and oviposition pr eference (short-distance response) were tested. The four lines were id entical in their settling behaviour, preferring P. cactophila. The ana lysis of the oviposition preference tests showed significant line effe cts which correlated with the laboratory results. Thus a genetic compo nent for oviposition preference under laboratory and field conditions was demonstrated and this strengthens the evidence for genotype-specif ic habitat selection in D. buzzatii. One low line, however, did not di ffer significantly from the two high lines under field conditions. A l aboratory retest of this low line showed that the laboratory preferenc e had not changed. The reason for the difference in the two situations is unknown but undoubtedly is attributable to uncontrolled variables under the field situation. Settling behaviour and oviposition response , in general, appear to be proximately linked to differences in the vo latiles produced by the different yeast species.