DOHM, M.R.*; MOORE, S.L.; MUIR, C.C.; REZA, A.M.; PRICE, D.K.; MAUTZ, W.J.: A comparison of cold tolerance of Hawaiian Drosophila populations
Hawaiian picture-winged Drosophila generally are found at elevations above 1000 m on wet, volcanic slopes. At these elevations, nighttime temperatures can drop below 10 C. With increasing degradation of suitable habitat at lower elevations, cold tolerance may be an important limit on range expansion. We, therefore, initiated a study of the cold tolerance characteristics of adult flies from laboratory populations (2 D. silvestris: PMAA “Hilo-side,” SKFR “Kona-side,” and 1 D. heteroneura) derived from individuals 3 generations removed the wild. The D. heteroneura population was sympatric to the Kona D. silvestris. We measured knockdown performance at 4 C and recovery (wake-up) time at room temperature to assess cold tolerance of these populations. A molecular, population-level phylogeny was constructed from DNA sequencing of the cytochrome oxidase subunit II (COII) from wild-caught flies of the same populations to facilitate species comparisons. The PMAA D. silvestris population clustered more closely with D. heteroneura than with its conspecific Kona population. One SKFR D. silvestris individual appeared to have a D. heteroneura COII sequence. Species differences were found for log10-knockdown times, but not log10-wakeup times. Flies from the single known D. heteroneura population were significantly less cold tolerant than the more widely distributed D. silvestris populations. We found no sex dimorphism, but significant, repeatable individual differences for cold tolerance. Based on their highly localized population structure, our thermal tolerance results suggest that Hawaiian Drosophila, in particular the rare D. heteroneura, may be limited in their potential to employ upslope range expansion.
