WITHIN-GENERATION AND BETWEEN-GENERATION EFFECTS OF TEMPERATURE ON THE MORPHOLOGY AND PHYSIOLOGY OF DROSOPHILA-MELANOGASTER

We investigated the effects of developmental and parental temperatures on several physiological and morphological traits of adult Drosophila melanogaster. Flies for the parental generation were raised at either low or moderate temperature (18 degrees C or 25 degrees C) and then m ated in the four possible sex-by-parental temperature crosses. Their o ffspring were raised at either 18 degrees C or 25 degrees C and then s cored as adults for morphological (dry body mass, wing size, and abdom inal melanization [females only]), physiological (knock-down temperatu re, and thermal dependence of walking speed), and life history (egg si ze) traits. The experiment was replicated, and the factorial design al lows us to determine whether and how paternal, maternal, and developme ntal temperatures (as well as offspring sex) influence the various tra its. Sex and developmental temperature had major effects on all traits . Females had larger bodies and wings, higher knock-down temperatures, and slower speeds (but similar shaped performance curves) than males. Development at 25 degrees C (versus at 18 degrees C) increased knock- down temperature, increased maximal speed and thermal performance brea dth, decreased the optimal temperature for walking, decreased body mas s and wing size, reduced abdominal melanization, and reduced egg size. Parental temperatures influenced a few traits, but the effects were g enerally small relative to those of sex or developmental temperature. Flies whose mother had been raised at 25 degrees C (versus at 18 degre es C) had slightly higher knock-down temperature and smaller body mass . Flies whose father had been raised at 25 degrees C had relatively lo nger wings. The effects of paternal, maternal, and developmental tempe ratures sometimes differed in direction. The existence of significant within- and between-generation effects suggests that comparative studi es need to standardize thermal environments for at least two generatio ns, that attempts to estimate ''field'' heritabilities may be unreliab le for some traits, and that predictions of short-term evolutionary re sponses to selection will be difficult.