LOCAL ADAPTATION TO REGIONAL CLIMATES IN PAPILIO-CANADENSIS (LEPIDOPTERA, PAPILIONIDAE)

Papilio canadensis encounters shorter, cooler summers in interior Alas ka than in northern Michigan: average thermal sums are 583 vs. 985 Cel sius degree-days (10 degrees C base); mean daily temperature is 14.4 v s. 18.8 degrees. The temperature physiology of P. canadensis could be evolutionarily conserved, or the species may be a composite of regiona lly adapted populations. We evaluated these hypotheses by comparing th e developmental physiology of P. canadensis from Alaska and Michigan a cross a range of temperatures in the laboratory and held. Higher tempe ratures generally resulted in more rapid larval development, but the e ffects varied with insect population and host. At low temperatures (12 degrees), Alaskan larvae grew faster than Michigan larvae (fifth inst ars doubled their fresh mass in 5.8 vs. 9.1 d), primarily due to 40% h igher consumption rates. At high temperatures (30 degrees), Alaskan la rvae grew slower, faster, or the same as Michigan larvae, depending up on host. Effects of host quality were greatest at high temperatures. E levated respiratory expenses in Alaskan larvae (35% higher than Michig an larvae) made them especially sensitive to host quality at high temp eratures. Dry matter digestibility and nitrogen use efficiency differe d across hosts, but not between populations or across temperatures. Mo lting accounted for 35-51 % of development time. Alaskan larvae comple ted their fifth molt faster than Michigan larvae at 12 degrees (11.8 v s. 17.8 d), but not at 30 degrees (3.1 vs. 2.9 d). In both populations , molt was more temperature sensitive than growth at low temperatures (Q(10) of 5.65 vs. 3.04 from 12 to 18 degrees), but less temperature s ensitive at high temperatures (Q(10) of 1.60 vs. 2.06 from 18 to 30 de grees). Survival differed across temperatures, but not between populat ions. Under ideal basking conditions, larvae in the held were able to elevate body temperatures approximate to 10 degrees above ambient, but such conditions were rare in Alaska and larvae were usually near ambi ent temperature. Alaskan larvae were no better than Michigan larvae at selecting high radiation microsites or converting solar radiation int o heat. Growth rates of Alaskan larvae were the same in the field and laboratory when fed the same foliage and exposed to the same mean dail y air temperature. We incorporated P. canadensis temperature responses into a life history development model, then used a 48-yr climatic rec ord to evaluate the fitness contributions of apparent adaptations to A laskan summers. On a good host, at Alaskan temperatures, Alaskan P. ca nadensis had an estimated fitness 3.0 times greater than Michigan P. c anadensis. Furthermore, the Michigan population was predicted to go ex tinct in 31 of 48 yr at Alaskan temperatures. Changes in growth temper ature responses made the greatest contribution to enhanced fitness in Alaska, followed by increased mass of neonates, enhanced molting abili ties at low temperatures, and a reduced size threshold for pupation. A nalysis of fitness trade-offs suggested that extreme summers have been more important than average summers in shaping adaptive responses. Re gional adaptation to climate allows P. canadensis to maintain a broade r geographic distribution than would otherwise be possible, but northe rn distribution limits are probably still constrained by summer temper atures.