2003. Dietary conservatism may facilitate the initial evolution of aposematism. -Oikos 101: 458-466.It has generally been assumed that warningly coloured organisms pay a cost associated with their increased visibility, because naïve predators notice and eat them. This cost is offset by their enhanced protection from educated predators who associate the colour pattern with unprofitability. However, some studies have suggested that avoidance of novel prey by avian predators (''dietary conservatism'') can actually place novel colour morphs at a selective advantage over familiar ones, even when they are highly conspicuous. To test this idea, we experimentally simulated the appearance of a single novel-coloured mutant in small populations (20 individuals) of palatable artificial prey. The colour morph frequencies in each ''generation'' were determined by the relative survival of the previous generation under predation by birds. We used wild-caught European robins Erithacus rubecula foraging on pastry ''prey'' of different colours. The aim was to test whether prey selection by predators prevented or facilitated the novel colour morph persisting in the prey population over successive generations. We found that the novel colour morph quickly increased to fixation in 14/40 prey ''populations'', and at least once each in 8 of the 10 birds tested. Novel mutants of the classic aposematic colours (red and yellow) reached fixation most frequently, but even the green and blue novel morphs both increased to fixation in 2/40 trials. Novel colours reached fixation significantly faster than could be accounted for by drift, indicating active avoidance by the birds. These results suggest that a novel colour morph arising in a prey population can persist and increase under the selective pressure imposed by predators, even to the local exclusion of the original morph, despite being fully palatable. The consequences of this finding are discussed in relation to receiver psychology, the evolution of aposematism and the existence of polymorphism in Mü llerian mimics.
By oligonucleotide-directed mutageneses, 13 substitutions of amino acids at the carboxy-terminal region of rat liver cytochrome P-450d were done as follows: (A) Phe-449----Tyr; (B) Gly-450----Ser; (C) Leu-451----Ser; (D) Gly-452----Glu; (E) Lys-453----Glu; (F) Arg-454----Leu; (G) Arg-455----Gly; (H) Cys-456----Tyr; (I) Cys-456----His; (J) Ile-457----Ser; (K) Gly-458----Glu; (L) Glu-459----Ala; (M) Ile-460----Ser. The CO-bound reduced forms of the wild type and mutants B-G, J, L, and M gave Soret peaks at 448 nm. The CO complex of mutant A gave a Soret peak at 445 nm. The intensities of the CO-bound forms of mutants A, C, D, and J were very small compared with that of the wild-type complex. The CO-reduced forms of mutants H, I, and K did not give a Soret peak around 450 nm at all. The 448-nm peak of mutant F was unstable and quickly disappeared with the concomitant appearance of a peak at 420 nm.(ABSTRACT TRUNCATED AT 250 WORDS)
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