Behaviourally Driven Gene Expression Reveals Song Nuclei in Hummingbird
letters to nature Two cautionary points, one perhaps encouraging and another less 2. Wagner, G. P., Chiu, C. & Hansen, T. F. Is Hsp90 a regulator of evolvability? J. Exp. Zool. 285, 116±118 so, emerge from our study. First, it is evident that a high mutation (1999). 3. Holland, J. et al. Rapid evolution of RNA genomes. Science 215, 1577±1585 (1982). rate is not always bene®cial. The adaptive neighbourhood of an 4. Domingo, E. & Holland, J. J. in The Evolutionary Biology of Viruses (ed. Morse, S. S.) 161±184 (Raven, adaptive peak can constrain evolvability, despite a high mutation New York, 1994). rate. A high rate can lead to a high mutational load, as seen during 5. Fraile, A. et al. A century of tobramovirus evolution in an Australian population of Nicotiana glauca. J. Virol. 71, 8316±8320 (1997). the evolution by clone B. Thus, evolutionary changes in a popula- 6. Chao, L. Evolution of sex and the molecular clock in RNA viruses. Gene 205, 301±308 (1997). tion of RNA viruses, whether under clinical treatment or otherwise, 7. Burch, C. L. & Chao, L. Evolution by small steps and rugged landscapes in the RNA virus f6. Genetics should not automatically be interpreted as adaptive to the virus. 151, 921±927 (1999). Second, as had already been noted12, if multiple peaks exist, a shift to 8. Fenster, C. B, Galloway, L. F. & Chao, L. Epistasis and its consequences for the evolution of natural populations. Trends Ecol. Evol. 12, 282±286 (1997). a new adaptive peak can be triggered by a costly resistance mutation 9.
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