TABLE 1.

Relative fitness of chimeric viruses measured in competitions with parental viruses

Virus	Nonlimited lifespan			Rapid turnover
	SIVMneCL8	SIVMne170	Fitnessa	SIVMneCL8	SIVMne170	Fitness
SIVMneCL8		Win	High		Lose	Low
SIVMne170	Lose		Low	Win		High
8/170xr-sub	Equal	Win	High	Equal	Lose	Low
8/170	Lose	Equal	Low	Equal	Lose	Low
170/8	Equal	Win	High	Win	Equal	High

^a“High” and “low” fitness phenotypes were defined from the relative fitness of SIVMneCL8 and SIVMne170 (in bold). For chimeric viruses, the phenotype was determined from competitions with each of the parental variants. The outcome of the competition was labeled according to the relative fitness value of the chimera (w). For 0.1 < |w| < 0.1, the outcome was judged as a tie (labeled as equal); for w > 0.1, the outcome was judged as “lose” (chimera is less fit); for w > 0.1, the outcome was judged as “win” (chimera is more fit). The chimera's phenotype was assigned as “high” when the chimera had equal fitness with the high-fitness parental strain and won competition with the low-fitness parental strain (w > 0.1). The chimera's phenotype was assigned as “low” when the chimera had equal fitness with the low-fitness parental strain and lost the competition with the high-fitness parental strain.

^b8/170xr-su chimera contains a portion of the SIVMne170 sequence responsible for syncytium formation, including the vpx/vpr genes and the SU portion of the env gene, in the background of SIVMneCL8; 8/170 chimera contains the 5′ half of SIVMneCL8 and the 3′ half of SIVMne170; 170/8 chimera contains the 5′ half of SIVMne170 and the 3′ half of SIVMneCL8.