Figure 7.

Beneficial effects of sexual activity on male immunity declines over time. The first experiment (A), had six treatments: Virgin males (□), males allowed to interacted with females for two days and then separated from females and held in single sex groups for 4 (∇), 3 (▲), 2 (●), 1(♦) and 0 (■) days prior to infection (n = 50 per treatment). Males separated from females for 4 days had survivorship comparable to that of virgins (p = 0.51, Cox proportion regression). The survivorship of males separated from females for 3, 2, 1 and 0 days had significantly higher survivorship compared to both virgins and males separated from females for 4 days (all p < 0.05). The experiment was repeated in two more independent blocks with three treatments each- (A) Males separated from females for 4 days, (B) Males separated from females for 1 day and (C) a separate virgin male treatment for each of these two sexually active male treatments. Fifty males were infected for each treatment × block combination. We found no significant effect of block and hence pooled the data from the two blocks for analysis. Survivorship of males held as virgins (□) was significantly lower than survivorship of males separated from females for 1 day (♦) (B, p < 0.0001, Cox proportion regression analysis). Survivorship of virgin males (□) and males separated females for four days (∇) was not different (C, p = 0.4, Cox proportion regression analysis). Sham infected controls for all the treatments were run independently and no mortality was observed. All sham infected controls are indicated by a single dashed line.