Sex differences in Immunity as a Function of Sexual Selection.

<p>The thick solid line represents the case when the condition-dependence of reproduction and the effect of immunity on condition are equal for the sexes; under these circumstances, when sexual selection is absent or weak, males should invest more in immune defense than should females (i.e., thick, solid black line is above the dashed line, in the region of M>F investment in immunity). As the strength of sexual selection increases, the female bias in investment in immunity increases. However, if parasites have particularly strong negative effects on condition in males, and/or if male reproductive success is highly dependent on condition, relative to those same effects in females, males should invest more in immunity than should females, even when sexual selection is strong (thin solid line raised above the thick solid line, and never crossing dashed line). Of course, the converse situation may mean that males never invest more in immunity than do females (lower thin solid line). Adapted from Stoehr and Kokko <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000267#ppat.1000267-Stoehr1" target="_blank">[14]</a>.