The relationship of body condition, superoxide dismutase, and superoxide with sperm performance
Sperm competition theory predicts a negative correlation between somatic investment and traits that aid in pre- and postcopulatory sexual selection. Sperm performance is critical for postcopulatory success but sperm are susceptible to damage by free radicals such as superoxide radicals generated during mitochondrial respiration (mtSOx). Males can ameliorate damage to spermatozoa by investing in the production of antioxidants, like superoxide dismutase (SOD), which may act as a mechanistic link to pre- and postcopulatory trade-offs. Some male Australian, color-polymorphic painted dragon lizards (Ctenophorus pictus) possess a yellow throat patch (bib) that females prefer over nonbibbed males and are also more likely to win male-male contests indicating that males with bibs may be better at monopolizing females. We tested whether the sperm performance in nonbibbed males was superior to that of bibbed males. We show that overall sperm performance was not different between the bib-morphs, however, higher mtSOx levels were negatively correlated with sperm performance in bibbed males, but not of nonbibbed males. Blood cell mtSOx levels are negatively correlated with SOD activity in the plasma in all males early in the breeding season but SOD was lower in bibbed males. Nonbibbed males maintain a positive correlation between body condition and SOD activity over time while bibbed males do not. Together, these data suggest physiological associations between body condition, SOD activity, and sperm performance are linked to the expression of a yellow gular patch, which may be related to intrinsic differences in the metabolism of bibbed versus nonbibbed males.