Environmental context shapes sex-specific costs of reproduction in a dioecious plant

Trade-offs between current reproduction and future performance are fundamental constraints on evolution. In dioecious plants, females and males can differ in how much of a limiting resource they allocate to reproduction, creating trade-offs that could be sex specific and environmentally dependent. If so, physiological differences in resource use are expected to coincide with differential costs of reproduction for females versus males, but how these costs are expressed across environmental contexts remains poorly understood.

We tested the hypothesis that the expression of sex-specific reproductive trade-offs is environmentally dependent in dioecious broadleaf arrowhead (Sagittaria latifolia). We conducted a 2-year common garden experiment manipulating nutrient availability and reproductive investment to quantify sex-specific physiological costs using photosynthetic measurements and indices of nitrogen content.

As expected, the expression of reproductive trade-offs depended on both sex and resource availability. At the lowest nutrient level, males experienced reproductive costs as reduced leaf nitrogen content and photosynthesis following flowering in year 1 and as reduced leaf nitrogen content and size in year 2. Across all nutrient conditions, females showed fewer detectable physiological costs.

Together with results from previous studies of S. latifolia, our study shows that males and females incur reproductive costs in different physiological currencies, with males allocating more nitrogen than females. These costs become evident only under nitrogen limitation, highlighting how environmental context governs the expression of sex-specific life-history trade-offs.