Patterns of Mayfly Phosphorus Content Across a Phosphorus Gradient

Phosphorus (P) availability is an important factor in organism growth and is positively correlated with growth rate.  We asked what happens to nymphal Baetis sp. and Neochoroterpes nanita mayfly mass and % P between sexes across a P gradient spanning 7 central Texas streams. Periphyton % P increased from 0.01% to 0.25% across streams, representing a dietary P subsidy for these grazing mayflies.  Percent P between sexes of Baetis did not differ within sites after accounting for individual mass, whereas N. nanita females were more P enriched than males in the largest size class, and the magnitude of female P enrichment increased across the P gradient.  High P site Baetis were 4X as massive, and N. nanita were 2X as massive as individuals from low P sites.  Low P site Baetis sexes of did not differ in mass within size classes, but high P site Baetis females were at least 25% larger than males.  N. nanita females were usually larger than males at low P sites, and always at least 30% larger at high P sites.