Fig. 1.

Effects of sodium manipulation on eye size and thoracic protein in monarchs. Monarchs reared on roadside-collected milkweed had 16 times the amount of sodium in their larval diet than those reared on milkweed collected from prairies 500 m away. Shown are differences in (A) thoracic protein and (B) relative eye width for adult males and females. For eye width, least square means (and SEs) are plotted from a model that also included body size (wing length) and head alignment accuracy (statistics in Table 3).