| Male and female Uca were video-taped feeding on patches of diatom Cylindrotheca closterium. Using fluorometric analysis of chlorophyll, experiments showed males and females had different intake rates, and that the sexes differed in the relationship between intake rate and food level. Females had higher intake rates than males, but the ratio of female:male intake rate varied with food level, being greater at low levels. Intake rate remains constant past a certain sex-specific food abundance, regardless of further increases in resource levels.;Intake rate was a product of the rate at which food was transferred to the mouth (scoop rate), and the rate at which food was extracted by the mouthparts. Scoop rate increased with food level, and extraction decreased exponentially with decreased processing time. Females had higher scoop rates at equivalent food levels, and higher extraction rates at equal processing times. High scoop rates mean small processing times, so extraction declines with feeding rate, producing static intake rate at high food concentration.;The above differences among the sexes have behavioral and morphological consequences. Males displace females from high quality patches, which compensates for their lower intake rates. Females have more setae than males, allowing them to sustain higher extraction rates. It was suggested that the male master claw evolved through ecological divergence, rather than sexual selection.;The energetic cost of foraging was estimated by measuring both O;Animals used their predicted leaving rule, maximizing patch-specific NEI. Comparison of altered and normal males showed that the leaving rule was not fixed, but based on direct assessment of intake rate. |
