Predatory dipteran larva contributes to nutrient sequestration in a carnivorous pitcher plant

Abstract

<p class="first" id="d7458742e150">The fluids of <i>Nepenthes</i> pitcher plants are habitats to many specialized animals known as inquilines, which facilitate the conversion of prey protein into pitcher-absorbable nitrogen forms such as ammonium. <i>Xenoplatyura beaveri</i> (Diptera: Mycetophilidae) is a predatory dipteran inquiline that inhabits the pitchers of <i>Nepenthes ampullaria</i>. Larvae of <i>X. beaveri</i> construct sticky webs over the fluid surface of <i>N. ampullaria</i> to ensnare emerging adult dipteran inquilines. However, the interaction between <i>X. beaveri</i> and its host has never been examined before, and it is not known if <i>X. beaveri</i> can contribute to nutrient sequestration in <i>N. ampullaria. Xenoplatyura beaveri</i> individuals were reared in artificial pitchers in the laboratory on a diet of emergent <i>Tripteroides tenax</i> mosquitoes, and the ammonium concentration of the pitcher fluids was measured over time. Fluid ammonium concentration in tubes containing <i>X. beaveri</i> was significantly greater than those of the controls. Furthermore, fluid ammonium concentrations increased greatly after <i>X. beaveri</i> larvae metamorphosed, although the cause of this increase could not be identified. Our results show that a terrestrial, inquiline predator can contribute significantly to nutrient sequestration in the phytotelma it inhabits, and suggest that this interaction has a net mutualistic outcome for both species. </p>