Ecology and natural history of swimming pitcher mites (Creutzeria spp., Histiostomatidae) from the traps of Nepenthes pitcher plants

Abstract

Pitcher plants of the genus Nepenthes trap and digest invertebrate prey to supplement their nutrient requirements using fluid-containing, modified leaves known as 'pitchers'. Pitchers are habitats to many aquatic metazoan and microbial species known as 'inquilines'. Mites (Histiostomatidae) are a common but poorly studied inquiline taxonlittle is known of their life cycles and their interactions with other inquiline taxa. The objectives of this study were to (1) investigate interspecific interactions between inquiline Creutzeria mites, microbes and Endonepenthia schuitemakeri (Diptera: Phoridae) (2) quantify the net nutritional benefit of Creutzeria mites and other inquilines on Nepenthes gracilis nitrogen sequestration and (3) determine if E. schuitemakeri can act as dispersal agents for Creutzeria mites. In the first part of the study, Creutzeria mites were reared in vitro under simulated pitcher conditions for varying lengths of time. Their populations were found to increase exponentially with time, peaking 24.2 days into the experiment and decreasing thereafter. In the second experiment, in vitro experiments were established with different combinations of E. schuitemakeri larvae, ant prey biomass, ant prey species and Creutzeria mite addition. Mite population, fluid microbe density and total pitcher-available nitrogen were measured at the end of 24 days as determined in the first part of the study. Confirmatory path analyses suggested that Creutzeria mites competed with microbes for prey resources (negative effect of microbe density on mite population) were not facilitated by E. schuitemakeri (no effect of E. schuitemakeri on mite population) and had a neutral to negative effect on pitcher nutrient sequestration (weak negative effect of mite population on pitcher-available nitrogen). However, Creutzeria deutonymphs could not be found on any of the E. schuitemakeri adults emerged during the experiments, suggesting these utilize other inquiline species as dispersal agents, or require environmental/ stress trigger factors to form deutonymphs.

Investigation of an Elevational Gradient Reveals Strong Differences Between Bacterial and Eukaryotic Communities Coinhabiting Nepenthes Phytotelmata

“…This is likely because oribatids are relatively large-bodied and pigmented, while histiostomatids are generally smaller and transparent, and thus more likely to be overlooked or lost when being filtered from the pitcher fluid. We are uncertain whether the oribatid mites function as inquilines or prey, though the latter appears more likely given their lack of obvious aquatic adaptations compared to Histiostomatidae [88]. The prey spectrum is dominated by ants; there were a total of 1172 ants across all samples (mean ± standard deviation = 75.4 ± 35.5) compared to a total of 122 prey items identified as other insects (mean ± standard deviation = 3.70 ± 4.16).…”