Dipteran larvae and microbes facilitate nutrient sequestration in the Nepenthes gracilis pitcher plant host

The fluid-containing traps of Nepenthes carnivorous pitcher plants (Nepenthaceae) are often inhabited by organisms known as inquilines. Dipteran larvae are key components of such communities and are thought to facilitate pitcher nitrogen sequestration by converting prey protein into inorganic nitrogen, although this has never been demonstrated in Nepenthes. Pitcher fluids are also inhabited by microbes, although the relationship(s) between these and the plant is still unclear. In this study, we examined the hypothesis of digestive mutualism between N. gracilis pitchers and both dipteran larvae and fluid microbes. Using dipteran larvae, prey and fluid volumes mimicking in situ pitcher conditions, we conducted in vitro experiments and measured changes in available fluid nitrogen in response to dipteran larvae and microbe presence. We showed that the presence of dipteran larvae resulted in significantly higher and faster releases of ammonium and soluble protein into fluids in artificial pitchers, and that the presence of fluid microbes did likewise for ammonium. We showed also that niche segregation occurs between phorid and culicid larvae, with the former fragmenting prey carcasses and the latter suppressing fluid microbe levels. These results clarify the relationships between several key pitcher-dwelling organisms, and show that pitcher communities facilitate nutrient sequestration in their host.

[1]  G. Kerth,et al.  Ecological outsourcing: a pitcher plant benefits from transferring pre‐digestion of prey to a bat mutualist , 2017 .

[2]  David W. Armitage Bacteria facilitate prey retention by the pitcher plant Darlingtonia californica , 2016, Biology Letters.

[3]  G. Dykes,et al.  Bacterial communities associated with the pitcher fluids of three Nepenthes (Nepenthaceae) pitcher plant species growing in the wild , 2014, Archives of Microbiology.

[4]  M. Rott,et al.  Characterization and heterologous expression of a PR-1 protein from traps of the carnivorous plant Nepenthes mirabilis. , 2014, Phytochemistry.

[5]  W. Federle,et al.  A Novel Type of Nutritional Ant–Plant Interaction: Ant Partners of Carnivorous Pitcher Plants Prevent Nutrient Export by Dipteran Pitcher Infauna , 2013, PloS one.

[6]  M. Rott,et al.  Secreted pitfall-trap fluid of carnivorous Nepenthes plants is unsuitable for microbial growth. , 2013, Annals of botany.

[7]  Sabulal Baby,et al.  Distribution of naphthoquinones, plumbagin, droserone, and 5-O-methyl droserone in chitin-induced and uninduced Nepenthes khasiana: molecular events in prey capture. , 2011, Journal of experimental botany.

[8]  N. Kikuchi,et al.  Isolation and characterization of novel lipases from a metagenomic library of the microbial community in the pitcher fluid of the carnivorous plant Nepenthes hybrida. , 2011, Journal of bioscience and bioengineering.

[9]  C. von Mering,et al.  In Situ Enzyme Activity in the Dissolved and Particulate Fraction of the Fluid from Four Pitcher Plant Species of the Genus Nepenthes , 2011, PloS one.

[10]  Thomas Lendl,et al.  Traps of carnivorous pitcher plants as a habitat: composition of the fluid, biodiversity and mutualistic activities. , 2011, Annals of botany.

[11]  B. Gowen,et al.  Ion fluxes across the pitcher walls of three Bornean Nepenthes pitcher plant species: flux rates and gland distribution patterns reflect nitrogen sequestration strategies , 2010, Journal of experimental botany.

[12]  A. Ellison,et al.  The Pitcher Plant Sarracenia purpurea Can Directly Acquire Organic Nitrogen and Short-Circuit the Inorganic Nitrogen Cycle , 2009, PloS one.

[13]  A. Ellison,et al.  Linking the brown and green: nutrient transformation and fate in the Sarracenia microecosystem. , 2008, Ecology.

[14]  J. Midgley,et al.  Density-dependent outcomes in a digestive mutualism between carnivorous Roridula plants and their associated hemipterans , 2007, Oecologia.

[15]  J. Midgley,et al.  Digestive mutualism, an alternate pathway in plant carnivory , 2003 .

[16]  J. Bronstein Conditional outcomes in mutualistic interactions. , 1994, Trends in ecology & evolution.

[17]  S. Heard Processing Chain Ecology: Resource Condition and Interspecific Interactions , 1994 .

[18]  M. Mogi,et al.  Aquatic arthropod communities in Nepenthes pitchers: the role of niche differentiation, aggregation, predation and competition in community organization , 1992, Oecologia.

[19]  R. Beaver Biological Studies of the Fauna of Pitcher Plants [Nepenthes] in West Malaysia , 1979, Annales de la Société entomologique de France (N.S.).