Feeding of biofilm-dwelling nematodes examined using HPLC-analysis of gut pigment contents

Abstract

The natural feeding behaviour of the nematodes Chromadorina bioculata (Schultze in Carus 1857) and Chromadorina viridis (Linstow 1876) was studied in situ, within epilithic biofilms of the Garonne River (France). Based on their feedingtype characteristics and population dynamics, it was hypothesised that these species feed selectively on microphytobenthos (MPB) within the biofilm, and that among MPB groups, diatoms are preferred. Highperformance liquid chromatography (HPLC) was used for separation, identification and quantification of pigments both in nematode guts and in the biofilm. This is the first time that nematode gut pigment contents were examined under natural conditions. Diatoms dominated the MPB which also comprised cyanobacteria and green microalgae. The comparison between chlorophyll a content in nematode guts versus in the biofilm showed that C. bioculata and C. viridis fed opportunistically (non-selectively) on MPB within the biofilm. Only diatom biomarker pigments were found in nematode guts suggesting that they could preferentially fed on diatoms among MPB groups. However, the non-detection of biomarker pigments for other microphyte groups could be also linked to HPLC detection limits. It was estimated that Chromadorina nematodes daily ingested on average 0.03-0.67% of the MPB standing stock. This grazing covered only a small part of their energetic requirements, suggesting that besides MPB they probably also fed on other biofilm food sources. Some considerations on the applicability of the HPLC gut pigment analysis technique for the examination of nematode feeding are also presented.

Selective Feeding of Bdelloid Rotifers in River Biofilms

“…The maximum feeding pressure exerted by bdelloid rotifers on the total MPB biomass in the biofilm was low, as it was previously observed for nematodes in the same site of the Garonne river [18]. Values for rotifer ingestion rates were however on average 70 fold higher than those of nematodes, resulting in a 14 fold higher grazing pressure exerted on the MPB biomass by rotifers than by nematodes.…”

“…bioturbation, grazing and excretion), the meiofauna can affect key processes such as primary production, bacterial development and organic matter fluxes [10-15]. A few recent studies address biofilm-dwelling meiofauna feeding habits, highlighting the importance of pelagic to benthic vertical imports through rotifer and ciliate filtration activity [16], or exploring nematode feeding selectivity to budget their implication in phototrophic carbon transfer [17,18]. …”

“…However, this issue, and especially the quantitative and qualitative in situ uptake of primary producers by meiofauna still receives little consideration in freshwater systems [10,17,18,22-25]. …”

“…[29,30]). Especially, HPLC gut pigment quantification allows to examine selective microphyte feeding within complex-clustered benthic habitats such as muds or biofilms [18,31]. …”

Chlorophyll and its degradation products in the two-spotted spider mite, Tetranychus urticae: observations using epifluorescence and confocal laser scanning microscopy

“…For instance, silkworm excretes up to four different chlorophyll derivatives, of which two were identified as 13 2 -HO phaeophytin a and b (Nakatani et al 1981). Pigment concentrations from guts of nematodes feeding on microphytobenthic organisms (Majdi et al 2012) and caterpillars feeding on plants (Shao et al 2011) show the presence of chlorophyll and chlorophyll breakdown products (e.g., pheophorbide a and pheophytin a) (Hendry et al 1987). The two-spotted spider mite, a polyphagous species that feeds on more than 1,100 host plants, sucks the plant cell content of leaf mesophyll ( Van der Geest 1985).…”