Life cycle and calculation of the intrinsic rate of natural increase of two bacterivorous nematodes, Panagrolaimus sp. and Poikilolaimus sp. from chemoautotrophic Movile Cave, Romania

Abstract

The life cycle and somatic growth of two bacterivorous nematodes, Panagrolaimus sp. and Poikilolaimus sp., isolated from chemoautotrophic microbial mats in Movile Cave, Romania, were studied in monoxenic cultures at 20°C with Escherichia coli as the food source. A method is described that allows simultaneous investigation of the somatic growth pattern, age-specific fecundity, and age-specific mortality of single individuals with high accuracy. Somatic growth curves of the species are presented. During juvenile development, both species showed a strict linear increase in body length, whereas body weight increased exponentially. Growth was continuous without lag phases. The relationships between fresh weight, W (μg), and body length, L (mm), were W = 1.6439L2.7672 for Poikilolaimus sp. and W = 0.2085L4.0915 for Panagrolaimus sp. Life tables and fecundity schedules for the two species are presented. In addition, demographic parameters were calculated. For Panagrolaimus, the intrinsic rate of natural increase (rm), calculated according to the Lotka equation, was 0.309, the net reproductive rate (R0) 64, the mean generation time (T) 13.8 days and the minimum generation time (Tmin) 9.5 days. The corresponding values for Poikilolaimus were rm = 0.165, R0 = 108, T = 26.2 and Tmin = 19.5. Panagrolaimus produced fewer progeny than Poikilolaimus during its life but exhibited faster population growth due to its faster maturation. It showed a distinct post-reproductive period, whereas Poikilolaimus remained fertile until death.

Food choice of two bacteria-feeding nematode species dependent on food source, food density and interspecific competition

“…The two baeterivorous nematodes Panagrolaimus and Poikilolaimus, isolated (see Riess et ai, 1999;Muschiol, 2009) from Movile Cave (Romania), were cultured at 20°C on nematode growth Geldte (NGG) plates following the protocol of Muschiol & Traunspurger (2007).…”

“…For both nematode species, an overnight culture of E. coli (OP50) in LB (lysongeny broth) medium was washed (12 000 rpm, 10 min, pellet resuspended in sterile Volvic water), checked spectrophotometdcally (ODÖOO) to determine the different bactedal densities and used as food sources (Muschiol & Traunspurger, 2007). In relation to the maximum populadon growth rates of Panagrolaimus and Poikilolaimus (Schroeder et al, 2010) and to simulate succession of the natural floating mats in the cave (Sarbu et ai, 1996;Rohwerder et ai, 2003;Hutchens et al, 2004), bacteda concentrations between 10^ and 10' cells ml"' were chosen.…”

“…This ecosystem depends especially on the primary production of sulphur-and methaneoxidising bacteria (Sarbu et al, 1996;Rohwerder et al, 2003;Hutchens étal, 2004;Schroedereía/., 2010). However, Panagrolaimus seems to be specialised to higher, and Poikilolaimus to lower, bactedal densities (Muschiol & Traunspurger, 2007;Schroeder et al, 2010). Expanding on this observation, the specific aims of this study were to determine: 0 the preferred food sources (bacteda, algae, glucose) and food densities of Panagrolaimus and Poikilolaimus, ii) whether they switch their preferred food density when subjected to intra-and interspecific competition; and (•//) whether differential food choice can largely explain the coexistence of these two species and the absence of competitive exclusion in the unchanging environment of Movile Cave.…”

“…(Rhabditidae). These two bacterivorous nematodes coexist in a highly homogeneous and stable environment, compete for the same food resources, and play a major role in the cave's food web (Riess et ai, 1999;Muschiol & Traunspurger, 2007;Muschiol et al, 2008). Both nematode species are members of a highly specialised meiofaunal community inhabiting floating chemoautotrophic microbial mats in an isolated groundwater ecosystem (Muschiol, 2009;Schroeder et ai, 2010).…”

Life at the extreme: meiofauna from three unexplored lakes in the caldera of the Cerro Azul volcano, Galápagos Islands, Ecuador

“…A very recent complete desiccation of this very small lake could be the reason for this. However, many nematode species possess very short life cycles in the range of days to weeks (Muschiol and Traunspurger 2007) and thus can be assumed to be quick colonizers. Thus, the complete lack of nematodes in Side Lake is more probably the result of its high pH (10.0), as a nematicidal effect of alkaline pH levels has repeatedly been reported in the literature (e.g.…”