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First published online November 19, 2004
Journal of Experimental Biology 207, 4415-4425 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01290

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How a low tissue O₂ strategy could be conserved in early crustaceans: the example of the podocopid ostracods

Laure Corbari, Pierre Carbonel and Jean-Charles Massabuau^*

Laboratoire d'Ecophysiologie et Ecotoxicologie, des Systèmes Aquatiques, UMR 5805, Université Bordeaux 1 and CNRS, Place du Dr B. Peyneau, 33120 Arcachon, France

View larger version (35K): [in a new window]   Fig. 1. Experimental set-up for ventilatory analysis by video recording. Animals were free ranging in a vertical layer of natural sediment and ventilatory activity was measured by visual inspection through the animals. Analysis was performed under dim light by means of infra-red (IR) camera and micro-spotlight (see text for details).

View larger version (53K): [in a new window]   Fig. 2. Morphofunctional anatomy of Cyprideis sp., a typical podocopid ostracod from the Bay of Arcachon. (A) In situ picture in the experimental micro-aquarium. Note the size of the animal in comparison to the sand particles (sp). (B) Schematic drawing (right valve not shown) illustrating the ventilatory flow pattern (white arrows) through the animal. The inspired water enters from the anterior aspect and superfusates the soft body. Ant, anterior; post, posterior; d, dorsal; v, ventral; scaphognathites, ventilatory plates. Scale bar, 250 µm.

View larger version (30K): [in a new window]   Fig. 3. Ventilatory response of Cyprideis torosa to consecutive 3-day exposure periods at reference water PO2=21 kPa, hypoxia, PO2=3 kPa, and recovery PO2=21 kPa. See text for details. (A,B) Typical ventilatory pattern (fR, ventilatory frequency) in two specimens of Cyprideis during 1 h observation periods at PO2=21 kPa. Both activities are contrasted and characterized by alternations of ventilatory bursts and pauses. (C–E) Ventilatory activity per hour (C; min h–1), burst number per hour (D; h–1), mean ventilatory frequency within burst per minute (E; fR, min–1) at PO2=21 and 3 kPa (grey-shaded). Each data point (mean ± 1 S.D.) was obtained from a single podocopids, randomly chosen and analysed during the 1 h period. The ventilatory frequency within burst was also analysed during a 3-day recovery period (days 7 and 9) at PO2=21 kPa (E). One symbol per individual, N=10 animals. No significant change was observed as a function of water PO2 and time.

View larger version (9K): [in a new window]   Fig. 4. Ventilatory response to 2 h exposure periods at various oxygenation levels for all studied podocopids (N=56–106 animals; same data as in Table 2). (A) Respiratory frequencies within bursts, fR, are given as means ± 1 S.E.M. (B) Number of apnoeic animals during each exposure period expressed as percentages of the studied animals. No significant difference was observed as a function of PO2.

View larger version (20K): [in a new window]   Fig. 5. Relationship between animal positioning (frequency distribution at different depths shown by the grey bars; scale, lower x axis) and O2 profiles (one symbol type per O2 profile; scale, upper x axis) as a function of sediment depth in naturally occurring (open and closed triangles, circles and open squares, left panel) and experimentally manipulated O2-gradients (water column PO2=21 or 40 kPa). Analyses were performed at days (d) 0, 4, 7 and 11. As O2 penetration velocity varied from core to core for the same water column, values of PO2, O2 profiles are grouped by similar near anoxic-zone depths (thickness, 1 mm; dotted lines) independent of exposure time. The animal's position followed the O2 profiles, and were independent of sediment depth and time. N is the number of analysed cores per O2 profile penetration depth.

View larger version (15K): [in a new window]   Fig. 6. (A) Frequency distribution of ostracods as a function of water PO2 in the sediment. Note that the values are not normally distributed and the podocopids were most frequently present in the range 3–5 kPa. (B) Frequency distribution of arterial PO2 in the Chinese crab Eriocheir sinensis in normoxia (PO2=21 kPa) from Forgue et al. (1992). (C) Frequency distribution of tissue PO2 in mammalian brains at 37°C (cerebral cortex of rat from Lübbers; Siesjö, 1978). Note the impressive similarity of oxygen status, despite the large evolutionary gap.

View larger version (60K): [in a new window]   Fig. 7. Ostracod morphology and gas diffusion distance in two typical podocopids. Inset, section positioning view of A and B: a, longitudinal section, view A; b, sagittal section, view B. (A) Longitudinal view in an Argilloecia specimen. (B) Sagittal view in a Cyprideis specimen. The diffusion distance between water in the domiciliar cavity and the most central tissues never exceeds 60 µm. Ant, anterior; post, posterior; d, dorsal; v, ventral; sc, scaphognathite. Scale bars, 100 µm.

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