Embryonic development and endosymbiont transmission mode in the symbiotic clamLucinoma aequizonata(Bivalvia: Lucinidae)

Abstract

Lucinoma aequizonata is a large lucinid clam which lives in reducing mud around 500m deep. Adults harbor intracellular chemoautotrophic sulfur-oxidizing bacteria in specialized gill cells called bacteriocytes. The embryonic and early larval development of L. aequizonata is described by using light and scanning electron microscopy. Gametes were obtained by injection of 0.2ml of 4 mM serotonin solution in seawater into the posterior adductor muscle. The oocytes, 200 ym in diameter, are surrounded by a glycoprotein capsule which gives to the egg a total diameter of 500ym. The development which occurs at 10°C is slow. The first polar body is detected 2.5 h after contact between sperm and oocytes (T0+2.5 h), and the first cleavage begins 10 h later (T,+12.5 h). The following successive cleavages produce a nonciliated morula, then a ciliated gastrula which begins to rotate within the egg-capsule at T0+4.5 days. At this stage, the first shell pellicle appears on the dorsal side of the embryo. At T0+8 days, the trochophore larvae develop discrete ciliary bands which constitute the prototroch. Typical straight-hinge veligers, D-shaped larvae, hatch from the egg-capsule 12 days after fertilization. The newly hatched larvae are 240 ym in length and 200 ym in height, and the straight hinge 150pm long. To elucidate the symbiont transmission mode, two symbiont-specific primers were designed and used in amplifications by PCR. This primer set was unsuccessful in amplifying symbiont DNA targets from mature gonads, spawned oocytes, eggs, and veligers whereas successful amplifications were obtained from symbiont-containing gill tissues. These data rule out the vertical transmission mode and strongly suggest that the symbionts are environmentally transmitted to the new host generation in L. aequizonata as for all tropical lucinids examined to date. 94 0. Gros et al. / IRD 36 (1 999) 93-1 03Introduction laboratory without symbionts using sterilized sand.

Detection of the Free-Living Forms of Sulfide-Oxidizing Gill Endosymbionts in the Lucinid Habitat ( Thalassia testudinum Environment)

“…The environmental transmission mode was strongly suggested to occur in two oligochaetes (19) and in a few vestimentiferans based on molecular data obtained from mature gonads (8) and on ultrastructural observations of embryonic and larval stages (4,35,42). In bivalves, the symbiont transmission mode appears to be family specific, as suggested previously (23): vertical in Solemyidae (7,33) and Vesicomyidae (8,9) and environmental in Lucinidae (21,23,25,26).…”

Diversity and dynamics of bacterial communities in early life stages of the Caribbean coral Porites astreoides

“…Vertical transmission of bacteria has been documented among diverse marine invertebrate phyla (Bright and Bulgheresi, 2010) including but not limited to bryozoans (Haygood and Davidson, 1997), sponges (Enticknap et al, 2006;Schmitt et al, 2007;Sharp et al, 2007), ascidians (Hirose, 2000) and bivalves (Cary, 1994;Krueger et al, 1996;Gros et al, 1999;Fiala-Medioni et al, 2002), but this is the first Figure 2 Phylogenetic affiliations and habitat classifications of bacterial sequences obtained from P. astreoides larvae. Cloned sequences, grouped by the P. astreoides developmental stage in which it was detected, show the origin of the closest sequence match, according to the RDP (Ribosomal Database Project) and BLAST (GenBank).…”

Macro-Ecology of Gulf of Mexico Cold Seeps

“…Nutrient transfer from symbiont to host appears to be through intracellular digestion (Distel & Felbeck 1987), although this has not yet been verified for all species. Environmental symbiont transmission has been shown in L. aequizonata and all other lucinids examined to date (Gros et al 1999). Lucinids and thyasirids form extensive subsurface feeding tubes to acquire sulfide from deeper anoxic sediment layers (Turner 1985, Distel & Felbeck 1987.…”