Spirostomum spp. (Ciliophora, Protista), a suitable system for endocytobiosis research

Summary. Among ciliate genera, only Paramecium and Euplotes species have been studied extensively as host organisms of bacterial endocytobionts. In this article, we show that members of the genus Spirostomum may also serve as a suitable system for endocytobiosis research. Two strains of Spirostomum minus (Heterotrichea, Ciliophora) collected in Germany and Italy, respectively, were found to harbor different types of bacterial infections. Bacteria of various sizes and shapes were observed in the cytoplasm or in the nuclei of the ciliates. The bacteria in the cytoplasm were either surrounded by a peribacterial membrane or lay naked. One of the bacterial species was found in the vicinity of the contractile fibrillar system (myonemes) of the ciliates. In rare cases, another type of bacteria was observed associated with mitochondria. The macronuclei of both the Italian and the German strains were crowded with endocytobionts. The endonuclear bacteria in the two S. minus strains differed with respect to their cytoplasmic structures but they were of similar size and both were rod shaped. According to the results of in situ hybridization, the endonuclear bacteria of the Italian strain belong to the subgroup of alphaproteobacteria, whereas the bacteria associated with the fibrillar system appeared to be gram-positive bacteria with high G+C content. While both the German and the Italian strains were found to permanently maintain their endocytobionts, they were at least partly colonized by different bacteria. This is taken as an indication that geographically separated populations of ciliates may be stably infected by different endocytobionts, possibly due to different ecological conditions. For S. minus and S. ambiguum a total of 7 different bacterial endocytobionts have now been recorded. We recommend the members of the genus Spirostomum as a suitable system for endocytobiosis research. Correspondence and reprints (present address): Laboratorio di Protistologia, Dipartimento di Etologia, Ecologia ed Evoluzione, Università di Pisa, Via A. Volta 4, 56126 Pisa, Italy.     

Behaviour of dictyostelium discoideum amoebae and Escherichia coli grown together in chemostat culture

When Dictyostelium discoideum amoebae and Escherichia coli were grown together in chemostat culture damped oscillations in the popullation densities of the organisms occurred followed by a sudden increase in bacterial numbers and a concommitant decrease in the number of amoebae. After the system had come to equilibrium altering the dilution rate resulted in a monotonic change in the experimental variables to new steady state levels. A square wave increase in the concentration of limiting nutrient in the feed medium during the oscillatory phase of culture produced a sinusoidal response indistinguishable from that prior to the perturbation. The results are more complicated than those predicted by simple models of microbial predator-prey dynamics although they correspond most nearly to models which incorporate saturation kinetics.     

<Emphasis Type="Italic">Acanthamoeba castellanii</Emphasis> an environmental host for <Emphasis Type="Italic">Shigella dysenteriae</Emphasis> and <Emphasis Type="Italic">Shigella sonnei</Emphasis>

The interaction between Shigella dysenteriae or Shigella sonnei and Acanthamoeba castellanii was studied by viable counts, gentamicin assay and electron microscopy. The result showed that Shigella dysenteriae or Shigella sonnei grew and survived in the presence of amoebae for more than 3 weeks. Gentamicin assay showed that the Shigella were viable inside the Acanthamoeba castellanii which was confirmed by electron microscopy that showed the Shigella localized in the cytoplasm of the Acanthamoeba castellanii. In conclusion, the relationship between Shigella dysenteriae and Shigella sonnei with Acanthamoeba castellanii is symbiotic, and accordingly free-living amoebae may serve as a transmission reservoir for Shigella in water.     

Foraging Ants as Scavengers on Entomopathogenic Nematode-Killed Insects

Ants were the most apparent invertebrate scavengers observed foraging on entomopathogenic nematode-killed insects (i.e., insect cadavers containing entomopathogenic nematodes and their symbiotic bacteria) in the present study. Workers of the Argentine ant,Linepithema humile(Mayr), scavenged nematode-killed insects on the surface and those buried 2 cm below the soil surface. Ant workers scavenged significantly more steinernematid-killed (60–85%) than heterorhabditid-killed (10–20%) insects. More 4-day-postinfected cadavers (hosts died within 48 h after exposure to nematodes) were scavenged than 10-day-postinfected cadavers. Ten-day-postinfected hosts contained live infective juvenile nematodes therefore ants may serve as phoretic agents. Other ant species, includingVeromessor andrei(Mayr),Pheidole vistanaForel,Formica pacificaFrancoeur, andMonomoriom ergatogynaWheeler, also scavenged nematode-killed insects. These ant species removed or destroyed about 45% of the steinernematid-killed insects. These results suggest that survival of steinernematid nematodes may be more significantly impacted by invertebrate scavengers, especially ants, than that of heterorhabditid nematodes, and placement of steinernematid-killed insects in the field for biological control may be an ineffective release strategy. Because entomopathogenic nematodes kill insects with the help of symbiotic bacteria, we tested the role of these bacterial species in deterring invertebrate scavengers by injecting bacteria (without nematodes) into insects and placing the cadavers in the field. None of the insects killed by the symbiotic bacterium,Photorhabdus luminescens(Thomas and Poinar) fromHeterorhabditis bacteriophoraPoinar, were scavanged, whereas 70% of the insects killed by the symbiotic bacterium,Xenorhabdus nematophilus(Poinar and Thomas) fromSteinernema carpocapsae(Weiser), and 90% of the insects killed byBacillus thuringiensisBerliner were scavenged by the Argentine ant. We conclude thatP. luminescensis responsible for preventing ants from foraging on heterorhabditid-killed hosts.     

Bacteriolytic activities of the free-living soil amoebae,Acanthamoeba castellanii,Acanthamoeba polyphaga andHartmannella vermiformis

Bacteriolytic activities of axenically grown free-living soil amoebaeAcanthamoeba castellanii, Acanthamoeba polyphaga andHartmannella vermiformis towards various Gram-positive and Gram-negative bacteria were determined. A spectrophotometric assay revealed that the specific bacteriolytic activities of bothAcanthamoeba species were higher as those of the threeHartmannella strains.Bacillus megaterium, Bacillus subtilis, Chromatium vinosum, Micrococcus luteus andPseudomonas fluorescens were more easily lysed than the other bacteria tested.Agrobacterium tumefaciens, Klebsiella aerogenes andSerratia marcescens were hardly affected at all by the amoebal bacteriolytic activities. Among the Gram-negative bacteria we observed differences in lysis sensitivity while the Gram-positive bacteria tested were sensitive to lysis. Isoelectric focusing (IEF) gel-electrophoresis in the pH range 3–10 was performed to separate the bacteriolytic isoenzymes of amoebae. Bacteriolytic patterns were shown by using an activity assay in which lysis bands were formed in the agar/bacteria gel-overlay. The activity assay revealed remarkable differences in typical banding patterns for bacteriolytic activities among amoebae. Distinct differences between typical pI points of bacteriolytic activities inAcanthamoeba andHartmannella were shown. Bacteriolytic activities ofHartmannella were more pronounced and observed in the isoelectric points (pI) range of 4.0–9.3 while forAcanthamoeba the range was pI 4.5–8.9.Abbreviations IEF isoelectric focusing - PAA-IEF polyacrylamide-isoelectric focusing - CCAP culture collection of algae and protozoa - AS amoeba saline medium - pI isoelectric points     

The effects of host plant on the coccinellid functional response: Is the conifer specialist Aphidecta obliterata (L.) (Coleoptera: Coccinellidae) better adapted to spruce than the generalist Adalia bipunctata (L.) (Coleoptera: Coccinellidae)?

Female Aphidecta obliterata consumed an average of 26.6 ± 5.8 Elatobium abietinum and males consumed an average of 19.9 ± 3.2 Elatobium abietinum, but there was no significant difference in the number consumed between the sexes. In Petri dish trials, the larval stages of A. obliterata and all stages of Adalia bipunctata appeared to exhibit a Type II response to prey density, although A. obliterata adults showed a more linear response to prey density. There was no significant difference between the functional responses of the 3rd instars of the two coccinellid species, but there was a significant difference between the responses shown by the 1st instars, with A. obliterata larvae consuming more than those of A. bipunctata, especially at low densities, suggesting that the two species respond differently to an increase in prey density.At low prey densities, adults and 4th instars of both species exhibited a similar response to an increase in prey density but at higher densities the 4th instars and adult stages of A. bipunctata showed higher attack rates when compared with the same stages of A. obliterata.Adult and 4th instar A. obliterata exhibited Type II functional responses on spruce sections. The 4th instar A. obliterata larva appeared to be a more effective predator than the adult of the species, and was more effective when compared with adult A. bipunctata at lower prey densities but A. bipunctata adults appeared to be a more effective predator at higher prey densities.The host plant affected the rate of consumption by adult A. obliterata as adults on Sitka spruce sections consumed significantly higher numbers of aphids than their counterparts on Norway spruce. This was most noticeable at densities above 16 aphids.The distributions of the two coccinellid species in the olfactometer were significantly affected by the presence of host plant material. Aphidecta obliterata adults were found in significantly higher numbers in the Sitka spruce chambers than the control chambers (those without plant material). Adalia bipunctata adults were found in significantly lower numbers in the Norway spruce chamber than the control chamber.Although A. bipunctata has a higher level of voracity than A. obliterata, the latter is more adapted to the spruce environment and the boom and bust population dynamics of E. abietinum.     

Impact of flowering buckwheat on Lepidopteran cabbage pests and their parasitoids at two spatial scales

We assessed the potential of annual buckwheat, Fagopyrum esculentum Moench, to lead to improved parasitism of lepidopteran cabbage pests over four years. Pest, parasitism, and hyperparasitism rates were monitored in replicated cabbage plots (12 × 20 m) with or without 3 m wide buckwheat borders from 2000 to 2003. Floral borders did not significantly increase egg, larval, or pupal densities of cabbage looper, Trichoplusia ni (Hübner), imported cabbageworm, Pieris rapae (L.), or diamondback moth, Plutella xylostella (L.). Buckwheat increased parasitism rates by Voria ruralis (Fallen) on T. ni larvae and Cotesia rubecula (Marshall) on P. rapaelarvae over four years. Parasitism by Diadegma insulare (Cresson) on P. xylostella larvae was higher in buckwheat than control plots in the first year, and parasitism by Euplectrus plathypenae (Howard) on T. ni larvae was lower in buckwheat than control plots in the second year. The hyperparasitoid Conura side (Walker) attacked D. insulare all four years, but buckwheat did not affect hyperparasitism rates. The effect of spatial scale on pest densities and parasitism in 2001 was evaluated by comparing plots separated at least 67 m (nearby) versus 800 m apart (isolated). T. ni pupae and P. rapae eggs and pupae were more abundant in plots in closer proximity, whereas P. xylostella densities did not vary by the spatial separation of plots. Tachinids and Pteromalus puparum (L.) attacked more P. rapae in nearby plots. E. plathypenae responded to the treatment × scale interaction, parasitizing more in control than buckwheat when plots were isolated but not when plots were nearby.     

Prevalence of agglutinating antibodies against<Emphasis Type="Italic"> Listeria monocytogenes</Emphasis> in chicks of the white stork (<Emphasis Type="Italic">Ciconia ciconia</Emphasis> Linnaeus, 1758) in Poland

In 2002 and 2003, blood samples from white stork (Ciconia ciconia) chicks were examined for the presence of antibodies against Listeria monocytogenes. Listeria antibodies were detected in 121 (59%) of 205 chick samples. The probability of Listeria antibodies being present increased with chick age; chicks detected with Listeria antibodies were in better condition than those without the bacterium.     

Amoebae of the genera Vannella Bovee, 1965 and Platyamoeba isolated from fish and their phylogeny inferred from SSU rRNA gene and ITS sequences

Twenty strains of flattened amoebae including 17 isolated from fish were characterised morphologically both at light microscopical and ultrastructural levels and assigned to either the genus Vannella Bovee, 1965 or the genus Platyamoeba Page, 1969. Sequence-based phylogenetic analyses of SSU rRNA genes from a data set representing a total of 29 strains of flattened amoebae strongly indicated that morphological features discriminating between these genera do not reflect phylogenetic relationships of representative strains. Contrary to a previous study, strains of this expanded assemblage formed clusters that did not reflect their environmental origin. Monophyletic groups were of mixed origins and contained freshwater as well as marine strains of both genera isolated in geographically distant localities of various continents. These findings were supported by results of phylogenetic analyses of selected strains based on ITS sequences. However, topologies of acquired ITS trees were not congruent with results inferred from SSU rRNA analyses.     

Remarkable Salinity Tolerance of Seven Species of Naked Amoebae (gymnamoebae)

The salinity tolerance of naked amoebae collected from sites ranging from ca. 0‰ to 160‰ were compared in laboratory experiments. Amoebae were collected from hypersaline ponds around the perimeter of the Salton Sea, California, where salinities averaged 160‰, and directly from the shoreline waters of the Sea where salinities were generally between 44 and 48‰. Naked amoebae were also collected from the intertidal zone of a Florida beach, a habitat subject (on occasion) to salinity fluctuations within the range 6–85‰. From these combined sites, 6 clones of amoebae were isolated for salinity tolerance experiments (2 marine beach isolates, 2 Salton Sea isolates, and 2 hypersaline pond isolates). A seventh clone, Acanthamoeba polyphaga, a common freshwater/soil amoeba, was obtained from a Culture Collection. Laboratory experiments compared the effects of gradually changing culture salinity versus no salinity acclimatization. Growth rate and culture yield were used as indices of effect. Generally, amoebae were tolerant over a wide range of salinity conditions (in terms of growth and yield) and were not markedly influenced by pre-conditioning to salinity changes throughout the experiments. Overall, the freshwater amoeba Acanthamoeba grew between 0 and 12‰, the marine clones grew in the range of 2–120‰, and the Salton Sea clones reproduced between 0 and 138 ‰. The hypersaline clones were the most resilient and grew between 0 and 270‰ salt. The survival and activity of large populations of naked amoebae in sites subject to salinity fluctuations suggest that they should be considered in future studies to better understand their, as yet, undefined ecological role.     

Relations of intraspecific variations in fecundity, clutch size, and oviposition frequency to the body size in three species of stoneflies, Sweltsa sp., Isoperla aizuana, and Stavsolus japonicus

Most stoneflies oviposit several times during their adult stage. In this study, the relations among oviposition frequency, the number of eggs per egg mass, and body size were examined in the chloroperlid stonefly Sweltsa sp. and two perlodid stoneflies, Isoperla aizuana and Stavsolus japonicus. It was found that larger individuals tended to oviposit more frequently than smaller ones, but the relation was significant only in Isoperla aizuana. In Sweltsa sp. and Isoperla aizuana, the number of eggs per egg mass was higher for the less-frequently ovipositing individuals than for those ovipositing more frequently, and the number of eggs per egg mass decreased with successive oviposition events. Stavsolus japonicus showed the same tendency but it was not statistically significant.     

Synthetic oligonucleotide probes for detection of mercury-resistance genes in environmental freshwater microbial communities in response to pollutants

Mercury-resistance genes were detected byin situ hybridization using new synthetic oligonucleotide probes specific formerA andmerB genes according to the published sequences of the corresponding enzymes. These DNA probes were used for the detection of specific mercury-resistant microorganisms isolated from the Rhine River which had been polluted 3 years previously in 1986. Mercuric reductase and organomercurial lyase genes persist in the bacterial genome even after the disappearance of the pollutant but are absent in axenic amoebae. A total of 49 bacterial isolates showed DNA homologies with the³²P-labelled DNA probes and 15 free-living amoebae were selected due to their harboured symbiotic mercury-resistant bacteria.     

Indirect immunofluorescent staining of the microtubules in interphase and mitotic amoebae of the myxomycetePhysarum polycephalum

Summary The microtubules ofPhysarum amoebae have been decorated with rat antibodies against yeast tubulin. The indirect fluorescent staining observed in interphase amoebae and in flagellated amoebae is consistent with the three-dimensional reconstructions previously deduced from electron microscopic studies. Mitotic amoebae exhibit a pattern of fluorescence which is similar to that exhibited by mammalian cells and is consistent with the previous electron microscopic studies, except that we also observe pole-pole microtubule fibers during metaphase and anaphase and the presence of a typical midbody during cytokinesis. The various types of tripolar mitosis which are observed suggest that there is a regulatory mechanism allowing the formation of pseudo-bipolar mitotic apparatuses in amoebae possessing more than two mitotic centers during mitosis. The mitotic center, located in the middle of the centrosphere, is not fluorescent after staining of the monoasters induced with taxol suggesting the absence of tubulin in the mitotic center.     

The type III secretion system is involved in Escherichia coli K1 interactions with Acanthamoeba

The type III secretion system among Gram-negative bacteria is known to deliver effectors into host cell to interfere with host cellular processes. The type III secretion system in Yersina, Pseudomonas and Enterohemorrhagic Escherichia coli have been well documented to be involved in the bacterial pathogenicity. The existence of type III secretion system has been demonstrated in neuropathogenic E. coli K1 strains. Here, it is observed that the deletion mutant of type III secretion system in E. coli strain EC10 exhibited defects in the invasion and intracellular survival in Acanthamoeba castellanii (a keratitis isolate) compared to its parent strain. Next, it was determined whether type III secretion system plays a role in E. coli K1 survival inside Acanthamoeba during the encystment process. Using encystment assays, our findings revealed that the type III secretion system-deletion mutant exhibited significantly reduced survival inside Acanthamoeba cysts compared with its parent strain, EC10 (P < 0.01). This is the first demonstration that the type III secretion system plays an important role in E. coli interactions with Acanthamoeba. A complete understanding of how amoebae harbor bacterial pathogens will help design strategies against E. coli transmission to the susceptible hosts.     

Prey Preference by the StinkbugPerillus bioculatus,a Predator of the Colorado Potato Beetle

Perillus bioculatus(F.) is sometimes considered a generalist but has most often been recorded as predator of Colorado potato beetle (CPB),Leptinotarsa decemlineata.(Say). This study was designed to analyze prey selection inP. bioculatuswith respect to factors that may lead to specialization. To establish if parental prey determines preference in na?&#x0308;ve progeny, prey selection experiments were conducted with the CPB and two unusual prey, the yellow mealwormTenebrio molitor(L.) and the house cricketAcheta domesticus(L.). Na?&#x0308;ve nymphs reared from yellow mealworm-fed parents in the absence of contact with the CPB initiated feeding more frequently on CPB (81.4%) than on cricket prey (69.6%) (P = 0.038), suggesting genetically inheritable preference for CPB. Progeny from CPBfed parents initiated feeding more frequently on CPB prey (93.3%) than on yellow mealworm prey (76.6%) (P = 0.0001), but progeny from yellow mealwormfed parents initiated feeding on yellow mealworm prey as frequently (89.2%) as on CPB (95.0%) (P = 0.613). Similarly, progeny from CPB-fed parents established proboscis contact more frequently on CPB (39.2%) than on house cricket prey (25.0%) (P = 0.008), whereas those from cricket-fed parents probed house cricket prey as frequently (12.5%) as CPB prey (15.4%) (P = 0.416). Results confirm specialization ofP. bioculatustoward CPB or related prey and suggest genetically inheritable as well as maternally reinforcible affinity toward CPB prey. However, affinity of na?&#x0308;ve nymphs for the CPB can be lowered by rearing parents on alternative prey, increasing their chances of survival when alternative prey must be relied upon.     

Floral development in Adonideae (Ranunculaceae)

Floral development and floral phyllotaxis in species of Adonis, Callianthemum, and Trollius (Ranunculaceae) were studied with scanning electron microscopy. The floral organs are initiated in spiral sequence and the flowers have spiral phyllotaxis. The sepal primordia are broad, crescent-shaped, and truncate, but those of petals, stamens, and carpels are rather hemispherical. A relatively long plastochron appears to be present between the last sepal and the first petal as compared with the short and equal plastochrones of all subsequent floral organs. Maturation of the stamens within the androecium appears to be centripetal. The carpels have a short ascidiate zone. Placentation is uniformly lateral, even in Adonis and Callianthemum, which have only one fertile ovule per carpel (versus median in other genera of Ranunculoideae with a single fertile ovule). In Adonis and Callianthemum at the tip of the carpel the ventral slit is gaping and the stigma is broadly exposed, whereas in Trollius the stigma is narrower and more pronouncedly decurrent along the ventral slit. The petals in Callianthemum and Trollius are more conspicuously delayed in development than those in Adonis as compared with sepals and stamens. A short carpel stipe is formed early in Callianthemum but later in Adonis and Trollius. In Trollius farreri (commonly having only five carpels in contrast to other species of Trollius) the carpels form a single (spiral) series. Thus floral development is similar in all three genera and, at a lower level, Adonis and Callianthemum are especially close but have different autapomorphies, which reflects the current classification of the genera.     

Comparison of polyamine and S-adenosylmethionine contents of growing and encysted Acanthamoeba isolates

We have used High Performance Liquid Chromatography to determine metabolite characteristics of three recent isolates of Acanthamoeba which exhibit cultural characteristics consistent with those of established potential pathogens. Growing amoebae and dormant cysts of these isolates were explored in regard to their qualitative and quantitative intracellular levels of polyamine and S-adenosylmethionine metabolites. The polyamine found in the greatest concentration in the growing cells was 1,3-diaminopropane (DAP), followed by spermidine (SPD). A low level of putrescine was also found in the growing cells. These polyamines significantly decreased in concentration as the amoebae differentiated to cysts. N⁸-acetylspermidine and acetylspermine were found in both developmental stages while acetylcadaverine was found only in growing amoebae and N¹-acetylspermidine only in cysts. Acetylputrescine was present in both stages of two isolates but only in the growing amoebae of the third isolate. Spermine was not detected in any of the isolates.S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) were present in growing amoebae but SAM was undetectable or barely detectable in cysts. SAH also decreased in concentration during encystation of two of the isolates to a level comparable to that of the other isolate.The developmental transition from growing amoebae to dormant cysts is characterized metabolically by a threshold adjustment in concentration of SAM, SAH and of the polyamines (esp., DAP and SPD).     

Cannibalism and Interspecific Predation in a Phytoseiid Predator Guild from Cassava Fields in Africa: Evidence from the Laboratory

Interspecific predation and cannibalism are common types of interaction in phytoseiid predator guilds, but the extent and nature of these interactions have not been determined yet in phytoseiid guilds composed of African native and neotropical exotic phytoseiid predators found in cassava habitat in southern Africa. We determined in laboratory experiments the level of cannibalism and interspecific predation among the three phytoseiid mite species Euseius fustis, Iphiseius degenerans, and Typhlodromalus aripo in the absence of food and in the presence of limited or abundant quantities of two food types – Mononychellus tanajoa and maize pollen – commonly found on cassava in Africa. When confined without food, only two T. aripo females laid each two eggs within 5 days, and this species survived longer than I. degenerans and E. fustis. In the presence of con- or hetero-specific larvae or protonymphs, the three species fed more on the former than on the latter, and more on hetero-specifics than on con-specifics. Oviposition rates of the three species did not exceed 0.7 egg/female/day on con- and hetero-specific immatures. Typhlodromalus aripo and E. fustis survived longer on con-specific and hetero-specific larvae and on hetero-specific protonymphs than in the absence of any food, while T. aripo survived longer than the two other species on the same diets. Provision of limited quantity of food decreased interspecific predation rate by I. degenerans and T. aripo, but not by E. fustis, and increased oviposition rate and longevity of all three species. Provision of abundant food, however, eliminated cannibalism by all three species and further reduced interspecific predation rates, but their oviposition and longevity remained relatively unchanged compared with limited food provision. Potential consequences of cannibalism and interspecific predation among phytoseiid mites on cassava for the biological control of M. tanajoa are discussed.     

Phylogeny of cardinalfishes (Teleostei: Gobiiformes: Apogonidae) and the evolution of visceral bioluminescence

The cardinalfishes (Apogonidae) are a diverse clade of small, mostly reef-dwelling fishes, for which a variety of morphological data have not yielded a consistent phylogeny. We use DNA sequence to hypothesize phylogenetic relationships within Apogonidae and among apogonids and other acanthomorph families, to examine patterns of evolution including the distribution of a visceral bioluminescence system. In conformance with previous studies, Apogonidae is placed in a clade with Pempheridae, Kurtidae, Leiognathidae, and Gobioidei. The apogonid genus Pseudamia is recovered outside the remainder of the family, not as sister to the superficially similar genus Gymnapogon. Species sampled from the Caribbean and Western Atlantic (Phaeoptyx, Astrapogon, and some Apogon species) form a clade, as do the larger-bodied Glossamia and Cheilodipterus. Incidence of visceral bioluminescence is found scattered throughout the phylogeny, independently for each group in which it is present. Examination of the fine structure of the visceral bioluminescence system through histology shows that light organs exhibit a range of morphologies, with some composed of complex masses of tubules (Siphamia, Pempheris, Parapriacanthus) and others lacking tubules but containing chambers formed by folds of the visceral epithelium (Acropoma, Archamia, Jaydia, and Rhabdamia). Light organs in Siphamia, Acropoma, Pempheris and Parapriacanthus are distinct from but connected to the gut; those in Archamia, Jaydia, and Rhabdamia are simply portions of the intestinal tract, and are little differentiated from the surrounding tissues. The presence or absence of symbiotic luminescent bacteria does not correlate with light organ structure; the tubular light organs of Siphamia and chambered tubes of Acropoma house bacteria, those in Pempheridae and the other Apogonidae do not.     

Growth, reproduction and survival of a tropical sea anemone (Actiniaria): benefits of hosting anemonefish

The ecological performance of the sea anemone Heteractis magnifica was examined during a 36-month experiment with respect to season and the presence and numbers of a mutualist (orange-fin anemonefish Amphiprion chrysopterus). Anemones primarily grew during the autumn, with most asexual reproduction occurring in winter; mortality was not strongly seasonal. Individual growth rates did not differ between anemones harboring one or two anemonefish, but these rates were three times faster than for anemones lacking Amphiprion. Anemones with two anemonefish had the highest fission rate, whereas those without anemonefish had the lowest. By contrast, anemones that were not defended by anemonefish suffered higher-than-expected mortality. As a consequence, anemones with two Amphiprion had the greatest net increase in surface area, and those lacking anemonefish had a negligible gain that was statistically indistinguishable from zero after three years. Anemonefish not only enhanced anemone survivorship as previously believed, they also fostered faster growth and more frequent asexual reproduction.