Salinity dependence of sexual and asexual reproduction in the rotifer Brachionus plicatilis

A salinity dependent mictic response was observed in a clone of Brachionus plicatilis cultured in the 2 to 4 salinity range. This response was related to asexual exponential reproduction rates (G) and could be divided into three categories: (a) no mixis occurred at a salinity of 35 S and above, where G values were lower than 0.30 d^-1, (b) low mictic levels in rotifers cultured at 2 and 30 S, where G values ranged between 0.40 to 0.50 d^-1, and (c) high mictic levels in rotifers cultured at salinities ranging between 4 and 20 S, where G values ranged between 0.50 to 0.85 d^-1. Fluctuations in mictic levels varied with time during the course of the experiments. Results suggest that salinity conditions leading to optimal parthenogenic reproduction also support mixis.     

A protein signal triggers sexual reproduction in Brachionus plicatilis (Rotifera)

The defining feature of the life cycle in monogonont rotifers such as Brachionus plicatilis (Muller) is alternation of asexual and sexual reproduction (mixis). Why sex is maintained in such life cycles is an important unsolved evolutionary question and one especially amenable to experimental analysis. Mixis is induced by a chemical signal produced by the rotifers which accumulates to threshold levels at high population densities. The chemical features of this signal were characterized using size exclusion, enzymatic degradation, protease protection assays, selective binding to anion ion exchange and C3 reversed phase HPLC columns, and the sequence of 17 N-terminal amino acids. These studies were carried out over two years beginning in 2003 using B. plicatilis Russian strain. When rotifer-conditioned medium was treated with proteinase K, its mixis-inducing ability was reduced by 70%. Proteinase K was added to medium auto-conditioned by 1 female ml⁻¹ where typically 17% of daughters became mictic and mixis was reduced to 1%. A cocktail of protease inhibitors added to conditioned medium significantly reduced degradation of the mixis signal by natural proteases. Conditioned medium subjected to ultrafiltration retained mixis-inducing activity in the >10 kDa fraction, but the <10 kDa fraction had no significant activity. The putative mixis signal bound to an anion exchange column, eluting off at 0.72 M NaCl. These fractions were further separated on a C3 reversed phase HPLC column and mixis-inducing activity was associated with a 39 kDa protein. Seventeen amino acids from the N-terminus have strong similarity to a steroidogenesis-inducing protein isolated from human ovarian follicular fluid. The 39 kDa protein is an excellent candidate for the rotifer mixis induction signal.     

Effect of temperature,salinity and food level on sexual and asexual reproduction in Brachionus plicatilis (Rotifera)

The reproductive response of sexual and asexual female Brachionus plicatilis (Muller) was examined over temperatures ranging from 20° to 40°C, salinities from 5 to 40 S, and food levels from 0.25 to 20 g Chlorella vulgaris dry-weight per ml. Reduced food levels, as well as temperature and salinity extremes, reduced reproduction of both sexual and asexual females, but did so differentially. Reproduction by sexual females was reduced to a greater extent at environmental extremes than asexual females. The broad, flat reproductive response curve of asexual females extended beyond the limits of the narrower, more sharply peaked curve of sexual females. Thus zones of exclusively asexual reproduction exist at environmental extremes where sexual reproduction is physiologically restricted. These results are corroborated by a comparison of the lifetime fecundity of individual sexual and asexual females over a 20°C temperature range. No differences in lifetime fecundity occurred between sexual and asexual females at 18° and 28°C. At 38°C, however, asexual female fecundity reached its highest level, while sexual female fecundity declined 15%. The appearance of sexual females in rotifer populations in the result of both inducible and repressible factors.     

Resting egg formation and hatching of the S-type rotifer Brachionus plicatilis at varying salinities

Several live specimens of the blue-ringed octopus Octopus maculosus were collected from the Philippines in November 1985, and from Japan in February 1986, and the distribution of toxicity, along with toxin composition, in the posterior salivary gland and other soft parts were examined. Tetrodotoxin (TTX: 1400 mouse units g^-1) was detected in the posterior salivary gland of a Japanese specimen, while not only the salivary gland but other soft parts were toxic in the Philippine specimens. The Philippine specimens contained TTX and anhydrotetrodotoxin, the Japanese specimen TTX, 4-epitetrodotoxin, and an unknown toxin. The posterior salivary gland, intestine and other parts were excised from the Philippine specimens and examined for bacterial flora. Twenty-two dominant strains were isolated and cultured in a 2xORI medium (Ocean Research Institute, Simidu and Tsukamoto 1985) at 20°C for 20 to 48 h. Cells were harvested by centrifugation, and disrupted by ultrasonication. The toxins were partially purified from the cell lyzate by ultrafiltration and Bio-Gel P-2 column-chromatography. Instrumental analyses disclosed that 16 of the 22 strains produced TTX and/or related substances. Six strains which clearly exhibited TTX productivity were identified as Alteromonas (2 strains), Bacillus (2), Pseudomonas (1) and Vibrio (1), based on biochemical and biological characteristics. Of these, one strain each of Bacillus and Pseudomonas produced TTX at a level detectable by the mouse assay.     

Mass culture of the rotifer Brachionus plicatilis and its evaluation as a food for larval anchovies

Growth rates of anchovy larvae, Engraulis mordax, reared for 19 days under constant environmental conditions on a diet of laboratory-cultured organisms, exceeded the growth rates of anchovies fed on a diet of wild plankton. The rotifer Brachionus plicatilis was found to be a nutritous food source when fed to the larvae in concentrations of 10 to 20/ml and in combination with the dinoflagellate Gymnodinium splendens (100/ml). Optimum conditions were determined for mass culture of the rotifer. A high food concentration was the most important parameter needed to assure a high yield of rotifers. Large volumes (464 I) of the unicellular flagellate Dunaliella sp. were cultured for feeding the rotifers. The rotifer culture technique described produces approximately 2.5×10⁶ organisms/day, providing a reliable food source for rearing studies. The lengths of B. plicatilis (without eggs) ranged between 99 and 281 , most rotifers being larger than 164 and less than 231 . Individuals weighed 0.16 g and contained 8×10^-4 cal.     

Seasonality of polypide recycling and sexual reproduction in some erect Antarctic bryozoans

The seasonality of polypide cycling has been investigated for three species of erect bryozoans from Antarctica: Isoseculiflustra rubefacta (Kluge, 1914), Nematoflustra flagellata (Waters, 1904) and Himantozoum antarcticum (Calvet, 1905). Approximately ten colonies of each species were collected monthly by SCUBA divers over a 14 mo period during 1992/1993, and the status of each individual zooid was classified as differentiating/regenerating, active (feeding autozooids), degenerate (brown body) or sexually reproductive (ovicells present, or zooid containing a larva). Polypide cycling in all three species was distinctly seasonal. New zooids formed at the growth margin and typically contained actively feeding polypides for ≃9 mo before these polypides degenerated into brown bodies in the austral winter (June). Very few polypides were active in the period from June to August, when water-column food levels were at their lowest; after this period new polypides differentiated. Individual zooids typically underwent a total of five (I. rubefacta and N. flagellata), or at least four (H. antarcticum) complete polypide cycles before becoming senescent. Polypide lifetimes generally became shorter as the age of the zooid increased. Sexual reproduction was also distinctly seasonal in these species, with bands of ovicells or sexually reproductive zooids being formed each year in late summer once a given colony had grown to a threshold size (or age). Larvae were then brooded for ≃10 mo before being released in January/February (N. flagellata) or February/March (H. antarcticum). The seasonal patterns of polypide cycling are related clearly to the variations in food availability, and these species appear to have the longest zooid lifetime (≃5 yr) and the slowest polypide cycling (once per year with polypide lifetimes up to 10 mo) reported for any bryozoan so far. Received: 7 May 1995 / Accepted: 19 November 1997     

Genetic analysis of sexual reproduction in the dendrophylliid coral Balanophyllia elegans

The ahermatypic scleractinian Balanophyllia elegans has served as a model of limited larval dispersal in an aclonal species. However, other species from the same family (Dendrophylliidae) produce larvae asexually, and closely connected polyps of B. elegans, potentially the result of asexual reproduction, are commonly observed in the field. Here, we use a combination of laboratory experiments, controlled crosses, and genetic surveys of field-collected individuals to demonstrate (1) marker allozymes are inherited in accordance with Mendel's laws, (2) polyps that are connected in the field are not genetically identical, and (3) laboratory manipulation of a single polyp can produce a second polyp on the aboral side of the original, but not adjacent to the original. In combination, these results suggest that the larvae of B. elegans result from mictic sexual reproduction, and that connected polyps result not from asexual budding but rather from the fusion of genetically distinct individuals.     

Study of zooplankton emergence pattern and resting egg diversity of recently dried waterbodies in North Maharashtra Region

Seasonal patterns of temperature, pH, conductivity dissolved oxygen, phosphate and sulphate have been studied on the basis of physico-chemical characteristics of pond ecosystem. Importance of soil egg banks and their contribution to the diversity in freshwater ecosystem has been studied. We have focussed our attention on soil egg bank diversity and zooplankton emergence patterns of some recently dried aquatic habitats, comparing to that of neighbouring temporary pools with the permanent ponds. The emergence pattern from the soil egg bank followed an orderly succession from Protists-Rotifers and Crustaceans have been investigated. Dominant Protists emerged from the egg bank were Lacrymaria within rotifers. They were the first to emerge followed by Hexarthra blooms. The diversity of zooplankton in permanent ponds was significantly higher (i.e., 19) than the diversity in the ephemeral pools (i.e., 08). However; the zooplankton abundance in the ephemeral pools was higher with more than an order of magnitude, than that in ponds. Interestingly the number of species recorded in the egg bank was more than those present in the water columns of the pools. We have recorded 08 species of rotifera i.e. Lecane sp L curvicornis, L. bulla, K. quadrata, B. patulus, B. rubens, Branchionus calyciflorus, Testudinella sp which were not present in the neighboring permanent or ephemeral waterbodies during that period. Unequivocally suggest that in order to understand the zooplankton biodiversity; it is also important to evaluate the diversity of egg bank present in the sediment. A total 19 species were recorded including Copepoda 06 sp, Cladocera 05 sp and Rotifera 08 sp.     

Relationship between growth rate and egg production in the copepod Acartia clausi hudsonica

Egg production by Acartia clausi hudsonica ceases at low concentrations of Isochrysis galbana as food and at high levels reaches a maximum that increases with temperatures in the natural range. This increase parallels the rate of production of fecal pellets. Females without males can produce about 400 eggs before entering a generally short postreproductive period. Weight increments between copepodite stages are exponential and, assuming isochronal durations of stages and that development time of older stages is the same mutiple of embryonic duration at all temperatures, a temperature-dependent rate is estimated for pre-adult growth. We demonstrate that this growth rate also predicts the observed maximal rate of egg production by the nongrowing adult females. Published data for other copepod species (except Pseudocalanus) are inadequate for wider testing of this hypothesis, but available data do suggest that no such simple rule governs total output of eggs by females of different species.     

Spatial and temporal variability in egg production rates of the calanoid copepod Acrocalanus inermis

Egg production rate of the copepod Acrocalanus inermis was measured at 3 stations in south Kaneohe Bay, Hawaii in August 1977 and July–October 1979. The egg production rates were significantly variable spatially, but temporal variability over a time scale of weeks was larger than spatial variability. In three experiments, egg production rates were correlated with ambient concentrations of particulate matter, a crude estimate of food concentration. Most values for egg production rates ranged between 5 and 16.9 eggs female^-1 d^-1.     

Comparative aspects of sexual reproduction in the Caribbean coral genus Diploria (Scleractinia: Faviidae)

The increasing decline of Caribbean reef-building species underlines the importance of more information on their reproductive biology and ecology. This study compares the reproductive biology of the three species of Diploria, an important Caribbean reef-building genus affected by bleaching and disease, by: (a) characterizing their gametogenetic cycles simultaneously, (b) exploring the spatial and temporal variability in reproductive traits within and across species, (c) assessing fecundity and the minimum size of sexual reproduction, and (d) comparing information with other studies in the Caribbean. Starting in 1999, one tissue core was collected every month (for 17 months) from each of at least five large, tagged colonies of each species in La Parguera, Puerto Rico. Three more temporally spaced samplings were done during summer of 2000 and winter–spring of 2001 and 2002. Tissues were fixed in Helly’s solution, rinsed in fresh water, decalcified with 10% HCl, and preserved in 70% ethanol, embedded in paraplast, cut, and thin slides (7 μm) prepared and stained with Heidenhain’s Aniline-Blue method. Maximum egg size, number of eggs and spermaries were measured and gametogenetic cycles assessed. Microscopic observations confirmed that all three species were simultaneous hermaphrodites with a single, annual gametogenetic cycle. Spermatocytes and oocytes developed within the same mesentery but were not intermingled. Female gametes developed several months earlier than that of males, but both reached maturation simultaneously. Minor differences in the onset of gametogenesis were found for D. strigosa and D. clivosa, with both spawning after 10 p.m. between 8 and 10 days after the August and/or September full moons. D. labyrinthiformis on the other hand, began oogenesis in early July and spawned after 11 p.m. between 7 and 10 days after the April and/or May full moons. Spatial and temporal variability in mean number of spermaries and eggs/mesentery among colonies within and among species were found. D. labyrinthiformis had consistently significant higher mesenterial and polyp fecundity compared to the other two species over the 3 years. Average egg diameter varied between 240 and 246 μm and was similar among the three species. D. strigosa and D. clivosa sexual reproductive characteristics were similar to those of other large broadcast spawning Faviidae (i.e. Montastraea spp) in the region. In contrast, D. labyrinthiformis was a spring spawner (similar to Colpophyllia natans in Puerto Rico), which together with its significantly different micromorphology suggests that it might be phylogenetically more distant to the other taxa.     

Divide or broadcast: Interrelation of asexual and sexual reproduction in a population of the fissiparous hermaphroditic seastar Nepanthia belcheri (Asteroidea: Asterinidae)

Asexual and sexual reproduction were studied in an intertidal population of Nepanthia belcheri (Perrier) at Townsville, Queensland, Australia, by regular sampling over a year (March 1976-March 1977) and by histological analysis of gonads. Fission reached a peak in early winter (April–June), when about 45% of the population showed evidence of recent fission. Propensity for fission was unrelated to longest arm length. Seven-armed seastars predominated in the population and these underwent fission in two stages to produce one 3-armed fragment and two 2-armed fragments. Fission planes were not related to numbers or positions of madreporites. Hermaphroditism was a normal sexual condition in the population. Almost all gonads contained oocytes, but some gonads functioned as ovaries (without spermatogenic tissue) while others functioned as testes. Seastars with mature ovaries were significantly larger than those with mature testes, indicating protandry, as in other hermaphroditic asteroids. However, fission complicates the pattern of gonad development by causing regression or retardation of gonads and by apparently having a masculinizing effect, so that ovaries may change to testes in fission products. There was a period of sexual reproduction in early summer (October–November). This followed the period of intense fission and regeneration, and a population change from predominately functional females to males. Consequently there was an extreme imbalance against mature females at sexual reproduction, further reducing potential fecundity. Thus, sexual reproduction was very subordinate to fission as the means of recruitment. The 450 m diam eggs probably give rise to pelagic lecithotrophic development and, if this is the case, N. belcheri retains the advantage of complementing reliable recruitment from fission with a dispersive phase. The combination of fission and hermaphroditism is particularly advantageous for a very sparse dispersal of larvae, as a functionally dioecious population may develop from one larva settling in a new locality.     

Experimental support for the use of egg uniformity in parasite egg discrimination by cuckoo hosts

Common cuckoo (Cuculus canorus) parasitism drastically reduces the reproductive success of their hosts and selects for host discrimination of cuckoo eggs. In a second stage of anti-parasite adaptation, once cuckoos can lay eggs that mimic those of their hosts, a high uniformity of host egg appearance within a clutch may favour cuckoo egg discrimination. Comparative evidence provides indirect support for this hypothesis although experimental support is currently lacking. Here, we studied the effect of experimentally decreased uniformity of host egg appearance on cuckoo egg discrimination by great reed warbler (Acrocephalus arundinaceus) hosts in a population in which long-term cuckoo parasitism has led to high levels of cuckoo–host egg mimesis. We manipulated host clutch uniformity by adding extra spots to fresh host eggs just after they were laid. Rejection of non-mimetic experimental eggs added to these nests was compared with those in control nests in which uniformity was not altered. Previously, by over-painting real spots in a control group of nests, we showed a negligible effect of our paints on hosts’ perception of their eggs. We show that for the great reed warbler, non-mimetic experimental eggs were relatively more tolerated in experimental nests, i.e. with lower uniformity (40%) than in control nests (5%). This is the first experimental study, to our knowledge, which demonstrates a reduced discrimination of foreign eggs as a consequence of an increase of egg phenotypes variation perception in a cuckoo host.     

Effect of food availability on egg production and packaging in the intertidal scavenging gastropod Nassarius festivus

Individuals of the scavenging gastropod Nassarius festivus (Powys) were maintained for 12 weeks at one of the three ration levels, i.e. one meal every 2, 7 or 14 d, and the effect on growth and fecundity were determined. The number and size of egg capsules, number of eggs per capsule and the calorific value of eggs together with the egg capsules decreased as food availability decreased. The size of the eggs, however, was not affected. At the end of the experiment, the cumulative mortalities were high for individuals maintained at the high and medium ration and were 56.3% and 50%, respectively, whereas the mortality was only 16.7% at the low ration. There was no increase in the shell length but a decrease in the total wet weight for all the treatments. As food availability decreased, the proportion of consumed energy allocated to reproduction decreased from 7.2% to 1.4%. This plastic life history may be a mechanism enabling scavengers to survive in an environment of which the food availability is patchy and unpredictable. Received: 14 August 1998 / Accepted: 23 July 1999     

Laboratory studies of the marine copepod Centropages typicus: egg production and development rates

Egg production and development rates of Centropages typicus (Krøyer) were studied in the laboratory under carying food and temperature conditions. Egg production rates in the laboratory ranged from 0 to 124 eggs female^-1 d^-1 and increased with food concentration up to a critical food concentration (P_c) above which egg production was constant. Egg production rates were influenced by temperature, with more eggs being produced at 15°C than at 10°C. Thalassiosira weisflogii and Prorocentrum micans were determined to be equally capable of supporting egg production at concentrations above P_c at 15°C. Rate of egg production was independent of adult female size when food and temperature were constant. Egg production rates of freshly captured females ranged from 0 to 188 eggs female^-1 d^-1 and were higher in April and May than in June or July. Hatching rates of eggs increased with increased temperature; 95% of the eggs at 15°C hatched within 48 h, while only 8% of the eggs at 10°C hatched within 48 h. Development rates, determined at 10°C in excess concentrations of T. weisflogii, were 23.0 d from egg release to copepodid state I, 27.0 d to stage II, 29.5 d to stage III, 32.2 d to stage IV, 38.5 d to stage V and 49 d to adulthood based on the average time required for 50% of the organisms in an experiment to attain a given stage. Adult males were usually observed 2 to 4 d before adult females, and therefore have a slightly faster rate of development. The effects of temperature, food type and food concentration on egg production and the seasonal appearances of diatoms in the New York Bight may account for the observed seasonal cycles in abundance of C. typicus in these coastal waters.     

Reproductive conflicts and egg discrimination in a socially polymorphic ant

The ability to discriminate against competitors shapes cooperation and conflicts in all forms of social life. In insect societies, workers may detect and destroy eggs laid by other workers or by foreign queens, which can contribute to regulate reproductive conflicts among workers and queens. Variation in colony kin structure affects the magnitude of these conflicts and the diversity of cues used for discrimination, but the impact of the number of queens per colony on the ability of workers to discriminate between eggs of diverse origin has so far not been investigated. Here, we examined whether workers from the socially polymorphic ant Formica selysi distinguished eggs laid by nestmate workers from eggs laid by nestmate queens, as well as eggs laid by foreign queens from eggs laid by nestmate queens. Workers from single- and multiple-queen colonies discriminated worker-laid from queen-laid eggs, and eliminated the former. This suggests that workers collectively police each other in order to limit the colony-level costs of worker reproduction and not because of relatedness differences towards queens’ and workers’ sons. Workers from single-queen colonies discriminated eggs laid by foreign queens of the same social structure from eggs laid by nestmate queens. In contrast, workers from multiple-queen colonies did not make this distinction, possibly because cues on workers or eggs are more diverse. Overall, these data indicate that the ability of F. selysi workers to discriminate eggs is sufficient to restrain worker reproduction but does not permit discrimination between matrilines in multiple-queen colonies.     

Parental care and the cost of reproduction in a Mediterranean fish

Summary Symphodus tinca is a common near-shore Mediterranean labrid fish in which females may sometimes spawn their eggs over hundreds of square meters, or alternatively spawn into well-defined algal nests. Eggs spawned in either manner are fertilized, but widely scattered eggs receive no parental care, whereas eggs spawned into nests are usually guarded by the male until they hatch. Here, I report weight changes of individual marked fish that engaged in a variety of different reproductive behaviors during three breeding seasons. Males gained weight at 0.15% per day outside the spawning season, and added 29–78% to their overall body weight between reproductive seasons, even following substantive weight losses in a spawning season (up to 20% among nesting males). Nesting and nest-guarding males lost an average of 0.32% and 0.41% of their body weight per day in 1986 and 1987. This cost is four times greater than reproduction for nonnesting males, which registered a 0.03% daily weight gain. Actively spawning females lost 0.06% of their body weight daily during the spawning season. While long-term growth rates did not appear to be substantially affected by reproduction in either sex or by parental care in males, present work does not exclude the possibility that such long-term effects may exist.     

Limb regeneration and subsequent asymmetry in a male secondary sexual character influences sexual selection in wolf spiders

Males of the brush-legged wolf spider Schizocosa ocreata (Hentz) have conspicuously decorated forelegs used in courtship and agonistic displays. Approximately one in five juvenile males has a missing or regenerating foreleg, and regeneration of a leg lost during development usually results in the absence of a decorative tuft on that leg. The subsequent asymmetry in this male secondary character significantly decreases success in both courtship of females and male-male agonistic interactions. Experimental removal of tufts from one leg of previously successful symmetric males produces similar results. As a test for concomitant behavioral effects, female spiders were shown video images of a courting male with symmetric tufts and the same video image altered to have asymmetric tufts. Female receptivity to the asymmetric video image was lower. In contrast to fluctuating asymmetry resulting from developmental instability, leg tuft asymmetry in S. ocreata most likely arises from a single event during ontogeny – possibly leg loss from an aggressive or predator encounter  – and may serve as a quality indicator in female mate choice. Received: 27 July 1995/ Accepted after revision: 19 November 1995     

Diet and egg production of the copepod Acartia tonsa in Florida Bay. II. Role of the nutritional environment

 As part of an ongoing study of changes in the trophic pathways of Florida Bay's pelagic ecosystem, the nutritional environment (seston protein, lipid and carbohydrate levels), diet (taxon-specific microplankton ingestion rates) and egg production rate of the important planktonic copepod Acartia tonsa were measured off Rankin and Duck Keys in July and September 1997 and in January, March and May 1998. Rankin Key has been the site of extensive sea grass mortality and persistent ultraplankton blooms since 1987. Duck Key has experienced neither of these perturbations. Protist (auto-plus heterotroph) biomass was approximately twice as high off Rankin as off Duck Key. Diatoms, dinoflagellates and heterotrophic protists dominated the food environment off Rankin Key, while cells <5 μm diam often predominated off Duck Key. Protein and carbohydrate concentrations were higher off Rankin Key than Duck Key, while average lipid levels were usually low at both stations. Ingestion rates at both stations frequently approached temperature- and food-dependent maxima for the species, exceeding 100% of estimated body C d⁻¹ on 3 of 5 occasions off Rankin Key. Egg production rates, however, were consistently low (Rankin: 3 to 16 eggs copepod⁻¹ d⁻¹; Duck: 1 to 12 eggs copepod⁻¹ d⁻¹), and gross egg production efficiencies (100% × egg production C/ingested C) averaged <10%. At Duck Key, egg production rate varied with temperature and food concentration, while off Rankin Key, egg production was strongly correlated with seston protein content. The efficiency with which lipids (which were scarce in the seston) were transferred from the diet to the eggs increased exponentially with decreasing seston lipid content. Egg production efficiencies based on protein, however, were independent of seston protein content and never exceeded 10%. Received: 23 December 1998 / Accepted: 23 March 2000