Parthenogenetic reproduction of Diaphanosoma celebensis (Crustacea: Cladocera): influence of salinity on feeding, survival, growth and neonate production

 Effect of salinity on the feeding rate and parthenogenetic reproduction of asexual females of the cladoceran Diaphanosoma celebensis Stingelin was studied. Short-term (10 h) grazing experiments were conducted using Isochrysis galbana as feed at 5, 17, 25 and 30 psu salinity. Gut pigment concentration showed a significantly higher rate of feeding at lower salinities. Survival, growth, maturity attainment and neonate production of asexual females reared in the above four test salinities indicated preference for lower salinities (5 and 17 psu). The mean size of adult females decreased from 909 to 593 μm, mean life span from 24 to 5 d, mean neonate production from 12 to 2 and mean size of neonates from 434 to 400 μm as the salinity increased from 5 to 30 psu. Salinity variations also affected the size and age of primiparous females. Resting egg formation and sexual reproduction did not occur at the tested salinities. The results indicate that D. celebensis is adapted to low saline, estuarine environments. Received: 14 January 2000 / Accepted: 24 March 2000     

Metabolic differences between “demersal” and “pelagic” development of the Antarctic sea urchin Sterechinus neumayeri

 Early development of the Antarctic sea urchin Sterechinus neumayeri was examined under two differ-ent culture regimes: one to simulate development near-bottom (“demersal development”) and the other to simulate the development of embryos in the water column (“pelagic development”). When embryos of both treatments reached the hatching blastula stage at 5 d post-fertilization (−1.5 °C), the blastulae that had undergone demersal development evidenced significant differences (by ANOVA or suitable non-parametric comparison) in the following: a thicker blastoderm layer (12%, P < 0.001), higher ash-free dry weights (19%, P < 0.01), lower mass-specific respiration rates (50%, P < 0.001), higher incorporation rates of ³⁵S-methionine into protein (23%, P < 0.003), and a differential pattern of protein synthesis. When embryos developed demersally, they remained in the jelly-coat material released with the eggs at spawning. Quantitative isolation of this jelly-coat material in S. neumayeri demonstrated that it contained a significant amount of organic matter, 115 ng ash-free dry mass per egg, equivalent to 17% of the egg's initial organic mass. Uptake of external nutrients during embryogenesis may be a significant component of the physiological energetics of this polar invertebrate by allowing the utilization of jelly-coat material released by a female during spawning. Received: 21 April 1999 / Accepted: 5 June 2000     

Short retention times of stomach temperature loggers in free-living seabirds: is there hope in the spring?

Stomach temperature loggers have proved useful for the study of feeding activity in free-living seabirds, but their usage has been restricted because they are frequently dislodged and lost during the seabirds' regular regurgitation of indigestible prey remains. In the present study we examine the incidence of spontaneous regurgitation (pellet production) in free-living seabirds, consider the effect this has on the likely retrieval of stomach temperature loggers and present a structural modification of the logger housings which leads to a much lower incidence of regurgitation. Systems were tested on albatrosses, cormorants, gannets and penguins. Received: 15 July 1997 / Accepted: 31 October 1997     

Simultaneous hermaphroditism in the marine shrimp Lysmata wurdemanni (Caridea: Hippolytidae): an undescribed sexual system in the decapod Crustacea

Simultaneous hermaphroditism with outcrossing, a previously unconfirmed sexual system in decapod crustaceans, is documented in the shrimp Lysmata wurdemanni (Gibbes), using time-lapse video observations on mating in pairs of “female-phase” (FP) individuals. Copulations between FPs resulted in successful spawning and development of embryos. However, female-phase hermaphrodites maintained in isolation were unable to self-fertilize spawned eggs. All smaller individuals possessed characters typical of caridean males, including male gonopores, appendices masculinae, ejaculatory ducts, and cincinnuli on the first pleopods. However, the gonad of these male-phase (MP) individuals was an ovotestis with an undeveloped ovarian portion. FPs, which spawn eggs and incubate embryos, also had male gonopores and an ovotestis terminating in ejaculatory ducts containing sperm. In FPs, male pleopod characters were absent or reduced, and a female incubatory character, expanded pleopod flanges, showed a greater relative size. Smaller size classes of the population were composed only of MPs while larger size classes consisted of both MPs and FPs. “Transitionals,” individuals with MP characters but an ovotestis containing vitellogenic oocytes, were rare and overlapped completely in size with FP and larger MP individuals. It is suggested that not all MPs transform into FP hermaphrodites. Social interactions may mediate MP change into FP hermaphrodites in L. wurdemanni. The social system of L. wurdemanni and other Lysmata spp. may determine the exact form of the sexual system in these species. Received: 26 October 1997 / Accepted: 21 April 1998     

Elemental (C, N and P) analysis of metamorphosing bonefish (Albula sp.) leptocephali: relationship to catabolism of endogenous organic compounds, tissue remodeling, and feeding ecology

Whole-body carbon (C), nitrogen (N) and phosphorus (P) content, and stable-isotope composition (¹³C:¹²C and ¹⁵N:¹⁴N), were followed during metamorphosis of bonefish (Albula sp.) larvae (leptocephali). Metamorphosing larvae depend entirely on endogenous carbon compounds (some of which contain N and P) as an energy source. Two fundamental questions are (1) Do the demands of extensive tissue remodeling during metamorphosis require the efficient retention of N and P during the catabolism of carbon compounds? (2) What effect does the lack of feeding have on stable-isotope composition? Our results showed that both C and N decreased by ～35 to 40%, reflecting the utilization of neutral lipid (triacylglycerols) and N-containing compounds (phosphatidylethanolamine and keratan sulfate glycosaminoglycan) as energy sources, and indicating that larvae have little or no capacity to retain N. Evidence suggested that collagen breakdown, measured as a loss of hydroxyproline content, also contributed to N loss. Stable-isotope ratios, expressed as ¹³C and ¹⁵N, showed no statistically significant differences in early and advanced metamorphosing larvae. In contrast to C and N, phosphorus was conserved during metamorphosis and most probably is utilized in the increased bone mineralization occurring in advanced larvae. We show, however, that advanced larvae are P-limited and that normal ossification is dependent upon a supply of exogenous P obtained after the resumption of feeding. The N:P ratio of 12.3 in early larvae decreased to 8.1 in advanced larvae owing to the conservation of P as N was lost. The mean ¹⁵N value in early metamorphic larvae (11.6‰) is consistent with results from other studies, and provides further support for the view that premetamorphic leptocephali feed at a very low trophic level.     

Effects of UV radiation of different wavebands on pigmentation, 15N-ammonium uptake, amino acid pools and adenylate contents of marine diatoms

Three marine diatoms Lauderia annulata Cleve, Odontella sinensis (Greville) Grunow and Thalassiosira rotula Meunier were exposed to ultraviolet (UV) radiation of different wavebands under controlled laboratory conditions (0.035 vol% CO₂, 18 °C). Several changes in the patterns of pigments in these organisms were seen depending on the waveband of UV radiation and species examined. UV-B and UV-B plus UV-A radiation led to a reduction in the overall pigment content of all three diatoms. The uptake of ¹⁵N-ammonium was less affected by 5-h UV-A (WG 320) but significantly reduced after UV-B and UV-B plus UV-A exposure. The pattern of free amino acid pools varied depending on the applied UV wavebands and the tested diatom. The main protein-bound amino acids of T. rotula decreased after 5-h UV irradiance except leucine. Contents of adenosine 5′-mono-, di-, and triphosphate (AMP, ADP and ATP) were affected differently by UV radiation; ATP values increased at the end of UV-B and UV-B plus UV-A exposure. These results have been discussed with reference to the impact of the different UV sources and the influence on the nitrogen metabolism in connection to pigments and supply with energy. Received: 13 May 1997 / Accepted: 11 October 1997     

Consequences of communal gall occupation and a test for kin discrimination in the aphid Tamalia coweni (Cockerell) (Homoptera: Aphididae)

This study investigated the consequences of communal gall induction on individual and group fitness in the aphid Tamaliacoweni. The possibilities that kin discrimination and foundress density are factors favoring communal gall occupation were examined. Clonally produced aphid foundresses were collected to create two treatments: clonal groups and groups of less closely related individuals. These were confined on suitable host plant tissue to compare their respective propensities towards communal behavior. There were no significant differences in the frequencies of communal gall occupation; therefore, active kin discrimination by T.coweni foundresses apparently does not play a role in their communal behavior, within the context of this experiment. In a second experiment, aphid foundress density on the host plant was manipulated in three treatments and was correlated with the frequency of communal gall occupation. Individual fitness was inversely related to the mean number of foundresses per gall. These results suggest that communal gall occupation does not necessarily represent mutual cooperation but may instead be the outcome of competition for limited gall sites on the host plant. However, natural selection at the clonal level may favor communal gall occupation under the conditions of resource limitation and high within-group relatedness. Received: 26 September 1997 / Accepted after revision: 28 March 1998