Comparisons of population density and genetic diversity in artificial and wild populations of an arborescent coral,Acropora yongei: implications for the efficacy of “artificial spawning hotspots”

We are developing techniques to restore coral populations by enhancing larval supply using “artificial spawning hotspots” that aggregate conspecific adult corals. However, no data were available regarding how natural larval supply from wild coral populations is influenced by fertilization rate and how this is in turn affected by local population density and genetic diversity. Therefore, we assessed population density and genetic diversity of a wild, arborescent coral, Acropora yongei, and compared these parameters with those of an artificially established A. yongei population in the field. The population density of wild arborescent corals was only 0.27% of that in the artificial population, even in a high‐coverage area. Genetic diversity was also low in the wild population compared with the artificial population, and approximately 10% of all wild colonies were clones. Based on these results, the larval supply in the artificial population was estimated to be at least 1,400 times higher than that in wild A. yongei populations for the same area of adult population.     

Swimming and cleaning in the free-swimming phase of Argulus larvae (crustacea, branchiura)--appendage adaptation and functional morphology

The free-swimming early larval stages of Argulus foliaceus (Linneaus) (Branchiura) are studied using digital video, light microscopy, and SEM. We analyze and document the mode of swimming in the hatching stage of A. foliaceus and the subsequent juvenile stages with fully developed thoracopods. We present new observations and an analysis of the functional morphology of a cleaning behavior in the first stage. This stage swims very efficiently using the large exopods of the second antennae in concert with the mandibular palp (naupliar limbs), while the subsequent stages use the now developed thoracopods for propulsion. This posterior shift in propulsion is similar to--but independent from--what is seen in other crustaceans. The hatching stage has previously been referred as a "metanauplius" but as the first and second maxillae are developed and active, and buds of all four thoracopods are present, it is too advanced to be included in the naupliar phase. The hooks of the first antennae and the distal hooks of the maxillae are demonstrated to function not only as attachment organs (to the host), but also to play a significant role in the cleaning of the naupliar swimming appendages. A digital video-based analysis of the swimming mode is provided. The larval swimming pattern is generally similar to that of other crustaceans such as Branchiopoda and Cirripedia, but autapomorphies of the Branchiura include the following: 1) While actively swimming, the naupliar appendages are almost straight during the recovery stroke and 2) they have a relatively small deflection during movement ( approximately 25 degrees or approximately 35 degrees for mandible and second antenna respectively), 3) the larval mandible has a uniramous palp which is the retained exopod. The morphological implications of the transition from the possibly nonfeeding pelagic, or free-swimming, first larval stage to the feeding, parasitic second stage are discussed and compared with other crustaceans.     

Larval stop,delayed development and survival in overcrowded cultures of Drosophila melanogaster: Effect of urea and uric acid

Uric acid and urea added to non-crowded cultures of D. Melanogaster are able to reproduce the larval stop (cessation in development) detected in highly competitive situations. The quantitative analysis of media as well as of larvae and pupae reveals the presence of both compounds as natural waste products of nitrogen metabolism in Drosophila. The nature of their effect is discussed in terms of larval intoxication as a mechanism which may account for the effects usually observed in crowded cultures: development delay, lower survival and also larval stop (which can only be detected by interrupting the competitive process by an overfeeding technique).     

Captive hybridization of two geographically isolated pygmy angelfish species,Centropyge fisheri and Centropyge resplendens

This study documents the rearing of two pygmy angelfish species, Centropyge fisheri and Centropyge resplendens, and the early life history and reproduction of their hybrid offspring. A C. fisheri female, collected from Hawaii, and a C. resplendens male, captive‐bred from parental stock collected from Ascension Island, were maintained at the hatchery facility for 7 months. Continuous spawning was achieved at a photoperiod cycle of 14L:10D and a water temperature of 26·5° C, range ±1° C. Over the 110 day period, the C. fisheri female spawned 102 times, 57% of which resulted in embryos (fertilized eggs). The mean ±s.d. fecundity per spawn was 730 ± 459 eggs (range 52–1967). Fertility (% eggs that developed into embryos) of all eggs that were preserved was 22·4 ± 25·6%. A total of 235 hybrid juveniles were raised through metamorphosis with an average larval survival of 16·4%. Eight F₁ hybrid juveniles isolated for further study began to display signs of reproductive behaviour c. 300 days post‐hatch (dph). Spawn resulting in non‐fertile eggs were first obtained 319 dph, and fertilized eggs developing into embryos were obtained after 411 dph from at least two female individuals. While no attempt was made at rearing the F₂ larvae, embryo and larval development were normal up to 8 dph. Reproduction and development observed for all hybrid generations in this study were normal, similar to other Centropyge species and indicates a very close phylogenetic relationship between what are currently considered distinct species, e.g. C. fisheri and C. resplendens.     

Pathophysiological influences of the Heterorhabditis bacteriophora complex on fifth-instar larvae of the red humped caterpillar, Schizura concinna: Changes in feeding rate,larval weight,and frass production

At 28.5°C, oral dosages of the invasive juveniles of Heterorhabditis bacteriophora and intrahemocoelic injections of its associated bacterium, Xenorhabdus luminescens, resulted in a decrease in larval feeding rate, larval wet weight, and frass production in its host, the seventh-instar larvae of Schizura concinna.     

Characteristics of larvae of the southwestern corn borer, Diatraea grandiosella, obtained from populations present in tropical and temperate regions

A comparative study was undertaken of southwestern corn borers (Diatraea grandiosella) collected from south central Mexico (19°N latitude) and southeast Missouri (37°N latitude). All the life stages of the Mexican insects were found to be larger or heavier, or both, than were those of the Missouri insects. Mexican larvae grew at a higher rate and attained a significantly heavier body weight than did Missouri larvae. Although both Mexican and Missouri larvae underwent ecdyses during diapause, Mexican larvae ecdysed more frequently than did the Missouri larvae at 23°C light:dark 12 h:12 h. Larvae that ecdysed most frequently did not necessarily spend longer in diapause. Electrophoresis of the fat body and haemolymph proteins of Mexican and Missouri larvae revealed similar patterns. The fat body of diapausing Mexican larvae contained substantial amounts of a diapause-associated protein which has been characterized previously from the fat body of Missouri Larvae. Double immunodiffusion confirmed that the diapause-associated protein of the Mexican larvae was identical to that present in the Missouri larvae. Smaller amounts of this protein appear to be present in the fat body of diapausing Mexican larvae than are present in that of diapausing Missouri larvae.     

Larval development of the invasive charru mussel,Mytella strigata (Bivalvia: Mytilidae)

ABSTRACT

The South American charru mussel, Mytella strigata, was recently recorded in Singapore waters, possibly introduced into Southeast Asia through shipping. The mussels have rapidly spread across estuarine coastal mudflats. Adult mussels were collected, spawned in aquaria and larvae were successfully cultured to the juvenile stage in the laboratory. The larval morphology and development of M. strigata is described in this paper. D-shaped veligers were produced within 20 h of fertilization and were approximately 75 µm in shell length. These larvae were capable of settlement two weeks post fertilization. Given an adequate amount of food, they were able to grow up to 1 mm in shell length within 30 days. The larval shell of M. strigata possesses anterodorsal G2 hinge teeth as distinct wavy ledges, with a pitted resilial ridge clearly evident in the juvenile shell.     

Peptidergic and serotonergic immunoreactivity in the metamorphosing ophiopluteus of Ophiactis resiliens (Echinodermata, Ophiuroidea)

Abstract. Antibodies against the echinoderm-specific neuropeptide S1 and against 5HT were used to examine the fate of the larval nervous system during metamorphosis in the ophiuroid Ophiactis resiliens . In contrast to most echinoderms, the onset of peptidergic and serotonergic expression was delayed to the advanced ophiopluteus stage, in particular for 5HT. In advanced ophioplutei, peptidergic immunoreactivity was located in simple fibres associated with the ciliated bands, a stomach nerve ring, and cells along the antero-lateral arms. 5HT immunoreactivity was concentrated in 2 oral ganglia in the adoral projections, located at the posterior rim of the mouth. Clusters of 5HT-positive cells were also found along the antero-lateral arms. The ophiopluteus lacked a serotonergic (or peptidergic) anterior ganglion. In echinoids, holothuroids, and crinoids, anterior ganglia are thought to have a sensory role in settlement and metamorphosis. Given that ophioplutei metamorphose in the plankton and that larval structures degenerate before settlement, the absence of apical ganglia correlates with the lack of a functional role for larval structures in substrate selection and settlement. Although most of the larval nervous system degenerated during metamorphosis, the adoral projections and associated oral ganglia appeared to be incorporated into the juvenile mouth, suggesting a potential role for larval neurons in contributing to oral neuronal structures in the adult. S1-positive neurons and fibres in the rudiment developed de novo and in parallel with development of the epineural canal. This structure gives rise to the primordia of the adult circumoral nerve ring and radial nerves, indicating that differentiation of the adult nervous system begins in the early stages of metamorphosis.     

Synthesis and deposition of chitin in larvae of the Australian sheep blowfly,Lucilia cuprina

Chitin synthesis in third-instar Lucilia cuprina larvae cultured at 23 °C was investigated using in vivo and in vitro systems, the latter with whole and with homogenized integuments. Synthesis was at a maximum between 24 and 48h after ecdysis from the second instar. Chitin was deposited in layers, and labeled GlcNAc was rapidly cleared from the hemolymph. In in vitro homogenate systems, the rapid conversion of UDP-([¹⁴C]GlcN)Ac to ([¹⁴C]GlcN)Ac and its 1-phosphate derivative contributed to the low incorporation of this precursor into chitin. The extent of the conversion was reduced by the addition of KCN or phenylthiourea. In in vivo and in vitro tissue systems the level of incorporation of ([¹⁴C]ClcN)Ac was higher than that of UDP-([¹⁴C]GlcN)Ac. However, in in vitro homogenate systems there was no difference unless UTP was added when the level of incorporation of only ([¹⁴C]GlcN)Ac was increased (by a factor of 9). Incorporation of UDP-([¹⁴C]GlcN)Ac, but not that of ([¹⁴C]GlcN)Ac, was decreased when larvae were deprived of food. Soluble oligosaccharides were detected in in vitro homogenate systems. They were formed during chitin synthesis and may represent newly initiated chitin chains. A reappraisal of current ideas on chitin synthesis in insects is needed.     

Exploring spatial distributions of larval yellow perch Perca flavescens, bluegill Lepomis macrochirus and their prey in relation to wind

The objectives of the present study were to determine if spatial differences existed between zooplankton, larval yellow perch Perca flavescens and bluegill Lepomis macrochirus (<13 mm total length, L(T)) in Pelican Lake (332 ha), NE, U.S.A. It was hypothesized that wind could act as a transport mechanism for larval fishes in this shallow lake, because strong winds are common at this geographic location. Potential spatial differences were explored, relating to zooplankton densities, size structure and densities of larval P. flavescens and L. macrochirus. Density differences (east v. west side of the lake) were detected for small- (two occasions), medium- (two occasions) and large-sized (one occasion) L. macrochirus larvae. No density differences were detected for small P. flavescens larvae; however, densities of medium- and large-sized P. flavescens were each higher on the west side of the lake on two occasions. There was no evidence that larval P. flavescens and L. macrochirus distributions were related to wind because they were not associated with large wind events. Likewise, large wind event days did not result in any detectable spatial differences of larval P. flavescens and L. macrochirus densities. There appeared to be no spatial mismatch between larval densities and associated prey in the years examined. Thus, wind was not apparently an influential mechanism for zooplankton and larval P. flavescens and L. macrochirus transport within Pelican Lake, and spatial differences in density may instead be related to vegetation and habitat complexities or spawning locations within this shallow lake.     

Ecdysteroid levels and developmental events during larval moulting in the silkworm, Bombyx mori

In the silkworm, Bombyx mori, apolysis of the spiracle is the first visible sign of the initiation of a larval moult. After spiracular apolysis, the characteristic sequence of new spiracle formation can be recognized easily through the cuticle around the old spiracle. This sequence, called the spiracle index, was used as the basis for a precise developmental chronology of the larval moulting period. At certain spiracle-index stages, histological changes in the larval ventral abdominal integument were also examined. By allatectomy and abdominal ligations, the critical periods for the secretion of juvenile hormone and ecdysone respectively were found to be at the initiation of spiracular apolysis and at the time when general apolysis was complete. The haemolymph-ecdysteroid level as measured by radioimmunoassay was about 30–50 ng/ml during the first 2 days of the 4th instar, 60–70 ng/ml at the time of initiation of spiracular apolysis, and 200 ng/ml at the time of completion of apolysis of the general body surface. The maximal level of the hormone was about 290 ng/ml at the mid-moulting period. The relationship between the ecdysteroid titre and morphological events occurring during the larval moult was discussed.     

Transgenerational marking of marine fish larvae: stable-isotope retention, physiological effects and health issues

This study examined the toxicological and physiological responses of a commercially important coral-reef grouper, Plectropomus leopardus (Serranidae), to injection of enriched stable-isotope barium chloride (BaCl₂) solution. Thirty adult P. leopardus were subject to one of two ¹³⁸BaCl₂ injection treatment groups (corresponding to dosage rates of 2 and 4 mg ¹³⁸Ba kg⁻¹ body mass), and a control group in which fish were injected with 0·9% sodium chloride (NaCl) solution. Fish from each group were sampled at post-injection intervals of 48 h and 1, 3, 5 and 8 weeks, at which time blood and tissue samples were removed from each fish. Residual concentrations of Ba and ¹³⁸Ba:¹³⁷Ba ratios were measured in muscle, gonad, liver and bone tissues of each experimental fish. Elevated Ba concentrations were detected in all treatment fish tissue samples within 48 h post injection. Residual Ba concentrations decreased throughout the remainder of the 8 week experimental period in all tissues except bone. The BaCl₂ injection had no significant effects on measured whole blood variables or on the plasma concentrations of steroid hormones. Enriched Ba stable isotopes can therefore be used at low dosages to mark larvae of commercially important marine fishes, without adverse effects on the health of the fishes or on humans who may consume them.     

Seasonal distribution and duration of the planktonic stage of Dover sole, Solea solea, larvae in the Bay of Biscay: an hypothesis

The possibility of deriving a prediction about the effect of seasonal variations in the duration of the planktonic larval phase on the dispersal of larval Dover sole was investigated. During six cruises, from February to May 1992, the distribution of sole larvae was studied along a 100-km transect, from the offshore spawning grounds to the coastal nurseries of the Bay of Biscay (France). Samples ( n = 189) were collected with a suprabenthic sampler, and vertical profiles of water temperature and salinity were recorded simultaneously. Counts of otolith increments of larval stage 4b (onset of metamorphosis) were used to estimate the duration of the planktonic life. Duration of the larval phase decreases by about 15 days (37%) with water temperature increase (between 8° in February and 11.2° C in May). Sole larvae occur from the coastal area to 100 km offshore. Within the same cruise, no difference in the duration of the planktonic life was observed between the larvae caught in the onshore and the offshore area. In spite of seasonal differences in abundance, the extent and the shape of the larval distributions during the period of study suggest that the seasonal variations in the duration of the planktonic life did not affect the larval distribution.     

雷氏黄萤幼虫呼吸系统和呼吸行为

研究雷氏黄萤Luciola leii Fu and Ballantyne幼虫的呼吸系统及其呼吸行为。结果表明:雷氏黄萤幼虫的呼吸系统中只有气管无气囊。前胸、中胸和后胸均分布有气门,无气管鳃,腹部1~8节分布有气门和气管鳃,气门腔基部和气管鳃基部相连,呈"√"状,气管鳃内气管与气门气管相连通。雷氏黄萤幼虫的呼吸行为分为3种:利用胸部气门呼吸、腹部气门呼吸和气管鳃呼吸,其中以腹部气门呼吸为主。     

眉斑并脊天牛幼虫龄数及各龄特征

测定头壳宽度室内观察结果表明,眉斑并脊天牛Glenea cantor(Fabricius)幼虫有4龄。1~4龄幼虫的头壳宽度分别为(0.66±0.20),(1.45±0.20),(2.22±0.23),(3.26±0.29)mm。其龄数(Y)与幼虫头壳宽(X)度符合关系式Y=0.2975+1.1606X。在25℃条件下,1~4龄幼虫的平均龄期分别为(5.25±0.60),(4.94±0.58),(5.98±0.63)d和(22.92±1.28)d,整个幼虫期为(39.09±2.14)d。还对眉斑并脊天牛各龄幼虫的形态特征作了描述。     

Midgut pH in different instars of three Aedes mosquito species and the relation between pH and susceptibility of larvae to a nuclear polyhedrosis virus

Midgut pH values were determined for second, third, and fourth instar larvae of Aedes epactius, A. atropalpus, and A. scutellaris. Larvae were fed mixtures of pH indicators and kaolin clay and observed with a stereoscope to determine midgut pH. No significant difference was found in midgut pH values among the three species when the same instar was compared. However, significant differences were found in the length of the high (9.0 to 10.0) pH region when comparing the three instars for each species. Increasing age of treated A. epactius larvae caused a decrease in susceptibility to a nuclear polyhedrosis virus—from 56% infection for 12-hr-old larvae declining to 8% infection for 72-hr larvae. The increased length of the high pH region may relate to decreasing susceptibility of A. epactius to a nuclear polyhedrosis virus as the larvae age.