Occurrence of additional Zoea-VI larvae in the mud crab, Scylla paramamosain (Estampador), reared in the laboratory

Mud crabs, Scylla spp. , are commercially important in many Indo-Pacific countries. The larval development of mud crabs has been reported previously as five zoeal and one megalopal stages. This paper reports larval rearing experiments that revealed variability in larval developmental stages in the mud crab Scylla paramamosain, one of four mud crab species. In addition to normal five zoeal stages, an alternative pathway of developing through six zoeal stages was observed for the crab. There were evidences suggested that the appearance of the additional Zoea-VI larvae was associated with unfavourable dietary conditions, including poor quality of diet, inadequate quantity of dietary supply and a period of starvation for newly hatched larvae. Based on exuviae and larval specimens, the morphology of the additional Zoea-VI larvae was described.     

The larval development of an Australian limnadiid clam shrimp (Crustacea, Branchiopoda, Spinicaudata), and a comparison with other Limnadiidae

The adult morphology of the Australian Limnadopsis shows some remarkable differences to that of other Limnadiidae. These differences are not reflected in its larval development. In Limnadopsis parvispinus, larval development comprises six stages. In stages I and II only the three naupliar appendages are present: the antennule as a small bud, the biramous antenna as the main swimming organ, and the mandible. The antennal protopod bears two endites, the proximal naupliar process and a more distal endite. In stage III a bifid naupliar process (in earlier stages not bifid) and the first signs of the carapace and trunk limb anlagen (undifferentiated rudiments) appear. In stage IV the carapace anlagen become more pronounced. The number of trunk limb anlagens increases to five, and differentiation has commenced. In stage V the first five pairs of trunk limbs are differentiated to varying degrees. The anterior-most four pairs of trunk limbs are subdivided into five endites, a small endopod, an exopod and an epipod. The bivalved carapace covers the anterior-most limbs. In larval stage VI the carapace is larger and the trunk limbs are further differentiated. A general pattern in the sequence of larval stages is the increasing number of sensilla on the antennules. From the last larval to the first postlarval stage, a significant change in morphology takes place. The trunk limbs are now used for swimming. Typical larval organs are much smaller than in the last larval stage. A comparison with other representatives of the Limnadiidae shows a high degree of correspondence, with most differences explained by the heterochronous appearance of characters during development. Five to seven stages are described for all studied Limnadiidae, including one particular stage in which four fully developed setae, a bifid naupliar process and the first signs of carapace anlagen are present. These characters are found in stage III in L. parvispinus, Limnadia stanleyana, Eulimnadia texana, and Imnadia yeyetta but in stage IV in E. braueriana and L. lenticularis. Based on a comparison of the larval stages of six limnadiid and one cyzicid species, we conclude that at least six naupliar stages belong to the limnadiid ground pattern.     

Comparison of otolith and scale readings for age and growth estimation of common dentex Dentex dentex

Three methods of age estimation were compared for Dentex dentex. Based on sectioned otoliths, scales appeared to be relevant only up to 5 years and whole otoliths up to 12 years. The maximum estimated age was 36 years, which constitutes to date the oldest age reported.     

Biology of the harlequin fish Othos dentex (Serranidae), with particular emphasis on sexual pattern and other reproductive characteristics

Key biological characteristics of the harlequin fish Othos dentex, a representative of a monospecific genus of the Anthiinae (Serranidae), were determined from samples collected around reefs on the south coast of Western Australia. The females of this relatively long‐lived species (maximum recorded age in this study = 37 years) attained only a slightly greater maximum total length and age than males and neither the length nor the age‐frequency distributions showed a conspicuous sex‐based bimodality. Furthermore, gonads from a wide size and age range of O. dentex were shown by histology, at several locations along their length, to always comprise exclusively either ovarian or testicular tissues. Thus, O. dentex is a gonochorist, a sexual pattern only previously recorded definitively for one other anthiine serranid, i.e. Epinephelides armatus, which also occurs in south‐western Australia. Similar to E. armatus, O. dentex possesses ‘solid’ testes with a central sperm duct, thereby differing in structure from those typically found in serranids, in which there is a central membrane‐bound ‘ovarian’ lumen and peripherally located sperm sinuses. The gonadal characteristics and sexual pattern of these two gonochoristic anthiines are not consistent with a recent proposal for the trends exhibited by the evolution of gonochorism and protogyny within the Serranidae. Othos dentex has indeterminate fecundity and a protracted spawning period (7 months) and, on the basis of underwater observations and a low gonado‐somatic index (I_G) for males, is a pair spawner, which is unusual for a gonochorist of a serranid or member of a related family. While the large spots on the lower half of the body of O. dentex are shown quantitatively to be similarly yellow in juveniles and adult females, they then become blue in males at maturity and this intensifies during the spawning period, when they presumably play an important role in agonistic interactions among males and courtship with females. The attainment of maturity and rapid growth by O. dentex early in life may reflect selection pressures to reduce predation mortality during that period. Total mortality in the population is moderately low during later life, implying that the current fishing pressure on O. dentex is relatively light.     

The Opecoelidae (Digenea) of sparid fishes of the western Mediterranean. IV.Peracreadium Nicoll, 1909 andCainocreadium Nicoll, 1909

The generaPeracreadium Nicoll, 1909 andCainocreadium Nicoll, 1909 are redefined and their validity discussed. Only one species ofPeracreadium, P. characis (Stossich, 1886) n. comb., is believed to occur in the Mediterranean region. This species, which is restricted toDiplodus [=Puntazzo] puntazzo and had previously been considered to be aspecies inquirenda, is redescribed and distinguished from other species of the genus; a neotype is designated.Cainocreadium labracis (Dujardin, 1845), the only species of the genus occurring in the Mediterranean region, is described fromDentex dentex and discussed in relation to its more usual host, the moronidDicentrarchus labrax.

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Résumé Les auteurs redéfinissent et discutent la validité des genresPeracreadium Nicoll, 1909 etCainocreadium Nicoll, 1909. Dans le genrePeracreadium, une seule espèceP. characis (Stossich, 1886) n. comb. a été trouvée jusqu'à ce jour en Méditerranée; elle parasiteDiplodus (=Puntazzo) puntazzo. Cette espèce était considérée comme unespecies inquirenda; elle est redécrite et comparée aux autres espéces de ce genre; un néotype lui est attribué. Dans le genreCainocreadium, une seule espèceC. labracis (Dujardin, 1845) est connue de Méditerranée. Celle-ci est redécrite à partir d'exemplaires trouvés chezDentex dentex.

     

Identification of adults and larvae in Spiochaetopterus (Polychaeta, Chaetopteridae): consequences for larval transport and recruitment

This work is based on recent studies describing new species in Spiochaetopterus (Annelida Polychaeta). New morphological features were brought to light in studies of adults from widely separate areas. A parallel study of planktonic larvae in three areas (northern Atlantic Ocean, Gulf of California, Mediterranean Sea) led to the isolation of several larval categories, each related to an already described species. The large number of species already described shows that the founder species has been subjected to an intense adaptive radiation and that in spite of the ability of larvae to disseminate, each species now inhabits only a limited geographical area. Teleplanic larvae are thus not as effective as is generally supposed in controlling the adult area. The new paradigm implies that individuals from widely separate areas belong to species other than Spiochaetopterus costarum. Although larvae of each species are capable of covering long distances, larval transport may be interrupted at various stages of the life cycle for a variety of reasons. The most powerful causes of failure are not linked to the lifespan of planktonic larvae, but rather to constraints on the ability to realize physiological functions, including fecundation. The putative cosmopolitanism of S. costarum, before new species were described, was the result of both inadequate morphological examination and the use of questionable ecological arguments linked to larval dispersal.     

The Opecoelidae (Digenea) of sparid fishes of the western Mediterranean. V.Allopodocotyle Pritchard, 1966

Allopodocotyle pedicellata (Stossich, 1887) is redescribed fromSparus aurata from off Corsica and off Provence, France andA. jaffensis (Fischthal, 1980) is redescribed fromSparus pagrus, Dentex dentex andPagellus erythrinus from off Corsica. The status of the genus and these two species is briefly discussed.

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Résumé Allopodocotyle pedicellata (stossich, 1887) est redécrit chezSparus aurata des côtes de la Corse et de la Méditerranée française.A. jaffensis (Fischthal, 1980) est redécrit à partir d'exemplaires provenant deSparus pagrus, Dentex dentex et Pagellus erythrinus des côtes de la Corse. Le statut du genre et de ces deux espèces est discuté.

     

Identification of Mediterranean Diplodus spp. and Dentex dentex (Sparidae) by means of DNA Inter-Simple Sequence Repeat (ISSR) markers

The aim of this paper was to test the effectiveness of Inter-Simple Sequence Repeat (ISSR) technique in detecting specific molecular markers to genetically discriminate some species of teleost fish. As model species, we used four Mediterranean sea bream species (i.e. Diplodus annularis, D. puntazzo, D. sargus sargus, and D. vulgaris), and the common Mediterranean dentex Dentex dentex. Furthermore, the occurrence in our samples of two partially albino sparids (suspected, on a morphological basis, to probably belong to D. sargus sargus and to D. dentex, respectively) allowed ISSRs to be tested on doubtful specimens. Eight ISSR primers produced 95 out of 97 scorable polymorphic loci with a large number (63) of species-private bands. Maximum parsimony analysis, ΔK statistics, and assignment test were consistent in separating the five species and solving the taxonomic position of specimens of dubious attribution. The results obtained evidence the usefulness of ISSR markers in specimen and species identification, particularly when the morphological traits of fish make the classification problematic.     

Complete larval development of the hermit crabs Clibanarius aequabilis and Clibanarius erythropus (Decapoda: Anomura: Diogenidae), under laboratory conditions, with a revision of the larval features of genus Clibanarius

The complete larval development (four zoeae and one megalopa) of Clibanarius aequabilis and C. erythropus, reared under laboratory conditions, is described and illustrated. The larval stages of the two northeastern Atlantic Clibanarius species cannot be easily differentiated. Their morphological characters are compared with those of other known Clibanarius larvae. The genus Clibanarius is very homogeneous with respect to larval characters. All Clibanarius zoeae display a broad and blunt rostrum, smooth abdominal segments and an antennal scale without a terminal spine. Beyond the second zoeal stage, the fourth telson process is present as a fused spine, and the uropods are biramous. In the fourth larval stage all species display a mandibular palp. The Clibanarius megalopa presents weakly developed or no ocular scales, symmetrical chelipeds, apically curved corneous dactylus in the second and third pereiopods, and 5–11 setae on the posterior margin of the telson. Apart from the number of zoeal stages, Clibanarius species may be separated, beyond the second zoeal stage, by the telson formula and the morphology of the fourth telson process.     

SEM investigations of the larval development of Imnadia yeyetta and Leptestheria dahalacensis (Crustacea: Branchiopoda: Spinicaudata)

This paper presents a SEM documentation of the larval development of the two most abundant Austrian conchostracan species, Imnadia yeyetta (Limnadiidae) and Leptestheria dahalacensis (Leptestheriidae). As in several previously examined spinicaudatan species, five larval stages were documented: Nauplius 1, Nauplius 2, Metanauplius, Peltatulus, and Heilophore. Additionally, three postlarval stages of L. dahalacensis and the first larval instars of Eoleptestheria ticinensis and Limnadia lenticularis are shown and compared with the examined stages. Species identification of conchostracan larval stages is possible by using surface structures, and using SEM methods, except for L. lenticularis which can be identified more easily on the characteristic shape of the labrum.     

Prey utilization by Chaoborus punctipennis Say in a small,eutrophic reservoir

Prey selection by 2nd-, 3rd-, and 4th-instar larvae of Chaoborus punctipennis was evaluated by comparing larval crop contents to the species structure of the zooplankton community in a small, eutrophic lake. The rotifers, Brachionus caudatus and Trichocerca similis, were positively selected by and comprised most of the diet of 2nd- and 3rd-instar larvae. Rotifers comprised 67% of all prey items identified in the crops of even 4th-instar larvae. Whereas 2nd-and 3rd-instar larvae selected the two rotifers with equalfrequency, 4th-instar larvae selected Trichocerca significantly more frequently than they did Brachionus. Although copepods comprised only 8% of all prey identified in 3rd-instar crops, they comprised 33% of the crop contents of 4th-instar larvae. Both 3rd and 4th instars exhibited a positive electivity for Cyclops vernalis significantly more frequently than for Diaptomus pallidus. We conclude that the larvae of Chaoborus punctipennis can, and do, select between Trichocerca and Brachionus and between Cyclops and Diaptomus.The paper by Brooks and Dodson (1965) triggered a flurry of studies on aquatic predators and their ability to discriminate between available prey species. Although the original work dealt with vertebrate predators, it has become increasingly apparent that invertebrate predators may also exhibit considerable selectivity in choosing between prey categories. The larval stages of the various species of Chaoborus are ubiquitous lentic predators, especially in mesotrophic or eutrophic systems. Although there have been a number of recent publications which deal with the food habits and preferences of several species of Chaoborus, only a few studies have included analyses of larval crop contents and none of these have included Chaoborus punctipennis. This species is of particular interest because it is one of the smaller species in the genus, and perhaps for this reason, because it is frequently present in lakes which support large populations of planktivorous fish (von Ende 1979). The purpose of our research was to characterize the food habits and preferences of Chaoborus punctipennis in a small, eutrophic reservoir which supports a rather depauperate number of species of zooplankters.     

A preliminary study on gill metazoan parasites of Dentex dentex (Pisces: Sparidae) from the western Mediterranean Sea (Balearic Islands)

A preliminary study of the gill parasites from 61 common dentex (Dentex dentex, Pisces, Sparidae) was developed. Seven parasite species were found: one monogenean (Microcotyle erythrini), one udonellidean Udonella caligorum), one digenean trematode (Stephanostomum sp. metacercariae), three copepods (Caligus productus, Caligus diaphanus and Clavellopsis fallax) and one isopod (Gnathia vorax, praniza larvae). Only 1.6% of the fishes examined presented one parasitic species whilst the remainder had two parasitic species (13%), three (26%), four (21%), five (20%) and six different species (18%). The udonellidean U. caligorum was found as a hyperparasite or phoront of the three copepods. Prevalence and other ecological parameters as well as the spatial site of each parasite in the gill tissue are described. The multiparasitic combinations are also examined.     

A review of biology,fisheries and population structure of Dentex dentex (Sparidae)

The common dentex Dentex dentex (Linnaeus, 1758) is an iconic marine coastal fish in the Mediterranean Sea. It is a demersal sparid fish (0–200 m), that grows to a maximum length of 100 cm and a weight of 13 kg, with a relatively long life span (more than 20 years). As a high trophic level predator, it holds a key position in coastal marine food webs. The common dentex is of great economic importance for both artisanal (small-scale coastal fisheries) and recreational fishing. Despite its economic and ecological importance, scientific data on this species in its natural environment are still very scant. The global commercial catch of common dentex has fluctuated over the last 60 years on an interannual time scale, and has declined significantly since the 1990s. There are few data regarding fishing effort and total catch from recreational fishing for common dentex, but it appears that this species is particularly targeted by this activity. The common dentex is now classified as “vulnerable” in the Red List of Threatened Species in the Mediterranean Sea. This review summarizes the current literature on D. dentex in regard to biology, ecology, parasitology, population structure, commercial and recreational fishing, and management regulations. Future research directions to fill gaps in current knowledge are suggested.     

Hyperparasitism behaviour of the autoparasitoid <Emphasis Type="Italic">Encarsia tricolor</Emphasis> on two secondary host species

Hyperparasitism by virgin female Encarsia tricolor was studied by direct observation of its behaviour when contacting two secondary host species (Encarsia formosa and E. tricolor) at different host stages (first and second larval stage, third larval stage, and pupal stage). The searching and hyperparasitism behavioural sequence of E. tricolor was independent of the host stage of the whitefly (Aleyrodes proletella), and was similar to several related primary parasitoid species. In experiments with equal numbers of secondary hosts, encounter frequencies were equal for both secondary host species in all developmental stages observed. However, rates of hyperparastism were different according to host stage and host species. Hosts in the late larval stages were most preferred for hyperparasitization and the heterospecific E. formosa was more preferred as a secondary host than the conspecific, E. tricolor, in particular from the prepupal stage onwards. The window of vulnerability, i.e., the duration of the period in which a secondary host is susceptible to hyperparasitism, was largely determined by the occurrence and rate of melanization after the onset of pupation. The duration of a successful hyperparasitization event was longer than one that failed. Superparasitism occurred only once in all cases. The potential effect of autoparasitoids on biological control programs and the consequences for selection and release of an effective, yet ecologically safe agent are discussed. Handling editor: Torsten Meiners.     

The management of metabolic energy storage during the life cycle of mayflies: a comparative field investigation of the collector-gatherer <Emphasis Type="Italic">Ephemera danica</Emphasis> and the scraper <Emphasis Type="Italic">Rhithrogena semicolorata</Emphasis>

The concentration and seasonal dynamics of the major energy storage components, triglycerides and glycogen, were measured in two species of mayfly (Rhithrogena semicolorata and Ephemera danica) with contrasting life cycle strategies living in a small mountain stream. E. danica is a burrowing, semivoltine collector-gatherer; R. semicolorata is univoltine and scrapes periphyton from stones. This is the first publication which focuses on the role of metabolic energy sources during the larval life span of two mayfly species until the larvae emerge. Although triglycerides are the major energy reserve in both species (>84% of total energy storage) throughout the whole larval development their seasonal dynamic differed considerably. In R. semicolorata the triglyceride concentration declined during the last weeks prior to emergence in both sexes. The same pattern was found in female larvae of E. danica, but not in male E. danica. It is suggested that females use triglycerides in the last larval stages for egg maturation, which is completed in the last larval instar. In male E. danica the triglyceride concentrations remained high until emergence, presumably due to their high energy demands as adults for their swarming flights. Glycogen concentrations did not show such a difference between species and sexes. Its significance as a storage substrate for energy is rather low; however, concentrations decreased in both species and sexes prior to emergence.     

Coexistence of three differentDrosophila species by rescheduling their life history traits in a natural population

We present evidence for coexistence of three differentDrosophila species by rescheduling their life history traits in a natural population using the same resource, at the same time and same place.D. ananassae has faster larval development time (DT) and faster DT(egg-fly) than other two species thus utilizing the resources at maximum at both larval and adult stages respectively. Therefore,D. ananassae skips the interspecific competition at preadult stage but suffers more from intraspecific competition. However,D. melanogaster andD. biarmipes have rescheduled their various life history traits to avoid interspecific competition. Differences of ranks tests for various life history traits suggest that except for DT(egg-pupa), the difference of ranks is highest for the combination ofD. melanogaster andD. ananassae for all other life history traits. This difference is maintained by tradeoffs between larval development time and pupal period and between pupal period and DT(egg-pupa) inD. ananassae.     

Resource Partitioning among Parasitoids (Hymenoptera: Braconidae) of Phoracantha semipunctata in Their Native Range

The Eucalyptus longhorned borer, Phoracantha semipunctata (F.), is native to Australia, but it has been introduced without its natural enemies into many parts of the world in which its Eucalyptus spp. host has been planted. The beetle has developed large populations in these novel habitats and has been responsible for the mortality of large numbers of trees. Although there is a considerable catalogue of the parasitoids of the beetle in Australia, limited ecological information on the assemblage of parasitoids attacking P. semipunctata is available. We removed bark from 40 felled trees, recorded gallery width and bark thickness over parasitized larvae, and removed all parasitoids. Adult size, sex, and species were recorded when the parasitoid pupae eclosed. Syngaster lepidus Brullè, Jarra phoracantha Austin, Quicke, and Marsh, J. maculipennis Austin, Quicke, and Marsh, and J. painei Austin and Dangerfield were most commonly collected. The solitary parasitoid S. lepidus preferred smaller larvae than did the gregarious Jarra spp. The two species with shorter ovipositors, J. maculipennis and J. painei, parasitized larvae under thinner bark than did the other two species with longer ovipositors. There was a significant positive correlation between host larval size and number of parasitoid pupae of the gregarious species. Also, there was a significant positive correlation between host larval size and parasitoid adult size. The ecological relationships between this assemblage of parasitoids and their beetle host may be useful in establishing an effective biological control program.     

Genetic divergence and larval dispersal in two spider crabs (Crustacea: Decapoda)

The spider crabs Inachus dorsettensis (Pennant) and Hyas coarctatus Leach are widespread in subtidal areas of muddy sand or gravel around western Europe. Both species have a life cycle with an obligatory planktonic larval phase of several weeks, which might be expected to cause widespread larval dispersal and consequent genetic homogeneity over considerable distances. However, earlier work on both taxa has indicated differences in growth pattern between populations separated by tens of kilometres. This study was undertaken to determine whether these differences were purely environmental or whether, despite the short distances involved, differences may have a genetic basis. A study of gene frequencies, as indicated by allozymes in samples of adults collected off the Isle of Man (northern Irish Sea), indicates significant genetic differentiation between populations over a geographical distance of only about 40 km in both Inachus dorsettensis ( = 0.086 ± 0.048) and Hyas coarctatus ( = 0.023 ± 0.017). Variability measures differed between species, showing I. dorsettensis to have a mean number of alleles per locus of 2.5–2.6 and a range of gene diversity of 0.216–0.241, while H. coarctatus showed lower values of mean number of alleles (1.9–2.0) and a range of gene diversity from 0.122 to 0.124. Given the high expected larval mobility of the two species the results are most surprising. Possible explanations are discussed in relation to population discontinuities and patterns of larval drift.     

Prey preference and feeding capacity of the larvae ofAblattaria arenaria [Coleoptera: Silphidae], a snail predator

The larval stages ofAblattaria arenaria were provided with 4 different snail species:Monacha syriaca (Ehrenberg),Xeropicta derbentina (Krynicki),Candidula sp., andZebrina eburnea (Pfeiffer) to determine if the prey species affected developmental time and food preference of larvae. Functional response of each larval stage ofA. arenaria was also tested for increasing density ofX. derbentina, the most common prey species found in association withA. arenaria locally. The developmental time of each larval stage did not show any statistical difference when fed with different snail species. The total developmental time from egg hatch to adult emergence was 19.0, 19.1, 18.0 and 21.4 days for prey speciesM. syriaca, X. derbentina, Candidula sp., andZ. eburnea, respectively. When prey was offered to larvae either as a single species or as combination of several species,M. syriaca was the most preferred. The prey least consumed wasCandula sp. when prey was given separately, andZ. eburnea was least preferred when other prey species were present in the arena. The 3^rd larval stage did not eat anyZ. eburnea if other prey species were present. The amount of prey consumed by the 1^st larval stage did not show any statistical differences with increasing density ofX. derbentina. But the response of 2^nd and 3^rd larval stages was very similar to each other although the amount of prey they consumed was very different. They both showed a rapid increase in consumption rate at early densities, then a negatively but slowly accelerated rise to plateaus at higher densities, a type-2 functional response curve. All larval stages were very sensitive to starvation. Mortality started after the 2^nd day, and all individuals of all larval stages were dead by the 5^th day.