Influence of temperature on egg hatching, growth and survival of larvae of Heterobranchus longifilis Val. 1840 (Teleostei: Clariidae)

Eggs of Heterobranchus longifilis Val. 1840 were artificially fertilized and incubated at a range of temperatures (20, 23, 25, 27, 29 and 32°C). The time from fertilization to hatching decreased with increasing temperature. No eggs survived to hatch at 20 and 32°C incubation temperatures, while at 23 and 29°C hatching was only minimal. Optimum hatching was obtained at 25 and 27°C, which corresponds to the ambient temperature range during the breeding season. Larvae of H. longifilis were reared for 11 days post-hatching at 20, 25, 27, 29 and 32°C. Growth increased with temperature (P < 0.05), whereas survival depicted an inverse relationship. Growth was minimal at 20°C and larvae rarely survived to the end of the experiment. Optimum temperature for the primary nursing of H. longifilis larvae was within the 25–27°C temperature range.     

Egg performance on an egg-carrying bug. Experiments in the field

Selection of oviposition sites has direct influence on female fitness. Differences in offspring survival among sites should favour females to select oviposition sites with the highest survival. Golden egg bug females ( Phyllomorpha laciniata; Coreidae, Heteroptera) use conspecifics as oviposition substrates. Most eggs are laid on the back of the bug but they can be found on all body parts. Females never carry their own eggs, and males commonly carry eggs received without copulation with the donor. We examined differences in egg survival relative to paternity to the egg, host sex and body size and attachment of an egg on a host's body in the field. We also studied which bugs received eggs. Egg loss was surprisingly common: 30–80% of recaptured individuals lost eggs during a six-day period. Unexpectedly, host's paternity to the eggs did not affect egg survival. Also, egg loss did not differ among hosts in respect to other parameters studied. Males received more eggs than females, but survival of the eggs was not better on a male's back than on a female's back. Since egg loss is common in the golden egg bug, we suggest that female oviposition strategy to lay eggs on conspecifics is not perfect. This is due to active behaviour of potential hosts (for example, rejected oviposition attempts) or lack of suitable oviposition substrates (conspecifics) in the field. Since eggs do not survive unless carried, females may be acting opportunistically, doing the best job possible by laying eggs on available conspecifics.     

Contribution of copepods,cladocerans and cirripeds to phosphatase activity in mediterranean zooplankton

The hydrolysis of dissolved phosphoric esters by zooplankton was studied in Toulon seaport (N.W Mediterranean Sea, France). Zooplankton was collected on 90 m filters. The enzyme reaction was studied using paranitrophenyl phosphate (p-NPP) dissolved in sea water. The particulate material activity was expressed as V _max (reaction rate when the enzyme is saturated with substrate) using Eadie-Hofstee plots. The activity per L. was high in spring and decreased from summer to winter. Biomass and zooplankton abundance varied also widely during the year. There were significant correlations between activity per L. and the cirriped cyprid abundance. In contrast, during periods when cyprids were absent, positive correlations with copepod and cladoceran abundance were found. Specific activity varied also during the year, with high values in spring and low values in winter. This activity was positively correlated with cyprid abundance, but not with total zooplankton, copepod or cladoceran abundance. These results indicated that copepods and cladocerans contributed to the overall enzyme production, and that cirripeds could be responsible of high specific activities.     

Egg mortality in the pine processionary moth: habitat diversity,microclimate and predation effects

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Effect of light periodicity and intensity on the growth and survival of Heterobranchus longifilis Val. 1840 (Teleostei: Clariidae) larvae after 14 days of rearing

Heterobranchus longifilis Val. 1840 larvae were reared under two light intensities, 30 lux and 915 lux, and at varying photoperiods. Results show that maximum survival (82.5 ± 6.5% respectively) at 30 lux was obtained at continuous illumination [24 h light (L)], while the minimum (65 ± 21.2%) was at the 6 h L : 18 h dark (D) treatment. Survival at 24 h D averaged 71.3 ± 6.3%, with no significant difference (P < 0.05) in growth of larvae. Maximum larval survival at 915 lux was 87.5 ± 17.7% at the 18 h L treatment. Growth was not significantly different (P < 0.05) in the treatments. Comparison of the two light intensities showed that survival was better at a photoperiod above 12 h irrespective of intensity, while growth was significantly better at the 915 lux intensity.     

Distribution,diversity and density of wolbachial infections in cladocerans and copepods from Thailand

Species of the genus Wolbachia comprise a group of Rickettsia-like, maternally-inherited bacteria that cause several reproductive alterations in arthropod hosts. The best known are cytoplasmic incompatibility and feminization. Here, the first systematic surveys of wolbachial infections in cladocerans and copepods from six geographic regions of Thailand, including Northern, Northeastern, Western, Central, Eastern and Southern are reported. Using gene amplification assays with wsp and groE primers, wolbachiae were detected in 239 (4 spp.) of 1885 (57 spp.) copepods and cladocerans from all regions of Thailand surveyed. Screening results obtained with wsp primers or groE primers were similar in all cases. The presence of wolbachiae was only detected in copepods, not in cladocerans. Sex ratio analyses of the progeny of two species of copepods, Mesocyclops aspericornis and Mesocyclops thermocyclopoides, naturally or artificially infected with wolbachiae showed infection causes feminization (female-bias). The relative density if infection in naturally infected populations of three copepod species, M. thermocyclopoides, Heliodiaptomus elegans and Neodiaptomus blachei, were determined using real-time quantitative PCR assay based on the wsp gene. The density of wolbachiae in M. thermocyclopoides was significantly higher than in the other two species. These results suggest that wolbachial infections are distributed throughout Thailand, and that possibly the natural occurrence of these in copepods may be due to their predation on mosquito larvae. This apparent novel biology may have importance as a genetic drive system for control of vector borne diseases in the future.     

Egg size, offspring quality and food level in planktonic rotifers

1. For two species of planktonic rotifers, Brachionus calyciflorus and Synchaeta pectinata , neonates from larger eggs were more resistant to starvation than neonates from smaller eggs, so egg size was positively correlated with offspring quality.
2. Theories of optimal offspring size in zooplankton predict either a decrease in offspring size with increasing food level, or maximum offspring size at intermediate food levels. In experiments using acclimated, even-aged individuals, neither rotifer species changed its egg size as predicted by theory. B . calyciflorus egg size increased with increasing food concentration, while S . pectinata egg size did not change.
3. The lack of fit to theory may have occurred because of constraints on minimum or maximum egg size, constraints on total reproductive effort, or because offspring fitness is influenced by traits in addition to neonate starvation time.     

Egg-brooding, body size and predation risk in planktonic marine copepods

We investigated the interacting effects of copepod body size and the presence or absence of egg masses on the risk of predation by a visual predator. We conducted selection experiments involving three-spined sticklebacks (Gasterosteus aculeatus) and copepods ranging in body mass from 0.5 to 740 μg C: Oithona similis, Corycaeus anglicus, Pseudocalanus newmani, P. moultoni, Pseudodiaptomus marinus, and Paraeuchaeta elongata. We found that sticklebacks selected ovigerous females of the two smallest-bodied species of copepods (Oithona similis and Corycaeus anglicus). In contrast, the fish showed no significant selection for ovigerous females of the remaining, larger-bodied species. Unexpectedly, egg mass position (i.e., in a ventral, dorsal or lateral location on the urosome) appeared to influence predation risk more than did body size, resulting in higher predation risk for the cyclopoid and poecilostomatoid species than for the calanoid species we tested. Although the sticklebacks showed no statistically significant preference for ovigerous females of any of the four calanoid species, for each species the overall proportion of ovigerous females ingested was slightly greater than 0.50. Thus, whether body size influences the susceptibility of egg-brooding calanoid copepods to predation remains an open question. Received: 24 August 1998 / Accepted: 6 July 1999     

Distribution of cholecystokinin-immunoreactive cells in the gut of developing Atlantic cod Gadus morhua L. larvae fed zooplankton or rotifers

One of the main gastrointestinal hormones, cholecystokinin (CCK), was studied in order to advance understanding of the control of the digestive process in Atlantic cod Gadus morhua larvae after onset of first feeding. Larvae were fed either natural zooplankton or enriched rotifers in similar rearing systems and sampled from hatching to 22 days post-hatch (dph). CCK was visualized by immunohistochemistry and the first CCK-immunoreactive (IR) cells were detected at 8 dph corresponding to 6 days after first feeding. The CCK-IR cells were mostly found in the anterior midgut, and the number of CCK-IR cells was lower in the posterior midgut. They were also present in the hindgut of some of the larvae, but not in the foregut. No clear differences were found in the ontogenetic appearance and the distribution pattern of CCK-IR cells between the two dietary treatments. This indicates that the onset of CCK production in the gut as well as the spatial distribution of the CCK-IR cells is not differentially affected by these diets. To what extent the hormone production itself is influenced by dietary factors needs to be studied by more sensitive methods.     

Relative impacts of copepods, cladocerans and nutrients on the microbial food web of a mesotrophic lake

Calanoid copepods, rather than cladocerans, frequently dominatethe zooplankton of lakes in New Zealand. The potential consequencesof this domination for the microbial community of mesotrophicLake Mahinerangi, New Zealand, were determined by field experimentsin which Boeckella and Daphnia were added to in situ enclosuresin the presence and absence of added nutrients. Boeckella hamataat ambient densities (2 and 81^–1) rapidly and severelysuppressed ciliate population growth over 4 days, even whenmicrobial growth was enhanced by added nutrients, but effectsof copepods on other components of the microbial community (bacteria,photosynthetic picoplankton, heterotrophic nano-flagellates,algae) were slight. In contrast, Daphnia carinata at the samedensities (but 3-fold higher biomasses per litre) had a relativelyweak effect on ciliates, suppressing ciliate abundance onlyafter 4 days at 8 Daphnia 1^–1 (330 µg 1^–1);this daphniid density also depressed abundances of large bacterialrods, some photosynthetic picoplankton and the dominant alga,Cyclotella. These results highlight the relative importanceof specific trophic linkages in a microbial food web; they alsosuggest that the dominance of Boeckella in many southern hemispherelakes may account for relatively low ciliate abundances in theselakes.     

Effects ofBacillus thuringiensis var.San diego on predation effectiveness,development and mortality ofColeomegilla maculata lengi (Col.: Coccinellidae) larvae

Laboratory experiments were conducted to determine the effects of M-One^™ (Bacillus thuringiensis var.san diego) on larval instars ofColeomegilla maculata lengi Timberlake. Coccinellid larval development (from egg hatch to adult), completed on pollen treated with suspensions of M-One^™ at 20 ml/litre (5.6×10⁸ CPBIU/litre) and 200 ml/litre, took respectively 29.3 and 38.5 days compared with 21.9 days for the control (water). M-One^™ did not cause larval mortality.C. maculata third instars did not show any preference between eggs ofLeptinotarsa decemlineata (Say) treated with water or with M-One^™ at 20 ml/litre. However, at 200 ml M-One^™/litre, the number of eggs attacked was 34.7% lower than the eggs treated with water only, 48 h after the beginning of the test. These results indicate that the use of M-One^™, at the manufacturer's recommended field rate of 20 ml/litre, does not cause a major threat to larvalC. maculata populations.

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Résumé Des bioessais en laboratoire ont été effectués afin de déterminer si les larves de la coccinelle maculée,Coleomegilla maculata lengi Timberlake (Col.: Coccinellidae), sont affectées par M-One^™, un insecticide biologique préparé à partir de la bactérieBacillus thuringiensis var.san diego Berliner et utilisé dans la lutte contre le doryphore de la pomme de terre,Leptinotarsa decemlineata (Say) (Col.: Chrysomelidae). Le développement larvaire, effectué sur du pollen traité avec des concentrations de 20 ml M-One^™/litre (5,6×10⁸ unités internationales de doryphore/litre) et 200 ml M-One^™/litre, a nécessité 29,3 et 38,5 jours respectivement, comparativement à 21,9 jours pour le témoin (eau). M-One^™ n'a pas causé de mortalité chez les larves. Au cours d'un test de 48 h, les larves de stade III n'ont montré aucune préférence entre des œufs traités avec 20 ml M-One^™/litre et des œufs traités avec de l'eau. Par contre avec 200 ml M-One^™/litre, le nombre d'œufs attaqués a diminué significativement de 34,7% par rapport au témoin, 48 h après le début du test. Ces résultats indiquent que l'utilisation de M-One^™ à la concentration recommandée de 20 ml/litre ne représente pas une menace pour les populations larvaires de la coccinelle maculée.

     

Syltodinium listii gen. et spec. nov., a marine ectoparasitic dinoflagellate on eggs of copepods and rotifers

Syltodinium listii is described as a new marine ectoparasitic dinoflagellate. In culture experiments the species was found feeding on eggs of planktonic copepods and rotifers. The dinospore penetrates the host by a peduncle, and transforms into a trophont by sucking out the egg contents phagotrophically. After detaching from the host, the mature trophont settles down to become a palmelloid multiplication stage. By repeated binary fission, up to 16 or 32 gymnodinoid, colourless dinospores are formed inside a gelatinous envelope. The parasite retains its dinoflagellate (monadoid) nature throughout its whole vegetative life cycle. Even during the trophic and multiplication phase the species remains latently motile. Despite some resemblance toDissodinium, there are sufficient reasons for the establishment of the new genusSyltodinium. Dedicated to Dr. Dr. h. c. P. Kornmann on the occasion of his eightieth birthday     

Egg predation in forest bird communities on islands and mainland

Summary To examine if differences in egg predation rates could explain differences in bird community composition, egg predation was studied in two years on small islands in a South Swedish lake and on the nearby mainland using both natural and artificial nests.In plots with similar vegetation, the combined density of ground- and tree-nesting bird species did not differ between the islands and the mainland. Egg predation rates were similar on islands and the mainland for natural Turdus nests in two years, and for artificial Turdus and Phylloscopus nests. Unmarked and unvisited experimental nests suffered similar rate of egg predation as marked and visited nests. Egg predation rates were higher on natural nests when artificial nests were also put out, increasing the total nest density. Initial egg predation rates in artificial nests were also higher than later when nest density had decreased by 75%.The egg predators involved differed for artificial Phylloscopus nests between the islands and the mainland. Small mammals were apparently responsible for 29% of the predation on the mainland, but none on the islands. Artificial Turdus nests near crow nests suffered from a higher egg predation rate than nests further away from crow nests. Daily survival rates of Turdus nests increased from the laying to the incubation and further to the fledging state.Egg predation can not explain differences in bird community composition between islands and mainland in the present case.     

Effect of ant predation and abiotic factors on the mortality of medfly larvae,Ceratitis capitata,in the Argan forest of Western Morocco

The Argan Argania spinosa (L.) Skeels (Ericales: Sapotaceae) is an endemic and emblematic tree growing in the centre and the southwest of Morocco. Argan fruits are frequently infested by the Mediterranean fruit fly Ceratitis capitata Wied (Diptera: Tephritidae). To date, no control program has been undertaken in the Argan forest. This research is the first investigation of natural mortality factors of C. capitata larvae in the Argan forest. The study was conducted at two localities near the city of Essaouira with different climatic conditions. Observations were conducted using 260 late instar larvae which were individually deposited on the ground, under fruiting host trees, where they naturally fall to find a suitable pupation site. Overall, 42% of the larvae died before being able to burrow into the ground, irrespectively of the location. Larval survival and their likelihood of burrowing decreased with increasing ground temperature, as 53% of all the larvae deaths occurred at temperatures over 48°C. However, at lower ground temperature, predation by ants and spiders accounted for 47% of all mortality. Four species of ants carried out 94% of the captures. Monomorium subopacum Mayr (Hymenoptera: Formicidae), which frequently forages under Argan trees, was by far the most efficient predator, due to a powerful sting that rapidly immobilizes the prey. Our results suggest that the burrowing performance of larvae is constrained by high thermal conditions and the presence of ant predators at lower temperatures.     

Seven new species of Quadriacanthus Paperna, 1961 (Monogenea) from the gills of Heterobranchus longifilis and H. isopterus from the Ivory Coast,West Africa

The gills of two species of Siluriformes, Heterobranchus longifilis and H. isopterus collected from the Rivers Agnéby and Bia in the Ivory Coast (West Africa) revealed the presence of seven new species of Quadriacanthus Paperna, 1961 (Monogenea: Ancyrocephalidae). The following parasites are described: Quadriacanthus longifilisi n. sp., Q. thysi n. sp., Q. ayameensis n. sp., Q. agnebiensis n. sp., Q. simplex n. sp., Q. gourenei n. sp. and Q. macrocirrus n. sp.     

Culture techniques for studies on the growth, development and reproduction of copepods and cladocerans under laboratory and in situ conditions: a review

SUMMARY. This review deals with culture techniques in use to estimate individual growth, development and reproduction of copepods and cladocerans in cultures. The conceptual aspects of growth, reproduction and feeding behaviour are briefly summarized. Marine copepods are included, because the techniques employed for the cultivation of these animals are often more advanced than those used for freshwater crustaceans. Most of the studies reviewed here were carried out under defined laboratory conditions, but a few were under field conditions, generally in small in situ enclosures. The culture methods described in this review are based on 272 studies published between 1910 and 1987. A large number of different culture systems are critically discussed in relation to culture conditions and culture techniques and the taxa used. Particular attention is given to the effect of food quality, and the problem of how to apply laboratory measurements to field populations so as to limit errors to the minimum. A more detailed summary is given in the section on 'Recommendations' at the end of the review.     

Egg predation and predator-induced hatching plasticity in the African reed frog, Hyperolius spinigularis

Density regulation is assumed to be common, but is very rarely tested experimentally. Using annual plant communities, we tested the hypotheses that 1) regulation of abundance in plants occurs at the level of entire communities, not just within species, and 2) such regulation is strongest when resources are most limiting. We transplanted different amounts of seeds from two diverse source communities in Israel to an experimental garden and monitored plant densities and cover for two years under different irrigation regimes. Both total density and total plant cover showed strong evidence of community-level regulation; plots sown at higher than average natural density declined or stayed the same in total abundance over time, while plots sown at lower than average natural density increased in abundance over time. This convergence of community abundance was strongest with the lowest irrigation in both source communities, consistent with the hypothesis of stronger regulation when all resources are more limiting (light levels were high, regardless of irrigation level). The main mechanism of regulation was strong density dependent recruitment, while survival was either density independent or inversely density dependent. Thus, the results also emphasize the need for direct experimental studies of the population dynamic consequences of interactions, as well as of individual level consequences.     

A comparative study on morphology, growth rate and reproduction of Clarias gariepinus (Burchell, 1822), Heterobranchus longifilis Valenciennes, 1840, and their reciprocal hybrids (Pisces, Clariidae)

A detailed study on reproduction indicated that female C. gariepinus mature earlier (5–7 months) than female H. longifilis (12–14 months). In the reciprocal hybrids, female first sexual maturity was attained at 20–21 months. Both reciprocal hybrids and parental species displayed an equilibrated sex ratio. Macroscopical and microscopical observations revealed numerous abnormalities in gonadal development of the hybrids. GSI and fecundity in female hybrids were considerably lower than those found in the parental species. Moreover, intra-ovarian tumors occurred in 20% of the hybrids. In hybrid males, GSIs were generally higher than those found in the parental species, but the spermatozoa concentration in the semen was about 100 times less. Despite these abnormalities, viable larvae, resulting from F2 and backcross fertilizations, were obtained.     

Egg weight variation in relation to egg mortality and starvation endurance of newly hatched larvae in some satyrid butterflies

Abstract. 1. Egg weights decrease over the oviposition period in all of the five satyrid butterflies that have been studied, viz Parage aegeria L., Lasiommata petropolitana F., L.maera L., L.megera L. and Lopingaachine Scop. However, within each species, no correlation was found between variation in egg weight and egg mortality in 30% relative humidity or the ability of newly hatched larvae to survive without food for 1–4 days. 2. Although egg weights of Papilio machaon L. were similar to the highest satyrid egg weights, newly hatched larvae of P.machaon showed significantly higher mortality after 1 day of starvation when compared to all of the satyrid larvae. This indicates that the capability of newly hatched larvae to endure starvation is not necessarily correlated with egg weight, and consequently that this character trait of satyrid larvae has been selected for (i.e. should be regarded as an adaptation). It is noteworthy that this ability of satyrid larvae to endure starvation is coupled with the habit of many satyrid butterflies not to deposit their eggs directly on the larval host plants. 3. In 30% relative humidity, egg mortality of L.achine was 100% and that of P.aegeria 29.2%, whereas that of the three Lasiommata spp. was significantly lower. At 100% relative humidity egg mortality in L.achine dropped to 8%. Since egg weights are higher in L.achine than in the other four satyrids this indicates that egg resistance to desiccation is not necessarily correlated with egg size (as might be expected due to the area to volume ratio which is negatively correlated with egg size). Thus the resistance to desiccation which is found in the three Lasiommata spp. should be regarded as an adaptation to the habit of these three butterflies to deposit their eggs in relatively dry microhabitats. This resistance to desiccation is not found in eggs of the two forest-dwelling satyrids P.aegeria and L.achine which lay their eggs in microhabitats where the relative humidity is high.     

Analysis of production,early growth and survival ofClarias gariepinus (Burchell),Heterobranchus longifilis (Val.) (Pisces: Clariidae) and their F1 hybrids in ponds

Clarias gariepinus andHeterobranchus longifilis were successfully hybridized to produce reciprocal F₁ progeny during a two-year study.C. gariepinus produced significantly heavier spawn thanH. longifilis during the same period. Fertilized eggs were incubated in aerated static-water in fibre-glass troughs, and hatching rates were not found to be significantly different (P<0.05) between any two of the four catfish groups produced. Eight-day old fry of each group were reared in fertilized nursery ponds, and F₁ hybrids fromH. longifilis maternal parent had the best growth and survival rates at the end of 18 days. The reciprocal cross showed intermediate growth rate between both parents. At harvest, differential growth was less pronounced among both hybrids than among the parents.