Polystoma gallieni: Experimental evidence for chemical cues for developmental plasticity

Among monogeneans that display direct life cycles, plastic developmental strategies may have been selected to counter the lack of transmission opportunities. Within amphibian polystomatids, some species of the genus Polystoma develop into two different phenotypes depending on the host physiological stage to which free swimming larvae attach. When oncomiracidia infest old tadpoles, they develop slowly and migrate during host metamorphosis towards the bladder where they reach maturity. On the other hand when larvae infest young tadpoles, they develop rapidly into neotenic phenotypes that reproduce in the branchial chamber. These alternative developments are explored through experimental infestations with Polystoma gallieni, the specific polystome of the stripeless tree frog Hyla meridionalis. When oncomiracidia were left for 6 h in water in which young tadpoles had been previously maintained for one day, they mainly developed into the neotenic phenotype regardless of the tadpole stage they encountered later. This indicates that P. gallieni could collect released host-derived signals before physical contact with its host.     

Seaweed extracts as a natural control against the monogenean ectoparasite,Neobenedenia sp., infecting farmed barramundi (Lates calcarifer)

Aqueous extracts from common tropical seaweeds were evaluated for their effect on the life cycle of the commercially important ectoparasite, Neobenedenia sp. (Platyhelminthes: Monogenea), through the survival of attached adult parasites, period of embryonic development, hatching success and oncomiracidia (larvae) infection success. There was no significant effect of any extract on the survival of adult parasites attached to fish hosts or infection success by oncomiracidia. However, the extracts of two seaweeds, Ulva sp. and Asparagopsis taxiformis, delayed embryonic development and inhibited egg hatching. The extract of A. taxiformis was most effective, inhibiting embryonic development of Neobenedenia sp. and reducing hatching success to 3% compared with 99% for the seawater control. Furthermore, of the 3% of eggs that hatched, time to first and last hatch was delayed (days 14 and 18) compared with the seawater control (days 5 and 7). Asparagopsis taxiformis shows the most potential for development as a natural treatment to manage monogenean infections in intensive aquaculture with the greatest impact at the embryo stage.     

Reproductive Strategies of the Insidious Fish Ectoparasite,Neobenedenia sp. (Capsalidae: Monogenea)

Fish monogeneans are lethal parasites in aquaculture. We provide the first experimental evidence that a notorious fish monogenean, Neobenedenia sp., can produce viable eggs in isolation for three consecutive generations. We infected individual, isolated, farmed barramundi, Lates calcarifer (Bloch) with a single oncomiracidium (larva) of the hermaphroditic monogenean Neobenedenia sp. Isolated parasites reached sexual maturity at day 10 post-hatch (24°C, 35‰) and laid ∼3,300 embryonated eggs over 17 days. Egg production rapidly increased following sexually maturity on day 10 (58±15 eggs) and peaked on day 15 (496±68 eggs) before gradually decreasing. Neobenedenia sp. exhibited egg laying and egg hatching rhythms. Parasites laid eggs continuously, but egg production increased in periods of darkness (64.3%), while the majority of oncomiracidia (81%) emerged from eggs in the first three hours of light. Eggs laid by isolated ‘parent’ parasites hatched and individual emerging oncomiracidia were used to infect more individual, isolated fish, with three consecutive, isolated, parasite generations (F1, F2 and F3) raised in the laboratory. Infection success and egg hatching success did not differ between generations. Our data show that one parasite, in the absence of a mate, presents a severe threat to captive fish populations.     

Effect of clutch size on male egg-fanning behavior and hatching success in the goby, Eviota prasina (Klunzinger)

In fish that exhibit paternal care, the females often choose their mates on the basis of male traits that are indicative of the parental ability of the males. In a marine goby, Eviota prasina, males tend their eggs within their nests until hatching, and females prefer males that have longer dorsal fins and exhibit courtship behavior with a higher frequency as their mates. In order to clarify the relationship between these sexually selected traits and the parental ability of males of E. prasina, the factors affecting the hatching success of eggs within male nests and the male parental care behavior were examined in an aquarium experiment. Females spawned their eggs in male nests and the clutch size of females showed a high individual variation (range = 88-833 eggs). The hatching success of eggs within male nests showed a positive correlation with the time spent by males in fanning eggs and the clutch size. In contrast to the prediction, however, the hatching success did not show a significant correlation with the sexually selected traits, i.e., the male dorsal fin length and the frequency of courtship displays. Moreover, multiple regression analysis indicated that the time spent by the males in fanning was the most important factor affecting the survival rate of the eggs. The time spent by males in fanning behavior was influenced by the clutch size within their nests; the fanning behavior of males occurred with a higher frequency when they tended larger clutches. Males are required to invest a greater effort in egg-tending behavior to achieve a higher hatching success when they receive larger clutches, probably due to the greater reward for their parental behavior. Based on their mate choice, females may obtain other benefits such as high quality offspring.     

Reduction in fitness of female Asian longhorned beetle (Anoplophora glabripennis) infected with Metarhizium anisopliae

Bioassays were conducted to document the effects of Metarhizium anisopliae infection on adult female Asian longhorned beetle (Anoplophora glabripennis) reproduction before death and subsequent survival of offspring. The effect of infection on fecundity was evaluated for females already laying eggs and for newly eclosed females using M. anisopliae isolates ARSEF 7234 and 7711, respectively. Decreased longevity and oviposition compared with controls were observed in females that were already laying eggs when exposed to M. anisopliae ARSEF 7234. Newly eclosed females exposed to M. anisopliae ARSEF 7711 displayed shortened longevity (10.0 ± 0.7 days vs 74.3 ± 6.8 days for controls) and decreased oviposition (1.3 ± 0.7 eggs per ARSEF 7711-exposed female vs 97.2 ± 13.7 eggs per female for controls) compared with controls. Percentages of eggs that did not hatch were greater for both groups of fungal-treated females compared with controls and 60.0% of unhatched eggs contained signs of fungal infection. The percentage of larvae dying within 9 weeks of oviposition was higher for sexually mature females exposed to ARSEF 7234 compared with controls and >40% of dead larvae displayed signs of fungal infection. Thus, for both stages of females and both fungal isolates, fewer surviving larvae were produced after female fungal infection compared with controls. M. anisopliae infection affects female fitness by decreasing female longevity, by decreasing female oviposition before death and through horizontal transmission of M. anisopliae to offspring.     

Growth,reproductive biology and life cycle of the vermicomposting earthworm, Perionyx ceylanensis Mich. (Oligochaeta: Megascolecidae)

In the present study, an attempt has been made to study the growth, reproduction and life cycle of the earthworm, Perionyx ceylanensis Mich. in cowdung for the period of 340 days. Results showed that the overall mean growth rate was 1.79, 1.57 and 1.34 mg/worm/day respectively for the worms cultured singly, in batches of four and eight. Cocoon production rate was found between 0.85 and 0.94 cocoons/worm/day and the hatching success between 74.67% and 82.67%. The majority of the cocoons (95.16–96.77%) hatched only one hatchling. Worms raised singly also produced viable cocoons indicating that P. ceylanensis reproduce parthenogenetically. The life cycle of the worms cultured singly was ±57 days and it was ±50 days for the worms cultured in batches of four and eight. There is a vast scope to utilize P. ceylanensis for vermiculture practices due to short period of life cycle.     

Phenotypic variation in hatchling Chinese ratsnakes (Zaocys dhumnades) from eggs incubated at constant temperatures

We incubated eggs of the Chinese ratsnake Zaocys dhumnades at four constant temperatures (24, 27, 30 and 30 °C) to examine the effects of incubation temperature on hatching success and hatchling phenotypes. Incubation length increased nonlinearly as temperature decreased, with the mean incubation length being 76.7 d at 24 °C, 57.4 d at 27 °C, 47.3 d at 30 °C, and 44.1 d at 33 °C. Hatching successes were lower at the two extreme temperatures (69% at 24 °C, and 44% at 33 °C) than at the other two moderate temperatures (96% at 27 °C, and 93% at 30 °C). Incubation temperature affected nearly all hatchling traits examined in this study. Incubation of Z. dhumnades eggs at 33 °C resulted in production of smaller hatchlings that characteristically had less-developed carcasses but contained more unutilized yolks. Hatchlings from eggs incubated at 27 and 30 °C did not differ in any examined traits. Taking the rate of embryonic development, hatching success and hatchling phenotypes into account, we conclude that the temperature range optimal for incubation of Z. dhumnades eggs is narrower than the range of 24−33 °C but should be wider than the range of 27−30 °C.     

Host species diversity and post-blood feeding carbohydrate availability enhance survival of females and fecundity in Aedes albopictus (Diptera: Culicidae)

Aedes albopictus mosquito is an opportunistic blood feeder and has a broad host range. The feeding behavior and habits of this mosquito are liable to increase the transmission potential of arboviruses. The survival and fecundity in A. albopictus fed on different hosts and post-blood meal provision of sugar were investigated in a laboratory-reared colony. Adult survival of caged female A. albopictus that were fed on blood of two different hosts (double meal) was higher than the females fed only on one host (single meal) (mean survival: 70.2 ± 9.6 vs. 55.5 ± 5.5%, respectively) when held in the laboratory for 72 h after blood feeding. Mean survival of females provided 10% sucrose solution (in water) after a single or double blood meal was higher (90.5 ± 6.4% and 89.3 ± 6.5%, respectively) than in the respective groups receiving water only following blood feeding (double meal: 49.0 ± 9.6%; single meal: 45.3 ± 10.9%). Females receiving a double meal were more fecund on average (89.0 ± 6.6 eggs) than females provided a single meal (82.3 ± 8.2 eggs).     

Life cycle abbreviation in trematode parasites and the developmental time hypothesis: is the clock ticking?

The typical multi‐host life cycle of many parasites, although conferring several advantages, presents the parasites with a highly hazardous transmission route. As a consequence, parasites have evolved various adaptations increasing their chances of transmission between the different hosts of the life cycle. Some trematode species like the opecoelid Coitocaecum parvum have adopted a more drastic alternative strategy whereby the definitive host is facultatively dropped from the cycle, resulting in a shorter, hence easier to complete, life cycle. Like other species capable of abbreviating their life cycle, C. parvum does so through progenetic development within its intermediate host. Laboratory‐reared C. parvum can modulate their developmental strategy inside the second intermediate host according to current transmission opportunities, though this ability is not apparent in natural C. parvum populations. Here we show that this difference is likely due to the time C. parvum individuals spend in their intermediate hosts in the natural environment. Although transmission opportunities, i.e. chemical cues of the presence of definitive hosts, promoted the adoption of a truncated life cycle in the early stages of infection, individuals that remained in their amphipod host for a relatively long time had a similar probability of adopting progenesis and the abbreviated cycle, regardless of the presence or absence of chemical cues from the predator definitive host. These results support the developmental time hypothesis which states that parasites capable of facultative life cycle abbreviation should eventually adopt progenesis regardless of transmission opportunities, and provide further evidence of the adaptive plasticity of parasite transmission strategies.     

Effects of age, weight, hormones, and hibernation on breeding success in boreal toads (Bufo boreas boreas)

The goals of this study were to test the effects of exogenous hormones and hibernation on breeding behavior and gamete release by boreal toads (Bufo boreas boreas). Each year, a subset of 77 toads was hibernated and then paired with hibernated or nonhibernated mates and treated with luteinizing hormone releasing hormone analogue (LHRHa), human chorionic gonadotropin (hCG), or left untreated. Amplexus and egg and sperm production were recorded. At 1 yr of age, only 19% of pairs exhibited amplexus, and no sperm or eggs were produced. At 2 and 3 yr of age, most male toads treated with LHRHa exhibited amplexus (56.9% and 100%, respectively). Among 2-yr-old males, amplexus was more prevalent (P < 0.05) in those that were hibernated than in those that were nonhibernated (54.0% and 33.3%, respectively), but most males in each group (93.3% and 75%, respectively) produced sperm in response to LHRHa treatment. Only one 2-yr-old and two 3-yr-old females produced eggs. At 4 yr of age, eight females produced eggs, but two died from egg retention. More nonhibernated than hibernated females developed eggs (7 of 10 vs. 1 of 10, P < 0.05). Mean (±SD) weight of female toads producing eggs (58.9 ± 11.9 g) was greater (P < 0.05) than that of nonproducing females (43.6 ± 7.0 g). Similarly, four of seven nonhibernated females (58.8 ± 8.3 g) produced eggs at 5 yr of age. All eggs were produced by females treated once with LHRHa. Number of eggs per female varied (141 to 3307), and development to tadpoles was low (0 to 36.5%), although tadpoles did become toadlets. In conclusion, male and female boreal toads matured at 2 and 4 yr of age, respectively, and heavier females were more likely to produce eggs. To enhance breeding success, males should be hibernated and treated with LHRHa. In contrast, female productivity was enhanced by improving their body condition instead of subjecting them to hibernation prior to LHRHa treatment.     

FREQUENCY-DEPENDENT FITNESS CONSEQUENCES OF INTRASPECIFIC NEST PARASITISM IN SNOW GEESE

The reproductive efficiency, defined as the number of breeding recruits produced per egg laid; of intraspecific nest parasites; of hosts in parasitized nests; and of unparasitized nesting females, was measured for 14 years for lesser snow geese Anser caerulescens caerulescens nesting near Churchill, Manitoba, Canada. Relative efficiencies were 0.71–0.88, 0.91, and 1.0 for eggs of parasites, hosts, and unparasitized birds, respectively. Differences in the hatching probabilities of the three classes of eggs produced the efficiency differences. Parasitic success was limited by the parasites' failure to place more eggs than expected by chance into nests at the appropriate time relative to host incubation. Host nesting success was lower when more than one parasitic egg was added to the clutch. No differences in gosling survival and breeding recruitment probabilities were detected among any categories of goslings. Thus, hatching parasitic young are at no disadvantage relative to parental young, and there is no support for the hypothesis that increased success of host young at later stages of reproduction might offset negative effects at the egg stage. The hatching efficiency of parasitic eggs declined more rapidly than that of parental eggs as the parasitism rate increased. Efficiencies were similar when 3–4% of the eggs laid per year were parasitic, but relative parasitic efficiency was significantly lower when the parasitism rate was 8–9% or more. Using ancillary information and assumptions about the fecundity, viability, and behavioral flexibility of parasitic and parental females, we conclude that intraspecific nest parasitism could compete with nesting as a reproductive strategy in this population. The conditional use of parasitism by a large component of the population in certain years, however, combined with negative-frequency dependent success, limits the potential spread of a purely parasitic strategy in this population.     

Bemerkungen zur Biologie sowie Haltung und Vermehrung des Sokotra-Riesengeckos, Haemodracon riebeckii (Peters, 1882)

The Socotra Giant Gecko, Haemodracon riebeckii, is the largest species of lizard on Socotra Island. The nocturnal, arboreal and rupiculous living geckos are omnivorous. Two pairs were kept in terrariums and were fed with various insects (crickets, locusts, cockroaches), sweet fruits and other feeding stuff (such as meat, fish). Temporarily H. riebeckii was kept together with other lizards (Eublepharis macularius, Trachylepis socotrana), without any signs of aggressive behaviour. Juveniles and adults of both sexes are able to produce a sound. These acoustic signals seem to be related to predators, because never any intraspecific function could be observed. Within seven years of captive breeding two females produced 253 eggs. Usually two white and sticky soft-shelled eggs were laid within one clutch, more rarely a single egg was laid. The two eggs of a clutch were always laid on the same day. H. riebeckii belongs to the geckos that bury their eggs and practice some brood care, but no special parental care. The female is able to proof with her hind legs the deep and shape of a hollow in the substrate to bury the eggs, which were buried in a sticky and soft-shelled condition. They are oval in shape (egg length 16.4-19.8 mm, egg width 12.4-17.8 mm, quotient EL:EW 1.22±0.05) and have in the beginning a weight ranging from 1.7100 to 2.5201 g. As typical for geckos with hard-shelled eggs the egg weight decreases during the incubation period. The loss can be between 5.59 to 30.29%. The development of eggs up to hatching of young depends upon temperature and the germinal stage in the laid egg. The time difference between the hatching of the young within one clutch of two eggs was usually 1 to 5 days. In some cases there were, however, longer differences (up to 61 days), which are probably caused by different developmental stages of the embryos during the time of egg laying. The shortest incubation period recorded during our investigations was 83 days for eggs incubated at constant temperature of 28 to 29.5 °C and the longest 359 days at 26 to 26.5 °C. Constant high incubation temperatures caused a premature hatching of young. In normal hatched young were the yolk sac retracted and the navel closed. In premature hatched young were the yolk not resorbed and the mortality within the first three month comparatively high. The snout-vent length (SVL) of newly hatched young is from 27 to 39 mm and the tail length (TL) from 25 to 38 mm (SVL:TL index 0.90-1.27), the weight is from 0.7688 to 1.5366 g. Young specimens are distinguished from adults by the brown/white striped lower jaw and the white-banded tail. Young which hatched in the terrarium were eaten by the adults. A loss of young can be avoided if they are raised individually.     

Alternative life cycle strategies of Megalodiscus temperatus in tadpoles and metamorphosed anurans

Megalodiscus temperatus (Stafford, 1905) is a common paramphistome trematode of North American amphibians with a two host life cycle and has been reported to infect frogs and rarely tadpoles. In this study we document the alternative life cycle strategy of M. temperatus in tadpoles and metamorphosed anurans. We show through field work and experimental infections that M. temperatus can establish in both anuran life stages and worms become gravid and release eggs in both tadpoles and metamorphosed frogs. However, worms exhibit differences in route of infection, development, egg production, and diet in tadpoles and metamorphosed anurans. These alternative life history strategies of M. temperatus suggest different selective pressures on the development and reproductive success of these worms in tadpoles and metamorphosed anurans, and we discuss the evolutionary avenues for and constraints on amphibian trematode life cycles presented by these two different anuran life stages.     

Beyond Symbiosis: Cleaner Shrimp Clean Up in Culture

Cleaner organisms exhibit a remarkable natural behaviour where they consume ectoparasites attached to “client” organisms. While this behaviour can be utilized as a natural method of parasitic disease control (or biocontrol), it is not known whether cleaner organisms can also limit reinfection from parasite eggs and larvae within the environment. Here we show that cleaner shrimp, Lysmata amboinensis, consume eggs and larvae of a harmful monogenean parasite, Neobenedenia sp., in aquaculture. Shrimp consumed parasite eggs under diurnal (63%) and nocturnal (14%) conditions as well as infectious larvae (oncomiracidia) diurnally (26%). Furthermore, we trialled the inclusion of cleaner shrimp for preventative parasite management of ornamental fish, Pseudanthias squamipinnis, and found shrimp reduced oncomiracidia infection success of host fish by half compared to controls (held without shrimp). Fish held without cleaner shrimp exhibited pigmentation changes as a result of infection, possibly indicative of a stress response. These results provide the first empirical evidence that cleaner organisms reduce parasite loads in the environment through non-symbiotic cleaning activities. Our research findings have relevance to aquaculture and the marine ornamental trade, where cleaner shrimp could be applied for prophylaxis and control of ectoparasite infections.     

A new ovine Babesia species transmitted by Hyalomma anatolicum anatolicum

The pathogenicity and morphology of a large Babesia species, Babesia sp. Xinjiang, are described here. The parasite has very low virulence for sheep, and caused no detectable clinical symptoms. Splenectomized sheep infected with the parasite showed mild fever and low parasitemia and would recover gradually. If splenectomized sheep were immuno-suppressed with dexamethasone, the parasitemia could reach 8.5%, and death occurred. A splenectomized calf could not be infected with the Babesia species. Paired parasites were the typical form of the Babesia species in erythrocytes and the average size of a pair of parasites was 2.42 (±0.35) μm × 1.06 (±0.22) μm. Merozoites were found in the gut, salivary gland, haemolymph, ovary and eggs of female Hyalomma anatolicum anatolicum engorged on sheep infected with the parasites. The results of experimental transmission showed that the larval, nymph and adult stages of H. a. anatolicum could transmit the Babesia species to sheep.     

Investigation of Paradiplozoon homoion (Monogenea, Diplozoidae) life cycle under experimental conditions

Diplozoids (Diplozoidae, Monogenea) are fish ectoparasites with a direct life cycle without intermediate hosts. Their free swimming larva, the oncomiracidium, hatches from eggs, invades a fish host and metamorphoses into a post-oncomiracidial larval stage, the diporpa. Later, two diporpae fuse and live as a pair in cross-copulation during their adult life. An experimental study was designed to investigate the life cycle of Paradiplozoon homoion (Monogenea, Diplozoidae) parasitizing their common fish hosts, gudgeon (Gobio gobio). A total of 35 gudgeon parasitized by diplozoids were collected from their natural environment of the Vlára River, Czech Republic, and kept together in tanks with 41 non-parasitized gudgeons reared in a laboratory environment. In total, 100 adult specimens of P. homoion were collected from the Vlára River gudgeon and a new parasite generation was expected to be observed on fish reared in the laboratory environment. Eight days after the first diplozoid eggs appeared on fish gills, the presence of diporpae with one or two pairs of clamps was noted. The appearance of the first juveniles was recorded at the same time as diporpae. Development of P. homoion from egg to sexually mature adult stage took 33 days at a constant temperature of 20 degrees C. The development of eggs in adults of the second generation was observed 2 days after the first observation of these adults. The behavior of oncomiracidia was also studied and this free swimming stage of diplozoids survived for 22 h in the absence of a host. When host fish were experimentally infected by oncomiracidia, diporpae were found attached to the fish gill apparatus within 2 h of infection.     

Relatively low upper threshold temperature in lizards from cool habitats

We used the slender forest skink (Scincella modesta) as a model animal to test for the hypothesis that the upper threshold of incubation temperature is relatively low in lizards using shaded (and thus, cool) habitats. Eight gravid females were collected in early May 2005 from a population in Hangzhou, Zhejiang (eastern China). All females laid a single clutch of 7–13 eggs between mid-May and early June. Eggs were incubated at 24, 28 and 30 (±0.2) °C. None of eggs incubated at 30 °C hatched. Eggs incubated at 24 and 28 °C differed in incubation length but not in hatching success. The incubation length at 24 and 28 °C averaged 22.3 and 20.3 days, respectively. Hatchlings from eggs incubated at 24 and 28 °C did not differ in all examined morphological traits, but hatchlings from eggs incubated at 28 °C performed apparently worse in the racetrack than did their counterparts from eggs incubated at 24 °C. The temperature of 28 °C is close to the upper thermal threshold for successful embryonic development in S. modesta. Compared to other oviparous lizards using open (and thus, warm) habitats, the upper thermal threshold and the range of optimal temperatures for embryonic development are both lower in S. modesta. Our study supports the previous conclusion that species living in thermally different habitats may differ in the upper thermal threshold and the range of optimal temperatures for embryonic development.     

Chill sensitivity and cryopreservation of eggs of the greater wax moth Galleria mellonella (Lepidoptera: Pyralidae)

There is an increasing need for methods of cryopreservation of arthropods. In particular, Lepidoptera are extremely important in entomological applications for the protection of agricultural crops and forest ecosystems and also in many aspects of biodiversity conservation. Yet, few studies have dealt with cryopreservation techniques in species of this insect order.The aim of this study was to examine the chill sensitivity of eggs of the greater wax moth Galleria mellonella (L.) and the possibility to cryopreserve the eggs by vitrification methods.One day-old eggs were dechorionated with water solutions of 1.25% sodium hypochlorite and 0.04% Tween 80, treated with cryoprotective agents in two steps, subjected to rapid cooling by immersion in LN and stored in a mechanical freezer for 48 h at −140 °C. They exhibited survival rates of 1.6 ± 0.5% after being cooled in LN and 0.6 ± 0.2% after being stored in the mechanical freezer. 92.9% of the larvae that hatched from cryopreserved eggs completed development regularly, producing adults that bred and laid fertile eggs.The hatching rate of eggs in the F1 and F2 generations was higher than 90%. Adult emergences of the progeny of eggs stored at ultra-low temperatures allowed us to establish a laboratory colony.     

Near anoxia and sulfide as possible factors influencing the spatial distribution of Acartia tonsa and Acartia clausi: Comparative evaluation of egg tolerance

In many coastal and estuarine areas the planktonic copepods Acartia tonsa and Acartia clausi show a spatial separation with A. tonsa restricted to brackish waters and confined environments and A. clausi inhabiting areas more influenced by sea water. The hatching and viability of A. tonsa and A. clausi eggs exposed to anoxia and anoxia/sulfide (conditions that are frequent in bottom waters of the most confined areas) was evaluated to determine if these stress factors play a role in the distribution of these species. Subitaneous eggs, spawned by laboratory reared organisms, were incubated in near anoxia (< 7.59 × 10^− 3 mmol O₂ L^− 1) or anoxia/sulfide (∼ 1 mmol L^− 1) for different periods (1, 4, 8 and 15 days), then transferred to normoxic conditions. The exposure of the eggs to near anoxia and sulfide appears to induce the same response (quiescence) in both species. Exposure times ≤ 8 days to near anoxia or anoxia/sulfide did not affect egg viability, while 15 day exposure caused significant declines in hatching success of both species. A significant difference between the effects of near anoxia and anoxia/sulfide was observed when incubation lasted 15 days; hatching of eggs exposed to sulfide being higher than that of eggs exposed to near anoxia for both species. No significant differences were observed between the two species in hatching success of eggs exposed to both near anoxia and anoxia/sulfide (with the exception of eggs incubated in near anoxia for 4 days). The results indicate that the impact of anoxia and sulfide on the eggs of the two Acartia species cannot be a factor explaining the spatial distribution in coastal and brackish environments of these copepods.Feeding experiments on A. clausi were also performed. Suitability of different algal species to rear this copepod was evaluated and the results were compared with data previously obtained for A. tonsa. Differences in feeding needs between A. clausi and A. tonsa are discussed.