Egg predation by copepods in Daphnia brood cavities

Both field observations and enclosure experiments show that juvenile copepods enter Daphnia brood cavities to feed on Daphnia eggs and embryos. The ability to perform such in vivo exploitation is reported for both cyclopoid and calanoid copepods. Copepodites of Acanthocyclops robustus (G.O. Sars) were found to eat eggs in brood cavities of D. magna, D. pulex and D. pulicaria in experimental enclosures rich in algae. Copepodites of Eudiaptomus gracilus (G.O. Sars) were found in brood cavities of D. hyalina in a mesotrophic lake. The copepods' intrusions into brood cavities caused dramatic declines in the clutch size of infested Daphnia, and this predation effect could easily be confused with the effect of severe food limitation.     

Effects of maternal and embryo characteristics on post-fertilization provisioning in fishes of the genus <Emphasis Type="Italic">Gambusia</Emphasis>

Maternal provisioning of embryos in Gambusia (Poeciliidae) entails both production of large, yolky eggs and mother-to-embryo transfer of nutrients, the latter of which is readily quantified using injection of radiolabeled nutrients. We assayed patterns of nutrient transfer in broods of 26 Gambusia geiseri and 23 Gambusia affinis females, using injection of tritiated leucine. We examined maternal and embryo characteristics affecting the instantaneous rate of transfer and characterized the pattern of transfer to individual embryos within broods. Maternal (female size and condition) and brood characteristics (mean embryo size, developmental stage, brood size) did not predict the mean level of nutrient transfer to embryos in a brood for either species. Within broods, individual provisioning of embryos was not related to developmental stage, but was related to embryo mass in G. affinis with nutrient transfer higher to larger embryos. In addition, overall within-brood variation in nutrient transfer, measured as coefficient of variation in embryo radioactivity, was higher in G. affinis than in G. geiseri.     

Intraspecific variation in resistance of frog eggs to fungal infection

Documenting sources of variation in host viability at pathogen exposure within and among populations is an important task in order to predict host-pathogen evolutionary dynamics. In the present study, we investigated family and population variation in the degree of embryonic infection of the pathogenic fungus Saprolegnia spp., by infecting moor frog (Rana arvalis) eggs from six populations and exposing them to two different temperatures. We found a significant family effect on the degree of Saprolegnia-infection of eggs and embryos, suggesting that there is genetic variation in resistance among embryos, or variation among females in some aspect of maternally induced resistance. Furthermore, infection level differed significantly between temperatures, with most families having more infected eggs in the relatively colder temperature. However, eggs and embryos from the different populations showed different degrees of Saprolegnia-infection in the two temperatures, i.e., there was a significant population × temperature interaction on the proportion of infected eggs. Thus, the degree of Saprolegnia-infection is sensitive to variation at the level of the family, population and environmental conditions, suggesting that responses to fungal outbreaks will vary geographically and will be difficult to predict.     

The effects of food and temperature regimes on life-history responses to fish kairomones in Daphnia hyalina × galeata*

Life-history responses to two concentrations of fish released info-chemicals at two temperature and food regimes were investigated for one clone of Daphnia hyalina × galeata. The presence of fish kairomones had a negative impact on size at maturity, carbon allocation to individual eggs and size of neonates in all treatments. Food concentration and temperature had positive effects on size of adult stages, independent of kairomone treatment. However, kairomone treatment were not found to interact with food or temperature. Age at maturity was positively influenced by increased temperature and food concentrations, whereas no direct kairomone effects were detected for this trait. Clutch size was not directly influenced by kairomone treatment, whereas both food concentration and temperature had strong, positive effects.     

Does trimethylamine induce life-history reactions in Daphnia?

Laboratory experiments were carried out to investigate life-history reactions of Daphnia to trimethylamine (TMA), a substance, which has recently been found to induce a similar phototactic reaction in Daphnia as fish kairomones. The effects of different treatments (control, fish kairomone and TMA) on the life-history traits of five clones of D. magna and one clone of D. galeata and D. hyalina, respectively, were studied. Only D. magna exhibited significant reactions to TMA and to fish kairomone. D. galeata showed no significant responses to either TMA or to fish kairomone. D. hyalina reacted to the fish treatment with two traits (size and number of eggs at maturity). The comparison of the reaction norms to TMA and fish kairomone demonstrated that the directions of some responses to both factors were similar but were different for others such as for size at maturity. TMA resulted in a larger size at maturity in D. magna, whereas fish kairomone had no significant influence on this trait. We, therefore, conclude that trimethylamine is not the primary causative chemical agent in fish induced life-history adaptations in Daphnia.     

Feeding rate of slimy sculpin and burbot on young lake charr in laboratory reefs

Synopsis Predation and contaminants are two possible factors in the poor recruitment of young lake charr Salvelinus namaycush in the Great Lakes. We measured the feeding rate of slimy sculpins Cottus cognatus and burbot Lota lota on young lake charr (uncontaminated young from eggs of a hatchery brood stock and contaminated young from eggs of Lake Michigan lake charr) in laboratory test chambers with a cobble substrate. The median daily consumption rate of sculpins for all tests was 2 lake charr eggs (N = 22 tests; 95% confidence interval, 0–13) and 2 lake charr free embryos (N = 31 tests; 95% confidence interval, 0–10). Feeding rate did not differ between hatchery and contaminated prey. Slimy sculpins continued to feed on lake charr when another prey organism, the deepwater amphipod Pontoporeia hoyi, was present. Feeding by burbot on free embryos (4–36 d^–1) increased as the mobility of young increased, but burbot consumed about 10% of their body weight weekly in free-swimming young (140–380 d^–1). Predation on lake charr eggs by sculpins could be considerable over the 100 to 140 d incubation period, and burbot could eat large numbers of free-swimming lake charr as the young fish left the reef. Predation pressure on young lake charr may inhibit rehabilitation of self-sustaining populations of lake charr on some reefs unless a critical egg density has been reached.     

Life history responses of <Emphasis Type="Italic">Daphnia longispina</Emphasis> to mosquitofish (<Emphasis Type="Italic">Gambusia holbrooki</Emphasis>) and pumpkinseed (<Emphasis Type="Italic">Lepomis gibbosus</Emphasis>) kairomones

In the present study, the effect of chemical cues from two fish species (mosquitofish and pumpkinseed), at different concentrations, was tested in life history experiments with Daphnia longispina. The two fish species used represent the most abundant planktivores of many Mediterranean shallow lakes (SW Europe), where the indigenous fish communities have been replaced by such exotic assemblages. Results have shown a similar response of D. longispina to both fish species: kairomones stimulated daphnids to produce more offspring, which resulted in higher fitness (r), relatively to a fishless control. Fish presence also induced an earlier first reproduction, a smaller size at maturity of daphnids, and the production of smaller-sized neonates. Significant correlations with fish concentration (indirect measure of fish kairomone concentration) were found for size at maturity and neonate size, for both fish species. These results are in accordance to the “positive response” observed by other authors, which represents a defence mechanism to face losses caused by fish predators. The chemically mediated size reduction of mature females and neonates is an adaptive response to the size-selective predation exerted by fish. Pumpkinseed introduction is very recent in the lake of origin of the daphnids used in the experiments and its kairomone produced similar effects to mosquitofish in the life history of D. longispina. These results are contrary to the existence of a species-specific kairomone and support the hypothesis of a general fish kairomone. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Host-recognition kairomone from Sogatella furcifera for the parasitoid Anagrus nilaparvatae

A kairomone produced by the rice white-backed planthopper Sogatella furcifera (Horvath) for the mymarid egg parasitoid Anagrus nilaparvatae Pang et Wang was investigated. Eggs, female and male adults, nymphs, exuvia, honeydew, nymph-damaged plants and plants with S. furcifera eggs all elicited searching behavior in the parasitoid. Eggs, female adults and plants with eggs were the most attractive, while exuvia and honeydew evoked the weakest responses. The active compound(s) from S. furcifera female adults, nymphs and plants with eggs could be effectively extracted with methanol, acetone, n-hexane, ethyl ether and dichloromethane. Isolation of the active chemical(s) in three solvent extracts, the acetone and n-hexane extracts of S. furcifera female adults, and the acetone extract of S. furcifera nymphs, was accomplished by thin-layer chromatography. Only one fraction was active and had the same chemical properties in the three solvent extracts. Infra-red analysis of this fraction revealed a kind of ester with saturated and unsaturated fatty acids, which was previously found to be active in the same compound as the extracts from the nymphs and female adults of the rice brown planthopper, Nilaparvata lugens (Stål), and identified as palm oil. The results are discussed in relation to host location by A. nilaparvatae.     

Several workers lay eggs in the same brood cell in queenless honey bee (Apis mellifera) colonies

Queenless honey bee (Apis mellifera) colonies are often characterized by the presence of multiple eggs in brood cells. This is surprising because only one egg can be reared to maturity per cell. Moreover, worker honey bees cannot produce many eggs per day. There are several reasons that could explain the presence of multiple eggs in single cells: a) workers cannot control how many eggs they release; in this case we would expect all eggs to be from the same mother; b) excess eggs could be provided as food for the first larva to hatch in the absence of adequate brood care and this would again result in all eggs in one cell sharing the same mother; c) the number of cells available for oviposition may be limiting, obliging workers to lay eggs in cells that already contain eggs, resulting in eggs of mixed maternity. Here we show that the majority of brood cells in queenless colonies contain eggs from multiple mothers. Therefore our results suggest that the presence of multiple eggs in brood cells arises from a limitation on the number of suitable cells available for oviposition. Received 29 September 2008; revised 21 November 2008; accepted 24 November 2008.     

Influence of Host Pheromone on Egg Parasitism by Scelionid Wasps: Comparison of Phoretic and Nonphoretic Parasitoids

The kairomonal activity of the attractant pheromone for the spined soldier bug, Podisus maculiventris (Hemiptera: Pentatomidae), was investigated by exposing fresh pentatomid egg masses in field traps with or without synthetic pheromone. Predominantly two parasitoids were recovered from exposed eggs of P. maculiventris and Euschistus obscurus: Telenomus podisi Ashmead (a generalist pentatomid egg parasitoid) and Telenomus calvus Johnson (a phoretic specialist on Podisus eggs) (Hymenoptera: Scelionidae). The incidences of T. podisi from P. maculiventris and E. obscurus eggs placed in pheromone-baited and nonbaited traps were not significantly different, suggesting that this oophagous wasp does not use the spined soldier bug attractant pheromone as a kairomone. However, T. calvus was reared almost exclusively from egg masses of P. maculiventris placed inside pheromone-baited traps. These results suggest that T. calvus females orient to volatile chemicals emitted by spined soldier bug males as a searching strategy to find areas likely to contain host eggs, in addition to the previously discovered strategy of using the pheromone to guide their phoretic behavior. The data also indicate that T. calvus can distinguish between the egg masses of these pentatomid hosts at close range.     

Fertilization and Subsequent Development of Cattle Oocytes after Reduced Incubation with Spermatozoa

We studied the influence of the duration of the joint incubation of cattle oocytes and spermatozoa (18 versus 1 h) on fertilization, cleavage, and embryonic development in vitrountil the blastocyst stage. Spermatozoa of a bull of the Britanofrizskaya breed were used in the experiments. It was shown in the first experimental series that after a long-term incubation with the spermatozoa, the percentage of penetrated eggs increased 71.7 and 56.0% (p< 0.05) after 18-hour and 1-hour incubation, respectively. However, no differences were found in the number of normally fertilized eggs: 46.5 and 39.0%, respectively. In the second experimental series, no significant differences were found in either the number of cleaving embryos (41.2 and 32.2%, respectively) or the capacity of cleaving embryos to develop in vitrountil the blastocyst stage (21.7 and 15.8%, respectively). Thus, reduction in the time of the joint incubation of cattle gametes upon in vitrofertilization to 1 h did not reduce the number of normally fertilized eggs and did not affect their capacity for subsequent in vitrodevelopment.     

Mortality of Herring Eggs on Different Algal Substrates (Furcellaria spp. and Cladophora spp.) in the Baltic Sea – An Experimental Study

In the Baltic Sea, herring (Clupea harengus membras) spawns in the littoral zone, where its eggs are attached to algae or vascular plants. Field studies indicate that egg mortality can be very high (up to 100%) in eggs that are attached to red algae (Rajasilta et al., 1989, 1993). Because high mortality can be due to allelochemical effects of the algae, we studied the mortality of herring eggs on different algal substrates experimentally. Four types of substrates were tested: fresh Cladophora and Furcellaria, and Furcellaria that had decomposed six days or 23 days. The incubation time in the experiments was 3 days and incubation temperature 12–13 ^oC (ca. 700–800 h-degrees). The results were in accordance with observations made in field studies and indicated significant differences among the substrate types. In eggs attached to fresh Cladophora, mortality was significantly lower (mean=2.8%; n=20) than in those attached to Furcellaria, independently of the treatment of the algae. The highest values of mortality (mean=14.4%; n=20) were found in eggs attached to Furcellaria that had decomposed over a six days’ period. This suggested that Furcellaria contain some chemical substances, which can cause mortality in herring embryos and the effect seems to be dependent on the state of decomposition of the algae.     

In vitro evaluation of the action of the nematophagous fungi Duddingtonia flagrans, Monacrosporium sinense and Pochonia chlamydosporia on Fasciola hepatica eggs

This work evaluated the in vitro action of four isolates of the nematophagous fungi Duddingtonia flagrans (AC001), Monacrosporium sinense (SF53) and Pochonia chlamydosporia (VC1 and VC4) on eggs of Fasciola hepatica. The eggs were plated on 2% water-agar with the grown isolates and control without fungus. After 7, 14 and 21 days, the eggs were removed and classified according to the following parameters: effect type 1, lytic effect with no morphological damage to eggshells; type 2, lytic effect with morphological changes in eggshells and embryos; and type 3, lytic effect with morphological changes in embryos and eggshells, with hyphal penetration and internal egg colonization. Pochonia chlamydosporia showed ovicidal activity on F. hepatica eggs in the studied intervals of the type-3 effect, of 12.8% (VC1) and 16.5% (VC4); 14.4% (VC1) and 18.7% (VC4), 20.1% (VC1) and 21.5 % (VC4), over 7, 14 and 21 days respectively. No statistical difference was found (P > 0.01) among the isolates VC1 and VC4 for effects type 1, 2 and 3 during the studied intervals. Duddingtonia flagrans (AC001) and Monacrosporium sinense fungi only showed effect type 1, with no significant difference between them, with the following results: 60.1% (AC001) and 57.5% (SF53); 62.3% (AC001) and 62.0% (SF53); 66.5% (AC001) and 73.4% (SF53), over 7, 14 and 21 days respectively. Pochonia chlamydosporia fungi negatively influenced the in vitro F. hepatica viability. Therefore it can be considered as a potential biological control agent for this helminth.     

Dynamics of heat transfer to cold eggs in incubating bantam hens and a black grouse

Incubating birds transfer large amount of heat from the brood patch to the eggs during rewarming of cold eggs. If a vasoconstriction is present in the brood patch as in other parts of the body, it could possibly limit heat transfer to the eggs. To investigate this, heat transfer to water-circulated eggs was measured in incubating bantam hens (Gallus domesticus) and a black grouse hen (Lyrurus tetrix) during exposure to cold eggs. Egg temperature, egg surface temperature, heat production and cloacal temperature were also measured. At all levels of egg cooling, egg surface temperature and heat transfer to the eggs was stable throughout an exposure, except during resettling movements, which often changed egg surface temperature and the level of heart transfer. Egg surface temperature decreased linearly with egg temperature in both species, but was lower and more variable at low egg temperature in black grouse than in bantam hens. A higher proportion of the heat production was transferred to the eggs in the black grouse (corresponding to 109–118% of the increase above resting level) than previously reported in bantam hens. Clutch size did not affect this efficiency of heat transfer in black grouse. It is concluded that a vasoconstruction of the brood patch does not occur even under strong cold stress from the eggs. Heat transfer to the eggs is probably controlled more by behavioural adjustments than circulatory changes. An increase in brood patch blood flow probably occurs at relatively high egg temperature at the onset of egg rewarming. The efficiency of heat transfer, and thus the energetic cost of rewarming eggs, depends on the insulation of the bird and nest structure. The boreal/subarctic black grouse was able to reduce heat loss to the environment and transfer a higher proportion of its heat production to the eggs than the tropical bantam hen.Abbreviations AVAs arteriovenous anastomoses - HP heat production - HT heat transfer - T _a ambient temperature - T _b cloacal temperature - T _brp brood patch temperature - T _e egg temperature - T _es egg surface temperature     

Are blackcaps current winners in the evolutionary struggle against the common cuckoo?

Blackcaps Sylvia atricapilla reject artificial cuckoo eggs, and their eggs vary little in appearance within clutches, whereas among clutches eggs vary considerably. Low variation within clutches facilitates discrimination of parasitic eggs, whereas high variation among clutches makes it harder for the cuckoo to mimic the eggs of a certain host species. These traits have most probably evolved as counteradaptations against brood parasitism by the common cuckoo Cuculus canorus, even though blackcaps are not regularly parasitised today. In this study, we investigated how fine-tuned the rejection of parasitic eggs is in this species by introducing three types of eggs into their nests: a real non-mimetic egg the approximate size of a cuckoo egg, an artificial mimetic egg the size of a cuckoo egg and a real conspecific egg. As the rejection frequency of both mimetic and non-mimetic artificial cuckoo eggs has been shown to be high in previous studies, the variation in rejection behaviour between individuals is low, indicating that most individuals within the population are able to reject parasitic eggs. Thus, we predict that (1) the intraclutch variation in egg appearance should be generally low in all individuals, and that (2) regarding conspecific eggs, rejection decisions should be highly dependent on the degree of mimicry between parasitic and host eggs. We found support for these predictions, which indicates that due to their highly sophisticated countermeasures against brood parasitism, blackcaps can probably be regarded as current winners of the arms race with the common cuckoo. Furthermore, the high and consistent rejection frequency of cuckoo eggs found throughout Europe for this species supports the spatial habitat structure hypothesis, which claims that woodland-nesting species breeding near trees, like blackcaps, presumably experienced a high level of parasitism throughout their range in the past and, therefore, their rejection behaviour, once evolved, spread rapidly to all populations.     

Isolation and characterization ofgrandchildless-like mutants inDrosophila melanogaster

Summary Two temperature-sensitive sex-linkedgrandchildless (gs)-like mutations (gs(1)N26 andgs(1)N441) were induced by ethylmethane sulphonate inDrosophila melanogaster. They complemented each other and mapped at two different loci (1–33.8±0.7 forgs(1)N26 and 1–39.6±1.7 forgs(1)N441), which were not identical to those of any of thegs-like mutants reported in earlier work.Homozygous females of the newly isolated mutants produced eggs that were unable to form pole cells and developed into agametic adults. Competence of the embryos to form pole cells was not restored by wild-type sperm in either mutant; that is, the sterility caused by these mutations is controlled by a maternal effect.Fecundity and fertility ofgs(1)N26 females were low, and their male offspring showed a higher mortality than that of female offspring, causing an abnormal sex ratio. The frequency of agametic progeny was 93.1% and 55.8%, when the female parents were reared at 25° C and 18° C, respectively. In eggs produced by thegs(1)N26 females reared at 25° C, the migration of nuclei to the posterior pole was abnormal, and almost no pole cell formation occurred in these egg. Furthermore, half of these eggs failed to cellularize at the posterior pole. When the females were reared at 18° C, almost all of the eggs underwent complete blastoderm formation, and in half of these blastoderm embryos normal pole cells were formed.In the other mutant,gs(1)N441, the fecundity and fertility of the females were normal. The agametic frequency in the progeny was 70.8% and 18.6% when the female parents were reared at 25° C and 18° C, respectively. In the eggs laid by females reared either at 25° C or at 18° C, the migration of nuclei to the periphery and cellularization proceeded normally; nevertheless, in the majority of the embryos no pole cell formation occured at the stage when nuclei penetrated into the periplasm. When the females were reared at 18° C, some of the embryos from these females formed some round blastoderm cells with cytologically recognizable polar granules and nuclear bodies, which are attributes of pole cells. The temperature sensitive period ofgs(1)N441 was estimated to extend from stage 9 to 13 of King's stages of oogenesis.     

Combined effect of the insecticide carbaryl and the Chaoborus kairomone on helmet development in Daphnia ambigua

The cladoceran Daphnia ambigua was exposed to both the insecticide carbaryl and the kairomone released from the predator Chaoborus simultaneously, and its morphological changes were analyzed. Daphnia developed helmets in response to the kairomone, but not in response to carbaryl at low (sublethal) concentrations (1–3 µg 1^–1). However, the carbaryl enhanced the development of high helmets and prolonged the maintenance period of the helmets over instars in the presence of the kairomone. These results suggest that sublethal concentrations of the insecticide alter predator-prey interactions by inducing helmet formation in Daphnia, which may reduce vulnerability of the Daphnia to predation.     

Benefits of self-superparasitism in a polyembryonic parasitoid

Macrocentrus grandii is a polyembryonic parasitoid, with embryos that divide asexually within the host (European corn borer, Ostrinia nubilalis) to produce broods of clonal offspring. From a biological control standpoint, polyembryony seems advantageous because each parasitized host yields multiple parasitoids with minimal time and egg investment. When we observed M. grandii in the field, however, we found that the parasitoid virtually always invested additional time and, if possible, stings into hosts that it had already stung, apparently reducing some of the advantages of polyembryony. We therefore investigated and found support for two potential benefits that can be gained by self-superparasitism in this system. First, multiple stings allowed production of mixed-sex broods: 27% of multiply-stung versus 0% of singly-stung hosts produced mixed-sex broods. Second, multiple stings increased mean parasitoid progeny produced per host, primarily by reducing the chance of complete brood failure. Our results indicate substantial benefit for a second sting, but little benefit for three or more stings, even though M. grandii was sometimes observed to invest more than two stings within a single host. However, we also found that within-host larval competition is prevalent, suggesting that supernumerary stings may pay off in competition against conspecific larvae. Such additional investment within a single host would be particularly beneficial when hosts, rather than eggs, are limiting, but would decrease the overall efficacy of M. grandii as a biological control agent.     

Reproductive ecology of five pipefish species in one eelgrass meadow

Synopsis Synopsis Pipefishes have rarely been watched in the wild and have never before been followed in their common seagrass habitats. This study explores the reproductive ecology of five species of pipefishes living in a Swedish eelgrass meadow during parts of four breeding seasons, tagging four of the species. Pipefish are remarkable for their specialised paternal care: only males aerate, osmoregulate and nourish the developing embryos. Two of the species (Entelurus aequoreus andNerophis ophidion) have simple ventral gluing of eggs on the trunk while three species (Syngnathus acus, S. rostellatus andS. typhle) have fully enclosed brood pouches on their tails. Males of the former species receive eggs from one female while males of the genusSyngnathus receive partial clutches from several females. Sex ratios of adults on the site differed from equal to male-biased to female-biased, according to species.S. typhle were most numerous and were resighted most often. They were present throughout the breeding season whereas there were temporal shifts in the presence of the other species on the meadow and in some sex ratios. Most species occurred in the deeper, denser part of the meadow but there was some habitat separation by species and sex. All species tended to stay low in the eelgrass, primarily coming up above the eelgrass to display and mate. No species showed site fidelity either to a home range or to the meadow, withE. aequoreus adults spending least time on the meadow. Sexual size dimorphism differed: males were larger inS. rostellatus, the same size inS acus and smaller in the other species. Although the species overlap in habitat requirements and breeding season, the only observed interspecific interactions were abortive courtships betweenSyngnathus species.     

Partial age-specific life tables for Monochamus titillator in Dendroctonus frontalis infested loblolly pines

Partial age-specific life tables were constructed for Monochamus titillator(Fabricius) (Coleoptera: Cerambycidae) in Dendroctonus frontalisZimmermann (Coleoptera: Scolytidae) infested loblolly pine (Pinus taedaL.) trees. Successive life stages including egg, early larvae, mid-stage larvae, late larvae, and adult emergence were sampled within six sample trees. Generation mortality ranged from 60.94% to 98.61% in sample trees. Highest mortality typically occurred to eggs and mid-stage larvae. Possible mortality factors included resinosis, predaceous beetles, parasitoids, and woodpeckers. Dendroctonus frontalisbrood stages were determined for consecutive M. titillatorsampling. Monochamus titillatorand D. frontaliscoexisted and likely interacted in the phloem of host trees for at least 20 days.