Distribution and routes of drift migrations in larvae of three species of flatfish Bothus (Bothidae) in open waters of the northern Atlantic

On the basis of large collections, comprehensive data on the distribution of larvae of three species of flatfishes of the genus Bothus (B. ocellatus, B. robinsi, and B. podas) in the northern Atlantic are provided, and the routes of their drift migrations are discussed. Special attention is focused on discussing problems of identification of larvae of the listed species and the specification of evidence on meristic characters of adult flatfishes of these species used for the diagnostics of their larvae. It is shown that larvae of two American species of Bothus carried out from the shelves to the system of western boundary currents are widely distributed in the northern Atlantic drifting in waters of the Northern Subtropical Gyre (NSG). Some of them reach the Azores, and some are drifted along the periphery of the circulation system of the NSG currents towards North America. Unlike larvae of American species, larvae of the eastern Atlantic B. podas perform no transatlantic drift migrations, and the area of their distribution is confined to the waters of the eastern Atlantic. Such differences in the extent of latitudinal passive migrations between B. podas and western Atlantic species are explained according to Torson (1965) by differences in temperature conditions during the drift of larvae of species under comparison that directly affect the decrease (during water temperature increase) or increase (at temperature decrease) of the pelagic phase in their development. The latitudinal drift of larval B. podas from West Africa westwards proceeds due to currents that gradually warm during their motion, which causes a decrease of the dates of their staying in the pelagial. The transatlantic drift of larval American Bothus spp. from North America eastwards is observed in gradually cooling currents, which leads to an increase in the duration and extent of their passive migrations.     

On the ecology of the filter-feeding Neureclipsis bimaculata (Trichoptera, Polycentropodidae) in an acid and iron rich post-mining stream

Open-pit mining of lignite in East Germany has created landscapes with extreme environmental conditions. Post-mining aquatic habitats are characterized by low biodiversity and simple food webs due to the impact of acid mine drainage. In this study, the ecology of the filter-feeding caddisfly Neureclipsis bimaculata (L.) was examined, which is abundant in the acidic Floßgraben stream (pH 2.5–3.6) in Lower Lusatia, Germany. From benthic samples, we measured larval size and biomass and estimated population dynamics. The seston drift was sampled and retention efficiency of the larvae’s nets was assessed in a field tracer experiment to evaluate diet availability. Mean annual abundance was 1,380 ind m^?2 with a biomass of 1,010 mg m^?2. Annual secondary production of N. bimaculata was 8,450 mg m^?2. The larval microdistribution reflected the preference for in-stream wood and a limitation by low flow velocity. Morphometric factors of the larvae in the acidic stream were in the range of morphometric factors found in circumneutral streams that covered a range of trophic levels. Although coverage by iron particles reduced flow, the nets account for 63% of the mean particle retention. It is suggested that the retention efficiency and the availability of drifting organisms allowed the larvae to feed on 8.4 mg m^?2 per day, which revealed a ratio of biomass production to ingested food of 60%.     

Causes of larval drift of the fire salamander,Salamandra salamandra terrestris,and its effects on population dynamics

Summary The larval drift of the fire salamander was investigated over a period of three years in a mountain brook (Niederbergisches Land, F.R. Germany), as well in a laboratory water channel. The rate of larval drift fluctuated between 19% and 41% of the total population of larvae in a defined section of the brook during these three years. Most (83%) of the drifting larvae were hatchlings or very young stages. The drift was dependent on the strength of the current, the number of spawning females, the presence of suitable hiding places, sufficient space and adequate food. Hungry larvae drifted more often than satiated animals. The drift behaviour of hatchlings differed distinctly from that of older larvae. The significance of ecological factors on larval drift is discussed. It is evidently a more important factor in selection than has hitherto been recognized.     

Biochemistry of mosquito infection: Preliminary studies of biochemical change in Culex pipiens quinquefasciatus following infection with Lagenidium giganteum

The effect of infection of larvae of the mosquito Culex pipiens quinquefasciatus by the fungus Lagenidium giganteum has been studied from a biochemical standpoint. Methods were developed to analyze larval extracts that were essentially free of parasitic material. Biochemical parameters investigated on a per larva basis were protein, and the enzymes o-diphenol oxidase, glutamate transaminase, alkaline phosphatase, trehalase, and chitobiase. The behavior of the total amino acid and sugar pools were also examined. In general it was found that the infected larvae exhibited a significant decrease in rate of synthesis of most of the parameters studied and that the rates eventually fell to zero when compared to healthy control organisms. The progress of mycosis was correlated with visual evidence and it was concluded that the larvae were dying from starvation as a consequence of the utilization of their endogenous reserves by the parasite. Death of the larvae occurred as a general rule, in laboratory conditions, some 48 hr after initiation of infection by the fungus.     

Drift of macroinvertebrates in a channel carrying heated water from a power plant

Hourly drift samples were collected once each month over a 24 hour period for 10 months at the mouth of a channel returning heated coolant water from a steam electric generating station to a 330 ha reservoir. Most benthic macroinvertebrates existed at lower densities on the bottom of the channel than in the reservoir. No organisms were found in the channel during summer months when water temperatures reached 42.2°C. The most abundant organisms drifting from the channel were Chaoborus larvae which probably were drawn from the reservoir, through the condensors of the power plant, and down the effluent channel. The maixmum drift rate for Chaoborus larvae occured in August (8.91 × 10⁴ mg/day) while the minimum rate occurred in December (3.92 × 10² mg/day). Chaoborus larvae exhibited a diurnal periodicity in drift corresponding to their nightly emergence from bottom sediments in the reservoir.     

Species specific responses of common grassland plants to a generalist root herbivore (Agriotes spp. larvae)

Insect root herbivores can alter plant community structure by affecting the competitive ability of single plants. Our study aims at increasing knowledge on the impact of click beetle larvae (Elateridae, genus Agriotes) on grassland plant communities, by determining biomass responses as well as responses of the arbuscular mycorrhizal fungi (AMF) symbiosis to this widespread generalist root herbivore for eight common grassland plant species (Festuca rubra, Holcus lanatus, Poa pratensis, Achillea millefolium, Plantago lanceolata, Veronica arvensis, Medicago lupulina, Trifolium repens), belonging to three functional groups (grasses, herbs, legumes).The presence of larvae in the rhizosphere of individual plants had an overall negative effect on root biomass, which varied in degree between plant species, with more root biomass being removed from larger root systems. The effect of larvae on shoot biomass, total plant biomass and shoot/root ratio also differed in strength between plant species. Relative changes in root and total plant biomass ranged from a 71% and 55% loss, respectively, in V. arvensis to an 11% and 1% increase in T. repens, but were not related to root- or plant size. Root colonization by AMF and the length of extraradical AMF hyphae were not affected by larvae. The plant's functional group did not determine the response of the plant to feeding by larvae. Growth of larvae was positively correlated with root biomass, but did not depend on plant species or group identity.The results confirm the generalist nature of Agriotes spp. larvae, which depend on sufficient root quantity and are likely to feed most on those plant species whose roots are most abundant in their habitat. Their effect on the plant community may be generated through the ability of the respective plant species to cope with the herbivore damage, with tolerances being plant species rather than plant group specific.     

Effect of environment on the adaptive abilities of fry roach Rutilus rutilus (L.) (Cyprinidae) during early ontogenesis

In recent years a considerable decrease in the abundance of predatory fishes has been observed in spawning tributaries of the Rybinsk Reservoir caused by their intensive catching. The lack of encounters with predators before the downstream migration of young fish hampers the development of necessary skills of defensive behavior in the absence of predation experience. As a result, after downstream migration, the juveniles are incapable of adapting to the predation pressure in the reservoir and are subjected to intensive elimination. The adaptive potential of the roach Rutilus rutilus L. was experimentally studied in siblings raised from the larvae to the late fry stage both in the presence and absence of a predator. It has been found that the fry that was raised under different conditions differed in their adaptive potential in new environment conditions.     

Oceanic fronts in the Sargasso Sea control the early life and drift of Atlantic eels

Anguillid freshwater eels show remarkable life histories. In the Atlantic, the European eel (Anguilla anguilla) and American eel (Anguilla rostrata) undertake extensive migrations to spawn in the oceanic Sargasso Sea, and subsequently the offspring drift to foraging areas in Europe and North America, first as leaf-like leptocephali larvae that later metamorphose into glass eels. Since recruitment of European and American glass eels has declined drastically during past decades, there is a strong demand for further understanding of the early, oceanic phase of their life cycle. Consequently, during a field expedition to the eel spawning sites in the Sargasso Sea, we carried out a wide range of dedicated bio-physical studies across areas of eel larval distribution. Our findings suggest a key role of oceanic frontal processes, retaining eel larvae within a zone of enhanced feeding conditions and steering their drift. The majority of the more westerly distributed American eel larvae are likely to follow a westerly/northerly drift route entrained in the Antilles/Florida Currents. European eel larvae are generally believed to initially follow the same route, but their more easterly distribution close to the eastward flowing Subtropical Counter Current indicates that these larvae could follow a shorter, eastward route towards the Azores and Europe. The findings emphasize the significance of oceanic physical–biological linkages in the life-cycle completion of Atlantic eels.     

Inferring Processes from Spatial Patterns: The Role of Directional and Non–Directional Forces in Shaping Fish Larvae Distribution in a Freshwater Lake System

Larval dispersal is a crucial factor for fish recruitment. For fishes with relatively small-bodied larvae, drift has the potential to play a more important role than active habitat selection in determining larval dispersal; therefore, we expect small-bodied fish larvae to be poorly associated with habitat characteristics. To test this hypothesis, we used as model yellow perch (Perca flavescens), whose larvae are among the smallest among freshwater temperate fishes. Thus, we analysed the habitat association of yellow perch larvae at multiple spatial scales in a large shallow fluvial lake by explicitly modelling directional (e.g. due to water currents) and non-directional (e.g. due to aggregation) spatial patterns. This allowed us to indirectly assess the relative roles of drift (directional process) and potential habitat choice on larval dispersal. Our results give weak support to the drift hypothesis, whereas yellow perch show a strong habitat association at unexpectedly small sizes, when compared to other systems. We found consistent non-directional patterns in larvae distributions at both broad and medium spatial scales but only few significant directional components. The environmental variables alone (e.g. vegetation) generally explained a significant and biologically relevant fraction of the variation in fish larvae distribution data. These results suggest that (i) drift plays a minor role in this shallow system, (ii) larvae display spatial patterns that only partially covary with environmental variables, and (iii) larvae are associated to specific habitats. By suggesting that habitat association potentially includes an active choice component for yellow perch larvae, our results shed new light on the ecology of freshwater fish larvae and should help in building more realistic recruitment models.     

Contribution of fungal biomass to the growth of the shredder, Pycnopsyche gentilis (Trichoptera: Limnephilidae)

1.  1. It has been accepted that aquatic hyphomycetes colonising submerged leaves increase the nutritional value of leaf detritus and suggested that fungal biomass plays a greater role in the growth of shredders than leaf tissue itself. However, it is not clear what proportion of the nutritional needs of shredders is met by fungal biomass.
2.  We fed Pycnopsyche gentilis larvae with tulip poplar ( Liriodendron tulipifera ) leaf discs colonised by the aquatic hyphomycete, Anguillospora filiformis , which had been radiolabelled to quantify the contribution of fungal carbon to the growth of the shredder at different larval developmental stages. Instantaneous growth rates of larvae on this diet were also estimated.
3.  When provided with fungal-colonised leaves (14–16% fungal biomass), the third and the fifth instar larvae of P. gentilis grew at the rates of 0.061 and 0.034 day⁻¹, respectively, but on a diet of sterile leaves, both larval instars lost weight. The incorporation rates of fungal carbon were 31.6 μg C mg⁻¹ AFDM day⁻¹, accounting for 100% of the daily growth rate of the third instar larvae and 8.6 μg C mg⁻¹ AFDM day⁻¹, accounting for 50% of the daily growth rate of the fifth instar larvae.
4.  These results suggest that leaf material colonised by A. filiformis is a high quality food resource for P. gentilis larvae, and that fungal biomass can contribute significantly to the growth of these larvae. Differences in feeding behaviour and digestive physiology may explain the significantly greater assimilation of fungal biomass by the earlier instar than the final instar. To satisfy their nutritional needs the fifth instar larvae would have to assimilate detrital mass that may have been modified by fungal exoenzymes.     

Biogéographied'un groupe d'Échinides cénozoiques (Echinolampas et ses sous-genres Conolampas et Hypsoclypus)

Echinolampas is a subtropical genus living in rather shallow water; one may regards it as a climatic marker. The theory of continental drift affords a rather good explanation for its distribution in space during Cenozoic era. It appears in Old Wolrd during Paleocene and it occurs in Central America during Middle Eocene; that implies it had to cross the already broad Atlantic Ocean; but at that time this ocean is not as broad at it is now. Migration along the shelf area which rimmed North Atlantic might have been impossible, owing to disruption of land connection between Europe and North America. Probably the migration occured in low latitudes and pelagic larvae were transported by one of the two equatorial currents. Diversity of the genus has much decreased during Late Eocene. The cause may be chiefly due to climatic deterioration, resulting from marine communication between North Atlantic and Arctic Ocean. Echinolampas occurs for the first time in Australia during Oligocene. One may suggest the possibility of a link between this late evidence and the quite remote position till then of Australian continent. During Miocene, the relative decrease in Echinolampas diversity in the Mediterranean Basin occurs as a result of the welding between Asia and Africa.     

Drift behaviour and microhabitat selection in the preimaginal stages of Simulium chutteri (Diptera Simuliidae)

The aquatic stages of the cattle biting pest, Simulium chutteri Lewis utilize river flow in their dispersal and colonization behaviour. Peaks of drifting activity in S. chutteri larvae occurred in the early morning and late afternoon. It is deduced that female flies scatter eggs onto slow flowing waters upstream of rapids. Larvae hatch from drifting eggs and colonize substrates in slower flowing regions upstream of rapids, while later stage instars move into faster flowing regions within rapids where they complete their development. This microhabitat selection by S. chutteri leads to rapid attainment of large population sizes in suitable sections of river and reduces competition between different stage larvae. In their utilization of a variety of microhabitats the larvae of this species differ from co-existing simuliid species which restrict developmental stages to single habitats.Catastrophic drift was recorded for S. chutteri larvae and could be a mechanism to regulate population size.Drift of simuliid larvae off rapids was not related to benthic population densities in the rapids and was therefore not due to excessive production. It is concluded that larval drift off rapids is related to habitat disturbances associated with water flow fluctuations and the activity of aquatic predators and other animals.The distribution of S. chutteri in the Vaal River is restricted by oviposition requirements of the adult female. Knowledge of drift behaviour and water flow requirements of Simuliidae have been applied to manage the population size of S. chutteri in the Vaal River.     

Life-cycle nitrogen budget for the gypsy moth, Lymantria dispar, reared on artificial diet

Lymantria dispar larvae were reared on a wheat germ-based artificial diet from egg eclosion until pupation. Utilization efficiency of dietary nitrogen underwent an age-specific decrease from 75% in the first instar to 54 and 43% for last-instar female and male larvae, respectively. Relative rates (mg/day/mg biomass) of nitrogen consumption and assimilation also decreased during larval development, but the excretion rate of nitrogen was constant for all instars and both sexes. Larval % nitrogen decreased as the larvae matured, while the percentage in the frass increased. These data suggest that need for nitrogen decreases as the larva matures. While L. dispar is comparatively inefficient at assimilating dietary nitrogen, over one-half of that assimilated by the female larva is transferred to egg production by the adult.     

Sublethal effects of Texas brown tide on Streblospio benedicti (Polychaeta) larvae

The Texas brown tide bloom is noted for a concordant decline in benthic biomass and species diversity. However, the link between harmful effects induced by Texas brown tide and benthos has not been demonstrated. It has been proposed there may be a larval bottleneck, where larvae, but not adults, suffer adverse effects. This study was performed to test the effect of brown tide alga, Aureoumbra lagunensis, on mortality, growth and behavior of Streblospio benedicti larvae. Growth rates and swimming speeds, but not mortality rates, of polychaete larvae were reduced in cultures with brown tide relative to Isochrysis galbana, which is about the same size as brown tide. Results from this research indicate that brown tide does have harmful sublethal effects for one dominant species of meroplanktonic larvae, which could help explain reduced adult population size.     

Aquatic and terrestrial invertebrate drift in southern Appalachian Mountain streams: implications for trout food resources

1. We characterised aquatic and terrestrial invertebrate drift in six south‐western North Carolina streams and their implications for trout production. Streams of this region typically have low standing stock and production of trout because of low benthic productivity. However, little is known about the contribution of terrestrial invertebrates entering drift, the factors that affect these inputs (including season, diel period and riparian cover type), or the energetic contribution of drift to trout. 2. Eight sites were sampled in streams with four riparian cover types. Drift samples were collected at sunrise, midday and sunset; and in spring, early summer, late summer and autumn. The importance of drift for trout production was assessed using literature estimates of annual benthic production in the southern Appalachians, ecotrophic coefficients and food conversion efficiencies. 3. Abundance and biomass of terrestrial invertebrate inputs and drifting aquatic larvae were typically highest in spring and early summer. Aquatic larval abundances were greater than terrestrial invertebrates during these seasons and terrestrial invertebrate biomass was greater than aquatic larval biomass in the autumn. Drift rates of aquatic larval abundance and biomass were greatest at sunset. Inputs of terrestrial invertebrate biomass were greater than aquatic larvae at midday. Terrestrial invertebrate abundances were highest in streams with open canopies and streams adjacent to pasture with limited forest canopy. 4. We estimate the combination of benthic invertebrate production and terrestrial invertebrate inputs can support 3.3–18.2 g (wet weight) m⁻² year⁻¹ of trout, which is generally lower than values considered productive [10.0–30.0 g (wet weight) m⁻² year⁻¹]. 5. Our results indicate terrestrial invertebrates can be an important energy source for trout in these streams, but trout production is still low. Any management activities that attempt to increase trout production should assess trout food resources and ensure their availability.     

Reciprocal Effects between Burying Behavior of a Larval Dragonfly (Odonata: Macromia illinoiensis) and Zebra Mussel Colonization

Invasive zebra mussels (Dreissena polymorpha) often colonize dragonfly larvae, especially spawling species whose survivorship to emergence as terrestrial predators is consequently reduced. Using individuals of the sprawler, Macromia illinoiensis, as their own controls, we compared the burying behavior of penultimate instar larvae before (i.e. baseline) and after their colonization by zebra mussels under ambient conditions. Individuals that took longer to bury themselves when mussel-free had a higher rate of colonization by mussels over a five-day period compared to those that buried faster. In contrast, the depth at which individuals buried when mussel-free was not predictive of subsequent colonization rate. Although mean bury time did not differ between baseline and when an individual carried one or more mussels, colonized larvae buried more shallowly than when mussel-free. Moreover, attached mussels increased the risk of subsequent colonization by zebra mussels. After naturally losing all of their attached mussels, bury time and depth of individuals did not differ from their baseline behavior, indicating that the changes in the behavior of colonized individuals were due to mussel loads and not their time in captivity. Under natural conditions, the positive feed-back between mussel attachment and increasing vulnerability to colonization helps explain how mussel loads, which are lost at molting, can accumulate quickly over the duration of the final larval stadium. Because zebra mussel attachment decreases the crypsis that that a M. illinoiensis gains from burying, the invasive mussel may also make dragonfly larvae more detectable to visual predators.     

Sun Compass Orientation Helps Coral Reef Fish Larvae Return to Their Natal Reef

Reef fish sustain populations on isolated reefs and show genetic diversity between nearby reefs even though larvae of many species are swept away from the natal site during pelagic dispersal. Retention or recruitment to natal reefs requires orientation capabilities that enable larvae to find their way. Although olfactory and acoustically based orientation has been implicated in homing when larvae are in the reef’s vicinity, it is still unclear how they cope with greater distances. Here we show evidence for a sun compass mechanism that can bring the larvae to the vicinity of their natal reef. In a circular arena, pre-settlement larvae and early settlers (<24 hours) of the cardinal fish, Ostorhinchus doederleini, showed a strong SSE directional swimming response, which most likely has evolved to compensate for the locally prevailing large scale NNW current drift. When fish were clock-shifted 6 hours, they changed their orientation by ca. 180° as predicted by the tropical sun curve at One Tree Island, i.e. they used a time-compensated sun compass. Furthermore, the fish oriented most consistently at times of the day when the sun azimuth is easy to determine. Microsatellite markers showed that the larvae that had just arrived at One Tree Island genetically belonged to either the local reef population or to Fitzroy Reef located 12 kilometers to the SSE. The use of a sun compass adds a missing long-distance link to the hierarchy of other sensory abilities that can direct larvae to the region of origin, including their natal reef. Predominant local recruitment, in turn, can contribute to genetic isolation and potential speciation.     

Calliphorin,a major protein of the blowfly: Correlation between the amount of protein,its biosynthesis,and the titer of translatable calliphorin-mRNA during development

The amount of calliphorin, its biosynthesis, and the levels of translatable calliphorin-mRNA have been determined during the postembryonic development of Calliphora vicina R.-D. The amount of calliphorin increases in early third-instar larvae, reaching maximal levels in 6-day-old animals. It continuously decreases during late larval and pupal development to approximately one-half of the maximal levels and abruptly sinks during eclosion. The biosynthesis of calliphorin takes place only in 3- to 5-day-old larvae. Poly(A)⁺-RNA has been translated into proteins in a wheat germ cell-free system. Calliphorin-mRNA can be detected in 3- to 7-day-old larvae; maximal concentrations are observed in 4- and 5-day-old animals. No calliphorin-mRNA can be detected in prepupae, pupae, or imagos. The biosynthesis of calliphorin in blowfly larvae stops before a decrease of translatable calliphorin-mRNA is observed. This finding raises the question of the mechanism of in vivo inactivation of this specific mRNA.     

Study of intrapopulational variability of duration and temperature norms of development of the linden bug Pyrrhocoris apterus (Heteroptera, Pyrrhocoridae)

The existence of significant variability in duration and temperature norms of development between families within insect populations has been shown for the first time. This variability is inferfamily and therefore has genetic ground. Revealed for the first time is the statistically significant positive correlation between the regression coefficient of the development rate for temperature and the temperature threshold for development of eggs and larvae from different families. The greater the slope of the regression line of the development rate for temperature, the higher the temperature threshold value in this particular family. These results demonstrate for the first time the existence of genetic co-variation between the regression coefficient and the temperature threshold within the insect populations. It is suggested that the source of the interpopulational and interspecies changes in the temperature reaction norms of the insect development might be the intrapopulational hereditary variability of the development duration, regression coefficient, and the development threshold, this variability being an object of natural selection. It was shown that in all studied families and populations the values of the linear regression coefficient of development rates for temperature in eggs of the linden bug Pyrrhocoris apterus were markedly and statistically significantly higher, while the temperature threshold values—lower as compared with the corresponding parameters in larvae. These results obviously are in contradiction with the concept of the “isomorphism of development rates” (Jarosik et al., 2002), according to which the development threshold for all life cycle stages of a species should be the same, whereas only slopes of the regression lines of the development rate for temperature can differ. For the first time the absence of genetic covariation has been shown between the temperature norms of development of different life cycle stages of the species—eggs and larvae. This means that the regression coefficient as well as the sum of the degree-days and the development threshold in eggs and larvae are inherited independently and therefore they can be independently changed in evolution in correspondence with specific environmental conditions, under which these life cycle stages take place.