Larval photoresponses of the polyclad flatworm Maritigrella crozieri (Platyhelminthes,Polycladida) (Hyman)

Phototaxis by larvae of the flatworm Maritigrella crozieri was used to determine spectral sensitivity, the ontogeny of the phototactic pattern, and the lowest light intensity to induce a directional response (intensity threshold). Adult M. crozieri live in shallow water with the tunicate Ecteinascidia turbinata and have a planktonic larval phase lasting longer than 3 weeks. The primary spectral sensitivity maximum was at 500 nm, which is probably an adaptation to the spectrum available underwater at twilight. The phototactic threshold changed with age, as dark-adapted, 1-week-old larvae had a threshold (1.84×10¹⁷ photons m⁻² s⁻¹) an order of magnitude higher than that of 3-week-old larvae. Flatworm larvae are relatively insensitive to light as compared to other invertebrate larvae. Young larvae were positively phototactic at high light intensities and negative at low, a pattern typical of a predator avoidance shadow response. In contrast, older larvae were only positively phototactic, which would be useful for transport to shallow-water adult habitats.     

Influence of light intensity and wavelength on phototactic behaviour of larval silver perch Bidyanus bidyanus and golden perch Macquana ambigua and the effectiveness of light traps

Larval golden perch, Macquaria ambigua , and silver perch, Bidyanus bidyanus , were exposed to light gradients in wavebands centred on 400, 496, 601 and 695 nm at nominal quantum irradiance values of 0–1, 1–0 and 10 μmol m⁻² s^−l. Silver perch larvae displayed stronger phototactic behaviour than golden perch, and both species were most responsive to light in the 601 nm waveband. The intensity of phototactic responses in both species was greater at higher irradiance levels. Enhanced responsiveness to longer wavelengths reflects possible adaptations to life in turbid habitats where the underwater light field is dominated by yellow/orange wavebands.
At night, traps fitted with 12 h yellow lightsticks attracted more golden perch larvae than traps with blue, green, orange, red or no lightstick. The efficacy of yellow lightsticks may be due to yellow/orange wavebands not being attenuated under water as rapidly as blue or red wavebands. Yellow lightsticks also emit a greater intensity of light over a longer time than other colours tested, which may have increased the effectiveness of yellow traps. Light traps were ineffective during the day.     

Thermoregulation behaviour in codling moth larvae

Abstract. The thermoregulation behaviour of the codling moth, Cydia pomonella, is investigated in temperature gradient experiments with larvae feeding within apples, and with mature larvae searching for cocooning sites. Feeding larvae appear to prefer the apple hemisphere with a higher temperature (i.e. they build larger cavities in the radiated, warmer part of the fruit). The proportion of larval cavities in the warmer hemisphere is positively related to increasing apple temperature on that side, as well as to the temperature difference between the warm and the cool fruit hemisphere. The mechanism in feeding larvae can be termed as cryptic basking because, during microhabitat selection, the caterpillars exploit temperature differences that are caused explicitly by incident solar radiation. Fifth-instar larvae in search of cocooning sites show no temperature preference within the large gradient offered (9–29 °C), with no difference between males and females. During larval development, the insect changes its thermoregulation behaviour in response to a possible shift in benefits of an elevated body temperature with respect to environmental conditions. Both the thermoregulation behaviour and such a shift of behavioural response should be respected when simulating body temperatures of the species.     

Ontogenetic changes in the association between antipredator responses and growth variables

Abstract.  1. An organism's growth parameters are expected to depend on environmental constraints, such as predation risk and food supply. However, antipredator responses, food intake, and thus growth of an animal may be mediated by behavioural traits, which are likely to differ among developmental stages. In this study, it was investigated how the relationship between growth and behavioural antipredator responses changes during ontogeny in the time-constrained dragonfly species Libellula depressa , and which factors influenced specific behavioural decisions at different points in ontogeny.
2. The results revealed that behavioural strategies differed between larval developmental sages, depending on associations between larval growth, food supply, and predation risk. Early in ontogeny, faster development was correlated with high larval activity and high food supply. This resulted in high activity levels under high food conditions irrespectively of predator presence, and under low food supply in predator absence only. In the intermediate stage of development, all larvae displayed a high activity level, which was correlated in general with fast development. However, growth later in ontogeny was not only influenced by the activity level, but also by predator presence and food supply, with larvae reared under high food supply and/or in presence of predators attaining a higher final mass. Thus, not only the way in which larval growth parameters and behaviour are related changed during development, but also whether the factors influenced larval growth and behaviour. Once the larvae reached the ultimate stage of development, in which they overwinter, behavioural patterns observed were consistent with model predictions.
3. It is advocated that behavioural plasticity of prey organisms in different developmental stages should be analysed in the context of associated growth variables.     

The settlement behaviour of planulae larvae of the hermatypic coral Favia fragum (Esper)

Experiments on the settlement behaviour of planulae larvae of the reef coral Favia fragum (Esper) are described. The larvae are positively phototaxic upon release but reverse this and become attracted to dark surfaces, corners, crevices, and the undersides of objects on the bottom. Clean glass surfaces were preferred to surfaces covered with biological slime but there was no preference for rough against smooth surfaces. There was clear evidence of gregarious settlement behaviour, the planulae being able to recognize both adult colonies and previously settled juveniles. A distinction was made between crawling and swimming larvae, and the consequences of their differences in behaviour on the spatial distribution of Favia on reef are discussed. Settlement behaviour of Favia is similar in many respects to that of the Pacific reef coral Pocillopora damicornis (Dana) but is distinguished by gregarious settlement and by a preference for clean surfaces over surfaces covered with biological slime.     

Embryonic development and larval behavior of the kissing loach (<Emphasis Type="Italic">Parabotia curta</Emphasis>): adaptations to an ephemeral,hypoxic environment

Many teleost fishes in lowland fresh waters spawn in ephemeral flooded areas, the bottoms of which are prone to hypoxia. Little is known about how embryos and larvae deal with these potentially hostile environments. This study examines the functional and behavioral ontogeny of one such species, the kissing loach (Parabotia curta). Kissing loach eggs are demersal and adhesive. Hatching occurs at 24.8 ± 0.1 h post-fertilization at 25°C, much earlier than most fish species. The newly hatched larvae are precocious with no functional mouth, fins or eye pigmentation. Swimbladder inflation normally occurs at about 4 days posthatch, even before which the hatched larvae moved immediately toward the water surface to hang from water moss. Experiments with larvae 20 h after hatching showed that they spent significantly less time on the bottom in hypoxic water (2 mg/l) than in normoxic water, and suggest that hypoxia is a major directive factor in eliciting surfacing behavior. For the kissing loach, we have previously reported short-term spawning after the formation of flood areas as well as wide scattering of the spawned eggs in the temporal flooded areas. These traits with the present results of hatching at an early stage and the immediate upward movement of larvae are considered to be effective strategies for using ephemeral, hypoxic flooded areas for reproduction.     

The ontogeny of complement component C3 in Atlantic cod (Gadus morhua L.)--an immunohistochemical study

The complement system in fish is well developed and plays an important role in the immune response. Very little is known about the ontogeny of C3 in fish and no study has previously been done on the development of C3 in teleosts. In this study we have detected the presence of C3 in cod larvae from the age of 1 day post hatching (p.h.) till 57 days p.h., using immunohistochemistry. The specific primary antibodies used, were produced against the beta-chain of cod C3. Immunostaining on cod larvae sections revealed that C3 is detectable in the yolksac membrane from day 1 p.h., and in liver, brain, kidney and muscle from day 2 p.h. C3 was also detected in other organs such as eye, notochord, stomach, intestines, pancreas, heart and gills at different stages of cod larval development. These findings suggest that complement is not only important in immune defence against invading pathogens but may also play a role in the formation and generation of different organs.     

The ontogeny of chemically mediated antipredator responses of fathead minnows Pimephales promelas

The antipredator responses of adult and larval fathead minnows Pimephales promelas to chemical alarm cues prepared throughout ontogeny were tested using various behavioural assays. Larval epidermis was also examined during ontogeny using standard haematoxylin and eosin staining techniques. Adults elicited an antipredator response to chemical alarm cue made from larvae as young as 8–17 days post‐hatch. Interestingly, larvae did not possess visible club cells until 28–37 days post‐hatch and did not respond to conspecific chemical alarm cue until 48–57 days post‐hatch. These results suggest that chemical alarm cue may not be contained within club cells and that the components of larval and adult chemical alarm cue may be similar throughout ontogeny.     

The responses of carrot fly larvae, Psila rosae, to components of their physical enrivonment

Abstract. 1. The responses of third instar Psila rosae (F.) larvae to light, temperature, humidity and soil moisture were investigated in the laboratory.
2. Larvae were photonegative and preferred a temperature of about 15°C. Temperatures between 30 and 40°C adversely affected movement and over 40° C were lethal.
3. In choice chambers, larvae preferred humidities of 70–100% r.h. and larvae in sand avoided dry conditions (2.5% field capacity). The latter response became more marked as larvae approached the pre-pupal stage when moistures of 40% field capacity and lower were avoided.
4. Most larvae were found at a depth of 8 cm in sand of uniform moisture content and temperature, but variation in moisture content could alter this preference.
5. In August, most larval damage in the field occurred near the tip of the carrot tap root but was more evenly distributed over the roots in November. It is uncertain whether this was due to soil near the surface being drier in August or whether it was caused by behavioural differences between the two generations of carrot fly larvae.
6. During the summer of 1975, low soil moisture levels resulted in the total absence of larval mines on the carrot roots even though pupae were found at depths of 20–30 cm in the soil. Temperature had no effect on the distribution of mines on carrot roots except at the top 2 cm of the soil profile.     

Come to the dark side: habitat selection of larval odonates depends on background visual patterns

1. Determining which environmental traits enable animals to inhabit and choose preferred habitats is key to understanding ecological processes. Habitat complexity and background colour patterns can act as selective pressures on animal behaviour, and ultimately affect habitat choice. 2. To investigate the role of environmental features on habitat selection, this study looked at whether dragonfly and damselfly larvae show a preference between dark/light or complex environments. Last‐instar larvae of Micrathyria didyma (Odonata: Libellulidae) and Acanthagrion lancea (Odonata: Coenagrionidae) were collected in the Neotropical savanna, and five experiments in laboratory conditions were subsequently carried out. The first experiment tested the preference of larvae for leaves in contrast to a white background. The second experiment compared a preference for white and black backgrounds. As both experiments showed a significant preference for darker backgrounds, a predator was included in the black background in the third experiment, and a macrophyte was included in the white background in the fourth experiment. In this way, favourable and unfavourable conditions were included in the habitat of choice. The fifth experiment tested the influence of environmental complexity on habitat choice. 3. The results of these experiments showed that larvae choose darker backgrounds independently of predation risk, and that macrophytes are as attractive as a dark background. They also suggest that the coenagrionid, but not the libellulid, prefer more complex environments. 4. Overall, these findings suggest that larvae exhibit behavioural preferences for background colour and complexity, which may ultimately drive habitat occupation.     

The effect of invertebrate diets on lipids, fatty acid composition and physiological condition of pike larvae (Esox lucius)

The present study tests two invertebrate diets for pike larvae reared in floating cages. One diet contained mainly copepods and cladocerans such as Eucyclops serrulatus and Bosmina longirostris , while the other diet contained Eucyclops serrulatus together with a small proportion of large Chydoridae and chironomid larvae. During the first days of the experiment, the amount of food distributed to the larvae was insufficient (9–17.1 prey per larva and per day) and led to an increase in the mortality. Triacylglycerol contents of fry were low and dietary fatty acids were either catabolised or, concerning PUFA such as 22:6(n-3), incorporated into phospholipids. From day 13 to the end of the study (day 22), the most abundant diets distributed were accompanied by an increase in triacylglycerol PUFA and in triacylglycerol contents of larvae. During the same period weight and length growth were better for larvae reared on the copepod plus Chydoridae and chironomid diet, than for larvae reared on the copepod and Bosmina diet. The use of a lipid condition index based on the triacylglycerol/sterol ratio suggested that Chydoridae and chironomids positively influenced the growth and nutritional condition of larvae. The effects of prey type in terms of PUFA composition on pike larvae are discussed.     

Feeding behaviour of Japanese flounder larvae under laboratory conditions

Tank–reared Japanese flounder larvae, Paralichthys olivaceus , had a major feeding peak in the morning and a secondary peak in the afternoon throughout the larval development, with light being the primary factor regulating their feeding activity. The larvae consumed rotifers in preference to Artemia for up to 10 days, after which the food preference shifted to Artemia . Feeding rates of the larvae prior to 10 days post–hatch depended on prey density, but in the old larvae, feeding rates were independent of prey density. Maximum feeding rate occurred at 19° C. The occurrence of the attack posture, after its onset at first feeding (2 days post–hatch), increased up to 25 days, began to decrease when the larvae prepared to settle down, then disappeared after settlement. The occurrence frequency of the attack posture was positively related to fish density, but inversely related to starvation duration, and occurred most frequently at 19° C. This posture depended on prey density in larvae prior to 10 days post–hatch, but became independent of prey density as the larvae developed. It was obvious that, for flounder larvae, attack posture was a behavioural character closely related to feeding and subject to larval development and environmental factors.     

Critical involvement of dietary docosahexaenoic acid in the ontogeny of schooling behaviour in the yellowtail

To investigate involvement of the central nervous system in the ontogeny of behaviour, diets of differing quality were used to rear yellowtail Seriola quinqueradiata larvae and juveniles. Artemia nauplii enriched with oleic acid (OA), eicosapentaenoic acid (EPA), or two different concentration levels of docosahexaenoic acid (DHA) were fed to yellowtail larvae (L^T 7 mm; 13 days old) for 12 days, and their behavioural development was analysed together with growth, survival, activity and fatty acid composition. Yellowtail fed with DHA–enriched Artemia showed mutual attraction behaviour at 11 mm L^T, while those fed with OA– or EPA–enriched Artemia did not show this behaviour at the same size. While fish in the OA group showed poor growth, survival and activity index, fish in the EPA group were similar to the two DHA groups. In addition, most fish tested, including the OA group, showed clear optokinetic responses. Fatty acid composition of the diet was reflected in that of the fish body. Therefore, dietary DHA in the larval stage is considered to be essential for the development of schooling behaviour in the yellowtail.     

Behavior of red king crab larvae: phototaxis, geotaxis and rheotaxis

Zoeae of Paralithodes camtschatica were positively phototactic to white light intensities above 1 x 10(13) q cm-2 s-1. Negative phototaxis occurred at low (1 x 10(12) q cm-2 s-1), but not high intensities (2.2 x 10(16) q cm-2 s-1). Phototactic response was directly related to light intensity. Zoeae also responded to red, green and blue light. Zoeae were negatively geotactic, but geotaxis was dominated by phototaxis. Horizontal swimming speed of stage 1 zoeae < 4 d old was 2.4 +/- 0.1 (SE) cm s-1 and decreased to 1.7 +/- 0.1 cm s-1 in older zoeae (P < 0.01). Horizontal swimming speed of stage 2 zoeae was not significantly different from > or = 4 d old stage 1 zoeae. Vertical swimming speed, 1.6 +/- 0.1 cm s-1, and sinking rate, 0.7 +/- 0.1 cm s-1, did not change with ontogeny. King crab zoeae were positively rheotactic and maintained position in horizontal currents less than 1.4 cm s-1. Starvation reduced swimming and sinking rates and phototactic response.     

Phototaxis and the evolution of isogamy and 'slight anisogamy' in marine green algae: insights from laboratory observations and numerical experiments

The evolution of anisogamy in marine algae was studied through numerical simulations of gamete mating behaviour in three dimensions, using observed traits of marine green algae as input parameters. The importance of phototaxis became apparent from the numerical experiments: all gametes with phototactic systems are favoured over those without, but this advantage is reduced with increasing tank depth or shorter search times. Phototactic gametes were advantaged over non-phototactic gametes if the water was shallower than about 30–40 mm when the time available for gamete encounter was 1000 time steps (5.55 min). If gametes of both sexes are positively phototactic, slightly anisogamous species are at a disadvantage to isogamous species, which invalidates the sperm-limitation theory as a driver for the evolution of slight anisogamy. Conflicting selection forces of search efficiency and zygote fitness may be needed.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 321–327.     

Phototactic responses of larvae from the marine sponges Neopetrosia proxima and Xestospongia bocatorensis (Haplosclerida: Petrosiidae)

Abstract. Previous studies suggest that phototaxis in sponge larvae is generated by the bending of a tuft of long posterior cilia (LPC). The photoresponsiveness of these cilia is often assayed by examining their reaction to sudden changes in light intensity. Here, we document and describe the larvae of the tropical marine sponges Neopetrosia proxima and Xestospongia bocatorensis and examine the phototactic behavior of their larvae. Both species brood ovoid, tufted parenchymella larvae, clearly countering an earlier hypothesis that all petrosid sponges are oviparous. Larvae of N. proxima were positively phototactic and settled after 2 d, while larvae of X. bocatorensis were negatively phototactic and settled in as little as 4 h. In both species, LPC quickly responded to changes in the light intensity. When the light intensity is reduced, the larvae of N. proxima fold the cilia inwards immediately without beating, then flare them outwards, beating for a few seconds, and then gradually return to the neutral position while continuing to beat. In contrast, the larvae of X. bocatorensis flare the cilia outwards when the light intensity is reduced and fold them inwards when the light intensity is increased. Comparisons with reported ciliary responses to light for other species demonstrate that these responses do not show the hypothesized one-to-one correspondence with phototactic behaviors and are, therefore, of limited use in explaining the mechanisms that coordinate larval swimming.     

Life histories and habitat selection in Daphnia: divergent life histories of D. magna clones differing in phototactic behaviour

To test the hypothesis of co-adaptation of life histories and daytime vertical distribution (vertical migration behaviour) in Daphnia, life history characteristics were analysed for two positively, three negatively, and four intermediately phototactic Daphnia magna clones. Clones with different phototactic behaviour were found to have divergent life history strategies, with positively phototactic clones being good exploiters under the non-limiting conditions provided in the laboratory, i.e. low density (1 ind./1), high food concentration (6,5–7 10⁵ Scenedesmus cells/ml, restored daily) and high temperature (20° C). They realized a high intrinsic rate of increase at a small adult body size through rapid development, at a cost of producing small neonates. Negatively and intermediately phototactic clones had larger adult body sizes, and produced larger neonates that were more starvation-resistant than those of positively phototactic clones. Selection for high intrinsic rate of increase in intermediately phototactic clones was mediated through the production of large clutches.     

Baculovirus infection triggers a positive phototactic response in caterpillars to induce ‘tree-top’ disease

Many parasites manipulate host behaviour to enhance parasite transmission and survival. A fascinating example is baculoviruses, which often induce death in caterpillar hosts at elevated positions (‘tree-top’ disease). To date, little is known about the underlying processes leading to this adaptive host manipulation. Here, we show that the baculovirus Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) triggers a positive phototactic response in S. exigua larvae prior to death and causes the caterpillars to die at elevated positions. This light-dependent climbing behaviour is specific for infected larvae, as movement of uninfected caterpillars during larval development was light-independent. We hypothesize that upon infection, SeMNPV captures a host pathway involved in phototaxis and/or light perception to induce this remarkable behavioural change.     

Histopathological investigation of experimental ocular toxocariasis in gerbils

Male gerbils were inoculated intragastrically with embryonated Toxocara canis eggs. They were euthanised, and their eyes were excised at different days p.i. to identify the number of larvae as well as lesions resulting in these organs. In most animals, larvae were detected from day 5 to day 60 p.i. (end of the study). From days 10 to 20 p.i., larvae and haemorrhage were observed in the choroid and in the ciliary process. At days 30 and 40 p.i., some eyes had larvae surrounded by an infiltrate of neutrophils, oedema, haemorrhages and tissue damage in the retina or the ciliary process. On day 60 p.i., there were granulomatous lesions in the retina. This study provides a model for the study of ocular toxocariasis.     

The Ontogeny of Antipredator Behaviour in Paradise Fish Larvae (Macropodus opercularis): The Recognition of Eyespots

The ontogeny of antipredator behaviour of paradise fish was examined using a simple testing method. The results showed that the ability to recognize eyespots appears in larvae between 15 and 20 days old. At the same time, two horizontally placed eyespots produced the most pronounced effect on the behaviour of the larvae. Testing different inbred strains revealed that the ontogeny of antipredator behaviour is also under broad genetic control, as the response to a model predator was strong in one strain but weak in another. The results suggest that the recognition of eyespots coincides with larvae becoming more conspicuous to predators by the appearance of pigmentation and increasing level of swimming activity (exploration).