Behavioural responses of benthic and pelagic Arctic charr to substratum heterogeneity

Responses to environmental heterogeneity were studied in laboratory-reared offspring of two morphs of Arctic charr Salvelinus alpinus from Loch Rannoch, Scotland, one occupying the pelagic zone and feeding predominantly on zooplankton and the other being benthic in habit and feeding mainly on macroinvertebrates. When housed in groups in tanks with a black-and white striped base, benthic charr demonstrated a clear preference for dark areas, whereas pelagic fish positioned themselves at random with respect to substratum colour. In general, pelagic charr were much less aggressive than benthic charr. In pelagic fish, neither spacing nor aggression was affected by the visual heterogeneity of the substrate. In contrast, benthic charr swam closer together and fought more when housed over a uniform as opposed to a non-uniform substratum. The results are discussed in the context of habitat-specific visual requirements and of an interaction between visual complexity and territoriality previously described for Atlantic salmon Salmo salar .     

Indirect effects of the algivorous fish Plecoglossus altivelis altivelis on the growth of two insectivorous benthic fish

1. Animals exploiting different resources may nevertheless interact if one species indirectly alters the abundance and distribution of the food of the other. To analyse this indirect effect, we conducted experiments in artificial pools and in the field to investigate the influence of the algivorous fish Plecoglossus altivelis altivelis (known as the ayu) on two species of insectivorous benthic fish, Pseudogobio esocinus esocinus and the goby Gymnogobius petschiliensis .
2. In the pool experiments, algal biomass was not correlated with the number of ayu, but the percentage of blue-green bacteria rose as the number increased. The number of aquatic macroinvertebrates on the upper surface of ceramic tiles placed in the pool bed decreased as the number of ayu increased.
3. Although ayu and the benthic species did not interact directly, the reduction in invertebrate abundance on the upper surface of tiles in the pool reduced the growth rate of the benthic insectivores.
4. In field experiments, the introduction of ayu into habitats with P. esocinus esocinus or G. petschiliensis reduced the growth rate of these benthic fish. In the field experiment that was carried out over 5 years in the G. petschiliensis habitat, the population density of the goby decreased when ayu were stocked.
5. The ayu is a strong interactor or bioengineer in streams, affecting not only benthic algae but also aquatic invertebrates and fishes. We conclude that to predict the outcome of interspecific interactions amongst fishes in streams with high algal production, possible indirect effects must be considered alongside better known direct effects.     

Behavioural responses of a south-east Australian floodplain fish community to gradual hypoxia

1. Hypoxic conditions occur frequently during hot, dry summers in the small lentic waterbodies (billabongs) that occur on the floodplains of the Murray‐Darling River system of Australia. Behavioural responses to progressive hypoxia were examined for the native and introduced floodplain fish of the Ovens River, an unregulated tributary of the Murray River in south‐east Australia. 2. Given the high frequency of hypoxic episodes in billabongs on the Ovens River floodplain, it was hypothesised that all species would exhibit behaviours that would confer a degree of hypoxia‐tolerance. Specifically, it was hypothesised that as hypoxia progressed, gill ventilation rates (GVRs) would increase and aquatic surface respiration (ASR) would become increasingly frequent. Fish were subjected to rapid, progressive hypoxia from normoxia to anoxia in open tanks. 3. All tested species exhibited behaviours consistent with their use of potentially hypoxic habitats. As hypoxia progressed, GVRs increased and all species, with the exception of oriental weatherloach, began to switch increasingly to ASR with 90% of individuals using ASR at various oxygen concentrations below 1.0 mg O₂ L⁻¹. Australian smelt, redfin perch and flat‐headed galaxias were the first three species to rise to ASR, with 10% of individuals using ASR by 2.55, 2.29 and 2.21 mg O₂ L⁻¹ respectively. Goldfish and common carp were the last two species to rise to ASR, with 10% of individuals using ASR by 0.84 and 0.75 mg O₂ L⁻¹ respectively. In contrast to other species, oriental weatherloach largely ceased gill ventilation and used air‐gulping as their primary means of respiration during severe hypoxia and anoxia. 4. Australian smelt, redfin perch and flat‐headed galaxias were unable to maintain ASR under severe hypoxia, and began exhibiting erratic movements, termed terminal avoidance behaviour, and loss of equilibrium. All other species continued to use ASR through severe hypoxia and into anoxia. Following a rise to ASR, GVRs either remained steady or decreased slightly indicating partial or significant relief from hypoxic stress for these hypoxia‐tolerant species. 5. Behavioural responses to progressive hypoxia amongst the fish species of the Ovens River floodplain indicate a generally high level of tolerance to periodic hypoxia. However, species‐specific variation in hypoxia‐tolerance may have implications for community structure of billabong fish communities following hypoxic events.     

Behavioural responses of two cladocerans and two copepods exposed to fish kairomones

In natural predator–prey interactions, chemical communication is one of the most advantageous strategies for prey organisms because they can anticipate possible harm by means of phenotypic changes. This study compares the changes in the behaviour of four freshwater zooplankton species in the presence and absence of infochemicals from the same predator. The studied organisms are two copepods and two cladocerans living in highly variable freshwater environments. The analysis is focused on two predator defensive behaviours: a pre-encounter and a post-encounter response. First, we analysed the diel vertical migration (DVM) of the organisms inside 150?cm long transparent plastic tubes. Second, we used a novel hydraulic apparatus to quantify their ability to escape from a potential predator. The results revealed that the species have different behavioural patterns in the absence of infochemical. The differences were mainly in the way DVM developed and reflect their life histories and adaptive strategies relative to their natural environment. When faced with kairomones, the escape ability of the organisms was enhanced in all cases and DVM changed, although not always in agreement with the expected patterns. The interaction between each species and the multiple environmental components is discussed.     

Feeding patterns of the dominant benthic and demersal fish community in a temperate estuary

The diet and feeding relationships of the 12 most abundant benthic and demersal fish species of the Mondego Estuary, Portugal, were studied between June 2003 and May 2006. Fishes were caught during the night using a 2 m beam trawl. The stomach contents were analysed for prey identification, counting and weighing. According to prey importance in diets, three main feeding guilds were identified: (1) invertebrate feeders, (2) invertebrate and fish feeders and (3) plankton and invertebrate feeders. Besides these main feeding guilds, some fishes also presented fractions of algae and zooplankton in their stomach contents. The most abundant prey items were macroinvertebrates, with several polychaetes ( Nephtys spp., Capitellidae, Spionidae and Eunicidae), Corophium spp. and Crangon crangon among the dominant prey. Pomatoschistus spp. were the most preyed on fishes. Several fish species showed a tendency for a specialized diet, but almost all also showed some degree of opportunistic feeding by preying on other food resources. High diet overlap was found between some fish species, yet exploitative competition could not be concluded.     

Reduction of predation risk under the cover of darkness: Avoidance responses of mayfly larvae to a benthic fish

Summary Mayfly larvae of Paraleptophlebia heteronea (McDunnough) had two antipredator responses to a nocturnal fish predator (Rhinichthys cataractae (Valenciennes)): flight into the drift and retreat into interstitial crevices. Drift rates of Paraleptophlebia abruptly increased by 30 fold when fish were actively foraging in the laboratory streams but, even before fish were removed, drift began returning to control levels because larvae settled to the substrate and moved to areas of low risk beneath stones. This drifting response was used as an immediate escape behavior which likely decreases risk of capture from predators which forage actively at night. Surprisingly, drift most often occurred before contact between predator and prey, and we suggest that in darkness this mayfly may use hydrodynamic pressure waves for predator detection, rather than chemical cues, since fish forage in an upstream direction. Although drifting may represent a cost to mayfly larvae in terms of relocation to a new foraging area with unknown food resources, the immediate mortality risk probably out-weighs the importance of staying within a profitable food patch because larvae can survive starvation for at least 2 d. In addition to drifting, mayflies retreated from upper, exposed substrate surfaces to concealed interstitial crevices immediately after a predator encounter, or subsequent to resettlement on the substrate after predator-induced drift. A latency period was associated with this response and mayflies remained in these concealed locations for at least 3 h after dace foraging ceased. Because this mayfly feeds at night and food levels are significantly lower in field refugia under stones, relative to exposed stone surfaces, predator avoidance activity may limit foraging time and, ultimately, reduce the food intake of this stream mayfly.     

Behavioral responses to food odor in juvenile marine fish: Acuity varies with species and fish length

This study tested the hypothesis that acuity of behavioral responses to food odor in three commercially important species of marine fish would increase as juvenile length increased. Swimming activity among two size groups of fish was measured in the presence of a series of squid extract dilutions. Increased swimming activity in juvenile Pacific halibut Hippoglossus stenolepis Schmidt, walleye pollock Theragra chalcogramma Pallas, and sablefish Anoplopoma fimbria Pallas was stimulated above threshold concentrations of squid extract, expressed as dilution from full strength. Maximum chemosensory acuity was observed in smaller (8-14 cm total length, TL) Pacific halibut and walleye pollock, while larger sablefish (15-23 cm TL) continued to develop acuity. Response thresholds were highest (10^− 3 dilution) in Pacific halibut, at intermediate levels (10^− 4-10^− 6 dilution) in walleye pollock and smaller sablefish and reached the lowest levels (10^− 13 dilution) in larger sablefish. The widely held view that dissolved free amino acids (DFAA) are the primary chemosensory stimulants for fish food searching may not be valid for sablefish, as they detected squid extract at dilutions containing DFAA that appeared to be far below ambient sea water DFAA concentrations.     

Behavioural responses of the leaf-chewing guild to the presence of Eriocrania mines on silver birch (Betulapendula)

1. Interactions between early season leaf-miners from the genus Eriocrania Zeller (Eriocraniidae: Lepidoptera), and the leaf-chewing guild of silver birch (Betula pendula Roth) were investigated. 2. Field observations indicated that a negative association between damage caused by Eriocrania, and leaf-chewers could be observed under certain conditions, namely at higher damage densities in the final week of mine development on trees with relatively high densities of mines. 3. Experimental manipulation of Operophtera brumata L. (Geometridae: Lepidoptera) densities in the field confirmed the negative association between established mines of Eriocrania, and this species of free-living folivore. 4. The behaviour of O. brumata was modified further in the presence of mines. On branches where mined leaves were present, O. brumata larvae consumed a larger proportion of leaf tissue, by continuing to feed on the same leaf longer rather than shifting to a new leaf. Increased consumption may indicate some modification of leaf quality beyond the leaves occupied by Eriocrania. Alternatively, it may indicate an association between Eriocrania, and higher quality leaf material.     

Behavioural responses of the Colorado potato beetle to trichomes and leaf surface chemicals of Solanum tarijense

Wild Solanum species constitute a source of resistance to several pests and diseases of potato. Several species of wild tuber‐bearing potato have been identified as resistant to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), including Solanum tarijense Hawkes (Solanaceae). Our objective was to determine the mechanism of resistance of S. tarijense to the Colorado potato beetle and, because the resistance is limited to the adult stage of the insect, to study the host selection behaviour on resistant plants. In the field, Colorado potato beetles demonstrated a unique behaviour when in contact with S. tarijense, abandoning the plant by falling to the ground after a few minutes. The abundant trichomes on the leaves of S. tarijense induced the falling behaviour. However, on S. tarijense feeding remained low even after the trichomes were mechanically removed. Observations demonstrated that the normal sequence of behaviour leading to feeding was interrupted before adult beetles fed on S. tarijense leaves. Feeding experiments using volatile and non‐volatile fractions of leaf surface extracts identified a phagodeterrent effect of the volatile fraction. Our results contrast with a similar evaluation of the mode of resistance of Solanum berthaultii Hawkes, a close relative of S. tarijense, on which some feeding occurred and adults did not show falling behaviour. This study presents information on S. tarijense as a new source of resistance to the Colorado potato beetle that can be used for potato breeding.     

A context analysis of bobbing and fin‐flicking in a small marine benthic fish

Most antipredator strategies increase survival of individuals by signaling to predators, by reducing the chances of being recognized as prey, or by bewildering a predator''s perception. In fish, bobbing and fin‐flicking are commonly considered as pursuit‐deterrent behaviors that signal a predator that it has been detected and thus lost its surprise‐attack advantage. Yet, very few studies assessed whether such behavioral traits are restricted to the visual presence of a predator. In this study, we used the yellow black‐headed triplefin Tripterygion delaisi to investigate the association between these behaviors and the visual exposure to (a) a black scorpionfish predator (Scorpaena porcus), (b) a stone of a size similar to that of S. porcus, (c) a conspecific, and (d) a harmless heterospecific combtooth blenny (Parablennius sanguinolentus). We used a laboratory‐controlled experiment with freshly caught fish designed to test for differences in visual cues only. Distance kept by the focal fish to each stimulus and frequency of bobbing and fin‐flicking were recorded. Triplefins kept greater distance from the stimulus compartment when a scorpionfish predator was visible. Bobbing was more frequent in the visual presence of a scorpionfish, but also shown toward the other stimuli. However, fin flicks were equally abundant across all stimuli. Both behaviors decreased in frequency over time suggesting that triplefin become gradually comfortable in a nonchanging new environment. We discuss why bobbing and fin‐flicking are not exclusive pursuit‐deterrent behaviors in this species, and propose additional nonexclusive functions such as enhancing depth perception by parallax motion (bobbing) or signaling vigilance (fin‐flicking).     

Behavioural responses of freshwater phytoplanktonic flagellates to a temperature gradient

Photoresponses of motile phytoplanktonic flagellates have been widely studied, whereas the behavioural responses of these organisms to temperature, and their potential ecological consequences, have rarely been considered. This study investigated the population responses and individual swimming trajectories of five phylogenetically contrasting species of freshwater flagellates exposed to a gradient of temperature in micro-scale preference chambers. Population responses demonstrated a species-dependent diversity in thermoresponsive behaviour. Across a gradient of 9.8 to 15.1°;C which simulated the typical range of temperature across a thermocline in a temperate monomictic lake, Ceratium furcoides, Chlamydomonas moewusii, Dinobryon sertularia and Plagioselmis nannoplanctica all preferred the highest temperatures. In contrast, Euglena gracilis preferred the lowest temperature. Analysis of the swimming behaviour of individual cells confirmed preferences and demonstrated that, in all species, a combination of tactic and kinetic reactions was responsible for these accumulations. For the first time, controlled positive and negative thermotaxes towards a temperature preference were identified. This thermotactic orientation, in conjunction with a reduction in directionality of response in the preference zone and with ortho- and klino-thermokinesis, enabled cells to maintain position at preferred temperatures. Specifically, in all species apart from P. nannoplanctica, significant ortho-kinetic increases in swimming speed permitted rapid movement of cells away from unfavourable conditions, while a reduction in speed and a klino-kinetic increase in rate of turning (in all five species) maintained position within favoured temperatures. This ability to detect, orientate and accumulate within a temperature gradient may be triggered by physiological processes and presents ecological advantages. Behavioural response to temperature may optimize growth, influence the spatial and temporal distribution of flagellates, particularly the diel position of cells during migration, and contribute to the delineation of niche separation.     

Behavioural responses of larval container mosquitoes to a size-selective predator

Abstract.  1. The hypothesis that size-selective predation and species-specific prey behaviours facilitate the coexistence between larvae of invasive Aedes albopictus (Skuse) and U.S.A.-native Ochlerotatus triseriatus (Say) was tested experimentally with the predator Corethrella appendiculata (Grabham).
2. Larval behaviours associated with a higher risk of predation were identified, and prey behavioural responses were tested in either the physical presence of predators or in water containing predation cues. Larvae that thrashed on container bottoms had a higher risk of being captured by fourth instar C. appendiculata than did larvae resting on the water surface. Ochlerotatus triseriatus , but not A. albopictus , adopted low-risk behaviours in response to water-borne cues to predation. Both prey species reduced risky behaviours in the physical presence of the predator, but O. triseriatus showed a stronger response.
3. The vulnerability of 2nd and 3rd instar prey to predation was compared, and behavioural responses were correlated with prey vulnerability. Second instars of both species were more vulnerable to predation by C. appendiculata than were 3rd instars, and the 3rd instar A. albopictus was more vulnerable than O. triseriatus of the same stage. All instars of O. triseriatus showed a similar reduction of risky behaviours in response to the presence of C. appendiculata despite 4th instar prey being relatively invulnerable to size-selective predation.
4. Weaker predator avoidance, coupled with superior competitive ability, of invasive A. albopictus is likely to contribute to its coexistence with O. triseriatus in containers of the south-eastern U.S.A., where C. appendiculata can be abundant.     

Behavioural and gustatory responses of female Neobellieria (=Sarcophaga) bullata to sucrose and amino acids

Abstract. Unmated female Neobellieria (=Sarcophaga) bullata (Parker) (Diptera: Sarcophagidae) of different ages ranging from 1 to 24 days consistently preferred a solution of 100 mM/1 sucrose to one containing a mixture of six amino acids at a total concentration of 10 mM/1. When these solutions were used to stimulate the gustatory sensilla on the proboscis of 2- and 5-day-old flies, sucrose elicited a greater response from cells 1 and 2 in large and cell 1 in medium-length hairs, which could account for the feeding preference of the flies for this chemical.     

Behavioural responses of fishes to chemical cues: results from a new bioassay

A new behavioural bioassay for determining the locomotor response by fish to chemical cues is described. The assay combines a behavioural trough, capable of delivering up to 10 discrete plumes of treated water, together with a digital method for quantifying the movements of single fish. Sample responses of two whitefish, Coregonus clupeaformis , one to an attractant (a food extract) and one to a repellant (quinine monohydrochloride), are provided. Their locomotor responses are analyzed in terms of such parameters as total distance travelled, average velocity, number of turns, average excursion distance, and the number of times specific boundaries are crossed. The assay's sensitivity is demonstrated through concentration-response curves by Arctic char, Salvelinus alpinus , to the bile acid, taurocholic acid, and the amino acids, L-serine and L-alanine. Behavioural response threshold concentrations for these three substances were estimated to be 10⁻¹⁵, 10⁻ⁿ, and 10⁻⁹ m, respectively.     

Analysis of multiple aspects of a repeated signal: power and rate of rapping during shell fights in hermit crabs

Repeated activities used by animals during contests are assumedto act as signals advertising the quality of the sender. However,their exact functions are not well understood and observationsfit only a limited set of the predictions made by models ofsignaling systems. Experimental studies of contest behaviortend to focus on analysis of the rate of signaling, but individualperformances may also vary in magnitude. Both of these featurescan vary between outcomes and within contests. We examined changesin the rate and power of shell rapping during shell fights inhermit crabs. We show that both rate and power decline duringthe course of the encounter and that the duration of pausesbetween bouts of shell rapping increases with an index of thetotal effort put into each bout. This supports the idea thatthe vigor of shell rapping is regulated by fatigue and couldtherefore act as a signal of stamina. By examining differentinteracting components of this complex activity, we gain greaterinsight into its function than would be achieved by investigatinga single aspect in isolation.     

Spatial and temporal predictability of the parasite community structure of a benthic marine fish along its distributional range

The search for consistent patterns of organisation in parasite communities remains a central theme in parasite community ecology. However, to date, much evidence comes from studies without replication in both space and time; when replicate communities are examined, repeatable patterns are rarely observed. Here we determine, using nested subset analyses, whether the infracommunities of ectoparasites and endoparasites of a benthic marine fish (Sebastes capensis) show non-random structure. Then we examine the spatial repeatability of parasite community structure across the host's distribution in the southern Pacific, and the temporal repeatability of ectoparasite community structure from one locality. In total, 537 fish were captured from different latitudes (between 11 degrees S and 52 degrees S) along the Pacific coast of South America; a further 122 specimens were captured in two other years from one of the sampling localities, Valdivia (40 degrees S). In spite of variation in fish sizes among samples, fish size generally did not correlate with either ecto- or endoparasite species richness. The ecto- and endoparasite species richness of the component communities were also not correlated with fish sample size across the nine localities. Significant nested patterns were found in the ectoparasite communities of S. capensis at all eight localities, except at latitude 52 degrees S. Significant nested patterns were also found in the endoparasite infracommunities of S. capensis at seven of the nine localities, the exceptions being those from latitudes 11 degrees S and 20 degrees S. On a temporal scale, significant nestedness was observed in the ectoparasite infracommunities of S. capensis during each of the 3 years of sampling at Valdivia. In general, the same parasite species are responsible for the repeatability of nested patterns, though their importance varies among localities. The spatial and temporal predictability of the parasite community structure in S. capensis may be associated with the fish's benthic habitat and territorial behavior, suggesting that host biology may be a key determinant of the structure of parasite communities.     

The cost of being a caring mother: the ignored factor in the reproduction of marine invertebrates

Investment in reproduction ranges from gamete production to active parental care, and marine invertebrates span this range. However, the cost of parental care has not yet been systematically quantified, nor incorporated into life history studies of marine invertebrates, in contrast to most other animal taxa. Since oxygen is a limiting factor in egg masses of marine invertebrates, we studied patterns of oxygen partial pressure over time in embryo masses of Brachyuran crabs, and correlated these results with the cost of providing oxygen to the embryos. We found that: (1) oxygen is limiting in the embryo masses, (2) female crabs show an active brooding behaviour that we think helps to provide oxygen to the embryo mass, and (3) there is a substantial parental investment associated with brooding behaviours. Oxygen limitation and parental investment seem to be associated in many taxa of marine invertebrates, and we suggest that oxygen provision to the embryos may be a critical factor determining parental investment in this group.