Ontogeny of turbiditaxis in hatchery‐reared Japanese anchovy Engraulis japonicus

The ontogenetic change in turbiditaxis (i.e. attraction to turbid waters) was examined in the larvae and juveniles of Japanese anchovy Engraulis japonicus by testing three levels of turbidity (0, 20 and 100 ppm of kaolin). Larvae of 12, 20 and 30 mm standard length (L_S) exhibited turbiditaxis to both 20 and 100 ppm of kaolin, whereas 6 mm L_S larvae and 45 mm L_S juveniles did not exhibit any turbiditaxis. Turbiditaxis might explain the ontogenetic habitat shift from coastal to offshore waters reported for this species.     

Ontogeny of antipredator performance in hatchery-reared Japanese anchovy Engraulis japonicus larvae exposed to visual or tactile predators in relation to turbidity

Laboratory experiments revealed distinct effects of turbidity on the survival of Japanese anchovy Engraulis japonicus larvae when exposed to either visual (jack mackerel Trachurus japonicus) or tactile (moon jellyfish Aurelia aurita) predators. The experiments were conducted in 30 l tanks with three levels of turbidity obtained by dissolving 0, 50 or 300 mg l(-1) of kaolin. Predators were introduced to experimental tanks followed by larvae of E. japonicus ranging from 5 to 25 mm standard lengths (L(s) ). When exposed to T. japonicus, the mean survival rate of larvae was significantly higher in 300 mg l(-1) treatments compared to the other turbidity levels. When exposed to A. aurita, however, there was no difference in the survival rates among different turbidity treatments. The survival rates when exposed to either predator improved with larval growth. The logistic survivorship models for E. japonicus larvae when exposed to A. aurita had an inflection point at c. 12 mm L(s) , suggesting that their size refuge from A. aurita is close to this value. Comparison to a previous study suggests a high vulnerability of shirasu (long and transparent) fish larvae to jellyfish predation under turbidity. This study indicates that anthropogenic increases of turbidity in coastal waters may increase the relative effect of jellyfish predation on fish larvae.     

Intraretinal variability and specialization of cones in Japanese anchovy (Engraulis japonicus,Engraulidae)

The retina of anchovies is characterized by an unusual arrangement and ultrastructure of cones. In the retina of Japanese anchovies, Engraulis japonicus, three types of cones are distributed into rows. The nasal, central, temporal, and ventro‐temporal regions of the retina were occupied exclusively by the long and short cones. Triple cones, made up of two lateral components and one smaller central component, were found only in the dorsal and ventro‐nasal retinal regions. In the outer segments of all short and long cones from the ventro‐temporal region, the lamellae were oriented along the cell axis and were perpendicular to the lamellae in the long cones, providing a morphological basis for the detection of polarization. This lamellar orientation is unique to all vertebrates. The cones were examined with respect to regional differentiation in their size and spectral properties via light microscopy, transmission electron microscopy, and microspectrophotometry. Various dimensions of cones were measured in preparations of isolated cells. The cones from the ventro‐temporal region had different dimensions than cones of the same type located in other retinal regions. Triple cones from the dorsal region were significantly larger than triple cones from the ventro‐nasal region. The spectral absorbance of the lateral components of triple cones in the ventro‐nasal retina was identical to the absorbance of all long and short cones from the ventro‐temporal region. These are shifted to shorter wavelengths relative to the absorbance of the lateral components of the triple cones located in the dorsal retina. Thus, the retina of the Japanese anchovy shows some features of regional specialization common in other fishes that improves spatial resolution for the upwards and forwards visual axis and provides spectral tuning in downwelling light environment. That results from the differentiation of cone types by size and by different spectral sensitivity of various retinal areas. J. Morphol. 277:472–481, 2016. © 2016 Wiley Periodicals, Inc.     

Late Pleistocene divergence and subsequent population expansion of two closely related fish species, Japanese anchovy (Engraulis japonicus) and Australian anchovy (Engraulis australis)

Climatic oscillations during the Pleistocene ice ages produced great changes in species' geographical distribution and abundance, which could be expected to have genetic consequences. Living in the temperate upwelling zones of the northwestern Pacific, Japanese anchovy (Engraulis japonicus) might have been affected by these severe climatic oscillations. To investigate the effects of Pleistocene climatic changes on the evolution in Japanese anchovy, fragments of 522 bp at the 5' end of mitochondrial DNA control region were sequenced for 241 individuals from 13 localities and 37 individuals of Australian anchovy. Japanese anchovy and Australian anchovy are reciprocally monophyletic and a late Pleistocene transequatorial divergence between the two species was indicated. High levels of haplotype diversity (>0.99) were found for all samples, indicating a high level of genetic diversity. Analyses of molecular variance and the conventional population statistic F(ST) revealed no significant genetic structure throughout the range of Japanese anchovy. Both mismatch distribution analyses and neutrality tests suggested a late Pleistocene population expansion for both Japanese anchovy (79,000-317,000 years ago) and Australian anchovy (45,000-178,000 years ago).     

Kinetic and structural properties of two isoforms of trypsin isolated from the viscera of Japanese anchovy, Engraulis japonicus

Two isoforms of anchovy trypsin (aT-I and aT-II) were purified from the visceral extracts by (NH₄)₂SO₄ fractionation followed by affinity chromatography, gel filtration, and ion-exchange chromatography. The homogeneity of the purified preparation was evidenced by both native- and SDS-PAGE, and further by gelatin zymography. Identities of aT-I and aT-II as trypsins were established by N-terminal amino acid sequencing, which matched exactly to the corresponding stretches of their respective amino acid sequences obtained by molecular cloning [Ahsan et al. (2000), Marine Biotechnol., in press]. Both isoforms were completely inhibited by serine protease inhibitors as well as by specific trypsin inhibitors. The purified anchovy trypsins showed considerably higher catalytic efficiencies (k_cat/K_m) than bovine trypsin as measured toward benzoyl-arginine p-nitroanilide (BAPA) and benzoyl-arginine ethyl ester (BAEE) at 25°C; in particular, aT-II was 35 times more efficient than its mammalian counterpart against BAPA. This was due mainly to a dramatic decrease of K_m values for anchovy trypsins, which are indicative of an evolutionary response toward increased substrate binding at suboptimal temperatures in the marine environment.     

Seasonal variability in growth of larval Japanese anchovy Engraulis japonicus driven by fluctuations in sea temperature in the Kii Channel, Japan

Seasonal variability in the growth of larval Japanese anchovy Engraulis japonicus was examined through otolith microstructure analysis based on the samples collected from the northern side (inner area, IA) and the southern side (outer area, OA) of the Kii Channel from April 2006 to March 2007. Growth trajectories (otolith backcalculated mean standard length of 5 day intervals from 5 days after hatch to 24 days) as well as the most recent 5 day mean growth rate of larvae before capture ( G ₅) differed among months. Growth trajectories showed the same pattern as G ₅. In IA, mean ± s.d. G ₅ ranged from 0·31 ± 0·04 mm day⁻¹ (January) to 0·73 ± 0·06 mm day⁻¹ (October). In OA, mean ± s.d. G ₅ ranged from 0·36 ± 0·05 mm day⁻¹ (January) to 0·79 ± 0·11 mm day⁻¹ (August). G ₅ values declined from November to January and then started to increase. In general, the seasonal patterns of growth were similar between IA and OA, and a clear seasonal pattern in growth was identified. When the relationships among larval growth rate, sea temperature, zooplankton density and larval density were examined, growth rate was positively related with sea temperature in both areas and not related with the other factors. The similar pattern in growth observed between IA and OA was probably due to the low spatial variability in sea temperature compared to its seasonal variability.     

Ontogeny of routine swimming speed and startle responses in red drum, with a comparison of responses to acoustic and visual stimuli

Routine swimming speed of larval red drum Sciaenops ocellatus increased throughout development but most rapidly for larvae >10 mm L _T. Red drum of all sizes swam faster than predicted by published summary equations based on other species, possibly due to more advanced development at a given length. Frequency and magnitude of startle responses increased over the larval period for both types of stimuli with most of the improvement taking place before larvae reached 8 mm L _T. Time to response for an acoustic and visual stimulus decreased early in the larval period but levelled off after 10 mm L _T. Response distance and response speed for both stimuli generally increased throughout the larval period, but response duration remained constant. Visually stimulated responses were generally longer in duration and distance covered than acoustically stimulated responses, while mean response speeds were similar.     

Timing and plasticity of shoaling behaviour in the zebrafish, Danio rerio

The zebrafish has become a major model system for biomedical research and is an emerging model for the study of behaviour. While adult zebrafish express a visually mediated shoaling preference, the onset of shoaling behaviour and of this preference is unknown. To assess the onset of these behaviours, we first manipulated the early social environment of larval zebrafish subjects, giving them three model shoaling partners of the same pigment phenotype. We then assayed the subjects' preferences using binary preference tests in which we presented subjects with two shoals, one shoal of fish exhibiting the same pigment pattern phenotype as their models and another shoal with a radically different pigment pattern. To determine whether or not the visually mediated preference could be altered once it was established, we further manipulated the social environment of a number of subjects, rearing them with one model shoal and testing them, then changing their social consorts and retesting them. Our results demonstrate that larval zebrafish shoal early in their development, but do not exhibit a shoaling preference until they are juveniles. Moreover, we find that the shoaling preference is stable, as changing the social environment of fish after they had acquired a preference did not change their preference. These data will facilitate investigations into the mechanisms underlying social behaviour in this vertebrate model system.     

The effects of flow on schooling Devario aequipinnatus: school structure,startle response and information transmission

To assess how flow affects school structure and threat detection, startle response rates of solitary and small groups of giant danio Devario aequipinnatus to visual looming stimuli were compared in flow and no‐flow conditions. The instantaneous position and heading of each D. aequipinnatus was extracted from high‐speed videos. Behavioural results indicate that (1) school structure is altered in flow such that D. aequipinnatus orient upstream while spanning out in a crosswise direction, (2) the probability of at least one D. aequipinnatus detecting the visual looming stimulus is higher in flow than no flow for both solitary D. aequipinnatus and groups of eight D. aequipinnatus; however, (3) the probability of three or more individuals responding is higher in no flow than in flow. These results indicate a higher probability of stimulus detection in flow but a higher probability of internal transmission of information in no flow. Finally, results were well predicted by a computational model of collective fright response that included the probability of direct detection (based on signal detection theory) and indirect detection (i.e. via interactions between group members) of threatening stimuli. This model provides a new theoretical framework for analysing the collective transfer of information among groups of fishes and other organisms.     

Lack of predator‐odor detection and avoidance by a songbird,the House Wren

ABSTRACT Recent studies suggest that songbirds have a better sense of smell than initially suspected. Work is now focused on determining how birds use their sense of smell to enhance survival and reproduction. One question is whether birds use smell to detect and avoid predators. We examined the reaction of House Wrens (Troglodytes aedon) to the odor of a potential predator in their nests. On two different days of the nestling stage, we placed papers infused with the urine and anal scent gland material of a mustelid (American mink, Neovison vison), a neutral odoriferous substance (cologne, garlic, or vinegar), or water in nest boxes. The proportion of individuals that hesitated to enter nest boxes after first arrival did not differ significantly between treatments on either day. We also found no significant differences on either day in the time it took wrens to first enter nest boxes, time spent in nest boxes after first entry, the propensity to stay in nest boxes and brood young, or latency to return to nest boxes after first exposure to treatments. Our results suggest that House Wrens either did not detect or did not respond to foreign odors in nest cavities, including the odor of a mustelid predator. In a similar study ( Amo et al. 2008 . Functional Ecology 22: 289–293), adult Blue Tits (Cyanistes caeruleus) were less likely to enter nest boxes that contained the odor of a mustelid. One explanation for this difference is that Blue Tits may have a better sense of smell than House Wrens. Alternatively, or additionally, Blue Tits may be inherently (or as result of experience) more prone than House Wrens to avoid unusual odors or, specifically, the odor of mustelid predators in their nests. Additional studies are needed to determine the extent to which songbirds use their sense of smell to detect and avoid nest predators.     

Some aspects of the embryonic and postembryonic development of the Japanese anchovy Engraulis japonicus Temminck et Schlegel, 1846 in Vostok Bay, Sea of Japan

This study revealed additional data concerning the spawning period of the Japanese anchovy Engraulis japonicus Temminck et Schlegel, 1846 in Vostok Bay (Peter the Great Bay, Sea of Japan). The spawning of E. japonicus in this area ends in September at a water temperature of 17.5 ± 3°C. Some important peculiarities of the embryonic and postembryonic development of E. japonicus in the natural environment are described. The anchovy larvae have characteristic upper and lower rows of melanophores and subcaudal paired rows of melanophores on the trunk. Regular alternating rows of long and short cones were found in the retina of the early larval stages (TL 5.5 ± 0.1 mm). The planes of the photoreceptive lamellae in the outer segments of the short cones are oriented parallel to the long cell axis, which evidently provides sensitivity to polarized light.     

Genetic analysis of the populations of Japanese anchovy Engraulis japonicus from the Yellow Sea and East China Sea based on mitochondrial cytochrome b sequence

Japanese anchovy Engraulis japonicus was not only a commercial species but also a key link in the marine food chain in the Yellow Sea and East China Sea. However, in recent years, E. japonicus experienced a deep recession caused by over fishing. Therefore, determination of population genetic structure is essential to underpin resource recovery and to aid delineating and monitoring populations for fishery management. In this study, sequence variation of a 402-bp fragment of mitochondrial cytochrome b (cyt b) gene from ten populations of E. japonicus in the Yellow Sea and East China Sea was determined, detecting 73 haplotypes. Haplotype diversities and nucleotide diversities for the ten populations ranged from 0.4706 ± 0.1177 (D) to 0.9935 ± 0.210 (WH), and from 0.0014 ± 0.0013 (D) to 0.0090 ± 0.0053 (WH), respectively. Analysis of molecular variance (AMOVA) showed no significant differences at all hierarchical levels, and almost all F_ST values were non-significant, indicating no significant population genetic structure in the Yellow Sea and East China Sea. Two indistinct clades with low support values were detected and the analysis of haplotype frequency distribution showed no significant geographic differences among populations. These results supported the null hypothesis that E. japonicus within the Yellow Sea and East China Sea constituted a panmictic mtDNA gene pool. Based on the present study, the existence of separate genetic stocks in the Yellow Sea and East China Sea were not detected. Strong dispersal capacity of planktonic larvae, and ocean current could be the reasons for genetic homogeneity in this species in the Yellow Sea and East China Sea.     

Contrasting migration behaviour of Daphnia pulicaria and D. galeata x hyalina, in avoidance of predation by 0+perch (Perca fluviatilis)

In spring and early summer, a small population of the large-bodied Daphnia pulicaria coexists with a much larger population of the medium-sized hybrid Daphnia galeata × hyalina in the epilimnion of Lake Maarsseveen (The Netherlands). When large shoals of juvenile perch (Perca fluviatilis) appear in the open water, both species start to migrate vertically. Since D. pulicaria has a larger body-size than D. galeata × hyalina, and is therefore competitive dominant over the hybrid, it is unlikely that both species interact via their common food resource, but they react both to fish predation. However, since they differ in size, and therefore in vulnerability for fish predation, both species adopt different strategies. The smaller bodied, and less vulnerable D. galeata × hyalina exhibits diel vertical migration ascending to the surface at dusk, and staying there during the night. In this way, benefiting from the higher temperatures of the surface layers. In contrast, the large-bodied, and more vulnerable D. pulicaria selects the deep cold hypolimnion water layers as refuge against fish predation. In this way it benefits from a safe habitat, free from fish predators, but on the other hand suffers from low water temperatures, which decrease its fitness. It is likely that the relatively higher temperature in the upper water layers serves as a proximate factor for the downward migration of D. pulicaria.     

Cost of exposure to trematode cercariae and learned recognition and avoidance of parasitism risk by fathead minnows Pimephales promelas

Fathead minnows Pimephales promelas exposed to cercariae of the trematode Ornithodiplostomum sp. incurred a significant mass loss 17 days after exposure to 20 or 120 cercariae. Parasite‐naïve P. promelas showed no evidence of innate recognition or avoidance of cercariae. After a single exposure to cercariae, however, fish responded to chemical and visual cues of dead (thawed) cercariae with a reduction in activity. Encounter rate with cercariae, and hence infection rate, increased with fish activity. The data indicated that experienced P. promelas associated parasitism risk with novel chemical and visual cues that later triggered avoidance behaviour. Parallels and interactions between antiparasite behaviour and antipredator behaviour open new avenues for behavioural ecological research in risk‐sensitive decision‐making.     

Morphological characteristics of eyes and retinas of two sardines (Sardinops melanostictus and Etrumeus sadina,Clupeidae) and an anchovy (Engraulis japonicus,Engraulididae)

The morphology of the eyes and distribution of retinal ganglion cells in two sardine species (Sardinops melanostictus and Etrumeus sadina, Clupeidae) and the Japanese anchovy (Engraulis japonicus, Engraulididae) were investigated anatomically and histologically. The eyes of the sardines faced a slightly dorsolateral direction with the visual field extended obliquely upward. In contrast, the eyes in the anchovy were almost laterally directed. It was hypothesized that the sardines may have an advantage in receiving more downward irradiance compared with the anchovy. The lens muscle was larger in these three species than in many other teleosts, and its surface was entirely melanin‐pigmented. Also, the lens muscle directly and tightly adhered to the backside surface of the iris. The relative area of the lens muscle to the area of the lens, a referential value of the relative power of visual accommodation were notably larger in the species studied than in other teleost values that have been previously reported. A higher M/L% value of these clupeid fishes could facilitate fast and wide ranging visual accommodation and was considered to be associated with maintaining and/or re‐establishing school formations quickly. Analysis of topographical distributions of cells in the ganglion cell layer showed that cell density was highest in the ventrotemporal quadrant of the retina (temporal of the optic cleft) in all three species. Another potentially important role for the black‐pigmented lens muscle may be to block the specialized retinal area from intense sunlight that scatters and irradiates upward or laterally in the surface waters that they inhabit. Thus, the sardine and anchovy may take advantage of efficient detection of visual signals in the frontal‐upward direction and further improve visibility of the target in this direction. J. Morphol. 276:415–424, 2015. © 2014 Wiley Periodicals, Inc.     

Living with the enemy: avoidance of hyenas and lions by cheetahs in the Serengeti

Predator avoidance is likely to play a strong role in structuringspecies communities, even where actual mortality due to predationis low. In such systems, mortality may be low because predatoravoidance is effective, and if the threat of predation is liftedthen entire community structures may be altered. Where competitionis intense, then competitor avoidance may have a similar impacton communities. Avoidance behaviors have been documented fora wide range of species, but this is the first attempt to documentavoidance behavior within a large carnivore community. Audioplayback techniques are used to examine the risk perceivedby cheetahs from their two main competitors that are also theirmain predators, lions and hyenas. The results from these experimentsshow that cheetahs actively moved away from lion and hyenaplayback experiments, compared with dummy playbacks where no sound was played. Cheetahs showed no differences in their responsesto playbacks dependent on their sex or reproductive status,suggesting they were responding principally to a competitionrather than a predation threat. However, cheetahs were muchless likely to hunt after competitor playbacks than after dummyplaybacks, and this resulted in a lower kill rate after competitorplaybacks, demonstrating that the perceived presence of competitors had a noticeable impact on the foraging rate of cheetahs. Furthermore,while cheetahs moved just as far following lion playbacks asafter hyena playbacks, they spent significantly more time lookingat the loudspeaker and were less likely to make a kill afterlion playbacks, suggesting that cheetahs perceive lions tobe a greater threat than hyenas.     

Relative influence of habitat structure,species interactions and rainfall on the post‐fire population dynamics of ground‐dwelling vertebrates

The long‐term impacts of wildfires on animal populations are largely unknown. We used time‐series data based on a tracking index, from coastal NSW spanning 28 years after a wildfire, to investigate the relative influence of habitat structure, species interactions and climate on post‐fire animal population dynamics. The fire had an immediate impact on habitat structure, reducing and simplifying vegetation cover, which then underwent post‐fire successional change including an increase and plateau in tree canopy cover; an increase, stabilization and then decline in shrub cover; and an increase in ground litter cover. Population changes of different animal species were influenced by different components of successional change, but there was also evidence that species interactions were important. For example, bandicoots (Isoodon obesulus and Perameles nasuta combined) increased concurrent with an increase in shrub cover then declined at a faster rate than a direct association with senescing shrub cover would suggest, while the feral cat (Felis catus) population changed with the bandicoot population, suggesting a link between these species. Potoroos (Potorous tridactylus) increased 10 years after the fire concurrent with the closing tree canopy, but there was also evidence of a negative association with feral foxes (Vulpes vulpes). Variation in rainfall did not have significant effects on the population dynamics of any species. Our results suggest that changes in habitat structure play a key role in the post‐fire dynamics of many ground‐dwelling animals and hence different fire regimes are likely to influence animal dynamics through their effects on habitat structure. However, the role of predator–prey interactions, particularly with feral predators, is less clear and further study will require manipulative experiments of predators in conjunction with fire treatments to determine whether feral predator control should be integrated with fire management to improve outcomes for some native species.