Food Capture Research Articles

Influence of flow speed on the functional response of a passive suspension feeder, the spionid polychaete Polydora cornuta

Passive suspension feeders rely on surrounding flow to deliver food particles to them. Therefore, the classic conception of functional response (feeding rate vs. food concentration) may require modification to account for flow speed as a second independent variable. I compared the functional response of Polydora cornuta at different velocities and determined whether food capture was proportional to particle flux (concentration × velocity). To understand feeding responses at a mechanistic level, I measured the functional responses in terms of contact and capture rates and determined particle retention efficiency. Experiments were run separately with two sizes of food particles, and with juvenile or adult worms. For both worm sizes and both particle sizes, capture rate in weak flow was directly related to concentration, but in strong flow it was constant. Worms were therefore unable to benefit from abundant food when in strong flow. The critical velocity at which the capture rate became constant was lower for adult worms than for juvenile worms, and it was lower for small particles than for large particles. Retention efficiency was constant among all treatments, and the results for contact rate were essentially the same as for capture rate. Therefore, the mechanics of particle contact must explain the effects of velocity on the functional response. Contact rate was not a constant proportion of particle flux; treatments with similar fluxes yielded different contact rates depending on the strength of flow. The results appeared to be caused by a velocity-induced behavioral change in appendage posture that affects contact rates: in moderate flow, worms form their feeding palps into helical coils, which they tighten as the velocity increases. I suggest this behavior constrains suspension feeding rates and the mechanical selection between particle sizes when worms are in strong flow, and that the effect changes with ontogeny. Because the results are consistent with patterns in measured growth rates of P. cornuta, I hypothesize that this influence of velocity on the functional response can constrain growth and population dynamics in this species.

Overview of phenotypic plasticity in echinoid larvae, ‘Echinopluteus transversus’ type vs. typical echinoplutei

Many sea urchin echinoplutei exhibit phenotypic plasticity, increasing arm length to enhance food capture in nutrient poor conditions. We tested this phenomenon in species with contrasting larval forms reared in similar feeding conditions. Heliocidaris tuberculata has a typical echinopluteus larva with 4 pairs of arms while Centrostephanus rodgersii larvae have only 1 pair of arms (‘Echinopluteus transversus ’ type larva). Larvae were exposed to high, medium and no food treatments. The ratio ‘postoral arm length’ to ‘midline body length’ (PO:MBL) was used to document phenotypic plasticity. Fed H. tuberculata larvae developed short postoral arms and low PO:MBL, while starved larvae developed long postoral arms and high PO:MBL, indicative of plastic arm growth. In contrast, well fed C. rodgersii larvae had the longest arms and high PO:MBL, indicating the absence of plastic arm growth. Taking MBL into account, ANCOVA revealed that differences among treatments were due to PO. The hypothesis that starved C. rodgersii larvae would develop long arms was not supported. Principal component analysis confirmed that larvae in different food treatments had distinct morphologies and that H. tuberculata and C. rodgersii had opposite growth patterns with respect to food treatment. We suggest that ‘Echinopluteus transversus ’ type larvae are adapted for long distance dispersal, and with only 2 arms for feeding and swimming, there may be an imperative to maintain arm length irrespective of food conditions. Phenotypic plasticity in echinopluteal arm growth is not universal and may be influenced by phylogeny, latitude and the hydromechanics of larval form.

From cells to coastlines: how can we use physiology to forecast the impacts of climate change?

The interdisciplinary fields of conservation physiology, macrophysiology, and mechanistic ecological forecasting have recently emerged as means of integrating detailed physiological responses to the broader questions of ecological and evolutionary responses to global climate change. Bridging the gap between large-scale records of weather and climate (as measured by remote sensing platforms, buoys and ground-based weather stations) and the physical world as experienced by organisms (niche-level measurements) requires a mechanistic understanding of how ;environmental signals' (parameters such as air, surface and water temperature, food availability, water flow) are translated into signals at the scale of the organism or cell (e.g. body temperature, food capture, hydrodynamic force, aerobic capacity). Predicting the impacts of how changing environments affect populations and ecosystems further mandates an understanding of how organisms ;filter' these signals via their physiological response (e.g. whether they respond to high or low frequencies, whether there is a time lag in response, etc.) and must be placed within the context of adult movement and the dispersal of larvae and gametes. Recent studies have shown that patterns of physiological stress in nature are far more complex in space and time than previously assumed and challenge the long-held paradigm that patterns of biogeographic distribution can be based on simple environmental gradients. An integrative, systems-based approach can provide an understanding of the roles of environmental and physiological variability in driving ecological responses and can offer considerable insight and predictive capacity to researchers, resource managers and policy makers involved in planning for the current and future effects of climate change.

Nutritional ecology of sea urchin larvae: influence of endogenous and exogenous nutrition on echinopluteal growth and phenotypic plasticity in Tripneustes gratilla

Summary 1 Marine invertebrates use egg nutrients to develop the functional feeding larva and then enter a facultative feeding period (FFP) when development can proceed without food because larvae are supported by maternal reserves. Facultative feeding reduces starvation risk and so is important for larval success. It may also influence egg size evolution because FFP length correlates with egg size. 2 We quantified energetic lipid (triglyceride, TG) utilisation in unfed and fed larvae as an index of larval nutritive condition in the tropical echinoid Tripneustes gratilla during the FFP to determine if fed larvae would use the buffer provided by endogenous provisions to improve their condition or accelerate development. We predicted that: (i) the condition of unfed and fed larvae should diverge before egg TG is exhausted and/or (ii) that the size of fed larvae should outstrip that of unfed larvae. 3 Temperate echinoplutei exhibit phenotypic plasticity, increasing the length of their food capture apparatus (arms) in nutrient-poor conditions. We examined the generality of this phenomenon in a morphometric analysis of growth in the tropical larva of T. gratilla. We hypothesized that plastic arm growth in starved larvae would occur before the FFP ends as a bet hedging strategy to prepare for hard times ahead when lack of reserves may render this response impossible. 4 We found that fed larvae diverged in condition (higher TG) but not in size compared with starved larvae before egg energetic lipids were exhausted. In addition, unfed larvae showed plastic arm growth before the end of the FFP. 5 Lack of divergence in growth of unfed and fed larvae suggests there may be an imperative to maintain a nutrient storage buffer against starvation due to unpredictable future planktonic food supply. The FFP of T. gratilla exceeds 8 days, considerably longer than that of other echinoids with similarly sized eggs, emphasizing that egg quality may be more important than egg size as a predictor of the FFP in fecundity-time models of egg evolution.

Food capture kinematics in the deep-water chain catshark Scyliorhinus retifer

The chain catshark (Scyliorhinus retifer) is a member of one of the most well studied groups of elasmobranchs (Order: Carcharhiniformes), yet its feeding strategy is unknown due to the inaccessible deep water environment in which it lives (greater than 200 m). To investigate the feeding biology of captive S. retifer, high-speed videography was used to document the kinematic events during capture of two differently sized fish pieces, ‘large’ (scaled to the mouth width), and ‘small’ (scaled to one-half the mouth width). Despite a significant delay in the timing of select kinematic variables for large food captures, a multivariate analysis of the feeding behaviour indicated that overall, food capture kinematics and strike behaviour in S. retifer were not statistically different between large and small items (MANOVA, Wilks' Lambda P =0.598, df=4,24). Food capture in S. retifer was suction-dominant, with items being drawn into the mouth about twice the distance that the predator moved. While suction-dominant food capture appears to be an advantage to benthic predators, it contrasts sharply with the phylogenetic position of S. retifer among several ram-feeding carcharinoid sharks including Cephaloscyllium ventriosum, a member of the same family (Scyliorhinidae). Thus, feeding mode in carcharinoid sharks seems to reflect their ecology and does not appear to have been phylogenetically constrained.

Feeding, fasting and foraging success during chick rearing in macaroni penguins

Foraging behaviour and energy expenditure were measured continuously throughout the chick-rearing period of free-ranging macaroni penguins Eudyptes chrysolophus. These data were integrated with values obtained from the literature on body mass, assimilation efficiency, body reserve consumption and deposition rates, chick growth and energy expenditure and energy content of food in a new type of algorithm to predict (with 95% confidence limits (CL)) foraging success and daily changes in body mass. A successfully breeding pair of macaroni penguins will capture 111.7 kg (95% CL: 79.4 to 158.0 kg) of prey during the chick-rearing period. The crucial phase of the chick rearing period was around the time that chicks creche, when prey consumption rates more than dou- bled as the male assisted in foraging and recovered from a long fast. Female macaroni penguins extracted 2.28 (1.60 to 3.26) and males extracted 2.84 (2.02 to 3.99) g of prey from their environment for every minute spent submerged during foraging. Only 15.3 (14.7 to 15.6)% of all prey consumed was fed to chicks. While food capture rates increase in the middle of the breeding season, this may be more a function of greater food availability than a response to demands from their chick. Male and female macaroni penguins have differing breeding strategies with the male showing the characteris- tics of a capital then income breeder while the female has a strategy that shows characteristics of both capital and income strategies simultaneously. The high synchronicity and precise timing of the mac- aroni penguin breeding season and timing of the increase in prey capture rates suggest an influx of prey to their foraging area during the middle of the breeding season. A depletion of prey resources in the foraging area used during the breeding season could affect foraging success and have pro- found effects on the body condition and composition of this species and its ability to raise chicks suc- cessfully.

Allometric and ontogenetic patterns related to feeding of a neotropical fish, Satanoperca pappaterra (Perciformes, Cichlidae)

Abstract – This study aims to analyse whether Satanoperca pappaterra changes its feeding habit throughout ontogenetic development, and whether morphological ontogenetic patterns are related to its feeding habit and food capture. We collected 258 individuals in the Cuiabá river basin (Brazil) for analyses. There was a weak relationship between diet and body size, as evidenced by size class and multivariate analyses, and niche breadth did not vary strongly during ontogenetic development. Eight morphometric variables were measured in each individual. We found an isometric relationship for mouth height and width, and for head length. We found positive allometry for snout length and body height in relation to body length, whereas this relationship for intestine length and eye diameter showed negative allometry. These results suggest that morphology and consequently diet vary weakly during ontogenetic development of S. pappaterra.

Elaboração de modelos de estudo das arcadas dentárias superior e inferior de cães mestiços (Canis familiares, Linnaeus, 1756)

The digestive apparel is constituted by the digestive tract (mouth, esophagus, stomach, intestines and the anus) and the glands attached (salivary glands, liver, and pancreas) that secrete enzymes to act on the food and help in its digestion and absorption. The teeth act on the capture and triturating of food in the oral cavity and are mineralized, resistant and whitened organs. They are implanted in the dental alveolus through a fibrous articulation called gomphosis and present topographic, morphological and functional differences (incisive, canines, pre-molars and molars) in different stages of development (deciduous and permanent teeth). This work presents a technique for the making of molds, modeling and models of the superior and inferior dental arcades in mongrel dogs to be used as auxiliary didactical material during practical classes of Descriptive Anatomy of Domestic Animals at the Veterinary Medicine School, University Center of Maringa – CESUMAR (PR). A molding apparatus was made from a plastic bottle and was carried out with the use of alginate; after that, models in plaster were made and then the identification of the morphological and topographic differences in the teeth in the superior and inferior arcades were carried out.

Size heterogeneity, growth potential and aggression in juvenile yellowtail kingfish (Seriola lalandi Valenciennes)

The ontogenetic development of size heterogeneity and aggression was monitored in commercial culture tanks of yellowtail kingfish (Seriola lalandi Valenciennes). Size heterogeneity increased substantially with the introduction of Artemia as a food source at 12 days post-hatch (DPH), and was correlated with the appearance of aiming behaviour, a precursor to more direct aggressive interactions. Chasing behaviour started at approximately 19 DPH (10-12 mm total length), with the main aggressors being large-grade individuals comprising 8% of the population. At any one time, only 10-30% of this grade carried out all of the chases, meaning that a very small proportion of the entire population (1%) was responsible for most of the aggressive interactions. The main recipients of aggression were the small grade, comprising 42% of the population, while the medium grade (50% of the population) were generally not aggressive and received only a low to moderate level of aggression. A grading trial showed that large-grade juveniles only displayed aggressive behaviour in the presence of size heterogeneity, and that medium- or small-grade juveniles did not establish an agonistic hierarchy in the absence of large individuals. A high level of aggression in the ungraded control treatment was associated with mortality of most of the small individuals. Even in the absence of aggression, the small-grade juveniles failed to gain weight or show an increase in the RNA/DNA ratio after 12 days. The large- and medium-grade larvae showed an isometric increase in RNA/DNA ratio during development, indicating that faster-growing individuals are likely the result of better food capture or processing traits rather than better protein synthesis rates. Decreasing size heterogeneity and aggression via grading mostly benefits the medium-grade individuals, as the majority of small individuals within a batch appear to be on a degenerative developmental trajectory irrespective of an aggressive environment. 15-20 individuals measured for total length or weight (Less)

Ontogeny of feeding behavior and cranial morphology in the whitespotted bambooshark Chiloscyllium plagiosum

Morphological and behavioral development of the feeding apparatus over early ontogeny can profoundly affect the ability of an organism to obtain nourishment, ultimately impacting survival. The interplay between morphology and behavior over the first year of life was studied in the whitespotted bambooshark Chiloscyllium plagiosum (Bennett 1830) beginning in March of 2002 using high-speed videography and dissection. Externally measured variables describing cranial growth, and jaw weight, scaled at or near isometry while jaw and hyoid musculature, especially the coracohyoideus, demonstrated considerable hypertrophication. The difference between the volume of the buccal cavity when open and closed scaled with substantial positive allometry while the time to reach maximum jaw and hyoid abduction exhibited weak allometry, resulting in the capacity for more rapid and greater volumetric intake during feeding. In addition, the relative forward motion of the predator during a strike decreased over ontogeny and the feeding modality became more suction-dominated. Kinematic variables exhibited little variability and the primary aspect of food capture that was modulated in response to food type was the forward motion of the predator. An increase in capture success was noted for live, elusive shrimp over ontogeny indicating that morphological and behavioral changes have direct consequences for prey acquisition. Conservation of head shape coupled with a narrow behavioral repertoire is hypothesized to increase prey capture success in the wild over ontogeny as individuals become more proficient in the execution of a single, low-variability, suction-dominated capture behavior.

Transgressive Sanctity: The Abrek in Chechen Culture

After the surrender of Imam Shamil in 1859, North Caucasian mountaineers were faced with the problem of developing new modes of expressing their cultural and political aspirations. As the promise of independent statehood offered by the imamate faded from the realm of possibility, the noble bandit of the Caucasus, known to natives by the term abrek, rose in cultural significance. The institution of the abrek is ancient to the Caucasus Mountains. It is linked as a social practice to amanatstvo, in which a member of one clan was found guilty of a crime demanding blood revenge and sought refuge with another clan, changing his identity in some ways in the process. (1) In addition to changing places and therefore identity, as the amanant did, the abrek took on the task of providing for the community through the practice of raiding. Though often violent, the raids initiated by abreks should be distinguished from other forms of aggression that took place between villages and clans. The aim of raiding was the capture of livestock and other food, and it was governed by rules of reciprocity. When one village raided another, it was expected that the raided village would return the favor. Such is the indigenous practice of abrechestvo (to employ the Russian term), which acquired an anti-colonial layer of meaning only during the latter half of the 19th century, as contacts with the Russian army and other branches of the colonial, administrative order increased in both intensity and frequency. I focus here on the abrek as a latter-day social phenomenon representing what I call sanctity, by which I mean to indicate a particular form of religiosity that is constituted through its violation of the secular codes of colonialism. This abrek (the embodiment of transgressive sanctity) was born in the second half of the 19th century, with the decline in political power of Caucasian mountaineer society, the rise of empire, and the concomitant need for cultural expression in autonomous and indigenous registers. If the abrek was born in the 19th century as a politically loaded phenomenon, he reached his apotheosis in terms of cultural and political significance in the 20th century in Soviet representations of indigenous resistance during the tsarist period and, finally, in the post-Soviet imagery of mountaineer resistance to Soviet atrocities, such as deportation. I focus primarily on the images of the abrek produced by Chechens and by those who wrote about them, because the Chechen experience is in many ways paradigmatic of this particular aspect of the North Caucasian experience, anti-colonial resistance to Russian rule. Chechen culture thus offers a richly nuanced archive for the historical and literary study of North Caucasian culture in general. It is important, however, to place the Chechen experience inside its Caucasian context and to remember that the abrek was not a uniquely Chechen phenomenon. The word, of uncertain origin (for details on the etymology, see below), is found in every North Caucasian language, which testifies to the centrality of this practice to the social life of the mountaineers in the past. But, more important for the present context, the abrek as cultural symbol is amply reflected in North Caucasian literature and in Georgian literature as well. (2) With regard to the present, I simply note that the abrek is one element in an unexamined genealogy of images and histories that has led or, rather, been reduced to the stereotype of the Chechen bandit in Western and Russian media reports on Chechen culture and history. The following pages trace this genealogy with the hope not merely of shedding light on the abrek in history, as a cipher for reading the colonialism of the past, but with the additional goals of unpacking this image for the present and of interpolating colonialist stereotypes with their indigenous counter-images. (Though I should draw attention to the problematic fact that stereotypes and counter-images belong to the same discourse, and that any attempt to disentangle colonial representations from the anti-colonial images conceived in response to them is an exercise in futility. …

Feeding mechanism of the polychaete Sabellaria alveolata revisited: comment on Dubois et al. (2005)

ABSTRACT: Recently, Dubois et al. (2005; Mar Ecol Prog Ser 301:159–171) described the feedingmechanisms of the sabellariid polychaete Sabellaria alveolata and concluded that it is a ciliarysuspension feeder that uses alternately a downstream- and an upstream-collecting system. We re-investigated both the ciliated epithelia (scanning electron microscopy and transmission electronmicroscopy) and the function (video microscopy) of the tentacle crown of S. alveolata . We foundthat the tentacles of intact and undisturbed S. alveolata have a large number of stiff ciliary spikes,each flanked by an actively beating cirrus, but no structured flow of water is created and onlyminor local currents can be seen. Clearly, S. alveolata has neither a ciliary downstream-collectingsystem nor a proper ciliary pump as found in upstream-collecting bryozoans, phoronids andbrachiopods. Our findings indicate that S. alveolata ’s tentacle crown is designed for passive suspen-sion feeding and thus dependent on ambient currents to bring suspended food particles into contactwith the tentacles. The significance of the conspicuous ciliary spikes remains unknown, but ourobservations suggest that mucus is involved in both capture and transport of food particles.KEY WORDS: Suspension feeding · Particle capture · Video-microscope observations · Ciliated tentacles · Ciliary spikes ·

Foraging and mobility in three species of Aciculata (Annelida: Polychaeta)

Aspects of feeding, such as food capture and ingestion, as well as mobility of the polychaetes Eurythoe complanata, Marphysa formosa and Diopatra aciculata, from São Sebastião Channel (São Sebastião, state of São Paulo) were observed in laboratory conditions. Eurythoe complanata, a carnivorous species, fed exclusively on pieces of fish with the aid of strong muscular retractable lips, and detected the presence of food by chemical stimuli. Diopatra aciculata, an omnivorous species, captured and ingested different kinds of food with the aid of its jaws, generating a flow of water through its tube by which it detects the presence of food and oxygenates its gills. Marphysa formosa also used its jaws to bite and lacerate food. These species showed greater or lesser degrees of intolerance to light.

Degeneration after sexual differentiation in hydra and its relevance to the evolution of aging

Aging occurs in most multicellular animals, yet some primitive animals do not show any sign of aging. This raises the following question: How have metazoans acquired the trait of aging in the course of evolution? Comparative studies of various species have provided a clue to this question by showing that sexually reproducing organisms predominantly undergo aging. The evolutionary theory “pleiotropy” also postulates aging as a price for facilitating the reproduction in the early life stage of an organism. For investigating the association between sexual reproduction and aging, a sexual phase-inducible organism in a laboratory would be suitable. One of such organisms is hydra, a genus of Cnidaria. Asexual hydra has been considered to be immortal, but there is the possibility that hydra undergoes aging after sexual reproduction. To search for signs of aging in hydra, we studied sexually differentiated Hydra oligactis at the individual and cellular levels. As a result, we found a significant decline in the capacities for food capture, contractile movements, and reproduction. More importantly, we discovered an exponential increase in the mortality rate of the population. These observations suggest that the degenerative process in H. oligactis represents the aging process. Furthermore, we found that the number of germ cells increased, whereas the number of somatic cells concomitantly decreased. The observed change of the cell composition is thus consistent with the “pleiotropy” theory of aging.

Comparison of feeding guild structure and ecomorphology of intertidal fish assemblages from central California and central Chile

The hypothesis of ecological and morphological convergence of the taxonomically distinct intertidal fish assemblages from central California, USA, and central Chile was tested by comparing the feeding guild structures and the morphologies associated with food capture and processing of guild members from each region. We determined the diets of the most abundant intertidal fishes from 3 central California sites by examining gut contents. A matrix of dietary overlap among species within the Californian and Chilean assemblages (diets of Chilean fishes determined in another study) was constructed, and statistically significant guilds were determined using a bootstrapping procedure. Ten morphological features were examined for species in each region, and the relationship between diet and consumer morphology was evaluated. Three feeding guilds, omnivore, microcarnivore, and carnivore, were common to both regions, but a fourth guild, polychaete feeders, was unique to California. Feeding guild structure was not associated with phylogenetic relatedness within either assemblage. An assemblage-wide relationship between diet and morphology was found in each assemblage, but only a few associations between diet and morphology were common to both regions. In both California and Chile, omnivores tended to have longer digestive tracts and closer-set gill rakers, microcarnivores tended to have larger relative mouth heights, and all carnivorous fishes tended to have shorter guts and more widely spaced gill rakers. Overall, interregional morphological patterns were associated with phylogenetic relatedness, rather than with dietary similarities.

Prey capture behavior and kinematics of the Atlantic cownose ray, Rhinoptera bonasus

The structurally reinforced jaws of the cownose ray, Rhinoptera bonasus testify to this species’ durophagous diet of mollusks, but seem ill-suited to the behaviors necessary for excavating such prey. This study explores this discordance by investigating the prey excavation and capture kinematics of R. bonasus. Based on the basal suction feeding mechanism in this group of fishes, we hypothesized a hydraulic method of excavation. As expected, prey capture kinematics of R. bonasus show marked differences relative to other elasmobranchs, relating to prey excavation and use of the cephalic lobes (modified anterior pectoral fin extensions unique to derived myliobatiform rays). Prey are excavated by repeated opening and closing of the jaws to fluidize surrounding sand. The food item is then enclosed laterally by the depressed cephalic lobes, which transport it toward the mouth for ingestion by inertial suction. Unlike in most sharks, upper jaw protrusion and mandibular depression are simultaneous. During food capture, the ray's spiracle, mouth, and gill slit movements are timed such that water enters only the mouth (e.g., the spiracle closes prior to prey capture and reopens immediately following). Indigestible parts are then hydraulically winnowed from edible prey portions, by mouth movements similar to those used in excavation, and ejected through the mouth. The unique sensory/manipulatory capabilities of the cephalic lobes, as well as the cownose ray's hydraulic excavation/winnowing behaviors and suction feeding, make this species an effective benthic predator, despite its epibenthic lifestyle.

Intake rate at differently scaled heterogeneous food distributions explained by the ability of tactile‐foraging mallard to concentrate foraging effort within profitable areas

The ability to respond to spatial heterogeneity in food abundance depends on the scale of the food distribution and the foraging scale of the forager. The aim of this study is to illustrate that a foraging scale exists, and that at larger scaled food distributions foragers benefit from the ability to subdivide a continuous (non‐discrete) heterogeneous environment into profitable and non‐profitable areas. We recorded search patterns of mallards Anas plathyrhynchos foraging in shallow water on cryptic prey items (millet seeds), distributed at different scales. A small magnet attached to the lower mandible allowed us to record in great detail the position and movements of the bill tip within a feeding tray underlain by magnet sensors. Instantaneous intake rate was determined in a subsequent experiment. We successfully determined the foraging scale (about 2×2 cm), defined as the scale above which foragers do respond (coarse scaled distribution) and below which foragers do not respond (fine scaled distribution) to spatial heterogeneity, by concentrating foraging effort within areas of high food density. A response resulted in a significantly higher intake rate, compared to a homogeneous distribution with an equal overall density. Unlike systematic search cell revisitation was common in trials, and at coarse scaled food distributions even slightly (but significantly) more frequently observed than predicted for random search. Mallards respond to food capture by restricting displacement (area restricted search) at food distributions that are considered to be clumped for the forager (large scaled coarse distributions). We argue that partitioning the environment at the foraging scale in itself could be a mechanism to concentrate foraging efforts within profitable areas, because mallard were able to respond to heterogeneity at coarse scaled food distributions even when non‐clumped (i.e. without conducting area restricted search).

Modulation in Feeding Kinematics and Motor Pattern of the Nurse Shark Ginglymostoma cirratum

Studies of feeding in bony fishes have almost universally demonstrated the ability of individuals to modulate their method of capture in response to differing stimuli. Preliminary evidence indicates that morphologically specialized inertial suction feeding sharks are the most likely fishes to lack inherent modulatory ability. We examined the ability of the nurse shark, Ginglymostoma cirratum, to modulate its feeding behavior based on different food types and sizes. G. cirratum is an inertial suction feeding fish that is apparently stereotyped in its food capture behavior. Electromyography showed no statistical difference between feeding motor patterns based on food type (squid or fish) or size (gape width or twice gape width), although there were slight inter-individual differences in the onset of muscle firing for some muscles. Kinematic analysis showed a statistical difference in variables associated with durations for different food types, with the durations for all variables being faster for squid bites than fish bites, but no difference based on the size of the food item. This apparent lack of modulation may be associated with specialization of the morphology and behavior of G. cirratum for obligate suction prey capture. This functional specialization constrains the method in which G. cirratum captures prey but does not appear to result in dietary specialization. An unusual post capture spit-suck manipulation allows this shark to handle and ingest large prey.

Diet‐induced phenotypic plasticity in the skull morphology of hatchery‐reared Florida largemouth bass, Micropterus salmoides floridanus

Abstract – Hatchery‐reared Florida largemouth bass, Micropterus salmoides floridanus, feed on inert pellet food while their wild counterparts capture elusive prey. Differences in levels of prey elusivity often mandate the use of alternate methods of prey capture. This study examines whether elusivity‐based variation in prey capture translates to a phenotypic change during skull development, and if this change results in a functional difference in the feeding mechanism. The developmental pattern of the skull was conserved between hatchery and wild bass until 80–99 mm TL. At this point, wild bass quickly developed morphological changes of the jaw apparatus including a more fusiform head and elongated jaw structures. Natural development in hatchery bass, however, was retarded at this size. Post‐release, the skulls of hatchery fish converged towards those of wild bass by 135 mm TL. Despite variation in skull development, no theoretical advantage in food capture was found between these two groups.

Use of Long-Term Stored Vector Information in the Neotropical Ant Gigantiops destructor

We investigated how the formicine ant Gigantiops destructor can use vector information to navigate within the cluttered environment of the rain forest. Displaced foragers use skylight information to move in the theoretical feeder-to-nest direction, whether they are prevented from updating their path-integrator during foraging or captured at the departure from their nest, i.e. with a current accumulator state very close to zero. Only ants that have collected food are able to download a long-term stored reference vector pointing in the nest direction, irrespective of the current accumulator state of their path-integrator stored in a working memory and independent of familiar landmarks. Depending on the release sites, ants that became lost at a maximum distance of 50 cm could still hit and recognize their familiar route, or they engaged in a systematic search for it centered on the release sites. In contrast to Cataglyphis desert ants, Gigantiops ants do not rely primarily on the current accumulator state of their egocentric path integrator. Such a long-term vector-based navigation primed by food capture is well adapted for a tropical ant foraging during periods spanning several hours. This could prevent the numerous cumulative errors in the evaluation of the angles steered that might result from a continuously running path-integrator operating during complex foraging patterns performed at ground or arboreal levels and during passive displacement in response to heavy rain.