Rotational stability in stalked crinoids and the function of wing plates in Pterotocrinus depressus

Baumiller, Tomasz K. & Plotnick, Roy E. 1989 07 15: Rotational stability in stalked crinoids and the function of win2–. plates in Pterotocrinus depressus. Lethaia , Vol. 22, pp. 317–326. Oslo. ISSN 0024–1164.
An unusual feature of the Mississippian camerate crinoid Pterotocrinus depressus is its tegmen with five wing-like appendages (wing plates). It has been suggested that the wing plates served as anti-predatory devices, hydrodynamic baffles, or outriggers for stabilization and support on the substrate. We propose two alternative hypotheses. First, the wing plates may have served as splitter plates, which would have acted to reduce drag on the organism. Second. wing plates served as stabilizing fins or rudders, allowing the passive maintenance of an efficient feeding posture in moving water. Experimental analyses of the forces acting on model crinoids, with and without the wing plates, support the hypothesis of the rudder function. A model developed for maintenance of stability in moving water should be applicable to all suspension feeders. * Crinoids, paleobiomechanics, biological rudders .     

Zooid orientation structures and water flow patterns in Paleozoic bryozoan colonies

Anstey, Robert L. 1981 12 15: Zooid orientation structures and water flow patterns in Paleozoic bryotoan colonies. Lethaia . vol. 14, pp. 287–302. Oslo. ISSN 0024–1164.
By means of direct physical evidence provided by zooecial orientation structures, active water flow systems in Paleozoic bryozoans are inferred to be variously centripetal, centrifugal, or basipetal. Monticules, previously assessed as excurrent water outlets, fall into three additional functional types: incurrent, bypassed, and funnel. In one species circular zoarial fenestrations served as excurrent water outlets. Water flow patterns are strongly correlated with zoarial growth form, which vanes in a general way with inferred habitat conditions in ancient environments. Monticular astogeny and phylogeny include a graded series of sizes, types, and functions. Analogy with zooidal polarities in extant stenolaemates suggests that colony bases and centripetal monticules in the Paleozoic orders were anally budded, but that erect branches and centrifugal monticules were orally budded, a character shared only by the freshwater Phylactolaemata. * Bryozoa, Stenolaemata, functional morphology, monticule function, hydrodynamics, feeding currents, Palaeozoic .     

Biodynamic and phyletic paradigms for sensory organs in camerate crinoids

A Haugh, Bruce N. 1978 04 IS: Biodynamic and phyletic paradigms for sensory organs in camerate crinoids
Functional analysis of thecal pores and associated fixed pinnules of camerate crinoids reveals that they may have been organized into an integrated current-sensing biologic system. Paleobiologic, biodynamic, and geometric evidence reveals a potential for sensing the direction and intensity of horizontal water currents. An ahistoric paradigm predicts that the inferred sensory organs could have elicited several alternative feeding postures and a survival posture in response to current intensity. Possession of long anal tubes is judged to be related to the sensory function. By virtue of these adaptations certain camerates may have been discriminatory rheophilic feeders in complex fdter feeding communities. An historically founded phyletic paradigm suggests that a functional change in thecal pores and pinnules occurred in the Early Mississippian as an evolutionary concourse in several independent lineages. This specialized sensory innovation may have signifcantly contributed to the 'flowering' of camerates in rheic carbonate environments as well as their demise in terrigenous clastic environments. Phyletic paradigms illustrate the advantage of functional analysis of fossil structures at several points in time and especially at the acme of development when structure and function are commonly most clearly delimited.     

Early ontogeny of coal grunter from hormone-induced spawnings and laboratory-reared embryos and larvae

Spawning of coal grunter Hephaestus carbo was successfully induced using doses of human chorionic gonadotrophin (hCG) between 500 and 3000 IU kg (body weight)⁻¹. Water hardened eggs are telolecithal, amber in colour, spherical, transparent, demersal and slightly adhesive with a single large oil droplet and perivitelline space 47% of total egg volume. Cleavage begins 10–15 min after fertilization. Epiboly begins 6h after fertilization and continues for 4 h. Invagination of the neural tube is apparent 11·5 h after fertilization, followed by progressive organogenesis up to hatching 60–80 h after fertilization. An invagination in the yolk, consistent in shape, position and time of appearance among embryos spawned from numerous brood stock pairs, was visible in all fertilized eggs between neurulation (11-5 h) and early organogenesis (20 h). The functional significance of this yolk invagination is unknown. Newly-hatched larvae (4·2 mm L _T) are elongate and possess well developed eyes, a functional mouth, and a large yolk sac. Yolk is fully resorbed and first feeding occurs at 6 days posthatching. The sequence of fin formation is caudal, second dorsal and anal, first dorsal, pectoral and pelvic. The prefiexion larval stage lasts for c. 8 days and flexion of the notochord is complete within a further 8–9 days. Squamation commences at 30 days posthatching and transition to the juvenile life stage is complete by 35–40 days posthatching.     

Ecology and signal evolution in lizards

Current models of signal evolution explain diversity by invoking a variety of social, perceptual and environmental factors. Social systems and spacing patterns determine the active space of signals and their function. Receiver sensory systems and habitat characteristics interact to constrain signal design. These factors are traditionally implicated in promoting directional evolutionary change, leading to increases or decreases in signal complexity. We examine macro-evolutionary trends in signal design, as reflected by display modifier repertoire size, for 124 species of iguanian lizards to identify the importance of ecological factors in display evolution. Possessing a small home range, being arboreal and feeding on moving prey are all correlated with the evolution of large repertoires. However, living in closed habitats is associated with increased evolutionary change in repertoire size, producing greater signal diversity. Ecological factors can thus act either directionally or to promote evolutionary lability.   © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 127–148.     

Visual position stabilization in the hummingbird hawk moth, Macroglossum stellatarum L. I. Behavioural analysis

Optomotor responses of freely flying hawk moths, Macroglossum stellatarum, were characterized while the animals were hovering in front of and feeding on a dummy flower. Compensatory translational and rotational movements of the hawk moth were elicited by vertical grating patterns moving horizontally, mimicking imposed rotational and translational displacements of the animal in the horizontal plane. Oscillatory translational and rotational pattern motion leads to compensatory responses that peak in the frequency range between 2 Hz and 4 Hz. The control systems mediating the translational and rotational components of the optomotor response do not seem to influence each other. The system mediating translational responses is more sensitive in the fronto-lateral part of the visual field than in the lateral part; the opposite is true for the rotational system. The sensitivity of the translational system does not change along the vertical, whereas the rotational system is much more sensitive to motion in the dorsal than in the ventral part of the visual field. These sensitivity gradients may reflect an adaptation to the specific requirements of position stabilization in front of flowers during feeding. Accepted: 13 August 1997     

The feeding ecology of Axiothella rubrocincta (Johnson) (Polychaeta: Maldanidae)

The feeding ecology of Axiothella rubrocincta (Johnson) from Tomales Bay, California, is described. This worm inhabits a U-shaped tube of agglutinated sand grains and mucus. Morphological adaptations such as nuchal and anal plaques prevent the tube from becoming clogged. Foreign debris entering the tube is either consumed or incorporated into the tube wall. The proboscis and notosetae are probably used to clean the tube wall. A. rubrocincta combines feeding and burrowing activities to form the funnel and complete the tube: it does not ingest sediment while burrowing. Organic matter deposited into the funnel is buried there by sand slides originating at the rim of the funnel. The concentration of organic matter within the funnel is significantly higher than for non-funnel sediments. A. rubrocincta consumes food from the upper 2 cm of the substratum and is 4.6% efficient as a depositfeeder. It also feeds within the funnel and can ingest large quantities of food. This feeding process is described. A. rubrocincta irrigates its tube at a rate of 5.1 ml sea water/g/h while feeding, and briefly reverses this current to a rate of 0.1 ml/g/h when defaecating. The rhythmic activity patterns are integrated: the mean defaecation and inverse pumping time is 14.4 min at 15 ± 1 C.     

Accounting for spatial pattern when modeling organism-environment interactions

Statistical models of environment-abundance relationships may be influenced by spatial autocorrelation in abundance, environmental variables, or both. Failure to account for spatial autocorrelation can lead to incorrect conclusions regarding both the absolute and relative importance of environmental variables as determinants of abundance. We consider several classes of statistical models that are appropriate for modeling environment-abundance relationships in the presence of spatial autocorrelation, and apply these to three case studies: 1) abundance of voles in relation to habitat characteristics; 2) a plant competition experiment; and 3) abundance of Orbatid mites along environmental gradients. We find that when spatial pattern is accounted for in the modeling process, conclusions about environmental control over abundance can change dramatically. We conclude with five lessons: 1) spatial models are easy to calculate with several of the most common statistical packages; 2) results from spatially-structured models may point to conclusions radically different from those suggested by a spatially independent model; 3) not all spatial autocorrelation in abundances results from spatial population dynamics; it may also result from abundance associations with environmental variables not included in the model; 4) the different spatial models do have different mechanistic interpretations in terms of ecological processes – thus ecological model selection should take primacy over statistical model selection; 5) the conclusions of the different spatial models are typically fairly similar – making any correction is more important than quibbling about which correction to make.     

Double function of aptychi (Ammonoidea) as jaw elements and opercula

Lehmann, U. & Kulicki, C. 1990 10 15: Double function of aptychi (Ammonoidea) as jaw elements and opercula. Lethaia , Vol. 23, pp. 325–331. Oslo. ISSN 0024–1164.
Aptychi are calcitic coverings on the outer surface of organic ammonite lower jaws. They are similar in shape to that of the corresponding ammonite apertures. This observation and additional features of many aptychi are in harmony with their former interpretation as protective opercula. We suggest that they served as opercula in addition to functioning as jaws. The primary function of the lower jaws was thus secondarily extended to that of protective shields when they acquired their calcitic covering, while as lower jaws their importance dwindled to that of a more passive abutment. Phylogenetically, this seems to have started slowly in some anaptychi and became obvious with the first aptychi. ▭ Ammonites, aptychus, operculum, jaw apparatus, evolution, function .     

Predicting predation through prey ontogeny using size-dependent functional response models

The functional response is a critical link between consumer and resource dynamics, describing how a consumer's feeding rate varies with prey density. Functional response models often assume homogenous prey size and size-independent feeding rates. However, variation in prey size due to ontogeny and competition is ubiquitous, and predation rates are often size dependent. Thus, functional responses that ignore prey size may not effectively predict predation rates through ontogeny or in heterogeneous populations. Here, we use short-term response-surface experiments and statistical modeling to develop and test prey size-dependent functional responses for water bugs and dragonfly larvae feeding on red-eyed treefrog tadpoles. We then extend these models through simulations to predict mortality through time for growing prey. Both conventional and size-dependent functional response models predicted average overall mortality in short-term mixed-cohort experiments, but only the size-dependent models accurately captured how mortality was spread across sizes. As a result, simulations that extrapolated these results through prey ontogeny showed that differences in size-specific mortality are compounded as prey grow, causing predictions from conventional and size-dependent functional response models to diverge dramatically through time. Our results highlight the importance of incorporating prey size when modeling consumer-prey dynamics in size-structured, growing prey populations.     

Biomechanics of microscopic appendages: functional shifts caused by changes in speed

Many diverse animals use arrays of hair-like structures to perform important jobs such as feeding, gas exchange, smelling, and swimming. Since these functions involve hair interactions with the surrounding water or air, analysis of the fluid dynamics of diverse hair-bearing appendages reveals how the morphology of an array of hairs affects it performance. Mathematical and physical models of flow between cylinders have shown that arrays of large, rapidly moving cylinders are leaky sieves, whereas little fluid moves through a row of small, slow rods. The purpose of the present study was to test this prediction for realistic appendage morphologies and to elucidate whether the design of a hairy leg can affect the range of speeds in which this transition in function occurs. We studied flow through hairy food-capturing appendages (second maxillae) of calanoid copepods, abundant planktonic crustaceans whose feeding on unicellular algae forms an important link in many marine food webs. Using dynamically scaled physical models, we found that hairy appendages undergo a transition between paddle- and sieve-like function at a critical range of sizes and speeds. The coarser the mesh of hairs on second maxillae, the smaller the size and speed at which this functional shift occurs. Thus, a simple increase in size (ontogenetic or evolutionary) or speed can generate a novel function (a paddle can become a filter), but the morphology of a hairy appendage determines the size and speed range at which leakiness to fluid flow can be affected by behavior or growth.     

Vestibular postural control model

Current models for physiological components and a posture control experiment conducted with three normal subjects form the basis for a model which seeks to describe quantitatively the control of body sway when only vestibular motion cues are used. Emphasis is placed on delineating the relative functional roles of the linear and the angular acceleration sensors and on modeling the functional interface between these sensors and the initiation of compensatory responses at the ankle joint.The model predicts the form of the postural response to a small sway disturbance; including initial detection of sway, characteristics of the transient correction, and maintenance of stability. The model suggests that postural stability requires a short time constant integration of semicircular canal output. Separation of semicircular canal and utricular otolith function into sway motion detector and static reference sensors respectively is demonstrated.This work was supported by NASA under Grant NGR-22-009-156.     

Functional response of juvenile pink and chum salmon: effects of consumer size and two types of zooplankton prey

Feeding rate experiments were conducted for pink salmon Oncorhynchus gorbuscha fry [mean fork length ( L _F) 39 mm], juveniles (103–104 mm L _F) and juvenile chum salmon Oncorhynchus keta (106–107 mm L _F). Fishes were presented with small copepod ( Tisbi sp.) or larger mysid shrimp ( Mysidopsis bahia ) prey at varying densities ranging from 1 to 235 prey l⁻¹ in feeding rate experiments conducted at water temperatures ranging from 10·5 to 12·0° C under high light levels and low turbidity conditions. Juvenile pink and chum salmon demonstrated a type II functional response to mysid and copepod prey. Mysid prey was readily selected by both species whereas the smaller bodied copepod prey was not. When offered copepods, pink salmon fry fed at a higher maximum consumption rate (2·5 copepods min⁻¹) than larger juvenile pink salmon (0·4 copepods min⁻¹), whereas larger juvenile chum salmon exhibited the highest feeding rate (3·8 copepods min⁻¹). When feeding on mysids, the maximum feeding rate for larger juvenile pink (12·3 mysids min⁻¹) and chum (11·5 mysids min⁻¹) salmon were similar in magnitude, and higher than feeding rates on copepods. Functional response models parameterized for specific sizes of juvenile salmon and zooplankton prey provide an important tool for linking feeding rates to ambient foraging conditions in marine environments, and can enable mechanistic predictions for how feeding and growth should respond to spatial-temporal variability in biological and physical conditions during early marine life stages.     

Development of the respiratory swimbladder of Pangasius sutchi

The swimbladder of Pangusius sutchi first appears on the dorsal surface of the oesophagus at about 5 days after hatching. The swimbladder has double chambers when it is separated by a medial septum at 8–10 days. Alveoli start to develop and function in air-breathing at 12–14 days. Their number is increased by subdivision, and the respiratory portion grows towards the centre. Morphometric analysis shows that the swimbladder increases in respiratory surface, volume and surface area: volume ratio during development. On a histological basis, the development of the swimbladder is divided into three distinct periods: a blind tube, a double chamber and an alveolus period. It is characteristic that the flat epithelial cell arises from a primordial cuboidal cell and that a double capillary system is arranged in the interalveolar septa. Multilamellar bodies appear and a blood-air barrier is established when the swimbladder becomes functional.     

Integration of pecking,filter feeding and drinking mechanisms in waterfowl

This paper is one of several contributions in a series, illustrating the application of a specific deductive methodology to explain diversity of form. The methodology facilitates the explanation of feeding morphologies in various ducks as a transformation of the mallard's feeding design maximized for specific proportions of performance that are contributed by pecking and filter feeding mechanisms.The earlier described anatomy and formal analyses of the three mechanisms in the mallard served as the initial conditions used in simulation models. Four elements of the feeding system were chosen that play a major role in all three mechanisms. For each element, the main parameter was selected: storage capacity of the rostral mouth cavity, transport capacity of the rostral mouth tube, storage capacity of the caudal mouth cavity and transport capacity of the caudal mouth tube. The boundary conditions for the simulation were determined from internal organismic constraints. The total food uptake of the mallard was regarded as the function to be maximized. This object function is the summation of the food uptake by one second of pecking and one second of filter feeding. The drinking mechanism was shown not to interfere, since that mechanism operates sufficiently whenever the pumping mechanism works properly.The object function, made up by the pecking and filter feeding performances was graphed. From these graphs a morphospace was developed: the region within which modifications of the mouth design are feasible. This procedure allowed examination of the general hypothesis that different modifications of one design for a complex multi-role system are explainable from differences in proportions of the functional performance contributed by each of the roles.Two predictions were evaluated more specifically: 1) If filter feeding performance must increase for a specific change in total food uptake, the volume of the rostral mouth cavity must increase; this requires widening and lengthening of the rostral maxillar portion and also a phase shift in jaw and lingual motion patterns, increasing the stroke volume. 2) If pecking performance must increase, the transport capacity of the rostral mouth tube must increase; this requires shortening of the maxillar mid portion. These two predictions regarding change in mouth morphology were borne out by shovelers and tufted ducks, respectively.The deductive analysis of the feeding system's morphospace allowed the explanation of the wide diversity of forms in the duck mouth designs as emerging from the great radiation capacity of the ancestral duck's mouth design: it is a versatile, potentially multi-role system in which pecking, drinking and filter feeding mechanisms are mutually very tolerant and, by epiphenomena, includes the elements of a grazing mechanism. In addition, the deduced morphospace was shown to explain phenotypic plasticity, since it explains the occurrence of two morphotypes that develop due to habitat discrimination: one type that has been forced to filter feed, and one type that feeds by pecking.Address reprint requests to Dr. G.A. Zweers     

Modeling spatiotemporal abundance of mobile wildlife in highly variable environments using boosted GAMLSS hurdle models

Modeling organism distributions from survey data involves numerous statistical challenges, including accounting for zero‐inflation, overdispersion, and selection and incorporation of environmental covariates. In environments with high spatial and temporal variability, addressing these challenges often requires numerous assumptions regarding organism distributions and their relationships to biophysical features. These assumptions may limit the resolution or accuracy of predictions resulting from survey‐based distribution models. We propose an iterative modeling approach that incorporates a negative binomial hurdle, followed by modeling of the relationship of organism distribution and abundance to environmental covariates using generalized additive models (GAM) and generalized additive models for location, scale, and shape (GAMLSS). Our approach accounts for key features of survey data by separating binary (presence‐absence) from count (abundance) data, separately modeling the mean and dispersion of count data, and incorporating selection of appropriate covariates and response functions from a suite of potential covariates while avoiding overfitting. We apply our modeling approach to surveys of sea duck abundance and distribution in Nantucket Sound (Massachusetts, USA), which has been proposed as a location for offshore wind energy development. Our model results highlight the importance of spatiotemporal variation in this system, as well as identifying key habitat features including distance to shore, sediment grain size, and seafloor topographic variation. Our work provides a powerful, flexible, and highly repeatable modeling framework with minimal assumptions that can be broadly applied to the modeling of survey data with high spatiotemporal variability. Applying GAMLSS models to the count portion of survey data allows us to incorporate potential overdispersion, which can dramatically affect model results in highly dynamic systems. Our approach is particularly relevant to systems in which little a priori knowledge is available regarding relationships between organism distributions and biophysical features, since it incorporates simultaneous selection of covariates and their functional relationships with organism responses.     

Modelling the subgenual organ of the honeybee, Apis mellifera

In a recent study on the honeybee (Apis mellifera), the subgenual organ was observed moving inside the leg during sinusoidal vibrations of the leg (Kilpinen and Storm 1997). The subgenual organ of the honeybee is suspended in a haemolymph channel in the tibia of each leg. When the leg accelerates, the inertia causes the haemolymph and the subgenual organ to lag behind the movement of the rest of the leg. To elucidate the biophysics of the subgenual organ system of the honeybee, two mathematical models to simulate the experimentally observed mechanical response are considered. The models are a classical mass-spring model and a newly developed tube model consisting of an open-ended, fluid-filled tube occluded by an elastic structure midway. Both models suggest that the subgenual organ included in the haemolymph channel resembles that of an overdamped system. In resembling the biophysics of the subgenual organ system in the honeybee, we consider the tube model to be the better of the two because it simulates a mechanical response which complies best with the experimental data, and the physical parameters in the model can be related to the␣constituent parts of the subgenual organ included in the haemolymph channel. Received: 25 July 1997 / Accepted in revised form: 8 December 1997     

Experimental and mathematical modeling studies of protozoan predation on bacteria

The predation of bacteria by protozoan in both continuous and batch cultures was studied using experimental and modeling techniques. The predator organism was the ciliate, Tetrahymena pyriformis. The bacterium, Aerobacter aerogenes, served as the prey. Several batch growth responses were observed each initiated at a different nutrient level. Continuous cultures were conducted over a range of dilution rates. The models studied were partially successful in simulating the empirical data. Deviations between the model and the actual population behavior are discussed and possible explanations for the differences proposed.     

Switching to a feeding method that obstructs vision increases head-up vigilance in dabbling ducks

A major assumption in most models of foraging is that feeding and vigilance are mutually exclusive. A recent experimental study challenged this hypothesis and demonstrated that birds are able to detect predators while pecking seeds on the ground (head-down vigilance). Experimental obstruction of head-down vigilance makes birds increase head-up vigilance (i.e. the classical overt vigilance posture). For many foragers in the wild, visibility varies between habitats and foraging methods. We compared the vigilance of Teal Anas crecca and Shoveler Anas clypeata when foraging with their eyes above the water surface (shallow feeding, only the bill submerged) and when foraging with their eyes underwater (deep feeding, head and neck underwater, or upending), at three wintering sites in western France. Birds of both species spent less time in head-up vigilance during shallow foraging than during deep foraging, with no significant difference between sites, which suggests that they are capable of some vigilance during shallow foraging. During deep foraging, the time spent vigilant increased because the frequency of scans was much higher, while scan length decreased. However, these differences could have resulted from variations in the availability of food at different depths. In an experiment where the food availability was constant, we observed the same pattern, with a higher frequency of scans during deep foraging. This study therefore provides strong support for the idea that vigilance and foraging are not always mutually exclusive and shows that switching between searching methods can cause vigilance time – and, as a consequence, loss of feeding time – to vary. This should be taken into account in future field and experimental studies of the trade-off animals make between vigilance and feeding.