Gulps, wheezes, and sniffs: how measurement of beak movement in sea turtles can elucidate their behaviour and ecology

This study was performed to assess the extent to which an intermandibular angle sensor (IMASEN) may be used to elucidate the behaviour of six captive loggerhead turtles. The measuring system was glued to the beak of turtles and set to measure the intermandibular distance at 5 Hz while the turtles fed (on anchovies, squid, and live crabs), swam, rested, and breathed. The behaviour of the equipped turtles was filmed and compared afterwards to the sensor readings. The IMASEN output data allowed quantification of the number of food items ingested as well as the time between food seizure and deglutition and the type of food ingested. However, nonfeeding turtles exhibited regular jaw movements with a reduced amplitude of ca. 2.2 mm, which clearly differed from feeding movements and were caused by buccal oscillations. Such movements of the base of the buccal cavity generate a steady flow of water pass the chemosensory organs and were interrupted only during food ingestion, resting, and breathing. Breathing was clearly distinguishable by the IMASEN. The beak sensor is thus a reliable system to investigate a number of behaviours in sea turtles which encompass foraging, buccal oscillation, and respiratory frequency. It has potential for allocating time to different activities in free-ranging sea turtles and thus allows us to gain insight to their foraging and diving strategies.     

Effects of increased suspended sediment on growth rate and gill condition of two southern Appalachian minnows

Despite the recognition that increased suspended sediment concentration (SSC) is a correlate of imperilment for native riverine fishes, research is limited on the effects of SSC on small non-game species. This study quantifies the impact of suspended sediment on fish growth and gill condition of two stream-dwelling minnows. Specific growth rate (i.e., percent change in mass per day) and gill condition (i.e., lamellar thickness and interlamellar area) were measured in young-of-year whitetail shiners, Cyprinella galactura, and federally threatened spotfin chubs, Erimonax monachus, exposed for 21 days to increased SSC (0, 25, 50, 100, and 500 mg L⁻¹). Exposure to elevated SSC caused a significant decrease in specific growth rate in both species and at all life stages tested. The effect of increased SSC was greatest in spotfin chubs, which exhibited a 15-fold decrease in specific growth rate at the highest treatment (500 mg L⁻¹). Effects of increased SSC were least for 8–9-month-old whitetail shiners, which had growth rates similar to controls for 25, 50, and 100 mg L⁻¹ treatments. These minnows exhibited a greater response to increasing SSC than salmonids at low to moderate SSC, and a lesser response at higher sediment levels. Gill damage was minimal at the three lowest treatment levels, moderate at 100 mg L⁻¹ and severe at 500 mg L⁻¹, indicating that respiratory surfaces of upland minnows may be much more sensitive than other species. Specific growth rate decreased significantly with increasing gill lamellar thickness, suggesting that respiratory impairment is one mechanism responsible for negative impacts of excessive sediment on small riverine fishes.     

Decomposition rate of organic substrates in relation to the species diversity of soil saprophytic fungi

Despite the great interest concerning the relationship between species diversity and ecosystem functioning, there is virtually no knowledge as to how the diversity of decomposer microbes influences the decomposition rate of soil organic matter. We established a microcosm study in which the number of soil fungi was investigated in relation to the systems ability to (i) degrade raw coniferous forest humus, and (ii) use resources that were either added to the systems or released into the soils after a disturbance (drought). With the exception of the most diverse treatment, in each of the six replicates of each of the six diversity treatments (1, 3, 6, 12, 24 or 43 taxa), fungal taxa were randomly chosen from a pool of 43 commonly isolated fungal species of raw humus. Two months after initiation of the study CO₂ production increased as fungal diversity increased, but in the species-poor end of the diversity gradient only. Addition of various energy resources to the microcosms generally increased the level of soil respiration but did not affect the shape of the diversity-CO₂-production curve. Rewetting the soil after severe drought resulted in a rapid flush of CO₂, particularly in the most diverse communities. The biomass of the fungi in the non-disturbed soils, and soil NH₄-N concentration and soil pH in both disturbed and non-disturbed systems were slightly but significantly higher in the diverse than in the simple systems. Fungal species richness had no influence on the organic matter content of the humus at the end of the experiment. The results suggest that the functional efficiency of fungal communities can increase with the number of fungal taxa. This diversity effect was, however, significant at the species-poor end of the diversity gradient only, which implies considerable functional equivalency (redundancy) among the decomposer fungi.     

Effects of acclimation and acute temperature change on specific dynamic action and gastric processing in the green shore crab, Carcinus maenas

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10 °C or 20 °C and subsequently exposed to treatment temperatures of 5, 15, or 25 °C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10 °C acclimated group exposed to acute test temperatures. The Q₁₀ values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20 °C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20 °C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20 °C acclimated crabs, with the highest value measured at the treatment temperature of 15 °C. The decline in total SDA after acute exposure to 5 and 25 °C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20 °C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10 °C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones.     

Specific dynamic action in the sunflower star, Pycnopodia helianthoides

The effects of meal size and meal type on specific dynamic action (SDA) were investigated in a large, active asteroid, the sunflower star, Pycnopodia helianthoides. When the sunflower stars were fed clam flesh totalling 5%, 10%, or 20% of their body weight there was a step-wise increase in the scope, time to peak oxygen consumption, duration of the response and total SDA. The change in the rate of oxygen consumption was slower than other organisms, and oxygen uptake remained elevated for over 12 d following consumption of the largest meal. There were also differences in the characteristics of the SDA if sunflower stars consumed a whole clam versus the shucked flesh of a clam. The time to reach peak oxygen consumption was greater for sunflower stars consuming a whole clam. This occurred because the clam had to be opened before they could digest the flesh; a smaller initial peak comprising 3.5% of the total SDA represented the energy require to open the clam valves. When the sunflower stars were fed different prey items (e.g. butter clam, purple urchin and herring) of similar wet organic mass, there was no difference in the time to peak, peak oxygen uptake or total SDA despite the fact that the prey items differed in protein, lipid and caloric content. There was an increased duration for which oxygen uptake remained elevated for sea stars that consumed the urchin meal. Five of the seven sunflower stars that consumed urchins exhibited a smaller second peak in oxygen uptake, totalling approximately 8.5% of the SDA energy budget. This likely represented the energy required to eject the urchin test from the stomach. Although the sunflower star is much larger and more active than other sea stars, it displayed similar SDA responses to other members of the Asteroidea, indicative of the low metabolic rate of this class.     

Cotranscriptional expression of mitochondrial genes for subunits of NADH dehydrogenase, nad5, nad4, nad2, in Marchantia polymorpha

Three genes for the subunits of the NADH dehydrogenase (nad5, nad4, and nad2) are tandemly clustered on the liverwort mitochondrial genome. Their gene products showed high levels of amino acid sequence identity with the corresponding subunits from higher plant mitochondria (82.8–84.4%), and significant levels of identity with those from liverwort chloroplast (32.0–33.5%), Podospora anserina mitochondria (21.4–45.9%), and human mitochondria (18.4–27.9%). In addition, these three subunits from liverwort mitochondria have conserved amino acid residues in their central regions. The gene nad5 is interrupted by a 672 by group I intron, while genes nad4 and nad2 are interrupted by group II introns of 899 by and 1418 bp, respectively. Northern blot analysis using exon-intron specific probes indicated that these three genes are transcribed as a single precursor mRNA of 9.6 kb in length and are processed into mature mRNA molecules in liverwort mitochondria. Several regions of this nad gene cluster are repeated in the liverwort mitochondrial genome.Communicated by R.G. Herrmann     

Interpopulation variation in prey use and feeding biomechanics in Caribbean triggerfishes

The relationships between prey utilization and jaw biomechanics were explored in two Caribbean populations (La Parguera and Mona Island) of four trigger-fishes. The volumetric contribution of major prey types and six biomechanical features of the jaws that characterize biting strength were contrasted between populations. At Mona, Xanthichthys ringens ate 45% benthic organisms, whereas conspecifics at La Parguera fed exclusively on plankton. Balistes vetula at Mona consumed 63% soft and nonelusive invertebrates, in contrast to their La Parguera conspecifics, which consumed 62% hard prey. Differences in diet between populations were associated with differences in jaw biomechanics. Xanthichthys at Mona had jaw muscles, bones, and closing-lever ratios larger than those of fish at La Parguera, indicating a stronger bite. Balistes at Mona had 50% smaller jaw bones, muscles, and closing-lever ratios than their La Parguera conspecifics, indicating a weaker but swifter bite. Melichthys niger and Cantherhines macrocerus ate similar prey at the two locations and showed little difference in trophic anatomy. We hypothesize that the interpopulation differences in morphology are induced by the activities of feeding on different prey and enhance the feeding ability of fishes for locally dominant prey. Plasticity of the feeding mechanism may be a widespread attribute of fish feeding systems that promotes the ability of species to occupy multiple habitat types successfully.     

Relationships of leaf dark respiration to leaf nitrogen, specific leaf area and leaf life-span: a test across biomes and functional groups

Based on prior evidence of coordinated multiple leaf trait scaling, we hypothesized that variation among species in leaf dark respiration rate (R _d) should scale with variation in traits such as leaf nitrogen (N), leaf life-span, specific leaf area (SLA), and net photosynthetic capacity (A _max). However, it is not known whether such scaling, if it exists, is similar among disparate biomes and plant functional types. We tested this idea by examining the interspecific relationships between R _d measured at a standard temperature and leaf life-span, N, SLA and A _max for 69 species from four functional groups (forbs, broad-leafed trees and shrubs, and needle-leafed conifers) in six biomes traversing the Americas: alpine tundra/subalpine forest, Colorado; cold temperate forest/grassland, Wisconsin; cool temperate forest, North Carolina; desert/shrubland, New Mexico; subtropical forest, South Carolina; and tropical rain forest, Amazonas, Venezuela. Area-based R _d was positively related to area-based leaf N within functional groups and for all species pooled, but not when comparing among species within any site. At all sites, mass-based R _d (R _d-mass) decreased sharply with increasing leaf life-span and was positively related to SLA and mass-based A _max and leaf N (leaf N _mass). These intra-biome relationships were similar in shape and slope among sites, where in each case we compared species belonging to different plant functional groups. Significant R _d-mass−N _mass relationships were observed in all functional groups (pooled across sites), but the relationships differed, with higher R _d at any given leaf N in functional groups (such as forbs) with higher SLA and shorter leaf life-span. Regardless of biome or functional group, R _d-mass was well predicted by all combinations of leaf life-span, N _mass and/or SLA (r ²≥ 0.79, P < 0.0001). At any given SLA, R _d-mass rises with increasing N _mass and/or decreasing leaf life-span; and at any level of N _mass, R _d-mass rises with increasing SLA and/or decreasing leaf life-span. The relationships between R _d and leaf traits observed in this study support the idea of a global set of predictable interrelationships between key leaf morphological, chemical and metabolic traits. Received: 23 May 1997 / Accepted: 16 December 1997     

Microwear and morphology: functional relationships between human dental microwear and the mandible

Microscopic pits and scratches form on teeth during chewing, but the extent to which their formation is influenced by mandibular morphology is unknown. Digitized micrographs of the base of facet nine of the first, second, and third mandibular molar were used to record microwear features from an archaeological sample of modern humans recovered from Semna South in northern Sudan (n=38; 100 BC to AD 350). Microwear patterns of the molar row are correlated with mandibular corpus width and depth, and with mandibular length. Variations in shear and compression at the base of facet nine during chewing were inferred. It may be that some correlations between microwear and mandibular morphology are predictable, reflecting similar aspects of masticatory loading, though the full extent of the relationship remains to be resolved.     

Trap architecture in carnivorous Utricularia (Lentibulariaceae)

Within carnivorous plants, the bladderworts (Utricularia) possess the most complicated traps whose mechanisms are not yet completely understood. For the first time, a representative survey of different traps from both subgenera (Utricularia and Polypompholyx) is presented.

Based on scanning- and transmission electron microscopy, traps of 14 species of Utricularia (out of 215 species) representing 11 sections (out of 35 sections) and including all life forms (aquatic, epiphytic, and terrestrial) were investigated. Additionally, it was tested whether life forms correlate with trapping mechanisms. Most morphological and anatomical features of the traps vary considerably between the different life forms, e.g. position of trap and trap entrance as well as form and position of trap appendages. Morphological data support the basal position of subgenus Polypompholyx within the genus. Some characteristics of the traps of terrestrial Utricularia multifida (subgenus Polypompholyx) differ remarkably from traps of the other species, e.g. trap-door anatomy and trap walls. This might be an indication for a primordial (non-suction) trapping mechanism in the former species, similar to that of the eel-traps of the closely related genus Genlisea.     

Scaling and jumping: gravity loses grip on small jumpers

There are several ways to quantify jumping performance, a common definition being the height gained by the body's centre of mass (CM) in the airborne phase. Under this definition, jump height is determined by take-off velocity. According to the existing literature on jumping and scaling, take-off velocity, and hence jumping performance is independent of size because the energy that differently sized geometrically scaled jumpers can generate with their muscles is proportional to their mass. In this article it is shown, based on a simple energy balance, that it is incorrect to presume that jump height does not depend on size. Contrary to common belief, size as such has does have an effect on take-off velocity, putting small jumpers at a mechanical advantage, as is shown analytically. To quantify the effect of size on take-off velocity, a generic jumper model was scaled geometrically and evaluated numerically. While a 70-kg jumper took off at 2.65 m/s and raised its CM by 0.36 m after take-off, a perfectly geometrically similar jumper of 0.7 g reached a take-off velocity of 3.46 m/s and raised its CM by 0.61 m. The reason for the better performance of small jumpers is their higher efficacy in transforming the energy generated by the actuators into energy due to vertical velocity of the CM. Considering the ecological and evolutionary relevance of different definitions of jump height, size-dependent efficacy might explain why habitual jumping is especially prominent among small animals such as insects.     

New characters for the functional interpretation of primate scapulae and proximal humeri

The study of muscle function in nonhuman primates through the technique of electromyography (EMG) has facilitated the identification of specific functional roles for muscles in particular behaviors. This has led to a more complete understanding of the biomechanics of certain regions of the musculoskeletal system, and should facilitate our ability to identify morphological features useful in the functional interpretation of fossil material. The current paper represents one such investigation of a new set of morphometric characters of the scapula and proximal humerus suggested by EMG analyses of shoulder muscle function. A set of new metric variables were examined on the scapulae and proximal humeri of 25 species of extant anthropoid primates, as well as on casts of scapulae and humeri of three fossil primate taxa. The variables are primarily related to the line of action and attachments of the rotator cuff muscles. The position of the scapular spine, the degree of lateral expansion of the subscapular fossa, the size and shape of the subscapularis insertion facet on the lesser tubercle, and the orientation of the infraspinatus insertion facet on the greater tubercle all appear to successfully sort the extant taxa into locomotor groups. Their appearance on the fossil specimens generally supports previous functional interpretations of each taxon's locomotor abilities based on a variety of other characters, suggesting that these traits are equally applicable to fossil material. © Wiley-Liss, Inc.     

Viability explanation

This article deals with a type of functional explanation, viability explanation, that has been overlooked in recent philosophy of science. Viability explanations relate traits of organisms and their environments in terms of what an individual needs to survive and reproduce. I show that viability explanations are neither causal nor historical and that, therefore, they should be accounted for as a distinct type of explanation.The investigations for this paper were supported by the Foundation for Philosophical Research (SWON), which is subsidized by the Netherlands Organization for Scientific Research (NWO). I am grateful to Theo Kuipers and Ton Derksen for their useful comments on early versions, to Josje Lodder for improving my logic, and to Jaap van Brakel for his help in structuring this article.     

The arboreal leaping theory of the origin of pterosaur flight

Three theories about the origin of flight in pterosaurs have been proposed: 1) the arboreal parachuting theory (passive falling from trees leading to gliding and eventually to powered flight); 2) the cursorial theory (bipedal running and leaping leading directly to powered flight); and 3) the arboreal leaping theory (active leaping between branches and trees leading to powered flight). The available evidence as to the functional morphology of pterosaurs, and in particular their hindlimb, is reviewed and used to test the three theories. Pterosaurs were well suited for arboreality and their hindlimb morphology argues against cursoriality, but supports an arboreal leaping lifestyle for early pterosaurs or their immediate ancestors.     

Comparative morphology of the somatic musculature in species of Hexarthra and Polyarthra (Rotifera, Monogononta): Its function in appendage movement and escape behavior

Species of Hexarthra and Polyarthra are freshwater rotifers with well-known escape behaviors that result from interactions with planktonic predators. Both rotifers bear a suite of mobile appendages that function in evasive maneuvers and saltatory jumps through the water column, but the anatomical and functional bases of these actions are poorly understood. Here, we use a combination of phalloidin staining, confocal laser scanning microscopy, and video analysis to describe the morphology of the somatic muscles that supply the mobile appendages in order to understand how they function in escape behavior. Results show that species of Hexarthra, which bear six radially distributed limbs, possess a highly complex trunk musculature that supplies the inside of each limb with its own abductor and adductor muscles, i.e., a direct muscle supply. The singular dorsal and ventral limbs each receive a pair of large abductor and adductor muscles (four muscles total per limb), while the paired dorsolateral and ventrolateral limbs each receives three muscles (two abductors, one adductor per limb). Contraction of the abductor muscles creates a power stroke in the form of an anterior sweep of the limbs, which leads to a three-dimensional tumbling of the rotifer through the water column. Alternatively, species of Polyarthra possess 12 blade-like appendages that are arranged into four equal bundles; each bundle receives an indirect muscle supply that attaches to the shoulder of the paddles. A single longitudinal paddle muscle supplies each dorsolateral bundle, while a pair of longitudinal paddle muscles supplies each ventrolateral bundle. Contraction of these muscles, whether singly or in concert, functions to abduct the paddles in a power stroke, leading to rotation of the body and movement of the rotifer. The recovery stroke is hypothesized to be a multi-step process that begins with reorientation of the appendages prior to adduction, followed by contraction of various muscles to antagonize the paddle muscles. In total, these observations reveal novel complexities in the rotifer muscular system that aids our understanding of the biophysics of predator avoidance in appendage-bearing rotifers.     

Buccal capsule development as a consideration for phylogenetic analysis of Rhabditida (Nemata)

 Bacterial feeding nematodes in the order Rhabditida including Zeldia punctata (Cephalobidae) and Caenorhabditis elegans (Rhabditidae) differ profoundly in the buccal capsule parts and associated cells. We carried out a range of tests to determine which buccal capsule parts and cells are evolutionarily homologous between the representative species of the two families. Tests included reconstruction of the buccal capsule and procorpus with transmission electron microscopy (TEM), nuclei position and morphology using 4,6-diamidino-2-phenylindole (DAPI) staining, and cell lineage using four dimensional (4D) microscopy. The lining of the buccal capsule of Z. punctata and additional Cephalobidae includes four sets of muscular radial cells, ma, mb, mc and md, in contrast to C. elegans and additional Rhabditidae, which has two sets of epithelial cells (e1, e3) and two sets of muscle cells (m1, m2). Cell lineage of a nematode closely related to Z. punctata, Cephalobus cubaensis, supports the hypothesis that in cephalobids the e1 and e3 cells become hypodermal cells or are programmed to die. Our findings contradict all previous hypotheses of buccal capsule homology, and suggest instead that ma and mb in Z. punctata are homologous to m1 and m2 in C. elegans respectively. We also hypothesize that ma and mb could be homologous to primary and secondary sets of stylet-protractor muscle cells in the plant parasitic Tylenchida. Received: 24 March 1998 / Accepted: 24 July 1998     

Variability,function and phylogenetic significance of periostracal microprojections in unionoid bivalves (Mollusca)

Microprojections of unionoid shells are virtually unstudied but could be important characters for resolving questions on the phylogeny and ecology of these bivalves. By investigating 26 unionoid and three species of their closest living relatives, the Trigonioida, using scanning electron microscopy, we identified three types of periostracal microprojections. (1) Microridges were present only in one species from each of the two unionoid families Mycetopodidae (Anodontites trapesialis) and Iridinidae (Chambardia bourguignati) and may represent a synapomorphy for the mycetopodid‐iridinid clade. In A. trapesialis, microridges were additionally equipped with (2)ensp;flag‐like projections (microfringes), possibly a synapomorphic character for the Mycetopodidae. Examination of partially bleached specimens indicated that both microridges and microfringes are predominantly or purely organic. In contrast, previously undescribed (3) spicule‐like spikes represent calcifications within the periostracum. These were found in 20 of the 29 species and four of the six unionoid families. Spikes were particularly large and abundant in umbonal (juvenile) shell regions and species characteristic of fast‐flowing habitats. These structures may thus serve in protecting the periostracum and shell underneath, and/or stabilizing life position by increasing shell friction. Microfringes and microridges, on the other hand, possibly aid in the orientation of the mussel within the sediment.