Visual discrimination abilities in the gray bamboo shark (Chiloscyllium griseum)

This study assessed visual discrimination abilities in bamboo sharks (Chiloscyllium griseum). In a visual discrimination task using two-dimensional (2D) geometric stimuli, sharks learned to distinguish between a square, being the positive (rewarded) stimulus, and several negative stimuli, such as two differently sized triangles, a circle, a rhomboid and a cross. Although the amount of sessions to reach the learning criterion and the average trial time needed to solve each new task did not vary significantly, the number of correct choices per session increased significantly with on-going experiments. The results indicate that the sharks did not simply remember the positive stimulus throughout the different training phases. Instead, individuals also seemed to learn each negative symbol and possibly had to “relearn” at least some aspects of the positive stimulus during each training phase. The sharks were able to distinguish between the 2D stimulus pairs at a learning rate corresponding to that found in teleosts. As expected, it took the sharks longer to learn a reversal task (with the positive stimulus now being the negative one) than to discriminate between the other stimulus pairs. Nevertheless, the present results suggest that bamboo sharks can learn visual discrimination tasks, succeed in a reversal task and probably retain (some) information about a previously learned task when progressing to a new one.     

Red and white muscle activity and kinematics of the escape response of the bluegill sunfish during swimming

Summary We quantified midline kinematics with synchronized electromyograms (emgs) from the red and white muscles on both sides of bluegill sunfish (Lepomis macrochirus) during escape behaviors which were elicited from fish both at a standstill and during steady speed swimming. Analyses of variance determined whether or not kinematic and emg variables differed significantly between muscle fiber types, among longitudinal positions, and between swimming versus standstill trials.At a given longitudinal location, both the red and white muscle were usually activated synchronously during both stages of the escape behavior. Stage 1 emg onsets were synchronous; however, the mean durations of stage 1 emgs showed a significant increase posteriorly from about 11 to 15 ms. Stage 2 emgs had significant posterior propagation, but the duration of the stage 2 emgs was constant (17 ms). Posterior emgs from both stages occurred during lengthening of the contractile tissue (as indicated by lateral bending). Steady swimming activity was confined to red muscle bursts which were propagated posteriorly and had significant posterior decrease in duration from about 50% to 37% of a cycle. Fish performed escape responses during all phases of the steady swimming motor pattern. All kinematic events were propagated posteriorly. Furthermore, no distinct kinematic event corresponded to the time intervals of the stage 1 and 2 emgs. The rate of propagation of kinematic events was always slower than that of the muscle activity. The phase relationship between lateral displacement and lateral bending also changed along the length of the fish. Escape responses performed during swimming averaged smaller amplitudes of stage 2 posterior lateral displacement; however, most other kinematic and emg variables did not vary significantly between these two treatments.Abbreviations A angle of lateral flexion (bending) of midline at a single point in time - A1, A2 change in A from T₀ to T₁ and from T₁ to T₂ - AMX maximal lateral flexion concave towards the side of the stage 1 emg - AMXR equals AMX minus A at T₀ - AT1, AT2 lateral flexion at T₁ and T₂ - DUR1, DUR2 durations of stage 1 and stage 2 emgs - emg electromyogram - ON2 onset time of stage 2 emg - RELDUR relative duration of steady swimming emg - T₀, T₁, T₂ times of stage 1 emg onset, latest stage 1 emg offset and latest stage 2 emg offset standardized such that T₀ = 0 - TAMX, TAMN, TYMX times of maximal lateral flexion, no lateral flexion and maximum lateral displacement - Y1, Y2 amounts of lateral displacement from T₀ to T₁ and from T₁ to T₂ - YMXR relative amount of lateral displacement from T₀ to TYMX     

The locomotory function of the fins in the squid Loligo pealei

Kinematic data of high spatial and temporal resolution, acquired from image sequences of adult long-finned squid, Loligo pealei, during steady swimming in a flume, were used to examine the role of fins and the coordination between fin and jet propulsion in squid locomotion. Fin shape and body outlines were digitized and used to calculate fin wave speed, amplitude, frequency, angle of attack, body deformation, speed, and acceleration. L. pealei were observed to have two fin gait patterns with a transition at 1.4-1.8 mantle lengths per second (L_m s^-1) marked by alternation between the two patterns. Fin motion in L. pealei exhibited characteristics of both traveling waves and flapping wings. At low speeds, fin motion was more wave-like; at high speeds, fin motion was more flap-like and was marked by regular periods during which the fins were wrapped tightly against the mantle. Fin cycle frequencies were dependent on swimming speed and gait, and obvious coordination between the fins and jet were observed. Fin wave speed, angle of attack, and body acceleration confirmed the role of fins in thrust production and revealed a role of fins at all swimming speeds by a transition from drag-based to lift-based thrust when fin wave speed dropped below swimming speed. Estimates of peak fin thrust were as high as 0.44-0.96 times peak jet thrust in steady swimming over the range of swimming speeds observed. Fin downstrokes generally contributed more to thrust than did upstrokes, especially at high speeds.     

The locomotory function of the fins in the squid Loligo pealei

Kinematic data of high spatial and temporal resolution, acquired from image sequences of adult long-finned squid, Loligo pealei, during steady swimming in a flume, were used to examine the role of fins and the coordination between fin and jet propulsion in squid locomotion. Fin shape and body outlines were digitized and used to calculate fin wave speed, amplitude, frequency, angle of attack, body deformation, speed, and acceleration. L. pealei were observed to have two fin gait patterns with a transition at 1.4-1.8 mantle lengths per second (Lm s-1) marked by alternation between the two patterns. Fin motion in L. pealei exhibited characteristics of both traveling waves and flapping wings. At low speeds, fin motion was more wave-like; at high speeds, fin motion was more flap-like and was marked by regular periods during which the fins were wrapped tightly against the mantle. Fin cycle frequencies were dependent on swimming speed and gait, and obvious coordination between the fins and jet were observed. Fin wave speed, angle of attack, and body acceleration confirmed the role of fins in thrust production and revealed a role of fins at all swimming speeds by a transition from drag-based to lift-based thrust when fin wave speed dropped below swimming speed. Estimates of peak fin thrust were as high as 0.44-0.96 times peak jet thrust in steady swimming over the range of swimming speeds observed. Fin downstrokes generally contributed more to thrust than did upstrokes, especially at high speeds.     

Development of the pectoral, pelvic, dorsal and anal fins in cultured sea bream

The pectoral fin girdle was the first element of the fins to develop in Sparus aurata. By 3·1mm L _N (notochord length) the cleithrum was ossified and the cartilaginous caracoid-scapula was present. The fin was fully developed at 11·6 mm L _S (standard length) and by 16·0 mm L _S most elements of the fin were ossified. The pelvic fins were the last pair to develop and rudiments of these were first detected at 7·9 mm L _S. The pelvic fin and girdle were completely formed and ossified at 16·0 mm L _S. The development of dorsal and anal fins began at c. 6·5–7·0 mm L _S with the formation of 10 cartilaginous dorsal proximal radials and eight cartilaginous ventral proximal radials. The three cartilaginous predorsals (supraneurals) appeared at 7·7 mm L _S and the ossification of dorsal and anal proximal and distal radials began, respectively, at 10·5 mm L _S and 11·3 mm L _S. Ossified structures in the fins were also classified according to their origin, as being either dermal or endochondral. Finally the chronology of appearance of fin structures in S. aurata was compared with that reported for other Sparidae, Engraulidae and Haemulidae.     

How swimming fish use slow and fast muscle fibers: implications for models of vertebrate muscle recruitment

We quantified the intensity and duration of electromyograms (emgs) from the red and white axial muscles in five bluegill sunfish (Lepomis macrochirus) which performed three categories of behavior including steady swimming and burst and glide swimming at moderate and rapid speeds. Steady swimming (at 2 lengths/s) involved exclusively red muscle activity (mean posterior emg duration = 95 ms), whereas unsteady swimming utilized red and white fibers with two features of fiber type recruitment previously undescribed for any ectothermic vertebrate locomotor muscle. First, for moderate speed swimming, the timing of red and white activity differed significantly with the average onset time of white lagging behind that of red by approximately 40 ms. The durations of these white emgs were shorter than those of the red emgs (posterior mean = 82 ms) because offset times were effectively synchronous. Second, compared to steady and moderate speed unsteady swimming, the intensity of red activity during rapid unsteady swimming decreased while the intensity of white muscle activity (mean white emg duration = 33 ms) increased. Decreased red activity associated with increased white activity differs from the general pattern of vertebrate muscle recruitment in which faster fiber types are recruited in addition to, but not to the exclusion of, slower fiber types.     

Anatomy and muscle activity of the dorsal fins in bamboo sharks and spiny dogfish during turning maneuvers

Stability and procured instability characterize two opposing types of swimming, steady and maneuvering, respectively. Fins can be used to manipulate flow to adjust stability during swimming maneuvers either actively using muscle control or passively by structural control. The function of the dorsal fins during turning maneuvering in two shark species with different swimming modes is investigated here using musculoskeletal anatomy and muscle function. White‐spotted bamboo sharks are a benthic species that inhabits complex reef habitats and thus have high requirements for maneuverability. Spiny dogfish occupy a variety of coastal and continental shelf habitats and spend relatively more time cruising in open water. These species differ in dorsal fin morphology and fin position along the body. Bamboo sharks have a larger second dorsal fin area and proportionally more muscle insertion into both dorsal fins. The basal and radial pterygiophores are plate‐like structures in spiny dogfish and are nearly indistinguishable from one another. In contrast, bamboo sharks lack basal pterygiophores, while the radial pterygiophores form two rows of elongated rectangular elements that articulate with one another. The dorsal fin muscles are composed of a large muscle mass that extends over the ceratotrichia overlying the radials in spiny dogfish. However, in bamboo sharks, the muscle mass is divided into multiple distinct muscles that insert onto the ceratotrichia. During turning maneuvers, the dorsal fin muscles are active in both species with no differences in onset between fin sides. Spiny dogfish have longer burst durations on the outer fin side, which is consistent with opposing resistance to the medium. In bamboo sharks, bilateral activation of the dorsal in muscles could also be stiffening the fin throughout the turn. Thus, dogfish sharks passively stiffen the dorsal fin structurally and functionally, while bamboo sharks have more flexible dorsal fins, which result from a steady swimming trade off. J. Morphol. 274:1288–1298, 2013. © 2013 Wiley Periodicals, Inc.     

Performance of iSharkFin in the identification of wet dorsal fins from priority shark species

The past decade has seen a considerable rise in international concern regarding the conservation status of sharks and rays. The demand for highly prized shark commodities continues to fuel the international trade and gives fisheries incentive to use these resources, which have a low intrinsic capability to recover. Recognising the urgency for regulation, many countries voted to include more shark and ray species in the Appendices of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, the identification of fins in fisheries landings before they enter international trade is a major limitation for CITES compliance. This study reports the current performance of the iSharkFin system, a machine learning technology which aims to allow users to identify the species of a wet shark dorsal fin from its image. Photographs of 1147 wet dorsal fins from 39 shark species, collected in 12 countries, were used to train the algorithm over a four-year period. As new cohorts of images were used to test the performance of the learning algorithm, the accuracy of species assignments of known specimens was variable but did increase, reaching 85.3% and 59.1% at genus and species level respectively. The accuracy in predicting CITES-listed sharks versus unlisted sharks was 94.0% based on the 39 species currently represented in the baseline. Our results suggest that if supplied with high data inputs for specific fisheries assemblages and accompanied by user training, iSharkFin has promise for site-specific development as a rapid field identification tool in fisheries monitoring, and as a screening tool alongside traditional field morphology to detect potential CITES specimens for fisheries compliance and enforcement.     

Unilateral ablation of trunk superficial neuromasts increases directional instability during steady swimming in the yellowtail kingfish Seriola lalandi

Detailed swimming kinematics of the yellowtail kingfish Seriola lalandi were investigated after unilateral ablation of superficial neuromasts (SNs). Most kinematic variables, such as tail‐beat frequency, stride length, caudal fin‐beat amplitude and propulsive wavelength, were unaffected but lateral amplitude at the tip of the snout (A₀) was significantly increased in SN‐disrupted fish compared with sham‐operated controls. In addition, the orientation of caudal fin‐tip relative to the overall swimming direction of SN‐disrupted fish was significantly deflected (two‐fold) in comparison with sham‐operated control fish. In some fish, SN disruption also led to a phase distortion of the propulsive body‐wave. These changes would be expected to increase both hydrodynamic drag and thrust production which is consistent with the finding that SN‐disrupted fish had to generate significantly greater thrust power when swimming at ≥1·3 fork lengths (L_F) s^?1. In particular, hydrodynamic drag would increase as a result of any increase in rotational (yaw) perturbation and sideways slip resulting from the sensory disturbance. In conclusion, unilateral SN ablation produced directional instability of steady swimming and altered propulsive movements, suggesting a role for sensory feedback in correcting yaw and slip disturbances to maintain efficient locomotion.     

Influence of sex and habitat on the size and shape of anal and dorsal fins of the blackstripe topminnow Fundulus notatus

The size and shape of the anal and dorsal fin in the blackstripe topminnow Fundulus notatus from lake and stream habitats across multiple ages and sexes were examined. Differences in the size and shape of anal and dorsal fins were sex‐specific and not related to habitat differences. Males have longer and more pointed anal fins and longer, larger and more pointed dorsal fins than females. These sex differences occur predominantly in the older age class. The angle (i.e. pointedness) of the dorsal and anal fins is tightly correlated suggesting that fins follow a similar growth trajectory as individuals become sexually mature.     

Early development of dorsal and pelvic fins and their supports in hatchery-reared red-spotted grouper, Epinephelus akaara (Perciformes: Serranidae)

Early morphogenesis of dorsal and pelvic fins and their supports in the larval and juvenile red-spotted grouper, Epinephelus akaara, was examined using a hatchery-reared series. The dorsal spine anlage first appeared suspended in the middle part of the finfold at ca. 2.5 mm TL. Dorsal and pelvic supports appeared by the time the fish reached ca. 3 mm and started to ossify at ca. 3.5 mm. Elongated spines and their supports developed synchronously in both dorsal and pelvic fins. The formation of dorsal fin supports proceeded from anterior to posterior. The ossification of supports was completed by ca. 33 mm. Spinelets on the second dorsal spine and pelvic spine appeared by ca. 3 mm. In specimens larger than 36 mm, all spinelets on the second dorsal spine and pelvic spine had disappeared. The maximum size of the second dorsal spine and pelvic spine lengths relative to TL were ca. 45% and 44% at 3.3 mm in fish size, respectively. Thereafter, their proportions decreased gradually. Considering the order of development of the elongated spines and mucous cells in the early life stages, the elongated spines might function as antipredator devices. Received: June 20, 2000 / Revised: April 28, 2001 / Accepted: June 11, 2001     

Biology of the Galapagos shark,Carcharhinus galapagensis, in Hawai'i

Synopsis Catch records from the Hawai'i Cooperative Shark Research and Control Program, which operated in Hawai'i from 1967–1969, were examined and data on the Galapagos shark,Carcharhinus galapagensis were analyzed. A total of 304 Galapagos sharks was caught, predominantly with longlines. More female sharks were caught than males, and the catch was skewed geographically. On the island of O'ahu the highest catch rates occurred along the north and south coasts. High catch rates also occurred near points of land, where longshore currents converge. Average depth of capture was greater for juveniles (45.1 m) and mature males (60.2 m), than for subadults (38.8 m) and mature female sharks (34.2 m). Males appear to reach maturity between 205 and 239 cm total length, and females between 215 and 245 cm. Litter size ranged from 4 to 16 pups, with an average of 8.7. In Hawaiian waters Galapagos sharks are born at just over 80 cm total length. Mating and parturition apparently occur early in the year, and gestation is estimated to be about 12 months. Stomach contents consisted mainly of teleosts and benthic prey, and ontogenetic changes in diet occurred as sharks increased in size. Sharks consumed a smaller proportion of teleosts and more elasmobranchs with increasing size. Dietary diversity also increased with increasing size of shark.     

Ontogeny of the umbilical cord and placenta in the Atlantic sharpnose shark,Rhizoprionodon terraenovae

Synopsis The Atlantic sharpnose shark is a viviparous anamniote that develops an epitheliochorial yolksac placenta. Initially, contents of the yolksac nourish the embryos. Yolk is partially digested in the yolk syncytial-endoderm complex and subsequently transferred to the vitelline circulation. Yolk is also transported by ciliary activity of the yolk stalk ductus to the fetal gut for digestion. When embryos are 4.0cm in length, vascular ridges, termed appendiculae, develop on the yolk stalk. As yolk stores are depleted, the yolksac differentiates into the fetal portion of the placenta and the uterus abutting the yolksac differentiates into the maternal portion of the placenta. The yolk stalk differentiates into an elongate umbilical cord. The uterine epithelium produces secretions that are positive by the periodic acid-Schiff and alcian blue methods and metachromatic when stained with toluidine blue. Uterine capillaries are continuous and the surface epithelium is active both in secretion and transport of nutrients. When the embryos are 7–10cm in length, appendiculae are elongate, branched and populated by separate microvillar and granulated cells. Appendiculae may function as a paraplacental nutrient absorptive organ and be involved in the regulation of osmolarity of periembryonic fluids. The fetal placenta has two functional regions: a proximal portion that is presumed to function as a steroid producing organ and a distal portion that effects nutrient and metabolic exchange between the mother and fetus. Characteristics of the fetal placenta include endocytotic activity, crystalline-like cytoplasmic bodies and fenestrated capillaries. Fetal and maternal components of the placenta are separated by the egg envelope.     

Patterns of hind limb motor output during walking in the salamander Dicamptodon tenebrosus,with comparisons to other tetrapods

Based on similarity of motor patterns of lizards, crocodiles, birds and mammals, various authors have concluded that a number of homologous muscles across these taxa demonstrate neuromuscular conservatism. This hypothesis remains untested for more basal taxa. Therefore, a quantitative electromyographic study of the hind limb during treadmill walking (mean speed of 0.75 SVL/s) in the salamander Dicamptodon tenebrosus was undertaken. Muscles located ventrally on the hind limb become active just before foot placement on the substrate, and maintain activity through the first half of the stance phase. Dorsally located muscles begin activity at or just before the start of the swing phase, and fire through the first half of swing. Several muscles showed a secondary EMG burst during the stride. The second burst in most ventral muscles occurred in late stance. In all dorsal muscles with double bursts, the second burst occurred in the middle of stance. Comparison of electromyographic onset and offset values for Dicamptodon to those for presumed homologues in other tetrapods reveals similarity in activity patterns for all ventral and two dorsal muscles despite anatomical rearrangements, supporting the hypothesis of neuromuscular conservatism for some muscles but not others.Abbreviations BF biceps femoris muscle - CDF caudofemoralis muscle - CPIT caudalipuboischiotibialis muscle - Dist distal - EDC extensor digitorum communis muscle - EMG electromyogram - EXF extensor cruris et tarsi fibularis muscle - EXT extensor cruris tibialis muscle - FMFB femorofibularis muscle - FPC flexor primordialis communis muscle - Gastroc gastrocnemius muscle - ILFB iliofibularis muscle - ILFM iliofemoralis muscle - ILTA extensor iliotibialis pars anterior muscle - ILTP extensor iliotibialis pars posterior muscle - ISC ischiocaudalis muscle - ISF ischioflexorius muscle - ISFM ischiofemoralis muscle - ITCR iliotrochantericus cranialis muscle - ITM iliotrochantericus medius muscle - MG medial gastrocnemius muscle - PFM pubifemoralis muscle - PIFE puboischiofemoralis externus muscle - PIFI puboischiofemoralis internus muscle - PIT puboischiotibialis muscle - Prox proximal - PTB pubotibialis muscle - Sol soleus muscle - ST semitendinosus muscle - SVL snout-vent length     

Trade-off between steady and unsteady swimming underlies predator-driven divergence in Gambusia affinis

Differences in predation intensity experienced by organisms can lead to divergent natural selection, driving evolutionary change. Western mosquitofish (Gambusia affinis) exhibit larger caudal regions and higher burst-swimming capabilities when coexisting with higher densities of predatory fish. It is hypothesized that a trade-off between steady (constant-speed cruising; important for acquiring resources) and unsteady (rapid bursts and turns; important for escaping predators) locomotion, combined with divergent selection on locomotor performance (favouring steady swimming in high-competition scenarios of low-predation environments, but unsteady swimming in high-predation localities) has caused such phenotypic divergence. Here, I found that morphological differences had a strong genetic basis, and low-predation fish required less hydromechanical power during steady swimming, leading to increased endurance. I further found individual-level support for cause-and-effect relationships between morphology, swimming kinematics and endurance. Results indicate that mosquitofish populations inhabiting low-predation environments have evolved increased steady-swimming abilities via stiffer bodies, larger anterior body/head regions, smaller caudal regions and greater three-dimensional streamlining.     

Spatio-temporal gait characteristics during transitions from trot to canter in horses

Gaits can be defined based upon specific interlimb coordination patterns characteristic of a limited range of speeds, with one or more defining variables changing discontinuously at a transition. With changing speed, horses perform a repertoire of gaits (walk, trot, canter and gallop), with transitions between them. Knowledge of the series of kinematic events necessary to realize a gait is essential for understanding the proximate mechanisms as well as the control underlying gait transitions. We studied the kinematics of the actual transition from trot to canter in miniature horses. The kinematics were characterized at three different levels: the whole-body level, the spatio-temporal level of the foot falls and the level of basic limb kinematics. This concept represents a hierarchy: the horse's center of mass (COM) moves forward by means of the coordinated action of the limbs and changes in the latter are the result of alterations in the basic limb kinematics. Early and short placement of the fore limb was observed before the dissociation of the footfalls of one of the diagonal limb pairs when entering the canter. Dissociation coincided with increased amplitude and wavelength of the oscillations of the trunk in the sagittal plane. The increased amplitude cannot be explained solely by the passive effects of acceleration or by neck and head movements which are inconsistent with the timing of the transition. We propose that the transition is initiated by the fore limb followed by subsequent changes in the hind limbs in a series of kinematic events that take about 2.5 strides to complete.     

Composition of the excitatory drive during swimming in two amphibian embryos: Rana and Bufo

It has recently been shown that spinal neurons in Xenopus embryos receive cholinergic and electrotonic excitation during swimming, in addition to the well documented excitatory amino acid (EAA)-mediated excitation. We have now examined the composition of the excitatory drive during swimming in embryos of two further amphibian species, Rana and Bufo, which have somewhat different motor patterns. Localised applications of antagonists show that presumed motoneurons in Rana and Bufo embryos receive both cholinergic and EAA input during swimming. There is also a further chemical component which is blocked by Cd²⁺ and a small Cd²⁺-insensitive component, which is usually non-rhythmic. Rhythmic Cd²⁺-insensitive components, presumed to be phasic electrotonic potentials, were only seen in a small proportion of Bufo neurons and in no Rana neurons. While EAA and cholinergic inputs therefore appear to be consistent features of excitatory drive for swimming in amphibian embryo motoneurons, electrotonic input apparently occurs less commonly. Antagonist specificity was tested using applied agonists in Rana. Results of these tests also suggested that the further, unidentified Cd²⁺-sensitive component seen during swimming could represent an incomplete block of AMPA receptor-mediated excitation.Abbreviations AMPA -Amino-3-hydroxy-5-methyl- 4-isoxazolepropionic acid - CNQX 6-Cyano-7- nitroquinoxaline-2,3-dione - D-AP5 D(-)-2- Amino-5-phosphonopentanoic acid - DHE Dihydro--erythroidin - DMPP 1,1-dimethyl-4- phenylpiperazinium - HEPES N-[2-hydroxyethyl] piperazine-N-[2-ethanesulphonic acid] - NMDA N-methyl-D-aspartic acid     

Importance of mechanics and kinematics in determining the stiffness contribution of the vertebral column during body-caudal-fin swimming in fishes

Whole-body stiffness in fishes has important consequences for swimming mode, speed and efficiency, but the contribution of vertebral column stiffness to whole-body stiffness is unclear. In our opinion, this lack of clarity is due in part to the lack of studies that have measured both in vitro mechanical properties of the vertebral column as well as in vivo vertebral kinematics in the same species. Some lack of clarity may also come from real variation in the mechanical role of the vertebral column across species. Previous studies, based on either mechanics or kinematics alone, suggest species-specific variation in vertebral column locomotor function that ranges from highly stiff regimes that contribute greatly to whole-body stiffness, and potentially act as a spring, to highly compliant regimes that only prohibit excessive flexion of the intervertebral joints. We review data collected in combined investigations of both mechanics and kinematics of three species, Myxine glutinosa, Acipenser transmontanus, and Morone saxatilis, to illustrate how mechanical testing within the context of the in vivo kinematics more clearly distinguishes the role of the vertebral column in each species. In addition, we identify species for which kinematic data are available, but mechanical data are lacking. We encourage further investigation of these species to fill these mechanical data gaps. Finally, we hope these future combined analyses will identify certain morphological, mechanical, or kinematic parameters that might be associated with certain vertebral column functional regimes with respect to body stiffness.     

EMG of serratus anterior and trapezius in the chimpanzee: scapular rotators revisited.

The importance of arm-raising has been a major consideration in the functional interpretation of differences in shoulder morphology among species of nonhuman primates. Among the characters that have been associated with enhancement of the arm-raising mechanism in hominoid primates are the relative enlargement of cranial trapezius and caudal serratus anterior, as the main scapular rotators, as well as changes in scapular morphology associated with their improved leverage for scapular rotation. Yet in an EMG study of cranial trapezius and caudal serratus anterior function in the great apes, Tuttle and Basmajian (Yrbk. Phys. Anthropol. 20:491-497, 1977) found these muscles to be essentially inactive during arm-raising. Although Tuttle and Basmajian suggest that the cranial orientation of the glenoid fossa in apes has reduced the demand for scapular rotation during arm-raising, subsequent EMG studies on other primate species suggest that these muscles do play a significant role in arm motion during active locomotion. This paper presents a reexamination of muscle recruitment patterns for trapezius and caudal serratus anterior in the chimpanzee. All but the lowest parts of caudal serratus anterior were found to be highly active during arm-raising motions, justifying earlier morphological interpretations of differences in caudal serratus anterior development. The lowest digitations of this muscle, while inactive during arm-raising, displayed significant activity during suspensory postures and locomotion, presumably to control the tendency of the scapula to shift cranially relative to the rib cage. Cranial trapezius did not appear to be involved in arm-raising; instead, its recruitment was closely tied to head position.