Wrist tendon moment arms: Quantification by imaging and experimental techniques

Subject-specific musculoskeletal models require accurate values of muscle moment arms. The aim of this study was to compare moment arms of wrist tendons obtained from non-invasive magnetic resonance imaging (MRI) to those obtained from an in vitro experimental approach. MRI was performed on ten upper limb cadaveric specimens to obtain the centrelines for the flexor carpi radialis (FCR), flexor carpi ulnaris (FCU), extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor carpi ulnaris (ECU), and abductor pollicis longus (APL) tendons. From these, the anatomical moment arms about each of the flexion-extension (FE) and radioulnar deviation (RUD) axes of the wrist were calculated. Specimens were mounted on a physiologic wrist simulator to obtain functional measurements of the moment arms using the tendon excursion method. No differences were observed between anatomical and functional values of the FE and RUD moment arms of FCR, ECRL and ECRB, and the RUD moment arm of ECU (p > .075). Scaling the anatomical moment arms relative to ECRB in FE and ECU in RUD reduced differences in the FE moment arm of FCU and the RUD moment arm of APL to less than 15% (p > .139). However, differences persisted in moment arms of FCU in RUD, and ECU and APL in FE (p < .008). This study shows that while measurements of moment arms of wrist tendons using imaging do not always conform to values obtained using in vitro experimental approaches, a stricter protocol could result in the acquisition of subject-specific moment arms to personalise musculoskeletal models.     

Co-contraction of the pronator teres and extensor carpi radialis during wrist extension movements in humans.

In order to elucidate the functional significance of excitatory spinal reflex arcs (facilitation) between musculus (M.) pronator teres (PT) and M. extensor carpi radialis (ECR, longus: ECRL, brevis: ECRB) in humans, activities of the muscles were studied with electromyography (EMG) and electrical neuromuscular stimulation (ENS). In EMG study, activities of PT, ECRL, ECRB, and M. flexor carpi radialis during repetitive static (isometric) wrist extension and a series of a dynamic motion of wrist flexion/extension in the prone, semiprone, and supine positions of the forearm were recorded in 12 healthy human subjects. In the prone, semiprone, and supine positions, PT and ECR showed parallel activities during the static extension in all, eight, and eight subjects, respectively, and at the extension phase during the dynamic motion in all, eight and five subjects, respectively. These findings suggest that co-contraction of PT and ECR occurs during wrist extension movements at least with the prone forearm. The facilitation must be active during the co-contraction. In ENS study, ENS to PT was examined in 11 out of the 12 and that to ECRL was in the 12 subjects. Before ENS, the forearm was in the prone, semiprone, and supine positions. In all the subjects, ENS to PT induced a motion of forearm pronation to the maximum pronation. ENS to ECRL induced motions of wrist extension to the maximum extension and abduction (radial flexion) to 5-20 degrees of abduction regardless of the positions of the forearm. Moreover, it induced 30-80 degrees supination of the forearm from the prone position. Consequently, combined ENS to PT and ECRL resulted in motions of the extension and abduction while keeping the maximum pronation. These findings suggest that the co-contraction of PT and ECR during wrist extension movements occurs to prevent supinating the forearm. Forearm supination from the prone position should be added to one of the actions of ECRL.     

The importance of abductor pollicis longus in wrist motions: A physiological wrist simulator study

The abductor pollicis longus (APL) is one of the primary radial deviators of the wrist, owing to its insertion at the base of the first metacarpal and its large moment arm about the radioulnar deviation axis. Although it plays a vital role in surgical reconstructions of the wrist and hand, it is often neglected while simulating wrist motions in vitro. The aim of this study was to observe the effects of the absence of APL on the distribution of muscle forces during wrist motions. A validated physiological wrist simulator was used to replicate cyclic planar and complex wrist motions in cadaveric specimens by applying tensile loads to six wrist muscles – flexor carpi radialis (FCR), flexor carpi ulnaris, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis, extensor carpi ulnaris (ECU) and APL. Resultant muscle forces for active wrist motions with and without actuating the APL were compared. The absence of APL resulted in higher forces in FCR and ECRL – the synergists of APL – and lower forces in ECU – the antagonist of APL. The altered distribution of wrist muscle forces observed in the absence of active APL control could significantly alter the efficacy of in vitro experiments conducted on wrist simulators, in particular when investigating those surgical reconstructions or rehabilitation of the wrist heavily reliant on the APL, such as treatments for basal thumb osteoarthritis.     

A new technique for the selective recording of extensor carpi radialis longus and brevis EMG.

Tennis Elbow or Lateral Epicondylalgia is manifested by pain over the region of the lateral epicondyle of the humerus, related to use of the wrist extensor muscles. Extensor carpi radialis longus (ECRL) and brevis (ECRB) have been implicated in the dysfunction associated with Lateral Epicondylalgia. For muscles in the human forearm, particularly those in close proximity, selective recordings are nearly impossible without the use of fine wire, indwelling electrodes. These can be inserted in precise locations and have small recording areas. Standard electromyography texts indicate, however, that the activity of ECRL and ECRB cannot be distinguished, even with intramuscular electrodes. We present a new technique for determining the most appropriate sites at which to insert intramuscular electrodes for selective recordings of ECRB and ECRL. The location of ECRB and ECRL was measured on 10 cadaver specimens, 5 right arms and 5 left arms. The distance from the muscle origin to (1) insertion, (2) largest portion of the muscle belly, (3) most proximal fibres and (4) most distal fibres were measured and expressed relative to forearm length. The mean distance and 95% confidence interval was calculated for each of the four measures. These data indicated a significant separation of the belly of each muscle along the length of the forearm. These relative distances were used to mark electrode insertion points on three volunteers. Fine wire electrodes were used to record the electromyogram in three participants. Each participant was required to perform isometric contractions to produce (1) wrist extension torque, (2) radial deviation torque, (3) elbow flexion torque and (4) finger extension. The electromyographic recordings show clear differentiation of ECRB and ECRL with the relative activation patterns reflecting the underlying anatomical organisation of the two muscles. This technique provides an important objective method that can be used in conjunction with manual muscle testing to provide a means of ensuring accurate intramuscular electromyographic recording from these two muscles.     

Neuromechanical control of the forearm muscles during gripping with sudden flexion and extension wrist perturbations

The purpose of this study was to investigate how gripping modulates forearm muscle co-contraction prior to and during sudden wrist perturbations. Ten males performed a sub-maximal gripping task (no grip, 5% and 10% of maximum) while a perturbation forced wrist flexion or extension. Wrist joint angles and activity from 11 muscles were used to determine forearm co-contraction and muscle contributions to wrist joint stiffness. Co-contraction increased in all pairs as grip force increased (from no grip to 10% grip), corresponding to a 36% increase in overall wrist joint stiffness. Inclusion of individual muscle contributions to wrist joint stiffness enhanced the understanding of forearm co-contraction. The extensor carpi radialis longus (ECRL) and brevis had the largest stiffness contributions (34.5 ± 1.3% and 20.5 ± 2.3%, respectively), yet muscle pairs including ECRL produced the lowest co-contraction. The muscles contributing most to wrist stiffness were consistent across conditions (ECRL for extensors; Flexor Digitorum Superficialis for flexors), suggesting enhanced contributions rather than muscular redistribution. This work provides investigation of the neuromuscular response to wrist perturbations and gripping demands by considering both co-contraction and muscle contributions to joint stiffness. Individual muscle stiffness contributions can be used to enhance the understanding of forearm muscle control during complex tasks.     

Quantification of the forearm muscles mechanical properties using Myotonometer: Intra- and Inter-Examiner reliability and its relation with hand grip strength

The primary objective of this study was to investigate the reliability of the myotonometer in the mechanical properties of the forearm muscles [m. extensor carpi radialis brevis (ECRB), and m. flexor carpi ulnaris (FCU)] in healthy individuals. The secondary objective was to investigate the relationship between the handgrip strength and mechanical properties of these forearm muscles. The mechanical properties (muscle tone, stiffness, and elasticity) of the ECRB and FCU were measured using the MyotonPRO device. Examiner 1 performed two sets of measurements with a time interval of 30 min to determine intra-examiner reliability. Examiner 2 performed measurements during the interval between the two sets of examiner 1. The intra- and inter-examiner reliabilities were excellent (ICC˃0.82) for muscle tone, stiffness, and elasticity of the FCU. Both intra- and inter-examiner reliability in the evaluation of ECRB muscle tone, elasticity, and stiffness was moderate to excellent (ICCs = 0.56–0.98). The muscle tone and stiffness properties of the FCU were positively correlated with the handgrip strength (p <.05). The study findings indicate that the MyotonPRO device is a reliable tool to quantify ECRB, and FCU muscles mechanical properties in healthy individuals.     

Fatigue effect on cross-talk in mechanomyography signals of extensor and flexor forearm muscles during maximal voluntary isometric contractions

Objective:This paper presents the analyses of the fatigue effect on the cross-talk in mechanomyography (MMG) signals of extensor and flexor forearm muscles during pre- and post-fatigue maximum voluntary isometric contraction (MVIC).Methods:Twenty male participants performed repetitive submaximal (60% MVIC) grip muscle contractions to induce muscle fatigue and the results were analyzed during the pre- and post-fatigue MVIC. MMG signals were recorded on the extensor digitorum (ED), extensor carpi radialis longus (ECRL), flexor digitorum superficialis (FDS) and flexor carpi radialis (FCR) muscles. The cross-correlation coefficient was used to quantify the cross-talk values in forearm muscle pairs (MP1, MP2, MP3, MP4, MP5 and MP6). In addition, the MMG RMS and MMG MPF were calculated to determine force production and muscle fatigue level, respectively.Results:The fatigue effect significantly increased the cross-talk values in forearm muscle pairs except for MP2 and MP6. While the MMG RMS and MMG MPF significantly decreased (p<0.05) based on the examination of the mean differences from pre- and post-fatigue MVIC.Conclusion:The presented results can be used as a reference for further investigation of cross-talk on the fatigue assessment of extensor and flexor muscles’ mechanic.     

Anatomical partitioning of three multiarticular human muscles.

To examine neuromuscular partitioning within human muscles, the innervation patterns and muscle fiber architecture of the flexor carpi radialis (FCR), extensor carpi radialis longus (ECRL) and lateral gastrocnemius (LG) muscles were examined. Consistent patterns of innervation between specimens were found within each of the three muscles. The nerve to the FCR clearly innervates three major architectural divisions of the muscle. The ECRL is innervated by two different muscle nerves. Branches of these nerves innervate at least two distinct anatomical subvolumes. However, the subvolumes of the ECRL defined by muscle architecture are not totally congruent with those defined by the innervation pattern. In the LG, the single muscle nerve branches into two main divisions, and these subsequently divide into branches which supply the three heads. However, each head does not receive a completely private nerve. These results indicate that human muscles are partitioned in a manner roughly similar to the divisions of the same muscles in cats and rats, but with less congruency of architecture and innervation.     

Surface electromyography of forearm and shoulder muscles during violin playing

The aims of this study were to explore muscle activity levels during different violin repertoires, quantify the general levels bilaterally in upper extremity muscles, and evaluate associations between muscle activity and anthropometrics characteristics. In 18 skilled violin players surface EMG was recorded bilaterally from trapezius (UT), flexor digitorum superficialis (FDS), extensor carpi ulnaris (ECU), extensor digitorum cummunis (EDC), and extensor carpi radialis (ECR) during A and E major scales played in three octaves and Mozart’s Violin Concerto no. 5. To compare side differences the static, median and peak levels of muscle activity were calculated from an amplitude probability distribution function (APDF). This study demonstrated that scales played as standardized tasks can be used to estimate the average muscle activity during violin playing. Comparing results from scales and the music piece revealed a similar muscle activity across all muscles in the music piece and E major scales. The static, median and peak EMG levels were higher in left than in right forearm muscles with left ECU presenting the highest peak load of 30 %MVE. Females demonstrated a higher muscle activity than males, but this was in accordance with differences in anthropometric measures.     

Dystrophin deficiency compromises force production of the extensor carpi ulnaris muscle in the canine model of duchenne muscular dystrophy

Loss of muscle force is a salient feature of Duchenne muscular dystrophy (DMD), a fatal disease caused by dystrophin deficiency. Assessment of force production from a single intact muscle has been considered as the gold standard for studying physiological consequences in murine models of DMD. Unfortunately, equivalent assays have not been established in dystrophic dogs. To fill the gap, we developed a novel in situ protocol to measure force generated by the extensor carpi ulnaris (ECU) muscle of a dog. We also determined the muscle length to fiber length ratio and the pennation angle of the ECU muscle. Muscle pathology and contractility were compared between normal and affected dogs. Absence of dystrophin resulted in marked histological damage in the ECU muscle of affected dogs. Central nucleation was significantly increased and myofiber size distribution was altered in the dystrophic ECU muscle. Muscle weight and physiological cross sectional area (PCSA) showed a trend of reduction in affected dogs although the difference did not reach statistical significance. Force measurement revealed a significant decrease of absolute force, and the PCSA or muscle weight normalized specific forces. To further characterize the physiological defect in affected dog muscle, we conducted eccentric contraction. Dystrophin-null dogs showed a significantly greater force loss following eccentric contraction damage. To our knowledge, this is the first convincing demonstration of force deficit in a single intact muscle in the canine DMD model. The method described here will be of great value to study physiological outcomes following innovative gene and/or cell therapies.     

Muscle geometry affects accuracy of forearm volume determination by magnetic resonance imaging (MRI)

Upper extremity musculoskeletal modeling is becoming increasingly sophisticated, creating a growing need for subject-specific muscle size parameters. One method for determining subject-specific muscle volume is magnetic resonance imaging (MRI). The purpose of this study was to determine the validity of MRI-derived muscle volumes in the human forearm across a variety of muscle sizes and shapes. Seventeen cadaveric forearms were scanned using a fast-spoiled gradient echo pulse sequence with high isotropic spatial resolution (1mm(3) voxels) on a 3T MR system. Pronator teres (PT), extensor carpi radialis brevis (ECRB), extensor pollicis longus (EPL), flexor carpi ulnaris (FCU), and brachioradialis (BR) muscles were manually segmented allowing volume to be calculated. Forearms were then dissected, muscles isolated, and muscle masses obtained, which allowed computation of muscle volume. Intraclass correlation coefficients (ICC(2,1)) and absolute volume differences were used to compare measurement methods. There was excellent agreement between the anatomical and MRI-derived muscle volumes (ICC = 0.97, relative error = 12.8%) when all 43 muscles were considered together. When individual muscles were considered, there was excellent agreement between measurement methods for PT (ICC = 0.97, relative error = 8.4%), ECRB (ICC = 0.93, relative error = 7.7%), and FCU (ICC = 0.91, relative error = 9.8%), and fair agreement for EPL (ICC = 0.68, relative error = 21.6%) and BR (ICC = 0.93, relative error = 17.2%). Thus, while MRI-based measurements of muscle volume produce relatively small errors in some muscles, muscles with high surface area-to-volume ratios may predispose them to segmentation error, and, therefore, the accuracy of these measurements may be unacceptable.     

A simulation analysis of the combined effects of muscle strength and surgical tensioning on lateral pinch force following brachioradialis to flexor pollicis longus transfer

Biomechanical simulations of tendon transfers performed following tetraplegia suggest that surgical tensioning influences clinical outcomes. However, previous studies have focused on the biomechanical properties of only the transferred muscle. We developed simulations of the tetraplegic upper limb following transfer of the brachioradialis (BR) to the flexor pollicis longus (FPL) to examine the influence of residual upper limb strength on predictions of post-operative transferred muscle function. Our simulations included the transfer, ECRB, ECRL, the three heads of the triceps, brachialis, and both heads of the biceps. Simulations were integrated with experimental data, including EMG and joint posture data collected from five individuals with tetraplegia and BR-FPL tendon transfers during maximal lateral pinch force exertions. Given a measured co-activation pattern for the non-paralyzed muscles in the tetraplegic upper limb, we computed the highest activation for the transferred BR for which neither the elbow nor the wrist flexor moment was larger than the respective joint extensor moment. In this context, the effects of surgical tensioning were evaluated by comparing the resulting pinch force produced at different muscle strength levels, including patient-specific scaling. Our simulations suggest that extensor muscle weakness in the tetraplegic limb limits the potential to augment total pinch force through surgical tensioning. Incorporating patient-specific muscle volume, EMG activity, joint posture, and strength measurements generated simulation results that were comparable to experimental results. Our study suggests that scaling models to the population of interest facilitates accurate simulation of post-operative outcomes, and carries utility for guiding and developing rehabilitation training protocols.     

Effect of pelvis impact angle on stresses at the femoral neck during falls

Improved understanding is required of how the mechanics of the fall affect hip fracture risk. We used a hip impact simulator to determine how peak stresses at the femoral neck were affected by pelvis impact angle, hip abductor muscle force, and use of a wearable hip protector.We simulated falls from standing (2 m/s impact velocity) involving initial hip abductor muscle forces of 700 or 300 N. Trials were acquired for impact to the lateral aspect of the greater trochanter, and impact to the pelvis rotated 5°, 10° and 15° anteriorly (positive) or posteriorly (negative). Measures were acquired with and without a commercially available hip protector. During trials, we measured three-dimensional forces with a load cell at the femoral neck, and derived peak compressive and tensile stresses.Peak compressive stress increased 37% (5.91 versus 4.31 MPa; p < 0.0005) and peak tensile stress increased 209% (2.31 versus 0.75 MPa; p < 0.0005) when the pelvis impact angle changed from 15° anterior to −15° posterior. For lateral impacts, the peak tensile and compressive stresses averaged 73% and 8% lower, respectively, in the 700 N than 300 N muscle force condition, but the effect was reversed for anteriolateral or posteriolateral impacts. The attenuation in peak compressive stress from the hip protector was greatest for posteriolateral impacts (−15 to −5°; 36–41%), and least for anteriolateral (+15°; 10%).These results clarify the effects on hip fracture risk during a fall of pelvis impact angle and muscle forces, and should inform the design of improved hip protectors.     

The effects of upper limb posture and a sub-maximal gripping task on corticospinal excitability to muscles of the forearm

Variations in handgrip force influences shoulder muscle activity, and this effect is dependent upon upper limb position. Previous work suggests that neural coupling between proximal and distal muscles with changes in joint position is a possible mechanism but these studies tend to use artificially constrained postures that do not reflect activities of daily living. The purpose of this study was to examine the effects of upper limb posture on corticospinal excitability to the forearm muscles during workplace relevant arm positions. Motor evoked potentials (MEPs) were elicited in four forearm muscles via transcranial magnetic stimulation at six arm positions (45°, 90° and 120° of humeral elevation in both the flexion and abduction planes). MEPs were delivered as stimulus–response curves (SRCs) at rest and at constant intensity during two gripping tasks. Boltzmann plateau levels were smaller for the flexor carpi radialis in flexion at 45° versus 90° (p = 0.0008). Extensor carpi radialis had a greater plateau during flexion than abduction (p = 0.0042). Corticospinal excitability to the forearm muscles were influenced by upper limb posture during both the resting and gripping conditions. This provides further evidence that upper limb movements are controlled as a whole rather than segmentally and is relevant for workplace design considerations.     

Failure of neuromuscular propagation during human maximal voluntary contraction

The mechanism for fatigue of the adductor pollicis was studied in normal subjects during maximal voluntary contractions (MVC) sustained for 90-100 s, by comparing the force and electrical response of this muscle to voluntary motor drive with that obtainable with artificial stimulation of the ulnar nerve. The adequacy of nerve stimulation was checked by recording simultaneously the electrical response of a nonfatiguing muscle, the abductor of the small finger. The decrease in force and in the natural electrical activity with fatigue was accompanied by a parallel decrease in the amplitude of synchronous muscle action potentials (M waves) evoked by artificial stimulation of the ulnar nerve at different frequencies. The decline in M-wave amplitude in the adductor pollicis was not due to a submaximal nerve stimulation, since the amplitudes recorded simultaneously from the nonfatiguing abductor digiti minimi remained unchanged. The force and the electrical responses from the adductor pollicis recovered in parallel with a half time of approximately 1 min. These results suggest that the loss of force of the adductor pollicis with fatigue and its subsequent recovery are largely determined by the extent of neuromuscular propagation failure. The slow recovery of the M-wave amplitude during repetitive stimulation suggests that it may be related to some aspect of muscle metabolism.     

Nuclear DNA content of the Solanum spp. in the series Etuberosa as determined by laser flow cytometry

Nuclear DNA content was determined in three accessions of Solanum brevidens, three accessions of S. etuberosum, and one accession of S. fernandezianum, which are diploid (2n = 2×= 24), closely related, non tuber-bearing wild potato species belonging to the series Etuberosa (Solanaceae). The plants were grown in vitro at 18°C or at 25°/22°C (day/night). S. brevidens was also grown in soil in the glasshouse at 25°/19°C (day/night), and in growth chambers at 18°C or 32°C. Leaf nuclei were isolated using a chopping method and stained with propidium iodide. Chicken red blood cells (CRBC; 2.33 pg) were added to the samples of nuclei as internal standards. The fluorescence of plant nuclei relative to CRBC was measured with an EPICS PROFILE flow cytometer. The 2C values of in vitro-grown S. brevidens and S. etuberosum were similar (1.48–1.54 pg, depending on the accession), but they were smaller than the 2C value of S. fernandezianum (1.63 pg). The 2C values of S. brevidens and S. etuberosum were generally smaller than those of the diploid species S. berthaultii (1.60–1.61 pg) and the diploid clones of S. tuberosum (1.60–1.72 pg). A similar relative difference of nuclear DNA content was found also between tetraploid S. brevidens and tetraploid S. tuberosum (2C = 3.15–3.16 pg and 3.50–3.62 pg, respectively). High (32°C) and low (18°C) growth temperatures caused abnormal changes in morphology and reduced fertility in S. brevidens in the growth chamber. The 2C values of S. brevidens grown at 25°/19°C (day/night) or at 32°C were similar, whereas the 2C values were c. 10% lower at 18°C.     

Changes of agonist and synergist muscles activity during a sustained submaximal brake-pulling gesture

We analyzed the time course of changes in muscle activity of the prime mover and synergist muscles during a sustained brake-pulling action and investigated the relationship between muscle activity and braking force fluctuation (FF). Thirty-two participants performed a continuous fatiguing protocol (CFP) at 30% of maximal voluntary contraction (MVC) until failure. Surface electromyography was used to analyze root mean square (RMS) values in the flexor digitorum superficialis (FD), flexor carpi radialis (FC), extensor digitorum communis (ED), extensor carpi radialis (EC), brachioradialis (BR), biceps brachii (BB), and triceps brachii (TB). The FF and RMS in all muscles increased progressively (P<0.01) during the CFP, with sharp increments at time limit particularly in FD and FC (P<0.001). The RMS of the FD and FC were comparable to the baseline MVC values at time limit, in comparison to the other muscles that did not reach such levels of activity (P<0.003). The three flexor/extensor ratios used to measure coactivation levels decreased significantly (P<0.001). In contrast to RMS, MVC was still depressed at the minute 10 of recovery. The results suggest that the time limit was mainly constrained by fatigue-related mechanisms of the FD and FC but not by those of other synergist and antagonist muscles.     

Phylogeography of the red alga Gracilariopsis tenuifrons (Gracilariales) along the Brazilian coast

Changes in the sea level during the Holocene are regarded as one of the most prevalent drivers of the diversity and distribution of macroalgae in Brazil, influenced by the emergence of the Vitória-Trindade seamount chain (VTC). Gracilariopsis tenuifrons has a wide geographic distribution along the Brazilian coast, from Maranhão state (2°48′64.3" S) to Santa Catarina state (27.5°73′83" S). The knowledge of historical processes affecting diversity may allow the development of conservation strategies in environments against anthropogenic influence. Therefore, knowledge about phylogeography and populational genetic diversity in G. tenuifrons is necessary. Six populations were sampled along the northeastern tropical (Maranhão—MA, Rio Grande do Norte—RN, Alagoas—AL, and Bahia—BA States) and southeastern subtropical (São Paulo “Ubatuba”—SP1 and São Paulo “Itanhaém”—SP2 States) regions along the Brazilian coast. The genetic diversity and structure of G. tenuifrons were inferred using mitochondrial (COI-5P and cox2-3 concatenated) DNA markers. Gracilariopsis tenuifrons populations showed an evident separation between the northeast (from 2°48′64.3" S to 14°18′23" S; 17 haplotypes) and the southeast (from 23°50′14.9" S to 24°20′04.7" S; 10 haplotypes) regions by two mutational steps between them. The main biogeographical barrier to gene flow is located nearby the VTC. The southeast region (São Paulo State) is separated by two subphylogroups (SP1, three haplotypes and SP2, six haplotypes), and Santos Bay (estuary) has been considered a biogeographical barrier between them. The presence of genetic structure and putative barriers to gene flow are in concordance with previous studies reporting biogeographic breaks in the southwest Atlantic Ocean, including the genetic isolation between northeast and southeast regions for red and brown algae in the vicinity of the VTC.     

Influence of post-treatment temperature, solvents and emulsifiers on the toxicity of cypermethrin to larvae of Spodoptera litura (Fab.)

Larvae of the tobacco caterpillar, Spodoptera litura (Fab.) were topically bioassayed with cypermethrin emulsion formulation and proprietary EC in combination with different solvents and emulsifiers for their toxicity at 16 ± 2°C and 27 ± 1°C. Among different solvents, the descending order of efficacy (with relative toxicity in parenthesis) against 9 ± 1 day old larvae of S. litura (Fab.) at 16 ± 2°C than 27 ± 1°C was: xylene (7.41), aromex (5.54), cyclohexane (4.93), C-IX (3.93), benzene (2.40) and toluene (2.26). With emulsifier, the order was: Triton X-100 (7.41), SN₄S (4.60), Teepol (2.90), Tween-80 (1.49), Swascofix DP-50 (1.28), SN₄R (1.10) and S₅₂B (1.07). However, the proprietary cypermethrin EC was 2.31 times more toxic at 16 ± 2°C than at 27 ± 1°C.     

Parasites as biological tags for stock discrimination of the Brazilian flathead Percophis brasiliensis in the south-west Atlantic

Three stocks of the Brazilian flathead Percophis brasiliensis were identified on the coast of Argentina and Uruguay using parasites as biological tags. A total of 177 fish were examined and 23 parasite species were found. Fish were caught in four zones: north of the Argentine–Uruguayan Common Fishing Zone (34°30′–36°30′ S; 53°30′–56°00′ W), south of the Argentine–Uruguayan Common Fishing Zone (38°08′ S 57°32′ W), El Rincón zone (39–41° S; 60–62° W) and San Matías Gulf (41°40′–42°10′ S; 63°50′–65°00′ W). Discriminant analyses allowed the identification of three discrete stocks in the four zones (86·44% of classified samples were correctly identified), with P. brasiliensis from both north and south of the Argentine–Uruguayan Common Fishing Zone clumping together, as a single stock. Some species were important in discriminating among groups, Anisakis simplex was related to southern areas, while Grillotia sp., Corynosoma australe and Hysterothylacium sp. were important in determining the position of fish from the Argentine–Uruguayan Common Fishing Zone. These results were corroborated by comparing parasite prevalence and abundance among zones. The main differences were observed in those comparisons involving fish from the San Matías Gulf. Fish from the Argentine–Uruguayan Common Fishing Zone were characterized by higher infections of Grillotia sp., C. australe, Corynosoma cetaceum and Hysterothylacium sp., while the samples from El Rincón and San Matías Gulf showed higher infections of A. simplex. Samples from San Matías Gulf were characterized by lower levels of parasitism for all other species. Differences in environmental factors and their influence on the distribution of zooplankton and other hosts in the food web may be differentially shaping the parasite community structure in each zone, resulting in identifiable stocks of the P. brasiliensis. The present study confirmed the existence of regional biological tags that delineated fish assemblages.