Quantitative assessment of grasping strength in platyrrhine monkeys.

OBJECTIVES: Despite the longstanding importance of grasping adaptations in theories of primate evolution, quantitative data on primate grasping strength remain rare. We present the results of two studies testing the prediction that callitrichines-given their comparative retreat from a small-branch environment and specialization for movement and foraging on tree trunks and large boughs-should be characterized by weaker grasping forces and underdeveloped digital flexor muscles relative to other platyrrhines. METHODS: First, we directly measured manual grasping strength in marmosets (Callithrix jacchus) and squirrel monkeys (Saimiri boliviensis), using a custom-constructed force transducer. Second, we reanalyzed existing datasets on the fiber architecture of forearm and leg muscles in 12 platyrrhine species, quantifying digital flexor muscle physiological cross-sectional area (i.e., PCSA, a morphometric proxy of muscle strength) relative to the summed PCSA across all forearm or leg muscles. RESULTS: Callithrix was characterized by lower mean and maximum grasping forces than Saimiri, and callitrichines as a clade were found to have relatively underdeveloped manual digital flexor muscle PCSA. However, relative pedal digital flexor PCSA did not significantly differ between callitrichines and other platyrrhines. CONCLUSIONS: We found partial support for the hypothesis that variation in predominant substrate usage explains variation in empirical measurements of and morphological correlates of grasping strength in platyrrhines. Future research should extend the work presented here by (1) collecting morphological and empirical metrics of grasping strength in additional primate taxa and (2) extending performance testing to include empirical measures of primate pedal grasping forces as well.

Myology of the pelvic limb of the brown-throated three-toed sloth (Bradypus variegatus).

Tree sloths rely on their limb flexors for bodyweight support and joint stability during suspensory locomotion and posture. This study aims to describe the myology of three-toed sloths and identify limb muscle traits that indicate modification for suspensorial habit. The pelvic limbs of the brown-throated three-toed sloth (Bradypus variegatus) were dissected, muscle belly mass was recorded, and the structural arrangements of the muscles were documented and compared with the available myological accounts for sloths. Overall, the limb musculature is simplified by containing muscles with generally long and parallel fascicles. A number of specific and informative muscle traits are additionally observed in the pelvic limb of B. variegatus: well-developed hip flexors and hip extensors each displaying several fused bellies; massive knee flexors; two heads of the m. adductor longus and m. gracilis; robust digital flexors and flexor tendons; m. tibialis cranialis muscle complex originating from the tibia and fibula and containing a modified m. extensor digitorum I longus; appreciable muscle mass devoted to ankle flexion and hindfoot supination; only m. extensor digitorum brevis acts to extend the digits. Collectively, the findings for tree sloths emphasize muscle mass and organization for suspensory support namely by the hip flexors, knee flexors, and limb adductors, for which the latter two groups may stabilize suspensory postures by exerting appreciable medially-directed force on the substrate. Specializations in the distal limb are also apparent for sustained purchase of the substrate by forceful digital flexion coupled with strong ankle flexion and supination of the hind feet, which is permitted by the reorganization of several digital extensors. Moreover, the reduction or loss of other digital flexor and ab-adductor muscles marks a dramatic simplification of the intrinsic foot musculature in B. variegatus, the extent to which varies across extant species of two- and three-toed tree sloths and likely is related to substrate preference/use.

Robust locomotor performance of squirrel monkeys (Saimiri boliviensis) in response to simulated changes in support diameter and compliance.

Arboreal environments require overcoming navigational challenges not typically encountered in other terrestrial habitats. Supports are unevenly distributed and vary in diameter, orientation, and compliance. To better understand the strategies that arboreal animals use to maintain stability in this environment, laboratory researchers must endeavor to mimic those conditions. Here, we evaluate how squirrel monkeys (Saimiri boliviensis) adjust their locomotor mechanics in response to variation in support diameter and compliance. We used high-speed cameras to film two juvenile female monkeys as they walked across poles of varying diameters (5, 2.5, and 1.25 cm). Poles were mounted on either a stiff wooden base ("stable" condition) or foam blocks ("compliant" condition). Six force transducers embedded within the pole trackway recorded substrate reaction forces during locomotion. We predicted that squirrel monkeys would walk more slowly on narrow and compliant supports and adopt more "compliant" gait mechanics, increasing stride lengths, duty factors, and an average number of limbs gripping the support, while the decreasing center of mass height, stride frequencies, and peak forces. We observed few significant adjustments to squirrel monkey locomotor kinematics in response to changes in either support diameter or compliance, and the changes we did observe were often tempered by interactions with locomotor speed. These results differ from a similar study of common marmosets (i.e., Callithrix jacchus, with relatively poor grasping abilities), where variation in diameter and compliance substantially impacted gait kinematics. Squirrel monkeys' strong grasping apparatus, long and mobile tails, and other adaptations for arboreal travel likely facilitate robust locomotor performance despite substrate precarity.

Jaw kinematics and tongue protraction-retraction during chewing and drinking in the pig.

Mastication and drinking are rhythmic and cyclic oral behaviors that require interactions between the tongue, jaw and a food or liquid bolus, respectively. During mastication, the tongue transports and positions the bolus for breakdown between the teeth. During drinking, the tongue aids in ingestion and then transports the bolus to the oropharynx. The objective of this study was to compare jaw and tongue kinematics during chewing and drinking in pigs. We hypothesized there would be differences in jaw gape cycle dynamics and tongue protraction-retraction between behaviors. Mastication cycles had an extended slow-close phase, reflecting tooth-food-tooth contact, whereas drinking cycles had an extended slow-open phase, corresponding to tongue protrusion into the liquid. Compared with chewing, drinking jaw movements were of lower magnitude for all degrees of freedom examined (jaw protraction, yaw and pitch), and were bilaterally symmetrical with virtually no yaw. The magnitude of tongue protraction-retraction (Txt), relative to a mandibular coordinate system, was greater during mastication than during drinking, but there were minimal differences in the timing of maximum and minimum Txt relative to the jaw gape cycle between behaviors. However, during drinking, the tongue tip is often located outside the oral cavity for the entire cycle, leading to differences between behaviors in the timing of anterior marker maximum Txt. This demonstrates that there is variation in tongue-jaw coordination between behaviors. These results show that jaw and tongue movements vary significantly between mastication and drinking, which hints at differences in the central control of these behaviors.

The Stabilizing Function of the Tail During Arboreal Quadrupedalism.

Locomotion on the narrow and compliant supports of the arboreal environment is inherently precarious. Previous studies have identified a host of morphological and behavioral specializations in arboreal animals broadly thought to promote stability when on precarious substrates. Less well-studied is the role of the tail in maintaining balance. However, prior anatomical studies have found that arboreal taxa frequently have longer tails for their body size than their terrestrial counterparts, and prior laboratory studies of tail kinematics and the effects of tail reduction in focal taxa have broadly supported the hypothesis that the tail is functionally important for maintaining balance on narrow and mobile substrates. In this set of studies, we extend this work in two ways. First, we used a laboratory dataset on three-dimensional segmental kinematics and tail inertial properties in squirrel monkeys (Saimiri boliviensis) to investigate how tail angular momentum is modulated during steady-state locomotion on narrow supports. In the second study, we used a quantitative dataset on quadrupedal locomotion in wild platyrrhine monkeys to investigate how free-ranging arboreal animals adjust tail movements in response to substrate variation, focusing on kinematic measures validated in prior laboratory studies of tail mechanics (including the laboratory data presented). Our laboratory results show that S. boliviensis significantly increase average tail angular momentum magnitudes and amplitudes on narrow supports, and primarily regulate that momentum by adjusting the linear and angular velocity of the tail (rather than via changes in tail posture per se). We build on these findings in our second study by showing that wild platyrrhines responded to the precarity of narrow and mobile substrates by extending the tail and exaggerating tail displacements, providing ecological validity to the laboratory studies of tail mechanics presented here and elsewhere. In conclusion, our data support the hypothesis that the long and mobile tails of arboreal animals serve a biological role of enhancing stability when moving quadrupedally over narrow and mobile substrates. Tail angular momentum could be used to cancel out the angular momentum generated by other parts of the body during steady-state locomotion, thereby reducing whole-body angular momentum and promoting stability, and could also be used to mitigate the effects of destabilizing torques about the support should the animals encounter large, unexpected perturbations. Overall, these studies suggest that long and mobile tails should be considered among the fundamental suite of adaptations promoting safe and efficient arboreal locomotion.

Jaw kinematics and tongue protraction-retraction during chewing and drinking in the pig.

Mastication and drinking are rhythmic and cyclic oral behaviors that require interactions between the tongue, jaw and a food or liquid bolus, respectively. During mastication, the tongue transports and positions the bolus for breakdown between the teeth. During drinking, the tongue aids in ingestion and then transports the bolus to the oropharynx. The objective of this study was to compare jaw and tongue kinematics during chewing and drinking in pigs. We hypothesized there would be differences in jaw gape cycle dynamics and tongue protraction-retraction between behaviors. Mastication cycles had an extended slow-close phase, reflecting tooth-food-tooth contact, whereas drinking cycles had an extended slow-open phase, corresponding to tongue protrusion into the liquid. Compared with chewing, drinking jaw movements were of lower magnitude for all degrees of freedom examined (jaw protraction, yaw and pitch), and were bilaterally symmetrical with virtually no yaw. The magnitude of tongue protraction-retraction (Txt), relative to a mandibular coordinate system, was greater during mastication than during drinking, but there were minimal differences in the timing of maximum and minimum Txt relative to the jaw gape cycle between behaviors. However, during drinking, the tongue tip is often located outside the oral cavity for the entire cycle, leading to differences between behaviors in the timing of anterior marker maximum Txt. This demonstrates that there is variation in tongue-jaw coordination between behaviors. These results show that jaw and tongue movements vary significantly between mastication and drinking, which hints at differences in the central control of these behaviors.

Not all fine-branch locomotion is equal: Grasping morphology determines locomotor performance on narrow supports.

Fine-branch models have long played a central role in primate evolutionary research. Nevertheless, recent studies of positional behavior in nonprimate arboreal mammals have challenged the idea that synapomorphic primate features, such as grasping extremities, uniquely facilitated access to the fine-branch zone. We test the alternative hypothesis that grasping extremities specifically improve locomotor performance in a fine-branch environment by examining how support diameter influences locomotor mechanics in one sciurid rodent (Sciurus carolinensis) and two platyrrhine primates (Callithrix jacchus and Saimiri boliviensis). These species were chosen to broadly model different stages in the evolution of primate grasping morphology. The results showed that transitioning from broad to narrower supports required the greatest kinematic adjustment in squirrels and the least adjustment in squirrel monkeys, with marmosets displaying an intermediate level of adjustment. Moreover, on any given support, squirrels' locomotor mechanics differed from marmosets' in a manner consistent with a greater need for stability, despite superficial ecomorphological similarities between sciurid rodents and callitrichine primates. Morphological analyses of autopodial size and proportions suggest that variation in locomotor performance more closely tracked variation in overall hand and foot size rather than digit length per se. Indeed, a broad comparative analysis revealed that for their body mass, primates have longer hands than similarly sized arboreal rodents and marsupials (although only the primate-rodent comparison was significant after incorporating phylogenetic relatedness). Inclusion of fossil stem primates (plesiadapiforms) and euprimates (adapiforms) in these analyses suggests that this primate-wide grade shift in relative autopodial size must have occurred early in the evolutionary history of the group. Overall, our findings show that basal primate morphological adaptations may have specifically facilitated improved locomotor performance in a fine-branch niche, rather than merely permitting access to the environment. As such, future adaptive hypotheses of primate origins should incorporate the import of primate-like morphology on locomotor performance as well.

The evolution of anti-bat sensory illusions in moths.

Prey transmit sensory illusions to redirect predatory strikes, creating a discrepancy between what a predator perceives and reality. We use the acoustic arms race between bats and moths to investigate the evolution and function of a sensory illusion. The spinning hindwing tails of silk moths (Saturniidae) divert bat attack by reflecting sonar to create a misleading echoic target. We characterized geometric morphometrics of moth hindwings across silk moths, mapped these traits onto a new, robust phylogeny, and found that elaborated hindwing structures have converged on four adaptive shape peaks. To test the mechanism underlying these anti-bat traits, we pit bats against three species of silk moths with experimentally altered hindwings that created a representative gradient of ancestral and extant hindwing shapes. High-speed videography of battles reveals that moths with longer hindwings and tails more successfully divert bat attack. We postulate that sensory illusions are widespread and are underappreciated drivers of diversity across systems.

Ontogeny of myosin isoform expression and prehensile function in the tail of the gray short-tailed opossum (Monodelphis domestica).

Terrestrial opossums use their semiprehensile tail for grasping nesting materials as opposed to arboreal maneuvering. We relate the development of this adaptive behavior with ontogenetic changes in myosin heavy chain (MHC) isoform expression from 21 days to adulthood. Monodelphis domestica is expected to demonstrate a progressive ability to flex the distal tail up to age 7 mo, when it should exhibit routine nest construction. We hypothesize that juvenile stages (3-7 mo) will be characterized by retention of the neonatal isoform (MHC-Neo), along with predominant expression of fast MHC-2X and -2B, which will transition into greater MHC-1ß and -2A isoform content as development progresses. This hypothesis was tested using Q-PCR to quantify and compare gene expression of each isoform with its protein content determined by gel electrophoresis and densitometry. These data were correlated with nesting activity in an age-matched sample of each age group studied. Shifts in regulation of MHC gene transcripts matched well with isoform expression. Notably, mRNA for MHC-Neo and -2B decrease, resulting in little-to-no isoform translation after age 7 mo, whereas mRNA for MHC-1ß and -2A increase, and this corresponds with subtle increases in content for these isoforms into late adulthood. Despite the tail remaining intrinsically fast-contracting, a critical growth period for isoform transition is observed between 7 and 13 mo, correlating primarily with use of the tail during nesting activities. Functional transitions in MHC isoforms and fiber type properties may be associated with muscle "tuning" repetitive nest remodeling tasks requiring sustained contractions of the caudal flexors.NEW & NOTEWORTHY Little is understood about skeletal muscle development as it pertains to tail prehensility in mammals. This study uses an integrative approach of relating both MHC gene and protein expression with behavioral and morphometric changes to reveal a predominant fast MHC expression with subtle isoform transitions in caudal muscle across ontogeny. The functional shifts observed are most notably correlated with increased tail grasping for nesting activities.

Effects of support diameter and compliance on common marmoset (Callithrix jacchus) gait kinematics.

Locomotion is precarious in an arboreal habitat, where supports can vary in both diameter and level of compliance. Several previous studies have evaluated the influence of substrate diameter on the locomotor performance of arboreal quadrupeds. The influence of substrate compliance, however, has been mostly unexamined. Here, we used a multifactorial experimental design to investigate how perturbations in both diameter and compliance affect the gait kinematics of marmosets (Callithrix jacchus; N=2) moving over simulated arboreal substrates. We used 3D-calibrated video to quantify marmoset locomotion over a horizontal trackway consisting of variably sized poles (5, 2.5 and 1.25 cm in diameter), analyzing a total of 120 strides. The central portion of the trackway was either immobile or mounted on compliant foam blocks, depending on condition. We found that narrowing diameter and increasing compliance were both associated with relatively longer substrate contact durations, though adjustments to diameter were often inconsistent relative to compliance-related adjustments. Marmosets also responded to narrowing diameter by reducing speed, flattening center of mass (CoM) movements and dampening support displacement on the compliant substrate. For the subset of strides on the compliant support, we found that speed, contact duration and CoM amplitude explained >60% of the variation in substrate displacement over a stride, suggesting a direct performance advantage to these kinematic adjustments. Overall, our results show that compliant substrates can exert a significant influence on gait kinematics. Substrate compliance, and not just support diameter, should be considered a critical environmental variable when evaluating locomotor performance in arboreal quadrupeds.

Tail function during arboreal quadrupedalism in squirrel monkeys (Saimiri boliviensis) and tamarins (Saguinus oedipus).

The need to maintain stability on narrow branches is often presented as a major selective force shaping primate morphology, with adaptations to facilitate grasping receiving particular attention. The functional importance of a long and mobile tail for maintaining arboreal stability has been comparatively understudied. Tails can facilitate arboreal balance by acting as either static counterbalances or dynamic inertial appendages able to modulate whole-body angular momentum. We investigate associations between tail use and inferred grasping ability in two closely related cebid platyrrhines-cotton-top tamarins (Saguinus oedipus) and black-capped squirrel monkeys (Saimiri boliviensis). Using high-speed videography of captive monkeys moving on 3.2 cm diameter poles, we specifically test the hypothesis that squirrel monkeys (characterized by grasping extremities with long digits) will be less dependent on the tail for balance than tamarins (characterized by claw-like nails, short digits, and a reduced hallux). Tamarins have relatively longer tails than squirrel monkeys, move their tails through greater angular amplitudes, at higher angular velocities, and with greater angular accelerations, suggesting dynamic use of tail to regulate whole-body angular momentum. By contrast, squirrel monkeys generally hold their tails in a comparatively stationary posture and at more depressed angles, suggesting a static counterbalancing mechanism. This study, the first empirical test of functional tradeoffs between grasping ability and tail use in arboreal primates, suggests a critical role for the tail in maintaining stability during arboreal quadrupedalism. Our findings have the potential to inform our functional understanding of tail loss during primate evolution.

Moth tails divert bat attack: evolution of acoustic deflection.

Adaptations to divert the attacks of visually guided predators have evolved repeatedly in animals. Using high-speed infrared videography, we show that luna moths (Actias luna) generate an acoustic diversion with spinning hindwing tails to deflect echolocating bat attacks away from their body and toward these nonessential appendages. We pit luna moths against big brown bats (Eptesicus fuscus) and demonstrate a survival advantage of ∼ 47% for moths with tails versus those that had their tails removed. The benefit of hindwing tails is equivalent to the advantage conferred to moths by bat-detecting ears. Moth tails lured bat attacks to these wing regions during 55% of interactions between bats and intact luna moths. We analyzed flight kinematics of moths with and without hindwing tails and suggest that tails have a minimal role in flight performance. Using a robust phylogeny, we find that long spatulate tails have independently evolved four times in saturniid moths, further supporting the selective advantage of this anti-bat strategy. Diversionary tactics are perhaps more common than appreciated in predator-prey interactions. Our finding suggests that focusing on the sensory ecologies of key predators will reveal such countermeasures in prey.

Angular momentum and arboreal stability in common marmosets (Callithrix jacchus).

Despite the importance that concepts of arboreal stability have in theories of primate locomotor evolution, we currently lack measures of balance performance during primate locomotion. We provide the first quantitative data on locomotor stability in an arboreal primate, the common marmoset (Callithrix jacchus), predicting that primates should maximize arboreal stability by minimizing side-to-side angular momentum about the support (i.e., Lsup ). If net Lsup becomes excessive, the animal will be unable to arrest its angular movement and will fall. Using a novel, highly integrative experimental procedure we directly measured whole-body Lsup in two adult marmosets moving along narrow (2.5 cm diameter) and broad (5 cm diameter) poles. Marmosets showed a strong preference for asymmetrical gaits (e.g., gallops and bounds) over symmetrical gaits (e.g., walks and runs), with asymmetrical gaits representing >90% of all strides. Movement on the narrow support was associated with an increase in more "grounded" gaits (i.e., lacking an aerial phase) and a more even distribution of torque production between the fore- and hind limbs. These adjustments in gait dynamics significantly reduced net Lsup on the narrow support relative to the broad support. Despite their lack of a well-developed grasping apparatus, marmosets proved adept at producing muscular "grasping" torques about the support, particularly with the hind limbs. We contend that asymmetrical gaits permit small-bodied arboreal mammals, including primates, to expand "effective grasp" by gripping the substrate between left and right limbs of a girdle. This model of arboreal stability may hold important implications for understanding primate locomotor evolution.

Median fin function during the escape response of bluegill sunfish (Lepomis macrochirus). I: Fin-ray orientation and movement.

The fast-start escape response is critically important to avoid predation, and axial movements driving it have been studied intensively. Large median dorsal and anal fins located near the tail have been hypothesized to increase acceleration away from the threat, yet the contribution of flexible median fins remains undescribed. To investigate the role of median fins, C-start escape responses of bluegill sunfish (Lepomis macrochirus) were recorded by three high-speed, high-resolution cameras at 500 frames s(-1) and the 3-D kinematics of individual dorsal and anal fin rays were analyzed. Movement and orientation of the fin rays relative to the body axis were calculated throughout the duration of the C-start. We found that: (1) timing and magnitude of angular displacement varied among fin rays based on position within the fin and (2) kinematic patterns support the prediction that fin rays are actively resisting hydrodynamic forces and transmitting momentum into the water. We suggest that regions within the fins have different roles. Anterior regions of the fins are rapidly elevated to increase the volume of water that the fish may interact with and transmit force into, thus generating greater total momentum. The movement pattern of all the fin rays creates traveling waves that move posteriorly along the length of the fin, moving water as they do so. Flexible posterior regions ultimately act to accelerate this water towards the tail, potentially interacting with vortices generated by the caudal fin during the C-start. Despite their simple appearance, median fins are highly complex and versatile control surfaces that modulate locomotor performance.

Median fin function during the escape response of bluegill sunfish (Lepomis macrochirus). II: Fin-ray curvature.

Although kinematic analysis of individual fin rays provides valuable insight into the contribution of median fins to C-start performance, it paints an incomplete picture of the complex movements and deformation of the flexible fin surface. To expand our analysis of median fin function during the escape response of bluegill sunfish (Lepomis macrochirus), patterns of spanwise and chordwise curvature of the soft dorsal and anal fin surfaces were examined from the same video sequences previously used in analysis of fin-ray movement and orientation. We found that both the span and chord undergo undulation, starting in the anterior region of either fin. Initiated early in Stage 1 of the C-start, the undulation travels in a postero-distal direction, reaching the trailing edge of the fins during early Stage 2. Maximum spanwise curvature typically occurred among the more flexible posterior fin rays, though there was no consistent correlation between maximum curvature and fin-ray position. Undulatory patterns suggest different mechanisms of action for the fin regions. In the anterior fin region, where the fin rays are oriented dorsoventrally, undulation is directed primarily chordwise, initiating a transfer of momentum into the water to overcome the inertia of the flow and direct the water posteriorly. Within the posterior region, where the fin rays are oriented caudally, undulation is predominantly directed spanwise; thus, the posterior fin region acts to ultimately accelerate this water towards the tail to increase thrust forces. Treatment of median fins as appendages with uniform properties does not do justice to their complexity and effectiveness as control surfaces.

Musculoskeletal morphology and regionalization within the dorsal and anal fins of bluegill sunfish (Lepomis macrochirus).

Ray-finned fishes actively control the shape and orientation of their fins to either generate or resist hydrodynamic forces. Because of the emergent mechanical properties of their segmented, bilaminar fin rays (lepidotrichia), and actuation by multiple muscles, fish can control the rigidity and curvature of individual rays independently, thereby varying the resultant forces across the fin surfaces. Expecting that differences in fin-ray morphology should reflect variation in their mechanical properties, we measured several musculoskeletal features of individual spines and rays of the dorsal and anal fins of bluegill sunfish, Lepomis macrochirus, and assessed their mobility and flexibility. We separated the fin-rays into four groups based on the fin (dorsal or anal) or fin-ray type (spine or ray) and measured the length of the spines/rays and the mass of the three median fin-ray muscles: the inclinators, erectors and depressors. Within the two ray groups, we measured the portion of the rays that were segmented vs. unsegmented and branched vs. unbranched. For the majority of variables tested, we found that variations between fin-rays within each group were significantly related to position within the fin and these patterns were conserved between the dorsal and anal rays. Based on positional variations in fin-ray and muscle parameters, we suggest that anterior and posterior regions of each fin perform different functions when interacting with the surrounding fluid. Specifically, we suggest that the stiffer anterior rays of the soft dorsal and anal fins maintain stability and keep the flow across the fins steady. The posterior rays, which are more flexible with a greater range of motion, fine-tune their stiffness and orientation, directing the resultant flow to generate lateral and some thrust forces, thus acting as an accessory caudal fin.

Naïve bats discriminate arctiid moth warning sounds but generalize their aposematic meaning.

Naïve red (Lasiurus borealis Müller) and big brown (Eptesicus fuscus Beauvois) bats quickly learn to avoid noxious sound-producing tiger moths. After this experience with a model tiger moth, bats generalize the meaning of these prey-generated sounds to a second tiger moth species producing a different call. Here we describe the three-dimensional kinematic and bioacoustic details of this behaviour, first, as naïve bats learn to deal with an unpalatable model tiger moth and subsequently, as they avoid acoustic mimics. The tiger moths' first clicks influenced the bats' echolocation behaviour and the percentage of interactions that included terminal buzzes was associated with capture and investigatory behaviour. When the mimic was introduced, the bats decreased both their minimum distance to the tiger moth and the time at which they broke off their attack compared with their exposure to the model on the night before. These kinematic signatures closely match the bats' behaviour on their first night of experience with the model. Minimum distances and time of pursuit cessation increased again by the last night of the mimic's presentation. These kinematic and bioacoustic results show that although naïve bats generalize the meaning of aposematic tiger moth calls, they discriminate the prey-generated signals as different and investigate. Extrapolating to experienced bats, these results suggest that acoustic predators probably exert potent and fine-scaled selective forces on acoustic mimicry complexes.

5(S)-Hydroxy-6,8,11,14-E,Z,Z,Z-eicosatetraenoate stimulates PC3 cell signaling and growth by a receptor-dependent mechanism.

5(S)-Hydroxy-6,8,11,14-E,Z,Z,Z-eicosatetraenoate (5-HETE) causes PC3 cells to grow by an unknown mechanism. We find that it also induces the cells to activate extracellular signal-regulated kinases and Akt. Pertussis toxin inhibits both responses. 5-HETE, 5-oxo-6,8,11,14-E,Z,Z,Z-eicosatetraenoate, and 5-oxo-15-hydroxy-eicosatetraenoate are known to stimulate leukocytes by a receptor coupled to pertussis toxin-sensitive G proteins. Their respective relative potencies in leukocytes are 1, 10, and 3. In PC3 cells, however, these values are 10, 1, and 0. PC3 cells, we propose, express a non-leukocyte-type, G protein-coupled, 5-HETE receptor. This novel receptor and the extracellular signal-regulated kinase and Akt pathways it recruits may contribute to the progression of prostate adenocarcinoma.

Comparison of isometric contractile properties in hindlimb extensor muscles of the frogs Rana pipiens and Bufo marinus: functional correlations with differences in hopping performance.

The leopard frog (Rana pipiens) is an excellent jumper that can reach high take-off velocities and accelerations. It is diurnal, using long, explosive jumps to capture prey and escape predators. The marine toad (Bufo marinus) is a cryptic, nocturnal toad, typically using short, slow hops, or sometimes walking, to patrol its feeding area. Typical of frogs with these different locomotor styles, Rana has relatively long hindlimbs and large (by mass) hindlimb extensor muscles compared to Bufo. We studied the isometric contractile properties of their extensor muscles and found differences that correlate with their different hopping performances. At the hip (semimembranosus, SM), knee (peroneus, Per) and ankle (plantaris longus, PL), we found that Rana's muscles tended to produce greater maximum isometric force relative to body mass, although the difference was significant only for PL. This suggests that differences in force capability at the ankle may be more important than at other joints to produce divergent hopping performances. Maximum isometric force scaled with body mass so that the smaller Rana has relatively larger muscles and force differences between species may reflect size differences only. In addition, Rana's muscles exhibited greater passive resistance to elongation, implying more elastic tissue is present, which may amplify force at take-off due to elastic recoil. Rana's muscles also achieved a higher percentage of maximum force at lower stimulus inputs (frequencies and durations) than in Bufo, perhaps amplifying the differences in force available for limb extension during natural stimulation. Twitch contraction and relaxation times tended to be faster in Rana, although variation was great, so that differences were significant only for Per. Fatigability also tended to be greater in Rana muscles, although, again, values reached significance in only one muscle (PL). Thus, in addition to biomechanical effects, differences in hopping performance may also be determined by diverse physiological properties of the muscles.