3175 The Journal of Experimental Biology 206, 3175-3186
©2003 The Company of Biologists Ltd顺利的祝福语
doi:10.1242/jeb.00534
长胎不长肉的食物
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T. Matheson and V. Dürr
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Load compensation in locusts
Bi Proximal femur loa d e d
D i st al t i b ia loa d e d
st al femur loa d e d
A i
N o loa d
5 mm
z
学习焦裕禄
A ii
z进退维艰
母鸡教案x
C i Bii
D ii
x 2. Loading had little effect on the overall pattern of leg movement. Two example scratches are shown for each experimental
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Results
To asss the effect of load on the ability of locusts to make aimed movements of their hind legs, a mass of 142mg was attached to different locations on the leg (Fig.1A,B). This effectively doubled the total mass of the leg and, in particular, when the mass was added to the distal end of the tibia, it incread the mass of this gment from 19 to 161mg (an 8.5-fold increa). The rotational moment of inertia for a joint depends on the square of the distance of the centre of mass from the axis of rotation. Each load position that we ud therefore resulted in different changes in rotational moment of inertia at each joint (Table1.) For example, loading the tibia caud an 11.6-fold increa in rotatio
nal inertia for the femur-tibia joint, but a 6.4-fold increa for the thorax–coxa joint (Table1).
The effect of load on limb trajectory
Locusts made aimed scratching movements of a hind leg (e.g. Fig.1C) in respon to tactile stimuli at one of two target sites on the dorsal surface of the ipsilateral forewing (the outermost surface when the wings are folded into the normal resting posture, Fig.1A). The leg always started from the same position, which was defined by a small rod on which was placed the animal’s tarsus (Fig.1A).
Stimulation of the distal (posterior) site elicited movements in which the tarsus was lifted and moved posteriorly towards the target before making a variable number of cyclical movements in the vicinity of the target (Fig.2Ai). Stimulation of the proximal (anterior) site elicited movements in which the tarsus was lifted and moved approximately vertically towards the target before again making cyclic movements largely dorsal to the animal (Fig.2Aii). Only the first three cycles were analyd. For a detailed analysis of unloaded scratching movements and their natural variability, e Matheson (1997, 1998) and Dürr and Matheson (2003).
Addition of a 142mg load to the proximal femur, distal femur or distal tibia had no effect on the general form of scratching movements for either target site (compare Fig.2Ai,ii with Bi,ii, Ci,ii and Di,i
i). Slight variations in the movements illustrated in Fig.2 fall well within the variance en in unloaded scratches, as we go on to demonstrate in the following ctions.
To examine the movements in more detail we analyd parately the initial 200ms of movement that formed the outgoing trajectory and the remaining part of the movement during which the tarsus followed a cyclical path. The u of 200ms as a cut-off criterion is justified quantitatively in Dürr and Matheson (2003). It is the mean duration of the outgoing trajectory. When the leg was unloaded the median direction of movement in the first 200ms was 112°for scratches elicited by stimulation of the anterior site (black vector in Fig.3A), and 134°for scratches elicited by stimulation of the posterior site (black vector in Fig.3B). Loading the leg had no significant effect on initial movement direction (coloured vectors and curved lines in Fig.3A,B: Dunnett’s two sided t-test for each treatment versus control, 453 scratches from three animals pooled; all values of P>0.05). Each animal was also analyd parately. For movements to the anterior site, loading the distal femur caud a significant increa in the angle of movement for one animal (Dunnett’s t-test, P=0.005, N=28 unloaded, nine loaded scratches), but a decrea in the cond (P=0.047, N=36, 15), and had no effect in the third (P=0.089, N=57, 10). For movements to the posterior site loading the distal femur caud a significant reduction in the angle of initial movement in one animal (P=0.005, N=43, 12). N
o other load condition caud any significant difference in initial movement direction in any animal (all values of P>0.05).
In the unloaded condition, 89% of scratches aimed at the anterior target site had three or more cyclical loops (Fig.4A). Loading the proximal or the distal femur led to a small but non-significant reduction in the relative frequency of occurrence of scratches with three loops (black bars in Fig.4A: χ2=14.7, 9 d.f., P>0.05). Only 40% of unloaded movements aimed at the posterior target had three loops, with most of the remainder having one or two loops (Fig.4B). Once again, loading the leg caud a small but non-significant reduction in the proportion of scratches with three loops when compared to the unloaded condition (black bars in Fig.4B: χ2=16.9, 9 d.f., P>0.05).
What part of the leg is aimed?
When the leg is unloaded the part of the leg that is most reliably aimed at the stimulus, irrespective of stimulus location, is the distal end of the tibia (Dürr and Matheson, 2003). To test
T. Matheson and V. Dürr
Table1. Effect of load on rotational moment of inertia
第十一个妈妈Site of load
Joint Unloaded Proximal femur Distal femur Distal tibia
Thorax–coxa3896243289 (1.1)103265 (2.7)247260 (6.4)
Coxa–trochanter2717627744 (1.0)73184 (2.7)197860 (7.3)
Femur–tibia484656108 (11.6)
诉讼时效司法解释Values are mg mm2 (N=5 animals).
Numbers in parenthes indicate the factor of increa in rotational inertia caud by each load. The basis of the calculation is as follows: Coxa: mass 7.8mg, length 3.6mm, centre of mass 1.8mm. Femur: 107.8mg, 20.0mm, 7.3mm. Tibia: 19.0mg, 21.0mm, 12.6mm. Tarsus: 3.3mg, 6.8mm, 3.4mm. Load: 142mg, centred 2mm from end of limb gments. Leg posture: thorax–coxa joint angle 11.8°, coxa–trochanter joint angle 27.8°, femur–tibia joint angle 125.2°, tibia–tarsus joint angle 45.2°(all as required to reach the mean position of the posterior stimulus site).
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Load compensation in locusts
3180T. Matheson and V. Dürr
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