1976] Gittelman — Swimming Ability of Notonectidae 
321 
a greater proportion of prey stranded on the water film than do 
Buenoa, but less so than Martarega. However, since Buenoa 
and Notonecta are found in static water, one expects them to 
be more similar to each other than either is to Martarega, which 
is the case. 
Significant differences between mechanical advantages of 
Notonecta spp. were found to exist. In the present Table 1 these 
R 1 /R 2 coefficients are reproduced. The R 1 /R 2 coefficient of 
insulata, the largest backswimmer, is smallest of the species studied. 
The coefficient of lunata is smaller than that of undulata and 
irrorata, but the latter two are not significantly different from 
each other. The magnitude of R 1 /R 2 appears to increase with 
body size in all but insulata. 
If as I proposed earlier (Gittelman 1974), low values of me- 
chanical advantage are adaptations for low acceleration swim- 
ming (e.g. continual swimming against a current), then of these 
4 species of Notonecta, insulata should be best able to swim against 
a current. The following is a test of this prediction. 
Table 1. Measurements# (in mm), R t /R 2 coefficients# and the maximum water 
current where position could be maintained of 4 species of Notonecta 
(Notonectidae). Current speeds with different letters are significantly 
different at the P<0.01 level (2-tailed t-test). x, mean; s, standard 
deviation. 
Water current 
Species 
Body 
length 
r 2 
(leg length) 
R i 
(lever arm) 
R i/R 2 
(cm/sec) 
X s 
N. insulata 
14.50 
14.93 
0.458 
0.031* 
8.74 a 
2.39 
N. lunata 
9.78 
9.83 
0.317 
0.032* 
4.15 b 
1.57 
N. undulata 
11.87 
11.63 
0.390 
0.034 
6.21 c 
2.26 
N. irrorata 
13.83 
13.14 
0.471 
0.036 
4.19 b 
1.58 
#data taken from Gittelman (1974). 
* Significantly different from next R t /R 2 value at P<0.05 level (2-tailed t-test). 
