1978] 
Morris & G wynne — Cyphoderris 
163 
different males provide the other 6 points. C. bucked? s regression is 
based on 12 different individuals, 3 at two different temperatures 
each. Each of the 13 C. strepitans pulse rates derives from a different 
individual; all those at temperatures of 8°C and below are field 
recordings. Pulse rates were calculated from an oscilloscope display 
in which a single beam sweep embraced 3-13 pulses. Successive, 
single-sweep samples (3-6), were averaged to obtain each plotted 
value. The coefficients of determination indicate a very good fit to 
the calculated regression lines. Although the C. monstrosa regres- 
sion line is different from the strepitans and buckelli lines the slopes 
and Y intercepts of the latter two species are not significantly 
different. 
C. strepitans males stridulate at very low temperatures. Previous 
reports cite minimal singing temperatures for acoustic Orthoptera 
of about 7°C [e.g. Fulton (1925) for the tree cricket Oecanthus 
fultoni (under the name of O. niveus) and Frings and Frings (1957) 
for the katydid Neoconocephalus ensiger ]. On May 17, 1977, at the 
holotypic site, one of us (D.T.G.) heard three of four males singing 
from branches and logs near the ground when the air temperature at 
waist level was —0.5° C. On June 4 and 5, 1978, tape recordings were 
made of males singing at temperatures as low as 2° C (see Figure 8). 
Following the recording the thermometer bulb was placed close to 
the singing male’s perch. There is a suggestion in the plotted rates in 
Figure 8 of a departure from linearity at very low temperatures. 
In conclusion, the song of C. monstrosa differs from the other 
two species in both the shape of the pulse amplitude envelope and in 
pulse rate, both these parameters being useful diagnostic features. 
C. buckelli and C. strepitans, however, have virtually identical 
calling songs: song intensities, carrier frequencies, and pulse ampli- 
tude envelopes provide no basis for human discrimination; the pulse 
rates, especially, are indistinguishable at any given temperature. 
It is interesting to note that Alexander (1969) has questioned the 
traditional interpretation that reproductive isolating mechanisms 
evolved to prevent “mating mistakes” between species. He suggested 
(citing evidence from acoustical insects) that species differences 
have most likely arisen as a result of the different selection pressures 
operating on populations while they are in allopatry. He reasoned 
that if this is so, among other things, we should rarely find identical 
pair forming signals among allopatric or allochronic species. C. 
strepitans and C. buckelli are allopatric (Figure 5) and by the above 
