PROGRESS IN PROTOZOOLOGY

THE MOLECULAR DIVERSITY OF TETRAHYMENA PYRIFORMIS 253
Table 5
The locations of the contractile vacuole pores on the cell surface,
measured as the fraction of the circumference of the cell from the
oral kinety
Species
Mean Location of CVP's
% of Cell Circumference
Amicronucleate species
T. pyriformis (A) 22.5
T. elliotti (B) 23.5
T. furgasoni (C) 24.5
T. Iwoffi (E) 24.8
Micronucleate species
T. thermophila (1) 21.3*
T. americcinis (2) 24.9
T. borealis (3) 22.0
T. hegewischi (5) 24.5
T. canadensis (7) 22.5
^ • ( 6 > 23.9
T. pigmentosa ^
23.8
T. tropicalis (9) 24.5
T. hyperangnlaris (10) 29.8*
T. austral is (11) 24.3
T. capricornis (12) 24.8
T. sonneborni (13) 24.6
T. nipissingi (14) 29.7
N a n n e y et al. (1980).
* indicate extreme values.
cients of variation. Moreover, the DNA content is slightly heritable in
vegetative growth; a cell with low content tends to produce daughters
with low content. Rectification occurs episodically, by means of an added
round of DNA synthesis or an additional cell division without an intervening
S phase. Nevertheless, the subline variability in DNA content
is large enough to cast doubt on the significance of the differences in
the means. DNA content is not a useful diagnostic character.
The measurements of DNA content in other species show that the
entire genus is similar in scale, though differences in other characteristics
are well established. The high coefficients of variation in the other
species indicate that DNA content is regulated in much the same imprecise
way as in the T. pyrijormis species cluster.
Generally, attempts to distinguish among the species of this cluster
using gross organismic characters have had limited success. Either the
species are tightly clustered according to some numerical measure, or
they show no variation at all. Charles Ray Jr. (1956), for example,
studied the chromosomes in the micronuclei of several species (T. thermo-
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