210
WILLIAM MACNAE
U . vocans always inhabits open flats and only rarely occurs under the
shelter of any vegetation.
I n September the upper lethal temperature was lower by 2°C than
it was in January. There is then, some degree of acclimatization to the
higher summer temperatures. L4 similar acclimatization has been shown
by Vernberg and Tashian (1959) to occur in the fiddler crabs of the
eastern American salt marshes.
Edney mentions no acclimatization towards low temperatures. At
Inhaca the lower lethal temperatures lay between 7°C and 8.5"C with
U. urvi l l ei
and U. gaimardi showing the lowest. This is consistent with
the fact that in South Africa these two species extend farther to the
south than any of the others (Macnae, 1963). This distribution into
areas where air and water temperatures in estuaries reach levels below
the lower lethal limit a t Inhaca suggests that these two species at least
are capable of acclimatization to low temperatures. Ono (1965) records
that U. lactea hibernates in Japan!
Edney's work also gives an explanation for the distribution at
Inhaca of these five species. From this one may deduce that all species
of Uca which are restricted to shady places will behave to temperature
as do U . urvi l l ei
and U . gaimardi and also that those preferring open
sunny glades will show upper lethal temperatures closer to those of
U . lactea f. annulipes and U . inversa. Verwey (1930) recorded that for
U . bellator (= U . signatus) and U . consobrinus (de Man) the highest
near-lethal temperature in gradually rising temperatures was 42°C.
These two species show a distribution pattern similar to U . inversa and
U . lactea f. annulipes : U . bellator resembling U . iwversa but occurring
on flats of finer particles.
Edney also studied, on a small number of specimens only, and in
what amounted to a pilot experiment, the relationships of these five
species to loss of weight by transpiration of water. U . urvillei and U .
vocans lost weight most rapidly ; U . lactea f. annulipes and U . inversa
least rapidly with U . gaimardi intermediate. This again is consistent with
their known habits of exposure and distribution in the mangal of Inhaca.
Although no experimental work appears to have been done on the
transpiration rates or on the lethal temperatures of the other crabs in
the mangal, one may presume that most would resemble U . gaimardi
or even U . urvillei for most of the mangrove crabs live in shady situations and rarely expose themselves t o the sun in the way U . inversa,
U . bellator or U . lactea (either form) do.
No figures are a t present available which compare the humidity of
the air within a mangal with that in the neighbourhood but outside the
mangal, it may be assumed to 'Me higher,
WILLIAM MACNAE
U . vocans always inhabits open flats and only rarely occurs under the
shelter of any vegetation.
I n September the upper lethal temperature was lower by 2°C than
it was in January. There is then, some degree of acclimatization to the
higher summer temperatures. L4 similar acclimatization has been shown
by Vernberg and Tashian (1959) to occur in the fiddler crabs of the
eastern American salt marshes.
Edney mentions no acclimatization towards low temperatures. At
Inhaca the lower lethal temperatures lay between 7°C and 8.5"C with
U. urvi l l ei
and U. gaimardi showing the lowest. This is consistent with
the fact that in South Africa these two species extend farther to the
south than any of the others (Macnae, 1963). This distribution into
areas where air and water temperatures in estuaries reach levels below
the lower lethal limit a t Inhaca suggests that these two species at least
are capable of acclimatization to low temperatures. Ono (1965) records
that U. lactea hibernates in Japan!
Edney's work also gives an explanation for the distribution at
Inhaca of these five species. From this one may deduce that all species
of Uca which are restricted to shady places will behave to temperature
as do U . urvi l l ei
and U . gaimardi and also that those preferring open
sunny glades will show upper lethal temperatures closer to those of
U . lactea f. annulipes and U . inversa. Verwey (1930) recorded that for
U . bellator (= U . signatus) and U . consobrinus (de Man) the highest
near-lethal temperature in gradually rising temperatures was 42°C.
These two species show a distribution pattern similar to U . inversa and
U . lactea f. annulipes : U . bellator resembling U . iwversa but occurring
on flats of finer particles.
Edney also studied, on a small number of specimens only, and in
what amounted to a pilot experiment, the relationships of these five
species to loss of weight by transpiration of water. U . urvillei and U .
vocans lost weight most rapidly ; U . lactea f. annulipes and U . inversa
least rapidly with U . gaimardi intermediate. This again is consistent with
their known habits of exposure and distribution in the mangal of Inhaca.
Although no experimental work appears to have been done on the
transpiration rates or on the lethal temperatures of the other crabs in
the mangal, one may presume that most would resemble U . gaimardi
or even U . urvillei for most of the mangrove crabs live in shady situations and rarely expose themselves t o the sun in the way U . inversa,
U . bellator or U . lactea (either form) do.
No figures are a t present available which compare the humidity of
the air within a mangal with that in the neighbourhood but outside the
mangal, it may be assumed to 'Me higher,