54
A. R. MAIN
finzd-tas
dorsdicr dig8 burrows in sandy situations. The desert
species L. qenceri occupies sandy river couraea. Both could presumably
rehydrate in the same way that Heleioporus eyrei does.
All the foregoing obeorvationa help in understanding why there ia no
significant difference between burrowing species in per cent loss of body
weight a t death (Bentley et al., 1958, Main and Bentley, 1904). Differences in speed of rehydration after dehydration to 76% of initial body
weight a;e significant. Bentley et al. (1958) and Main and Bentley (1964)
have compared rates of rehydration of a number of speaiea of frogs of
the following genera: Hyla, C y c h a m , Noladen, Neobatrachua, and
Hekiopmm (see Table I V for summary).
The four species of Hyla tested, rehydrated aa follows (rng waterfcm2
body surface/h): H. 7nowei 142, H . mrulea 109, and H. latoplnu&z 97.
This speed of rehydration waa significantly faster (p < 0.01) than for
Hyla rubcUa (66) which compares with Heleiopma parnmuphilus (44),
H . irwrndus (56), H . eyrei (52-6), H . austrdiacw, (60), H . albq?runctatus
(57.7), Nwbatrachzcs pelobatoidea ( 3 3 ) and N . txntral& (65.7). Species
whose speed of rehydration is greater than H. rubella are Neobatrachua
8utor (84-8), Cycloraraa platycelpira2ua (92) and Neobatrcrchw, ZOihmorei
(99.4). The differences in rates of rehydration between Hekiopoms
species are not significant. The differences between N . plobatride.9 and
N . centralis are Significant (p < 0.01), between N. centralis and N. sutor
significant ( p < O e O l ) , and between N . gutor and N . wilsmorei not
significant. These data suggest that in droughts of several years’ duration desiccation does occur and is sufficiently common for natural
selection to produce different rates of water uptake in dehydrated
animals of different species.
Field observations show that some desert frogs such as Cyclot.ana
and Neobatrachus breed shortly after rainfall. In one obsemed case
Neobatruchu8 species bred a t dusk within a few hours of rain having
fallen ir a thunderstorm. An hour and a half after dusk, breeding was
terminated by a fall in air and water temperature. Bmedmg was not
resumed on subsequent nights. While breeding is reetricted to such
brief episodes it is easy to see the advantage to a partly dehydrated
frog of being able to rehydrate rapidly and enter a breeding congress
quickly and it is thought that speed of rehydration is a biologically
relevant uleasure of the fitness of a frog species for life in arid and
demrt conditions. A eimilar conclusion WM reached by Warburg (1906).
E. CONSPECTUS O F ADAPTATIOWS TO ARIDITY
The adaptation of a species to arid environmente is likely to result
from a combination of characters. For example fecundity, length of
A. R. MAIN
finzd-tas
dorsdicr dig8 burrows in sandy situations. The desert
species L. qenceri occupies sandy river couraea. Both could presumably
rehydrate in the same way that Heleioporus eyrei does.
All the foregoing obeorvationa help in understanding why there ia no
significant difference between burrowing species in per cent loss of body
weight a t death (Bentley et al., 1958, Main and Bentley, 1904). Differences in speed of rehydration after dehydration to 76% of initial body
weight a;e significant. Bentley et al. (1958) and Main and Bentley (1964)
have compared rates of rehydration of a number of speaiea of frogs of
the following genera: Hyla, C y c h a m , Noladen, Neobatrachua, and
Hekiopmm (see Table I V for summary).
The four species of Hyla tested, rehydrated aa follows (rng waterfcm2
body surface/h): H. 7nowei 142, H . mrulea 109, and H. latoplnu&z 97.
This speed of rehydration waa significantly faster (p < 0.01) than for
Hyla rubcUa (66) which compares with Heleiopma parnmuphilus (44),
H . irwrndus (56), H . eyrei (52-6), H . austrdiacw, (60), H . albq?runctatus
(57.7), Nwbatrachzcs pelobatoidea ( 3 3 ) and N . txntral& (65.7). Species
whose speed of rehydration is greater than H. rubella are Neobatrachua
8utor (84-8), Cycloraraa platycelpira2ua (92) and Neobatrcrchw, ZOihmorei
(99.4). The differences in rates of rehydration between Hekiopoms
species are not significant. The differences between N . plobatride.9 and
N . centralis are Significant (p < 0.01), between N. centralis and N. sutor
significant ( p < O e O l ) , and between N . gutor and N . wilsmorei not
significant. These data suggest that in droughts of several years’ duration desiccation does occur and is sufficiently common for natural
selection to produce different rates of water uptake in dehydrated
animals of different species.
Field observations show that some desert frogs such as Cyclot.ana
and Neobatrachus breed shortly after rainfall. In one obsemed case
Neobatruchu8 species bred a t dusk within a few hours of rain having
fallen ir a thunderstorm. An hour and a half after dusk, breeding was
terminated by a fall in air and water temperature. Bmedmg was not
resumed on subsequent nights. While breeding is reetricted to such
brief episodes it is easy to see the advantage to a partly dehydrated
frog of being able to rehydrate rapidly and enter a breeding congress
quickly and it is thought that speed of rehydration is a biologically
relevant uleasure of the fitness of a frog species for life in arid and
demrt conditions. A eimilar conclusion WM reached by Warburg (1906).
E. CONSPECTUS O F ADAPTATIOWS TO ARIDITY
The adaptation of a species to arid environmente is likely to result
from a combination of characters. For example fecundity, length of