Hydrobiologia 298: 179-181, 1995.
D. Belk, H. J. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture II.
©1995 Kluwer Academic Publishers.
179
Observations on the effects of incubation at inhibitory temperature on
subsequent hatching of anostracan cysts
Denton Belk & Tannis S. Nelson
Biology Department, Our Lady of the Lake University of San Antonio, San Antonio, Texas 78207-4666, USA
Abstract
Hatching progressively decreased for cysts of Branchinecta lindahli Packard when they were incubated for 6 and
12 hours at a temperature known to inhibit hatching (30°C) prior to transfer to a favorable hatching temperature
of 15°C. Cysts of Thamnocephalus platyurus Packard, by contrast, hatched normally at 28°C after transfer from
48,72, and 96 hour incubation periods at the inhibitory low temperature of 10°C.
Introduction
Branchinecta lindahli Packard, 1883 and Thamnocephalus platyurus Packard, 1877 inhabit many of the
same temporary pool basins in the southwestern United
States (Belk, 1977). Since T. Platyurus hatches only
when these pools fill during hot weather and B. lindahli hatches only when these same pools refill during
cold weather, cysts of these two species will rehydrate
as a result of routine yearly seasonal changes during
pool filling cycles when water temperature conditions
are above or below those need for hatching. Cysts
experiencing temperatures outside those required for
hatching remain dormant. During the transition periods between seasons, it is not uncommon for weather
conditions to shift rather rapidly from cold to hot or
visa versa. In such situations, hydrated cysts originally
experiencing a period of unfavorable hatching temperature conditions could quickly experience a change to
favorable hatching temperatures without redrying. We
report on experiments testing the reaction of cyst of
these two species to temperatures that rapidly change
from inhibitory for hatching to stimulative for hatching.
Hatching decreased for B. lindahli cysts the longer
they remained hydrated at an inhibitory temperature.
This pattern of response was absent from cysts of
T. platyurus which hatched readily once they were
moved from inhibitory to stimulative temperature conditions.
Methods and materials
We used heated and refrigerated water baths in air conditioned laboratories to control temperature in hatching containers filled with deionized water as a hatching
medium. Water in the hatching containers reached test
temperatures in less than 15 minutes of being placed
in a water bath. Water level was maintained in the test
containers by frequent additions of water at the test
temperature. In testing cysts of Branchinecta lindahli,
all temperatures were accurate to within 0.25 DC. In
testing cysts of Thamnocephalus platyurus, all temperatures were accurate to within 2 dc. All experiments
were continuously illuminated with bright fluorescent
lights (cool white).
For the B. lindahli study, Belk counted replicates
of 100 cysts into each of 12 20-ml beakers. The cysts
were originally deposited in filtered habitat water by
females collected in Pima County, Arizona (DB 148)
on 8 April 1973 and stored in the same water in the
dark until counted on 20 July 1973. Belk removed all
excess water from each beaker and let them air dry
at room conditions for 19 hours. He then added about
15 ml of aerated, deionized water to each beaker placing four at 15°C and the other eight at 30 dc. Four
of the replicates in the 30°C water bath were moved
to the 15 °C water bath after 6 hours and the other
four after 12 hours. Larvae were removed and counted
each day. On 25 July, Belk removed the water from all
the beakers and redried the cysts. He then repeatedly
refilled each beaker and placed them to hatch at 15°C
through four drying and rewetting cycles. The fourth
D. Belk, H. J. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture II.
©1995 Kluwer Academic Publishers.
179
Observations on the effects of incubation at inhibitory temperature on
subsequent hatching of anostracan cysts
Denton Belk & Tannis S. Nelson
Biology Department, Our Lady of the Lake University of San Antonio, San Antonio, Texas 78207-4666, USA
Abstract
Hatching progressively decreased for cysts of Branchinecta lindahli Packard when they were incubated for 6 and
12 hours at a temperature known to inhibit hatching (30°C) prior to transfer to a favorable hatching temperature
of 15°C. Cysts of Thamnocephalus platyurus Packard, by contrast, hatched normally at 28°C after transfer from
48,72, and 96 hour incubation periods at the inhibitory low temperature of 10°C.
Introduction
Branchinecta lindahli Packard, 1883 and Thamnocephalus platyurus Packard, 1877 inhabit many of the
same temporary pool basins in the southwestern United
States (Belk, 1977). Since T. Platyurus hatches only
when these pools fill during hot weather and B. lindahli hatches only when these same pools refill during
cold weather, cysts of these two species will rehydrate
as a result of routine yearly seasonal changes during
pool filling cycles when water temperature conditions
are above or below those need for hatching. Cysts
experiencing temperatures outside those required for
hatching remain dormant. During the transition periods between seasons, it is not uncommon for weather
conditions to shift rather rapidly from cold to hot or
visa versa. In such situations, hydrated cysts originally
experiencing a period of unfavorable hatching temperature conditions could quickly experience a change to
favorable hatching temperatures without redrying. We
report on experiments testing the reaction of cyst of
these two species to temperatures that rapidly change
from inhibitory for hatching to stimulative for hatching.
Hatching decreased for B. lindahli cysts the longer
they remained hydrated at an inhibitory temperature.
This pattern of response was absent from cysts of
T. platyurus which hatched readily once they were
moved from inhibitory to stimulative temperature conditions.
Methods and materials
We used heated and refrigerated water baths in air conditioned laboratories to control temperature in hatching containers filled with deionized water as a hatching
medium. Water in the hatching containers reached test
temperatures in less than 15 minutes of being placed
in a water bath. Water level was maintained in the test
containers by frequent additions of water at the test
temperature. In testing cysts of Branchinecta lindahli,
all temperatures were accurate to within 0.25 DC. In
testing cysts of Thamnocephalus platyurus, all temperatures were accurate to within 2 dc. All experiments
were continuously illuminated with bright fluorescent
lights (cool white).
For the B. lindahli study, Belk counted replicates
of 100 cysts into each of 12 20-ml beakers. The cysts
were originally deposited in filtered habitat water by
females collected in Pima County, Arizona (DB 148)
on 8 April 1973 and stored in the same water in the
dark until counted on 20 July 1973. Belk removed all
excess water from each beaker and let them air dry
at room conditions for 19 hours. He then added about
15 ml of aerated, deionized water to each beaker placing four at 15°C and the other eight at 30 dc. Four
of the replicates in the 30°C water bath were moved
to the 15 °C water bath after 6 hours and the other
four after 12 hours. Larvae were removed and counted
each day. On 25 July, Belk removed the water from all
the beakers and redried the cysts. He then repeatedly
refilled each beaker and placed them to hatch at 15°C
through four drying and rewetting cycles. The fourth