pIes were made between populations. The number of
eggs initially contained within samples is unknown.
Ethogram
Initial observations of behavior were compiled into
an ethogram of clam shrimp behavior following the
guidelines outlined in Martin & Bateson (1993).
Clam shrimp time budget
The LTER Playa population was the only population
used for the remainder of the study due to the availability of information on population dynamics for this site
under field conditions. Individual LTER Playa clam
shrimp were uniquely marked using a small dot of
Testers enamel paint. Clam shrimp molt from the inside
of the carapace so paint marks are not lost with subsequent molts and provide a fairly permanent means of
identification. Though clam shrimp can be sexed within three days of hatching, they cannot be marked for
individual identification until five days after hatching
when the carapace no longer collapses when paint is
applied.
Sample groups were established in the laboratory and housed in plastic mouse cages. The bottoms
of the cages were lined with 1 cm of 'clean' sand
(i.e., sand free from Branchiopod eggs). Groups were
composed of seven hermaphrodites and three males
to reflect natural population sex ratios (see Results).
The tanks were monitored using instantaneous scan
sampling techniques as described by Altmann (1974).
During each scan, the behavior of each clam shrimp
was recorded during that moment in time. The order in
which the clam shrimp were scanned was determined
haphazardly based upon the order in which individuals
came into view. Each tank was scanned six times a day
at one hour intervals until less than half of the individuals (4 clam shrimp) remained within the sample
population. Clam shrimp that died within the first two
days of scanning were replaced with clam shrimp of
the same sex and hatch date. Three control tanks were
set up with the same sex ratios as the sample tanks but
with minimal handling of the clam shrimp and no paint
marking to determine whether handling and marking
techniques had an adverse effect on life span.
Mating behavior
Other behavioral observations of E. texana were conducted using the focal animal technique outlined
Table 1. Sex ratios and number of viable eggs hatching
within four populations of an androdioecious clam shrimp
Eulimnadia texana from 250 ml soil samples.
Population # of x±s.d.
Total # of
Percentages
tanks clam shrimp indo hatched herm.: males
LTER
10
l7±7.2
170
70:30
SWP3
10
37±8.8
374
100:0
SWP4
10
34±5.0
342
60:40
SWP5
10
30±7.6
328
58:42
75
by Altmann (1974). Groups consisting of either a
male and a non-gravid hermaphrodite, two males
and a non-gravid hermaphrodite, or two non-gravid
hermaphrodites and a male, were collected from rearing tanks and isolated in a plastic 'dixie' cup containing
125 ml of aged tap water. Pairs were observed using
focal animal observation techniques for two hours and
all interactions were recorded. If the two hour observation was complete and either outcrossing or selfing
appeared to be eminent, the observation was extended
to include observation of egg fertilization. No observation ever lasted longer than 2 hours and 25 minutes.
Each focal animal was only used once.
Analysis
Data are presented as means (±sd). For statistical procedures, an a level <0.05 is considered significant
throughout this study.
Results
Sex ratios
The sex ratios for the four populations are presented in
Table 1. In SWP4, SWP5, and the LTER population,
sex ratios were skewed in favor of hermaphrodites.
No males were ever found in the SWP3 population.
Table 1 also provides the average number of clam
shrimp hatching from a 250 ml soil sample for each
population. There is no significant difference in total
viable eggs hatching between the SWP3, SWP4 and
SWP5 populations (X 2 =3.l9, df=2, P>O.l). The
LTER Playa population had a significantly lower number of eggs hatch, however, when compared to the three
puddle populations (X 2 = 81.9, df= 3, P
eggs initially contained within samples is unknown.
Ethogram
Initial observations of behavior were compiled into
an ethogram of clam shrimp behavior following the
guidelines outlined in Martin & Bateson (1993).
Clam shrimp time budget
The LTER Playa population was the only population
used for the remainder of the study due to the availability of information on population dynamics for this site
under field conditions. Individual LTER Playa clam
shrimp were uniquely marked using a small dot of
Testers enamel paint. Clam shrimp molt from the inside
of the carapace so paint marks are not lost with subsequent molts and provide a fairly permanent means of
identification. Though clam shrimp can be sexed within three days of hatching, they cannot be marked for
individual identification until five days after hatching
when the carapace no longer collapses when paint is
applied.
Sample groups were established in the laboratory and housed in plastic mouse cages. The bottoms
of the cages were lined with 1 cm of 'clean' sand
(i.e., sand free from Branchiopod eggs). Groups were
composed of seven hermaphrodites and three males
to reflect natural population sex ratios (see Results).
The tanks were monitored using instantaneous scan
sampling techniques as described by Altmann (1974).
During each scan, the behavior of each clam shrimp
was recorded during that moment in time. The order in
which the clam shrimp were scanned was determined
haphazardly based upon the order in which individuals
came into view. Each tank was scanned six times a day
at one hour intervals until less than half of the individuals (4 clam shrimp) remained within the sample
population. Clam shrimp that died within the first two
days of scanning were replaced with clam shrimp of
the same sex and hatch date. Three control tanks were
set up with the same sex ratios as the sample tanks but
with minimal handling of the clam shrimp and no paint
marking to determine whether handling and marking
techniques had an adverse effect on life span.
Mating behavior
Other behavioral observations of E. texana were conducted using the focal animal technique outlined
Table 1. Sex ratios and number of viable eggs hatching
within four populations of an androdioecious clam shrimp
Eulimnadia texana from 250 ml soil samples.
Population # of x±s.d.
Total # of
Percentages
tanks clam shrimp indo hatched herm.: males
LTER
10
l7±7.2
170
70:30
SWP3
10
37±8.8
374
100:0
SWP4
10
34±5.0
342
60:40
SWP5
10
30±7.6
328
58:42
75
by Altmann (1974). Groups consisting of either a
male and a non-gravid hermaphrodite, two males
and a non-gravid hermaphrodite, or two non-gravid
hermaphrodites and a male, were collected from rearing tanks and isolated in a plastic 'dixie' cup containing
125 ml of aged tap water. Pairs were observed using
focal animal observation techniques for two hours and
all interactions were recorded. If the two hour observation was complete and either outcrossing or selfing
appeared to be eminent, the observation was extended
to include observation of egg fertilization. No observation ever lasted longer than 2 hours and 25 minutes.
Each focal animal was only used once.
Analysis
Data are presented as means (±sd). For statistical procedures, an a level <0.05 is considered significant
throughout this study.
Results
Sex ratios
The sex ratios for the four populations are presented in
Table 1. In SWP4, SWP5, and the LTER population,
sex ratios were skewed in favor of hermaphrodites.
No males were ever found in the SWP3 population.
Table 1 also provides the average number of clam
shrimp hatching from a 250 ml soil sample for each
population. There is no significant difference in total
viable eggs hatching between the SWP3, SWP4 and
SWP5 populations (X 2 =3.l9, df=2, P>O.l). The
LTER Playa population had a significantly lower number of eggs hatch, however, when compared to the three
puddle populations (X 2 = 81.9, df= 3, P