76
Ethogram
The major types of behaviors observed in initial observations are listed and described in Table 2. Behavioral categories have been broken down into those
common to both reproductive forms, those specific
to hermaphrodites, and those specific to males.
Clam shrimp time budget
Tanks were scanned over a period of 11 days for a
total of 7 hours and 33 minutes of observations. Time
budgets were computed for both males (N = 12) and
hermaphrodites (N = 28) using the methods outlined
in Martin & Bateson (1993). These results are summarized in Fig. 1. No distinction was made between
feeding and swimming behaviors because the two
occur simultaneously. These activities were the primary behaviors for both sexual forms.
The reproductive status of the hermaphrodites
was recorded during each scan. Hermaphrodites were
gravid 72% of the observation time. Hermaphrodites
appear to dig burrows and may drop their clutches
underground. On several occasions, males were seen
entering burrows, but I never saw males digging their
own. In six instances, males were seen clasping gravid
hermaphrodites just prior to egg laying. This may be a
form of pre-mate guarding.
Mortality rates were calculated for both the scan
tanks and the control tanks. There was no difference in
mortality rates between the two tank types (X 2 = l.28,
df= 1, P>0.2). Pooling all tanks, male mortality was
higher than that of hermaphrodites (X 2 = 4.51, df= 1,
P<0.05), especially starting on day 8 of life (Fig. 2).
On average, hermaphrodites lived 50% longer than
males. Each population was initially set up with a 3:7
ratio of males to hermaphrodites. By the end of the
observations, there was a 1:4 ratio in each of the scan
tanks. Pennak (1989) reported that Eubranchiopoda
males typically die within an hour after outcrossing.
This was not true for E. texana and probably not for
other Eubranchiopoda as well (Belk, pers. comm.).
Clam shrimp mating behavior
During focal animal studies (N = 178 groups), outcrossing occurred 95 times (53%), selfing occurred
20 times (11 %) and no fertilization was evident either
due to selfing or to outcrossing in 63 of the observations (35%) (Fig. 3). In 46 of these cases, no contact was seen between the male and the hermaphrodite
during the two hour observation period. In all other cases, the male periodically clasped the carapace
of a non-gravid hermaphrodite for several seconds at
a time (first clasping by males; X= 8±1O.2 min after
isolation; range 0-35 min; N = 132). Whenever the
hermaphrodite struggled, the male released his hold
and outcrossing did not occur (N= 37). At other times
the hermaphrodite did not struggle when clasped by
the male, but instead, passively allowed the male to
push it around the cup (N = 95). The hermaphrodite'S
legs would continue to beat, suggesting active feeding,
but it's antennae would remain motionless, suggesting
that the male was providing all active locomotion for
the pair (for definitions of 'swimming' and 'feeding'
see Table 1). This behavior was always a precursor to
outcrossing. The average pre-outcrossing clasp time
for these observations was 27 ±36.8 min (range = 2120 min; N = 95). Near the end of the clasping period,
the male forced much of his lower body up into the
hermaphrodite'S carapace by the ovaries and began to
make thrusting movements with the posterior portion
of his abdomen (x=26±lOA thrusts; range = 15-41
thrusts; counts made for 52 observations). In all cases
(N = 95), the eggs moved out of the ovary and up into
the brood chamber while the male was thrusting, suggesting that this is when sperm transfer and fertilization
occur. As soon as the eggs entered the brood chamber,
the male released the hermaphrodite and outcrossing
was assumed to have occurred. Male thrusting and egg
movement are both visible under the microscope. In 94
of the outcrossings, hermaphrodite molting occurred
prior to fertilization, (x molting = ll±5.8 min prior to
fertilization; range = 6-20 min; N = 94). In the 95th
outcrossing, no molting was seen during the observation but the clasping male began to thrust into the
hermaphrodite'S carapace anyway and egg movement
still followed.
In the 20 observations in which selfing occurred,
the males performed periodic clasping of the
hermaphrodite's carapace for several seconds at a time
but the hermaphrodites always struggled and the males
never clasped the hermaphrodites for extended periods
of time (> 1 min). Prior to selfing, the hermaphrodite
lay motionless on the substrate for up to several hours
(x=65.3±34.6 min; range = 13-120+ min; N=20).
Molting occurred on average 12.1±4.9 minutes prior to selfing (range = 2-22 min; N = 20) and then the
eggs moved into the brood chamber. No male ever
attempted to clasp these hermaphrodites after they had
molted.
Ethogram
The major types of behaviors observed in initial observations are listed and described in Table 2. Behavioral categories have been broken down into those
common to both reproductive forms, those specific
to hermaphrodites, and those specific to males.
Clam shrimp time budget
Tanks were scanned over a period of 11 days for a
total of 7 hours and 33 minutes of observations. Time
budgets were computed for both males (N = 12) and
hermaphrodites (N = 28) using the methods outlined
in Martin & Bateson (1993). These results are summarized in Fig. 1. No distinction was made between
feeding and swimming behaviors because the two
occur simultaneously. These activities were the primary behaviors for both sexual forms.
The reproductive status of the hermaphrodites
was recorded during each scan. Hermaphrodites were
gravid 72% of the observation time. Hermaphrodites
appear to dig burrows and may drop their clutches
underground. On several occasions, males were seen
entering burrows, but I never saw males digging their
own. In six instances, males were seen clasping gravid
hermaphrodites just prior to egg laying. This may be a
form of pre-mate guarding.
Mortality rates were calculated for both the scan
tanks and the control tanks. There was no difference in
mortality rates between the two tank types (X 2 = l.28,
df= 1, P>0.2). Pooling all tanks, male mortality was
higher than that of hermaphrodites (X 2 = 4.51, df= 1,
P<0.05), especially starting on day 8 of life (Fig. 2).
On average, hermaphrodites lived 50% longer than
males. Each population was initially set up with a 3:7
ratio of males to hermaphrodites. By the end of the
observations, there was a 1:4 ratio in each of the scan
tanks. Pennak (1989) reported that Eubranchiopoda
males typically die within an hour after outcrossing.
This was not true for E. texana and probably not for
other Eubranchiopoda as well (Belk, pers. comm.).
Clam shrimp mating behavior
During focal animal studies (N = 178 groups), outcrossing occurred 95 times (53%), selfing occurred
20 times (11 %) and no fertilization was evident either
due to selfing or to outcrossing in 63 of the observations (35%) (Fig. 3). In 46 of these cases, no contact was seen between the male and the hermaphrodite
during the two hour observation period. In all other cases, the male periodically clasped the carapace
of a non-gravid hermaphrodite for several seconds at
a time (first clasping by males; X= 8±1O.2 min after
isolation; range 0-35 min; N = 132). Whenever the
hermaphrodite struggled, the male released his hold
and outcrossing did not occur (N= 37). At other times
the hermaphrodite did not struggle when clasped by
the male, but instead, passively allowed the male to
push it around the cup (N = 95). The hermaphrodite'S
legs would continue to beat, suggesting active feeding,
but it's antennae would remain motionless, suggesting
that the male was providing all active locomotion for
the pair (for definitions of 'swimming' and 'feeding'
see Table 1). This behavior was always a precursor to
outcrossing. The average pre-outcrossing clasp time
for these observations was 27 ±36.8 min (range = 2120 min; N = 95). Near the end of the clasping period,
the male forced much of his lower body up into the
hermaphrodite'S carapace by the ovaries and began to
make thrusting movements with the posterior portion
of his abdomen (x=26±lOA thrusts; range = 15-41
thrusts; counts made for 52 observations). In all cases
(N = 95), the eggs moved out of the ovary and up into
the brood chamber while the male was thrusting, suggesting that this is when sperm transfer and fertilization
occur. As soon as the eggs entered the brood chamber,
the male released the hermaphrodite and outcrossing
was assumed to have occurred. Male thrusting and egg
movement are both visible under the microscope. In 94
of the outcrossings, hermaphrodite molting occurred
prior to fertilization, (x molting = ll±5.8 min prior to
fertilization; range = 6-20 min; N = 94). In the 95th
outcrossing, no molting was seen during the observation but the clasping male began to thrust into the
hermaphrodite'S carapace anyway and egg movement
still followed.
In the 20 observations in which selfing occurred,
the males performed periodic clasping of the
hermaphrodite's carapace for several seconds at a time
but the hermaphrodites always struggled and the males
never clasped the hermaphrodites for extended periods
of time (> 1 min). Prior to selfing, the hermaphrodite
lay motionless on the substrate for up to several hours
(x=65.3±34.6 min; range = 13-120+ min; N=20).
Molting occurred on average 12.1±4.9 minutes prior to selfing (range = 2-22 min; N = 20) and then the
eggs moved into the brood chamber. No male ever
attempted to clasp these hermaphrodites after they had
molted.