tions at 24°C were incubated in 50 ml glass culture
dishes in a controlled temperature chamber with continuous illumination. The number of emerging nauplii
were scored every day until new no hatchings were
observed. We did not examine all the possible straintemperature combinations because only a limited number of cysts were produced at 29.5 °C for all populations, at 15°C for the La Mata, and at 24°C for the
sexual population.
The following life-history traits were calculated for
every female: the mean offspring number per brood
(OB), total offspring production per female (OF), the
number of broods (BN), the offspring produced per day
during the reproductive period (ODR), the mean interval of time between broods (lB) and the encystment
percentage (EP). Female lifespan was scored from the
very day of hatch until death (FL), the prereproductive period (PRE) from the day of hatch until the first
brood parturition day and the female reproductive period (FR) from the first to the last brood day.
Statistical analysis
Before analyses, the encystment percentage data was
normalized by arsine transformations (Sokal & Rohlf,
1981) and data from the remainder life-history traits
were also normalized by the root transformation of
Box & Cox (1964). Due to the factthatthe sexual strain
died before reproduction at 29.5 DC, we performed two
different two-way ANOVA tests for each life-history
trait. The first test was set with the three populations as
one factor and two temperatures 15 ° and 24°C as the
other factor. The second analysis was conducted with
the two parthenogenetic populations as one factor and
the three temperatures studied as the other. The relationship between the length of the reproductive period
and the total offspring production for every strain was
tested by a linear regression analysis (Sokal & Rohlf,
1981).
The analyses performed on the FL included all
replicates. In the Case of OB, BN, EP, PRE and FR the
replicates which had not produced at least one brood
were eliminated since the above mentioned variables
could not be obtained. To calculate IB, the repliactes
with less than two broods were excluded for the same
reason. ODR was not scored in those repliactes with
only one brood since in that case OB and ODR had the
same values.
When there were significant differences at P:::;0.05
for any of the factors means were compared with the
Tukey's multiple range test (Sokal & Rohlf, 1981).
297
Results
Lifespan components
The relationship between time needed for females to
reach maturity and temperature (Fig. 1) is not strictly linear (Tables 2, 4). Maturation times at 24°C are
one-half those at 15°C, but remain at the same level at
29.5 DC. The sexual popUlation has the shortest maturation period and the La Trinidad population the longest
one (Tables 2, 4). For parthenogenetic and the sexual
populations respectively, the length of the reproductive period and lifespan show a different response to
temperature (Fig. 1). The sexual population presents
the maximum values at 15°C, whereas values from
the La Mata and the La Trinidad populations peak
at 24°C (Fig. 1). The La Trinidad population has the
longest reproductive and lifespan period and the sexual
popUlation the shortest (Tables 2, 4). Full development
of sexual individuals at 29.5 °C was never obtained
due to premature mortality, as it can be observed with
its short lifespan (Fig. 1).
The reproductive period as a percentage of lifespan
is not constant, but shifts with temperature (Fig. 2). The
reproductive period of parthenogenetic popUlations, as
a ration of total lifespan, reaches its peak values at
24°C, while for the sexual population it is maintained
constant, near 40% of lifespan at 15 °C and 24°C. For
all populations except La Mata at 29.5 DC, the amount
of time spent in reproduction is significantly and positively (P<0.05) to their reproductive output.
Reproductive traits
Interbrood interval as well as the rate of offspring production per day during the reproductive period (Fig. 3)
show similar response to temperature for all populations. This fact is reflected statistically by the lack of
interaction (Tables 1, 3). However, there are significant differences among the three populations studied.
The sexual population has the shortest interbrood interval and the La Trinidad population the lowest rate of
offspring produced per day (Tables 1,3).
Different responses to temperature were evident
between parthenogenetic and sexual populations in
the number of broods, offspring production per brood
and the total offspring production per female (Fig. 4;
Table 1). Parthenogenetic populations achieve the
highest values for these variables at 24°C (Fig. 4,
Table 3), and the sexual population shows little variation between 15 ° and 24°C (Fig. 4). The sexual and
dishes in a controlled temperature chamber with continuous illumination. The number of emerging nauplii
were scored every day until new no hatchings were
observed. We did not examine all the possible straintemperature combinations because only a limited number of cysts were produced at 29.5 °C for all populations, at 15°C for the La Mata, and at 24°C for the
sexual population.
The following life-history traits were calculated for
every female: the mean offspring number per brood
(OB), total offspring production per female (OF), the
number of broods (BN), the offspring produced per day
during the reproductive period (ODR), the mean interval of time between broods (lB) and the encystment
percentage (EP). Female lifespan was scored from the
very day of hatch until death (FL), the prereproductive period (PRE) from the day of hatch until the first
brood parturition day and the female reproductive period (FR) from the first to the last brood day.
Statistical analysis
Before analyses, the encystment percentage data was
normalized by arsine transformations (Sokal & Rohlf,
1981) and data from the remainder life-history traits
were also normalized by the root transformation of
Box & Cox (1964). Due to the factthatthe sexual strain
died before reproduction at 29.5 DC, we performed two
different two-way ANOVA tests for each life-history
trait. The first test was set with the three populations as
one factor and two temperatures 15 ° and 24°C as the
other factor. The second analysis was conducted with
the two parthenogenetic populations as one factor and
the three temperatures studied as the other. The relationship between the length of the reproductive period
and the total offspring production for every strain was
tested by a linear regression analysis (Sokal & Rohlf,
1981).
The analyses performed on the FL included all
replicates. In the Case of OB, BN, EP, PRE and FR the
replicates which had not produced at least one brood
were eliminated since the above mentioned variables
could not be obtained. To calculate IB, the repliactes
with less than two broods were excluded for the same
reason. ODR was not scored in those repliactes with
only one brood since in that case OB and ODR had the
same values.
When there were significant differences at P:::;0.05
for any of the factors means were compared with the
Tukey's multiple range test (Sokal & Rohlf, 1981).
297
Results
Lifespan components
The relationship between time needed for females to
reach maturity and temperature (Fig. 1) is not strictly linear (Tables 2, 4). Maturation times at 24°C are
one-half those at 15°C, but remain at the same level at
29.5 DC. The sexual popUlation has the shortest maturation period and the La Trinidad population the longest
one (Tables 2, 4). For parthenogenetic and the sexual
populations respectively, the length of the reproductive period and lifespan show a different response to
temperature (Fig. 1). The sexual population presents
the maximum values at 15°C, whereas values from
the La Mata and the La Trinidad populations peak
at 24°C (Fig. 1). The La Trinidad population has the
longest reproductive and lifespan period and the sexual
popUlation the shortest (Tables 2, 4). Full development
of sexual individuals at 29.5 °C was never obtained
due to premature mortality, as it can be observed with
its short lifespan (Fig. 1).
The reproductive period as a percentage of lifespan
is not constant, but shifts with temperature (Fig. 2). The
reproductive period of parthenogenetic popUlations, as
a ration of total lifespan, reaches its peak values at
24°C, while for the sexual population it is maintained
constant, near 40% of lifespan at 15 °C and 24°C. For
all populations except La Mata at 29.5 DC, the amount
of time spent in reproduction is significantly and positively (P<0.05) to their reproductive output.
Reproductive traits
Interbrood interval as well as the rate of offspring production per day during the reproductive period (Fig. 3)
show similar response to temperature for all populations. This fact is reflected statistically by the lack of
interaction (Tables 1, 3). However, there are significant differences among the three populations studied.
The sexual population has the shortest interbrood interval and the La Trinidad population the lowest rate of
offspring produced per day (Tables 1,3).
Different responses to temperature were evident
between parthenogenetic and sexual populations in
the number of broods, offspring production per brood
and the total offspring production per female (Fig. 4;
Table 1). Parthenogenetic populations achieve the
highest values for these variables at 24°C (Fig. 4,
Table 3), and the sexual population shows little variation between 15 ° and 24°C (Fig. 4). The sexual and