74
to the nature of sex determination, populations typically consist of many more hermaphrodites than males
(Sassaman, 1989; pers. obs.).
Behavioral information on E. texana is largely
unavailable in the primary literature and would be a
useful supplement to ongoing evolutionary and genetic studies which are examining the significance of sex,
inbreeding and outcrossing. To that end, this contribution provides an account of male and hermaphrodite
behavior in the form of an ethogram, time budget and
detailed descriptions of mating behavior.
Methods
Study populations
Four populations of E. texana have been identified
just northeast of the Dona Ana Mountains, 40 km
NNE of Las Cruces, Dona Ana County, New Mexico.
These populations are all located within 4 km of one
another. Three of the populations are located along the
access road to the New Mexico State University College Ranch, next to South Well. These populations are
referred to as SWP3, SWP4 and SWP5 (South Well
puddle populations). Each of these sites consists of a
distinct depression less than 10 meters in length and
with a depth no greater than 1 meter at the lowest point.
SWP5 is almost directly across a dirt road, 35 m from
SWP3. SWP4 is 130 m west of SWP3 on the same
side of the road. There is sparse vegetation immediately around these puddles predominantly consisting of
various grass species. There is little to no vegetation
within the puddles themselves. These sites typically
fill with water at least once every year as a result of
summer rainfall and remain filled for three days to several weeks depending upon further water inputs (pers.
obs.). Other than E. texana, these sites are also occupied by populations of Scaphiopus couchii tadpoles,
which hatch well after the clam shrimp mature (and
thus do not present a severe predation problem) and are
also used as watering holes by cattle (pers. obs.).
The fourth population occurs within the playa portion of the NSF Long-Term Ecological Research site
on the New Mexico State University College Ranch
(LTER Playa), approximately 4 km west of the other three sites. The playa encompasses a 12-ha basin
(Creusere & Whitford, 1976). The LTER Playa has
considerably more vegetation than the SWP populations, including Prosopis, Panicum, Amaranthus,
Hymenoxis, and Helianthus (MacKay et aI., 1990).
The ecology and population dynamics of this site have
been studied quite extensively (see Creusere & Whitford, 1976; Medland, 1989; VanVactor, 1989; MacKay
et aI., 1990 for an overview). This site receives an average rainfall of 21 0 mm annually (MacKay et al., 1990).
The majority of this precipitation (55%) is attributed to convectional rainstorms during the late summer
months (VanVactor, 1989; MacKay et aI., 1990). The
site is relatively level and does not flood as often as the
SWP popUlations, typically flooding once every three
to ten years and remaining flooded for several weeks
(MacKay etal., 1990). In addition to E. texana, MacKay et aI., (1990), indicate that this site is also inhabited
by the tadpole shrimp, Triops longicaudatus, and fairy
shrimp species, Thamnocephalus platyurus and Streptocephalus texanus (D. Belk indicates that the report of
S. texan us populations within the LTER Playa is likely
a misidentification of a mixed popUlation of S. mackini
and S. dorothae). The life cycles of these species all
overlap (MacKay et al., 1990). Cattle have not been
allowed within the site since 1972 (MacKay et aI.,
1990).
General sampling and rearing methods
Numerous samples of the first 1-2 cm of soil were
collected from each study site; soil within each site
was mixed to ensure randomness. Sample populations were established in the laboratory by placing 250 ml soil samples in plastic mouse cages
(30 cm x 12 cm x 15 cm) and hydrating them with
4 liters of aged tap water. The tanks were kept on a 24
hour light cycle using incandescent bulbs in reflectors
to maintain summer-like temperatures of approximately 30°C and were supplemented with tadpole food
pellets until algal growth was initiated. Clam shrimp
hatched within approximately 24 hours of wetting.
Tadpole shrimp, Triops longicaudatus, also hatched
from the same soil samples and were removed from
the tanks as soon as possible to prevent predation.
Sex ratio calculations
Sex ratios were calculated for all four populations. Ten
tanks were set up from each population (40 tanks total)
using the methods just outlined. Sex was determined
for every individual hatching within a tank. Sex ratios
were computed following the procedures outlined in
Sassaman (1989) as soon as sexual dimorphism was
apparent (approximately three days after hatching).
Comparisons of total viable eggs per 250 ml soil sam-
to the nature of sex determination, populations typically consist of many more hermaphrodites than males
(Sassaman, 1989; pers. obs.).
Behavioral information on E. texana is largely
unavailable in the primary literature and would be a
useful supplement to ongoing evolutionary and genetic studies which are examining the significance of sex,
inbreeding and outcrossing. To that end, this contribution provides an account of male and hermaphrodite
behavior in the form of an ethogram, time budget and
detailed descriptions of mating behavior.
Methods
Study populations
Four populations of E. texana have been identified
just northeast of the Dona Ana Mountains, 40 km
NNE of Las Cruces, Dona Ana County, New Mexico.
These populations are all located within 4 km of one
another. Three of the populations are located along the
access road to the New Mexico State University College Ranch, next to South Well. These populations are
referred to as SWP3, SWP4 and SWP5 (South Well
puddle populations). Each of these sites consists of a
distinct depression less than 10 meters in length and
with a depth no greater than 1 meter at the lowest point.
SWP5 is almost directly across a dirt road, 35 m from
SWP3. SWP4 is 130 m west of SWP3 on the same
side of the road. There is sparse vegetation immediately around these puddles predominantly consisting of
various grass species. There is little to no vegetation
within the puddles themselves. These sites typically
fill with water at least once every year as a result of
summer rainfall and remain filled for three days to several weeks depending upon further water inputs (pers.
obs.). Other than E. texana, these sites are also occupied by populations of Scaphiopus couchii tadpoles,
which hatch well after the clam shrimp mature (and
thus do not present a severe predation problem) and are
also used as watering holes by cattle (pers. obs.).
The fourth population occurs within the playa portion of the NSF Long-Term Ecological Research site
on the New Mexico State University College Ranch
(LTER Playa), approximately 4 km west of the other three sites. The playa encompasses a 12-ha basin
(Creusere & Whitford, 1976). The LTER Playa has
considerably more vegetation than the SWP populations, including Prosopis, Panicum, Amaranthus,
Hymenoxis, and Helianthus (MacKay et aI., 1990).
The ecology and population dynamics of this site have
been studied quite extensively (see Creusere & Whitford, 1976; Medland, 1989; VanVactor, 1989; MacKay
et aI., 1990 for an overview). This site receives an average rainfall of 21 0 mm annually (MacKay et al., 1990).
The majority of this precipitation (55%) is attributed to convectional rainstorms during the late summer
months (VanVactor, 1989; MacKay et aI., 1990). The
site is relatively level and does not flood as often as the
SWP popUlations, typically flooding once every three
to ten years and remaining flooded for several weeks
(MacKay etal., 1990). In addition to E. texana, MacKay et aI., (1990), indicate that this site is also inhabited
by the tadpole shrimp, Triops longicaudatus, and fairy
shrimp species, Thamnocephalus platyurus and Streptocephalus texanus (D. Belk indicates that the report of
S. texan us populations within the LTER Playa is likely
a misidentification of a mixed popUlation of S. mackini
and S. dorothae). The life cycles of these species all
overlap (MacKay et al., 1990). Cattle have not been
allowed within the site since 1972 (MacKay et aI.,
1990).
General sampling and rearing methods
Numerous samples of the first 1-2 cm of soil were
collected from each study site; soil within each site
was mixed to ensure randomness. Sample populations were established in the laboratory by placing 250 ml soil samples in plastic mouse cages
(30 cm x 12 cm x 15 cm) and hydrating them with
4 liters of aged tap water. The tanks were kept on a 24
hour light cycle using incandescent bulbs in reflectors
to maintain summer-like temperatures of approximately 30°C and were supplemented with tadpole food
pellets until algal growth was initiated. Clam shrimp
hatched within approximately 24 hours of wetting.
Tadpole shrimp, Triops longicaudatus, also hatched
from the same soil samples and were removed from
the tanks as soon as possible to prevent predation.
Sex ratio calculations
Sex ratios were calculated for all four populations. Ten
tanks were set up from each population (40 tanks total)
using the methods just outlined. Sex was determined
for every individual hatching within a tank. Sex ratios
were computed following the procedures outlined in
Sassaman (1989) as soon as sexual dimorphism was
apparent (approximately three days after hatching).
Comparisons of total viable eggs per 250 ml soil sam-