Hydrobiologia 298: 73-81, 1995.
D. Bellc, H. 1. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture II.
© 1995 Kluwer Academic Publishers.
73
Mating behavior and time budget of an androdioecious crustacean,
Eulimnadia texan a (Crustacea: Conchostraca)
Lana Knoll
Department of Biology, New Mexico State University, l..o,s Cruces, NM 88003, USA
Key words: androdioecious crustacean, Eulimnadia texana, behavior, mating
Abstract
The clam shrimp, Eulimnadia texana (Crustacea, Conchostraca), is found in freshwater ephemeral environments
throughout the United States. Individual clam shrimp of this species are either hermaphroditic or male, a relatively
rare mating system for animals known as androdioecy. Comparison of sex ratios between four neighboring populations of E. texana in Southern New Mexico showed wide variation in the ratio of males to hermaphrodites with
males making up as much as 42% of some popUlations and not occurring at all within others. Since little is known
about the behavior of this species, an ethogram and time budget were prepared based on observations of laboratory
populations. Males attempt to clasp hermaphrodites prior to mating. Precopulatory mate guarding occurs in this
species. Outcrossing generally occurs during mate guarding and after the hermaphrodite molts. Hermaphrodites,
however, seem to control the mating process. Successful mating by males never occurred if the hermaphrodite
struggled with him; hermaphrodites will self in the presence of males.
Introduction
The clam shrimp, Eulimnadia texana (Crustacea: Conchostraca) is found across North America (Sassaman,
1989). This species inhabits small ephemeral ponds
that typically appear due to spring and summer rains.
The puddles dry up and the eggs remain dormant until
the puddles reform. Eulimnadia texana is androdioecious, a rare situation in animals in which a species has
both male and hermaphroditic individuals (Sassaman
& Weeks, 1993). Hermaphrodites can self or outcross
with a male, but they cannot exchange sperm with other hermaphrodites (Sassaman & Weeks, 1993). The
body of the clam shrimp is encased within a translucent, carapace through which most organs are visible.
Clam shrimp have numerous pairs of legs which are
used for feeding. Eulimnadia texana feeds primarily
on algae though it will eat other types of detritus when
algae is limited (Medland, 1989).
Pronounced sexual dimorphism allows easy identification of males and hermaphrodites. In the males,
the first two pairs of thoracic appendages have been
modified into claspers for grasping the hermaphrodite
during outcrossing. Absence of such an adaptation prevents hermaphrodites from outcrossing with one another (Sassaman & Weeks, 1993). The hermaphrodite's
unfertilized eggs lie in paired ovaries along its digestive tract and are visible under a microscope. When fertilization occurs, the eggs move into a brood chamber
where they are contained in a mucous mass between the
hermaphrodite's dorsum and the carapace. The eggs
are visible to the naked eye and aid in sexing the clam
shrimp.
Research involving this species has focused primarily on the genetics and theoretical implications of this
mating system (see Strenth, 1977; Sassaman, 1989;
Sassaman & Weeks, 1993; Ottoetal., 1993). Sassaman
& Weeks (1993) have shown that sex determination
occurs at a single autosomal locus and that individuals are either monogenic hermaphrodites (those which
produce only hermaphroditic offspring), amphigenic
hermaphrodites (those which produce both male and
hermaphroditic offspring), or male. Monogenic individuals are homozygous dominant at the autosomal
locus, amphigenic individuals are heterozygous, and
males are homozygous recessive (Sassaman & Weeks,
1993). This system is very similar to the reproductive
systems of many Notostracans (Sassaman, 1991). Due
D. Bellc, H. 1. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture II.
© 1995 Kluwer Academic Publishers.
73
Mating behavior and time budget of an androdioecious crustacean,
Eulimnadia texan a (Crustacea: Conchostraca)
Lana Knoll
Department of Biology, New Mexico State University, l..o,s Cruces, NM 88003, USA
Key words: androdioecious crustacean, Eulimnadia texana, behavior, mating
Abstract
The clam shrimp, Eulimnadia texana (Crustacea, Conchostraca), is found in freshwater ephemeral environments
throughout the United States. Individual clam shrimp of this species are either hermaphroditic or male, a relatively
rare mating system for animals known as androdioecy. Comparison of sex ratios between four neighboring populations of E. texana in Southern New Mexico showed wide variation in the ratio of males to hermaphrodites with
males making up as much as 42% of some popUlations and not occurring at all within others. Since little is known
about the behavior of this species, an ethogram and time budget were prepared based on observations of laboratory
populations. Males attempt to clasp hermaphrodites prior to mating. Precopulatory mate guarding occurs in this
species. Outcrossing generally occurs during mate guarding and after the hermaphrodite molts. Hermaphrodites,
however, seem to control the mating process. Successful mating by males never occurred if the hermaphrodite
struggled with him; hermaphrodites will self in the presence of males.
Introduction
The clam shrimp, Eulimnadia texana (Crustacea: Conchostraca) is found across North America (Sassaman,
1989). This species inhabits small ephemeral ponds
that typically appear due to spring and summer rains.
The puddles dry up and the eggs remain dormant until
the puddles reform. Eulimnadia texana is androdioecious, a rare situation in animals in which a species has
both male and hermaphroditic individuals (Sassaman
& Weeks, 1993). Hermaphrodites can self or outcross
with a male, but they cannot exchange sperm with other hermaphrodites (Sassaman & Weeks, 1993). The
body of the clam shrimp is encased within a translucent, carapace through which most organs are visible.
Clam shrimp have numerous pairs of legs which are
used for feeding. Eulimnadia texana feeds primarily
on algae though it will eat other types of detritus when
algae is limited (Medland, 1989).
Pronounced sexual dimorphism allows easy identification of males and hermaphrodites. In the males,
the first two pairs of thoracic appendages have been
modified into claspers for grasping the hermaphrodite
during outcrossing. Absence of such an adaptation prevents hermaphrodites from outcrossing with one another (Sassaman & Weeks, 1993). The hermaphrodite's
unfertilized eggs lie in paired ovaries along its digestive tract and are visible under a microscope. When fertilization occurs, the eggs move into a brood chamber
where they are contained in a mucous mass between the
hermaphrodite's dorsum and the carapace. The eggs
are visible to the naked eye and aid in sexing the clam
shrimp.
Research involving this species has focused primarily on the genetics and theoretical implications of this
mating system (see Strenth, 1977; Sassaman, 1989;
Sassaman & Weeks, 1993; Ottoetal., 1993). Sassaman
& Weeks (1993) have shown that sex determination
occurs at a single autosomal locus and that individuals are either monogenic hermaphrodites (those which
produce only hermaphroditic offspring), amphigenic
hermaphrodites (those which produce both male and
hermaphroditic offspring), or male. Monogenic individuals are homozygous dominant at the autosomal
locus, amphigenic individuals are heterozygous, and
males are homozygous recessive (Sassaman & Weeks,
1993). This system is very similar to the reproductive
systems of many Notostracans (Sassaman, 1991). Due