262
Nevertheless, sex ratios as well as behavioral components may constitute important additional information. Metalimnadia, for example, always occurs in
bisexual populations and sexually maturing communities are characterized by sex ratios beginning approximately at 1: 1. Nevertheless, they later show an increasing numerical predominance of males, as female mortality is very high (Roessler, 1991).
Female mortality is apparently highly influenced
by the behavior of the males, as they permanently disturb, with copulatory intent, the feeding activities of the
females and remain attached to their valves much more
than is normally observable in other species. Females
react by closing their valves and slowing down or
temporarily stopping filtering movements. They start
to sink to the bottom; but the males do not release
the females and often push them forward through the
water. The final effect of the permanent stress is a very
low growth rate of the females and an early death,
because egg production requires a good part of the
energy balance. Preliminary experiments in laboratory
cultures revealed that in the absence of males, females
grow and survive at the same rates as males (Roessler,
1991 and Roessler, unpublished data).
Males seem unaffected, as their filtering movements do not stop. Normally, the suctorial disks of the
claspers are used very effectively to keep their bodies
attached to smooth surfaces during feeding. Because
males increase in size much faster than females and
outlive them, older populations of Metalimnadia consist of large numbers of big males and only a few,
smaller females (Roessler, 1991).
So sex ratio and behavioral elements may prove
to be important species-specific characteristics. Moreover, this information can help to explain certain morphological features, such as in this specific case, the
size relationship between sexes.
Acknowledgments. The studies on conchostracans were supported by funds from the Colombian Institute for Development of
Science and Technology 'Francisco Jose de Caldas' (COLCIENCIAS) and the Los Andes University. I am especially indebted to the
staff of the Colombian Hydrometeorological Institute (HIMAT) for
the cooperation during several national expeditions. I thank Dr Denton Belk for his critical and stimulating revision of the manuscript
and Trudy Sassaman for typing and copy-editing the final draft.
References
Alonzo, M & M. Alcaraz, 1984. Huevos resistentes de crusUiceos
eufilopodos no clad6ceros de la peninsula Iberica: Observaci6n
de la morfologie externa mediante tecnicas de microscopfa electr6nica de barrido. Oecologfa acuatica 7: 73-78.
Belk, D., 1989. Identification of species in the conchostracan genus
Eulimnadia by egg shell morphology. J. crust. BioI. 9: 115-125.
Botnariuc, N. & T. Orghidan, 1941. Sur une nouvelle espece du
genre lmnadia trouvee en Roumanie et sur les Imnadiidae n. fam.
Bull. Sec. sci. Acad. Roumanie 24: 239-246.
Martin, J. W. & D. Belk, 1988. Review of the clam shrimp family
Lynceidae Stebbing, 1902 (Branchiopoda: Conchostraca), in the
Americas. J. crust. BioI. 8: 451-482.
Martin, J. W. & D. Belk, 1989. Eulimnadia ovilunata and E. ovisimilis, new species of clam shrimps (Crustacea, Branchiopoda,
Spinicaudata) from South America. Proc. bioI. Soc. Wash. 102:
894--900.
Mattox, N. T., 1952. A new genus and species of Limnadiidae from
Venezuela (Crustacea: Conchostraca). J. Wash. acado Sci. 42:
23-26.
Mura G. & A. Thiery, 1986. Taxonomical significance of scanning
electron microscopic morphology of the Euphyllopds resting eggs
from Marocco. Part 1. Anostraca. Vie Milieu 36: 125-131.
Roessler, E. W., 1982a. Estudios tax6nomicos, ontogeneticos,
ecol6gicos y etol6gicos sobre los ostracodos de agua dulce
en Colombia. II. Contributci6n al conocimiento del desarrollo
embrionario tardio y de los procesos de la eclosi6n del huevo en
Heterocypris bogotensis Roessler (Ostracoda, Podocopa, Cyprididae). Caldasia 13: 453-466.
Roessler, E. W. 1982b. Estudios tax6nomicos, ontogeneticos,
ecol6gicos y etol6gicos sobre los ostracodos de agna dulce en
Colombia. III. E1 prenauplio y su papel en la eclosi6n del huevo en
el genero Chlamydotheca Saussure 1858 (Osctracoda, Podocopa,
Cyprididae). Caldasia 13: 635--646.
Roessler, E. W., 1989. Estudios sobre los entomostraceos de Colombia. III. Estudio tax6nomico de una nueva especie Colombiana,
Eulimnadia colombiensis (Arthropoda, Crustacea, Conchostraca). Caldasia 16: 58-65.
Roessler, E. W., 1990. Estudios sobre entomostraceos de Colombia.
II. Una nueva especie de Eulimnadia Packard 1874 (Crustacea,
Conchostraca). Rev. Acad. Col. Cienc. Ex. Fis. Nat. 17: 595-603.
Roessler, E. W., 1991 a. Estudios sobre los entomostraceos de Colombia. V. Limnadia orinoquiensis, una nueva especie de la familia
Limnadiidae Sars, 1896 (Arthropoda, Crustacea, Conchostraca).
Caldasia 16: 377-386.
Roessler, E. W., 1991b. Estudios sohre los entomostraceos de
Colombia. VI. Paraimnadiidae, una nueva familia de CrustaceaConchostraca. Rev. Acad. Col. Cienc. Ex. Fis. Nat. 18: 93-104.
Roessler, E. w., 1995. Review of Colombian Conchostraca (Crustacea), Ecological aspects and life cycles, family Cyclestheriidae.
Hydrobiologia 298 (Dev. Hydrobiol. 103): 113-124.
Roessler, E. W. & M. Sanchez, 1986. Estudios sobre los 'Entomostraceos' de Colombia. I. Contribuciones al conocimiento de
la historia natural de Cyclestheria hislopi (Baird, 1859), (Arthropoda, Crustacea, Conchostraca), con enfasis en aspectos bioecologicos y del ciclo vital. Caldasia 14: 679-707.
Sars, G. 0.,1901. Contributions to the knowledge ofthe fresh-water
Entomostraca of South America, as shown by artificial hatching
from dried material. Arch. Math. Naturv. 23: 1-102.
Shen, C.-J. & A.-Y. Dai, 1987. A new and rare species of Conchostraca from Yunnan Province, China (Crustacea: Conchostraca).
Acta zootax. Sinica 12: 353-356.
StraSkraba, M., 1965. Taxonomic studies on Czechoslovak Conchostraca. 1. Family Limnadiidae. Crustaceana 9: 263-273.
Nevertheless, sex ratios as well as behavioral components may constitute important additional information. Metalimnadia, for example, always occurs in
bisexual populations and sexually maturing communities are characterized by sex ratios beginning approximately at 1: 1. Nevertheless, they later show an increasing numerical predominance of males, as female mortality is very high (Roessler, 1991).
Female mortality is apparently highly influenced
by the behavior of the males, as they permanently disturb, with copulatory intent, the feeding activities of the
females and remain attached to their valves much more
than is normally observable in other species. Females
react by closing their valves and slowing down or
temporarily stopping filtering movements. They start
to sink to the bottom; but the males do not release
the females and often push them forward through the
water. The final effect of the permanent stress is a very
low growth rate of the females and an early death,
because egg production requires a good part of the
energy balance. Preliminary experiments in laboratory
cultures revealed that in the absence of males, females
grow and survive at the same rates as males (Roessler,
1991 and Roessler, unpublished data).
Males seem unaffected, as their filtering movements do not stop. Normally, the suctorial disks of the
claspers are used very effectively to keep their bodies
attached to smooth surfaces during feeding. Because
males increase in size much faster than females and
outlive them, older populations of Metalimnadia consist of large numbers of big males and only a few,
smaller females (Roessler, 1991).
So sex ratio and behavioral elements may prove
to be important species-specific characteristics. Moreover, this information can help to explain certain morphological features, such as in this specific case, the
size relationship between sexes.
Acknowledgments. The studies on conchostracans were supported by funds from the Colombian Institute for Development of
Science and Technology 'Francisco Jose de Caldas' (COLCIENCIAS) and the Los Andes University. I am especially indebted to the
staff of the Colombian Hydrometeorological Institute (HIMAT) for
the cooperation during several national expeditions. I thank Dr Denton Belk for his critical and stimulating revision of the manuscript
and Trudy Sassaman for typing and copy-editing the final draft.
References
Alonzo, M & M. Alcaraz, 1984. Huevos resistentes de crusUiceos
eufilopodos no clad6ceros de la peninsula Iberica: Observaci6n
de la morfologie externa mediante tecnicas de microscopfa electr6nica de barrido. Oecologfa acuatica 7: 73-78.
Belk, D., 1989. Identification of species in the conchostracan genus
Eulimnadia by egg shell morphology. J. crust. BioI. 9: 115-125.
Botnariuc, N. & T. Orghidan, 1941. Sur une nouvelle espece du
genre lmnadia trouvee en Roumanie et sur les Imnadiidae n. fam.
Bull. Sec. sci. Acad. Roumanie 24: 239-246.
Martin, J. W. & D. Belk, 1988. Review of the clam shrimp family
Lynceidae Stebbing, 1902 (Branchiopoda: Conchostraca), in the
Americas. J. crust. BioI. 8: 451-482.
Martin, J. W. & D. Belk, 1989. Eulimnadia ovilunata and E. ovisimilis, new species of clam shrimps (Crustacea, Branchiopoda,
Spinicaudata) from South America. Proc. bioI. Soc. Wash. 102:
894--900.
Mattox, N. T., 1952. A new genus and species of Limnadiidae from
Venezuela (Crustacea: Conchostraca). J. Wash. acado Sci. 42:
23-26.
Mura G. & A. Thiery, 1986. Taxonomical significance of scanning
electron microscopic morphology of the Euphyllopds resting eggs
from Marocco. Part 1. Anostraca. Vie Milieu 36: 125-131.
Roessler, E. W., 1982a. Estudios tax6nomicos, ontogeneticos,
ecol6gicos y etol6gicos sobre los ostracodos de agua dulce
en Colombia. II. Contributci6n al conocimiento del desarrollo
embrionario tardio y de los procesos de la eclosi6n del huevo en
Heterocypris bogotensis Roessler (Ostracoda, Podocopa, Cyprididae). Caldasia 13: 453-466.
Roessler, E. W. 1982b. Estudios tax6nomicos, ontogeneticos,
ecol6gicos y etol6gicos sobre los ostracodos de agna dulce en
Colombia. III. E1 prenauplio y su papel en la eclosi6n del huevo en
el genero Chlamydotheca Saussure 1858 (Osctracoda, Podocopa,
Cyprididae). Caldasia 13: 635--646.
Roessler, E. W., 1989. Estudios sobre los entomostraceos de Colombia. III. Estudio tax6nomico de una nueva especie Colombiana,
Eulimnadia colombiensis (Arthropoda, Crustacea, Conchostraca). Caldasia 16: 58-65.
Roessler, E. W., 1990. Estudios sobre entomostraceos de Colombia.
II. Una nueva especie de Eulimnadia Packard 1874 (Crustacea,
Conchostraca). Rev. Acad. Col. Cienc. Ex. Fis. Nat. 17: 595-603.
Roessler, E. W., 1991 a. Estudios sobre los entomostraceos de Colombia. V. Limnadia orinoquiensis, una nueva especie de la familia
Limnadiidae Sars, 1896 (Arthropoda, Crustacea, Conchostraca).
Caldasia 16: 377-386.
Roessler, E. W., 1991b. Estudios sohre los entomostraceos de
Colombia. VI. Paraimnadiidae, una nueva familia de CrustaceaConchostraca. Rev. Acad. Col. Cienc. Ex. Fis. Nat. 18: 93-104.
Roessler, E. w., 1995. Review of Colombian Conchostraca (Crustacea), Ecological aspects and life cycles, family Cyclestheriidae.
Hydrobiologia 298 (Dev. Hydrobiol. 103): 113-124.
Roessler, E. W. & M. Sanchez, 1986. Estudios sobre los 'Entomostraceos' de Colombia. I. Contribuciones al conocimiento de
la historia natural de Cyclestheria hislopi (Baird, 1859), (Arthropoda, Crustacea, Conchostraca), con enfasis en aspectos bioecologicos y del ciclo vital. Caldasia 14: 679-707.
Sars, G. 0.,1901. Contributions to the knowledge ofthe fresh-water
Entomostraca of South America, as shown by artificial hatching
from dried material. Arch. Math. Naturv. 23: 1-102.
Shen, C.-J. & A.-Y. Dai, 1987. A new and rare species of Conchostraca from Yunnan Province, China (Crustacea: Conchostraca).
Acta zootax. Sinica 12: 353-356.
StraSkraba, M., 1965. Taxonomic studies on Czechoslovak Conchostraca. 1. Family Limnadiidae. Crustaceana 9: 263-273.