form from all continents except Australia (Baird, 1859;
Barnard, 1929; Roessler & Sanchez, 1986; Roessler,
1995b; Sars, 1887; Stuhlmann, 1888).
Nevertheless, Cyclestheria generally does not compete with other conchostracans, because its appearance
does not coincide with the ephemeral existence of the
'normal' conchostracan populations. Also, Cyclestheria does not appear in temporary bodies of water with
a short duration. The species is especially adapted to
somewhat larger, longer-lasting temporary water bodies with abundant vegetation. It is not characteristic of
the very initial phases of the ecological succession of
temporary waters, but generally appears three, four or
five weeks after succession has started. This form can
persist in larger temporary pools throughout the duration of the pools and is able, as mentioned before (and
reported by other authors), to survive in permanent
water bodies.
Limnadiidae
The most widespread and common species within
the Colombian conchostracan fauna are in the family Limnadiidae and particularly the genus Eulimnadia. In Colombia, I found three species of this genus:
E. colombiensis, Roessler, 1989; E. magdalenensis
Roessler, 1990; and possibly E. geayi Daday, 1927.
The head shape of the latter Colombian form agrees
with Daday's description and the egg shell morphology is as redescribed by Martin (1989). Nevertheless,
the morphology of the telson is somewhat different.
In Colombia, E. c.f geayi has been found only in the
northern extensions of the lower Magdalena Valley
(Fig. 1). Daday reported his species from Venezuela.
If the two forms represent the same species, a geographic link over the northeast parts of Colombia can
be expected (see below).
Little is known about the ecology of this species.
I found it in the typical Eulimnadia habitat, shortlived shallow ponds, in several cases with abundant
residues of crude petroleum, testifying to the frequent
oil spills caused by the guerrillas in this region. Nevertheless, the organisms were apparently not affected
by the petroleum.
The other two species, E. magdalenensis and
E. colombiensis seem to be generally distributed in
Colombia. They were found in the Cauca and Magdalena valleys, and in the extensive lowlands east of
the Oriental Cordillera and near the Orinoco Rivers,
often in mixed populations. A closer look at the spatial distribution patterns of these species revealed an
127
interesting difference in their use of temporary habitats
(Fig. 1).
E. colombiensis is totally absent from the upper
Magdalena Valley and E. magdalenensis was never
found east of the Cordillera Oriental in the vicinity of the mountain range. E. magdalenensis nevertheless reappears near the Orinoco sympatrically with
E. colombiensis in mixed populations of varying composition. Mixed populations of the two species with
similar variation in relative abundances, were also
found in the lower Magdalena Valley and in the Cauca
Valley (Fig. 1).
From distribution patterns, spatial and temporal
variations, and from correlations with specific local climate and topographic conditions, I deduce that E. magdalenensis is adapted to temporary ponds with a very
short duration and high temperatures. E. colombiensis,
by contrast, inhabits ponds of somewhat longer duration and lower temperatures. The relationship between
rainfall pattern and the species distributions is shown
in Fig. 2, for three areas of Colombia. In the upper
Magdalena Va1\ey, a typical bimodal distribution corresponds to a relatively low average rainfall per year.
Only Eulimnadia magdalenensis is present (Figs 2a, d).
East of the Andes, in the lowlands and in the vicinity
of the mountain range, a high average rainfall provides
favorable conditions for E. colombiensis (Figs 2b, d).
Near the Orinoco, as well as in the lower Magdalena
Valley, intermediate and highly variable conditions can
be found and here the two forms cohabit sympatrically
(Figs 2c, d). Although the available data, as illustrated for the upper Magdalena Valley, do not represent a
very arid area, the highly drainable soil, the bimodal
annual rainfall pattern and a corresponding high solar
radiation along with high water temperatures create
significantly different environmental conditions.
As shown in my paper about the taxonomical
aspects, E. magdalenensis reacts to the higher temperatures that occur frequently in very small ponds, with
the usual general acceleration of development and also
shows a differential rate of organogenesis favoring the
reproductive system (Roessler, 1995a).
The accelerated development of the reproductive
system results in sexual maturation at earlier stages.
This phenomenon, known as neoteny, enables this
species to survive in freshwater habitats of very short
duration. Sexually mature specimens of this type are
usua1\y very small and show very narrow growth lines.
Sexual maturation occurs up to three stages earlier than
maturation in individuals which develop in moderate
Barnard, 1929; Roessler & Sanchez, 1986; Roessler,
1995b; Sars, 1887; Stuhlmann, 1888).
Nevertheless, Cyclestheria generally does not compete with other conchostracans, because its appearance
does not coincide with the ephemeral existence of the
'normal' conchostracan populations. Also, Cyclestheria does not appear in temporary bodies of water with
a short duration. The species is especially adapted to
somewhat larger, longer-lasting temporary water bodies with abundant vegetation. It is not characteristic of
the very initial phases of the ecological succession of
temporary waters, but generally appears three, four or
five weeks after succession has started. This form can
persist in larger temporary pools throughout the duration of the pools and is able, as mentioned before (and
reported by other authors), to survive in permanent
water bodies.
Limnadiidae
The most widespread and common species within
the Colombian conchostracan fauna are in the family Limnadiidae and particularly the genus Eulimnadia. In Colombia, I found three species of this genus:
E. colombiensis, Roessler, 1989; E. magdalenensis
Roessler, 1990; and possibly E. geayi Daday, 1927.
The head shape of the latter Colombian form agrees
with Daday's description and the egg shell morphology is as redescribed by Martin (1989). Nevertheless,
the morphology of the telson is somewhat different.
In Colombia, E. c.f geayi has been found only in the
northern extensions of the lower Magdalena Valley
(Fig. 1). Daday reported his species from Venezuela.
If the two forms represent the same species, a geographic link over the northeast parts of Colombia can
be expected (see below).
Little is known about the ecology of this species.
I found it in the typical Eulimnadia habitat, shortlived shallow ponds, in several cases with abundant
residues of crude petroleum, testifying to the frequent
oil spills caused by the guerrillas in this region. Nevertheless, the organisms were apparently not affected
by the petroleum.
The other two species, E. magdalenensis and
E. colombiensis seem to be generally distributed in
Colombia. They were found in the Cauca and Magdalena valleys, and in the extensive lowlands east of
the Oriental Cordillera and near the Orinoco Rivers,
often in mixed populations. A closer look at the spatial distribution patterns of these species revealed an
127
interesting difference in their use of temporary habitats
(Fig. 1).
E. colombiensis is totally absent from the upper
Magdalena Valley and E. magdalenensis was never
found east of the Cordillera Oriental in the vicinity of the mountain range. E. magdalenensis nevertheless reappears near the Orinoco sympatrically with
E. colombiensis in mixed populations of varying composition. Mixed populations of the two species with
similar variation in relative abundances, were also
found in the lower Magdalena Valley and in the Cauca
Valley (Fig. 1).
From distribution patterns, spatial and temporal
variations, and from correlations with specific local climate and topographic conditions, I deduce that E. magdalenensis is adapted to temporary ponds with a very
short duration and high temperatures. E. colombiensis,
by contrast, inhabits ponds of somewhat longer duration and lower temperatures. The relationship between
rainfall pattern and the species distributions is shown
in Fig. 2, for three areas of Colombia. In the upper
Magdalena Va1\ey, a typical bimodal distribution corresponds to a relatively low average rainfall per year.
Only Eulimnadia magdalenensis is present (Figs 2a, d).
East of the Andes, in the lowlands and in the vicinity
of the mountain range, a high average rainfall provides
favorable conditions for E. colombiensis (Figs 2b, d).
Near the Orinoco, as well as in the lower Magdalena
Valley, intermediate and highly variable conditions can
be found and here the two forms cohabit sympatrically
(Figs 2c, d). Although the available data, as illustrated for the upper Magdalena Valley, do not represent a
very arid area, the highly drainable soil, the bimodal
annual rainfall pattern and a corresponding high solar
radiation along with high water temperatures create
significantly different environmental conditions.
As shown in my paper about the taxonomical
aspects, E. magdalenensis reacts to the higher temperatures that occur frequently in very small ponds, with
the usual general acceleration of development and also
shows a differential rate of organogenesis favoring the
reproductive system (Roessler, 1995a).
The accelerated development of the reproductive
system results in sexual maturation at earlier stages.
This phenomenon, known as neoteny, enables this
species to survive in freshwater habitats of very short
duration. Sexually mature specimens of this type are
usua1\y very small and show very narrow growth lines.
Sexual maturation occurs up to three stages earlier than
maturation in individuals which develop in moderate