ARTÍCULOS CIENTÍFICOS - TÉCNICOS
Rev. Bol. Ecol. y Cons. Amb. 25: 51-67, 2009
Banco de huevos de resistencia revela una alta riqueza
específica de cladóceros en charcos temporales altoandinos
Resting egg bank reveals high cladoceran species richness
in high-altitude temporary peat land pools
Jorge S Coronel1, Ximena Aguilera1, Steven Decleck2 & Luc Brendonck2
RESUMEN
El análisis del banco de efipias (huevos de dormancia) presente en el sedimento de los cuerpos de agua ha resultado ser una
herramienta útil para el estudio de la diversidad de cladóceros en sistemas permanentes de agua. Este método ha sido
inexplorado en sistemas temporales que experimentan un periodo seco durante una parte del año. En este estudio se evaluó
la riqueza de especies del ensamblaje de cladóceros (Branchiopoda, Crustacea) obtenido mediante la eclosión de efipias
provenientes del sedimento de 61 charcos temporales de la cordillera del Tunari en Bolivia. La eclosión de efipias reveló más
especies de cladóceros (total= 24; promedio= 6.7) que el número obtenido de los muestreos del ensamblaje activo (total= 21;
promedio= 4.6). En promedio, el análisis de las efipias contribuyó con 2.1 especies de cladóceros por charco. El número de
cladóceros (ensamblaje activo + análisis de efipia) alcanzó un total de 28 especies. Análisis de redundancia indicaron diferencias
significativas entre la composición del ensamblaje activo y el ensamblaje obtenido por eclosión de las efipias. La cobertura
vegetal fue la principal variable que explicó una variación en la estructura del ensamblaje activo de cladóceros, mientras que
para el ensamblaje obtenido de la eclosión de efipias estuvieron la clorofila-a, el grosor de la capa de sedimento, y la conectividad
entre charcos.
Palabras claves: Bolivia, Charcos temporales andinos, huevos de dormancia, zooplancton de los Andes.
ABSTRACT
The use of egg bank analysis proved a valuable approach to uncover hidden diversity in permanent lakes. The efficiency of
the method remains largely unexplored in temporary aquatic systems that remain dry for a variable part of the year. We assessed
species richness of the cladoceran assemblage (Branchiopoda, Crustacea) from the dormant egg bank of 61 temporary peat
land pools in the high Andes of Bolivia. The analysis of the dormant egg bank yielded more species (total: 24; mean per peat
land pool: 6.7) than snapshot samples from active communities taken previously (total: 21; mean per peat land pool: 4.6). On
average, the dormant egg bank resulted in the detection of 2.1 (45%) more cladoceran species per peat land pool than on the
basis of active cladoceran assemblages. The accumulated (active plus dormant) cladoceran species richness of the study peat
land pools mounted up to 28 species. RDA analyses indicated a significant difference in assemblage composition between
dormant and active samples. Different environmental variables explained variation in the structure of the dormant and active
cladoceran assemblages. Water plant cover significantly explained variation in active assemblages, while a model constructed
by chlorophyll-a, sediment thickness, and connectivity explained variation in dormant cladoceran assemblages. The analysis
of the dormant assemblages was essential, not only in revealing the potential species richness but also for better understanding
assemblage structure of aquatic organisms.
Key words: Bolivia, Andean temporary pools, Resting eggs, Bolivian zooplankton, Egg-morphotype.
Unidad de Limnología y Recursos Acuáticos (ULRA), Universidad Mayor de San Simón, Cochabamba, Bolivia. Tel: ++591 (4) 423 5622; E-mail: js.crnl@gmail.com
Laboratory of Aquatic Ecology and Evolutionary Biology, Katholieke Universiteit Leuven, Naamsestraat 59 – 3000 Leuven, Belgium.
1
2
51
REVISTA BOLIVIANA DE ECOLOGÍA Y CONSERVACIÓN AMBIENTAL
INTRODUCTION
The cyclical and variable nature of the temporary pool
environment creates a habitat that is quite distinct from
permanent and more predictable habitats such as ponds
and lakes. Their inhabitants require specific adaptations
to deal with the variable and often extreme local environmental conditions, which often results in the presence
of unique species not found in any other habitat types
(Williams, 1997; Blaustein & Schwartz, 2001; De Meester
et al., 2005).
& Brendonck, 2008). Hatching of dormant eggs can be
biased because some populations seldom or never
produce dormant eggs (Jeppesen et al., 2003) or due
to variation among taxa in their response to specific
hatching stimuli (Cáceres, 1998).
The shape and external sculpturing (ornamentation) of
resting eggs were also suggested as a tool for identification at a higher taxonomic level and, in some cases,
even to species level (reviewed in Brendonck & De
Meester, 2003). Vandekerkhove et al., (2004a) showed
that morphological characters of resting eggs allowed
a rapid first estimation of cladoceran species richness
in 20 shallow European lakes.
A main feature of aquatic species permanently inhabiting
variable aquatic environments is the production of diapausing resting stages (dormant eggs) that allow survival
during droughts and recolonization after flooding (Wiggins
et al., 1980; Cáceres, 1997). Zooplanktonic organisms,
in particular, produce diapausing stages when environmental conditions become adverse (Brendonck & De
Meester, 2003). After deposition, most resting stages
sink to the bottom building a dormant egg bank. The largest fractions of viable (responsive) eggs usually occur
in the top three centimeters, the so-called “active egg
bank” (Brendonck & De Meester, 2003). At each occasion, usually only a variable portion of the egg bank hatches (Maia-Barbosa et al., 2003; García-Roger et al.,
2006). Such partial hatching constitutes a bet-hedging
strategy to buffer against extinction in the variable habitat,
where sometimes there is even not enough time for maturation and successful reproduction (Brendonck & De
Meester, 2003). The portion of resting eggs that does
not hatch at the first occasion may do so later under similar conditions (Brendonck et al., 1998). This process
results in the gradual accumulation of dormant eggs
from different seasons and years in a persistent egg
bank, integrating spatial and temporal variation in the
abundance and distribution of freshwater zooplankton
(Brendonck & De Meester, 2003). This property renders
the dormant egg bank a potentially valuable tool for
detecting hidden diversity with only a limited presence
in the water column and an attractive complementary
tool for the analysis of active community samples (Vandekerkhove et al., 2005a; Vandekerkhove et al., 2005b).
In this study we tested the efficiency of using egg bank
samples for detecting potential species richness in
temporary peat land pools in the high Andes of Bolivia.
By individual incubation of isolated egg morphotypes
from 61 pools we specifically aimed to 1) assign ephippia
morphotypes to species, 2) obtain a more integrated
picture of peat land cladoceran species richness and
composition by comparing the active and dormant
cladoceran assemblages, and 3) explore whether the
same environmental variables explain variation in
structure of dormant compared to active communities.
MATERIAL AND METHODS
Study site
Our study area is located in the Cordillera del Tunari
(Cochabamba) in the Bolivian Andes between the coordinates 66o08’- 66o22’ W and 17o10’-17o19’ S, at altitudes
ranging from 4000 to 4400 m.a.s.l. This area consists
of numerous small peat land systems (locally called bofedales) scattered over valleys and mountain slopes.
Most of these peat lands contain small temporary peat
land pools, of which the number typically varies between
1 and 8, although pools can be more numerous in some
of the larger peat land systems (Fig. 1). Peat land pools
are mostly temporary and fishless, characterized by high
water transparency and low values of conductivity, salinity, and total dissolved solids. The area is in general
cha-racterized by grassland vegetation with exception
of the peat land that is predominantly dominated by a
hard-tapestry vegetation of Distichia muscoides and
Plantago tubulosa (Navarro & Maldonado, 2002). This
area is subject to a dry (April – September) and rainy
(October – March) season.
The study of the dormant egg bank in permanent aquatic
systems revealed that the number of species hatching
from sediment samples in the laboratory was usually
higher than the number of species detected by snapshot
sampling from the active community (May, 1986; Vandekerkhove et al., 2005b). Some studies on temporary
pools, however, revealed a lower number of species
than detected in the active community samples (Boven
52
CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
Cordillera del Tunari
17o
N
Toro
Figure 1. Bofedal showing high-altitude peatland pools in
the Cordillera del Tunari of the Bolivian Andes.
Saito
San Ignacio
Taquiña
Sampling
Cochabamba
Samples of both, the active zooplankton community and
the dormant egg bank, were collected in 61 peat land
pools from 31 peat land systems spread over four
mountain valleys in the Cordillera del Tunari: Taquiña,
Toro, Saito, and San Ignacio (Fig. 2).
20 Kilometers
18o
o
66
The active community was collected in the middle of the
wet season between February and March 2004. In each
peat land pool, 3 to 15 L samples were taken with a tube
sampler (75 mm diameter and 1.5 m length) and filtered
through a 30-µm mesh. Samples were preserved in
sucrose-formaldehyde solution (5% final concentration).
In the dry season, for the dormant egg bank analysis,
the top three centimeters of sediment were collected
using a KC-sediment core sampler (0.7 meter long plexiglass tube of 5.2 cm diameter), until completing one
kilogram per pool. After collection, samples were wrapped
in aluminum foil and transported to the lab in a cooler
box.
o
65
Figure 2. Map of the study area. Stars indicate the study
mountain valleys in the Cordillera del Tunari in Cochabamba, Bolivia.
Sample Analysis
Zooplankton density estimates were based on counts
of at least 300 specimens per sample. The density of
potential zooplankton predators (cyclopoid copepods,
mites, and larvae of the coleopteran genera Ranthus,
Colymbetinae and Hydroporus, Hydroporinae) was also
assessed by counting specimens in each sample. Zooplankton and potential predators were counted using an
Olympus SZX12 stereo microscope.
For each peat land pool, the following environmental
variables were recorded: pH, conductivity (COND), chlorophyll-a (CHLa), pool surface (AREA), and water column
depth (DEPTH). Besides, we also measured the thickness
of the bottom sediment (SEDTH, measured as the
thickness of the bottom organic matter layer), the percentage of water plants covering the pool (WPCOV),
connectivity (CONN; measured as the number of peat
land pools that directly drained into the sampled pool),
number of neighboring peat land pools in a radius of 50
m (NGP), and distance to the nearest rivulet (DNR).
In order to isolate dormant eggs of each individual peat
land pool we removed gross material (mostly vegetal
debris) from each sample using sieves of 1000 µm and
500 µm, while fine material and resting eggs were
retained on a 63 µm sieve.
The retained resting eggs were isolated by the sugar
flotation method (Onbé, 1978; Marcus, 1990). We omitted
the sonication step because none of the sediment
53
REVISTA BOLIVIANA DE ECOLOGÍA Y CONSERVACIÓN AMBIENTAL
To explore for environmental variables that explain variation in community structure of cladoceran assemblages
obtained from dormant versus active community samples,
we used a standardized redundancy analyses (RDA).
All recorded environmental variables (explanatory variables) were log (X+1) transformed except for pH. The
RDA model was constructed using forward selection
(999 Monte Carlo permutations). Only significant variables
were retained. We evaluated the amount of variation
explained by each environmental variable included in
the model. Cladoceran densities (response variable)
were square-root transformed to minimize the effect of
high densities (ter Braak & Šmilauer, 2002). Only peat
land pools with samples allowing counts of at least 300
individuals were included in the analysis. Cladoceran
species with less than 5% of pool-occurrence were excluded from the analysis, since they can disproportionately
affect the results.
samples were compact. The following steps of the original
Onbé-Marcus method were retained: 1) filtration through
a 48 µm mesh, 2) centrifugation of the residue in a sugar
solution (1000 g table sugar in 1000 ml distilled water)
at 3000 rpm for three minutes, and 3) washing of the
supernatant over a 48 µm mesh using tap water.
The isolated resting eggs were sorted on the basis of
morphology and counted under a stereo microscope
(Olympus SZX12). Dormant egg density estimates were
based on counts of at least 300 specimens per sample.
To allow identification to species level, the unknown
resting egg types were incubated individually in 30-ml
multi-well plates containing the Aachener Daphnien
Medium (ADAM; Klüttgen et al., 1994) at a conductivity
of 30 µS cm-1. Multi-well plates were placed in an
incubator at 20oC with a photoperiod of 14 hours light
and 10 hours dark. Incubation medium was refreshed
every five days. For a period of two months, all multiwell plates were checked every four days for emerging
hatchlings. Hatchlings were transferred to 50-ml vessels
and fed Scenedesmus obliquus (100.000 cells ml-1) until
maturation. All cladocerans were identified to species
level using Paggi (1995), Alonso (1996) and Smirnov
(1996).
RESULTS
Ephippia morphotype analysis
We identified 24 different morphotypes of cladoceran
ephippia down to species level (Table 1; Appendix 1).
Most of the isolated ephippia contained one egg with
exception of those belonging to Daphnia pulex, Daphnia
peruviana, Macrothrix atahualpa, Ilyocryptus cf spinifer,
Paralona piagra and Streblocerrus serricaudatus that
presented two eggs. A similar morphotype was observed
for Ceriodaphnia cf dubia and C. cf laticaudata. On
average, most cladoceran ephippia hatched during the
first 8 days of incubation (Table 1).
Statistical analyses
Differences in composition between cladoceran assemblages obtained from both the dormant egg bank and
active cladoceran samples were tested with permutation
tests (999 permutations) on redundancy analysis models
(RDA; CANOCO 4.5). Nominal dummy variables constructed for the two cladoceran assemblages (dormant
and active) were used as explanatory variables and the
densities of individual species as response variables.
Cladoceran densities were square-root transformed to
minimize the effect of high densities (ter Braak & Šmilauer,
2002).
Composition and species richness of dormant and
active assemblages
Composition of the cladoceran assemblages obtained
from the resting egg bank versus those from the active
cladoceran samples differed significantly (RDA analysis:
Trace= 0.123; F= 17.2; p= 0.001).
To test for differences in species richness between dormant and active assemblages across all peat land pools
sampled (n = 61) we used a paired T-test for dependent
samples. In addition, the degree of association between
pool species richness derived from the dormant egg
bank analysis and species richness from active cladoceran samples was evaluated using product moment
correlations. Associations between environmental variables and species richness of the dormant and active
assemblages were also evaluated with product moment
correlations using the statistical software STATISTICA
V8.0, Statsoft INC., Tulsa, O.K.
The study of the dormant egg bank yielded 24 cladoceran
species, in comparison with 21 species in the active
cladoceran samples (Fig. 3). The number of cladoceran
species retrieved from the resting egg bank was significantly higher (mean per pool: 6.7 0.6) than the number
collected from the active assemblages (mean per pool:
4.6 0.4) (paired T-test = 6.3; df = 60; p = < 0.001; Fig.
4).
54
CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
Table 1. Cladoceran species detected in temporary peat land pools in the Cordillera del Tunari, Bolivia. Species are
ordered according to their frequency of occurrence (from high to low) in the 61 study peat land pools. ‘Average
densities’ refers to the mean number of eggs (eggs per Kg) for the dormant community and the mean number of
individuals (individuals per liter) for the active community, across all study pools. ‘DFH’ shows the number of days
for first hatch to occur. ‘Valley’ shows the mountain valleys where the respective species were found: a = Taquiña,
b = Toro, c = Saito, d = San Ignacio.
Species’ occurrence
Dormant
Chydorus brevilabris
Alona ossiani
Macrothrix atahualpa
Alona cambouei
Simocephalus mixtus
Alonella excisa
Camptocercus aloniceps
Alona davidi
Ceriodaphnia cf dubia
Graptoleberis testudinaria
Daphnia pulex
Alona glabra
Daphnia peruviana
Ephemerophorus hibridus
Paralona piagra
Pleuroxus caca
Ceriodaphnia cf laticaudata
Pleuroxus sp.
Streblocerus serricaudatus
Alona boliviana
Scapholeberis spinifera
Drepanothrix cf dentata
Pleuroxus cf aduncus
Alona.cf ossiani
Bosmina huaronensis
Ephemerophorus cf acanthodes
Ilyocryptus cf spinifer
Pleuroxus hardingi
52
55
53
42
47
30
23
17
22
11
7
4
5
7
6
0
8
6
5
3
2
2
2
1
0
0
1
0
Average densities
Active
Dormant
Active
59
51
46
44
37
48
24
12
14
9
6
6
5
2
3
9
0
0
0
1
1
0
0
0
1
1
0
1
26.30
48.67
61.75
26.20
35.20
8.49
9.26
9.85
9.36
3.67
1.31
0.74
0.16
4.28
0.67
0.00
3.34
1.38
2.92
0.75
0.08
0.44
0.13
0.30
0.00
0.00
0.11
0.00
71.63
6.47
10.40
3.04
6.30
5.04
2.07
0.68
2.40
0.30
0.07
0.05
0.17
0.30
1.54
0.17
0.00
0.00
0.00
1.02
0.02
0.00
0.00
0.00
0.00
0.01
0.00
0.10
Seventeen cladoceran species were detected in both
the active and dormant assemblages (Table 1), whereas
seven species (Ceriodaphnia cf laticaudata, Pleuroxus
cf aduncus, Pleuroxus sp., Streblocerus serricaudatus,
Drepanothrix cf dentata, Alona cf ossiani, and Ilyocryptus
cf spinifer) were exclusively observed in the dormant
assemblage (Table 1). Some cladoceran species were
uniquely present in the active cladoceran samples
(Pleuroxus caca, Bosmina huaronensis, Ephemerophorus
cf acanthodes, Pleuroxus hardingi) (Table 1). The accumulated (active plus dormant) cladoceran species richness of the study pools mounted up to 28 species (Table
1).
DFH
Valley
6
8
6
6
7
6
10
6
6
5
9
10
9
10
15
10
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
bc
abc
bcd
abd
bc
abc
a
bcd
ab
abcd
a
ab
ac
ac
ac
b
a
c
b
b
7
10
7
11
8
16
with species richness of the dormant community (Table
2).
Explanatory environmental variables of dormant and
active assemblages
For the active assemblage, the forward selection
procedure of the RDA analysis indicated water plants
as the main environmental variable explaining variation
in community structure (Trace = 0.063; F = 2.07; p =
0.49; Table 3).
For the dormant egg banks, a model including sediment
thickness, connectivity and chlorophyll-a explained a
significant portion of the variation in the assemblage
structure (Trace = 0.182; F = 2.15; p = 0.002; Table 3).
Species richness of active cladoceran samples was
significantly associated with water plant coverage and
55
REVISTA BOLIVIANA DE ECOLOGÍA Y CONSERVACIÓN AMBIENTAL
I. cf spinifer and S. spinifera) were easier to identify than
others because they still maintained some ornamental
characters of active individuals. Adults of Alona glabra,
for instance, usually present a tuberculated ornamentation
in their shield. This ornamentation was maintained in
their ephippia (Appendix 1). Cladoceran identification
solely based on ephippia morphotypes may result in an
underestimation of true species richness as similar
morphotypes sometimes occur among different species
(Vandekerkhove et al., 2004a). In our study, morphologically similar ephippia were observed in species within
the genera Ceriodaphnia and Pleuroxus.
26
24
22
Species richness
20
18
16
14
12
10
8
6
4
0
10
20
30
40
50
60
Although cladoceran assemblage composition derived
from the resting egg bank resembled the assemblage
obtained from active samples, on average 45% more
cladoceran species per peat land pool were detected
by egg bank analysis. This discrepancy may actually be
even much higher as still some species may not have
hatched at all (bet-hedging effects) in the single incubation
event (no multiple inundations). To our knowledge, a
higher species yield from dormant egg banks versus
ac-tive assemblage samples has mostly been reported
for permanent lakes (May, 1986; Havel et al., 2000;
Crispim & Watanabe, 2001; Vandekerkhove et al., 2004a;
2005a; 2005b). Vandekerkhove et al., (2004b) found on
average 35% more cladoceran species per lake in
dormant egg banks of 95 European permanent lakes
than in the corresponding active assemblage samples.
In rotifers from lake Loch, Great Britain, the assemblage
of resting eggs also contained higher species richness
than in the water column in any single year, but was
fully concordant with the assemblage observed over a
six year period (May, 1986).
70
Number of pools
Figure 3. Species accumulation curves for cladoceran
assemblages derived from active (empty symbols) and
dormant (filled symbols) samples across 61 high-altitude
temporary peat land pools of the Cordillera del Tunari,
Bolivia.
Cladocera species richness
14
12
10
8
6
4
2
0
-2
ACS
Although our results underline the efficiency of resting
egg bank analysis for species richness assessment of
zooplankton assemblages in temporary peat land pools,
other studies on temporary aquatic systems revealed
opposite results. In Kiskunság National Park (Hungary),
for instance, the resting egg banks of 12 temporary
pools yielded only 19 cladoceran species out of a total
of 32 species observed in the active assemblage samples
(Boven & Brendonck 2008). Incubation of the resting
egg banks from eight temporary pools in South Africa
did not yield higher species richness than active assemblage samples (De Roeck et al., in press). In these
examples, hatching success and low species yield may
have resulted from bet-hedging effects which are expected to be more important in the variable environment of
temporary pools. Bet-hedging occurs when only a fraction
of all viable resting eggs hatches under ideal conditions
DEB
Figure 4. Average of the total number of cladoceran species
recovered per pool from samples of the dormant egg bank
(DEB) and from snapshot active samples (ACS). Errors
bars represent 1 standard error of the mean.
DISCUSSION
The observed number of egg morphotypes in the dormant
egg bank yielded higher number of cladoceran species
than in active samples. Incubation of isolated unknown
egg morphotypes allowed identifying cladoceran ephippia
down to species level (Appendix 1). Some cladoceran
ephippia (e.g. A. glabra, C. aloniceps, G. testudinaria,
56
CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
Table 2. Pearson correlations for environmental variables and species richness of dormant and active community
samples. Only peat land pools with samples allowing counts of at least 300 individuals were included in the analysis.
Codes: TP = total phosphates, TN = total nitrates, pH = pH, COND = conductivity, ALK = alkalinity, TRANSP = water
transparency (Snell measure), DEPTH = water column depth, AREA = pool surface area, WPCOV = water plant cover,
CHLa = chlorophyll a, DNR = distance to the nearest rivulet, NGP = neighbor pools, CONN = connectivity, SEDTH =
thickness of the bottom sediment, Mac. Pred. = macroinvertebrate predators, Act. Sp. Rich = species richness from
active communities, Dor. Sp. Rich = species richness from dormant communities. **: P<0.01; ***: P<0.001.
TP
TN
pH
COND
ALK TRANSP DEPTH AREA WPCOV
TP
0.10
TN
0.17
0.16
pH
0.07 0.24
0.04
COND
0.05 0.24 0.31
0.18
ALK
0.09 -0.21 -0.26 0.02
TRANSP 0.08
0.14 0.52** 0.03 0.00 0.12 0.52**
DEPTH
0.17
0.08 0.25 -0.08 -0.24
0.14
AREA
-0.21
WPCOV -0.46** -0.03 -0.23 0.08 -0.30
-0.13 -0.25 0.26 0.09 -0.07 -0.58***
CHLa
0.01
0.14 -0.02 -0.07 -0.08 -0.05
DNR
0.01
0.23 0.10 -0.15 0.30
0.26
NGP
-0.14
0.15 0.18 -0.03 0.08
-0.31
CONN
0.18
0.29 -0.28 -0.16 0.13
SEDTH -0.06
-0.31
0.11 -0.07 -0.13 -0.23
Mac. Pred. 0.12
0.14
0.29 -0.11 0.18 -0.11 0.08
Act. Sp.
Rich
0.14
Dor. Sp. 0.33 -0.11 0.20 0.16 0.15
Rich
0.26
-0.10
-0.31
0.03
0.04
-0.01
0.26
-0.06
0.17
0.12
0.13
0.01
0.26
0.30
-0.04
-0.03
-0.08
0.02
0.06
0.06
0.05
0.28
0.31 -0.46**
0.24
0.14
-0.28
CHLA
DNR
NGP
0.01
0.06 -0.02
0.00 -0.14
-0.33 -0.04
0.07 0.21
0.09 0.12
0.31
0.13
-0.17
-0.02
-0.09
0.08
-0.12
0.07
-0.20
0.10
0.05
-0.28
-0.33 -0.17 0.73***
0.24
CONN SEDTH Mac.
Pred.
Act.
Sp.
Rich
0.08
Table 3. Environmental variable models explaining variation in cladoceran assemblages in dormant and active samples.
The total variation explained by the model, the percentage contributions of its constituents, and significance values
are shown. Only peat land pools with samples allowing counts of at least 300 individuals were included in the analysis.
See materials and methods for an explanation of the variable codes.
Variables
Co-variables
Total
Variation
%
Variation
F-ratio
p-value
0.063
2.079
0.049
0.182
2.156
0.002
3.147
2.445
1.928
0.002
0.020
0.046
Active community samples
Entire model
WPCOV
Dormant community samples
Entire model
SEDTH, CHLa, CONN
Individual contribution
SEDTH
CHLa
CONN
CHLa, CONN
SEDTH, CONN
SEDTH, CHLa
0.089
0.069
0.054
57
48.9
37.9
29.6
REVISTA BOLIVIANA DE ECOLOGÍA Y CONSERVACIÓN AMBIENTAL
between species richness of the dormant egg bank and
chlorophyll-a (Fig. 5b).
(Brendonck et al., 1998; Brendonck & De Meester, 2003).
In our study, the detection of cladoceran species living
in close association with the substrate (S. serricaudatus,
D. cf dentata, and I. cf spinifer) and that were therefore
absent from active assemblage samples shows the
effectiveness of the dormant egg bank analysis (DoleOlivier et al., 2000; Tremel et al., 2000; Fefilova et al.,
2006). Similar observations were reported by Vandekekhove et al., (2005b) who collected benthic taxa like
Ilyiocryptus sp, Alona sp., Leydigia sp., and Pleuroxus
sp., from the dormant egg bank. In our study, the absence
of the above mentioned species in the active samples
may be influenced by seasonal dynamics. Two months
of field sampling was too limited to collect cladoceran
species occurring at different times during the inundation
cycle. Seasonal dynamics in invertebrate communities
was shown as a typical phenomenon, even in temporary
pools (Lake et al., 1989; Lahr et al., 1999; Jocqué et al.,
2007; Boven & Brendonck, 2009).
The thickness of the sediment layer may influence
hatching requirements. Resting eggs displayed over thin
bottom sediments are certainly younger than those ones
buried in thick bottom sediments. Younger eggs rapidly
respond to environmental stimuli resulting in high rates
of hatchlings (Brendonck & De Meester, 2003). Sediment
layer thickness was negatively correlated with species
richness of the dormant assemblage (r =-0.33, p = 0.051;
Fig. 5c).
Connectivity significantly explained variation in dormant
assemblages but was not included in the explanatory
model for the active ones (Table 3). Species richness
decreased with connectivity (Fig. 5d). It is likely that community homogenization occurs in more connected peat
land pools through dispersal of dormant eggs. Patterns
of higher species richness in pools of intermediate isolation in comparison with highly connected pools were
also revealed by Vanschoenwinkel et al., (2007) in
temporary rock pools in South Africa. It remains unclear
why this pattern was revealed in our study only in dormant
and not in active communities. Probably the pattern was
obscured in active communities as several species were
missed. Further studies should elucidate whether these
species mainly occurred in isolated systems.
Cladoceran species only observed in the active assemblage (P. caca, P. hardingi, B. huaronensis, and E. cf
acanthodes) were probably missed from dormant
samples due to their low densities in the egg banks (see
Table 1). Moreover, these species occurred in very low
densities in the active assemblage in a specific mountain
valley (Table 1).
Different environmental variables explained variation in
the cladoceran assemblages of the active and dormant
samples (Table 3). Water plants were more important
for the active assemblages (Table 3). Species richness
was inversely correlated with water plant density
(r =-0.46, p = 0.001; Fig. 5a). Although vegetation may
increase the number of habitats, niches and food
resources and reduce the susceptibility of aquatic invertebrates to fish predation (Jeppesen et al., 1998; Diehl
& Kornijów, 1998), in fishless systems, water plants may
increase invertebrate predation pressure rather than
being a shelter (Meerhoff et al., 2006; 2007).
Our results suggest that the selection of resting egg on
the basis of morphotypes and their subsequent hatching
is a reliable method to estimate cladoceran species
richness in temporary high-altitude peat land pools. This
method may replace labor intensive field sampling, particularly in areas of difficult access and harsh climatic
conditions. However, care must be taken since different
species can produce morphologically similar eggs.
Results of assemblage structure analyses revealed that
variables explaining variation in dormant assemblages
were not concordant with those explaining variation in
active ones. This may result from the fact that egg banks
integrate eggs produced during years of variable environmental conditions, while the analysis was done on the
basis of single moment measurements. On the other
hand, higher species yields by incubation of the egg
bank may have contributed to a higher resolution to reveal assemblage structuring patterns. Analysis of the
dormant egg bank is therefore invaluable, not only in revealing the potential species richness but also for better
understanding assemblage structure of aquatic organisms.
Dormant egg bank analysis revealed important environmental variables that structure zooplankton assemblages.
In our study, chlorophyll-a was an important variable
structuring dormant assemblages. This result shows the
effectiveness of the dormant egg bank in detecting
environmental variables which cannot be detected by
the analysis of active assemblages. A data set with an
increased number of species probably offers a better
resolution in the analyses. Although a correlation does
not imply a cause – effect, there was a positive correlation
58
CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
a
1,15
Species richness DEB
1,10
Species richness ACS
b
1,20
1,15
1,05
1,00
0,95
0,90
0,85
0,50
0,75
1,10
1,05
1,00
0,95
0,90
0,85
0,80
0,70
0,65
1,55
1,60
1,65 1,70 1,75 1,80
1,85 1,90
0,75
0,2
1,95 2,00 2,05
0,4
0,6
0,8
1,20
c
1,20
1,2
1,4
1,6
1,8
2,0
2,2
2,4
d
1,15
1,10
Species richness DEB
Species richness DEB
1,15
1,05
1,00
0,95
0,90
0,85
0,50
0,75
0,4
1,0
Chlorophylla
Water plant coverage
1,10
1,05
1,00
0,95
0,90
0,85
0,80
0,6
0,8
1,0
1,2
1,4
1,6
1,8
0,75
-0,2
2,0
0,0
Thickness of the bottom sediment
0,2
0,4
0,6
0,8
1,0
1,2
Connectivity
Figure 5. Scatter plots showing the associations between ecological relevant variables for species richness recovered
from the dormant egg bank (DEB) and from active samples (ACS). Correlations were based on peat land pools with
samples allowing counts of at least 300 individuals.
ACKNOWLEDGEMENTS
BIBLIOGRAPHY
This research was funded by the Flemish University
Council (VLIR) in a cooperation agreement between the
Katholieke Universiteit Leuven (Belgium) and the
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postdoctoral grant from the National Fund for Scientific
Research, Flanders (FWO-Vlaanderen). Part of this
publication was supported by project G.0118.03 of the
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Appendix 1: Resting eggs morphotypes detected in the present study. Each picture shows the name of the species
hatched from a given morphotype. Characteristics: number of eggs per ephippium, size (length and width) and other
morphological characteristics used in the present study to identify morphotypes.
Characteristics:
1 egg
Length: 156µm, width: 90µm
Narrowing at posteroventral side, brown-dark color
Very alike to A. ossiani
Alona boliviana
100 µm
Characteristics:
1 egg
Length: 205µm, width: 153µm
Two detectable ridges on the egg
Alona cambouei
100 µm
Characteristics:
1 egg
Length: 113µm, width: 84µm
Transparent color
Egg covered by oval-shape valves
Very alike to A. ossiani
Alona cf ossiani
100 µm
Characteristics:
1 egg
Length: 229µm, width: 122µm
Narrowing at posteroventral side
Longitudinal ridges are observed.
Alona davidi
100 µm
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CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
Cont. Appendix 1.
Characteristics:
1 egg
Length: 164µm, width: 105µm
Oval shape
Tuberculated ornamentation.
Alona glabra
100 µm
Characteristics:
1 egg
Length: 135µm, wide: 79µm
Narrowing at posteroventral side
Without sculpturing on the valves
Very alike to A. boliviana.
Alona ossiani
100 µm
Characteristics:
1 egg
Length: 162µm, width: 103µm
Oval shape
Valves with a net like ornamentation
Alona excisa
100 µm
Characteristics:
1 egg
Length: 127µm, width: 67µm
Oval shape
Longitudinal ridges on the valves
Camptocercus aloniceps
100 µm
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REVISTA BOLIVIANA DE ECOLOGÍA Y CONSERVACIÓN AMBIENTAL
Cont. Appendix 1.
Characteristics:
1 egg
Length: 95µm, width: 67µm
Oval shape
Often with floating cells
Ceriodaphnia cf dubia
100 µm
Characteristics:
1 egg
Length: 152µm, width: 135µm
Like circular shape
Prominent postero ventral angle (*)
*
Chydorus brevilabris
100 µm
Characteristics:
2 eggs
Length: 167µm, width: 123µm
Egg in the dorsal part
Darkly colored
Daphnia peruviana
100 µm
Characteristics:
2 eggs
Length: 191µm, width: 119µm
Egg in the dorsal part
Dark-brown colored
Daphnia pulex
100 µm
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CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
Cont. Appendix 1.
Characteristics:
2 eggs
Length: 93µm, width: 88µm
Egg in the dorsal part
Transparent
Drephanotrix cf dentata
100 µm
Characteristics:
1 eggs
Length: 124µm, width: 109µm
Egg in the dorsal part, circular shape
Brown color
Ephemerophorus sp
100 µm
Characteristics:
1 eggs
Length: 239µm, width: 141µm
Egg in the dorsal part, oval shape
Brown colored with hexagons-like sculpturing on the valves
Graptoleberis testudinaria
100 µm
Characteristics:
2 eggs
Length: 109µm, width: 103µm
Transparent egg and circular shape
Like tuberculated valves with concentric rings
Ilyocryptus cf spinifer
100 µm
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REVISTA BOLIVIANA DE ECOLOGÍA Y CONSERVACIÓN AMBIENTAL
Cont. Appendix 1.
Characteristics:
2 eggs
Length: 101µm, width: 87µm
Egg in the dorsal part
Brown-dark colored
Macrothrix atahualpa
100 µm
Characteristics:
2 eggs
Length: 146µm, width: 130µm
Curved ridges on the valves
Transparent egg
Paralona piagra
100 µm
Characteristics:
1 egg
Length: 161µm, width: 126µm
Brown-dark colored
Pleuroxus aduncus
100 µm
Characteristics:
1 egg
Length: 171µm, width: 171µm
Prominent ridges and depressions on the valves
Brown-dark colored
Pleuroxus caca
100 µm
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CORONEL, J.S, X., AGUILERA, S., DECLECK & L., BRENDONCK: Running head: Hidden Andean diversity
Cont. Appendix 1.
Characteristics:
1 egg
Length: 177µm, width: 139µm
Rhombus-like sculpturing on the valves
Brown-dark colored
Pleuroxus sp
100 µm
Characteristics:
1 egg
Length: 94µm, width: 61µm
No sculpturing on the valves
Intense brown-dark colored
Schapholeberis spinifera
100 µm
Characteristics:
1 egg
Length: 177µm width: 107µm
Narrowing sharply at posteroventral side
No sculpturing on the valves with floating cells
Intense brown-dark colored
Simocephalus mixtus
100 µm
Characteristics:
2 eggs
Length: 161µm, width: 153µm
Small rhombus-like sculpturing on the valves
Brown-dark colored
Streblocerus serricaudatus
100 µm
67