VARIATION IN E G G SIZE OF THE FRESH-WATER PRAWN
MACROBRACHIUM AMAZONICUM
(DECAPODA: P A L A E M O N I D A E )
O. Odinetz Collart a n d H. Rabelo
A B S T R A C T
E g g size o f the fresh-water p r a w n M a c r o b r a c h i u m a m a z o n i c u m varied a m o n g ecologically
isolated or geographically distant populations o f the A m a z o n basin. T h e m e a n v o l u m e o f both
recently s p a w n e d n o n p i g m e n t e d eggs and older p i g m e n t e d - e y e d eggs was smaller in prawns
from the Tocantins River (0.14 a n d 0 . 2 0 mm3, respectively) than in those from the middle
A m a z o n (0.17 and 0.25 mm3). T h e largest eggs (0.19 a n d 0.27 mm3) w e r e displayed by females
from the Iquitos and G u a p o r e Rivers. Since the egg v olume was independent o f female body
size, it was attributed to population-specific characteristics. T h e egg size increased with the
distance o f the sampling site from the ocean, suggesting a progressive divergence o f this species
from a typical littoral population to an inland form, in a still active fresh-waterization process
similar to the pattern e v o l v e d a m o n g other species in the g e n u s M a c r o b r a c h i u m .
R�SUM�
L a taille des oeufs de la crevette d ' e a u d o u c e M a c r o b r a c h i u m a m a z o n i c u m varie entre des
populations écologiquement isolées ou géographiquement distantes dans le Bassin de l ' A m a zone. L e v o l u m e moyen, aussi bien des oeufs récemment émis et dépourvus d ' o e i l nauplien
pigmenté, q u e celui des oeufs plus agés présentant un oeil nauplien bien pigmenté, est significativement plus petit chez les individus collectés dans le fleuve Tocantins (respectivement 0.14
et 0.20 m m ' ) q u e chez des crevettes collectées dans le bassin m o y e n de l ' A m a z o n e ( 0 . 1 7 - 0 . 2 5
mm3); les plus grands oeufs ont éÃ
t© observés chez des femelles p r o v e n a n t d'Iquitos et du
Guaporé. Cette variation du v o l u m e des oeufs est indépendante de la taille de l'individu et des
caractéristiques de l ' e n v i r o n n e m e n t . Elle peut être reliée Ã
�la dispersion géographique des populations de M. a m a z o n i c u m dans le Bassin A m a z o n i e n . Le v o l u m e des oeufs a u g m e n t e avec la
distance du site de collection de l'océan, suggérant une divergence progressive de cette espèce
Ã
�partir de populations t y p i q u e m e n t littorales vers des formes d ' e a u douce, dans un processus
encore actif de continentalisation, similaire Ã
�celui qui caractérise l ' e n s e m b l e d e s autres espèces
du genre M a c r o b r a c h i u m .
The volume o f the eggs produced by
crustacean species is, in part, under genetic
control (Raven, 1961). It shows a general
pattern o f interspecific variation, decreasing
from colder to warmer waters over a northsouth latitudinal gradient, and from deepsea benthic to shallow coastal and epipelagic waters (e.g., Omori, 1974; Sastry, 1983).
In fresh-water decapods, large eggs appear
to be associated with landlocked species inhabitating plankton-poor, clear, and rather
acid waters, and small eggs mostly to anadromous and brackish species (Shokita,
1979; Magalhaes and Walker, 1988; Odinetz Collart and Magalhaes, 1994; Jalihal et
al., 1993). The same continentalization pattern has been described in M a c r o b r a c h i u m
nipponense (de Haan), where large eggs
were found in fresh-water lake and river
populations, small eggs in estuary popula-
tions, and intermediate-sized eggs in brackish-water populations. At times, the full size
range is seen in a single water system
(Chow et al., 1988; Mashiko, 1990). Crossing experiments between individuals o f M.
nipponense from two adjacent groups o f a
single drainage system suggested that the
egg-size differences a m o n g local, ecologically isolated populations are controlled as
a quantitative genetic trait (Mashiko, 1992;
Mashiko and Numachi, 1993).
The river prawn M a c r o b r a c h i u m a m a zonicum (Heller) occurs in South America
throughout the basins o f the Orinoco, A m azon, and Paraguay Rivers (Holthuis,
1952). It seems to be absent in estuaries despite successful laboratory larval culture in
saline water (Vargas and Paternina, 1977;
Guest, 1979; Guest and Durocher, 1979). In
the A m a z o n basin, this species is very
abundant
1975),
in
white
especially
waters
(sensu
in floodplain
Sioli,
lakes,
and
s c a r c e in a c i d b l a c k w a t e r s o f s m a l l h i g h land forest streams. M a c r o b r a c h i u m a m a zonicum
which
produces
incubate
hatching
zoea,
as
a
numerous
for
15-17
primitive
which completes
small
days
eggs
before
free-swimming
a prolonged larval
d e v e l o p m e n t w i t h 1 0 o r 11 l a r v a l s t a g e s i n
2 8 - 3 3 days (Magalhaes, 1985).
M a c r o b r a c h i u m a m a z o n i c u m s h o w s different reproductive
the
locality
patterns
sampled
depending
on
(Odinetz Collart and
M a g a l h a e s , 1994). In the L o w e r Tocantins,
this species displays a typical r e p r o d u c t i v e
pattern o f a n a d r o m o u s littoral p a l a e m o n i d s
with
mass
(Odinetz
spawning during
Collart,
1987,
falling waters
1991 a). I n c e n t r a l
A m a z o n i a , lacustrine p o p u l a t i o n s b r e e d all
year
long;
number
of
however, a significantly higher
eggs
is r e l e a s e d
during
waters (Odinetz Collart, 1991b,
The
cific
variations
of egg
size,
rising
1992).
present study, focused on
RESULTS
intraspe-
discusses
the
fresh-waterization process of distant populations,
considering
graphic
barriers
and
the
strength
Fig. 1. Collecting sites for Macrobrachium amazonicum, with their distance (D) from the Amazon River
estuary: (1) Tocantins River, Cameta district, D = 120
km; (2) Tucurui reservoir, D = 330 km; (3) Amazon
River, Manaus, Lago do Rei, D = 1,225 km; (4) Lago
de Tefe, Tefe district, D = 1,750 km; (5) Japura River,
Japura district, D = 2,200 km; (6) Ucayali River, D =
2,940 km; (7) Guapore River, Indian Reserve, D =
3,410 km.
of
species-specific
geodis-
persal abilities.
M A T E R I A L S AND M E T H O D S
O v i g e r o u s females were collected from the l o w e r
Tocantins, close to C a m e t a on the Tocantins R i v e r
(Site 1), in the Tucurui reservoir (Site 2), in the A m azon River, close to M a n a u s , L a g o do Rei (Site 3),
L a g o de Tefe, Tefe district (Site 4), Japura River, Japura district (Site 5), Ucayali River, Iquitos district
(Site 6), and from the G u a p o r e River (Site 7) close to
the G u a p o r e Indian reserve (Fig. 1 T h e distances o f
the sampling sites ( 1 - 7 ) to the estuary o f the A m a z o n
R i v e r were, respectively: 120, 330, 1,225, 1,750,
2,200, 3,410, and 2,940 km f r o m the ocean. S a m p l i n g
was c o n d u c t e d using traps o r hand nets during the
breeding season. A t every site, females with both pigm e n t e d - e y e d and n o n p i g m e n t e d eggs were collected.
Recently s p a w n e d eggs do not s h o w eye p i g m e n t a t i o n
in the e m b r y o . During incubation, the e g g v o l u m e
gradually increases and the e m b r y o n i c eye pigmentation appears a few days before hatching (Magalhaes,
1985; M a s h i k o , 1982). All s a m p l e s were preserved in
7 0 % alcohol.
P r a w n size was estimated using carapace length,
m e a s u r e d f r o m the posterior m a r g i n o f the orbital cavity to the posterior e d g e o f the cephalothorax. Ten eggs
were r e m o v e d from each f e m a l e a n d m e a s u r e d in the
laboratory to the nearest 0.01 m m with a binocular
micrometer. T h e e g g v o l u m e was calculated from the
f o r m u l a v = 7rlhl/6, where 1 a n d h are, respectively,
the long and short axes o f the ellipsoidal egg.
W h e n all 75 ovigerous prawns were considered, the mean volume o f nonpigmented
eggs varied from 0.1207 mm3 in a female
collected in Cameta, lower Tocantins, to
0.2188 mm3 in a prawn from Tefe. In eggs
with pigmented eyes, the mean volume
changed from 0.1648 mm3 in Cameta to
0.3272 mm3 in the Guapore River. Egg size
within the same clutch had a mean coefficient o f variation (SD/mean) o f 8.72%.
There was no significant difference in variation o f egg volume within a single clutch
between the two groups o f females, with
pigmented and nonpigmented eggs, nor between the six prawn populations ( P > 0.05;
two-way ANOVA). W h e n the seven populations were considered, the mean volume
increased 33.42% ± 8.6% from the nonpigmented to pigmented-eyed egg stage.
In Fig. 2, mean egg volumes are plotted
against parental cephalothorax length for
each female with pigmented or nonpigmented eggs. Mean egg volume was independent o f prawn size in both nonpigmented and eyed eggs (r = - 0 . 0 6 and r = - 0 . 1 7 ,
respectively; P > 0.05).
Developmental stage and sampling site
significantly affected the mean egg volume
when all the prawns collected were considered. The higher variance was associated
with developmental stage. The interaction
between these two factors was not signifi-
Table 1. Two-way A N O V A analyzing the effect o f
incubation stage ( N = 2 ) and sampling site ( N = 7 ) on
m e a n egg volume of the prawn M a c r o b r a c h i u m a m a zonicum
Fig. 2. Relationship in the female prawn (Macrobrachium amazonicum) between carapace length (mm)
and the mean egg volume (nim'), considering individuals with nonpigmented eggs (o) and eyed eggs (*).
cant (two-way ANOVA, Table 1). The multiple range analysis for A N O V A denoted a
statistically significant difference in egg
size between both Tocantins samples and
Guapore populations, and considered the
populations from near Manaus, Tefe, and
J a p u r a to be h o m o g e n e o u s ( B o n f e r r o n i
range test; P � 0.05).
The mean egg volume in each population
was calculated separately for females with
nonpigmented and pigmented-eyed embryos. For both groups, the prawns from the
Tocantins River (Site 1 and Site 2) had the
smallest eggs, and those from the Guapore
(Site 7) the largest eggs. For both incubation stages, the mean egg volume increased
with the distance of the sampling site from
the estuary (Fig. 3). Both regression lines
showed a statistically significant correlation
between the two parameters (P � 0.01), following the equations: V(mm3) = 0.1532 +
1.379 D (km); r = 0.834 for the nonpigmented samples, and V(MM3) = 0.196 +
2.296 D (km); r = 0.933 for the the eyed
samples.
large eggs, and (3) widely distributed species with an intermediate type o f development. They considered this pattern as an
adaptative response to the selection pressure o f plankton-poor inland waters.
Crustacean species display a general pattern o f variation in egg size described as a
geographical cline following water temperature (e.g., Patel and Crisp, 1960; Nishino,
1990). Mashiko (1990) recognized variation in egg size in populations o f Macrobrachium nipponense depending on the hyd r o g e o g r a p h i c f e a t u r e s o f their habitat.
Large eggs were found in fresh-water inland populations and small eggs in estuarine prawns, supporting the hypothesis of
an interspecific continental pattern. However, no mating behavioral incompatibility
nor fertilization failure in laboratory hybrids have been noted between groups with
different egg sizes, suggesting that geographic distance is the main mechanism of
reproductive isolation for M. nipponense in
a particular water system (Mashiko, 1992).
However, opposite results have been de-
DISCUSSION
Rodriguez (1981) separated South American palaemonids into three groups based
on marine affinity: Atlantic and Pacific littoral species which depend on brackish water for their survival, and typically continental species. In an analysis o f larval development, Magalhaes and Walker (1988)
r e g r o u p e d A m a z o n i a n p r a w n s into: (1)
coastal species which show complete development of numerous small-sized eggs,
(2) typically continental species characterized by abreviated metamorphosis of a few
Fig. 3. Relationship between the m e a n e g g size in
six populations o f M a c r o b r a c h i u m a m a z o n i c u m with
both n o n p i g m e n t e d (o) and eyed eggs (*), a n d the distance from the A m a z o n River estuary to their collecting sites. The regression lines follow the respective
equations: V(mm3) = 0 . 1 5 3 2 + 1.379 D (km), r =
0.834 for n o n p i g m e n t e d eggs; V ( m m ' ) = 0.196 +
2.296 D (km), r = 0.933 for eyed eggs.
scribed in P a l a e m o n paucidens de Haan,
with spawning o f many small eggs by small
individuals upstream in standing waters,
and laying of fewer but larger eggs in
colder running waters of the middle and
lower course o f the river (Nishino, 1990;
Mashiko, 1982).
Two distinct categories of eggs were
identified in M a c r o b r a c h i u m amazonicum
along the A m a z o n Basin: spawning small
eggs in the Tocantins River ( 0 . 1 4 - 0 . 2 0 mm3
in mean volume), and laying large eggs in
the upper course ( 0 . 1 9 - 0 . 2 6 mm3) and in
the Guapore River (0.20-0.27 MM3). Intermediate-sized eggs (0.17-0.25 mm3) were
collected in the middle course o f the A m azon River. The egg volume was independent o f female carapace length in each population (P � 0.01). Body size, growth rate,
and reproductive pattern are usually affected by environmental factors such as temperature, current velocity, food availability,
and p o p u l a t i o n density. K a m i t a ( 1 9 7 0 )
found that the body size of P a l a e m o n p a u cidens inhabiting rivers is greater than in
those living in lakes and swamps, though
he did not report egg sizes. In the Tocantins
basin, large prawns (mean carapace length
= 19.5 mm), collected in running waters,
and smaller individuals (mean carapace
length = 9.9 mm), sampled in a recently
impounded reservoir, had eggs o f about the
same volume. Thus, the difference in egg
size cannot be attributed to temporary environmental differences, but may be a population-specific character in each locality of
the A m a z o n Basin with the mean egg volume increasing with the distance o f the
sampling site from the ocean. Differences
in egg size were not significant between
populations inhabiting the same water system (the Tocantins River or the Middle Amazon floodplain) even over a wide geographical range, as from Manaus (Site 3) to
Tefe (Site 4), Japura (Site 5), and Iquitos
(Site 6), suggesting the presence of gene
flow between these four groups. In contrast,
the Tocantins River is not considered to be
part of the Amazon hydrological system,
and Site 1 exhibits water-current inversions
following tidal changes. The prawn populations collected in the Tocantins were statistically significantly smaller than those o f
the other groups. This seems to be a marine
adaptive trait. Guapore prawns are region-
ally isolated at ecologically different habitats from other middle A m a z o n populations, separated by a series o f waterfalls on
the Madeira River. Their large eggs appear
to be a typical inland trait.
In heterogeneous or geographically isolated environments, a single species may
present genetically diversified populations
due to the depression o f gene flow between
them. The difference in egg size between
the seven groups o f M. amazonicum in the
A m a z o n Basin suggests a progressive divergence o f this species from a typical littoral population to an inland form in a still
active adaptive process. These results are
consistent with the general patterns evolved
in the genus Macrobrachium: an increase in
egg size with proportionate reduction in the
number o f eggs, reduction in both the number of larval stages and the duration o f larval period, and increased larval survival in
populations from interior continental waters
(Jalihal et al., 1993).
ACKNOWLEDGEMENTS
This research was undertaken jointly with the Instituto Nacional de Pesquisas da Amazonia (INPA) within the ORSTOM/CNPq-INPA convention, with the financial support of the CNPq through a student grant.
The authors are grateful to Angela Pimentel and Adriana Enriconi for technical assistance, Dr. Bruce Nelson for corrections of the English, and Mario Barletta
for valuable suggestions.
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RECEIVED: 26 June 1995.
ACCEPTED: 3 M a y 1996.
Addresses: ( O O C ) O R S T O M , Institut Francais de
Recherche Scientifique p o u r le D e v e l o p p e m e n t en
Cooperation, D E C , 213 rue L a Fayette, Paris 7 5 4 8 0
Cedex 10, France; (HR) Institute Nacional de Pesquisas da A m a z o n i a , C P B A , C x . P 478, Manaus, A M
6 9 0 1 1 - 9 7 0 , Brazil.