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.I. Roldan et al. J. Exp. Mar. Biol. Ecol. 253 2000 63 –74 67
Table 2
a
Estimates of the power function by linear regression analysis Sample
Relation Ln a
b r
´ Rıo de la Plata
Lc Lt 0.444
0.639 0.769
N 5 35 B1 Lt
23.457 1.048
0.769 B2 Lt
21.701 0.908
0.757 Dp1 Lt
20.132 0.808
0.787 Dp2 Lt
20.007 0.910
0.920 Io Lt
24.279 1.246
0.796 ´
El Rincon Lc Lt
20.403 0.797
0.970 N 5 32
B1 Lt 22.018
0.773 0.709
B2 Lt 20.876
0.768 0.922
Dp1 Lt 21.132
0.976 0.984
Dp2 Lt 20.606
1.001 0.989
Io Lt 21.659
0.771 0.863
Pals Lc Lt
20.599 0.850
0.972 N 5 19
B1 Lt 23.243
0.991 0.881
B2 Lt 22.000
0.948 0.920
Dp1 Lt 20.900
0.953 0.984
Dp2 Lt 20.412
0.975 0.987
Io Lt 22.189
0.863 0.882
a
Lt, total length; Lc, head length; B1, mouth width; B2, mandible length; Dp1 and Dp2, snout to dorsal 1 and 2 distances; Io, interorbital length. All variables in mm.
was 264.09 mm total length average length of total samples. The relationship between
b
y versus Lt total length is y 5 aLt , which in lineal form is ln y 5 ln a 1 b ln Lt, where b is the allometric coefficient Table 2. Principal components analysis and discriminant
functions analysis were performed Bouroche and Saporta, 1983 by AMACP and AMDIS software.
3. Results
3.1. Genetic variation We interpreted the banding patterns of 25 enzyme systems to reflect 36 genetic loci
Table 1, 20 of which were monomorphic, with apparent Mendelian variation detected
Table 3 Basic statistics of the pectoral fin rays of S
. japonicus Sample
Mean S.D.
Range ´
Rıo de la Plata N 5 35
18.83 0.56
18–20 ´
El Rincon N 5 32 18.72
0.73 18–20
Pals N 5 19 18.05
0.87 16–19
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M .I. Roldan et al. J. Exp. Mar. Biol. Ecol. 253 2000 63 –74
for the remaining 16 loci Table 4. In eight of these polymorphic loci, the frequency of the common allele was higher than 0.95 in all samples. The remaining loci were
considered as highly polymorphic PGDH , G3PDH-1, G3PDH-2, G6PDH, GPI-
Table 4 Allele frequencies of 16 polymorphic loci of S
. japonicus sample size Locus
Allele South West Atlantic
Mediterranean Ocean
Sea ´
´ Rıo de la Plata
El Rincon Pals
102 102
23 AAT-
1 100
0.980 0.995
1.000 65
0.015 0.005
125 0.005
AAT- 2
-100 0.995
0.990 1.000
-108 0.005
0.010 PGM-
2 -100
0.995 0.995
1.000 -108
0.005 0.005
PGDH 100
0.899 0.931
0.957 110
0.061 0.037
117 0.035
0.021 0.043
120 0.005
0.005 83
0.005 G
3PDH-1 100
0.858 0.864
0.826 125
0.142 0.136
0.174 G
3PDH-2 100
1.000 0.995
0.870 105
0.005 0.130
G 6PDH
100 0.941
1.000 1.000
115 0.059
GPI- 2
100 0.686
0.717 0.522
76 0.309
0.222 0.435
112 0.005
0.061 0.043
GR 100
0.995 0.995
1.000 93
0.005 0.005
IDHP- 1
100 1.000
0.990 0.978
-200 0.005
0.022 400
0.005 IDHP-
2 100
0.995 0.995
1.000 82
0.005 0.005
LDH- 1
100 0.995
1.000 1.000
110 0.005
MDH- 4
100 0.990
0.995 1.000
133 0.005
78 0.005
0.005 PEP-LGG
100 0.966
0.970 0.804
92 0.025
0.152 117
0.010 0.030
0.043 PEP-LT
100 1.000
0.975 0.870
95 0.025
0.130 SOD
100 0.853
0.824 0.913
160 0.142
0.162 0.087
60 0.005
0.015
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2, PEP-LGG, PEP-LT, SOD with the frequency of variant alleles exceeding 5 in one or more samples. The average proportion of polymorphic loci 0.05 criterion among
´ the three collections was 13.9, ranging between 11.1 El Rincon and 16.7 Pals.
Overall average heterozygosity for all 36 loci was 0.043 and ranged between 0.036 El ´
Rincon and 0.054 Pals. ´
Only two of 35 tests for Hardy–Weinberg genotypic proportions were significant Rıo de la Plata G
3PDH-1, G6PDH due to a deficit of heterozygotes. Allele frequency differences among samples Table 5 were significant over all
collections at five loci G 3PDH-2, G6PDH, GPI-2, PEP-LGG, PEP-LT . This
significant variation is the basis for patterns of relationships and distinction among the collections that emerge through reinspection of Table 4, and the pairwise measures of
genetic variation. Collections from Atlantic and Mediterranean waters appear to be differentiated by
several criteria. Differences in the distribution of allele frequencies are evident at PGDH
110, G3PDH-2105, GPI-276, PEP-LGG92. Samples of both regions are separated in neighbour-joining clusters. Cavalli-Sforza and Edwards chord distance
´ ´
values between the Pals sample and Atlantic samples Rıo de la Plata, 0.082; El Rincon, 0.073 are the highest detected. The Atlantic and Mediterranean division is further
indicated by consideration of the variation over all loci. The higher gene diversity F ,
ST
Table 5 over all collections 0.025 is similar to the Atlantic vs. Mediterranean 0.021 samples.
The allelic distribution among the Atlantic samples shows no clear differentiation with
Table 5 F
analyses at all loci for different groupings of S . japonicus. Probabilities are based on contingency
ST
chi-squared analyses Locus
Total Atlantic
Atl. vs. samples
Med. AAT-
1 0.002
0.005 20.003
AAT- 2
0.000 0.000
0.000 G
3PDH-1 0.002
0.000 0.002
G 3PDH-2
0.084 0.000
0.084 G
6PDH 0.035
0.081 20.050
GPI- 2
0.025 0.005
0.020 GR
0.002 0.000
0.002 IDHP-
1 0.005
0.000 0.005
IDHP- 2
0.002 0.000
0.002 LDH-
1 20.002
0.002 20.004
MDH- 4
0.000 0.001
20.001 PGDH
0.004 0.001
0.003 PEP-LGG
0.063 0.000
0.063 PEP-LT
0.059 0.000
0.059 PGM-
2 0.002
0.000 0.002
SOD- 1
0.007 0.000
0.007 Totals
0.025 0.004
0.021 P , 0.05.
P ,0.001.
´ 70
M .I. Roldan et al. J. Exp. Mar. Biol. Ecol. 253 2000 63 –74
an incipient one only at G 6PDH115, GPI-2112, PEP-LT95. The overall similarity of
these collections is further reflected in their small distance 0.048. 3.2. Morphologic variation
In Fig. 2 individuals are plotted into the space defined by the two principal components of the morphologic diversity matrix; these first two axes explained 48.62
of the total variability. The first component explained 28.79 of the variability and was strongly influenced by variables related to head size: mouth width, mandible length and
interorbital length factor loading 0.77, 0.65 and 0.64, respectively. All Pals individuals were placed together with negative values for both components, and clearly separated
from Southern Atlantic fish. Although a small overlapping area 16.4 was observed between the two Argentinian samples, most individuals were distinguished according to
´ ´
their original sample, from Rıo de la Plata or from El Rincon. Greater head length but ´
´ lower mouth width and interorbital length in Rıo de la Plata compared with El Rincon is
the primary character difference. With respect to the discriminant function analyses, the number of individuals per
sample correctly classified averaged 65.1. The highest classification success rate was ´
´ observed in Pals with 100, with El Rincon and Rıo de la Plata samples showing 59.4
and 51.4, respectively.
Fig. 2. Principal components analysis based on morphologic data. Individuals are projected onto the plane formed by the first two principal components axes.
´ M
.I. Roldan et al. J. Exp. Mar. Biol. Ecol. 253 2000 63 –74 71
4. Discussion
