CC BY
43
Protistology 2 (3), 159-168 (2002)
Protistology
Genetic diversity and population structure of wild and cultivated brown sea mustard, Undaria pinnatifida
Man Kyu Huh and Hong Wook Huh
Department of Biology Education, Pusan National University, The Republic of Korea
Summary
Enzyme electrophoresis was used to estimate genetic diversity and population structure ofthe wild and cultivated sea mustard, Undaria pinnatifida (Harvey) Suringar. Compared with other ecologically and economically significant brown seaweed, population structure of this species has not been studied. The objectives of this study were to estimate the levels of genetic diversity in the wild and cultivated populations and to describe the distribution of genetic variation within and among its populations. In wild brown seaweed, eight of 18 loci (44.4%) showed polymorphism. The cultivated populations were found to have fewer alleles per locus (1.49 vs. 1.63), fewer effective alleles per locus (1.14 vs. 1.32), lower percent of polymorphic loci (31.7 vs. 43.3), and lower diversity (0.068 vs. 0.159) than wild populations. These parameters of genetic diversity indicate that cultivated populations are genetically depauperated compared to their presumptive progenitor and the domestication process has eroded the level of genetic variation of this species. Nevertheless, genetic diversity of this species was higher than average values for species with similar life history. The sexual reproduction, perennial nature, high fecundity, and colonization process are proposed as possible factors contributing to high genetic diversity.
Key words: brown seaweed, genetic diversity, population structure, Undaria pinnatifida
Introduction
Anatomical details are different in land plants and brown algae largely because the gene pools of the parent stocks from which they evolved were different, but the inner cortex of the brown algae and the phloem of vascular plants are remarkably similar in general form and they perform very efficiently the same function.
The Phaeophyta, or brown algae, are the most complex and highly evolved of the Bracteobionta, and
are among the most efficient of all plants in photosynthesis and conduction of food (Pearson, 1995). Although the kelps and the rockweeds are the best-known Phaeophycopsida, other brown algae are also interesting and ecologically important. The sea mustard, Undaria pinnatifida (Harvey) Suringar, is abundant in East Asian marine ecosystems (Lee and Ybon, 1998). The cultivation of this species has also been very popular in the southern coast of Korea. Although this species has been known from many morphological
© 2002 by Russia, Protistology
and ecological studies, its genetic diversity and population structure have not yet been investigated.
The Korean populations of U. pinnatifida are typically small and distributed in patches. Although molecular and biochemical approaches are now increasingly being applied in Korea to establish the taxonomic and phylogenetic relationships within the animals and plants (Huh, 1998, 2001), no population genetical studies have been conducted, especially on the population genetic structure of algae species. Nothing similar to xylem tissue exists in the seaweeds; it is not needed and therefore never evolved, because the plants are almost continuously immersed in water. Sexual reproduction by means of flagellated gametes, on the other hand, is a real advantage in brown seaweeds, although it would be a drawback in land plants which grow in more xeric environments.
The objectives of this study were to estimate the level of genetic diversity in this species, to describe how its genetic variation is distributed within and among its populations and to find out if domestication process eroded the levels of genetic variation of the cultivated populations of U. pinnatifida as has been shown in most cultivated species (Doebley, 1989).
Materials and Methods
Sampling procedure and enzyme electrophoresis
U. pinnatifida was collected from five wild and ten cultivated populations in Korea (Fig. 1). One hapteron per plant was collected during the period from April 2000 to June 2001. 25 to 37 plants were sampled from each population. Approximately 1 to 2 g haptera tissues were ground with a pestle in a cold mortar in 300 to 500 ^l of extraction buffer (0.1% 2-mercaptoethanol, 0.001 M EDTA, 0.01 M potassium chloride, 0.01 M magnesium chloride hexahydrate, 4% w/v 1g PVP, 0.10 M Tris-HCl buffer, pH 8.0).
Electrophoresis was performed using 12.0% starch gels according to the methods used by Soltis et al. (1983). Nine enzyme systems were assayed in this study. Esterase (EST), fluorescent esterase (FE), and peroxidase (PER) were resolved on system 9 of Soltis et al. (1983). Isocitrate dehydrogenase (IDH), malate dehydrogenase (MDH), malic enzyme (ME), 6-phosphogluconate dehydrogenase (PGD), phospho-glucomutase (PGM), and superoxide dismutase (SOD) were resolved on system 10 of Soltis et al. (1983).
All U. pinnatifida allozymes expressed phenotypes that were consistent in subunit structure and genetic interpretation with those from most other allozyme studies of plants (Weeden and Wendel, 1989).
Fig. 1. Collection localities for populations of Undaria pinnatifida as sources for allozyme analysis. W1: Kampo, Gyeongsangnam-do;
W2: Onsan, Ulsan-ci; W3: Keaje-kun, Gyeongsangnam-do; W4: Narodo, Chon-lanam-do; W5: Chindo-kun, Chonlanam-do. C1: Kurengpo-up, Gyeongsangbuk-do;
C2: Banajin, Ulsan-ci; C3: Kajang-up, Pusan-ci; C4: Youngdo-gu, Pusan-ci; C5: Chinhae-ci, Gyeongsangnam-do; C6: Sac-heon-ci, Gyeongsangnam-do; C7: Namhae-kun, Gyeongsangnam-do; C8: Kohung-kun, Chonlanam-do; C9: Chindo-kun, Chon-lanam-do; C10: Mokpo-ci, Chonlanam-do.
Data analysis
The following genetic parameters were calculated using a computer program developed by Loveless and Schnabel (Edwards and Sharitz, 2000): the percentage of polymorphic loci (PP for population level and PS for species level), mean number of alleles per locus (A), effective number of alleles per locus (AE), and gene diversity (HE) (Hamrick et al., 1992). Species (indicated
with the subscript S) and mean population (indicated with the subscript P) levels of genetic diversity were calculated as in Hartl and Clark (1989). Observed heterozygosity (HO) was compared with Hardy-Weinberg expected values using Wright’s fixation index (F) or inbreeding coefficients (Wright, 1965). These indices were tested for deviation from zero by cc2-statistics following Li and Horvitz (1953). Nei’s gene diversity formulae (HT, HS, DST, and GST) were used to evaluate the distribution of genetic diversity within and among populations (Nei, 1973, 1977). The GST coefficient, in particular, estimates relative degree of population differentiation. In addition, cc2-statistics were used to detect significant differences in allele frequencies among populations for each locus (Workman and Niswander, 1970).
Nei’s genetic identity (I) and genetic distance (D) were calculated for each pairwise combination of populations (Nei, 1972). Populations were clustered via the unweighted pairwise groups method using arithmetic average (UPGMA) (SAS Institute Inc., 1989). Bootstrapping was done using the PAUP (or PHYLIP) program to estimate the relative support for clades (Felsenstein, 1993).
The genetic structure within and among populations was also evaluated using Wright’s (1965) F statistics: F , F , and FST. F and F measure excesses of homozygotes or heterozygotes relative to panmictic expectations, within samples and within populations, respectively. Deviations of F and F from zero were tested using cc2-statistics (Li and Horvitz, 1953). Two indirect estimates of gene flow were calculated. Estimates of the number of migrants per generation (Nm) were based on GST or the average frequency of private alleles, found in only one population (Slatkin,
1985). Genetic diversity was tested against regions by Spearman rank to look for any correlation between genetic variation in the wild and cultivated populations (Zar, 1984). Correlation between geographical and genetic distances was tested using a modified Mantel’s test (Smouse et al., 1986).
Results
Genetic diversity
At the species level, eight of18 loci (44.4%) showed detectable polymorphism in at least one population (Table 1). The remaining ten loci (Mdh-3, Sod, Est-1, Est-2, Idh-2, Per-1, Per-2, Pgm-2, Me-1, and Me-2) were monomorphic in all populations. The twelve loci including both loci, Mdh-2 and Pgd, were mono-morphic in cultivated populations.
NEI'S GENETIC DISTANCE 0,25 0,20 0,15 0,10 0 05 0 00
I__________I__________I__________I_________I_________I
C8
--------- C10
------------------- C9
Fig. 2. A dendrogram showing the genetic relationships among the fifteen populations of Undaria pinnatifida, based on genetic distance data. For explanation of symbols see Fig. 1.
In wild populations an average of 43.3% of the loci were polymorphic within populations, with individual population values ranging from 38.9% to 44.4% (Table 2). The average number of alleles per locus (AP) was 2.46 across populations, varying from 2.29 to 2.75. The effective numbers of alleles per locus at the species level (4es) and at the population level (4EP) were 1.34 and 1.32, respectively. The mean genetic diversity within populations was 0.159. Significant differences in allele frequencies among populations of U. pinnatifida were found in five of the eight polymorphic loci (Table 3).
Total genetic diversity values (HT) varied between 0.205 (Mdh-1) and 0.650 (Mdh-2), giving an average of 0.380 over all polymorphic loci (Table 3). The interlocus mean variation of genetic diversity within populations (HS) was high (0.360).
In cultivated populations an average of 31.7% of the loci were polymorphic within populations, with individual population values ranging from 22.2% to 33.3% (Table 2). The average number of alleles per locus (AP) was 2.57 across populations, varying from 2.40 to 3.00. The effective numbers of alleles per locus at the
Table 1. Allelic frequencies at eight polymorphic loci for Undaria pinnatifida.
Loci and alleles Populations
W1 W2 W3 W4 W5 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10
Mdh-1
a b N 0.821 0.179 28 0.879 0.121 29 0.867 0.133 30 0.900 0.100 30 0.950 0.050 30
Mdh-2
a 0.143 0.173 0.162 0.414 0.027 0.140 0.182 0.152 0.105 0.146 0.262 0.135 0.140 0.200 0.220
b 0.486 0.442 0.581 0.586 0.405 0.360 0.432 0.303 0.290 0.479 0.476 0.558 0.440 0.480 0.520
c 0.257 0.231 0.257 0.000 0.568 0.380 0.386 0.333 0.447 0.375 0.262 0.307 0.420 0.320 0.260
d 0.114 0.154 0.000 0.000 0.000 0.120 0.000 0.212 0.158 0.000 0.000 0.000 0.000 0.000 0.000
N 35 52 37 35 37 25 28 33 29 24 31 26 30 25 25
Fe-1
a 0.100 0.132 0.176 0.257 0.207 0.524 0.569 0.167 0.133 0.240 0.161 0.120 0.109 0.179 0.130
b 0.783 0.618 0.608 0.595 0.655 0.262 0.190 0.537 0.667 0.620 0.714 0.760 0.239 0.161 0.167
c 0.117 0.250 0.216 0.149 0.138 0.214 0.241 0.296 0.200 0.140 0.125 0.120 0.652 0.660 0.703
N 30 34 37 37 29 30 29 27 30 25 28 25 30 28 27
Fe-2
a 0.097 0.114 0.000 0.100 0.429 0.146 0.104 0.167 0.200 0.240 0.167 0.179 0.000 0.081 0.138
b 0.581 0.600 0.614 0.700 0.571 0.625 0.708 0.666 0.667 0.660 0.750 0.714 0.797 0.677 0.862
c 0.194 0.157 0.243 0.200 0.000 0.229 0.188 0.167 0.133 0.100 0.083 0.107 0.203 0.177 0.000
d 0.129 0.129 0.143 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.065 0.000
N 31 35 35 35 35 30 28 27 30 25 28 28 32 31 29
Idh-1
a 0.121 0.136 0.231 0.484 0.219 0.783 0.182 0.150 0.125 0.925 0.796 0.879 0.943 0.931 1.000
b 0.879 0.864 0.769 0.516 0.781 0.217 0.818 0.850 0.875 0.075 0.204 0.121 0.057 0.069 0.000
N 33 33 26 31 32 30 25 30 32 30 27 33 35 36 32
Pgd
a b N 0.771 0.229 35 0.814 0.186 35 0.800 0.200 35 0.809 0.191 34 1.000 0.000 35
Per-3
a 0.859 0.883 0.879 0.927 0.855 1.000 0.852 0.879 0.833 0.870 0.793 0.797 0.923 0.815 0.860
b 0.141 0.117 0.121 0.073 0.145 0.000 0.148 0.121 0.167 0.130 0.207 0.203 0.077 0.185 0.140
N 32 30 33 34 31 30 27 29 27 27 29 32 26 27 25
Pgm-1
a 0.107 0.143 0.173 0.100 0.114 0.000 0.160 0.155 0.077 0.130 0.183 0.152 0.111 0.230 0.177
b 0.893 0.757 0.827 0.900 0.886 1.000 0.840 0.845 0.923 0.870 0.817 0.848 0.889 0.770 0.823
N 28 35 26 35 35 30 25 29 26 25 30 32 27 37 34
Notes: N: number of individuals
: abbreviation codes as in Fig. 1
species level (^ES) and at the population level (^EP) were 1.33 and 1.14, respectively. The mean genetic diversity within populations was 0.068. Significant differences in allele frequencies among populations of U. pinnatifida were found in all of the six polymorphic loci (Table 3).
Total genetic diversity values (HT) varied between 0.238 (Per-3) and 0.662 (Mdh-2), giving an average of 0.437 over all polymorphic loci (Table 3). The interlocus mean variation of genetic diversity within populations (HS) was high (0.374).
Population structure
For wild populations FIS, a measure of the deviation from random mating within the five populations, was 0.397, ranging from 0.256 (Mdh-1) to 0.551 (Fe-2) (Table 3). The observed significant and positive FIS value indicates that there was a significant deficit of heterozygotes in the populations. Analysis of fixation indices, calculated for all polymorphic loci in each population, showed a slight deficiency of
Table 2. Allozyme variation within 10 populations of Undaria pinnatifida.
Pop. Pp Ap A Ae Hop (SD) Hep (SD)
Wild populations
W1 44.4 2.63 1.72 1.31 0.081(0.011) 0.155(0.051)
W2 44.4 2.75 1.78 1.43 0.109(0.012) 0.189(0.056)
W3 44.4 2.38 1.61 1.32 0.102(0.012) 0.168(0.051)
W4 44.4 2.25 1.56 1.28 0.085(0.011) 0.155(0.049)
W5 38.9 2.29 1.50 1.23 0.078(0.011) 0.129(0.047)
Mean 43.3 2.46 1.63 1.32 0.091 0.159
SD 5.2 0.22 0.12 0.07 0.005 0.023
Cultivated populations
1 22.22 3.00 1.44 1.16 0.044(0.007) 0.063(0.059)
2 33.33 2.50 1.50 1.15 0.045(0.007) 0.074(0.054)
3 33.33 2.67 1.56 1.21 0.049(0.007) 0.083(0.058)
4 33.33 2.67 1.56 1.11 0.034(0.006) 0.054(0.054)
5 33.33 2.50 1.50 1.13 0.040(0.007) 0.065(0.052)
6 33.33 2.50 1.50 1.13 0.051(0.008) 0.072(0.052)
7 33.33 2.50 1.50 1.12 0.048(0.007) 0.071(0.047)
8 33.33 2.33 1.44 1.11 0.033(0.006) 0.058(0.046)
9 33.33 2.67 1.56 1.16 0.045(0.007) 0.081(0.053)
10 27.78 2.40 1.39 1.11 0.028(0.006) 0.059(0.045)
Mean 31.67 2.57 1.49 1.14 0.042 0.068
SD 3.46 0.19 0.06 0.03 0.002 0.016
Species 33.33 2.83 1.61 1.33 - 0.146
Notes: (PP) percentage of polymorphic loci, (AP) mean number of alleles per polymorphic locus, (A) mean number of alleles per locus, (AE) effective number of alleles per locus, (HOP) observed heterozygosity, and (HEP) Hardy-Weinberg expected heterozygosity or genetic diversity.
heterozygotes as compared to Hardy-Weinberg expectations (Table 4). For example, 97.4% of fixation indices were positive (38/39), of which 24 indices (63.2%) deviated significantly from zero (p < 0.05). Only one index was negative, and did not deviate significantly from zero.
Genetic identity values among pairs of populations ranged from 0.955 to 0.997. The majority of the genetic diversity observed at the polymorphic loci in wild U. pinnatifida occurred within populations (GST = 0.045). The indirect estimates of Nm based on GST value (5.36).
For cultivated populations FIS, a measure of the deviation from random mating within the 10 populations, was 0.376, ranging from 0.288 (Fe-2) to 0.485 (Mdh-2) (Table 3). The observed significant and positive FIS value indicates that there was a significant deficit of heterozygotes in the populations. Analysis of fixation indices, calculated for all polymorphic loci in each population, showed a slight deficiency of heterozygotes as compared to Hardy-Weinberg expectations (Table 4). For example, all fixation indices were positive (57/57), of which 27 indices
Table 3. The test of chi square values for allelic frequencies except
monomorphic loci.
Wild Cultivated
Locus Value df Value df
Mdh-1 5.038 4 -
Mdh-2 111.652*** 12 79.820*** 27
Fe-1 12.818 8 198.531*** 18
Fe-2 85.488*** 12 64.868*** 27
Idh-1 29.742*** 4 271.419*** 9
Pgd 17.369** 4 -
Per-3 2.041 4 17.443* 9
Pgm-1 27.655** 8 18.766** 9
Notes:*,** ,and *** indiate significance a tie 0 05, 0.01 дпсі 0.001 leéis, leEfediAeLy.
(47.4%) deviated significantly from zero (p < 0.05). None of the indices were negative.
Genetic identity values among pairs of populations ranged from 0.814 to 0.998. The six polymorphic loci observed in U. pinnatifida exhibited significant differences in allelic frequencies among populations (Table 3), but the majority of the genetic diversity observed at the polymorphic loci in U. pinnatifida occurred within populations (GST = 0.139). The indirect estimates of Nm based on GST value (1.54) and the one private allele (0.93) differed, with Nm values based on GST being on the average about four times as high as Nm estimated from private alleles.
The similarity among fifteen U. pinnatifida populations can be seen in the UPGMA dendrogram, where all populations cluster below a genetic distance of 0.25 (Fig. 2). The genetic relationships among the populations can be seen in the dendrogram, where two clades, one consisting of five wild populations and the other consisting of ten cultivated populations, were recognized.
In addition, the correlation between genetic distance and geographic distance was high and significant (r = 0. 544), indicating that geographically close populations tended to be genetically similar and about 70% (1 - r2) of the variation in genetic distance is due to unknown factors other than distance.
Discussion
Genetic diversity
Brown seaweeds are the dominant plants in marine habitats along the continental shelves and in estuaries
and bays of the colder parts of the temperate oceans (Pearson, 1995). Genetic diversity in U. pinnatifida is high in comparison with that of most plant species on land. For example, the genetic diversity of U. pinnatifida at the species level (HES = 0.169) is higher than that of a self-breeding system (0.124) or that in case of sexual or asexual reproduction (0.138). It is also higher than the genetic diversity of temperate-zone species (0.146) and in case of sexual reproduction (0.151), but less than that of geographically widespread plant species (0.202) (Hamrick and Godt, 1989).
Genetic diversity of U. pinnatifida is comparable with other marine algae species, although the use of different methods (e.g., the number of loci, populations sampled, and the enzyme systems studied) may preclude meaningful direct comparisons. Hwang et al. (1998) analyzed eleven taxa of Porphyra by starch gel electrophoresis. In U. pinnatifida, P, A, and HE were 44.4, 1.78, and 0.169, respectively. For Porphyra, the corresponding mean values were 21.7, 1.4, and 0.062, respectively. Thus, U. pinnatifida showed higher levels of polymorphic and genetic diversity than taxa of Porphyra by Wilcoxon’s signed-rank test (p< 0.05).
The relatively high level of genetic variation found in U. pinnatifida is consistent with several aspects of its biology. First, the breeding system of U. pinnatifida has an important role in genetic variability. Species with predominantly sexual reproduction tend to have greater genetic diversity overall and to maintain more variation within their populations than species with predominantly asexual reproduction (Hamrick and Godt, 1989; Huh, 1999). Second, long-living perennial species, like U. pinnatifida, generally
Table 4. EktrnHtes of gpntic diveeityststistis a sx polymorphic lad. in
Undada pistils.
Locus Hi- Hs DST Fis FiT Gst
Wild populations
Mdh-1 0.205 0.201 0.004 0.256 0.268 0.017
Mdh-2 0.650 0.595 0.055 0.417 0.466 0.084
Fe-1 0.519 0.509 0.010 0.483 0.593 0.019
Fe-2 0.570 0.534 0.035 0.551 0.579 0.062
Idh-1 0.360 0.326 0.035 0.346 0.409 0.096
Pgd 0.270 0.257 0.014 0.507 0.532 0.050
Per-3 0.209 0.208 0.001 0.339 0.343 0.006
Pgm-1 0.257 0.252 0.006 0.276 0.292 0.021
Mean 0.380 0.360 0.020 0.397 0.423 0.045
Cultivated populations
Mdh-2 0.662 0.642 0.019 0.485 0.500 0.029
Fe-1 0.649 0.514 0.136 0.395 0.522 0.209
Fe-2 0.447 0.432 0.015 0.288 0.311 0.033
Idh-1 0.387 0.193 0.194 0.388 0.695 0.501
Per-3 0.238 0.231 0.007 0.362 0.382 0.031
Pgm-1 0.242 0.234 0.008 0.338 0.360 0.033
Mean 0.437 0.374 0.063 0.376 0.462 0.139
N±es: (Ht) tatl Geretic cdves-ty (HS) gertlc diveEdtywdh;h jupuStdjns PsT)srong populations ( Fn)d3riatk:rE cf genotype fcejisrdes firm Hardy-Weirb^g sipolatons CT/aral peculators, Fi3)viit±rin ;ircti.\dcLlalpopulS:io^, ard GsT) pKpatfcim c£ trtalcpretC dvrst partli'ed among
populaiDB.
maintain relatively higher levels of variation than annuals (Hamrick and Godt, 1989). As populations of U. pinnatifida are older, opportunities for the accumulation of mutations should be high (Ledig,
1986). Third, plant species with high fecundity usually maintain high genetic diversity (Huh, 1999). The sporangia are born on a characteristic sporophyll, which has undulate-plicate laminate wings with a somewhat inflated and sterile margin (Lee and Yoon, 1998). Finally, high genetic diversity is associated with the species’ colonizing success (Hamrick and Godt 1989).
Colonizing species are often expected to be markedly depauperated in genetic variation within populations due to founder effects and genetic drift (Hamrick et al., 1992). U. pinnatifida has maintained a considerable amount of variation during the colo-
nization process despite being mostly distributed in East Asia. During colonization, individuals with high genetic diversity may survive natural selection.
Population structure
An Nm value greater than 1.0 is considered necessary to prevent divergence resulting from genetic drift (Wright, 1951). Although the level of gene flow is sufficiently high to counterbalance genetic drift, these values were lower than those obtained for other species with similar traits primarily because of isolation by sea and topography (Hamrick, 1987). The indirect estimation of gene flow based on GST was 1.54. It is similar to the ranges from 1.1 to 2.8 in eelgrass, Zostera marina (Ruckelshaus, 1998). Z. marina is also a perennial angiosperm inhabiting soft-bottom marine
Table 5. Wright‘s fixation indices and chi-square test for ten populations of
Undaria pinnatifida.
Pop Mdh-1 Mdh-2 Fe-1 Fe-2 Idh-1 Pgd Per-3 Pgm-1
Wild populations
W1 0.283 ** 0.449 0.548*** 0.682*** 0.160 0.681*** * 0.364* 0.267
W2 0.202 0.481*** 0.570*** 0.471*** 0.113 ** 0.534** 0.205 * 0.361*
W3 * 0.433 0.299 0.566*** 0.533*** 0.150 0.296 * 0.440* 0.341
W4 0.272 ** 0.478** ** 0.427** ** 0.449** 0.619*** ** 0.532** * 0.362* 0.218
W5 -0.035 * 0.376* 0.334 0.655*** ** 0.460** - * 0.361* 0.165
Cultivated populations
C1 - 0.377 0.315 0.238 0.324 - - -
C2 - 0.226 0.592*** 0.278 0.403 - * 0.424* * 0.417
C3 - ** 0.468** 0.573*** 0.347 0.235 - 0.202 0.354
C4 - 0.246 0.482 0.482 0.446 - 0.346 * 0.469*
C5 - 0.665*** 0.345 0.290 ** 0.649** - 0.195 0.250
C6 - ** 0.562** 0.061 0.061 * 0.440* - * 0.380* 0.234
C7 - * 0.411* * 0.402* 0.214 * 0.440* - 0.335 0.176
C8 - 0.615*** 0.411 0.335 ** 0.477** - * 0.689* 0.264
C9 - 0.625*** * 0.376* 0.364 * 0.364* - ** 0.518 ** 0.473**
C10 - 0.745*** 0.447* 0.430* - - 0.512* 0.402*
Notes: *, **, and *** indicate significance at the 0.05, 0.01, and 0.001 levels, respectively.
Monomorphic population (allele frequencies > 95%) for a particular locus is indicated with a dash.
habitats, ranging from the intertidal zone to depths of approximately 15 m in temperate latitudes (Den Hartog, 1970). Thus, it means that most part of migration occurs within populations. The mean Nm value of wild populations is higher than that of cultivated populations. Wild populations are far away from beach and farms. Farms are located in near sea and fixed with fences. Thus, cultivated populations are isolated from wild populations and fences interrupt gene flow between wild and cultivated populations.
A substantial heterozygote deficiency occurred in some populations and at some loci (F = 0.397 for wild and F = 0.376 for cultivated populations). Population structuring is not obvious and, as a result, a sample may consist of a group of heterogeneous subsamples from a population. If there are fairly large differences in allelic frequencies among these subsamples, when they are lumped together, there will be a net deficiency of
heterozygotes and an excess of homozygotes even if Hardy-Weinberg proportions exist within each subsample (Wahlund 1928). Our sampling included individuals from several patches per population, resulting in an overall deficiency of heterozygotes. This sampling method produced a Wahlund effect in our results (Hartl and Clark, 1989).
One of the most striking features of this study was the more significant difference within populations than among populations. When the sexual reproduction and outcrossing mating systems of U. pinnatifida are taken into account, the mean identity value of 0.971 among ten populations (Table. 5) is higher than expected for cogeneric species (Hamrick and Godt, 1989). This high value is not especially surprising when viewed on the narrow geographic area over which the U. pinnatifida collections were made. Mean genetic identity between populations is rather high, but it is unclear how the
populations are genetically homogeneous. It is highly probable that directional movement toward genetic similarity in a relatively homogeneous habitat operates among the populations of U. pinnatifida. The plants of U. pinnatifida are growing on rocks in lower tidal mark facing the open sea and to the depth of 15 m (Lee and Yoon, 1998).
The percentages of polymorphism were 44.4% for wild brown seaweed and 33.3% for cultivated brown seaweed. The cultivated populations were found to have fewer alleles per locus (1.49 vs. 1.63), fewer effective alleles per locus (1.14 vs. 1.32), lower percent of polymorphic loci (31.7 vs. 43.3), and lower diversity (0.068 vs. 0.159) than wild populations. Over the polymorphic loci, 24 alleles were detected in wild brown seaweed and 16 alleles were detected in cultivated brown seaweed. No unique allele was found in cultivated populations. Most of the cultivated alleles were a subset of wild alleles. These genetic diversity parameters indicated that cultivated populations were genetically depauperated compared to their presumptive progenitor and domestication process has eroded the level of genetic variation of this species.
High levels of genetic variability of the wild species are expected because they were not subject to any of the selection pressures ofdomestication, and the maintenance of high genetic variability would favor their survival under natural conditions (Doebley, 1989). As a result, domestication in U. pinnatifida reduces genetic diversity. This is in general accord with the concept that most crops show a reduction in levels of polymorphism compared to their presumed progenitors (Doebley, 1989).
References
Den Hartog C. 1970. The Sea-grasses of the World. North-Holland Publishing Co., Amsterdam. The Netherlands.
Doebley J. 1989. Isozymic evidence and the evolution of crop plants. In: Isozymes in Plant Biology (Eds. Soltis D.E. and Soltis P.S.). Dioscorides Press, Portland. pp. 46—72,
Edwards A.L. and Sharitz R.R. 2000. Population genetics of two rare perennials in isolated wetlands: Sagittaria isoetiformis and S. teris (Alismataceae). Am. J. Bot. 87, 1147-1158.
Felsenstein J. 1993. PHYLIP (Phylogeny Inference Package) version 3.5s. Distributed by the author. Department ofGenetics, Univ. Washington, Seattle. Hamrick J.L. 1987. Gene flow and distribution of genetic variation in plant species. In: Differentiation patterns in higher plants. (Ed. Urbanska K.). Academic Press, New Yark. pp.53-67. Hamrick J.L. and Godt M.J.W. 1989. Allozyme
diversity in plant species. In: Plant population genetics, breeding and genetic resources (Eds. Brown A.D.H., Clegg M.T., Kahler A.L. and Weir B.S.). Sinauer, Sunderland. pp. 43—63.
Hamrick J.L., Godt M.J.W. and Sherman-Broyles
5.L. 1992. Factors influencing levels of genetic diversity in woody plant species. New Forests. 6, 95-124.
Hartl D.L. and Clark. A.G. 1989. Principles of Population Genetics 2nd. Sinauer associates, Inc. Mass. p. 682.
Huh M.K. 1998. Allozyme variation and population structure of Corbicula papyraceae from Nam and Sumjin Rivers. Korean J. Genet. 20, 163-172 Huh M.K. 1999. Genetic diversity and population structure of Korean alder (Alnus japonica: Betu-laceae). Can. J. For. Res. 29, 1311-1316.
Huh M.K. 2001. Allozyme variation and population structure of Carex humilis var. nana (Cyperaceae) in Korea. Can. J. Bot. 79, 457-463.
Hwang M.S., Han M.H. and Lee I.K. 1998. Allozyme variation and species relationships in the genus Porphyra (Bangiales, Rhodophyta) from Korea. Algae. 13, 447-459.
Ledig F.T. 1986. Heterozygosity, heterosis, and fitness in outbreeding plants. In: Conservation biology (Ed. Soule M.E.). Sinauer Press, Sunderland. pp. 77-104.
Lee Y.P. and Ybon J.T. 1998. Taxonomy and morphology of Undaria (Alariaceae, Phaeophyta) in Korea. Algae. 13, 427-446.
Li C.C. and Horvitz D.G. 1953. Some methods of estimating the inbreeding coefficient. Am. J. Hum. Genet. 5, 107-117.
Nei M. 1972. Genetic distance between populations.
Am. Nat. 106, 282-292.
Nei M. 1973. Analysis of gene diversity in subdivided populations. Proc. Natl. Acad. Sci. USA. 70, 33213323.
Nei M. 1977. F-statistics and analysis of gene diversity in subdivided populations. Ann. Hum. Genet. 41, 225-233.
Pearson L.C. 1995. The Diversity and Evolution of Plants. CRC Press, Florida. p. 646.
Ruckelshaus M.H. 1998. Spatial scale of genetic structure and an indirect estimate of gene flow in eelgrass, Zostera marina. Evolution. 52, 330-343. SAS Institute Inc. 1989. SAS/STAT user’s guide: Ver.
6. SAS Institute. Cary NC.
Slatkin M. 1985. Rare alleles as indicators of gene flow.
Evolution. 39, 53-65.
Smouse P.E., Long J.C. and Sokal R.R. 1986. Multiple regression and correlation extensions ofthe Mantel test of matrix correspondence. Syst. Zool. 35, 627-632.
Sohn C.H. 1993. Porphyra, Undaria and Hizikia cultivation in Korea. Korean J. Phycol. 8, 207216.
Soltis D.E., Haufler C.H., Darrow D.C. and Gastony G.J. 1983. Starch gel electrophoresis of ferns: A compilation of grinding buffers, gel and electrode buffers, and staining schedules. Am. Fern J. 73, 9-27.
Wahlund S. 1928. Zusammersetung von Populationen und Korrelation-sercheiunungen von Standpunkt der Verebungslehre aus betrachtet. Hereditas. 11, 65-106.
Weeden N.F. and Wendel J.F. 1989. Genetics of plant isozymes. In: Isozymes in plant biology (Eds. Soltis
D.E. and Soltis P.S.). Dioscorides, Portland. pp. 42-72.
Workman P.L. and Niswander J.D. 1970. Population studies on southern Indian tribes. II. local genetic differentiation in the Papago. Am. J. Hum. Genet. 22, 24-49.
Wright S. 1951. The genetical structure of populations.
Ann. Eug. 15, 313-354.
Wright S. 1965. The interpretation of population structure by ^-statistics with special regard to systems of mating. Evolution. 19, 395-420.
Zar J.H. 1984. Biostatistical Analysis. 2nd ed. Prentice-Hall, Inc., NJ. P. 718.
Address for correspondence: Man Kyu Huh. Department of Biology Education, Pusan National University, Pusan, 609-735, The Republic of Korea. E-mail: [email protected].
The manuscript is presented by A.L.Yudin
Corrigendum
Due to a type-setting error, page 132 (Vol. 2, N 2, 2001; the article «Use of salinity tolerance data for investigation of phylogeny of Paramecium (Ciliophora, Peniculia)» contained a wrong Figure. We apologize for this mistake. Figure 2 on page 132 should be as follows:
Deputy Editor, Andrew Goodkov
