共查询到20条相似文献,搜索用时 78 毫秒
1.
Allozyme variation in global populations of striped mullet, Mugil cephalus (Pisces: Mugilidae) 总被引:5,自引:0,他引:5
The striped mullet, Mugil cephalus Linnaeus, 1758, is one of the few species of marine shore fish with a worldwide circumtropical distribution. Because of this
distribution and the dependency of M. cephalus on coastal waters during various phases of its life cycle, as well as nearshore living habits, questions have been raised
regarding levels of genetic divergence and gene flow among transoceanic populations. To cast more light on this, allozyme
variation at 27 presumptive gene loci was investigated in ten globally diverse populations. The observed heterozygosity ranged
from 0.018 (Hawaii) to 0.081 (Florida), averaging 0.050. The proportion of polymorphic loci showed a similar trend. Several
populations were characterised by fixed allelic differences. Estimated gene diversities were very high, the allele frequency
variation among populations was found to be 68%; genetic distances reached 0.242, with an average of 0.117. Estimated rates
of gene flow were high among Mediterranean populations (Nm = 7.26), and between Mediterranean and East Atlantic populations (Nm= 2.86), but extremely low between non-contiguous populations within the Indian, Pacific and Atlantic Oceans, where Nm ranged from 0.03 to 0.05.
Received: 7 April 1997 / Accepted: 4 February 1998 相似文献
2.
F. Maltagliati A. P. Peru M. Casu F. Rossi C. Lardicci M. Curini-Galletti A. Castelli 《Marine Biology》2000,136(5):871-879
The genetic relationships between morphologically indistinguishable marine and brackish populations of Syllis gracilis Grube, 1840 (Polychaeta: Syllidae) were studied by means of allozyme electrophoresis. Samples of S. gracilis from marine coastal and brackish-water habitats were examined for variation at 13 presumptive loci. In addition, a sample
of the closely related species S. prolifera (Krohn, 1852) was analysed. Five loci were multiallelic in at least one population of S. gracilis and eight loci in S. prolifera. Low to moderate levels of within-population genetic variability were found, with average expected heterozygosity values
ranging from H = 0.068 (±0.043 SE) to 0.187 (±0.069 SE) in the populations of S. gracilis; higher values were found in S. prolifera (H = 0.325 ± 0.076). The presence of various private alleles indicated a marked genetic divergence among populations of S. gracilis, with Nei's genetic distances ranging from D = 0.000 to 0.833 and a highly significant F
ST value. Furthermore, evidence for strong genetic heterogeneity between two sympatric marine populations was found. UPGMA cluster
analysis and multidimensional scaling pointed out a clear genetic divergence between brackish and marine populations. At least
two genetically divergent entities occurred in marine and brackish habitats. This could be due to local adaptation of individuals
coming from marine populations to brackish habitats, but more presumably to the occurrence of a species complex within S. gracilis.
Received: 6 June 1999 / Accepted: 7 February 2000 相似文献
3.
Starch-gel electrophoresis of allozymes was used to differentiate the two red mullet species (Mullus barbatus L. and M. surmuletus L.) in the Mediterranean Sea and, further, to investigate the genetic stock structure of M. barbatus in the eastern Mediterranean area. Twenty putative enzyme-coding loci were examined in eight M. barbatus samples caught in the Aegean and Ionian Seas (Greece) and in the Gulf of Lion (France), and two M. surmuletus samples caught in the Aegean and Gulf of Lion. A high degree of genetic polymorphism was found in both species. Species-specific
electrophoretic patterns were found in PGI* and PGM*. Estimates of variance of allele frequencies among samples (F
ST) and 2 analyses both revealed significant differences (P < 0.05) among the M. barbatus samples. Most of the genetic variation was among samples regardless of region. The mean value of Nei's genetic distance between
the two species was 0.329. Genetic distance among M. barbatus samples was low (maximum Nei's D = 0.012), with the sample from Platania differing most from other M. barbatus samples. This is probably be due to founder effects existing at this area. These results suggest that allozyme analysis may
provide important information on the genetic structure of the red mullet to ensure sustainable management of this species.
Received: 7 May 1997 / Accepted: 13 October 1997 相似文献
4.
This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F
ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation
is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much
higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies
between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested
that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the
basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at
“neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was
also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations
was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between
D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species
in Egypt; thus gene flow was not indicated between species.
Received: 24 October 1996 / Accepted: 27 November 1996 相似文献
5.
Genetic divergence among ten populations of small- and large-egg forms of the brackish-water polychaete Hediste japonica complex was investigated on 14 isozyme loci by electrophoretic analysis. The two forms were distinguishable by complete allele
substitutions at five loci, resulting in high genetic differentiation (Nei's D: 0.533 to 0.662). No genetic evidence of hybridization between the two forms was detected in sympatric populations in three
rivers. These results indicate that the two forms are reproductively isolated, clearly showing that the two forms are distinct
species. The genetic differentiation among populations was higher in the large-egg form (D: 0.005 to 0.111, G
ST: 0.435) than that in the small-egg form (D: 0.000 to 0.001, G
ST: 0.020). This genetic difference between the two forms seems to be attributable to a difference in their life histories.
The average expected heterozygosity was low in populations of both the large-egg form (0.005 to 0.068) and the small-egg form
(0.014 to 0.038) in comparison with other marine invertebrates.
Received: 11 April 1997 / Accepted: 8 September 1997 相似文献
6.
The genetic structure of Mycedium elephantotus (Pallas, 1766) populations from three regions around Taiwan was examined using allozyme electrophoresis. Eight loci were
scored from seven enzyme systems. Seven loci were polymorphic under the 95% criterion. The high ratio of observed to expected
genotypic diversities at the collection sites (G
O:G
E=0.8 to 1.0) indicate that M. elephantotus propagates predominantly by sexual reproduction. Allele frequencies of M. elephantotus differed significantly among regions (D=0.024 to 0.256, F
ST=0.032 to 0.218, p < 0.001), while populations among collection sites within each region were homogeneous (D=0.000 to 0.015, F
ST=0.010 to 0.022, p > 0.05). Genetic differentiation between populations from southern Taiwan and the Penghu Islands is greater than that between
southern and northern Taiwan populations, although the former two regions are much closer geographically. The UPGMA dendrogram
based on Nei's unbiased genetic distance showed a clear subdivision of populations into two groupings, northern Taiwan/Penghu
Islands and southern Taiwan. A higher level of gene flow was found between M. elephantotus populations in northern Taiwan and the Penghu Islands (N
m=7.56) than that between populations in southern Taiwan and other regions (N
m=0.90 to 1.72). The pattern of genetic subdivision among regions is consistent with the pattern of ocean currents, indicating
that genetic differentiation is likely driven by surface circulation vicariance.
Received: 2 December 1997 / Accepted: 15 September 1998 相似文献
7.
Allozyme variation at six polymorphic loci was examined in foliose dictyoceratid sponges from isolated reefs in the western Coral Sea. Four major genetic groups corresponding to the species Phyllospongia lamellosa, P. alcicornis, Carterospongia flabellifera and Collospongia auris were examined. A further two rare morphotypes from individual reefs formed genetic outliers to the P. lamellosa group, and may represent further taxa related to P. lamellosa. Gene frequencies in individual reef populations were largely in Hardy-Weinberg equilibrium, suggesting that random mating occurred in local populations of all four common species. Genetic variability was high and observed heterozygosities within populations ranged from 0.13 to 0.40. All four taxa showed significant genetic differentiation among populations (F
ST=0.05 to 0.36). Genetic distances (Nei's D) among populations within species ranged from 0 to 0.723 and increased with increasing geographical separation. There was evidence that genetic differentiation between populations to the north and to the south of the southern limit of the South Equatorial Current (SEC) divergence was greater than expected on the basis of their geographical separation. The SEC divergence may form a partial barrier to gene flow among populations of these ecologically important sponges on the submerged Queensland Plateau. Levels of migration among populations of three of the species was less than those required to prevent divergence of the populations through genetic drift (Nm<1). Restricted migration among populations may provide a mechanism to explain the occurrence of highly divergent populations of dictyoceratid sponges whose specific identity is not clear, and may allow them additionally to develop partial reproduction isolation from other populations. 相似文献
8.
An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm
Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by
distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined,
giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H
e
= 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable
enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme
locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F
is
(0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was
mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F
st
value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation
between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived
planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of
the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front,
relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time.
Received: 24 July 1997 / Accepted: 31 October 1997 相似文献
9.
Effects of contrasting modes of larval development on the genetic structures of populations of three species of prosobranch gastropods 总被引:1,自引:0,他引:1
M. G. Hoskin 《Marine Biology》1997,127(4):647-656
In south-eastern Australia, the prosobranch gastropods Morula marginalba (Blainville), Cominella lineolata (Lamarck) and Bedeva hanleyi (Angas) have similar fine-scale distributions, but appear to possess very different dispersal capabilities due to contrasting
modes of larval development. M.marginalba produce planktonic larvae, whereas C. lineolata and B. hanleyi undergo direct development in benthic egg capsules and emerge as crawling juveniles. To test for possible effects of contrasting
life histories on levels of genetic variation within and among populations, a survey was conducted of allozyme variation at
six polymorphic loci in 8 to 9 local populations of each species. Collections of snails were made between June 1992 and November
1993. Sampling ranges spanned between 162 and 180 km of coast. Regardless of larval type, proportions of single-locus genotypes
in each collection were consistent with the recruitment of offspring which had been generated through random mating. However,
genotypic diversity was lower in those species that undergo direct development. Loci surveyed in C. lineolata and B. hanleyi were polymorphic (i.e. frequency of most common allele <95%) in fewer populations than those examined for M.␣marginalba (P <0.001) and, where polymorphisms occurred, also possessed significantly fewer alleles (P <0.001). Consequently, average levels of expected heterozygosity were greater in populations of M. marginalba than in those of either of the other species (P <0.001). Genetic variation among populations, expressed as the standardised variance in allele frequencies (F
ST
), was inversely related to expected larval dispersal capability. The nine collections of M. marginalba showed little overall differentiation (F
ST
= 0.017; P <0.001), reflecting the ability of planktonic larvae to interconnect local populations, and so limit divergence due to drift
and natural selection. In contrast, there were high levels of allelic heterogeneity among the nine collections of C. lineolata (F
ST
= 0.523; P <0.001) and eight collections of B. hanleyi (F
ST
= 0.140; P <0.001). These data imply that for species which undergo direct development, local populations are effectively closed and
evolve largely independent of one another.
Received: 3 May 1996 / Accepted: 12 July 1996 相似文献
10.
Species of the toadfish genus Opsanus are increasingly used as experimental organisms in biomedicine and evolutionary/ecological physiology. Despite their importance,
little is known of the phylogenetic relationships among Opsanus species. DNA sequence data for portions of the mitochondrial 12S rRNA, cytochrome oxidase I and cytochrome b genes were generated
and analyzed from the four recognized Opsanus species and three outgroup taxa. Results of these analyses indicate an evolutionarily rapid divergence of three lineages
within the genus. O. beta and O. pardus were resolved within the same lineage, and could not be distinguished with these mitochondrial sequence data. These data
and paleoclimatic theory support a hypothesis of speciation based on the formation of allopatric populations during periods
of elevated water temperature in the northern Caribbean.
Received: 6 July 1999 / Accepted: 15 March 2000 相似文献
11.
We examined the genetic identities of 49 individuals of four species of eels in the genus Anguilla Shaw, A. anguilla, A. japonica, A. reinhardti and A. rostrata, using the random(ly) amplified polymorphic DNA (RAPD)-PCR technique. We used 15 random decamer primers. Out of the 22 148
amplification products detected, 454 markers were evaluated using Nei's distance coefficient, two numerical methods (neighbor-joining,
UPGMA), and phylogenetic analysis using parsimony (PAUP). Both numerical and parsimony methods were congruent and confirmed
the specific status of all four examined Anguilla species. In all dendrograms, all individuals of each of the species clustered together within four closed groups with highly
significant bootstrap values (between 97 and 100%). Additionally 1 to 18 species-specific monomorphic diagnostic fragments
were detected in three of the species; none were detected in A. anguilla. Mean interspecific genetic distances ranged from 0.384 to 0.559, with the minimum between A. anguilla and A. rostrata and the maximum between A. anguilla and A. reinhardti. Individuals collected at one locality and belonging to a single species did not cluster together, and neither were any diagnostic
monomorphic fragments found for individuals of single localities. This probably reflects a random dispersal of larvae in ocean
currents before they reach coastal waters. Among all possible species pairs, only the two Atlantic species were consistently
clustered in all dendrograms, with highly significant bootstrap values (100%). Additionally, we detected ten diagnostic markers
for this pair of eel species. From RAPD data, we suggest a phylogram which was routed by the descending analysis method: A. reinhardti appears to have been the first species to diverge from a putative common ancestor of the four eel species. Later, A. japonica separated from the hypothetical ancestor of the Atlantic species, which then split recently into A. anguilla and A. rostrata. The close relationship of A. anguilla and A. rostrata is indicated by their low genetic distance (GD = 0.384) and a high degree of shared RAPD fragments (SF = 71.2%); this compares with the following means for all other species pairs: ( = 0.531, = 44.2%). The prerequisites for using RAPD data for the reconstruction of phylogenies are discussed.
Received: 2 September 1999 / Accepted: 8 May 2000 相似文献
12.
The current contribution deals with the reproductive biology of a genus endemic to Brazil –Mussismilia Ortmann, 1890 – including all three species of the genus: M. braziliensis (Verrill, 1868), M. hartti (Verrill, 1868), and M. hispida (Verrill, 1902), which occur sympatrically in the studied area, the Abrolhos Reef Complex, Brazil. Sexuality patterns, modes
of reproduction, synchrony and spawning periods are reported, and were determined by histological examination of material.
All three species started to develop female and male gametes over different periods in the same breeding season. The three
species are probably broadcast spawners, since no embryos or planulae were observed in any species at any given time of the
year. Each reproductive cycle lasted approximately 11 months. Oogenesis and spermatogenesis started in different periods,
with spermaries appearing in approximately the eighth month of ovary development and lasting about 3 months. Reproductive
cycles were annual. Spawning probably occurred in consecutive months in each species. In M. braziliensis, spawning presumably happened between March and the middle of May in 1996 and 1997. Evidence suggested that spawning events
of M. hispida took place between the end of April and mid-June. M. hartti may have spawned between September and November. The data presented here suggested that all studied species have at least
one exclusive spawning period, asynchronically with the others. A possible exception may be the simultaneous (or close) spawnings
of M. braziliensis and M. hispida in May. It is suggested that asynchrony in spawning periods among species may reduce the chance of hybridization, gamete
waste and the competition for settlement surfaces. The occurrence of extended spawning periods for each species may also reduce
the risks of reproductive failure, due to temporary adverse conditions.
Received: 8 December 1998 / Accepted: 15 July 1999 相似文献
13.
Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations
were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F
ST
values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were
in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually
produced individuals (N*) to the sample size (N
i
)] and the minimum sexual input [this is the ratio of the number of genotypes (N
go
) over the sample size (N
i
)] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N
i
: = 1; N
go
:N
i
= 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies
may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal
or dispersal that occurred in the past.
Received: 27 March 2000 / Accepted: 29 June 2000 相似文献
14.
Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef 总被引:2,自引:0,他引:2
The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate
the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations.
S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore
reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from
December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies
in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of
multi-locus genotypes indicated a high number of unique genotypes (N
go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role
of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations
indicated that gene flow is restricted between some reefs (F
ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F
ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation.
Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern
in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene
flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further
from the coast.
Received: 10 July 2000 / Accepted: 5 October 2000 相似文献
15.
Results of isozyme electrophoresis were used to explore the genetic relationships between several Mediterranean morphs of
Cerithium (Gastropoda: Prosobranchia), for which taxonomy is currently uncertain because of high intraspecific variability and low
interspecific differentiation. The large species, classically known as C. vulgatum Bruguière, 1789 was identified at four sites (two in the French Mediterranean and two in southern Spain). Two different larval
types were found in the French sites, but poecilogony could not be demonstrated. Individuals collected from harbours were
not genetically distinct from open-sea populations of classic C. vulgatum. However, a population in the Embiez lagoon (French Mediterranean) which morphologically resembles C. vulgatum did display distinct genetic traits, supporting its status as a separate species. Of the small Cerithium species usually known as C. rupestre, two sympatric species (C.“rupestre” Risso, 1826 and C. lividulum Risso, 1826) were distinguished. Genotype frequencies within the analysed populations revealed much heterozygote deficiency.
F
ST
values (fixation index measuring the effects of population subdivision) suggest a higher genetic differentiation for C. lividulum populations than for C. vulgatum populations. We assume that a high larval dispersal capability (via planktotrophy) allows a high gene flow between populations
of C. vulgatum.
Received: 24 November 1998 / Accepted: 24 September 1999 相似文献
16.
The genetic relationships between morphologically indistinguishable marine and brackish-water populations of Monocelis lineata (O.F. Müller, 1774) (Proseriata: Monocelididae) were analysed by means of allozyme electrophoresis. Fifteen samples of M. lineata (13 from the Mediterranean and two from the Atlantic) from coastal marine and brackish-water habitats were examined for variation at 18 loci. Eleven loci were polymorphic in at least one population of M. lineata. Low levels of within-population genetic variability were found, with average observed and expected heterozygosity values ranging from Ho=0.015±0.015 to 0.113±0.044, and from
He=0.028±0.028 to 0.138±0.054, respectively. The occurrence of a number of private alleles indicated a marked genetic divergence among populations of M. lineata, with Rogers genetic distances ranging from
DR=0.003 to 0.676 and a highly significant FST value (0.918±0.012, P<0.001). UPGMA (unweighted pair-group method using arithmetic average) cluster analysis and multidimensional scaling showed a clear genetic divergence between marine and brackish-water populations. Moreover, Atlantic and Mediterranean populations were sharply separated. Our results suggest that M. lineata is a complex of sibling species.Communicated by R. Cattaneo-Vietti, Genova 相似文献
17.
The taxonomic status of the Montastraea annularis species complex is unclear. Much evidence has been accumulated to support the separation into 3 species, but the presence
of intermediate morphotypes and the apparent lack of effective reproductive barriers in some areas are yet unexplained. Several
authors have made a call for the introduction of new traits that can be used to resolve differences among closely related
coral species. We collected skeletal and tissue samples from corals within the M. annularis species complex (15 each of M. annularis, M. faveolata, and M. franksi) and 10 morphological intermediates from several reefs in the Florida Keys. Multivariate analysis of corallite skeletal measurements
supported the separation of the species complex into three taxa. We detected two main fluorescence emission peaks at 480 nm
(turquoise) and 515 nm (green) that were not distributed equally among the three species. Every M. annularis colony had a major turquoise fluorescence peak. Some had a weak green secondary fluorescence peak. Colonies of M. faveolata and M. franksi had either the green or turquoise fluorescence peak, but at significantly different frequencies. The intermediate morphotypes
proved to be highly heterogeneous with respect to both micromorphology and fluorescence, and their nature could not be fully
explained. We were not able to separate the three species using fluorescence characters alone, however this new trait does
increase our understanding of the taxonomic structure within the M. annularis species complex.
Received: 21 January 2000 / Accepted: 1 September 2000 相似文献
18.
Two morphologically indistinguishable but genetically very distinct polychaete species of the family Spionidae are found
in the Peter the Great Bay of the Sea of Japan. Both species bore into molluscan shells and occur sympatrically. They are
close in morphology to Polydora ciliata (Johnston, 1838) and some other members of the redefined P. ciliata species complex. The systematics of the two species is still under consideration by one of us (V.I.R.). A total of nine enzyme
systems comprising 12 isozyme loci were examined in both the species by means of starch gel electrophoresis. Nei's genetic
distance between them proved surprisingly high (D= 1.942) being the highest among estimates so far obtained for pairs of polydorid species. The levels of intraspecific genetic
variation in both species (Polydora sp. 1, H
e= 0.287 ± 0.064; Polydora sp. 2, H
e= 0.111 ± 0.045) are comparable to those of other electrophoretically studied polydorids. The problem of taxonomic integrity
of cosmopolitan marine invertebrate species is briefly discussed as well as the usefulness of isozymes as species-specific
characters suitable for unequivocal discrimination between sibling polydorid species. A list of enzymes characterized by interspecifically
variable numbers of expressed isozymes within polydorids is given and recommended for such a discrimination.
Received: 22 July 1997 / Accepted: 19 February 1998 相似文献
19.
J. M. Quattro D. S. Stoner W. B. Driggers C. A. Anderson K. A. Priede E. C. Hoppmann N. H. Campbell K. M. Duncan J. M. Grady 《Marine Biology》2006,148(5):1143-1155
Surveys of genetic variation within cosmopolitan marine species often uncover deep divergences, indicating historical separation
and potentially cryptic speciation. Based on broad geographic (coastal eastern North America, Gulf of Mexico, western Africa,
Australia, and Hawaii) and temporal sampling (1991–2003), mitochondrial (control region [CR] and cytochrome oxidase I [COI])
and nuclear gene (lactate dehydrogenase A intron 6 [LDHA6]) variation among 76 individuals was used to test for cryptic speciation
in the scalloped hammerhead, Sphyrna lewini (Griffith and Smith). CR and COI gene trees confirmed previous evidence of divergence between Atlantic and Indo-Pacific scalloped
hammerhead populations; populations were reciprocally monophyletic. However, the between-basin divergence recorded in the
mtDNA genome was not reflected in nuclear gene phylogenies; alleles for LDHA6 were shared between ocean basins, and Atlantic
and Indo-Pacific populations were not reciprocally monophyletic. Unexpectedly, CR, COI, and LDHA6 gene trees recovered a deep
phylogenetic partition within the Atlantic samples. For mtDNA haplotypes, which segregated by basin, average genetic distances
were higher among Atlantic haplotypes (CR: D
HKY=0.036, COI: D
GTR=0.016) than among Indo-Pacific haplotypes (CR: D
HKY=0.010, COI: D
GTR=0.006) and approximated divergences between basins for CR (D
HKY=0.036 within Atlantic; D
HKY=0.042 between basins). Vertebral counts for eight specimens representing divergent lineages from the western north Atlantic
were consistent with the genetic data. Coexistence of discrete lineages in the Atlantic, complete disequilibrium between nuclear
and mitochondrial alleles within lineages and concordant partitions in genetic and morphological characters indicates reproductive
isolation and thus the occurrence of a cryptic species of scalloped hammerhead in the western north Atlantic. Effective management
of large coastal shark species should incorporate this important discovery and the inference from sampling that the cryptic
scalloped hammerhead is less abundant than S. lewini, making it potentially more susceptible to fishery pressure. 相似文献
20.
We used random amplified polymorphic DNA (RAPDs) to examine small-scale spatial genetic structure in the red alga Delisea pulchra (Greville) Montagne at two locations near Sydney, Australia. We examined genetic structure among plants at four spatial scales
ranging from 2 km apart down to <50 cm apart between locations, among sites within locations, among quadrats within sites,
and among plants within quadrats. Haploid stages of D. pulchra were absent from the populations studied, suggesting that they are maintained through asexual reproduction of diploid plants.
Consistent with this, we found that 19 RAPD phenotypes scored in this study had multiple individuals, indicating the presence
of clones in these populations. However, there were no RAPD phenotypes common to two locations separated by only 2 km. Analysis
of molecular variance revealed that strong genetic differences occurred between plants from these two locations, with 46.3%
of the total genetic variation occurring at this scale, most probably reflecting limited gene flow. Within each location,
<25% of the genetic variation was attributable to differences among sites or quadrats, indicating gene flow at those smaller
scales. Most of the variation within each location occurred at the smallest spatial scale, among plants within 0.25 m2 quadrats. Nonetheless, some pairwise genetic distances (φST) between sites or quadrats within locations were large, indicating some genetic divergence on smaller scales. Genetic distance
was independent of spatial distance within both locations, suggesting that fine-scale differences within locations were most
probably caused by variation in fine-scale patterns of water movement or fine-scale natural selection. We assessed the impact
of one potential selective agent, grazing sea urchins, on the fine-scale genetic structure of D. pulchra. There was no evidence that grazing by sea urchins affected the genetic structure of D. pulchra. In combination with demographic data, our results indicated that local populations of D. pulchra within locations were relatively open and that fine-scale genetic structure was probably constrained by gene flow. At the
larger scale however, strong genetic differentiation indicated little gene flow between locations and restricted dispersal
of spores.
Received: 22 April 1999 / Accepted: 29 November 1999 相似文献