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1.
Mytilus trossulus Gould and M. edulis L. coexist in mixed populations in Atlantic Canadian waters. Although there is evidence that the two species hybridize in
natural populations and that hybrids produce progeny through backcrosses, no study of the microgeographic distribution of
the two forms and their hybrids has been made. Here we examine subtidal samples of mussels taken in July 1997 from two locations
in eastern Newfoundland (Canada) and from wave-exposed and protected environments within each location. Shell lengths ranged
from 15 to about 90 mm. Mussels were classified as pure forms or hybrids (F1, F2 and from backcrosses) based on four diagnostic markers, two allozyme loci (Mpi and Est-D) and two nuclear PCR-based DNA markers (ITS and Glu-5). In addition, a PCR-based mtDNA marker (COIII) was used to characterize the distribution of mtDNA mitotypes among pure and hybrid individuals. There were differences in
the proportions of pure M. edulis and M. trossulus between sites and between environments at one location. M. trossulus was the predominant species at one of the two exposed sites. In all four samples, M. trossulus was also the predominant form among small individuals. The frequency of hybrids was 26% overall and did not differ among
samples. Hybrids consisted mostly of backcrosses that were M. trossulus-biased among small mussels and M. edulis-biased among large ones. We conclude that both intrinsic genetic factors and extrinsic environmental factors influence the
relative frequency of M. edulis, M. trossulus and their hybrids.
Received: 29 June 1998 / Accepted: 4 November 1998 相似文献
2.
The mussel species Mytilus edulis L. and M. trossulus Gould coexist and hybridize throughout a large area that includes the north coast of Maine and Atlantic Canada. Previous studies provided genetic evidence for limited hybridization between the two species for mussels >15 mm. The present study used two genetic markers (ITS, Glu-5) to examine the genetic composition of early life-history stages by sampling veliger and pediveliger larvae, juveniles (<2.0 to 15.0 mm shell length) and adults (>15 mm shell length) in Trinity Bay, Newfoundland, during three consecutive years (1995–1997) to determine if differential mortality limits the relative abundance of hybrids. The relative frequency of the two species and the different hybrid genotypes was similar among the larvae, juveniles and small adult mussels. The double hybrid genotype (F1-like) was the rarest genotype observed. There was no evidence for differential mortality during the early life-history stages, and factors limiting production of hybrids appear to operate before the late larval stage. The observed frequency of hybrids is probably due to a combination of pre- and postzygotic reproductive isolating mechanisms operating early in the mussels life history. M. trossulus dominated the early life-history stages, possibly due to a higher population density and a greater reproductive output than M. edulis. Differential mortality may explain the observed decrease in frequency of M. trossulus and increase in frequency of M. edulis with increasing shell length. A similar frequency of hybrid mussels from larvae to the size class of 55 mm shell length may indicate a rate of mortality intermediate between the two parental species. The M. edulis–M. trossulus hybrid zone appears to be maintained by reproductive isolating mechanisms limiting the production of hybrids and life-history differences that allow the two species to coexist.Communicated by J.P. Grassle, New Brunswick 相似文献
3.
Two species of marine mussel, Mytilus edulis and M. galloprovincialis hybridize on the coasts of western Europe. Studies of hybrid mussel populations have shown that natural selection favors
M. galloprovincialis-like genotypes within this hybrid zone. Many hypotheses have been proposed to explain differential mortality in these populations.
This study tests two hypotheses addressing factors of mortality in a population, and describes yearly energy storage and reproductive
cycles of these two species and their hybrids. No evidence was found that the two taxa have different overall levels of reproductive
effort or parasite infestation. They do, however, have asynchronous spawning periods and divergent energy storage strategies.
In the year of this study, 1993, the M. edulis genotypic class spawned as a group in June and July. After spawning, they built up a high level of mantle energy-storage
tissues that are probably used for gametogenesis in the following winter and spring. The M. galloprovincialis genotypic group, however, spawned asynchronously, beginning in June and finishing by August, and did not build up high levels
of energy-storage tissues in summer. These results add a temporal component to the interpretation of selective forces acting
to shape this hybrid zone. Vulnerability of each species to mortality factors may differ because of their divergent reproductive
and energy-storage cycles.
Received: 15 January 1999 / Accepted: 26 July 2000 相似文献
4.
The musselsMytilus galloprovincialis andM. trossulus on the Pacific coast of North America 总被引:2,自引:0,他引:2
Most recent authors have called the bay mussels of the Pacific coast of North AmericaMytilus edulis Linnaeus, 1758. Thirteen samples ofedulis-like mussels were collected from California, Oregon, and Alaska, USA, in 1985, 1986 and 1987. Electrophoretic evidence from wight loci indicates that these samples consist of two genetically distinct groups, neither of which is similar toM. edulis from the Atlantic Ocean. Mussels in southern California are very similar toM. galloprovincialis Lamarck, 1819 from the Mediterranean Sea; it is probable thatM. galloprovincialis was introduced accidentally to southern California. Mussels in Oregon and Alaska are similar to those from the Baltic Sea and parts of eastern Canada; the nameM. trossulus Gould, 1850 has priority for this taxon. In central and nothern California,M. galloprovincialis, M. trossulus and their hybrids co-occur. Despite the presence of hybrids betweenM. galloprovincialis andM. trossulus, the genetic integrity which they maintain across large areas of the world warrants their recognition as two distinct species. 相似文献
5.
A strong clinal change in salinity occurs between the Baltic Sea and the North Sea, Atlantic Ocean, in the Danish Straits, where hybridization zone between mussels Mytilus edulis and M. trossulus has been reported. Eleven samples of mussels were studied from the Danish Straits and the inner Baltic Sea. Extensive introgression of M. edulis alleles from the North Sea into populations throughout the Baltic was ascertained for mitochondrial DNA (mtDNA) and two nuclear markers (ME15–16 and ITS). In the opposite direction, introgression of M. trossulus alleles into the M. edulis background was observed at the EFbis nuclear marker in populations from Kattegat (Danish Straits). While only M. edulis F (female) mtDNA was present in the Baltic, there were still strong differences in frequencies in the control region length variants between the Danish Straits and the inner Baltic samples, and weaker variation in coding region ND2–COIII haplotype frequencies. In the assays of the two mtDNA regions, various patterns of heteroplasmy were detected in 32% of all the studied individual mussels; this includes the presence of distinct, independently inherited M and F mitochondria in males, as well as the presence of two different distinguishable F genomes. The male-inherited M mtDNA genomes are quite common in the mussels from the Danish Straits, but very rare in males from the inner Baltic. Instead, a recombined control region variant (1r), which seems to have taken over the role of the M genome, was present in a number of specimens in the Baltic. Observations of heteroplasmy for two F genomes in some females and males confirm disruptions of the doubly uniparental inheritance mechanism in the hybrid Baltic Mytilus. 相似文献
6.
Two species of blue mussel, Mytilus galloprovincialis and M. trossulus, co-occur and hybridize along the Pacific coast of North America. Using a set of polymerase chain-reaction (PCR)-based genetic
markers which diagnostically identify these species, we show that they are sympatric from the Cape Mendocino region to the
Monterey Peninsula in northern and central California, USA. Mussels with hybrid genotypes were detected in all populations
sampled in the region of sympatry, and the frequency of hybrid genotypes in individual hybrid populations ranged from 13 to
44%. Significant frequencies of first-generation backcross genotypes were detected in two individual hybrid zone populations
(Berkeley and Monterey Marina) and in the hybrid zone as a whole, indicating that the potential exists for introgression between
M. galloprovincialis and M. trossulus. Despite this potential, we found no evidence of advanced introgression beyond first-generation backcrosses, suggesting that
gene flow between M. galloprovincialis and M. trossulus has been quite limited. The frequency of mussels with M. trossulus and hybrid genotypes declined abruptly south of Monterey Peninsula, while the frequency of mussels with M. galloprovincialis and hybrid genotypes declined precipitously north of Cape Mendocino. These abrupt genetic discontinuities indicate that this
blue mussel hybrid zone is presently positioned between two prominent coastal features and there is little, if any, export
of alleles from the hybrid zone into bordering parental populations.
Received: 20 August 1997 / Accepted: 26 October 1998 相似文献
7.
Morphological variation of Mytilus edulis and Mytilus trossulus in eastern Newfoundland 总被引:2,自引:0,他引:2
Allopatric populations of Mytilus species show distinct shell morphology which may be due to genetic and/or environmental effects. Sympatric populations of
Mytilus species show similar shell morphology which may be due to hybridization eroding morphological differences and/or the influence
of common environmental conditions. The present study examined shell morphology and shell shape from 16 sites in eastern Newfoundland
where M. edulis L. and M. trossulus Gould coexist in common environments with limited hybridization. Shell morphology was based on measurements of eight characters,
and shell shape was quantified by elliptic Fourier analysis of shell outlines. Significant differences were observed between
species for both shell morphology and shell shape across 16 sites sampled. The relatively small differences in morphology
and shape between the species were probably due to exposure to common environments rather than hybridization. Shell shape
for M. edulis was more eccentric compared to M. trossulus which was more elongated. Shell shape analysis of a range of size classes at one site showed a change from an eccentric to
an elongated shape going from the smaller to the larger size classes. Both species showed a similar trend, with the larger
M. edulis more eccentric and the larger M. trossulus more elongated.
Received: 17 July 1998 / Accepted: 6 January 1999 相似文献
8.
We examined natural selection within a population of marine mussels, sampled in southwestern England in June 1991, containing
a high frequency of hybrids between Mytilus edulis L. and M. galloprovincialis Lmk. This system is particularly tractable for the assessment of natural selection because hybridization is common and individual
mussels can be aged, allowing changes in the frequency of hybrid genotypes among age classes to be determined. We show that
strong viability selection occurs among hybrid genotypes which results in the virtual elimination of M. edulis–like genotypes from the population over a period of 3 years. Recombinant hybrid genotypes are intermediate in fitness, with
M. edulis–like genotypes having a lower survival rate and M. galloprovincialis–like genotypes having a higher survival rate than genotypes of mixed ancestry. Since intermediate fitness for hybrid genotypes
is inconsistent with endogenous selection models we conclude that the structure and position of this hybrid zone is probably
generated by exogenous selection. This pattern of selection is a recurring feature of this hybrid population and likely occurs
elsewhere in the hybrid zone. Selection against M. edulis–like genotypes appears to be offset by extensive immigration of larvae dispersed from pure populations of M. edulis.
Received: 14 July 1997 / Accepted: 24 February 1998 相似文献
9.
Mussel samples were collected at 4 to 6 wk intervals throughout 1987 from two hybridMytilus edulis/M. galloprovincialis populations, at Croyde Bay and Whitsand Bay, in southwest England. These were analyzed at two polymorphic loci which are diagnostic for allozyme differences which typifyM. edulis andM. galloprovincialis. Dry mantle weight as a function of shell length was determined for all individuals of each sample. Size-frequency data for the two populations was obtained in September 1987 and March 1988. For all genotypes at both sites, fecundity was a function of shell length, and in both populations the frequency ofM. galloprovincialis alleles was positively correlated with shell length. At both sites, allozyme genotype explained a significant amount of variation in mantle weight either when assessed as a main effect or when assessed as an interaction with shell length or time of collection. At Croyde,M. galloprovincialis mussels had greater estimated fecundity per unit length than theM. edulis mussels. Differences in the timing of spawning activity between theM. edulis and theM. galloprovincialis mussels were inferred, and these differences might act to reduce the amount of interbreeding at Croyde. At Whitsand, a reduced level of variability in the timing of spawning activity and fecundity between the genotypes was observed and explained by a higher degree of genetic mixing. Because theM. galloprovincialis mussels had (1) a greater estimated fecundity at any length, and (2) a greater mean length than theM. edulis mussels, the mean genotypic annual fecundity perM. galloprovincialis mussel was 2.8 times greater than an individualM. edulis mussel at Croyde, and 2.2 times greater than an individualM. edulis mussel at Whitsand. This evidence thatM. galloprovincialis mussels have an advantage in fecundity, and thus perhaps in fertility, taken together with the evidence thatM. galloprovincialis also has a higher viability, indicates directional selection in favour of theM. galloprovincialis phenotype. Because of the observed temporal stability of the population it seems likely that this selection is counterbalanced by a massive imigration ofM. edulis spat from neighbouring populations. 相似文献
10.
Along the west coast of North America, the invasive mussel Mytilus galloprovincialis and a native congener M. trossulus overlap in range and compete for habitat in an extensive hybrid zone along central California. The two species have been
shown to exhibit differential abiotic tolerances in laboratory studies, yet little is known about how such tolerances affect
spatial and temporal patterns of geographic distribution, particularly in areas of competition. We examined distributions
of the two congeners and their hybrids in neighboring intertidal and subtidal habitats in Bodega Bay, CA over 2 years, and
compared shell length and seasonal ubiquitin (Ub) conjugates to estimate protein turnover and physiological stress for the
species at each site. The two species were spatially segregated, with M. galloprovincialis dominating the subtidal habitat, and M. trossulus constituting a majority of the intertidal mussel population. Hybrid individuals appeared in low numbers at both sites. For
each habitat, there was no statistical difference between shell lengths of M. galloprovincialis and hybrids but M. trossulus mussels were statistically smaller than the other two. In regards to physiological performance, ubiquitin conjugate values
showed different seasonal cycles for the two species, suggesting different periods of peak environmental stress. The highest
levels of Ub-conjugated proteins were observed in winter for M. galloprovincialis and in summer for M. trossulus, consistent with the respective range edges for their distributions since Bodega Bay is near the northern range edge of the
invader and the southern edge of the native species. These findings suggest that future assessments of Mytilus populations along the California coast may need to consider vertical distributions and seasonal cycles as part of monitoring
and research activities. 相似文献
11.
Marine communities are experiencing unprecedented rates of species homogenization due to the increasing success of invasive
species, but little is known about the mechanisms that allow a species to invade and persist in a new habitat. In central
California, native (Mytilus trossulus Gould 1850) and invasive (Mytilus galloprovincialis Lamarck 1819) blue mussels and their hybrids co-exist, providing an opportunity to analyze the mechanisms that determine
the distributions of these taxa. Spatial and temporal variation in temperature and salinity and the relative frequencies of
these mussel taxa were examined between 2000 and 2004 at four sites in San Francisco Bay and four in Monterey Bay, which were
chosen for their different positions along inferred estuarine/oceanic gradients in the hybrid zone. Mussels were genetically
identified as the parent species or hybrids by amplifying regions of two species-specific loci: the adhesive byssal thread
protein (Glu-5′) and the internal transcribed spacer region of ribosomal DNA (ITS 1). The proportion of M. trossulus at the eight hybrid zone sites correlated negatively with average salinity (R
2=0.60) and positively with maximal temperature (R
2≥0.72), a somewhat unexpected result given what is known about the phylogeography of this species. The proportion of M. galloprovincialis showed the opposite pattern. The proportion of hybrids was correlated neither with habitat temperature nor salinity. Genotypes
of mussel populations at an additional 13 sites from Coos Bay, Oregon (latitude 43.35°N) to Long Beach, California (latitude
33.72°N), sampled at various intervals between 2000 and 2004, were also determined. This survey confirmed previous reports
that the hybrid zone lies between Monterey and the Cape Mendocino region (latitudes 36.63°N–40.5°N). Within Monterey and San
Francisco Bays, however, the temporal comparisons (1990s vs. 2000s) revealed abrupt changes in the proportions of the two
parent species and their hybrids on annual and decadal time scales. These changes indicate that the blue mussel populations
are in a highly dynamic state. The survey also showed that, regardless of habitat, M. trossulus is consistently of smaller average size than either M. galloprovincialis or hybrids.
相似文献
Caren E. BrabyEmail: |
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.
In Ireland, mussels on exposed rocky shores constitute an interbreeding mixture of two forms of mussels, the blue mussel,
Mytilus edulis, and the Mediterranean mussel, M. galloprovincialis. Results from an Irish study in the 1980s, using partially diagnostic allozyme markers, indicated that mussels higher up
the shore were more galloprovincialis-like than those lower down. In this study we set out to test two hypotheses: (a) recruits arriving on the shore are composed
of genetically distinct cohorts that settle preferentially at different levels on the shore, and maintain genetic distinctiveness
into adulthood; (b) recruits are genetically homogeneous, but once settled they diverge genetically over time, due to within-habitat
site specific-selection. The diagnostic Me 15/16 DNA marker was used to analyse the genetic composition of newly-settled spat recruiting to artificial substrates, which were
placed at two-week intervals from May–October 2002, on the mid- and low shore areas of two exposed sites in Galway Bay. Adult
mussels were also collected on each sampling date. Results did not support the preferential settlement hypothesis, i.e., the
genetic composition of primary settlers (≤ 500 μm) was similar between tidal heights and shores. Neither was there evidence
of post settlement selective mortality, as adults were genetically similar to settling spat. In spat and adults the frequency
of the M. galloprovincialis allele was high (0.56–0.80), due to high frequencies of M. galloprovincialis (> 37%) and hybrid (> 33%) genotypes, and correspondingly low frequencies of the M. edulis genotype (< 11%). Adult mussels from a nearby sheltered estuarine site, while significantly different to exposed shore mussels,
still had low frequencies of the M. edulis genotype (< 17%), indicating no apparent advantage for the genotype in this environment. There are indications that the genetic
composition of mussels may be changing on the Atlantic coasts of Ireland. 相似文献
14.
N. Kautsky 《Marine Biology》1982,68(2):143-160
Since Mytilus edulis L. is a biomass dominant in the Baltic much interest is focused on the ecology of the species. In this paper an attempt is made to quantitatively cover the reproductive cycle of a Baltic M. edulis population in order to provide data for energy flow models and to discuss aspects of recruitment in this species. Histological preparations of gonads showed that gametogenesis started with declining temperatures in autumn and proceeded very slowly through winter. At the beginning of March when food was supplied during the spring phytoplankton bloom, rapid maturation took place. This was also revealed by an increase in meat weight of the mussels. Only one spawning period was recorded, from the middle of May until the beginning of June, due to food being strongly limited to the population during the rest of the year. The length of the larval period was estimated as being 5 to 6 wk and settlement was registered from the end of June through July. In general the large annual variations found in the Baltic with regard to temperature and food abundance give rise to a more marked annual pattern in the reproductive cycle than is encountered in other seas. Fecundity was assessed for two populations from 4-and 15-m depths from studies covering two annual cycles of the changes in the relation of shell length — meat weight. The size-related fecundity was found to be equal in both populations and related to food abundance and not to growth or age. Fecundity, expressed as weight loss at spawning, ranged from 0% in 2-mm mussels and increased from 38 to 52% in 10-to 30-mm mussels. The fecundity as percentage of biomass in full-grown Baltic M. edulis is of similar magnitude as in full-grown mussels from other areas despite the smaller size of Baltic mussels. The reproductive output for the total 160 km2 research area was calculated as being 1 200 tons dry weight or 80% of the standing stock, which, due to the particular features of the Baltic M. edulis population probably represents the larger part of the total mussel production. This reproductive output, calculated as 8·107 eggs·m-2 and corresponding to 50% of the total annual zooplankton production, may thus consitute an important food source for herring larvae and carnivorous zooplankton. Recruitment was divided into two phases: (1) Recruitment of juveniles (=settlement of larvae), and (2) recruitment to breeding stock. Monitoring studies of settlement on ropes and the year round presence of high abundances of mussels <2 mm indicate that settlement is in excess of the demands for maintaining population size and that most settled mussels form a pool of competitively suppressed non-growing individuals. Not until death of an already established mussel will these become recruited to the breeding population. Thus recruitment is possible throughout the year which stabilizes the population and maintains it near the carrying capacity of the area with regard to food and space availability. 相似文献
15.
The blue mussels Mytilus edulis L. and M. galloprovincialis Lmk. hybridize in western Europe. Within hybrid populations nuclear alleles specific to M. galloprovincialis increase in frequency with age and size. This relationship changes with tidal height; alleles from M. galloprovincialis occur more frequently high in the intertidal zone, while M. edulis alleles predominate in the low intertidal zone. We tested the hypotheses that larvae with M. galloprovincialis alleles tend to settle higher in the intertidal zone, or that mussels redistribute themselves with respect to tidal height
after initial larval settlement. We sampled recently metamorphosed mussels every 2 weeks in a hybrid mussel population at
Whitsand Bay in southwest England throughout the summer of 1996. We observed four cohorts of newly settled mussels. There
was no evidence of differential settlement of mussels with different genotypes in connection with tidal height, or into shaded
versus unshaded microsites. Therefore, we rejected the preferential settlement hypothesis. There was substantial movement
of juvenile mussels in the first 4 weeks following initial settlement, but this “secondary settlement” did not result in genetic
differentiation with respect to tidal height. Further, significant differences in allele frequencies were found between primary
and secondary spat. This allele frequency change was in the opposite direction of that seen in the adult population, suggesting
newly settled larvae may be experiencing different selective pressures than adults. We propose that the genetic structure
of hybrid mussel populations with respect to tidal height is the consequence of differences in selection intensity.
Received: 30 April 1999 / Accepted: 5 May 2000 相似文献
16.
Many authors have considered the common mussels in temperate waters of the Northern and Southern Hemispheres to be a single cosmopolitan species,Mytilus edulis Linnaeus, 1758. Others have divided these mussels into several subspecies or species. Samples of mussels were collected from 36 locations in the Northern Hemisphere and nine locations in the Southern Hemisphere. Electrophoretic evidence from eight loci indicates that the Northern Hemisphere samples consist of three electrophoretically distinguishable species:M. edulis from eastern North America and western Europe;M. galloprovincialis Lamarck, 1819 from the Mediterranean Sea, western Europe, California, and eastern Asia; andM. trossulus Gould, 1850 from the Baltic Sea, eastern Canada, western North America and the Pacific coast of Siberia. Mussels from Chile, Argentina, the Falkland Islands and the Kerguelen Islands contain alleles characteristic of all three Northern Hemisphere species, but because they are most similar toM. edulis from the Northern Hemisphere, we suggest that they tentatively be included inM. edulis. These South American samples are morphologically intermediate between Northern HemisphereM. edulis andM. trossulus. Mussels from Australia and New Zealand are similar in allele frequency and morphometric characters toM. galloprovincialis from the Northern Hemisphere. FossilMytilus sp. are present in Australia, New Zealand and South America, which suggests that the Southern Hemisphere populations may be native, rather than introduced by humans. Morphometric characters were measured on samples which the allozyme data indicated contained a single species. Canonical variates analysis of the morphometric characters yields functions which distinguish among our samples of the species in the Northern Hemisphere. 相似文献
17.
Mitochondrial DNA (mtDNA) of Mytilus trossulus from the Gulf of Gdansk (southern Baltic) and M. edulis from Swansea Bay, South Wales, UK, collected in 1991, was studied by restriction-enzyme analysis. These two species were more similar to each other in haplotype frequencies than either was to M. galloprovincialis from Britain. M. trossulus resembles M. edulis in having a high frequency of heteroplasmy restricted to males. However, in contrast to M. edulis where restriction-site heteroplasmy predominates, in M. trossulus heteroplasmic individuals possess two genomes which differ in length by up to 3 kilobases. 相似文献
18.
The Mytilus species complex consists of three closely related mussel species: Mytilus trossulus, Mytilus edulis, and Mytilus galloprovincialis, which are found globally in temperate intertidal waters. Introduction of one or more of these species have occurred world-wide
via shipping and aquaculture. Stable hybrid zones have developed in areas where these species have come into contact, making
the invasion process complex. On the east coast of Vancouver Island (VI), British Columbia (BC), Canada, the native (M. trossulus) and introduced species (M. edulis and M. galloprovincialis), as well as their hybrid offspring, occur sympatrically. This study used a common environment experiment to quantify growth
and survival differences among native, introduced, and introgressed mussels on VI. Mussels were collected from an area of
known hybridization and reared in cages from May to August 2006. The cages were deployed at a local site as well as a remote
site (approximately 150 km apart), and the mussels were genotyped at two species-specific loci. Growth and survival, as fitness
measures, were monitored: native, introduced, and introgressed individuals were compared between and within sites to determine
whether growth and survival were independent of site and genotype. Overall, mussels reared at Quadra Island performed better
than locally-reared mussels at Ladysmith. Specifically, introgressed mussels reared at Quadra Island performed better than
all genotypes reared at Ladysmith, as well as better than native mussels reared at Quadra Island. Differences in survival
and growth among the native, introduced and introgressed mussels may serve to explain the complex hybridization patterns and
dynamics characteristic of the VI introgression zone. 相似文献
19.
Blue mussels in the genus Mytilus first arrived in the Atlantic Ocean from the Pacific during the Pliocene, following the opening of the Bering Strait. Repeated
periods of glaciation throughout the Pleistocene led to re-isolation of the two ocean basins and the allopatric divergence
of Mytilus edulis in the Atlantic and M. trossulus in the Pacific. Mytilus trossulus has subsequently colonized the northwest Atlantic (NW Atlantic) so that the two species are presently sympatric and hybridize
throughout much of the Canadian Maritimes and the Gulf of Maine. To estimate when M. trossulus arrived in the NW Atlantic, we have examined sequence variation within a portion of the female mtDNA lineage large untranslated
region (F-LUR) for 156 mussels sampled from three Pacific and eleven Atlantic populations of M. trossulus. Although we found no evidence of reciprocal monophyly for Pacific and NW Atlantic M. trossulus, limited gene flow between ocean basins has led to the divergence of unique sequence clades within each ocean basin. In contrast,
relative genetic homogeneity indicates high levels of gene flow within each basin. Coalescence-based analysis of the F-LUR
sequences suggests that M. trossulus recolonized the NW Atlantic from the northeast Pacific subsequent to a demographic expansion in the Pacific that occurred
~96,000 years before present (ybp). Estimates of timing of divergence for Pacific and NW Atlantic populations and the time
since expansion among NW Atlantic sequence clades indicate that M. trossulus arrived in the NW Atlantic more recently, between 20,000 and 46,000 ybp. Given that these estimates overlap with the dates
of peak ice in the NW Atlantic during the last glacial maximum (LGM, ~18,000–21,000 ybp), we suggest that colonization of
the NW Atlantic by M. trossulus occurred during, but more likely just subsequent to, the LGM and was followed by rapid temporal and spatial expansion in
the region. 相似文献
20.
K. Inoue S. Odo T. Noda S. Nakao S. Takeyama E. Yamaha F. Yamazaki S. Harayama 《Marine Biology》1997,128(1):91-95
The adhesive protein allele of mussels collected at 13 points in Japan from Hokkaido to Kyushu was analyzed by the polymerase
chain reaction using a set of primers which amplifies a part of the nonrepetitive region of the adhesive protein gene. While
most mussels exhibited a 126 bp fragment, characteristic of the pure Mytilus galloprovincialis, 55 of 64 mussels sampled at Hiura and 1 of 14 mussels at Hakodate Port exhibited 168 and 126 bp fragments. Sequence analysis
of the two fragments indicated that the 168 and 126 bp fragments are almost identical to previously reported sequences in
M. trossulus and M. galloprovincialis, respectively. Since the frequency of heterozygous individuals in Hiura is very high, it is unlikely that they are simple
hybrids. However, it is evident that mixing of genes occurred between the two species off Hokkaido.
Received: 6 September 1996 / Accepted: 9 October 1996 相似文献