The genetic effects of larval dispersal depend on spatial scale and habitat characteristics

We used allozymes to investigate the population genetics of the sea star Coscinasterias muricata throughout New Zealand, with emphasis on populations inhabiting the fjords on the west coast of the South Island. Mean genetic variability measured by Wright's F st for all the New Zealand populations was 0.061, indicating a moderate level of genetic divergence on a New Zealand wide scale. F st for populations from the fjord region was generally lower, ranging from 0.024 to 0.028, but it deviated from zero for all the loci examined. Evidence of isolation by distance was found when all populations were used in an analysis of log of the extent of gene flow between a pair of populations (M ) against the log of geographic distance (r 2 = 0.57, p < 0.001, Mantel test). Thus, a pattern of isolation by distance seems evident on this larger scale. However, pair-wise comparisons of genetic distances, measured as F st , of populations on the regional scale of the fjords on the west coast of the South Island showed no correlation, since high variation of F st (0.001 to 0.09) between populations separated by 20 to 105 km was detected. The overall pattern of genetic variation revealed in a cluster analysis of genetic identity, I, grouped all the fjord populations together with maximum genetic identities of 94.6% to the other South Island populations, but within the fjord region, populations were not segregated according to geographical location. We suggest that the relatively isolated hydrography of each fjord is a most likely explanation for why fjord populations form genetic clusters that are inconsistent with geographical distance. The New Zealand fjords changed from freshwater systems about 12 000 to 6500 yr ago, and genetic equilibrium for the populations that colonized the fjords may not have been reached yet. We suggest that the recent colonization of the fjords, and the physical isolation from the open coast and each other, are important in explaining the genetic pattern of fjord populations of C. muricata.

Section: Discussionsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Genetic subdivision of a sea star with high dispersal capability in relation to physical barriers in a fjordic seascape

Sköld¹,

Wing²,

Mladenov³

2003

“…Mayr 1970, Mileikovsky 1971, Cnsp 1974, Underwood 1974, Obrebski 1979, Jablonski & Lutz 1983, Valentine & Jablonski 1983, Grahame & Branch 1985, Scheltema 1986, Havenhand 1995, Levinton 1995, Wray 1995. Although considerable dispersal can also be ach~eved by egg masses and small juveniles in both aplanktonic and planktonic life cycles (Highsmith 1985, Jackson 1986, Scheltema 1986, Johannesson 1988, Jokiel 1989, O'Foighil 1989, Martel & Chia 1991, Giangrande et al 1994, Helmuth et al 1994, Gebruk et al 1997, and although free-living larvae do not guarantee extensive dispersal (Burton 1986, Prince et al 1987, Petersen & Svane 1995, Parsons 1996, long-lived larval stages confer greater dispersal potential in general (Shuto 1974, Jablonski & Lutz 1983, Jackson 1986, Emlet et al 1987, Grantham 1995, Palumbi 1995, Scheltema 1995. Under some current regimes, larvae may be retained near or return to the parental habitat despite a long period in the plankton (Johnson 1971, Knowlton & Keller 1986, Young & Chia 1987, Pollock 1992, Shanks 1995, Scheltema et al 19...…”

Section: Advantages and Disadvantages Of Dispersalmentioning

confidence: 99%

On the advantages and disadvantages of larval stages in benthic marine invertebrate life cycles

Pechenik¹

1999

594

424

many benthic marine invertebrates develop by means of free-livlng, dispersive larval stages. The presumed advantages of such larvae include the avoidance of competition for resources with adults, temporary reduct~on of benthic mortality while in the plankton, decreased likelihood of inbreeding in the next generation, and increased ability to withstand local extinction However, the direct~on of evolutionary change appears generally b~a s e d toward the loss of larvae in many clades, implying that larvae are somehow disadvantageous. Poss~ble disadvantages include dispersal away from favorable habitat, mismatches between larval and luvenile physiological tolerances, greater susceptib~lity to env~ronmental stresses, greater susceptibihty to predation. and vanous costs that may be associated with n~etanlorphosing in response to specific chemical cues and postponing n~etamorphosis in the absence of those cues. Understanding the forces responsible for the present distribution of larval and non-larval (aplanktonlc) development among benthic marine invertebrates, and the potential influence of human activities on the direct~on of future evolutionary change in 1-eproductlve patterns, will require a better understanding of the following issues. the role of macro-evolutionary forces in selecting for or against dispersive larvae, the relative tolerances of encapsulated embryos and free-living larvae to salinity, pollutant, and other environmental stresses; the degree to which egg masses, e g g capsules, and brood chambers protect developing embryos from environmental stresses; the relative magmtude of predation by planktonic and benthic predators on both larvae and early juveniles; the way In which larval and juvenile size affect vulnerability to predators; the extent to w h~c h encapsulation and brooding protect against predators; the amount of genetic change associated with loss of larvae from invertebrate life cycles and the time required to accomplish that change; and the degree to which continued input of larvae from other populations deters selection against dispersive larvae The prominence of larval development in modern life cycles may reflect difficulties In loslng larvae from llfe cycles more than selection for their retention.

“…Restriction of gene flow for species with high dispersal capacities could result either from physical (Quesada et al 1995, Parsons 1996 or biological barriers (Benzie et al 1992, Ford & Mitton 1993) to gene flow, or from natural selection (Koehn et al 1980, Schmidt & Rand 1999. Known circulation patterns in the southern Gulf of St. Lawrence and larval distribution patterns (Drouin et al 2002) suggest passive dispersion of the Semibalanus balanoides larvae from north to south of the Miramichi estuary (Lauzier 1965, Koutitonsky & Budgen 1991 For invertebrates with planktonic larvae, biological factors that may act on gene flow include food supply, predators and larval behavior (Burton 1983).…”

Section: Physical and Biological Barriersmentioning

confidence: 99%

“…Although for some groups of species this relationship seems to hold (seastars: Nishida & Lucas 1988, Williams & Benzie 1993, for others it does not (mussels: Koehn et al 1980, Hedgecock 1986, Quesada et al 1995scallops: Parsons 1996). Other causes, beside genetic drift, could explain the latter situations: (1) restriction of gene flow, including immigrant infertility (Burton 1983), nonrandom mating (Johannesson et al 1993), larval retention or directional dispersion mechanisms (Dando & Southward 1981, Mitton et al 1989, Parsons 1996, larval behavior (Burton & Feldman 1982), or (2) natural selection (Koehn et al 1980, Brown & Chapman 1991, McDonald 1991, Duggins et al 1995, Schmidt & Rand 1999.…”

Section: Introductionmentioning

confidence: 99%

Fecundity, growth rate and survivorship at the interface between two contiguous genetically distinct groups of Semibalanus balanoides

Brind’Amour¹,

Bourget²,

Tremblay³

2002

On the western coast of the Atlantic, according to the literature, 2 distinct groups of Semibalanus balanoides occur with a distinct interface near the Miramichi Estuary, New Brunswick, in the Gulf of St. Lawrence. On each side of this interface, the groups are characterized by clinal variations for MPI (mannose-6-phosphate isomerase) and GPI (glucose-6-phosphate isomerase). The present study was carried out to determine whether selection occurs at this interface, to establish how early in the sessile life period it occurs and to examine the selecting forces involved. Reciprocal transplant experiments of newly settled individuals to both sides of the interface were carried out. No significant differences specifically linked to source or destination were observed in growth or fecundity for the 2 groups at the sites studied for either control or transplanted individuals. However, differences in survival were observed; individuals transplanted south of the estuary showed lower survival than individuals transplanted north. An allozyme analysis of barnacle survivors for MPI and GPI, 2 alleles whose frequencies are known to vary abruptly in this region, indicated a change of allele frequency in transplanted individuals. The transplants' allele frequencies came to resemble those of adults from target sites, while no change occurred in transplanted individuals at control sites. Taken together with previous results, our study suggests that selection occurs very early in the newly settled individuals (spat).