Genetic heterogeneity, detected by PCR-SSCP, among samples of larval Pacific oysters (Crassostrea gigas) supports the hypothesis of large variance in reproductive success

Abstract

Differences in genetic composition among samples of larvae produced during a single spawning season by a semi-isolated population of Pacific oysters (Crassostrea gigas) in Dabob Bay, Washington, confirm a specific prediction of the hypothesis that this and other marine animals have large variances in reproductive success. To study the genetics of single larvae, we cloned and sequenced part of the mitochondrial genome and developed polymerase chain reaction (PCR) primers to amplify four segments totaling nearly 2300 base pairs, or 13% of the genome. PCR products were digested with restriction enzymes into smaller fragments, which were then screened for single-strand conformational polymorphisms (SSCP). Seven plankton samples (total N = 877), taken between 10 and 21 August 1993, showed a common composite PCR-SSCP haplotype that comprised from 53 to 85% of samples. Nevertheless, exact probability and permutation tests reveal that early and late samples from north Dabob Bay differed significantly from the rest. These differences cannot be ascribed to spatial variation and are consistent with the hypothesis that larvae are produced by relatively few adults, in accord with previous observations of substantial genetic drift in this large population.

Stock Identification of Gag, Mycteroperca microlepis, Along the Southeast Coast of the United States

“…This process can lead to diminished genetic variation, gene frequency differences among cohorts, and kinship among individuals within cohorts. The basic tenets of this hypothesis can be extracted from a number of lines of reasoning and are supported by a variety of empirical data (see Hedgecock, 1994;Ruzzante et al, 1996;Li and Hedgecock, 1998). In this light, the present data are perfectly understandable because the number of adults that contribute to a given year class could be limited by (1) decline in overall abundance (McGovern et al, 1998), (2) extremely skewed sex ratios compared with historical values McGovern et al, 1998), (3) variance in reproductive success owing to high fecundity of individual females (Collins et al, 1987;Hedgecock, 1994), and (4) the segregation of spawning grounds and nursery areas (Collins et al, 1987;Keener et al, 1988;Coleman et al, 1996;McGovern et al, 1998).…”

Temporal genetic homogeneity among shore crab (Carcinus maenas) larval events supplied to an estuarine system on the Portuguese northwest coast

“…According to the sweepstakes hypothesis, relatively few adults in each generation succeed in reproducing, as a result of stochastic processes leading to their reproductive activity coinciding with the correct oceanographic conditions conducive to spawning, fertilization, larval survival and recruitment (Hedgecock, 1994). Sweepstakes reproduction has been described in both invertebrates and fishes (Li and Hedgecock, 1998;Pujolar et al, 2006;Hedgecock et al, 2007b;Liu and Ely, 2009;Christie et al, 2010). Large discrepancies between the effective (N e ) and the census (N) population sizes usually resulting in very low N e /N ratios, are often reported among marine species (reviewed in Hauser and Carvalho, 2008) and are explained mainly by high variance in reproductive success.…”

“…Large discrepancies between the effective (N e ) and the census (N) population sizes usually resulting in very low N e /N ratios, are often reported among marine species (reviewed in Hauser and Carvalho, 2008) and are explained mainly by high variance in reproductive success. If this is the case, reduced genetic variability among cohorts of larvae or new recruits relative to the adult populations is expected (for example, Hedgecock et al, 2007b), as well as genetic differentiation among cohorts arriving at a population over time (for example, Li and Hedgecock, 1998). Moreover, larvae travelling in batches may be related by kin Veliz et al, 2006), increasing the likelihood of differences among cohorts, though such relatedness may not always be evident (Hernbinger et al, 1997).…”

Coalescence 2.0: a multiple branching of recent theoretical developments and their applications

“…This effect independent of natural selection and entirely driven by a high neutral variance of reproductive success, is named the "sweepstake reproduction" (Beckenbach 1994;Hedgecock 1994;Li & Hedgecock 1998;Hedgecock & Pudovkin 2011). One major consequence is that populations experience successions of strong random genetic drift followed by demographic expansions of few lineages.…”

“…3A and the model of Schweinsberg 2003). This has led to the development of empirical studies using genotyping in fish and crustaceans to confirm this effect for example in Pacific Oysters (Boom et al 1994;Boudry et al 2002) or atlantic cod (Li & Hedgecock 1998;Arnason et al 2000;Arnason 2004). …”