Variability in connectivity indicated by chaotic genetic patchiness within and among populations of a marine fish

Abstract

Despite substantial advances in our understanding of marine population dynamics, there is still much uncertainty as to what processes influence connectivity, gene flow and population structure. To explore this, we examined the spatial and temporal variation in population genetic structure of adult and recently settled bicolor damselfish Stegastes partitus, a coral reef fish. We genotyped adult and juvenile fish from 10 sites over 4 sample years at 9 microsatellite loci. We show spatial heterogeneity in adult and juvenile population structure; however, we found no evidence of a pattern of spatial genetic divergence. Furthermore, genetic structure changed through time and between life stages in an unpredictable manner. Using these data, we test whether pre-or postsettlement selection, sweepstakes effects or variability in connectivity can explain the observed chaotic genetic patchiness. Our results indicate that the contributions of various larval sources likely change through time as a result of stochastic processes such as oceanographic flow. Our results have implications for the management of marine populations, as spatial and temporal variability in connectivity may act to promote long term stability of populations. Therefore it is important that marine management efforts account for such heterogeneity in the design of protected areas.KEY WORDS: Connectivity · Temporal variability · Larval dispersal · Chaotic genetic patchiness · Genetic structure · Coral reef fish Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 417: [263][264][265][266][267][268][269][270][271][272][273][274][275] 2010 through time and space (Larson & Julian 1999). This fine-scale genetic heterogeneity, termed chaotic genetic patchiness (Johnson & Black 1982), is characterized by low level genetic differentiation among and between adult and recruit populations (i.e. low F ST ) that is not consistent in space or time (Johnson & Black 1984).There are 4 main hypotheses put forth to explain chaotic genetic patchiness (Larson & Julian 1999); each infers a different mechanism by which this pattern can be explained. These hypotheses are (1) localized postsettlement selection resulting from microgeographic variation in environmental conditions, (2) variable local natural selection on pre-settlement individuals generating variability in cohorts through space and time, (3) 'sweepstakes chance-matching' (Hedgecock 1994) created by variable reproductive success of the adult source populations as a result of stochastic processes. This causes a genetic drift effect during the larval stage and a subsequent reduction in genetic variability in the recruit populations, and (4) spatial and temporal variability in the genetic composition of recruits caused by fluctuations in the source of larvae (Selkoe et al. 2006).Post-settlement natural selection has been invoked to explain spatial genetic heterogeneity in a marine snail (Johannesson et al. 1995). Generally, however, most studies have shown that gen...

Local retention, dispersal and fluctuating connectivity among populations of a coral reef fish

“…Genomic DNA was extracted from samples using a platebased extraction method (Elphinstone et al 2003), and genotyping was performed as follows (full details are described in Hogan et al 2010). In brief, nine microsatellite loci were chosen from the literature (Williams et al 2003;Thiessen and Heath 2007) and screened for suitability.…”

“…At smaller spatial scales, Ospina-Guerrero et al (2008) found genetic homogeneity among sites within the Columbian Caribbean (*400 km), suggesting high levels of gene flow at this scale. However, three studies found weak (Hepburn et al 2009;Hogan et al 2010) to strong (Villegas-Sanchez et al 2010) genetic structuring at a similar scale in the MBRS, showing evidence of more restricted or variable gene flow. Christie et al (2010) found direct evidence of larval retention (i.e., self-recruitment) in Bahamian populations of S. partitus, on a backdrop of high gene flow among sites (*250 km).…”

“…The degree of temporal stability in larval dispersal connecting marine populations has not been empirically tested, yet temporal variability in dispersal and connectivity will determine predictability in population dynamics and will impact population genetic structure (Larson and Julian 1999;Selkoe et al 2006;Hogan et al 2010). In fact, Communicated by Craig Osenberg.…”

“…temporal changes in larval migration patterns have been implicated as a source of spatial and temporal patchiness in the genetic structure of marine populations (Selkoe et al 2006;Hogan et al 2010). Therefore, not only must we improve our understanding of larval dispersal pathways, local recruitment rates and population connectivity, we also need empirical estimates of the temporal component of variation in those variables for the effective management and conservation of marine populations (Sale et al 2005;Levin 2006;Jones et al 2007).…”

“…Christie et al (2010) found direct evidence of larval retention (i.e., self-recruitment) in Bahamian populations of S. partitus, on a backdrop of high gene flow among sites (*250 km). Furthermore, two studies found that genetic structure among populations was temporally unstable at the scale of seasons (Hepburn et al 2009) and years (Hogan et al 2010), and this was attributed to fluctuations in connectivity among reefs (Hogan et al 2010).…”