Within‐population spatial genetic structure, neighbourhood size and clonal subrange in the seagrass Cymodocea nodosa

Abstract

SynopsisIn the marine environment, both external fertilization and settlement are critical processes linking adult and early juvenile life-history phases. The success of both processes can be tightly linked in organisms lacking a larval dispersive phase. This review focuses on synchronous gamete release (¼ spawning) in fucoid algae. These brown macroalgae are important components of temperate intertidal ecosystems in many parts of the world, and achieve synchronous gamete release by integrating various environmental signals. Photosynthesis-dependent sensing of boundary-layer inorganic carbon fluxes, as well as blue light and green light signals, possibly perceived via a chloroplast-located photoreceptor(s), are integrated into pathways that restrict gamete release to periods of low water motion. Avoidance of turbulent and/or high flow conditions in the intertidal zone allows high levels of fertilization success in this group. Temporal patterns and synchrony of spawning in natural populations are reviewed. Most species/populations have a more or less semilunar periodicity, although phase differences occur both between and within species at different geographical locations, raising the possibility that tidal and diurnal cues are more important than semilunar cues in entraining the response. The ecological and evolutionary role(s) of synchronous spawning in the intertidal zone are considered, particularly with regard to hybridization/reproductive isolation in species complexes, and reproductive versus recruitment assurance in the intertidal zone, where synchronous spawning during calm periods may be important for recruitment assurance in addition to fertilization success. Ways in which the roles of spawning synchrony could be tested in closely related species with contrasting mating systems (outcrossing versus selfing) are discussed. IntroductionBroadcast spawning and external fertilization are common in many groups of marine organisms, despite the pitfalls of ensuring reproductive success in the sea. Perhaps the single most important factor favoring successful syngamy is the synchronous release of gametes from reproductive individuals. Indeed, the literature contains many striking examples of spawning synchrony, from the Palolo worm in the south Pacific (see Caspers 1984) to the mass spawning of many species of corals (Harrison and others 1984; Babcock and others 1986). In these and other examples, organisms respond to 1 or more cues from multiple environmental cycles, including daily (light-dark), tidal, semilunar, lunar, and seasonal, to synchronize gamete release (Morgan and Christy 1994;Yamahira 2004; Skov and others 2005). Tight control over the timing of gamete release, and therefore sensitivity to environmental cues, is very important for reproductive assurance in externally fertilizing species. Until recently, the prevailing paradigm has been that sperm limitation is widespread in the sea (reviewed by Levitan and Petersen 1995; but also see Yund 2000). This conclusion is mainly based on experimental stu...

Genetic diversity of a clonal angiosperm near its range limit: the case of Cymodocea nodosa at the Canary Islands

“…Several low frequency alleles found in Canary Island samples had not been reported for specimens collected from the Iberian Peninsula (Cadiz and Alfacs; Alberto et al 2005) (Fig. 3); some were exclusive to specific populations, while others were identified in several meadows from different islands.…”

“…We used resampling techniques on larger samples from a previous study (N = ca. 220 for 2 Iberian sites, Cadiz and Alfacs, in Alberto et al 2005) that evidenced spatial autocorrelation in order to test whether the smaller samples used here (N = 40) were large enough to detect a SGS pattern at least as large as detected before with larger sample size. To achieve this, larger data sets were randomly resampled so that they were identical in size to Canary Islands samples (N = 40), and the above-mentioned genet level SGS parameters were estimated.…”

“…In order to analyse biogeographical relatedness among Canary archipelago meadows, we computed Cavalli-Sforza distances from microsatellite allelic frequencies, and also included as an 'outgroup' the datasets from Cadiz (south Iberian Atlantic) and Alfacs (Iberian Mediterranean) from Alberto et al (2005). A neighbor-joining (NJ) tree was constructed and bootstrap resampling using 1000 replicates was performed.…”

Microscale genetic differentiation in a sessile invertebrate with cloned larvae: investigating the role of polyembryony

“…McFadden 1997 and references therein) and algae (e.g. Wright et al 2000;Hämmerli and Reusch 2003;Alberto et al 2005). The population genetic consequences of cloning meiotically produced embryos are less well understood (Engel et al 2004).…”

Clones in space—how sampling can bias genetic diversity estimates in corals: editorial comment on the feature article by Gorospe et al.

“…Positive spatial autocorrelation at very small distances (<100 m) has been reported for a number of marine taxa, notably those low dispersal ability (e.g., seagrasses: Alberto et al 2005;Migliaccio et al 2005;Ruggiero et al 2005, sponges: Calderon et al 2007Blanquer et al 2009, bryozoans: Pemberton et al 2007, and ascidians: Yund and O'Neil 2000David et al 2010), but whether positive spatial autocorrelation at relatively short distances is also common for taxa with extended larval durations is unknown. As demonstrated by all the aforementioned studies, incorporating spatially explicit approaches adds a valuable dimension to marine genetic research and can reveal subtle but important patterns of genetic diversity.…”