Reproductive phenology of the Mediterranean seagrasses Posidonia oceanica (L.) Delile, Cymodocea nodosa (Ucria) Aschers., and Zostera noltii Hornem.

The seagrass Cymodocea nodosa forms a unique community in the Canary Islands, where it is classified as an endangered species. Biogeographic theory predicts that clonal species on islands near their distributional limits might show lower proportions of sexual (versus clonal) reproduction, lower genetic diversity, and higher differentiation. We addressed these hypotheses by comparing the genetic structure of C. nodosa from 10 meadows in the 4 main Canary Islands with 2 Iberian sites (Atlantic and Mediterranean) using microsatellites. A resampling method was proposed to standardize, among samples, genetic variability statistics estimating genotypic richness (R) and allelic richness (Â). A high degree of genotypic richness at the Canary Islands (R = 0.30 -0.94, mean = 0.67) relative to Iberian sites revealed that C. nodosa performs effective sexual reproduction here. In contrast, lower Â suggested a founder effect during the colonization of the archipelago, and similar allelic composition across all islands indicated colonization from a single source. A hotspot of genetic diversity was observed in El Medano (Tenerife), probably associated with lower drift in this meadow, the largest of the archipelago. Predominant north-south surface currents and a greater distance to the mainland could explain lower allelic richness of 2 northwestern sites on different islands and greater similarity between them. All meadows were differentiated from each other and there was no correlation between genetic and geographic distances. This non-equilibrium migration-mutation system was therefore mostly influenced by diversity resulting from genetic drift, and less by the homogenizing effects of gene flow.

Section: Genotypic Richnessmentioning

confidence: 67%

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

Alberto¹,

Arnaud‐Haond²,

Duarte³

et al. 2006

“…The habitat for this population is characterized by a steep depth gradient with different depth-dependent physical (thermocline at 15 m depth) and biological features (e.g. temporal shifts in flower and fruit development) (Buia & Mazzella 1991). We hypothesize that different timing in the maturation of gametes between the shallow and deep portions of the populations acts as a physiological barrier leading to genetic isolation, and thus the creation of 2 sub-populations.…”

Section: Discussionmentioning

confidence: 99%

“…Meadows extend from 3 to 40 m depth, according to light and nutrient availability (Duarte 1991). Sexual reproduction has been shown to be sporadic and seedling establishment is unsuccessful in the Western Mediterranean basin (Caye & Meinesz 1984, Thelin & Boudouresque 1985, Buia & Mazzella 1991, Meinesz et al 1993. This is probably due to the stochastic nature of pollen and seed transport within and between populations, which is driven by both the current regime and local environmental forces (Caye & Meinesz 1984).…”

Section: Introductionmentioning

confidence: 99%

Population genetic structure and gene flow in the seagrass Posidonia oceanica assessed using microsatellite analysis

Procaccini¹,

Mazzella²

1998

Microsatellite markers were utilized in a study on population genetic diversity of the endemic Mediterranean seagrass Posidonia oceanica (L.) Delile. Five nuclear and one chloroplastic microsatellite markers detected low levels of polymorphism in 6 populations sampled along the coasts of Italy and Corsica (Western Mediterranean). The number of alleles per locus ranged from 1.5 to 2.0 and homozygosity was high within populations (f = 0.314). In the 120 individuals analyzed, only 32.5 % were distinct genotypes. Although gene flow seems to exist between geographically disjunct meadows (Nm -1.55), private alleles were found in some localities. In one population in particular (Lacco Ameno, Gulf of Naples), sampled at 2 different depths, a private allele was present only in the individuals of the shallow stand. Distance analysis identified genetic disjunction between the northern and the centralsouthern populations. This study indicates that (1) clonal growth is important in the maintenance of P. oceanica populations, (2) limited inbreeding occurs in P oceanica populations, which can be composed of clonal patches of different size, (3) gene flow exists, but genetic disjunction between populations can be influenced by local forces, and (4) microsatellites are powerful markers in detecting genetic variability in clonally reproducing species.

“…Orth PhiIIips et al (1983) Fukuda et al (1984) Gates (1984) Robertson & Mann (1984) Bodnar (1985 Kawasaki et al (1985) Takaba (1985) Hootsmans et al (1987) Kawasaki (1987) Kawasaki et al (1988) Harrison (1991) Churchill (1992 Murra y & Larkum ( 1 992) Harrison (1 993) Kawasaki (1993) Moore et al (1993) Olesen & Sand-Jensen (1994 Ruckelshaus (1994) van Lent & Verschuure (1995) Harwell & Orth (1999) Santamaria-Gallegos et al (1999Hootsmans et al (1987 Loques et al (1988) Loques et al (1990) Buia & Mazzella (1991 Goubin & Loques (1991) Harrison (1993) …”

mentioning

confidence: 99%

A review of issues in seagrass seed dormancy and germination:implications for conservation and restoration

Orth¹,

Harwell²,

Bailey³

et al. 2000

183

116

Seagrasses have received considerable attention over the past 2 decades because of the multiple ecological roles they play in estuarine and coastal ecosystems and concerns over worldwide losses of seagrass habitat due to direct and indirect human impacts. Restoration and conservation efforts are underway in some areas of the world, but progress may be limited by the paucity of information on the role of seeds in bed dynamics. Although flowering occurs in most of the 58 seagrass species, seed germination data exist for only 19 of the 42 species that have some period of dormancy, with only 93 published references to field and/or laboratory studies. This review addresses critical issues in conservation and restoration of seagrasses involving seed dormancy (e.g. environmental vs physiological), existence and type of seed bank (transient or persistent), and factors influencing seed germination (e.g. salinity, temperature, light). Results of many earlier published studies relating seed germination to various environmental factors may need re-examination given more recent published data which show a confounding influence of oxygen level on the germination process. We highlight the importance of conducting ecologically meaningful germination studies, including germination experiments conducted in sediments. We also identify questions for future research that may figure prominently in landscape level questions regarding protected marine or estuarine reserves, habitat fragmentation, and restoration.