Dataset Information

Range-wide population genetic structure of the Caribbean marine angiosperm Thalassia testudinum.

ABSTRACT: Many marine species have widespread geographic ranges derived from their evolutionary and ecological history particularly their modes of dispersal. Seagrass (marine angiosperm) species have ranges that are unusually widespread, which is not unexpected following recent reviews of reproductive strategies demonstrating the potential for long-distance dispersal combined with longevity through clonality. An exemplar of these dual biological features is turtle grass (Thalassia testudinum) which is an ecologically important species throughout the tropical Atlantic region. Turtle grass has been documented to have long-distance dispersal via floating fruits and also extreme clonality and longevity. We hypothesize that across its range, Thalassia testudinum will have very limited regional population structure due to these characteristics and under typical models of population structure would expect to detect high levels of genetic connectivity. There are very few studies of range-wide genetic connectivity documented for seagrasses or other sessile marine species. This study presents a population genetic dataset that represents a geographic area exceeding 14,000 km2. Population genetic diversity was evaluated from 32 Thalassia testudinum populations sampled across the Caribbean and Gulf of Mexico. Genotypes were based on nine microsatellites, and haplotypes were based on chloroplast DNA sequences. Very limited phylogeographic signal from cpDNA reduced the potential comparative analyses possible. Multiple analytical clustering approaches on population genetic data revealed two significant genetic partitions: (a) the Caribbean and (b) the Gulf of Mexico. Genetic diversity was high (H E = 0.641), and isolation by distance was significant; gene flow and migration estimates across the entire range were however modest, we suggest that the frequency of successful recruitment across the range is uncommon. Thalassia testudinum maintains genetic diversity across its entire distribution range. The genetic split may be explained by genetic drift during recolonization from refugia following relatively recent reduction in available habitat such as the last glacial maxima.

SUBMITTER: van Dijk KJ

PROVIDER: S-EPMC6194253 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Range-wide population genetic structure of the Caribbean marine angiosperm <i>Thalassia testudinum</i>.

van Dijk Kor-Jent KJ Bricker Eric E van Tussenbroek Brigitta I BI Waycott Michelle M

Ecology and evolution 20180829 18

Many marine species have widespread geographic ranges derived from their evolutionary and ecological history particularly their modes of dispersal. Seagrass (marine angiosperm) species have ranges that are unusually widespread, which is not unexpected following recent reviews of reproductive strategies demonstrating the potential for long-distance dispersal combined with longevity through clonality. An exemplar of these dual biological features is turtle grass (<i>Thalassia testudinum</i>) which ...[more]

PMID: 30377516

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Project description:The high prevalence of dioecy in marine angiosperms or seagrasses (>50% of all species) is thought to enforce cross-fertilization. However, seagrasses are clonal plants, and they may still be subject to sibling-mating or bi-parental inbreeding if the genetic neighborhood is smaller than the size of the genets. We tested this by determining the genetic neighborhoods of the dioecious seagrass Thalassia testudinum at two sites (Back-Reef and Mid-Lagoon) in Puerto Morelos Reef Lagoon, Mexico, by measuring dispersal of pollen and seeds in situ, and by fine-scale spatial autocorrelation analysis with eight polymorphic microsatellite DNA markers. Prevalence of inbreeding was verified by estimating pairwise kinship coefficients; and by analysing the genotypes of seedlings grown from seeds in mesocosms. Average dispersal of pollen was 0.3-1.6 m (max. 4.8 m) and of seeds was 0.3-0.4 m (max. 1.8 m), resulting in a neighborhood area of 7.4 m2 (range 3.4-11.4 m2) at Back-Reef and 1.9 (range 1.87-1.92 m2) at Mid-Lagoon. Neighborhood area (Na) derived from spatial autocorrelation was 0.1-20.5 m2 at Back-Reef and 0.1-16.9 m2 at Mid-Lagoon. Maximal extensions of the genets, in 19 × 30 m plots, were 19.2 m (median 7.5 m) and 10.8 m (median 4.8 m) at Back-Reef and Mid-Lagoon. There was no indication of deficit or excess of heterozygotes nor were coefficients of inbreeding (FIS) significant. The seedlings did not show statistically significant deficit of heterozygotes (except for 1 locus at Back-Reef). Contrary to our expectations, we did not find evidence of bi-parental inbreeding in this dioecious seagrass with large genets but small genetic neighborhoods. Proposed mechanisms to avoid bi-parental inbreeding are possible selection against homozygotes during fecundation or ovule development. Additionally, the genets grew highly dispersed (aggregation index Ac was 0.09 and 0.10 for Back-Reef and Mid-Lagoon, respectively); such highly dispersed guerrilla-like clonal growth form likely increases the probability of crossing between different potentially unrelated genets.

Dataset Information

Range-wide population genetic structure of the Caribbean marine angiosperm Thalassia testudinum.

Publications

Range-wide population genetic structure of the Caribbean marine angiosperm <i>Thalassia testudinum</i>.

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