Reproductive strategy, clonal structure and genetic diversity in populations of the aquatic macrophyte Sparganium emersum in river systems

Abstract

Many aquatic and riparian plant species are characterized by the ability to reproduce both sexually and asexually. Yet, little is known about how spatial variation in sexual and asexual reproduction affects the genotypic diversity within populations of aquatic and riparian plants. We used six polymorphic microsatellites to examine the genetic diversity within and differentiation among 17 populations (606 individuals) of Sparganium emersum, in two Dutch-German rivers. Our study revealed a striking difference between rivers in the mode of reproduction (sexual vs. asexual) within S. emersum populations. The mode of reproduction was strongly related to locally reigning hydrodynamic conditions. Sexually reproducing populations exhibited a greater number of multilocus genotypes compared to asexual populations. The regional population structure suggested higher levels of gene flow among sexually reproducing populations compared to clonal populations. Gene flow was mainly mediated via hydrochoric dispersal of generative propagules (seeds), impeding genetic differentiation among populations even over river distances up to 50 km. Although evidence for hydrochoric dispersal of vegetative propagules (clonal plant fragments) was found, this mechanism appeared to be relatively less important. Bayesian-based assignment procedures revealed a number of immigrants, originating from outside our study area, suggesting intercatchment plant dispersal, possibly the result of waterfowl-mediated seed dispersal. This study demonstrates how variation in local environmental conditions in river systems, resulting in shifting balances of sexual vs. asexual reproduction within populations, will affect the genotypic diversity within populations. This study furthermore cautions against generalizations about dispersal of riparian plant species in river systems.

Clonal Structure of Two Wild Lotus (Nelumbo nucifera Gaertn.) Populations Inferred from Amplified Fragment Length Polymorphism Fingerprints

“…The importance of sexual vs. clonal reproduction and its relationship to genetic variation in natural populations has been studied in several aquatic species [10,11]. The mode of reproduction corresponds to a remarkable difference in genotypic diversity [12]. Sexual reproduction in clonal plants is likely to bear genetic variation, whereas asexual reproduction reduces the variation.…”

Untitled

“…whose natural geographic range spans virtually the entire Australian mainland. In their 15 study spanning this entire range they found that downstream seed dispersal had less 16 influence than geographic distance on dispersal pattern with 40 % of the genetic variation 17 explained by latitude and moisture index. This study indicated that E. camaldulensis 18 should be treated as a number of different sub-species rather than a single variable taxon.…”

“…These characteristics make them useful not only for genome mapping 12 projects, but also in biological research, answering questions ranging in level from species 13 (phylogenetics), through population (genetic structure) and family (parentage 14 relatedness) to the individual (identity, sex) (Buschiazzo and Gemmell, 2006). 15 Unfortunately, this versatility comes at a cost as microsatellite discovery and validation 16 used to be both expensive and labor intensive. In addition, while there can be some 17 transferability between closely related species, markers can also be species specific, 18 meaning that for non-model organisms de-novo development of microsatellite loci is 19 often necessary (Lepais and Bacles, 2011a).…”

“…Specifically, 11 Takayama et al (2011) identifies the rapid and cost-effective development of 12 microsatellite loci in non-model plant species as a particularly useful application of NGS. 13 NGS services are offered through a number of different commercial products which 14 include 454 sequencing (used in the 454 Genome Sequencers, Roche Applied Science; 15 Basel), Solexa Technology (used in the Illumina (San Diego) genome analyser), the 16 SOLiD platform (Applied Biosystems; Foster City, CA, USA), the Polonator to be the most widely used NGS platform for microsatellite loci development in plants 1 (Zalapa et al, 2012). 2 3 The rivers and wetlands of semi-arid and arid areas of Australia are some of the 4 most hydrologically variable and unpredictable systems in the world (Puckridge et al,5 1998).…”

“…and Duma florulenta (Meisn) T.M. 15 Schust. are two of these larger woody perennial species that are common throughout the 16 Murray Darling Basin, NSW, Australia.…”