Contrasting patterns of clonality and fine-scale genetic structure in two rare sedges with differing geographic distributions

Abstract

For plants with mixed reproductive capabilities, asexual reproduction is more frequent in rare species and is considered a strategy for persistence when sexual recruitment is limited. We investigate whether asexual reproduction contributes to the persistence of two co-occurring, rare sedges that both experience irregular seed set and if their differing geographic distributions have a role in the relative contribution of clonality. Genotypic richness was high (R = 0.889 ± 0.02) across the clustered populations of Lepidosperma sp. Mt Caudan and, where detected, clonal patches were small, both in ramet numbers (⩽3 ramets/genet) and physical size (1.3 ± 0.1 m). In contrast, genotypic richness was lower in the isolated L. sp. Parker Range populations, albeit more variable (R = 0.437 ± 0.13), with genets as large as 17 ramets and up to 5.8 m in size. Aggregated clonal growth generated significant fine-scale genetic structure in both species but to a greater spatial extent and with additional genet-level structure in L. sp. Parker Range that is likely due to restricted seed dispersal. Despite both species being rare, asexual reproduction clearly has a more important role in the persistence of L. sp. Parker Range than L. sp. Mt Caudan. This is consistent with our prediction that limitations to sexual reproduction, via geographic isolation to effective gene exchange, can lead to greater contributions of asexual reproduction. These results demonstrate the role of population isolation in affecting the balance of alternate reproductive modes and the contextual nature of asexual reproduction in rare species.

Biodiversity hotspots and Ocbil theory

“…Strongly differentiated population systems are a hallmark of many Ocbil taxa, even those that are narrow range endemics (e.g., Cooper et al 2011;Barbosa et al 2012;Bonatelli et al 2014;Millar et al 2014;Binks et al 2015). A recent study in the SWAFR of the trap door spider genus Moggridgea exemplifies this pattern (Cooper et al 2011;Fig.…”

“…ecophysiological adaptations to old nutrient-poor P-limited soils (Lambers et al 2008(Lambers et al , 2010Venterink 2011;Laliberté et al 2012;Abrahão et al 2014;Oliveira et al 2015;Zemunik et al 2015). microrefugia and climate change (Cooper et al 2011;Keppel et al 2012;Ashcroft and Gollan 2013;Brendonck et al 2014;Mee and Moore 2014;Barrett and Yates 2015), the evolution of trees (Raven and Andrews 2010;Cramer 2012), clonality (Binks et al 2015), the occurrence of OCBISs (old, climatically buffered, infertile seascapes - Langlois et al (2012), significant gaps in Darwinian evolutionary theory (Hopper and Lambers 2009), old salt lake systems (Bui et al 2014a, b), and evolution of novel aquatic traits (Tuckett et al 2010;Davies and Stewart 2014). Seed biological studies are beginning to explore the relevance of Ocbil theory to their discipline (Tuckett et al 2010;Hidayati et al 2012;Wilman et al 2014;Alvarado et al 2015b;Edwards et al 2015;Ribeiro et al 2015).…”

Clonality as a driver of spatial genetic structure in populations of clonal tree species

“…Different genetic or environmental limitations may make the balance between sexual and asexual reproduction skewed toward asexual reproduction (Honnay and Bossuyt 2005;Binks et al 2015). Among them, geographic isolation limiting effective pollen movement may enhance the input of clonal reproduction in population that was recently reported by Binks et al (2015).…”

“…Recently, Santos-del- Blanco et al (2013) reported very similar values of Pareto index for P. canesces and P. alba, which were 1.224 and 1.118, respectively, and Chenault et al (2011) reported β = 1.07 for black poplar. Skewed frequency distribution of clone size demonstrating existence of a few large and many smaller genets is frequently noted among clonal plant populations (Ohsako 2010;Chenault et al 2011;Binks et al 2015).…”

“…Prolonged clonal growth along with selection and/or inter-clonal competition may eliminate less adapted clones, leading to monoclonal patches (Vandepitte et al 2009) and/ or genetic impoverishment of a population (Silvertown 2008). Also, clonal reproduction may enhance SGS in natural plant populations which may have profound genetic consequences (Chung et al 2005;Chenault et al 2011;Binks et al 2015) On the other hand, clonality confers important ecological advantages, such as the foraging response of plants (Louâpre et al 2012), reallocation of resources between ramets enabling avoidance from environmental stochasticity, and withstanding environmental perturbations or division of labour between connected ramets (Fischer and Kleunen 2001). Clonal plants life history traits show plasticity that allows them for dynamic interaction with habitat.…”