The Evolving Genetic History of a Population of Lathyrus sylvestris: Evidence From Temporal and Spatial Genetic Structure

Abstract

We analyze patterns of genetic microdifferentiation within a natural population of Lathyrus sylvestris, a perennial herb with both sexual reproduction and clonal growth. In a population from the northern foothills of the Pyrénées in southwestern France, a combined demographic and genetic investigation enabled the study not only of spatial genetic structure of the population, but also of the history of the population's spatial genetic structure over time. Excavation of all individuals allowed identification of clonemates. Age of each individual was determined by counting annual growth rings in the taproot, a method tested with individuals of known age planted in experimental gardens. Each individual was mapped, and genotypes of all individuals were determined using allozyme markers for a number of polymorphic loci. Distribution patterns and spatial genetic structure, both for all individuals and for different age classes, were analyzed using spatial autocorrelation statistics (Geary's Index, Moran's Index). Patterns of gene flow within the population were also studied using F‐statistics and tests for random associations of alleles. Because age, allele frequencies, and location were known for each individual, it was possible to study how spatial genetic structure changed over time. Results from all these diverse approaches are consistent with one another, and clearly show the following: (1) founder effects, with the study transect being first colonized by individuals at either end of the transect that were homozygous for different alleles at one marker locus; (2) a difference in spatial distribution of individuals originated from sexual reproduction (seedlings) and from clonal growth (connected individuals); (3) restricted gene flow, due to inbreeding among related, clumped individuals; and (4) increase in heterozygote deficit within the youngest cohort of individuals. The results indicate that genetic differentiation in time was much less marked than differentiation in space. Nevertheless, the results revealed that the studied population is experiencing demographic and genetic variation in time, suggesting that it is not at equilibrium. On the one hand, spatial structuring is becoming less marked due to the recombination of founder genotypes; on the other hand, as establishment of new individuals increases, a new spatial structure emerges due to mating between relatives.

Scaling of processes shaping the clonal dynamics and genetic mosaic of seagrasses through temporal genetic monitoring

“…These observations confirm the ecological concept of population based on distribution continuity as best adapted to clonal plants (Becheler et al, 2010), but suggest the possible existence of a spatial scale larger than sampling Figure 3 Conceptual illustration of scenarios proposed for explaining the spatio-temporal genetic structure. (a) Representation of the scenario described in Hossaert-McKey et al (1996). (b) Representation of the scenario proposed in the discussion, which fits better with our results.…”

“…These elements highlight the prevalence of an ISR strategy (Eriksson, 1993). A similar study was performed on a meadow of the terrestrial clonal plant Lathyrus sylvestris, studied in 2 successive years (Hossaert-McKey et al, 1996), where a similar pattern of clonal dominance fitted with a predominantly ISR strategy (Figure 3a). In contrast to the present work, a large spatial but low temporal genetic structure was observed and interpreted as the result of successive colonizations at the edge of the population having formed mosaics of genets: (i) colonizing space through vegetative elongation and (ii) producing seedling through reproduction among flowers of the same genet or its relatives, recruiting closed to the maternal plants (Hossaert-McKey, 1988;Hossaert-McKey and Jarry, 1992;HossaertMcKey et al, 1996).…”

“…However, the thorough appraisal of the dynamics of these genetic mosaics and of the recruitment strategies operating at different spatial and temporal scales in natural meadows cannot be inferred from a single instantaneous snapshot. Such an approach requires the assessment of the temporal evolution of clonal and genetic composition of patches, an approach that has rarely been used on clonal organisms (see Hossaert-McKey et al, 1996;Cronberg, 2002;Travis and Hester, 2005).…”

Temporal aspects of the fine-scale genetic structure in a population of Cinnamomum insularimontanum (Lauraceae)

“…For all data analyses, each of the four age-classes was considered separately as a subgroup (eg, Bacilieri et al, 1994;Berg and Hamrick, 1995;Hossaert-McKey et al, 1996). A locus was considered polymorphic if the frequency of the most common allele did not exceed 0.95.…”

Genetic diversity and recruitment of the tropical palm, Euterpe edulis Mart., in a natural population from the Brazilian Atlantic Forest

“…The recruitment process is associated with different biological and nonbiological factors (Hutchings, 1997), and in the last decade some workers have also tried to relate the recruitment process to plant genetics (Eguiarte et al, 1992;Murawski and Hamrick, 1992;Tonsor et al, 1993;Alvarez-Buylla and Garay, 1994;Hossaert-McKey et al, 1996;Doligez and Joly, 1997;Lee et al, 2000). Using allozyme markers, such studies have demonstrated a heterozygote increase towards the adult stages.…”