Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata

The transition to self-compatibility from self-incompatibility is often associated with high rates of self-fertilization, which can restrict gene flow among populations and cause reproductive isolation of self-compatible (SC) lineages. Secondary contact between SC and self-incompatible (SI) lineages might re-establish gene flow if SC lineages remain capable of outcrossing. By contrast, intrinsic features of SC plants that reinforce high rates of self-fertilization could maintain evolutionary divergence between lineages. Arabidopsis lyrata subsp. lyrata is characterized by multiple origins of self-compatibility and high rates of self-fertilization in SC-dominated populations. It is unclear whether these high rates of selfing by SC plants have intrinsic or extrinsic causes. We estimated outcrossing rates and examined patterns of pollinator movement for 38 SC and 40 SI maternal parents sampled from an admixed array of 1509 plants sourced from six SC and six SI populations grown under uniform density. Although plants from SI populations had higher outcrossing rates (mean tm = 0.78 ± 0.05 SE) than plants from SC populations (mean tm = 0.56 ± 0.06 SE), outcrossing rates among SC plants were substantially higher than previous estimates from natural populations. Patterns of pollinator movement appeared to contribute to lower outcrossing rates for SC plants; we estimated that 40% of floral visits were geitonogamous (between flowers of the same plant). The relatively high rates of outcrossing for SC plants under standardized conditions indicate that selfing rates in natural SC populations of A. lyrata are facultative and driven by extrinsic features of A. lyrata, including patterns of pollinator movement.

Do annual and perennial populations of an insect-pollinated plant species differ in mating system?

Background and Aims Theory predicts that outcrossing should be more prevalent among perennials than annuals, a pattern confirmed by comparative evidence from diverse angiosperm families. However, intraspecific comparisons between annual and perennial populations are few because such variation is uncommon among flowering plants. Here, we test the hypothesis that perennial populations outcross more than annual populations by investigating Incarvillea sinensis, a wide-ranging insect-pollinated herb native to China. The occurrence of both allopatric and sympatric populations allows us to examine the stability of mating system differences between life histories under varying ecological conditions. Methods We estimated outcrossing rates and biparental inbreeding in 16 allopatric and five sympatric populations in which both life histories coexisted using 20 microsatellite loci. In each population we measured height, branch number, corolla size, tube length and herkogamy for ~30 individuals. In a sympatric population, we recorded daily flower number, pollinator visitation and the fruit and seed set of annual and perennial plants. Key Results As predicted, outcrossing rates (t) were considerably higher in perennial (mean = 0.76) than annual (mean = 0.09) populations. This difference in mating system was also maintained at sympatric sites where plants grew intermixed. In both allopatric and sympatric populations the degree of herkogamy was consistently larger in outcrossing than selfing plants. Perennials were more branched, with more and larger flowers than in annuals. In a sympatric population, annuals had a significantly higher fruit and seed set than perennials. Conclusions Genetically based differences in herkogamy between annuals and perennials appear to play a key role in governing outcrossing rates in populations, regardless of variation in local ecological conditions. The maintenance of mating system and life history trait differentiation between perennial and annual populations of I. sinensis probably results from correlated evolution in response to local environmental conditions.

REPRODUCTIVE SYSTEM of Mimosa scabrella IN CONSECUTIVE REPRODUCTIVE EVENTS IN THE MOUNTAINOUS REGION OF SANTA CATARINA STATE

The reproductive system determines evolutionary inheritance of populations by establishing patterns of gametes union to originate the next generation. The objective of this study was to investigate the mating system of Mimosa scabrella Benth. (bracatinga), a Brazilian tree species with socioeconomic and ecological importance, in a population of the mountainous region of Santa Catarina state, in two consecutive reproductive events. The analyzes in the 2015 and 2016 reproductive events were lead with isoenzymatic markers and the mating system characterization was performed based on mixed crosses and correlated crosses models, and the means of each parameter were statistically compared. Among the results, the multilocus outcrossing rates (tm(2015): 0.925 and tm(2016): 0.845) showed high magnitude and differed from the unit; the self-fertilization rates were significantly different from zero (s (2015): (0.075 and(2016): 0.155) indicating that the species does not show self-incompatibility. In addition, the positive outcrossing rates among relatives (tm-ts(2015): 0.142 and tm-ts(2016): 0.170) suggest inbreeding crosses in the population. The highest proportions in offspring were half-sibs (2015: 0.736 and 2016: 0.579), suggesting predominance of randomness at crossings. From this it is concluded that M. scabrella has a mixed mating system, with predominance of crossing at population level.

Outcrossing Rate and Genetic Variability in Mexican Race Avocado

The blooming behavior of the avocado Persea americana Mill. is a sophisticated mechanism that prevents effective self-pollination, enables close pollination, and encourages cross-pollination. However, there is no information on outcrossing rate among Mexican race avocado genotypes (P. americana var. drymifolia Schltdl. & Cham.). Therefore, the objective of this study was to assess the outcrossing rate and genetic variability in progenies of Mexican race avocado genotypes by simple sequence repeat (SSR) and intersimple sequence repeat (ISSR) markers. SSR marker analysis showed a considerable genetic differentiation among avocado families [total expected heterozygosity (He) = 0.540], whereas the total heterozygosity value observed (Ho = 0.098) showed the presence of genetic structure per family. The total Nei’s unbiased average heterozygosity (nHe) value found with ISSR markers was 0.482. The results of the analysis of molecular variance (AMOVA) combining both type of markers showed that genetic variation within avocado families was 58.6%, and among families was 41.6% (P < 0.0001). The outcrossing population rate in P. americana var. drymifolia was 0.774 ± 0.091 (sd), and the ‘Criollo 3’ and ‘Plátano Temprano’ families showed the lowest (–0.083 ± 0.031) and highest (0.814 ± 0.060) outcrossing rates, respectively. Variability in outcrossing rate depends on many factors, including edaphoclimatic, agronomic, and genetic, and needs to be considered to define strategies for the conservation and genetic improvement of outstanding native genotypes. SSR and ISSR markers are useful for estimating genetic variability within and among families of avocado, as well as for determining the outcrossing rates among closely related individuals and with a rather small sample size.

Outcrossing Rates and Gene Flow in Natural Population of the Endangered Endemic Aquatic Lycophyte Isoetes yunguiensis as Revealed by ISSR Markers

In this study, mating system, genetic diversity, and genetic structure of the endangered endemic aquatic Isoetes yunguiensis in China was investigated using ISSR markers. The results of ISSR analyses showed that the estimate of multilocus outcrossing rate (tm) was high at species level (tm = 0.955), indicating that diploid I. yunguiensis is a predominant outcrossing species. Nine selected ISSR primers used in the study amplified 66 reproducible bands, 41 of which were polymorphic among 37 individuals. High level of genetic diversity was detected at the species level (PPB = 62.12%), whereas, relatively low genetic diversity existed within populations (PPB = 39.39%). Analysis of molecular variance (AMOVA) revealed that 31.99% of the genetic variation was attributable to differences between populations and the rest (68.01%) to variability within populationsof I. yunguiensis. Value of Fst (0.320) indicated that genetic differentiation between populations also was significant. These results showed that I. yunguiensis predominantly favors crossing, and has a high level of genetic diversity and highly significant genetic variation between and within populations. Gene flow (Nm) among populations is equal to 1.177. High outcrossing rates may be responsible for the high levels of genetic diversity observed in the I. yunguiensis population. To maintain the current level of genetic diversity for this species, we recommend increasing in situ conservation sites.