Selection occurs within linear fruit and during the early stages of reproduction in Robinia pseudoacacia

Abstract

BackgroundPollen donor compositions differ during the early stages of reproduction due to various selection mechanisms. In addition, ovules linearly ordered within a fruit have different probabilities of reaching maturity. Few attempts, however, have been made to directly examine the magnitude and timing of selection, as well as the mechanisms during early life stages and within fruit. Robinia pseudoacacia, which contains linear fruit and non-random ovule maturation and abortion patterns, has been used to study the viability of selection within fruit and during the early stages of reproduction. To examine changes in the pollen donor composition during the early stages of reproduction and of progeny originating from different positions within fruit, paternity analyses were performed for three early life stages (aborted seeds, mature seeds and seedlings) in the insect-pollinated tree R. pseudoacacia.ResultsSelection resulted in an overall decrease in the level of surviving selfed progeny at each life stage. The greatest change was observed between the aborted seed stage and mature seed stage, indicative of inbreeding depression (the reduced fitness of a given population that occurs when related individual breeding was responsible for early selection). A selective advantage was detected among paternal trees. Within fruits, the distal ends showed higher outcrossing rates than the basal ends, indicative of selection based on the order of seeds within the fruit.ConclusionsOur results suggest that selection exists both within linear fruit and during the early stages of reproduction, and that this selection can affect male reproductive success during the early life stages. This indicates that tree species with mixed-mating systems may have evolved pollen selection mechanisms to increase the fitness of progeny and adjust the population genetic composition. The early selection that we detected suggests that inbreeding depression caused the high abortion rate and low seed set in R. pseudoacacia.

Ovule positions within linear fruit are correlated with nonrandom mating in Robinia pseudoacacia

“…In our other study, selection component and paternity analyses of open-pollinated offspring further indicated that selection existed both within linear fruit and during the early stages of reproduction in R. pseudoacacia 28. Our previous study suggested that selection resulted in an overall decrease in the level of surviving selfed progeny at each life stage (aborted stage, mature seed stage, and seedling stage).…”

“…Our previous study showed high levels of inbreeding depression in R. pseudoacacia 28, which further reduced the selfed offspring in competitive pollination, combined with the disadvantage of self-pollen in the fertilization gradient within fruit. Because we did not determine the paternity of aborted seeds in competitive pollination, we could not ascertain whether the ovules fertilized by intercross pollen were aborted.…”

“…Our previous study suggested that selection resulted in an overall decrease in the level of surviving selfed progeny at each life stage (aborted stage, mature seed stage, and seedling stage). Within fruits, the stylar ends showed higher outcrossing rates than the basal ends, indicating selection based on the order of seeds within the fruit2829. These results suggest that a connection may exist between nonrandom mating and ovule position in R. pseudoacacia .…”

“…Once ovules were fertilized by self-pollen, some of them may be aborted due to early inbreeding depression. Although we did not determine the genotype of aborted seeds in either self- or outcross-pollen mixtures, we genotyped the aborted seeds of R. pseudoacacia in open pollination, and results showed that the aborted seeds exhibited a slight heterozygote deficit and showed high levels of inbreeding28. If some ovules fertilized by self-pollen in the pollen mixture succeed in maturing, some of them may not germinate, thus reducing the number of selfed offspring even further.…”

Effects of thermal-time artificial scarification on the germination dynamics of black locust (Robinia pseudoacacia L.) seeds

“…Therefore, based on the distribution of fruiting grafts, the inference is, with high probability, that selfpollination processes have been repeated, with the result that the seeds formed, in general, are incapable of germination (Yuan et al 2014). …”