RESUMEN
BACKGROUND AND AIMS: Under the microgametophytic competition hypothesis, a non-random pattern of seed abortion is expected, in which only the most vigorous seeds reach maturity. In a previous study, it was found that Bauhinia ungulata (Fabaceae) exhibits a pattern of seed abortion dependent on the position of the ovule within the ovary; ovules located in the stylar half of the fruit, close to the point of entry of pollen tubes to the ovary, have a low probability of seed abortion, whereas ovules in the basal half of the fruit are aborted with a high probability. METHODS: A series of experimental fruits was generated, in which ovules from either the stylar (treatments 1 and 2) or the basal (treatments 3 and 4) half of fruits were destroyed, to evaluate whether these patterns of selective seed abortion have an effect on the vigour of the offspring in B. ungulata. KEY RESULTS: Only 53 % of the seed from control fruits germinated. Seed set in fruits from treatments 1 and 2 showed a significantly lower (33-43 %) percentage of germination; the germination of seeds from fruits in treatments 3 and 4 (49-51 %) did not differ from control seeds. In addition, it was found that the differences in vigour of the offspring are not random with respect to the position of the ovule in the pod. CONCLUSIONS: The overall performance of the seeds correlated with their likelihood of maturation. Seeds located at the basal half of the treatment fruits showed lower values of vigour than seeds located on the stylar half. The differences were more marked for early measures of fitness.
Asunto(s)
Bauhinia/fisiología , Germinación/fisiología , Semillas/fisiología , Costa Rica , Reproducción/fisiologíaRESUMEN
BACKGROUND AND AIMS: It has been claimed that ovules linearly ordered within a fruit differ in their probabilities of reaching maturity. This was investigated by studying the effect the position of an ovule within the pod has on seed abortion and seed production in Bauhinia ungulata. METHODS: Fruits collected during the dry seasons of 1999, 2000 and 2001 were opened, and the number, position and status of each ovule within the fruit were recorded. A GLM model was used to assess the effects of population, tree identity and ovule position within the pod on ovule fertilization, seed abortion, seed damage and seed maturation in two populations of B. ungulata. KEY RESULTS: Nearly 30% of the ovules were not fertilized in 1999; this percentage dropped to 5% the following two years. Seed abortion (50%) and seed damage (15%) were the same every year during the study period. Only 15% of the initial ovules developed into mature seeds in 1999; this value increased to 35% in 2000 and 2001. However, seed survivorship was dependent on the position of the ovule within the pod; non-fertilized and early aborted ovules were found more often near the basal end of the ovary. The frequency of seed damage was not affected by position. Mature seeds were found mainly in the stylar half of fruits, where ovules are likely to be fertilized by fast pollen tubes. CONCLUSIONS: The pattern of seed production in B. ungulata is non-random but is dependent upon the position of the ovule within the pod. The results suggest that the seeds produced within a fruit might differ in their vigour.