title: How common is self-incompatibility across species of the herkogamous genus Ariocarpus?
abstract: OBJECTIVE
  Self-incompatibility (SI), the most effective mechanism to prevent selfing, may limit the number of compatible mates in populations. The seven species of Ariocarpus are endangered and predominantly outcrossers but fruit set may reach 1-20% after selfing. We aimed to determine whether SI is the underlying mechanism influencing mating in Ariocarpus species.
  
  
  METHODS
  We characterized the presence/absence of SI using pollination treatments (self-pollination, cross-pollination, natural pollination) in one population per species. We assessed SI using epifluorescence and generalized linear models (GLMs) to compare the presence of pollen tubes in the stigma, stylar transmitting tissue, and ovary among self- and cross-pollinated pistils 48 h after pollination. Following the same treatments, production of fruit set was noted and related to pollen tube growth.
  
  
  RESULTS
  Pollen tubes were found more frequently in the ovaries of natural and cross-pollinated flowers than in ovaries of self-pollinated. Stylar rejection of self-pollen indicated gametophytic SI, although pollen tubes reached the ovaries in six species (4-33% of pistils). Fruit set was lower after hand-pollinations than expected from pollen tube observations.
  
  
  CONCLUSIONS
  The low percentages of self-compatibility in all species in pollen tube growth and pollination experiments indicated that no species had complete self-sterility, suggesting the presence of partial SI. Reduced fruit set relative to pollen tube production could result from a threshold of insufficient pollination, early-acting inbreeding depression, or resource limitation. The origin of partial SI in Ariocarpus could respond to pressures such as pollen limitation and population size.
authors.affiliation: Departamento de Ecología de la Biodiversidad, Laboratorio de Genética y Ecología, Instituto de Ecología, Universidad Nacional Autónoma de México, Apartado Postal 70-275, Ciudad Universitaria, México, D. F., México.
authors.forename: Concepción
authors.initials: C
authors.lastname: Martínez-Peralta
authors.forename: Judith
authors.initials: J
authors.lastname: Márquez-Guzmán
authors.forename: María C
authors.initials: MC
authors.lastname: Mandujano
mesh_terms: D029421:Cactaceae / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D003433:Crosses, Genetic; D035264:Flowers / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D005638:Fruit / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D007178:Inbreeding; D016014:Linear Models; D011058:Pollen / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D053205:Pollen Tube / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D054817:Pollination; D012098:Reproduction; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D060436:Self-Incompatibility in Flowering Plants / Q000502:physiology*
keywords: Ariocarpus; Cactaceae; endemic species; hand-pollination treatments; natural populations; partial self-incompatibility; pollen tube growth; self-incompatibility