POLINIZACION Y VARIABILIDAD DE LA PRODUCCION DE SEMILLAS
EN PISTACIA LENTISCUS L. (ANACARDIACEAE)

por

PEDRO JORDANO *


Resuinen

JORDANO, P. (1988). Polinizaci6n y variabilidad de la producci6n de semillas en Pistacia lentiscus L. (Anacardiaeeae). Analesjard. Bot. Madrid 45(1): 213-231.

Se examina Ia importancia del aborto de semillas y de Ia producci6n de frutos partenoc‡rpicos en una poblaci—n de Pistacia lentiscus en el ‡rea de Do–ana (Huelva, Espa–a). Cuando no hay polinizaci—n pueden desarrollarse frutos partenoc‡rpicos, sin semillas viables; aparecen tambiŽn frutos con semillas vac’as, Si aborta el embri—n, y en ambos casos el fruto no suele Ilegar a madurar, aunque queda retenido en la planta. Los porcentajes medios de semillas viables fueron: para 1981, 19,89  15,82%, N=29 plantas; y para 1982, 43 38+11 90%, N =32 plantas. En 1981, a–o de fuerte Sequ’a, Ia mayor parte de las semillas vac’as procedieron de abortos, sin que la polinizaci—n apareciese como factor limitante; en 1982, las condiciones desfavorables -mayor precipitaci—n- durante Ia floraci—n aumentaron probablemente Ia partenocarpia como factor de inviabilidad de las semillas. La abscisi—n de frutos se dio, en Ia mayor’a de las plantas, tras el cuajado y antes de haber alcanzado el tama–o definitivo. Manteniendo constante el numero de frutos producidos, plantas de mayor tama–o cuajaron un mayor nśmero de semillas viables, pero Ia producci—n de semillas y frutos partenoc‡rpicos fue independiente del tama–o de Ia planta y solo estuvo asociada alas variaciones de Ia magnitud de Ia cosecha. El desfase fenol—gico, respecto a Ia floraci—n de los pies masculinos, y Ia presencia de pies masculinos pr—ximos, tambiŽn influyeron en el porcentaje de semiIlas viables. Se estudia el papel de Ia partenocarpia y de Ia abscisi—n de semillas como reguladores de Ia producci—n de frutos con semilla viable, y se consideran tambiŽn sus repercusiones en el proceso de dispersi—n endozo—cora de las semillas.

Palabras clave: Anacardiaceae, Pistacia, biologia reproductiva, floraci—n, fructificaci—n, anemofilia, partenocarpia, aborto de semillas, Do–ana, Espa–a.

Abstract

JORDANO, P. (1988). Pollination and variability of seed production in Pistacia lentiscus L. (Anacardiaceae). Anales jard. Bot. Madrid 45(1): 213-231 (in Spanish).

The incidence of parthenocarpy and seed abortion as causes of blank seed production in the dioecious, wind-pollinated shrub Pistacia lentiscus were examined in a natural population in the Do–ana area, Huelva province, Spain. Fruits with empty seeds resulted either from parthenocarpy, in absenee of pollination, or from embryo abortion, and in both cases the fruit with empty seed rarely matured but was retained on the plant. Average % of viable seeds were 1989+15,82% (N= 29 plants), and 43,38  11,90% (N= 32 plants) for 1981 and 1982, respectively. During 1981, with a severe drought, most fruit abscission was caused by embryo abortion, with a small incidenee of parthenocarpy. Increased rainfall during the flowering period of 1982 most likely impaired the conditions for wind transport of the pollen, and parthenocarpy was the main cause of fruit abscission. The highest rates of fruit shedding were recorded for most plants just after fruit set, well before the fruits had attained their full size. After adjusting for the effects of crop size variation, the number of viable seeds produced was positively correlated with plant size. The number of aborted seeds and parthenocarpic fruits was independent of plant size, being correlated only with crop size. The phenological uncoupling with the flowering of males and increased distance to males, caused by the neighborhood of other females, also contributed to reduced seed set. The role of parthenocarpy and seed abortion as regulators of fruit number is discussed in connection with the constraints derived by the wind-pollination syndrome; their implications for the endozoochorous dispersal of seeds by birds are also considered.

Key words: Anacardiaceae, Pistacia, reproductive biology, flowering, fruiting, wind-pollination, parthenocarpy, seed abortion, Do–ana, Spain.
Biological Jornal of the Linnean Society (1993), 50: 65-84. With 3 figures









Pollination biology of Prunus mahaleb L.:
deferred consequences of gender variation for fecundity and seed size

PEDRO JORDANO

Estacidn Bioldgica de Don'ana, CSIC, Apdo. 1056; E-41080 Sevilla, Spain

Received 9 March 1992, accepted for pnblication 20 Jnly 1992



This study describes the reproductive biology of Prunus mahaleb, a rosaccous treelet, in a southeastern Spanish population. The species is gynodioccious with 55.4% of the plants being male-fertile and 44.6% presenting non-functional, shrunken anthers with no pollen, and behaving as functional females. Individual trees produced the same flower morph in four consecutive study years. Fruit set in bagged inflorescences was absent in male-sterile trees and was very reduced in male-fertiles. Open-pollinated flowers of male-fertiles showed greater fruit set (mean = 29.1%) than male-steriles (mean = 25.3%). Average fruit set in three experimental treatments (control, selfed, and crossed) were 29.05%, 41.9% and 38.6%, respectively, for male-fertile trees; those for male-steriles were 25.3%, 0% and 39.2%, respectively. Seeds from male-sterile plants were heavier (71.33 mg) than those of male-fertile plants (66.05 mg) but did not differ in germination ability. Male-fertile and male-sterile trees differ significantly in average nectar concentration (73.5% and 55.9%, respectively) and nectar volume secreted/flower and day (0.142 microL and 0.171 ttl, respectively). A total of 41 species of insect flower visitors were recorded. Calliphorid and tachinid flies (41.97% of total visits), and andrenid bees (30.30%), were the most frequent visitors. The diversity of insect visitors was greater in male-fertile trees. Bees and flies accounted for 50.5% and 49.5%, respectively of total visits to male-fertile trees. Flies were far more frequent than bees at male-sterile flowers (76.9% and 23.1%, respectively). Male-sterile trees received higher average visitation (47 insects/census) than malefertile trees (32 insects/census). Individual trees showed a relative constancy of the fecundity rankings between years. Fruit production was significantly higher in male-sterile trees, with a fouryear average of 6558 fruits, in contrast with male-fertile trees which yielded 4670 fruits. This 1.77fold difference in favour of male-sterile trees over male-fertiles was not compensated by the greater fruit set of the latter. This is attributable to the lower outcrossing rate of male-fertiles, estimated as 52.68% from seed mass data. In addition, greater seed mass of female progeny, and higher visitation rate by insects might explain the maintenance of this polymorphism. These results have far-reaching implications for the demography and seed-dispersal ecology of this endozoochorus species.

KEY WORDS:- Cryptic breeding systems - fruit set - gynodioecy - Mediterranean - pollination Rosaceae.