Sexual Strategies in Plants

Abstract

SUMMARYIt is postulated that in one reproductive session the level of maternal expenditure of an angiosperm plant is determined by a temporal series of controls on the number of potential fruit in which an investm.ent is made. The serial adjustment hypothesis has three parts: A. The amount of maternal expenditure is regulated at many developmental units, particularly single flowers and fruit, at three principal sequential stages -the determination of flowers, the development of ovaries and the maturation of fruit. B. At each stage, the initiation or continuation of an investment requires an amount of available resources above a certain threshold. Hence maternal expenditure is continually adjusted to the resources available at each developmental site. C. The pattern of controls that maximizes the maternal fitness of a plant is selected. Many factors affect the relative advantages of regulation at the three stages, therefore species and sexual morphs appear to vary widely in their proportional use of the three stages. Regulation of flower determination has the general advantages of offering bidirectional adjustment of maternal investment, maintaining a constant ratio of maternal to paternal investment, and reducing wasted expenditure. The later stages, ovary and fruit regulation, allow secondary adjustnients of maternal investment in unpredictable circumstances and permit adjustment of the relative numbers of polliniferous and seminiferous flowers. The relative advantages of restricting the numbers of developing ovaries, or of maturing fruit, depend principally on the extent to which differences in the capacity of flowers to mature fruit are evident before anthesis.

EVIDENCE FOR SELECTIVE FRUIT PRODUCTION IN ASCLEPIAS

“…The cost entailed in providing surplus ovaries per umbel may be reduced by the related benefits of an increased floral display, which may increase pollinator attraction (Willson and Price, 1977, but not true in Lynch, 1977;Willson and Bertin, 1979) and pollen production (Willson and Rathcke, 1974;Willson and Price, 1977). Surplus ovaries may also function in satiation of herbivores and provide the flexibility to increase fruit set when resources are more available (Willson and Price, 1980; reviewed by Lloyd, 1980;Stephenson, 1981).…”

“…Fruit abortion has been hypothesized as a means by which plants can optimally distribute limited resources among the more economically packaged, higher quality seeds (Janzen, 1977a(Janzen, , 1977b Charnov, 1979;Lloyd, 1980;Stephenson, 1981;Bertin, 1982a; Lee andBazzaz, 1982a, 1982b). For some species, there is evidence for selective production of fruits based on paternity (Bertin, 1982a) and/or number of seeds per fruit (Heinicke, 1917;Stephenson, 1981;Bertin, 1982aBertin, , 1982b Lee andBazzaz, 1982a, 1982b).…”

“…This study differs from those of selective fertilization in that here, both pre-and post-fertilization selection are possible and multiseeded fruits instead of seeds produced by different pollen are compared. Finally, since flower abscission and fruit abortion entail a cost in terms of lost resources (Lloyd, 1979(Lloyd, , 1980Bookman, 1983), I attempted to determine compensating benefits of this potential mechanism of fruit selection by determining if any potentially advantageous characteristics were shared by pods, seeds, or seedlings of the pollen donors more successful at fathering pods.…”

A POLINIZAÇÃO MANUAL DO CUPUAÇUZEIRO (Theobroma grandiflorum)

“…Pode ter ocorrido que, o baixo índice de aborto observado no experimento foi porque os frutos danificados estavam dentro da "cota de contingência" de frutos que as plantas geralmente produzem a mais para cobrir os "eventos incertos", como o ataque de pragas e doenças, secas, etc. (LEE & BAZZAS, 1992;LLOYD, 1980 Durante as polinizações obtiveram-se alguns indicativos práticos como: a) Duas a três passadas de uma única antera bem cheia de pólen são suficientes para promover uma boa polinização. Com as anteras de um estame ainda bem cheias de pólen, pode-se polinizar duas flores.…”

Offspring Quality in Relation to Excess Flowers in Pultenaea Gunnii (Fabaceae)

“…There are also several plausible benefits for female fitness from nonfruiting flowers: elevation of the quantity or quality of pollen capture as a result of increased attractiveness (Willson and Rathcke 1974;Janzen 1977), exploitation of unusually high resource availability in some years (Lloyd 1980), hedging against loss of ovaries to herbivores and weather (Holtsford 1985), and expanding the range of ovary quality on which selective abortion can act (Janzen 1977;Stephenson 1981;Willson and Burley 1983;Koslowski and Sterns 1989). The last mechanism-widening the scope of selective abortion-is addressed here.…”