Reproduction in Polemonium: Assessing the Factors Limiting Seed Set

Zimmerman, Michael J.; Pyke, Graham H.

doi:10.1086/284815

Cited by 280 publications

(259 citation statements)

References 36 publications

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“…1 Zimmerman and Pyke 1988). Pollen limitation in the SBN population accounts for its lower fruit set, its lower fruit production, and the quantitative differences among the populations in overall fruit survivorship (Fig.…”

Section: Resultsmentioning

confidence: 99%

Geographic and population variation in pollinating seed-consuming interactions between senita cacti ( Lophocereus schottii ) and senita moths ( Upiga virescens )

Holland¹,

Fleming²

1999

Oecologia

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Interspecific interactions can vary within and among populations and geographic locations. This variation can subsequently influence the evolution and coevolution of species interactions. We investigated population and geographic variation in traits important to pollinating seed-consuming interactions between the senita cactus (Lophocereus schottii) and its obligate pollinating moth (Upiga virescens), both of which are geographically restricted to the Sonoran Desert. Female moths actively pollinate senita flowers and oviposit onto flowers. Their larvae consume developing seeds and fruit of flowers pollinated by females. Traits important to this interaction include fruit set from moth pollination, fruit survivorship, and costs of fruit consumption by larvae. We studied these traits for five populations at two widely separated geographic locations. On average, 37% of flowers set fruit, 22% of flowers produced mature fruit, and larvae consumed 25% of immature fruit pollinated by female senita moths. Senita cactus and senita moth interactions were strongly mutualistic in all populations that we studied. Although one population had statistically lower fruit set and fruit production than the other four, all five populations were qualitatively similar in fruit production, costs, and patterns of fruit survivorship. Hand-pollination experiments suggested that fruit set was resource-limited in all but this one population. Apparent pollen limitation in the one population explains the quantitative differences in fruit set and fruit survivorship among the populations. As predicted by theory and exemplified by the senita mutualism, specialized and/or obligate interactions vary little among populations and geographic locations.

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Section: Resultsmentioning

confidence: 99%

Geographic and population variation in pollinating seed-consuming interactions between senita cacti ( Lophocereus schottii ) and senita moths ( Upiga virescens )

Holland¹,

Fleming²

1999

Oecologia

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“…We conducted an additional pollen supplementation experiment in May and July 1998 following the approach of Zimmerman and Pyke (1988). This allowed us to assess pollen limitation and whether plants differentially allocate resources to flowers that have received excess pollen.…”

Section: Resource-versus Pollen-limited Fruit Setmentioning

confidence: 99%

Co-pollinators and specialization in the pollinating seed-consumer mutualism between senita cacti and senita moths

Holland

Fleming

2002

Oecologia

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Specialization of a plant on a particular pollinator may not evolve if co-pollinators are effective and abundant. This is particularly evident if fruit set is resource limited and cannot be increased above the levels produced by the actions of co-pollinators. The pollinating seed-consuming interaction between senita cacti and senita moths in the Sonoran Desert presents a paradox because it exhibits many traits resembling those of the highly specialized yucca/yucca moth system, but also involves co-pollinators. For 6 years, we studied how contributions of nocturnal senita moths and diurnal co-pollinating bees to fruit set depended on resource and pollen limitation, time of flower closing, and the onset and phenology of flowering. Fruit set was typically resource limited. Fruit set of flowers exposed only to senita moths was not different from resource-limited fruit set of control flowers. When only co-pollinating bees were allowed to visit flowers, however, fruit set became pollen limited. Only in one year when fruit set was pollen limited were bees able to increase fruit set beyond the level resulting from senita moth pollination. High temperatures commonly induced flowers to close before sunrise so that diurnal bees were unable to visit flowers. This was particularly important from 1998 to 2000, when flowering did not begin until late in spring when temperatures were already high enough to induce flowers to close before sunrise. Bees were typically functionally redundant with senita moths; excluding bees from visiting flowers did not alter fruit set. Nevertheless, extreme specialization of floral traits to exclude co-pollinators has not evolved in senita, possibly because there are times when bees do increase fruit set. This can occur when senita moths are rare, fruit set is pollen limited, cool temperatures prevent flowers from closing before sunrise, and flowering begins early in spring.

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“…The saturated model including the three-way interaction transect X focal plant gender X nearest-neighbor gender was signifneighborhood gender, neighborhood density and focal plant inflorescence number on the number of seeds per flower in the control inflorescences of the experimental plants. Although it is possible that control and treatment flowers on any given plant are not independent due to resource reallocation following pollen augmentation (Bierzychudek 1981;Zimmerman and Pyke 1988;Parker 1997), including the number of treatment seeds per flower as a covariate in the ANCOVA allowed me to do such an analysis with some degree of safety. The number of seeds produced by treatment and control flowers was positively correlated within plants (r=0.498), indicating that plant identity was more important in determining the relationship between treatment and control flowers than was the treatment itself.…”

Section: Population Sex Structurementioning

confidence: 99%

POPULATION SEX STRUCTURE AND REPRODUCTIVE FITNESS IN GYNODIOECIOUS SIDALCEA MALVIFLORA MALVIFLORA (MALVACEAE)

Graff

1999

Evolution

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Abstract.-The spatial distribution of females and hermaphrodites within gynodioecious populations is expected to exert considerable selective pressure on gender fitness through pollen limitation of seed set. If pollen flow is predominantly local, seed set in individual plants may be sensitive to the proximity of pollen donors; pollen limitation of seed set may occur if hermaphrodites are locally rare. Under such circumstances, female fitness will be negatively frequency dependent and hermaphrodite fitness will be positively frequency dependent. Given local seed dispersal, a nonrandom clumped distribution of the genders is expected in gynodioecious populations due to the heritability of gender in gynodioecious species. If gender fitness is frequency dependent, such structure should favor hermaphrodites and select against females. To test this hypothesis, I quantified the distribution of the genders in terms of nearest neighbors and neighborhood sex ratio in two populations of gynodioecious Sidalcea malvijlora malviflora. I then measured the effect of neighborhood sex ratio on open-pollinated seed set and pollen limitation in both manipulated and unmanipulated neighborhoods. Results indicate that the genders have a patchy distribution and that both genders are pollen limited and show an increase in seed set with an increase in neighborhood hermaphrodite frequency. The observed population sex structure favors hermaphrodites and disadvantages females. These results highlight the importance that population-level traits can have in determining individual fitness and the evolution of sex ratios in gynodioecious species.Key words.-Frequency-dependency, gynodioecy, pollen limitation, population structure, sex ratio, Sidalcea.Received September 30, 1998. Accepted June 8, 1999.A major issue in the evolution of plant sexual systems is how both hermaphrodite and female (male-sterile) individuals are maintained in populations of gynodioecious species. Recent modeling efforts have emphasized the role of population structure in determining sex ratios in gynodioecious populations. To date, most of these models have focused on among-population, rather than within-population structure, and on genotypic, rather than phenotypic, structure. Genotypic models address the cytonuclear inheritance of male sterility in which maternally inherited cytoplasmic genes code for male sterility, whereas nuclear genes restore male fertility (Saumitou-Laprade et al. 1994). These models suggest that the widely varying sex ratios found among gynodioecious populations are determined by metapopulation processes including mutation rates among sex-determining genes and the migration of alleles between separate populations (Frank 1989;

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Reproduction in Polemonium: Assessing the Factors Limiting Seed Set

Cited by 280 publications

References 36 publications

Geographic and population variation in pollinating seed-consuming interactions between senita cacti ( Lophocereus schottii ) and senita moths ( Upiga virescens )

Geographic and population variation in pollinating seed-consuming interactions between senita cacti ( Lophocereus schottii ) and senita moths ( Upiga virescens )

Co-pollinators and specialization in the pollinating seed-consumer mutualism between senita cacti and senita moths

POPULATION SEX STRUCTURE AND REPRODUCTIVE FITNESS IN GYNODIOECIOUS SIDALCEA MALVIFLORA MALVIFLORA (MALVACEAE)

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