Breeding systems in a secondary deciduous forest in Venezuela: The importance of life form, habitat, and pollination specificity

Breeding systems and mating systems of plants in a previously studied secondary deciduous forest were reanalysed in the context of new data. In this analysis, we increased the number of plant species (up to approximately 25% of the plant species in the community), included other life forms (23 annual and perennial species, plus habitat disturbance categories), and considered information about pollinator specificity. The frequencies of species with different sexual systems in a sample of 51 species were 82% hermaphrodite, 14% monoecious, and 4% dioecious. The frequencies of breeding systems in the sample of 49 hermaphroditic and monoecious species were 53% self-incompatible and 47% self-compatible. Self-compatible species included seven partially self-compatible, three self-compatible non-autogamous, and 13 self-compatible autogamous species. None of the species evaluated proved to be agamospermous. Fifty-five percent of the species tested were obligate outbreeders. The proportion of self-incompatible species was higher among trees and shrubs than among annual herbs. The proportion of self-compatible species for perennial herbs and lianas was not different. The association between annual herbs and autogamy was not strong: seven of 13 species were autogamous, five were partially self-compatible, and one was self-incompatible. The main characteristics or factors associated with breeding system were life cycle and successional stage. Short-lived species were mostly self-compatible, and xenogamy tended to be associated with forest and forest-border. In contrast, pollination specificity and life form were not consistently related to breeding system (self-compatibility or self-incompatibility) and mating system (xenogamy or autogamy).     

Reproductive biology of Lactoris fernandeziana (Lactoridaceae)

Lactoris fernandeziana, monotypic in its family, is endemic to the cloud forests of Robinson Crusoe Island. Although there has been considerable study of the relationships of Lactoris, as a rare species and as a putative primitive paleoherb, little is known of its reproductive biology. Knowledge of the latter is essential for effective conservation programs. The species is gynomonoecious. The overall proportion of flowers is ∼1 female:1 hermaphrodite. The inconspicuous semipendulous green flowers, usually in mixed-gender inflorescences, do not produce rewards. Hermaphrodite flowers are herkogamous and protogynous. Pollen grains are shed from the extrorse anthers in permanent dry tetrads. There is a mean of 12879 tetrads per hermaphrodite flower. Both flower types bear an average of ∼18 ovules. The P/O (pollen/ovule) ratios imply facultative or obligate xenogamy, but hand pollinations show that Lactoris is self-compatible. No floral visitors were ever observed, but stigmata of open-pollinated flowers bore tetrads, and 64% of such styles had pollen tubes. Flowers enclosed in large mesh (1 mm) bags bore similar numbers of tetrads and pollen tubes. Thus, we conclude that Lactoris is anemophilous, a syndrome perhaps reflected by the P/O ratio. Low genetic diversity (isozymes and DNA) supports selfing and implies limited distance wind pollen dispersal. The small size of the island, the ± 1000 extant Lactoris plants, coupled with anemophily, self-compatibility, and pendant flower position, have yielded a geitonogamous system with high seed set and low genetic diversity. If inbreeding depression is expressed, it is in seed germination and seedling vigor, for Lactoris is very difficult to cultivate. For this species, effective conservation practices need to focus on habitat preservation and promotion of outcrossing.     

The reproductive biology of the Mediterranean endemic Cyclamen balearicum Willk. (Primulaceae)

Knowledge of the reproductive biology of endemic plants improves our understanding of how mating system may be related to patterns of species abundance and provides a basis for the development of rational conservation programmes. In this paper we present natural population data on the floral biology and reproductive ecology of the endemic Mediterranean species Cyclamen balearicum Willk. This is a long-lived, diploid perennial herb which occurs in southern France in five fragmented and isolated regions and on the Balearic Islands of Mallorca, Menorca, Ibiza, Cabrera and Draponera. Our observations indicate a particularly scarce pollinator activity (rare syrphid visits) and dispersal by ants over small distances. A controlled pollination experiment in a natural population showed that in southern France C. balearicum is fully self-compatible and that selfing is autonomous and probably delayed (i.e. following opportunities for outcrossing). The proximity of stigmas and anthers will favour autonomous selfing. The high pollen/ovule ratio indicates nevertheless that C. balearicum has a mixed mating system. Patterns of variation in stigma-anther separation and pollen production per flower suggest that not only has the current mating system of the species evolved from an outcrossing ancestor but that due to the fragmentation and isolation of populations greater levels of selfing have evolved in southern France (and to an intermediate degree on Ibiza and Menorca). On the island of Mallorca where larger continuous belts of C. balearicum habitat still exist the species has floral traits indicating a more outcrossed mating system. To our knowledge this is the first paper to document such trends in floral traits in the endemic component of the Mediterranean flora.     

Expression level of the SLG gene is not correlated with the self-incompatibility phenotype in the class II S haplotypes of Brassica oleracea

In Brassica, the S-locus glycoprotein (SLG) gene has been strongly implicated in the self-incompatibility reaction. Several alleles of this locus have been sequenced, and accordingly grouped as class I (corresponding to dominant S-alleles) and class II (recessive). We recently showed that a self-compatible (Sc) line of Brassica oleracea expressed a class II-like SLG (SLG-Sc) gene. Here, we report that the SLG-Sc glycoprotein is electrophoretically and immunochemically very similar to the recessive SLG-S15 glycoprotein, and is similarly expressed in stigmatic papillae. Moreover, by seed yield analysis, we observe that both alleles are associated with a self-compatibility response, in contrast with the other known recessive S haplotypes (S2 and S5). By genomic DNA blot analysis, we show the existence of molecular homologies between the Sc and S15 haplotypes, but demonstrate that they are not identical. On the other hand, we also report that the S2 haplotype expresses very low amounts of SLG glycoproteins, although it exhibits a self-incompatible phenotype. These results strongly question the precise role of the SLG gene in the molecular mechanisms that control the self-incompatibility reaction of Brassica.     

The effect of interplant distance on mating success in federally threatened, self-incompatible Hymenoxys herbacea = H. acaulis var. glabra (Asteraceae)

We investigated large- and fine-scale effects of interplant distance on compatibility, seed set, and seed germination in a rare, self-incompatible perennial, Lakeside daisy (Hymenoxys herbacea = H. acaulis var. glabra). Plants were collected at the Marblehead Peninsula. Ohio, and transplanted to a greenhouse where they were hand-pollinated. For the large-scale analysis, 110 crosses were classified in three categories: Near crosses (0.75-6.70 m), Far crosses (17-72 m), and Very Far crosses (>900 ml. There was no significant effect of interplant distance on compatibility, seed set, or seed germination in these crosses. For the fine-scale analysis, we made 44 crosses with interplant distances ranging from 0.75 to 10 m. At this scale, interplant distance explained 10.9% of the variance of the seed/floret ratio, suggesting that local genetic structure may result in a modest amount of biparental inbreeding. We found no fine-scale effects of interplant distance on compatibility or percentage of seed germination, but it is possible that biparental inbreeding could affect later stages of the life cycle not included in this study. For all distance classes, >80% of the crosses were compatible, indicating that lack of compatibility between mates is not likely to limit seed production. Apparently, presumed population bottlenecks have not been severe enough for genetic drift to eliminate substantial numbers of self-incompatibility alleles.     

A comparison of levels of genetic polymorphism and self-compatibility in geographically restricted and widespread plant congeners

Summary Evolutionary theory predicts low levels of genetic polymorphism and high levels of self-compatibility in plant species with small ranges and few individuals. To test these predictions, I compared published data on electrophoretically detectable genetic variation and breeding systems for geographically restricted and widespread congeners in eleven genera. The restricted species exhibit significantly fewer polymorphic loci and alleles per polymorphic locus than do their widespread congeners. Although some rare species are genetically impoverished, others are nearly as polymorphic as their widespread congeners. The restricted species and their widespread congeners do not differ consistently with respect to breeding systems.     

The origin ofSenecio vulgaris (Asteraceae)

Senecio vulgaris L. (2n = 40) is suggested to be of autotetraploid origin fromS. vernalis Waldst. & Kit. (2n = 20). This conclusion is based on results obtained from experimental hybridisations and cytological observations, and the consideration of morphological affinities, patterns of geographical distribution and hybrid formation under natural conditions. The morphological differences between the two species are related to a difference in the breeding system. WhilstS. vernalis is self-incompatible,S. vulgaris is self-compatible and strongly self-pollinating. Equally, other self-pollinating taxa traditionally associated withS. vulgaris are shown to have evolved independently from outbreeding relatives. Within a narrow frame of relationship, annual weeds have evolved in different cytotaxonomic circumstances.     

Pollinator limitaton in a deceptive orchid, Pogonia japonica, on a floating peat mat

Deceptive orchid species that offer no floral rewards to pollinators often experience pollinator limitation because they. The breeding system and fruit set were investigated in order to examine pollinator limitation for a population of a deceptive orchid, Pogonia japonica , on a floating peat mat in Mizorogaike Pond, western Japan. Fruit sets for outcross-pollinated, self-pollinated and pollinator-excluded flowers were 75%, 80%, and 0%, respectively. Thus, this species was self-compatible but neither autogamous nor apogamous. The fruit set for open-pollinated flowers was 22.9% and 17.4% in 1994 and 1995, suggesting that pollinator limitation did occur in the field. Larger flowers were more likely to develop into fruit than smaller ones in open pollination (36% vs 8%). Thus, flower size seems to affect fruiting of this species. No effective visits by major pollinators such as bees, which could carry pollinia, were observed during 16.5 h of observation during daytime. Instead, thrips were often found moving on gynostemium or pollinia and circumstantial evidence that suggests thrips may partly transfer pollen in pieces out of a granular pollinium of P. japonica was obtained. Pogonia japonica should come to use thrips as a pollinator to supplement low fruit set under limited flower visitation by major pollinators.     

The inheritance of partial self-compatibility inBrassica oleracea L.: results from a half diallel homozygous for a highly recessive S-allele

Summary In a study of partial self-compatbility inBrassica oleracea, flower number, seeded siliqua and seed production were recorded on self- and cross-pollinated inflorescences of the progenies of a half diallel between five unrelated inbred plants homozygous for the same recessiveS-allele.On cross-pollinated inflorescences significant amounts of additively controlled genetic variation were found for seed set per flowering site and its two components, seeded siliquae per flower and seeds per seeded siliquae. Considerable heterosis and gene interaction were also present and a simple additive dominance model did not fully explain the observed variation.On self-pollinated inflorescences, additive gene action was absent for the seed production variates although differences between progenies were highly significant and heterosis was present. Complex gene interactions were considered to be responsible. The characteristics of the method of assessment used and the relationship between self- and outcross seed production are discussed. It appears unlikely that the component lines could be selected for reduced self seed set, but selection for higher outcross seed set may be possible.     

Genotype-dependent differences in S12-RNase expression lead to sporadic self-compatibility

Sporadic self-compatibility, the occasional fruit formation after otherwise incompatible pollinations, has been observed in some S ₁₂-containing genotypes of Solanum chacoense but not in others. We have sequenced this S ₁₂ allele and analyzed its expression in four different genotypes. The S₁₂-RNase levels were generally less abundant than those of other S-RNases present in the same plants. In addition, two-fold and five-fold differences in the amount of S₁₂-RNase and S ₁₂ RNA, respectively, were observed among the genotypes analyzed. A comparison with the genetic data showed that genotypes with the highest levels were fully and permanently self-incompatible, whereas those with the lowest levels were those in which sporadic self-compatibility had been observed. The mature protein contains four potential glycosylation sites and genotype-specific differences in the pattern of glycosylation are also observed. Our results suggest the presence of modifier genes which affect, in a genotype-dependent manner, the level of expression and the post-translational modification of the S₁₂-RNase.