Reproductive versatility in legumes: the case of amphicarpy in Trifolium polymorphum.

Amphicarpy is a fascinating reproductive strategy, defined as fruit produced both below the soil surface and as aerial fruit on the same plant. Trifolium polymorphum is a grassland species subject to herbivory that combines amphicarpy with vegetative reproduction through stolons. Underground flowers have been described as obligate autogamous and aerial ones as self-compatible allogamous, with aerial floral traits favouring cross-pollination. In the present work we performed different pollination treatments on aerial flowers to analyse rates of pollen tube development and offspring fitness, measured as fruit set, seed production and germination percentage. This last variable was compared to that of seeds produced underground. No significant differences were found between fruit set in self- and cross-pollinations. Seed production was higher in self-pollinations, which is consistent with the higher rate of pollen tube development observed in self-crosses. Spontaneous self-pollination is limited in aerial flowers; thus pollen transfer by means of a vector is required even within the same flower. Germination tests showed that aerial seeds produced after self- and cross-pollination did not differ in fitness, but underground seeds had higher germination percentage than aerial ones. Thus, we conclude that T. polymorphum has a mixed mating system. In grasslands with heavy grazing pressure, clonal propagation and underground seed production ensure persistence in the field. An intermediate level of selfing in aerial flowers ensures offspring, but morphological (herkogamy) and functional (dicogamy) floral traits maintain a window to incorporate genetic variability, allowing the species to tolerate temporal and spatial pressures.

Karyotypes, heterochromatin, and physical mapping of 18S-26S rDNA in Cactaceae.

Karyotype analyses in members of the four Cactaceae subfamilies were performed. Numbers and karyotype formula obtained were: Pereskioideae = Pereskiaaculeata(2n = 22; 10 m + 1 sm), Maihuenioideae = Maihuenia patagonica (2n = 22, 9 m + 2 sm; 2n = 44, 18 m + 4 sm), Opuntioideae = Cumulopuntia recurvata(2n = 44; 20 m + 2 sm), Cactoideae = Acanthocalycium spiniflorum (2n = 22; 10 m + 1 sm),Echinopsis tubiflora (2n = 22; 10 m + 1 sm), Trichocereus candicans (2n = 22, 22 m). Chromosomes were small, the average chromosome length was 2.3 mum. Diploid species and the tetraploid C. recurvata had one terminal satellite, whereas the remaining tetraploid species showed four satellited chromosomes. Karyotypes were symmetrical. No CMA(-)/DAPI(+) bands were detected, but CMA(+)/DAPI(-) bands associated with NOR were always found. Pericentromeric heterochromatin was found in C. recurvata, A. spiniflorum, and the tetraploid cytotype of M. patagonica. The locations of the 18S-26S rDNA sites in all species coincided with CMA(+)/DAPI(-) bands; the same occurred with the sizes and numbers of signals for each species. This technique was applied for the first time in metaphase chromosomes in cacti. NOR-bearing pair no.1 may be homeologous in all species examined. In Cactaceae, the 18S-26S loci seem to be highly conserved.

Karyotype studies in South American species of Solanum subgen. Leptostemonum (Solanaceae).

Mitotic chromosome numbers and karyotypes of 13 South American species (12 native and one naturalized) from four sections of SOLANUM subgen. LEPTOSTEMONUM were studied. Chromosome numbers of S. ACERIFOLIUM, S. AENICTUM, S. CONDITUM, S. CONSIMILE, S. INCARCERATUM, and S. PLATENSE are reported for the first time. The number 2n = 24 was found in most species, while 2n = 22 was found in S. MAMMOSUM and S. PLATENSE. The latter is the second SOLANUM with this unusual number. Satellites are always present and were visible in more than 50 % of the cells studied. Karyotypes are symmetrical: M and SM chromosomes are common, whereas ST chromosomes are rare. The karyotypes of S. AENICTUM, S. MAMMOSUM, and S. PANICULATUM are comparatively asymmetrical. Species can be distinguished by a combination of chromosome number, karyotype formulae, karyotype length, the position of satellites in a particular chromosome pair, and asymmetry indices. The phenogram obtained does not reflect the sectional arrangements or the systematic affinities of the species studied. In sect. ACANTHOPHORA, increased asymmetry is associated with derived characters (strong andromonoecy, winged seeds, mammiform fruits). Diversification in the subgenus is suggested to be related to visible chromosome rearrangements and cumulative, cryptic structural changes may have also played a relevant evolutionary role.

Breeding System and pollination of selected plants endemic to Juan Fernandez Islands.

We conducted field studies on the Juan Fernández Islands flora on the breeding system of 25 endemic species from 17 families. We recorded data on flower features, pollen and ovule number, pollen/ovule ratio, pollen size, self-compatibility, floral visitors, and pollination. Flowers are mostly hermaphrodite, inconspicuous, small, and green. Six species are dioecious. Over 80% of the cosexual species are self compatible. However, many species are dichogamous (mostly protandrous); thus, even the self-compatible species may require pollen transfer. Selfing through geitonogamy seems to be the most common system, and several species express mixed breeding systems. Floral visitors are uncommon to rare, except for two hummingbird species (one native and one endemic) that visit five species we studied. In more than 300 h of observation of flowers over three field seasons, we detected only 23 native insect visits representing ten species (Diptera, Lepidoptera, and Coleoptera). One species each of an introduced ant and an introduced bee were also observed on some flowers, all near the single human settlement of San Juan Bautista. Wind directly moving pollen, or indirectly via shaking the flowers, is the most important pollen distribution mechanism. The majority of the wind-pollinated species bear some typical anemophilous features, but also others not characteristic of wind pollination, that presumably represent the condition of their biotically pollinated ancestors. Floral features often reflect ancestral reproductive systems, so floral biology studies of oceanic islands in particular must be done with cognizance of presumed ancestral forms, because the observed characters can be misleading.

Allozyme diversity in endemic flowering plant species of the Juan Fernandez Archipelago, Chile: ecological and historical factors with implications for conservation.

The level and apportionment of allozyme diversity were determined for 29 endemic (and 1 native) species from the Juan Fernández Islands, Chile. Mean diversities at the species level (H(es) = 0.065) are low but comparable to those measured for other insular endemics in the Pacific. A high mean proportion (0.338) of species-level diversity resides among populations. Diversity statistics were compared for species in different ecological-life history trait categories and abundance classes. Species occurring in large populations and those present in scattered small populations have higher diversities than species occurring in one or two populations. Although not significant with the conservative statistical test employed, lower diversity was found in highly selfing species as compared to animal- or wind-pollinated species. The apportionment of genetic diversity within and among populations (G(ST) values) is not significantly different for any of the species categories. Of particular interest is the lack of difference between animal- and wind-pollinated species because previous analyses of large data sets showed higher differentiation between populations of animal- than wind-pollinated species. Historical factors, both ecological and phylogenetic in nature, can influence the level and apportionment of diversity within insular endemics, and thus ecological correlates of diversity seen in many continental species may not apply to endemics. The results have several conservation implications. The preservation of large populations or several small populations is important for conserving diversity within species because when species are reduced to one or two populations, allozyme diversity is sharply reduced. High mean G(ST) values for the species examined illustrate the need for conserving as many populations as possible, either in the wild or in the garden, to preserve maximal diversity within species. Effective conservation strategies require empirical knowledge of each species.

Flower Structure and Reproductive Biology in Aspidosperma quebracho-blanco (Apocynaceae), a Tree Pollinated by Deceit.

Flower structure, attractants, breeding system, and visitors were studied in Aspidosperma quebracho-blanco, a South American mass-flowering tree with simple moth-pollinated flowers and without floral reward. Flowers are protandrous, having an initial male phase for 2 d. The pendulous and horizontal flower position and protandry prevent self-pollination. Although an inconspicuous annular floral nectary is located at the ovary base, nectar is not secreted. Nonstructural, extrafloral nectaries have been found on the external surface of the calyx and corolla, the first report of the kind for the family. Ants, wasps, flies, and beetles collect the extrafloral exudate composed of fructose, glucose, and sucrose. Experiments indicate that natural selfing (autogamy) and agamospermy are unlikely to occur (0% success), but artificial selfing indicates self-compatibility (70% success). A very low natural fruit to flower ratio (0.03) was obtained. Floral features and nocturnal opening indicate that these flowers would be pollinated by moths that nocturnally visit the species (Noctuidae, Pyraloidea) finding no floral reward. We suggest a nonmodel deception mechanism: providing the same cues as most moth flowers, this tree seems to be dependent upon sympatric rewarding plants that share the same pollinators.

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.