Self-fertilization may have evolved in the peripheral population at the highest site of V. caracalla because of the benefits of reproductive assurance under reduced pollinator diversity.

No abstract

Reproductive phenology, floral biology, degree of self-incompatibility, and floral visitors of Erythrina falcata were studied in an Argentinean population. Flowering occurs during the dry season from late August to late October. Flower lifetime is 5-6 d. Phylogenetic studies indicate that E. falcata, together with E. fusca and E. crista-galli, are included in a basal clade within Erythrina. Its phylogenetic position, floral morphology, and nectar characteristics suggest a hummingbird-passerine mixed pollination system. The flowers are nontubular, and the vexillum (the upper petal of the corolla) covers the other remaining floral parts until displaced by a visiting passerine (Icterus cayanensis) or a hummingbird (Amazilia chionogaster). Both birds act as pollen vectors. Bees were observed as occasional pollinators. Nectar production begins at anther dehiscence and coincides with maximum stigmatic receptivity. The base of the keel forms a secondary nectar reservoir. Controlled pollinations showed that this species is self-incompatible, although a few fruits develop from selfing. Pollen:ovule ratio (43,200:7) is as expected for a xenogamous plant. Only 1 percent of the flowers set seeds under natural conditions. Possible explanations for the low reproductive success are discussed. RESUMENLa fenología reproductiva, la biología floral, el grado de auto-incompatibilidad y los visitantes florales de Erythrina falcata fueron estudiados en una población argentina. La floración ocurre durante la estación seca desde fines de Agosto hasta fines de Octubre. El tiempo de vida de las flores es de 5 a 6 días. Estudios filogenéticos indican que E. falcata, junto con E. fusca y E. crista-galli, están incluidos en un clado basal del género Erythrina. Su posición filogenética, la morfología floral y las características del nectar, sugieren un sistema de polinización mixto "colibrí-paseriforme." Las flores son no-tubulares y el vexilo (el pétalo superior de la corola) cubre las partes florales restantes hasta que es desplazado por un paserino (Icterus cayanensis) o un colibrí (Amazilia chionogaster). Ambas aves actúan como vectores de polen. También las abejas fueron observadas como polinizadores ocasionales. La producción de nectar comienza con la dehiscencia de las anteras y coincide con la máxima receptividad estigmática. La base de la quilla forma un reservorio secundario de néctar. Polinizaciones controladas mostraron que esta especie es auto-incompatible, aunque pocos frutos se desarrollan autógamicamente. La proporción Polen: ovulos (43.200:7) es la esperada para plantas xenógamas. Solo el 1 por ciento de las flores produjo semillas bajo condiciones naturales. Se discuten las posibles explicaciones del bajoéxito reproductivo observado.

Bacteriophages play significant roles in the composition, diversity, and evolution of bacterial communities. Despite their importance, it remains unclear how phage diversity and phage-host interactions are spatially structured. Local adaptation may play a key role. Nitrogen-fixing symbiotic bacteria, known as rhizobia, have been shown to locally adapt to domesticated common bean at its Mesoamerican and Andean sites of origin. This may affect phage-rhizobium interactions. However, knowledge about the diversity and coevolution of phages with their respective Rhizobium populations is lacking. Here, through the study of four phage-Rhizobium communities in Mexico and Argentina, we show that both phage and host diversity is spatially structured. Cross-infection experiments demonstrated that phage infection rates were higher overall in sympatric rhizobia than in allopatric rhizobia except for one Argentinean community, indicating phage local adaptation and host maladaptation. Phage-host interactions were shaped by the genetic identity and geographic origin of both the phage and the host. The phages ranged from specialists to generalists, revealing a nested network of interactions. Our results suggest a key role of local adaptation to resident host bacterial communities in shaping the phage genetic and phenotypic composition, following a similar spatial pattern of diversity and coevolution to that in the host.

The pollen:ovule ratio (P/O) has traditionally been used as a rough estimator of plant breeding systems. It has been shown that plant breeding systems are associated with particular floral traits. In this study, we determined the P/O in 21 Leguminosae species from Argentina and explored relationships between P/O and taxonomic position, flower size, floral rewards, pollen presentation and pollination mechanisms. According to the results, 15 out of the 21 species classified were obligate xenogamous, although some of them have been recorded as facultative xenogamous in previous studies. There was a significant effect of taxonomic position (genus), reward type and pollination mechanism on P/O. Species offering only nectar as a floral reward (which were species with a brush mechanism) had a significantly lower P/O than species offering pollen or pollen and nectar. Species with the brush pollination mechanism had the lowest P/O, while species with valvular and pump mechanism had the highest P/O. However, pollen presentation (primary and secondary) and flower size did not have a significant effect on P/O. Our results demonstrate that P/O variability is determined by taxonomic position and pollination mechanism in this plant group.