Trinidad Figueroa Fleming’s research while affiliated with National University of Salta and other places

A Correction to this paper has been published: https://doi.org/10.1038/s41396-021-00963-5

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.

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, called rhizobia, have been shown to locally adapt to domesticated common bean at its Mesoamerican and Andean origin sites. 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 are spatially structured. Our cross-infection experiments demonstrate that phage infection rates were overall higher on sympatric than on 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. Phages ranged from specialists to generalists, revealing a nested network of interactions. Our results suggest a key role of local adaptation to resident host bacteria communities in shaping phage genetic and phenotypic composition, following a similar spatial pattern of diversity and coevolution as the host.

The pump pollination mechanism is typical of basal clades within Papilionoideae and might be associated with less efficient pollen transfer systems, while the explosive tripping mechanism is considered more advanced and might represent the highest expression of the trend in pollen economy. Crotalaria pumila, C. stipularia, Desmodium incanum and D. subsericeum present secondary pollen presentation with pump and explosive pollination mechanisms, respectively. In the present study, we evaluate and compare (1) pollen removal, (2) pollen deposition and (3) pollen transfer efficiency of both mechanisms, considering single visits by Megachile spp., common pollinators of the four plant species in Salta Province, Argentina. Comparisons of visit durations are made in relation to the type of mechanism and rewards offered. We detected significant differences between both mechanisms in the proportion of pollen grains removed and deposited in a flower after a single visit of Megachile. We found that efficiency in pollen transfer was significantly higher for explosive mechanism (2.13 ± 0.42 pollen grains deposited per 100 removed) than for pump mechanism (0.33 ± 0.17 pollen grains deposited per 100 removed). This is the first study that compares efficiency between pollination mechanisms in this group of plants.

The repeated evolutionary transition from outcrossing to self-fertilization in angiosperms has been suggested to occur because selfing provides reproductive assurance. This transition is commonly associated with modifications of floral traits, among them herkogamy (the spatial separation between dehiscing anthers and the receptive stigma). Here, we investigate variation in levels of herkogamy in Desmodium incanum, D. pachyrrhizum, D. subsericeum and D. uncinatum, to determine the relationship between variation in this floral trait and self-pollen deposition. These species are self-compatible and bee-pollinated, with ornamental potential and may be used for forage given their high nutritional value. We studied natural populations located in Lerma Valley, Salta Province, Argentina. In January and February 2009, we marked and bagged 10 floral buds from 10 individual plants per species. The flowers were collected before their senescence; anther-stigma separation was measured immediately after collection with digital calipers (0.01 mm) as the distance between the surface of the stigma and the nearest anther. The stigmas were preserved in 70% ethanol. Pollen grains were counted under a microscope (10×) in the laboratory. There was significant variation in herkogamy levels among species. There was a negative correlation between anther-stigma distance and the number of selfpollen grains deposited on the stigma in isolated flowers. The variation in levels of herkogamy may represent a mechanism to ensure the production of some selffertilized progeny in the absence of pollinators.

As a first step in the characterization of native species of Papilionoideae from Northwestern Argentina with potential use as ornamentals, we determined the life cycle and floral characteristics of 21 species. It was observed that most species are perennial herbaceous plants. In most of them, the aerial part dies in winter time leaving an innovation zone of buds which produce new shoots in the following season. Considering the growth habit, half of them are vines, while the other species are erect, semi-erect or decumbent. All species presented flowers grouped in racemes or double racemes. The flowering periods were between December and April. The predominant colours of the corolla were yellow and pink. To analyze flower size, we set three categories: 6 to 18 mm, 19 to 29 mm and larger than 29 mm. Sixteen species are included in the first category, three species in the second and two in the third. In relation to floral rewards, 80% of species produce nectar and this feature enhances their attractiveness because of pollinator's presence.

Traditional breeding of ornamentals has led to a scent reduction of many floricultural varieties due to a negative correlation between flower longevity and fragrance. Vigna caracalla L. Verdc. (Leguminosae: Papilionoideae) produces large flowers with an intense, pleasant fragrance. The objective of this study was to identify, using headspace analysis, the major volatiles present in the floral bouquet of cut flowers. The eluted volatiles were analyzed using a gas chromatograph linked to a mass spectrometer. The volatile profile of V. caracalla flowers consists of a complex mixture, with a total of 29 compounds being detected in quantifiable amounts. Up to now, the studied fragrance related genes come mainly from few plant species; V. caracalla could be used as floral scent research material, and in the future, the genomic approach may be applied to cloning of fragrance related genes.

Vigna caracalla has the most complex flower among asymmetrical Papilionoideae. The objective of this study was to understand the relationships among floral characteristics, specialization, mating system and the role of floral visitors under different ecological contexts. Five populations were studied in north-western Argentina, from 700 to 1570 m a.s.l. Anthesis, colour and odour patterns, stigmatic receptivity, visitors and pollination mechanism were examined and mating-system experiments were performed. The petals are highly modified and the keel shows 3.75-5.25 revolutions. The sense of asymmetry was always left-handed. Hand-crosses showed that V. caracalla is self-compatible, but depends on pollinators to set seeds. Hand-crossed fruits were more successful than hand-selfed ones, with the exception of the site at the highest elevation. Bombus morio (queens and workers), Centris bicolor, Eufriesea mariana and Xylocopa eximia trigger the pollination mechanism (a 'brush type'). The greatest level of self-compatibility and autonomous self-pollination were found at the highest elevation, together with the lowest reproductive success and number of pollinators (B. morio workers only). 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.