Columnar Cacti Research Articles

Association between cacti and nurse plants: a quantitative literature review

The association between cacti and nurse plants has been reviewed by different authors. These reviews however were qualitative because only evaluated aspects such as species identity of cacti and nurse plants, probable explanatory causes of their association, and location of study sites. To our knowledge, there are no quantitative reviews that have evaluated the association between cacti and nurse plants for different subfamilies, tribes, and growth forms of cacti and nurse plants, and different plant communities and soil properties. To address these issues, we performed a quantitative review of the studies on the association between cacti and nurse plants. The studies were searched in the ISI Web of Knowledge from 1986 to 2021. Data obtained from studies were analyzed with the relative risk ratio and ratio of medians. Most studies on the association between cacti and nurse plants were performed mainly in Mexico and the USA. Globose, cylindrical, and columnar cacti of the subfamily Cactoideae, and tribes Cacteae, Cereeae, and Echinocereeae were associated to nurse plants of Asteraceae, Euphorbiaceae, and Fabaceae. However, other subfamilies (Opuntioideae) and tribes (Notocacteae) of cacti, and families (Asparagaceae) of nurse plants were not associated. Nurse plants ameliorated temperature, moisture, and nitrogen of soil. The association between cacti and nurse plants occurred in desert shrubland and tropical dry forest. Further studies are needed on the association between cacti and nurse plants that consider more cactus subfamilies and tribes in countries with high cactus diversity in Central and South America.

Enhanced mycorrhization in four species of columnar cacti under the Sonoran Desert tree <em>Olneya tesota</em>

Background: Columnar cacti survival in deserts occurs mainly under nurse plants, due to better conditions for germination and establishment, as greater humidity, and nutrient concentration. However, interactions like the association between arbuscular mycorrhizal fungi (AMF) and roots remain relatively unexplored. We evaluated the mycorrhizal status and soil rhizosphere properties of four columnar cacti species growing both under and outside their nurse plant. Hypotheses: Soil properties improvement under nurse plants has been correlated with the abundance of AMF. Therefore, a greater number of AMF structures and roots mycorrhization would be in facilitated plants, compared to the same species growing outside the nurse. Studied species: Nurse plant: Olneya tesota, facilitated species: Carnegiea gigantea, Pachycereus pringlei, Pachycereus schottii, and Stenocereus thurberi. Study site and dates: Central Gulf Coast subdivision of the Sonoran Desert, Sonora, Mexico; October 2020. Methods: Cacti roots and soil rhizosphere were collected under and outside the nurse plant. Roots were stained, and mycorrhizal colonization (MC), hairy roots (HR), visual density (VD), and number of spores were determined. Physicochemical soil properties were analyzed. Results: Values of MC, VD, spore number, organic matter (OM), nitrate, and total and assimilable phosphorous were higher under the nurse compared to bare areas. Conclusions: The hypothesis that mycorrhization parameters are greater in roots of cacti growing under the nurse was confirmed, besides previous knowledge about soil quality under nurse plants, suggesting that AMF play a significant role in the cacti facilitation process under nurses plants, and that nurse plant plays a significant role in AMF formation.

First Report of Pitaya Virus X Infecting Lophocereus schottii f. mieckleyanus (Thin-Stemmed Totem Pole Cactus) in the United States.

Lophocereus is a genus of three species of columnar cacti native to Arizona and Mexico (Lodi, 2015). These cacti produce several tall, ascending, columnar stems that branch at the base in a candelabra-like arrangement. The most common species, L. schottii is known as the senita cactus. Several unusual knobby-stemmed spineless forms of senita cactus have been found in nature in Baja California, Mexico, which are collectively known as totem pole cacti. The thin-stemmed totem pole cactus, L. schottii f. mieckleyanus is an important part of landscapes in southern Arizona. Cacti are clonally propagated which makes viral infections of economic importance in the ornamental/nursery industry. In February 2023, virus-like symptoms, such as mosaic and chlorotic spots were observed on the stems of L. schottii f. mieckleyanus grown in a nursery in Phoenix, AZ, USA. Total RNA was extracted from two symptomatic cacti (YPHC-61 A & B) following the protocol by Tzanetakis et al. (2007), and cDNA was synthesized using the Superscript IV Reverse Transcriptase (Invitrogen, Vilnius, Lithuania). Reverse transcription polymerase chain reaction (RT-PCR) performed with cactus virus X specific primers (Kim et al. 2016) targeting the coat protein (CP) gene failed to generate any amplicon, while potexvirus-replicase primers, Potex 2RC and Potex 5 (van der Vlugt and Berendsen 2002) targeting RNA-dependent RNA polymerase (RdRp) gene amplified an expected amplicon of ~580 bp from both the samples. One of the amplicons was Sanger sequenced and showed 90.7% nucleotide (nt) identity with pitaya virus X (PiVX) in the GenBank (MN982522). Sequence was submitted in the GenBank under the accession number OR425049. PiVX is a new species of the genus Potexvirus and is named after its origin from pitaya (Hylocereus spp.). Further, RT-PCR was conducted with PiVX-specific primers, CP 110F/CP 604R targeting CP gene (Bae and Park 2022) and RdRp gene (RdRp F 5' GCGTGGGCCCTGGAAAA-3'/RdRp R 5' CTAAGATTCATCAATTCACCTCTCC-3') (this study). Amplicons of ~500 and 1100 bp were obtained using primers, CP 110F/CP 604R and RdRp F/RdRp R, respectively. A BLAST search revealed 90.5% nt identity to PiVX CP sequences (OM802135 and OM802134) and 87.3% nt identity to RdRp sequences (MN982523 and LC654699) in the GenBank. Sequences of isolates YPHC-61A and YPHC-61B were submitted in the GenBank under accession numbers, OQ915350 and PP182358 (CP gene) and OQ915351 and PP209539 (RdRp gene). Phylogenetic analysis based on the combined sequence datasets of CP and RdRp genes also grouped YPHC-61A and YPHC-61B with PiVX isolates and separated from other potexviruses species. For a bioassay of the virus, sap extract from symptomatic cactus was mechanically inoculated onto indicator plant species, i.e., beans, alfalfa, and melon. Ten days post- inoculation, chlorotic lesions were observed on beans and alfalfa plants, while melon and mock-inoculated plants did not show any symptoms. Similarly, L. schottii f. mieckleyanus plants grafted with infected cactus showed chlorotic spots after 30 days post grafting. Mechanically inoculated beans, alfalfa, and cactus plants were found to be positive for PiVX based on RT-PCR and Sanger sequencing. PiVX has earlier been detected on Notocactus leninghausii f. cristatus (Park et al. 2018) and dragon fruit (Selenicereus undatus) plants in South Korea (Bae and Park 2022). To our knowledge, this is the first report of PiVX on L. schottii f. mieckleyanus in the United States and worldwide.

Germination responses of the invasive hedge cactus (Cereus uruguayanus) to environmental factors

AbstractHedge cactus (Cereus uruguayanus R. Kiesling; syn.: Cereus hildmannianus K. Schum.) is a columnar cactus that was introduced to Australia as an ornamental plant and has since become invasive in subhumid regions of Queensland and New South Wales. Compared with its congener, queen of the night (Cereus jamacaru DC.), which is currently invasive in both eastern and southern Africa, information on seed biology of C. uruguayanus is lacking. Experiments were conducted to study the effects of alternating day/night temperature, salt stress, water stress, and burial depth on germination and seedling emergence of four seed accessions of C. uruguayanus. Seeds were also subjected to a controlled aging test (CAT) to obtain an estimate of potential persistence under field conditions. The optimum temperature regime for germination of all accessions was 30/20 C. Germination decreased with an increase in sodium chloride (NaCl) concentration, but germination of all accessions (range 26% to 81%) occurred at 160 mM NaCl, indicating very high salt tolerance. Seed germination gradually decreased with an increase in water stress, but germination in all accessions (range 19% to 47%) occurred at −0.8 MPa. Seed viability and dormancy status were unaffected by exposure to salt level (320 mM NaCl) and water (−1.6 MPa) stress under which germination did not occur. Germination responses to all three factors were generally similar to those documented for C. jamacaru. The emergence of C. uruguayanus decreased with an increase in seed burial depth. The highest emergence (43%) was recorded for surface-sown seeds, and emergence was reduced to 0 at a burial depth of 2 cm. CAT results for two seed accessions indicated that seeds of C. uruguayanus are likely to demonstrate extended (>3 yr) persistence under field conditions, a prediction that is supported by evidence that germination of its small (2-mm) seeds is markedly reduced by burial.

Management practices of Cereus jamacaru DC in the Caatinga dry forest differentially affect its reproductive phenology, fruit set and nectar availability

The management of plants and landscapes can affect the reproductive cycle of species through changes in morphology, temporal distribution of resources, and productivity, with ecological implications. In this study, we investigated the influence of management practices on the reproductive phenology and nectar availability of Cereus jamacaru DC, a columnar cactus native to Brazil managed by local people in the Caatinga dry forest. Our results reveal that the traditional management practices alter the quantitative and spatiotemporal distribution of resources (flowers, fruits, and nectar) of individuals of C. jamacaru in the studied Caatinga. All populations exhibited annual patterns of flowering and fruiting. However, individuals of the ex situ managed population showed a distinct temporal distribution pattern of flowering, with flower buds and flowers more regularly distributed throughout the reproductive period, compared to individuals of the in situ and unmanaged populations. Management practices differentially affected the production of flower buds, flowers, and fruits with a positive effect on fruit set in the in situ managed population. In addition, individuals of managed populations presented anticipation in the average date of the emission peaks of flower buds and ripe fruits. Individuals from the in situ managed population had available a greater volume of nectar with a higher sugar concentration per flower (twice as high) compared to the ex situ managed population and unmanaged population. The management practices seem to provide advantageous conditions for individuals of C. jamacaru since they allow higher availability of resources (flowers, nectar, and fruits) for a longer period in the Caatinga dry forest. Thus, management practices can prolong the temporal distribution of flowers and fruits, providing more resources for specialized pollinators (Sphingids) and dispersers (birds, reptiles), which are groups vulnerable to anthropic disturbances and climate changes in the Caatinga dry forest. These practices ultimately contribute to the maintenance of key ecological interactions of other species dependent on these vectors, benefiting the whole plant and animal community in the Caatinga dry forest.

Pollen morphology of columnar cacti from Tehuacán-Cuicatlán Valley, Mexico

The most important centre of diversity and endemism of columnar cacti in Mexico is the Tehuacán-Cuicatlán Valley (Puebla-Oaxaca states). The aims of this paper are (1) to provide a detailed description of the recent pollen morphology of 19 registered species that are found in this valley and (2) to develop a synoptic table to differentiate groups of species. This synoptic table is based on morphological features of pollen grains and the density of structural and sculptural elements observed using light and scanning electron microscopy. All analysed pollen grains were stenopalynous: isopolar monads, large, tricolpate with perforate tectate exine (sexine-nexine ratio 1:1), columellate structure with pattern of columellae distribution and spinulose sculpture. The spinules were always wider than they were tall. Although the 19 species of columnar cacti analysed in this study show highly similar types of pollen grains, we were able to characterise each of them with combined microscopy techniques.

Fruit Juices of Etcho (Pachycereus pecten-aboriginum) and Giant Cardon (Pachycereus pringlei) are Sources of Health-Promoting Ingredients with Potential Anticancer Properties.

Mexico is one of the main diversification centers of cacti in the world, with more than 500 endemic species, most of which remain nutritionally and functionally uncharacterized. The columnar cacti of the genus Pachycereus comprise five underutilized endemic Mexican species, whose nutraceutical properties have only been studied in the P. weberi species. Therefore, this study aimed to evaluate the nutritional quality and bioactive properties of etcho (P. pecten-aboriginum) and giant cardon (P. pringlei) fruit. The physical, chemical, and nutritional composition of etcho and giant cardon fruits were characterized, as well as the profile and content of bioactive compounds, antioxidant activity (ABTS•+ and DPPH•), and antiproliferative capacity in cervical (HeLa) and breast cancer (MDA-MB-231, MCF-7, and T-47D) cell lines. Our results suggest that etcho and giant cardon fruits are rich sources of essential nutrients and bioactive phytochemicals (including K, Mg, P, dietary fiber, polyphenolic compounds, vitamin C, betalains, and myo-inositol) with antioxidant and anticancer potential by inhibiting the proliferation of all evaluated cell lines with IC50 values in the range of 198 to 287µg of gallic acid equivalents/mL. Therefore, etcho and giant cardon fruits could be used for nutraceutical purposes, and their consumption could promote health benefits.

Are 150 km of open sea enough? Gene flow and population differentiation in a bat-pollinated columnar cactus.

Genetic differentiations and phylogeographical patterns are controlled by the interplay between spatial isolation and gene flow. To assess the extent of gene flow across an oceanic barrier, we explored the effect of the separation of the peninsula of Baja California on the evolution of mainland and peninsular populations of the long-lived columnar cactus Stenocereus thurberi. We analyzed twelve populations throughout the OPC distribution range to assess genetic diversity and structure using chloroplast DNA sequences. Genetic diversity was higher (Hd = 0.81), and genetic structure was lower (GST = 0.143) in mainland populations vs peninsular populations (Hd = 0.71, GST = 0.358 respectively). Genetic diversity was negatively associated with elevation but positively with rainfall. Two mainland and one peninsular ancestral haplotypes were reconstructed. Peninsular populations were as isolated among them as with mainland populations. Peninsular haplotypes formed a group with one mainland coastal population, and populations across the gulf shared common haplotypes giving support to regular gene flow across the Gulf. Gene flow is likely mediated by bats, the main pollinators and seed dispersers. Niche modeling suggests that during the Last Glacial Maximum (c. 130 ka), OPC populations shrank to southern locations. Currently, Stenocereus thurberi populations are expanding, and the species is under population divergence despite ongoing gene flow. Ancestral populations are located on the mainland and although vicariant peninsular populations cannot be ruled out, they are likely the result of gene flow across the seemingly formidable barrier of the Gulf of California. Still, unique haplotypes occur in the peninsula and the mainland, and peninsular populations are more structured than those on the mainland.

Inter- and intra-annual variation in the pulsed flowering phenology of the columnar cactus Pilosocereus leucocephalus and its relation to temperature, rainfall and plant size

Floral phenology involves the initiation and development of ecological and physiological processes (e.g. pollination, germination, etc.) that contribute to the successful recruitment of a plant species. However, aspects related to the inter and intra-annual variation of flowering patterns have been poorly studied, including pulsed flowering, which is a rare phenology in angiosperm plants with only three cases known in the family Cactaceae. Here, we analyzed the pulsed flowering phenology of the columnar cactus Pilosocereus leucocephalus between and within years and its relation to rainfall, environmental temperature, and plant size. We recorded the number of receptive flowers displayed by an initial population of 82 individual plants for five consecutive years in central Veracruz, Mexico. We calculated and compared 14 descriptors of the phenological pattern and found variation in flower production both within and between years; however, across years, the phenological pattern was consistently extended, pulsed, slightly synchronous, and with a low reproductive potential. Flower production was positively correlated with the maximum temperature of the fifteenth day before anthesis and poorly correlated with rainfall at the study site. The accumulated flower number over five years was positively related to cactus size. Overall, our results support the idea that the pulsed floral phenology of this cactus is a result of resource limitation that forces individuals to rest and restore the resources needed for flower production.

Environmental gradualism explains variation in pollination systems of columnar cacti: Phylogenetic and trait evolution analyses

AbstractAimThe geographical dichotomy hypothesis (GDH) states several flowering plant groups have specialized pollination systems in tropical areas where resources are more reliable and pollinator communities tend to be more stable, than in extratropical areas. Our main goal was to understand the scope of the GDH and/or gradual environmental variation considering the evolutionary history of the pollination traits.LocationNeotropical tropics and adjacent extratropics.Major taxa studiedColumnar cacti.MethodsUsing a database composed of ~54 columnar cacti species (31.7% of the global columnar cactus species), four complex traits were analysed: pollination syndromes, reproductive systems, type of anthesis, and duration of anthesis. We conducted generalized linear models (GLMs), phylogenetic regressions, evolutionary trait optimization, and multivariate models with 19 bioclimatic variables and potential evapotranspiration.ResultsWeak phylogenetic signal was detected for all traits, giving consistent results between GLMs and phylogenetic regression analysis. The pollination syndrome and duration of anthesis varied with latitude, in contrast to the reproductive system and the type of anthesis. In the Southern Hemisphere, the pollinators were more diverse and the duration of anthesis was longer. Different evolutionary paths between hemispheres were detected and optimization showed a complex pattern in the evolution of traits, suggesting high homoplasy with multiple transformations by convergence and/or parallelism. The environmental models showed thermic seasonality may be at the core of the latitudinal variation of the pollination system.Main conclusionsWe did not detect a geographical dichotomy in pollination systems of the cacti, but rather a gradual change in different pollination attributes. Therefore, instead of a GDH, we propose an environmental gradient hypothesis (EGH). Environmental variables may be explaining the variation detected in pollination system traits by conditioning floral properties (morphology, phenology), diversity and distribution of pollinators, and/or coevolution occurrence. The complexity implied in these traits is consistent with high homoplasy levels and a differential evolutionary history between the hemispheres.

Influence of plant size and neighboring plants on the herbivory of the columnar cactus Pilosocereus leucocephalus

Background: Plant-plant facilitation provides benefits to the protected species since the host species reduces the intensity of stressful physical conditions. However, it has been hypothesized that the outcome of the interaction could be regulated by the characteristics of the interacting species and that herbivores could counteract the benefits of protective plants.
 Question: Can cactus size and identity of neighboring plants influence the herbivory of the columnar cactus P. leucocephalus?
 Studied species / Mathematical model: Pilosocereus leucocephalus (Poselg.) Byles & G.D. Rowley /One-way ANOVA, Repeated measures ANOVA, Analysis of covariance and linear regression.
 Study site and dates: San Ignacio, Veracruz, Mexico. April to May 2019.
 Methods: We randomly selected 60 P. leucocephalus plants growing underneath the canopy of seven species of shrubs and P. leucocephalus plants growing ≥ 3 m away from other species and exposed to full sunlight conditions. We obtained the size of the P. leucocephalus plants (size of main stem from ground to apex) and determined the intensity (number of bites on the stem) of vertebrate herbivory.
 Results: The number of bite scars by small vertebrate species was significantly higher on the stems of cacti established in open spaces than on those underneath the canopy of seven shrub species and increased significantly with the stem size of the protected species.
 Conclusions: We conclude that herbivory damage by rodents on a giant cactus in a dry tropical forest depends on cactus size and the identity, but not the shade, of the nearest neighbor.

Floral Specialization and Bat Pollination in Subtribe Cereinae (Cactaceae): A Morphological Approach

Cactaceae has many vertebrate-pollinated species, and in the subtribe Cereinae, several genera are indicated as being pollinated by bats. In this subtribe, we observed phenotypic specialization in floral morphological attributes associated with chiropterophily, allowing high precision in the determination of this pollination system. However, in loco pollination records of bats have been confirmed only in a few species. In this context, using a morphological approach, we studied the floral biology of 14 columnar cacti of Cereeae-Cereinae with emphasis on species with chiropterophilous attributes and confirmed the role of bats specialized in nectar consumption as pollinators of these taxa. The studied taxa have similarities in their floral bauplan, observed by analysing the overlap in the floral morphospace. The length and opening of the floral tube are important characteristics for pollen deposition. Approximately 156 visits by bats of the subfamilies Glossophaginae and Lonchophyllinae were observed among the studied taxa. Chiropterophily is the prevalent pollination system among Cereinae, and hereby, we verified this system in five of its genera. There is, however, much variation between diurnal and nocturnal systems within this subtribe, and variation among genera and within species of a given genus may reflect the evolutive pathways, this being worthy of future studies.

Relative importance of two bat species as pollinators of Neobuxbaumia tetetzo (Cactaceae): Evidences from morphometric and pollen load analyses

AbstractNeobuxbaumia tetetzo is a columnar cactus whose flowers are visited by the bat species Choeronycteris mexicana and Leptonycteris yerbabuenae. Although both bat species are considered the pollinators of N. tetetzo, the probability of pollination of each bat species has not been estimated. In this study, we determine the relative importance of C. mexicana and L. yerbabuenae as pollinators of N. tetetzo. The probability of pollination was estimated using two different approaches: (i) morphological correspondence between head (linear traits [total head length, snout length, and face height and width]) and cranial traits (shape traits) of bats and flower traits (linear [internal floral tube length including and excluding the nectary, corolla diameter, stamen length, style length, and corolla tube diameter] and shape traits), and (ii) pollen load analyses to estimate the percentage of occurrence (PO) and the pollination probability index (PPI). Our results showed a lack of a significant correspondence between both head and cranial traits of C. mexicana and the flowers of N. tetetzo, and linear morphological correspondence between total head length of L. yerbabuenae and flower length. Pollen loads of C. mexicana were composed by seven different pollen types, its PO and PPI were 41.87 ± 9.53% and 0.29, respectively. Leptonycteris yerbabuenae pollen loads were composed by three pollen types, with a PO of 78.29 ± 13.67% and a PPI of 0.67. Our results suggest that whereas C. mexicana has a low constancy to the flowers of N. tetetzo, L. yerbabuenae has a higher probability of pollination.

Seed shielding, an undescribed process that prevents seed from overheating (and dying) in extreme weather conditions

Sun exposure is a major threat to the survival of cacti seeds in desertic environments. During summer, fruits of the columnar cactus Pachycereus pringlei from San Esteban Island, northwestern Mexico, are eaten by herbivorous iguanas, and after digestion, seeds are deposited within their scats. We compared the germination percentage of wild seeds exposed to the sun while lying on the ground of the island, with that of seeds collected directly from the fruit, and seeds obtained from old and recently deposited iguana scats. Our results indicate that direct sun exposure causes drastic reduction in seed germination, and this negative effect is reduced in seeds shielded inside feces, although with a cost on germination. We discuss some of the possible implications of seed shielding in the population of P. pringlei.

Breeding Biology of the White-Throated Cacholote Pseudoseisura gutturalis ochroleuca, an Endemic Bird of the Monte Desert

The White-throated Cacholote Pseudoseisura gutturalis is a little studied, socially monogamous furnariid, endemic to arid Argentina. Here we provide novel information to characterize the breeding biology of the northern subspecies ochroleuca in the Monte Desert, Argentina, and discuss the similarities and differences with other Pseudoseisura species. Nests were bulky enclosed structures constructed with thorny sticks and twigs of native plant species (n = 15) and 47% of them had objects used as external decorations. Nests had an entrance tube oriented preferentially towards the northeast, probably to avoid the prevailing south-southeast winds at the study site, and were placed at a mean height of 2.1 m above the ground (n = 13). Most of the active nests (93%) were built in columnar cacti Trichocereus atacamensis that were healthier and with fewer branches than nearby available conspecifics. Mean clutch size was 3.2 white eggs (n = 9) and the incubation period was c. 18–20 days. Brood size ranged from one to three hatchlings (n = 12) and nestlings remained in the nest for 24–26 days until fledgling. Nests with complete clutches were found between 29 October and 1 February and nestlings were found between 1 November and 5 February. Nestlings were attended by both parents and were fed with arthropods (n = 63) and vertebrates (n = 7). Nest visitation rate per nestling was similar among nests with three and two nestlings and lower than for a nest with one nestling. The breeding success was high during the incubation (73%) and nestling rearing (82%) stages. Our data show that Pseudoseisura species are similar in some aspects of their breeding biology (e.g. nest dimensions, nest decorations, mating system, clutch size), whereas other aspects, such as nest-site selection, nestling period and nest attendance rate, are more variable among species.

Phylogenomics provides insights into the evolution of cactophily and host plant shifts in Drosophila

Cactophilic species of the Drosophila buzzatii cluster (repleta group) comprise an excellent model group to investigate genomic changes underlying adaptation to extreme climate conditions and host plants. In particular, these species form a tractable system to study the transition from chemically simpler breeding sites (like prickly pears of the genus Opuntia) to chemically more complex hosts (columnar cacti). Here, we report four highly contiguous genome assemblies of three species of the buzzatii cluster. Based on this genomic data and inferred phylogenetic relationships, we identified candidate taxonomically restricted genes (TRGs) likely involved in the evolution of cactophily and cactus host specialization. Functional enrichment analyses of TRGs within the buzzatii cluster identified genes involved in detoxification, water preservation, immune system response, anatomical structure development, and morphogenesis. In contrast, processes that regulate responses to stress, as well as the metabolism of nitrogen compounds, transport, and secretion were found in the set of species that are columnar cacti dwellers. These findings are in line with the hypothesis that those genomic changes brought about key mechanisms underlying the adaptation of the buzzatii cluster species to arid regions in South America.

Marine subsidies produce cactus forests on desert islands

In island systems, nitrogen-rich seabird guano is a marine subsidy that can shape terrestrial plant communities. In zones of nutrient upwelling such as the Gulf of California, copious seabird guano is commonplace on bird islands. Several bird islands host regionally unique cactus forests, especially of the large columnar cactus, cardón (Pachycereus pringlei). We show that a chain of interactions across the land-sea interface yields an allochthonous input of nitrogen in the form of seabird guano, fueling the production of some of the densest cactus populations in the world. Fish, seabird, guano, soil, and cactus samples were taken from the representative seabird island of San Pedro Mártir for nitrogen stable isotope ratio measurements, which were compared to soil and cactus samples from other seabird and non-seabird Gulf islands and terrestrial ecosystems throughout the range of the cardón. Isla San Pedro Mártir δ15N values are distinctively high, ranging from fish + 17.7, seabird + 19.7, guano + 14.8, soil + 34.3 and cactus + 30.3 compared to average values across non-bird sites of + 13.0 (N = 213, S.D. = 3.7) for soil and + 9.8 (N = 212, S.D. = 3.4) for cactus. These δ15N values are among the highest ever reported for plants. Seabird island soil and cactus δ15N values were consistently significantly enriched relative to mainland and non-bird islands, a relationship expected due to the progressive volatilization of 14N rich ammonia from decomposing guano deposits. Our findings demonstrate that seabird-mediated marine nutrient deposits provide the source for solubilized nitrogen on desert islands, which stimulate terrestrial plant production in the cardón cactus beyond that seen in either mainland ecosystems or non-seabird islands.

Latitudinal gradients in biotic interactions: Are cacti pollination systems more specialized in the tropics?

Biotic interactions are said to be more specialized in the tropics, and this was also proposed for the pollination systems of columnar cacti from North America. However, this has not yet been tested for a wider set of cactus species. Here, we use the available information about pollination in the Cactaceae to explore the geographic patterns of this mutualistic interaction, and test if there is a latitudinal gradient in its degree of specialization. We performed a bibliographic search of all publications on the pollination of cacti species and summarized the information to build a database. We used generalized linear models to evaluate if the degree of specialization in cacti pollination systems is affected by latitude, using two different measures: the number of pollinator guilds (functional specialization) and the number of pollinator species (ecological specialization). Our database contained information about the pollination of 148 species. The most frequent pollinator guilds were bees, birds, moths and bats. There was no apparent effect of latitude on the number of guilds that pollinate a cactus species. However, latitude had a small but significant effect on the number of pollinator species that service a given cactus species. Bees are found as pollinators of most cactus species, along a wide latitudinal gradient. Bat and bird pollination is more common in the tropics than in the extra-tropics. The available information suggests that cacti pollination systems are slightly more ecologically specialized in the tropics, but it does not support any trend with regard to functional specialization.

P450 gene family mediates allelochemical detoxification and tolerance to alkaloids in cactophilic Drosophila

AbstractCacti are characterized by the extensive production of a broad variety of toxic metabolites as an anti‐herbivore strategy but nevertheless cactophilic Drosophila spp. (Diptera: Drosophilidae) feed and breed on decaying cacti. The family of cytochrome P450 is a group of enzymes involved in the detoxification metabolism, which are critical for the adaptation of phytophagous insects, especially populations of Drosophila exploiting cacti. In this context, Drosophila buzzatii Patterson & Wheeler and Drosophila koepferae Fontdevila & Wasserman (Drosophilini), constitute an excellent model for the study of the genetic basis of tolerance to cacti allelochemicals. These closely related species allow testing to what extent a relatively small set of genes can explain host use patterns and their role in the divergent evolution of specialization. We evaluated the role of the P450 genes in the adaptation of these species to the use of one of their hosts, the columnar cactus Trichocereus terscheckii (Parm.) Friedrich & GD Rowley (Cactaceae). Experimentally evolved strains exhibiting different degrees of cactus specialization were exposed to artificial rearing media enriched with cactus allelochemicals and piperonyl butoxide (PBO), an inhibitor of P450 family activity. Our analyses showed a significant viability reduction in the presence of PBO, in the non‐tolerant strains of both species as well as in the strain historically subjected to mild concentrations of allelochemicals (the soft strain) of D. koepferae. We confirmed the key role of P450 genes for the evolution of cactus specialization but also found evidence for the evolution of other detoxification pathways.

Evolution of the odorant-binding protein gene family in Drosophila

Odorant-binding proteins (OBPs) are encoded by a gene family involved in the perception of olfactory signals in insects. This chemosensory gene family has been advocated as a candidate to mediate host preference and host shifts in insects, although it also participates in other physiological processes. Remarkable differences in the OBP gene repertoire have been described across insect groups, suggesting an accelerated gene turnover rate. The genus Drosophila, is a valuable resource for ecological genomics studies since it comprises groups of ecologically diverse species and there are genome data for many of them. Here, we investigate the molecular evolution of this chemosensory gene family across 19 Drosophila genomes, including the melanogaster and repleta species groups, which are mostly associated with rotting fruit and cacti, respectively. We also compared the OBP repertoire among the closely related species of the repleta group, associated with different subfamilies of Cactaceae that represent disparate chemical challenges for the flies. We found that the gene family size varies widely between species, ranging from 39 to 54 candidate OBPs. Indeed, more than 54% of these genes are organized in clusters and located on chromosomes X, 2, and 5, with a distribution conserved throughout the genus. The family sizes in the repleta group and D. virilis (virilis-repleta radiation) were smaller than in the melanogaster group. We tested alternative evolutionary models for OBP family size and turnover rates based on different ecological scenarios. We found heterogeneous gene turnover rates (GR) in comparisons involving columnar cactus specialists, prickly pear specialists, and fruit dwellers lineages, and signals of rapid molecular evolution compatible with positive selection in specific OBP genes. Taking ours and previous results together, we propose that this chemosensory gene family is involved in host adaptation and hypothesize that the adoption of the cactophilic lifestyle in the repleta group accelerated the evolution of members of the family.