Columnar Cacti Research Articles

Host Plant Adaptation in Cactophilic Species of the Drosophila buzzatii Cluster: Fitness and Transcriptomics.

Host plant shifts in herbivorous insects often involve facing new environments that may speed up the evolution of oviposition behavior, performance-related traits, morphology, and, incidentally, reproductive isolation. In the genus Drosophila, cactophilic species of the repleta group include emblematic species in the study of the evolution of host plant utilization. The South American D. buzzatii and its sibling D. koepferae are a model system for the study of differential host plant use. Although these species exhibit a certain degree of niche overlap, the former breeds primarily on decaying cladodes of Opuntia cacti while D. koepferae main hosts are columnar cacti of the genus Trichocereus. Opuntia sulphurea and Trichocereus terscheckii are among the main hosts in nature. These cacti differ in ecological (spatial and temporal predictability) and chemical characteristics. Particularly relevant is the presence of toxic alkaloids in T. terscheckii. Studies of the effects of these cacti and alkaloids revealed the remarkable impact on oviposition behavior, viability, developmental time, wing morphology, mating success, and developmental stability in both species. Recent whole-genome expression studies showed that expression profiles are massively affected by the rearing cactus, and that the presence of alkaloids is the main factor modulating gene expression in D. buzzatii. Functional enrichment analysis indicated that differentially expressed genes are related to detoxification processes and stress response-though genes involved in development are an important part of the transcriptomic response. The implications of our studies in the evolution of host plant use in the repleta group are discussed.

Natural History Notes for the Columnar, Globular and Semi-Epiphytic Cactus Species of the Island of Puerto Rico

Abstract: The island of Puerto Rico is home to five species of columnar, globular and semi-epiphytic cacti: Pilosocereus royenii, Melocactus intortus, Stenocereus fimbriatus, Leptocereus quadricostatus and Hylocereus trigonus. However, their ecology and natural history are still largely unknown. We visited a total of 12 sites during four years. We identified habitat preferences for each cactus species; recorded the incidence of fires and the invasion of grasses in these habitats. We also recorded bird-cactus interactions during 150 hrs. of observation. Observations on the reproduction biology of S. fimbriatus is provided for the first time, and differences of M. intortus morphology of two populations were assessed. Finally, we identify different threats to the Puerto Rican native cacti and dry forests. We also identified various questions on the basic ecology and biology of these cactus species that should be addressed in future works.

Areole Changes during Bark Formation on Saguaro Cacti

Spines are an important component of cactus species. Besides providing protection from predation, they reduce heat loading, reduce transpiration, and aid dispersal of stem segments for vegetative propagation among others. Bark formation occurs on surfaces of more than twenty species of columnar cacti in the Americas. For all species tested, bark formation is related to direct sunlight exposure. Extensive bark coverage leads to premature death for saguaro cacti (Carnegiea gigantea). Preliminary evidence indicates that changes in areoles with spines occurred during the bark formation on C. gigantea. Four hundred, sixty-one paired photographic images of areoles of north- and south-facing surfaces of shoots with bark percentages on adjacent troughs in 2017 were analyzed to determine differences between north- and south-facing surfaces. As in past studies, south-facing surfaces had higher bark percentages (mean bark coverage 62%) than north-facing surfaces (mean bark coverage 19%). For north and south areoles, mean numbers of central spines were 2.70/1.55; radial spines 3.20/1.50; and apex spines 1.81/1.13, respectively. When data were pooled to compare numbers of central, radial and apex spines as well as spine color and spine thickness, all were significantly related with bark percentages. Decreases in numbers and characteristics of spines precede bark formation on adjacent troughs. Overall, the results show that crests deteriorate faster than adjacent troughs. To our knowledge, this is the first report to document changes in spine numbers and characteristics with bark coverage on a cactus species.

Pollination system of two endemic Bolivian cacti: Harrisia tetracantha and Neoraimondia herzogiana

Columnar cacti may present different mating systems that vary according to distinct factors, and the studies of these systems are essential to preserve cactus species. Bolivia is the fourth country with most diversity of Cactaceae, still scarce information about the reproductive biology of the endemic cactus species is known. Therefore, we assessed the pollination type, pollination syndrome and flower visitors of the endemic columnar cacti Harrisia tetracantha and Neoraimondia herzogiana. We hypothesize that they would present cross and self-pollination as strategies to ensure reproduction in the bioclimatic variable dry inter-Andean valleys.

The Iconic Saguaro Cactus Across its Landscape

All photographs in this section are provided by authors of papers in our scientific journals and are used by permission. All copyrights reserved. The saguaro cactus (Carnegiea gigantea) is a long-lived columnar cactus that is among the most well-studied plants in the world. Long-term research indicates that saguaro establishment is generally episodic and strongly influenced by precipitation and temperature. Drought conditions can reduce survivorship of recently germinated saguaros up to 100%. Long-term drought will likely cause saguaro populations to decline as older or vulnerable saguaros die without new cohorts replacing them. However, the relative importance of local habitat variability and the coinciding drought impacts on establishing populations remain largely unexplored. We modeled saguaro establishment in response to drought in various habitat and soil types at Saguaro National Park. Recent, severe drought coincided with drastic declines in saguaro establishment that has seen few saguaros establishing in recent years. Overall, saguaro establishment was best explained by the interaction of drought and habitat type. The best model identified bajada and foothill plots as responding somewhat similarly to drought regardless of severity but foothill plots outperformed bajada plots regardless of drought severity. Furthermore, the predicted number of saguaros to establish in bajada or foothill plots dropped to near zero under the most severe drought but remained higher in slope plots, suggesting that the most suitable habitat type for establishing saguaros has shifted during the recent drought. These results reveal that saguaro establishment strongly correlates with drought but that the impact of drought varies with local habitats and their associated physical characteristics. Overall, our study shows that incorporating the range of local variability in how plants may respond to past climate conditions is important for predicting future response to climate change. The following image gallery is meant to illustrate the demographic complexity of saguaros and how the interactive dynamics of desert climate with landscape position influence population regeneration trends in Saguaro National Park. Photo by D. E. Winkler. Photo by D. E. Swann Photo by J. L. Conver. Photo by D. E. Winkler. Photo by D. E. Winkler. Photo by D. E. Swann. Photo by D. E. Winkler. Photo by D. E. Winkler. Photo by J. L. Conver. Photo by J. L. Conver. These photographs illustrate the article “The interaction of drought and habitat explain space–time patterns of establishment in saguaro (Carnegiea gigantea)” by Winkler et al., published in Ecology 99(3), https://doi.org/10.1002/ecy.2124

Behavioral evolution accompanying host shifts in cactophilic Drosophila larvae.

For plant utilizing insects, the shift to a novel host is generally accompanied by a complex set of phenotypic adaptations. Many such adaptations arise in response to differences in plant chemistry, competitive environment, or abiotic conditions. One less well‐understood factor in the evolution of phytophagous insects is the selective environment provided by plant shape and volume. Does the physical structure of a new plant host favor certain phenotypes? Here, we use cactophilic Drosophila, which have colonized the necrotic tissues of cacti with dramatically different shapes and volumes, to examine this question. Specifically, we analyzed two behavioral traits in larvae, pupation height, and activity that we predicted might be related to the ability to utilize variably shaped hosts. We found that populations of D. mojavensis living on lengthy columnar or barrel cactus hosts have greater activity and pupate higher in a laboratory environment than populations living on small and flat prickly pear cactus cladodes. Crosses between the most phenotypically extreme populations suggest that the genetic architectures of these behaviors are distinct. A comparison of activity in additional cactophilic species that are specialized on small and large cactus hosts shows a consistent trend. Thus, we suggest that greater motility and an associated tendency to pupate higher in the laboratory are potential larval adaptations for life on a large plant where space is more abundant and resources may be more sparsely distributed.

Reproductive biology of Oreocereus fossulatus (Cactaceae), a long‐lived columnar cactus endemic to the tropical Andes

AbstractThe geographic dichotomy hypothesis suggests that columnar cacti inhabiting the tropics depend on flower visitors (birds and bats) for their pollination, showing highly specialized animal‐pollinated systems. This pattern has been demonstrated for the northern hemisphere; however, our knowledge of the species of columnar cacti growing in the southern tropics is still scarce. In this study, we studied the reproductive biology of Oreocereus fossulatus (Cactaceae, Tribe Trichocereae), an endemic, columnar cactus of the tropical Andes, to determine if its pollination system tends to be more generalized (mixed systems of autogamy and xenogamy) than specialized (xenogamy) as a consequence of the geographic position of where it lives. Observations of the frequency of visits showed that Patagona gigas (Trochillidae) is its main pollinator. It visits the flowers when they are open, coinciding with the periods of greater floral reward (dusk and dawn of the first day of anthesis). The treatments of autogamy, xenogamy and geitonogamy produced fruits, showing that O. fossulatus exhibits a generalized pollination system, in the same way as its congeneric species O. celsianus, which is distributed farther south in the Prepuna biogeographical region. Our results suggest that species partially specializing in pollination by hummingbirds and, besides, capable of autopollination, could be common in the tropical and subtropical Andes, probably as a response to the unpredictable environments present in their ecosystems.

Genetic Diversity and Demographic History in the Cactophilic Drosophila repleta Species Group (Diptera: Drosophilidae) in North America Inferred from Mitochondrial DNA Barcodes.

Genetic diversity in mitochondrial DNA barcodes, comprising a segment of the cytochrome c oxidase subunit I (COI) gene, was used to infer demographic histories in selected taxa of the cactophilic Drosophila repleta species group in North America. Haplotype and nucleotide diversities were determined in 16 taxa based on both previously published and new sequences. Haplotype diversity (h) differed dramatically in different taxa, varying from h = 0 in Drosophila eremophila, Drosophila hexastigma, and Drosophila bifurca to h = 0.99 in Drosophila hamatofila. Genetic diversity indices and sample sizes were sufficient to infer demographic histories from mismatch distribution analysis and Bayesian skyline plots for 9 taxa: Drosophila mojavensis baja, Drosophila mojavensis sonorensis, Drosophila arizonae, Drosophila aldrichi, D. hamatofila, Drosophila spenceri, Drosophila mainlandi, Drosophila mettleri, and Drosophila nigrospiracula. Evidence was found for both population expansions and relatively stable populations in these species. Demographic history varied dramatically in subspecies of D. mojavensis, showing a relatively stable population size over time in D. m. sonorensis from the mainland Sonoran Desert whereas a large population expansion was evident in D. m. baja from the Baja California Peninsula, providing support for the hypothesis that the split of sister species D. mojavensis and D. arizonae from a common ancestor occurred on the mainland rather than the peninsula as proposed by others. No evidence was found for a causal relationship between a stable or expanding population and host plant shifts from prickly-pear cactus to columnar cacti, which has occurred independently in many taxa of the repleta group.

Weak population structure and no genetic erosion in Pilosocereus aureispinus: A microendemic and threatened cactus species from eastern Brazil.

Succulent cacti (Cactaceae) are among the most threatened taxonomic groups assessed to date. Here we evaluated the genetic diversity and population structure of a narrow endemic columnar cactus Pilosocereus aureispinus. This species is only found in a small area of c. 300 km2 of rocky savanna from eastern Brazil and it is currently classified as vulnerable (VU) on the International Union for Conservation of Nature (IUCN) red list. Eight microsatellite loci were genotyped for 91 individuals from four localities of the known P. aureispinus range. In contrast with expectations for narrow endemic species, we found relatively high levels of genetic diversity (e.g., HE = 0.390 to 0.525; HO = 0.394 to 0.572) and very low population structure based on the variation of six loci. All the analyzed individuals were clustered in one unique genetic group in assignment tests. We also generated the sequences of two plastid markers (trnT-trnL and psbD-trnT) and found no variation on a subsample of 39 individuals. We used Landsat 8 images and Normalized Difference Vegetation Index to estimate a potential extent of occurrence of c. 750 km2 for this species. Our results showed that P. aureispinus is not suffering from erosion of nuclear genetic variability due to its narrow distribution. However, we advocate that because of the extremely limited extent of occurrence, the ongoing anthropogenic disturbances in its habitat, and phylogenetic distinctiveness of P. aureispinus, this species should be classified as endangered (EN) on the IUCN Red List.

Effect of flower orientation on the male and female traits of Myrtillocactus geometrizans (Cactaceae).

Intra-individual variation in the production and size of reproductive traits has been documented in columnar cacti, being higher in equator-facing flowers. Such variation is attributed to the high amount of PAR intercepted by stems oriented towards the equator. Most studies focused on this phenomenon have documented the existence of intra-individual variation on traits associated with the female function; however, its impact on traits associated with the male function has been neglected. We tested the hypothesis that equator-facing flowers of Myrtillocactus geometrizans exhibit higher values on traits associated with both male and female functions than flowers facing against it. Number and size of anthers and ovaries, pollen:ovule ratio and number and quality of pollen grains (diameter, germinability, viability and pollen tube length) were estimated from reproductive structures facing north and south, and compared with t-tests between orientations. Number of anthers per flower, number of pollen grains per anther and per floral bud; pollen size, viability and germinability; pollen tube length; ovary length and pollen:ovule ratio were significantly higher in reproductive structures oriented towards the south (i.e. equator). These findings suggest that intra-individual variation in floral traits of M.geometrizans might be associated with different availability of resources in branches with contrasting orientation. Our results provide new evidence of the existence of a response to an orientation-dependent extrinsic gradient. To our knowledge, this is the first study documenting the existence of intra-individual variation on pollen quality and P:O ratio in Cactaceae species.

Characterization of endozoochorous dispersal of pitayo Stenocereus queretaroensis, in Autlán, Jalisco, Mexico

HIGHLIGHTS We compared dispersion by two species of bats with two species of birds, and concluded that bats are more efficient dispersers of this columnar cactus.The importance of specific plant-animal interactions for the fitness of the interacting groups is mostly driven by the morphological, physiological and behavioural traits of the two interacting species. This work aims to describe dispersal of seeds of the columnar cactus Stenocereus queretaroensis by its main fruit consumers (bats and birds), using the criteria of legitimacy and efficiency. A disperser is legitimate when seeds pass through the gut without losing germination capability, and is efficient if the seeds are transported to places where they have the potential for germination and establishment as seedlings. We conducted direct observations in order to identify the main consumer species of S. queretaroensis fruits. Seed germination was evaluated by comparing those that pass through the gut of two bat species, Artibeus lituratus and Leptonycteris yerbabuenae, and two bird species, Icterus pustulatus and Melanerpes chrysogenys, using the parameters germination percentage and germination rate. To evaluate seed deposition patterns by bats and birds within the study area, 20 seed traps were set: 10 below the canopies of local trees, and 10 in open spaces. Nine species of bats and 13 species of birds were found to consume S. queretaroensis fruits. The four tested species can be considered legitimate dispersers, but germination percentage differed among these disperser species. Seeds defecated by birds show the highest speed of germination and lowest average time to germinate, compared with control seeds. In terms of deposition patterns, however, the bats dropped the highest number of seeds, and deposited them both under the canopy and in open areas, whereas birds drop a lower amount and under the canopy only.

Variation in chromosome number and breeding systems: implications for diversification in Pachycereus pringlei (Cactaceae).

Polyploidy, the possession of more than two sets of chromosomes, is a major biological process affecting plant evolution and diversification. In the Cactaceae, genome doubling has also been associated with reproductive isolation, changes in breeding systems, colonization ability, and speciation. Pachycereus pringlei (S. Watson, 1885) Britton & Rose, 1909, is a columnar cactus that has long drawn the attention of ecologists, geneticists, and systematists due to its wide distribution range and remarkable assortment of breeding systems in the Mexican Sonoran Desert and the Baja California Peninsula (BCP). However, several important evolutionary questions, such as the distribution of chromosome numbers and whether the diploid condition is dominant over a potential polyploid condition driving the evolution and diversity in floral morphology and breeding systems in this cactus, are still unclear. In this study, we determined chromosome numbers in 11 localities encompassing virtually the entire geographic range of distribution of P. pringlei. Our data revealed the first diploid (2n = 22) count in this species restricted to the hermaphroditic populations of Catalana (ICA) and Cerralvo (ICE) Islands, whereas the tetraploid (2n = 44) condition is consistently distributed throughout the BCP and mainland Sonora populations distinguished by a non-hermaphroditic breeding system. These results validate a wider distribution of polyploid relative to diploid individuals and a shift in breeding systems coupled with polyploidisation. Considering that the diploid base number and hermaphroditism are the proposed ancestral conditions in Cactaceae, we suggest that ICE and ICA populations represent the relicts of a southern diploid ancestor from which both polyploidy and unisexuality evolved in mainland BCP, facilitating the northward expansion of this species. This cytogeographic distribution in conjunction with differences in floral attributes suggests the distinction of the diploid populations as a new taxonomic entity. We suggest that chromosome doubling in conjunction with allopatric distribution, differences in neutral genetic variation, floral traits, and breeding systems has driven the reproductive isolation, evolution, and diversification of this columnar cactus.

The interaction of drought and habitat explain space-time patterns of establishment in saguaro (Carnegiea gigantea).

The long-lived columnar saguaro cactus (Carnegiea gigantea) is among the most studied plants in the world. Long-term studies have shown saguaro establishment to be generally episodic and strongly influenced by precipitation and temperature. Water limitation through lower-than-average seasonal rainfall and elevated temperatures increasing evaporative loss can reduce survivorship of recent germinates. Thus, multi-year, extended drought could cause populations to decline as older saguaros die without replacement. Previous studies have related establishment to temporal variation in rainfall, but most studies have been on non-randomized plots in ideal habitat and thus might not have captured the full variability within the local area. We studied how saguaro establishment varied in space and which habitat features may buffer responses to drought on 36 4-ha plots located randomly across an elevation gradient, including substantial replication in landscape position (bajada, foothills, and slopes) in the two disjunct districts of Saguaro National Park in southern Arizona, USA. Recent, severe drought coincided with drastic declines in saguaro establishment across this ~25,000-ha area. Establishment patterns derived from the park-wide data set was strongly correlated with drought, but the Park's two districts and diversity of plots demonstrated substantially different population outcomes. Saguaro establishment was best explained by the interaction of drought and habitat type; establishment in bajada and foothill plots dropped to near-zero under the most severe periods of water limitation but remained higher in slope plots during the same time span. Combined with saguaro density estimates, these data suggest that the most suitable habitat type for saguaro establishment shifted to higher elevations during the time span of the recent drought. These results place into context the extent to which historical patterns of demography provide insight into future population dynamics in a changing climate and reveal the importance of understanding dynamics across the distribution of possible local habitat types with response to variation in weather.

Phylogeny and Circumscription of Cephalocereus (Cactaceae) Based on Molecular and Morphological Evidence

Cephalocereus, Neobuxbaumia, and Pseudomitrocereus (Cactaceae, Cactoideae, Echinocereeae) are related genera of columnar cacti native to Mexico with current ambiguous circumscription. We applied maximum parsimony and Bayesian inference methods to reconstruct the phylogeny of the Cephalocereus group using molecular data from seven chloroplast regions (petL-psbE, psbA-trnH, rpl16, rpl32-trnLUAG, trnL-F, trnQrps16, andycf1), simple coded indels, and 46 structural characters. The Cephalocereus group was recovered as monophyletic with high support values, whereas Neobuxbaumia appeared as paraphyletic, due to the polyphyly of Cephalocereus and the derived position of Pseudomitrocereus within this group. Topology was mostly congruent among the different phylogenetic methods explored, and three pervasive clades were observed. Two structural characters were confirmed as synapomorphies for the Cephalocereus group: prismatic crystals in the dermal system and a perianth woody cap persistent in the fruit. The derived position of Pseudomitrocereus suggests that new hypotheses must be explored regarding the possible hybrid origin of this taxon. We propose the transfer of all species of Neobuxbaumia, Cephalocereus, and Pseudomitrocereus to a single genus, in which Cephalocereus takes priority over the other names. Based on our results, a new circumscription for Cephalocereus is proposed, including a taxonomic synthesis, two new combinations (Cephalocereus multiareolatus and Cephalocereus sanchezmejoradae), and a key for species.

Experimental Evolution of Alkaloid Tolerance in Sibling Drosophila Species with Different Degrees of Specialization

Drosophila buzzatii and Drosophila koepferae are sibling species with marked ecological differences related to their patterns of host exploitation. D. buzzatii is a polyphagous species with a sub-cosmopolitan distribution, while D. koepferae is endemic to the mountain plateaus of the Andes, where it exploits alkaloidiferous columnar cacti as primary hosts. We use experimental evolution to study the phenotypic response of these cactophilic Drosophila when confronting directional selection to cactus chemical defenses for 20 generations. Flies adapted to cactus diets also experienced higher viability on alkaloid-enriched media, suggesting the selection of adaptive genetic variation for chemical-stress tolerance. The more generalist species D. buzzatii showed a rapid adaptive response to moderate levels of secondary metabolites, whereas the columnar cacti specialist D. koepferae tended to maximize fitness under harder conditions. The evolutionary dynamic of fitness-related traits suggested the implication of metabolic efficiency as a key mediator in the adaptive response to chemical stress. Although we found no evidence of adaptation costs accompanying specialization, our results suggest the involvement of compensatory evolution. Overall, our study proposes that differential adaptation to secondary metabolites may contribute to varying degrees of host specialization, favoring niche partitioning among these closely related species.

Comparative Analysis of Load Adaptation Strategies in Columnar Cacti and Hardwood Trees

Abstract: “Cacti are different.” This sentence holds true for many aspects of the functional morphology and anatomy of cacti in comparison to other perennial plants. The biomechanical adaptations, especially of tree-like columnar cacti, seem to be unique. The scope of this small review is to elucidate some of their specific load adaptation strategies and how they deviate from — or are similar to — typical hardwood trees.

Natural History of the Caatinga Endemic Vieira's Flower Bat, Xeronycteris vieirai

Xeronycteris vieirai is an endemic bat species described by Gregorin and Ditchfield in 2005 only five specimens of which have been collected to date. It is considered Data Deficient by the IUCN Red List. There is little information about this species, so its ecological requirements are poorly known although its diet has been speculated to be nectarivorous. Xeronycteris vieirai apparently has a distribution restricted to the semi-arid Brazilian Caatinga, a habitat that has been highly degraded. We present here the first information about the natural history of X. vieirai, obtained through a large research project aiming at the ecology and conservation of bats in the Caatinga of the states of Rio Grande do Norte and Pernambuco, northeastern Brazil. From June 2014 to October 2015 we captured 62 individuals of X. vieirai at five sites, which represent new records and expand its known distribution, establishing the northernmost record. Xeronycteris vieirai feeds on nectar of at least nine species of plants belonging to six families, and mainly on the columnar cactus Pilosocereus pachycladus. The species has peak activity at 1830 h and shows an apparently seasonally monoestrous reproductive cycle (June–December). Adult females have longer forearms than adult males and are significantly heavier; there is no bias in the sex ratio. A colony of approximately 20 individuals was observed in a well-ventilated cave with natural lighting, representing the first documented roost for the species. Finally, ectoparasites of the genus Trichobius were found on 85.7% of the individuals examined, with no difference in parasite load between males and females.

Effects of nurse plants and the granivore guild in the associational susceptibility of seeds from the columnar cactus Pilosocereus leucocephalus

The nurse-protégé interaction involves benefits for the protected species by the reduction in the abiotic stress intensity. Nurse plants, however, could affect other biotic interactions by reducing that natural benefit. Studies about plant-plant-animal interaction assume that plants can recover from and/or avoid granivory when they grow under higher resources availability; nevertheless, in early stages they could be subject to different pressures. Thus, the resistance or susceptibility to granivores could occur because of differential responses of the plants (nurse and protected) to the environment (abiotic factors) or as results of differential responses of the plants to granivores (biotic factors), altering the probability of the resistance or susceptibility of plants to herbivores. We evaluated diurnal and nocturnal granivore activity on P. leucocephalus seeds, and we also evaluated if a nurse species could determine the association type (i.e. associational resistance or susceptibility) from the intensity of the granivore in early stage (e.g. seeds) of the P. leucocephalus life cycle. We found higher granivory under nurse plants than in open spaces (the control group), indicating associational susceptibility. Furthermore, most of the granivory was performed by nocturnal animals (mice). These results suggest a cost/benefit of the nurse-protégé interaction, which can be modulated by the granivory.

Prickly problems of cacti phylogeny

Cactus Genomics![Figure][1] The genomes and relationships of columnar cacti, such as the saguaro, have been resolved. PHOTO: JAYPIERSTORFF/SHUTTERSTOCK The evolutionary history of cacti has been difficult to resolve. Copetti et al. sequenced the genomes of four species of columnar cacti,

A Distinctive and Host-Restricted Gut Microbiota in Populations of a Cactophilic Drosophila Species.

Almost all animals possess gut microbial communities, but the nature of these communities varies immensely. For example, in social bees and mammals, the composition is relatively constant within species and is dominated by specialist bacteria that do not live elsewhere; in laboratory studies and field surveys of Drosophila melanogaster, however, gut communities consist of bacteria that are ingested with food and that vary widely among individuals and localities. We addressed whether an ecological specialist in its natural habitat has a microbiota dominated by gut specialists or by environmental bacteria. Drosophila nigrospiracula is a species that is endemic to the Sonoran Desert and is restricted to decaying tissues of two giant columnar cacti, Pachycereus pringlei (cardón cactus) and Carnegiea gigantea (saguaro cactus). We found that the D. nigrospiracula microbiota differs strikingly from that of the cactus tissue on which the flies feed. The most abundant bacteria in the flies are rare or completely absent in the cactus tissue and are consistently abundant in flies from different cacti and localities. Several of these fly-associated bacterial groups, such as the bacterial order Orbales and the genera Serpens and Dysgonomonas, have been identified in prior surveys of insects from the orders Hymenoptera, Coleoptera, Lepidoptera, and Diptera, including several Drosophila species. Although the functions of these bacterial groups are mostly unexplored, Orbales species studied in bees are known to break down plant polysaccharides and use the resulting sugars. Thus, these bacterial groups appear to be specialized to the insect gut environment, where they may colonize through direct host-to-host transmission in natural settings.IMPORTANCE Flies in the genus Drosophila have become laboratory models for microbiota research, yet the bacteria commonly used in these experiments are rarely found in wild-caught flies and instead represent bacteria also present in the food. This study shows that an ecologically specialized Drosophila species possesses a distinctive microbiome, composed of bacterial types absent from the flies' natural food but widespread in other wild-caught insects. This study highlights the importance of fieldwork-informed microbiota research.