Cycad Species Research Articles

Decades of IUCN recommendations for biocontrol of invasive pest on the Guam cycad: you can lead policy-makers to conservation proposals but you cannot make them follow

Guam’s cycad known as Cycas micronesica has been threatened by a coalition of invasive herbivore species, and the armored scale Aulacaspis yasumatsui has emerged as the primary threat. This lethal cycad pest invaded Guam in 2003, and the Species Survival Council of the International Union for Conservation of Nature (IUCN) began publishing recommendations addressing protection of the cycad population in 2005. Sustained epidemic mortality caused the addition of C. micronesica to the United States Endangered Species Act in 2015. The need to establish a sustainable coalition of biological control organisms has been the constant advice throughout almost two decades of recommendations, yet the decision-makers who controlled the direction of policy and funding have not responded to the advice with success. Therefore, we describe the history of publications in which the IUCN has asserted that this singular conservation action is urgently required to save the cycad species. We then summarize contemporary recommendations to address the ongoing threats to this and other insular cycad species.

Ceratozamia guatemalensis (Zamiaceae): A new cycad species from Mesoamerica

Ceratozamia guatemalensis, a new cycad species from the Sierra de los Cuchumatanes, Huehuetenango, Guatemala, is described and compared with the geographically proximal congeners C. vovidesii and C. matudae, with which C. guatemalensis has been historically confused based on their pendulous seed cones, a rare trait in the genus. Nonetheless, a recent phylogenetic study suggests that C. guatemalensis and C. vovidesii are sister species, while C. matudae belongs to distant clade. The new taxon is easily distinguishable from both C. vovidesii and C. matudae by qualitative and quantitative traits based on vegetative and reproductive structures. Remarkably, C. guatemalensis is characterized by having significant morphometric differences from the other two species, such as the wider median leaflets and wider leaflet articulations, and qualitative traits such as the seed cones of green color. The description of C. guatemalensis represents the recognition of the first endemic Ceratozamia species from Guatemala. It should be considered Critically Endangered (CR) due to limited populations and the ongoing destruction of its habitat.

Ceratozamia alba (Zamiaceae): A new cycad species from the Selva El Ocote Biosphere Reserve in Chiapas, Mexico

Ceratozamia alba sp. nov., a new cycad species from the Selva El Ocote Biosphere Reserve in northern Chiapas, Mexico, is described and compared to its congeners. Our earlier observations led us to think that these populations belonged to C. robusta, given their geographic location and the general morphological resemblance of adult individuals. However, seedlings and juveniles are more similar to C. santillanii, another geographically proximal species with which it has a sister relationship. We have determined that C. alba is easily distinguishable from other Ceratozamia species by the whitish-green emerging leaves that turn bluish green upon maturation, and the bluish green male and female mature cones. In addition, C. alba possesses several morphometric trait variations that are significantly different from the two geographically proximal species mentioned above, such as leaf number, leaflet number, petiole and rachis length, and median leaflet width. Ceratozamia alba should be considered as a critically endangered species (CR) due to its low population size, ongoing habitat destruction, and extremely narrow distribution range.

Ceratozamia gigantea (Zamiaceae), a new species of cycad, endemic to the mountain karst forests of Tabasco, Mexico: what the reproductive structures revealed

Ceratozamia gigantea (Zamiaceae), a new species of cycad, endemic to the mountain karst forests of Tabasco, Mexico: what the reproductive structures revealed

Resource dilution effect rather than resource concentration hypothesis explains the patterns of pre-dispersal seed predation of an African cycad along an elevational gradient in South Africa.

The genus Encephalartos is entirely endemic to Africa, and like most cycad species, the genus is at risk of extinction. One of the threats jeopardising the future of the genus is reproduction failure, a failure that is still poorly understood. Our objective was to investigate what predisposes Encephalartos species to seed damages through predation, a potential cause of reproduction failure. We collected functional traits of 430 individuals of Encephalartos villosus, as well as data on pre-dispersal seed predation, habitat type and elevation in the Origi Gorge Nature Reserve, South Africa. Then, we analysed our data by fitting a structural equation model. We found that plants tend to be taller when moving from open to close habitat, whereas plant height tends to increase along elevation. In addition, taller plants tend to have more leaves, and plant canopy size shows significant positive relationship with elevation, plant height and number of leaves. These findings suggest a leaf height-canopy dimension strategy perhaps in response to environmental stresses imposed by elevation. We tested the effects of habitat types on seed production. Although there were significantly more seeds in open habitats, open habitats showed the lowest proportion of predated seeds. Finally, we tested the effects of elevation on seed production. We found that seed production decreases along elevation while the proportion of predated seeds increases. Under the resource concentration hypothesis, these findings (where there are more resources, predation is low) are unexpected, suggesting rather that it is the resource dilution effect that matches the pre-dispersal seed predation patterns in our study area. We suggest that anthropogenic pressures at lower elevation due to easy access may cause seed predators to shift towards higher elevation where they cause heavier damage to seed, thus perhaps contributing to the extinction risk of the genus Encephalartos.

Limited effects of xylem anatomy on embolism resistance in cycad leaves.

Drought-induced xylem embolism is a primary cause of plant mortality. Although c. 70% of cycads are threatened by extinction and extant cycads diversified during a period of increasing aridification, the vulnerability of cycads to embolism spread has been overlooked. We quantified the vulnerability to drought-induced embolism, pressure-volume curves, in situ water potentials, and a suite of xylem anatomical traits of leaf pinnae and rachises for 20 cycad species. We tested whether anatomical traits were linked to hydraulic safety in cycads. Compared with other major vascular plant clades, cycads exhibited similar embolism resistance to angiosperms and pteridophytes but were more vulnerable to embolism than noncycad gymnosperms. All 20 cycads had both tracheids and vessels, the proportions of which were unrelated to embolism resistance. Only vessel pit membrane fraction was positively correlated to embolism resistance, contrary to angiosperms. Water potential at turgor loss was significantly correlated to embolism resistance among cycads. Our results show that cycads exhibit low resistance to xylem embolism and that xylem anatomical traits - particularly vessels - may influence embolism resistance together with tracheids. This study highlights the importance of understanding the mechanisms of drought resistance in evolutionarily unique and threatened lineages like the cycads.

Transcriptome sequencing data provide a solid base to understand the phylogenetic relationships, biogeography and reticulated evolution of the genus Zamia L. (Cycadales: Zamiaceae).

Cycads are a key lineage to understand the early evolution of seed plants and their response to past environmental changes. However, tracing the evolutionary trajectory of cycad species is challenging when the robust relationships at inter- or infrageneric level are not well resolved. Here, using 2901 single-copy nuclear genes, we explored the species relationships and gene flow within the second largest genus of cycads, i.e. Zamia, based on phylotranscriptomic analyses of 90 % extant Zamia species. Based on a well-resolved phylogenetic framework, we performed gene flow analyses, molecular dating and biogeographical reconstruction to examine the spatiotemporal evolution of Zamia. We also performed ancestral state reconstruction of a total of 62 traits of the genus to comprehensively investigate its morphological evolution. Zamia comprises seven major clades corresponding to seven distinct distribution areas in the Americas, with at least three reticulation nodes revealed in this genus. Extant lineages of Zamia initially diversified around 18.4-32.6 (29.14) million years ago in Mega-Mexico, and then expanded eastward into the Caribbean and southward into Central and South America. Ancestral state reconstruction revealed homoplasy in most of the morphological characters. This study revealed congruent phylogenetic relationships from comparative methods/datasets, with some conflicts being the result of incomplete lineage sorting and ancient/recent hybridization events. The strong association between the clades and the biogeographic areas suggested that ancient dispersal events shaped the modern distribution pattern, and regional climatic factors may have resulted in the following in situ diversification. Climate cooling starting during the mid-Miocene is associated with the global expansion of Zamia to tropical South America that has dramatically driven lineage diversification in the New World flora, as well as the extinction of cycad species in the nowadays cooler regions of both hemispheres, as indicated by the fossil records.

Evolutionary trends of reproductive phenotype in Cycadales: an analysis of morphological evolution in Ceratozamia.

The size and shape of reproductive structures is especially relevant in evolution because these characters are directly related to the capacity for pollination and seed dispersal, a process that plays a basic role in evolutionary patterns. The evolutionary trajectories of reproductive phenotypes in gymnosperms have received special attention in terms of pollination and innovations related to the emergence of the spermatophytes. However, variability of reproductive structures, evolutionary trends and the role of environment in the evolution of cycad species have not been well documented and explored. This study considered this topic under an explicitly phylogenetic and evolutionary approach that included a broad sampling of reproductive structures in the genus Ceratozamia. We sampled 1400 individuals of 36 Ceratozamia species to explore the evolutionary pattern and identify and evaluate factors that potentially drove their evolution. We analysed characters for both pollen and ovulate strobili within a phylogenetic framework using different methods and characters (i.e. molecular and both quantitative and qualitative morphological) to infer phylogenetic relationships. Using this phylogenetic framework, evolutionary models of trait evolution for strobilar size were evaluated. In addition, quantitative morphological variation and its relation to environmental variables across species were analysed. We found contrasting phylogenetic signals between characters of pollen and ovulate strobili. These structures exhibited high morphological disparity in several characters related to size. Results of analyses of evolutionary trajectories suggested a stabilizing selection model. With regard to phenotype-environment, the analysis produced mixed results and differences for groups in the vegetation type where the species occur; however, a positive relationship with climatic variables was found. The integrated approach synthesized reproductive phenotypic variation with current phylogenetic hypotheses and provided explicit statements of character evolution. The characters of volume for ovulate strobili were the most informative, and could provide a reference for further study of the evolutionary complexity in Ceratozamia. Finally, heterogeneous environments, which are under changing weather conditions, promote variability of reproductive structures.

Eco-evolutionary evidence for the global diversity pattern of Cycas (Cycadaceae).

The evolution of the latitudinal diversity gradient (LDG), characterized by a peak in diversity toward the tropics, has captured significant attention in evolutionary biology and ecology. However, the inverse LDG (i-LDG) mechanism, wherein species richness increases toward the poles, remains inadequately explored. Cycads are among one of the oldest lineages of extant seed plants and have undergone extensive diversification in the tropics. Intriguingly, the extant cycad abundance exhibits an i-LDG pattern, and the underlying causes for this phenomenon remain largely elusive. Here, using 1,843 nuclear genes from a nearly complete sampling, we conducted comprehensive phylogenomic analyses to establish a robust species-level phylogeny for Cycas, the largest genus within cycads. We then reconstructed the spatial-temporal dynamics and integrated global environmental data to evaluate the roles of species ages, diversification rates, contemporary environment, and conservatism to ancestral niches in shaping the i-LDG pattern. We found Cycas experienced decreased diversification rates, coupled with the cooling temperature since its origin in the Eocene from continental Asia. Different regions have distinctively contributed to the formation of i-LDG for Cycas, with the northern hemisphere acting as evolutionary museums and the southern hemisphere serving as cradles. Moreover, water-related climate variables, specifically precipitation seasonality and potential evapotranspiration, were identified as paramount factors constraining Cycas species richness in the rainforest biome near the equator. Notably, the adherence to ancestral monsoonal climates emerges as a critical factor in sustaining the diversity pattern. This study underscores the imperative of integrating both evolutionary and ecological approaches to comprehensively unravel the mechanisms underpinning global biodiversity patterns.

Phylometagenomics of cycad coralloid roots reveals shared symbiotic signals.

Cycads are known to host symbiotic cyanobacteria, including Nostocales species, as well as other sympatric bacterial taxa within their specialized coralloid roots. Yet, it is unknown if these bacteria share a phylogenetic origin and/or common genomic functions that allow them to engage in facultative symbiosis with cycad roots. To address this, we obtained metagenomic sequences from 39 coralloid roots sampled from diverse cycad species and origins in Australia and Mexico. Culture-independent shotgun metagenomic sequencing was used to validate sub-community co-cultures as an efficient approach for functional and taxonomic analysis. Our metanalysis shows a host-independent microbiome core consisting of seven bacterial orders with high species diversity within the identified taxa. Moreover, we recovered 43 cyanobacterial metagenome-assembled genomes, and in addition to Nostoc spp., symbiotic cyanobacteria of the genus Aulosira were identified for the first time. Using this robust dataset, we used phylometagenomic analysis to reveal three monophyletic cyanobiont clades, two host-generalist and one cycad-specific that includes Aulosira spp. Although the symbiotic clades have independently arisen, they are enriched in certain functional genes, such as those related to secondary metabolism. Furthermore, the taxonomic composition of associated sympatric bacterial taxa remained constant. Our research quadruples the number of cycad cyanobiont genomes and provides a robust framework to decipher cyanobacterial symbioses, with the potential of improving our understanding of symbiotic communities. This study lays a solid foundation to harness cyanobionts for agriculture and bioprospection, and assist in conservation of critically endangered cycads.

Past, present and future in the geographical distribution of Mexican Tepezmaite cycads: Genus Ceratozamia.

Ceratozamia morettii, C. brevifrons, and C. tenuis are cycads considered endangered in montane forests in the center of Veracruz state. However, the amount of theoretical and empirical information available on the historical distribution of these species and how they could be affected in the future by the effects of climate change still needs to be increased. Our objective was to generate information on the spatial distribution of the species since the last glacial maximum, present, and future. To map the spatial distribution of species, we created a potential distribution model for each species. The spatial data used for the models included 19 bioclimatic data variables in the present, at the last glacial maximum using two models (CCSM4 and MIROC), and in the future (2080) using two models of the RCP 8.5 scenario of climate change (HadGEM2-CC and MIROC5). We found that each species occupies a unique ecoregion and climatic niche. Ceratozamia morettii and C. tenuis have a similar pattern with an expansion of their distribution area since the last glacial maximum with a larger distribution area in the present and a projected reduction in their distribution under future climatic conditions. For C. brevifrons, we also showed an increase in their distributional area since the last glacial maximum. We also showed that this expansion will continue under future climatic conditions when the species reaches its maximum distributional area. Projections about the future of these endemic cycad species show changes in their habitat, highlighting that temperate zone species (C. morettii and C. tenuis) will face imminent extinction if no effort is made to protect them. On the other hand, the tropical climate species (C. brevifrons) will be favored.

An integrative taxonomic and phylogenetic approach reveals a new genus of Australasian Cycas-pollinating weevils (Coleoptera: Curculionidae: Cossoninae)

Abstract Cycas is the second-largest genus of cycads in Australia and the sole cycad genus in Papua New Guinea. In contrast to the other Australian cycads, which are mainly pollinated by weevils of the Tranes group of Molytinae, the Australian Cycas species are pollinated by tiny weevils belonging to the subfamily Cossoninae but representing an unnamed genus. This study evaluates the taxonomic status of these weevils by combining morphological examination with molecular phylogenetic analyses and species delineation based on mitochondrial DNA. The results reveal that the Cycas-pollinating weevils in Australia comprise only one species, here described as Zimmiodes australis gen. et sp. nov., with another species in Papua New Guinea, described as Zimmiodes papuanus sp. nov. The phylogenetic analyses and morphological comparison reveal that Zimmiodes belongs in the tribe Pentarthrini of Cossoninae and that the related Tychiodes group includes not only Tychiodes Wollaston, Tychiosoma Wollaston and Nanoplaxes Heller but also Tyrpetes Heller and is also assignable to Pentarthrini. The conspecificity of Zimmiodes weevils from all Australian Cycas species sampled suggests the likely taxonomic oversplitting of the Australian Cycas species and thus provides new insights into the taxonomy of the Australian cycads.

Speciation and conservation genetic assessment of two endangered cycad species

AbstractUnderstanding the driving forces of speciation is a central question in evolutionary biology. Cycas bifida (Dyer) K. D. Hill and Cycas micholitzii Dyer are two morphologically similar Cycas (Cycadaceae) species with deeply pectinate megasporophylls and dichotomously divided leaflets. Geographically, they are isolated by the Red River Fault Zone (RRFZ), which acts as a biogeographical barrier for many Cycas species. In this study, we investigated the divergence, genetic diversity, genetic structure, and demographic history of C. bifida and C. micholitzii to uncover the speciation mechanisms for the two endangered species. Results revealed high historical gene flow but low contemporary gene flow between the two species, with a deep divergence occurring in the Late Miocene. The long‐term geographical isolation and ecological niche differentiation were identified as important factors in driving the divergence of the two species, supported by significant isolation by distance testing, barrier analysis, and niche consistency detection. Geographical isolation by the RRFZ played a pivotal role in facilitating their divergence by constraining gene flow. Conservation genetic analyses indicated high genetic diversity within both species, coupled with disparate responses to Pleistocene climate fluctuations: C. micholitzii experienced population expansion, while C. bifida displayed a mild bottleneck effect. To ensure the protection and long‐term sustainability of two threatened species, relevant conservation guidelines were proposed based on the assessment of their genetic diversity and structure. This study furnishes valuable insights into the mechanisms underpinning species divergence and delivers actionable recommendations for cycad conservation.

The metabolism of nonstructural carbohydrates, lipids, and energy in two Cycas species with differential tolerance to unexpected freezing stress.

With the climate warming, the occurrence of freezing events is projected to increase in late spring and early autumn in the Northern Hemisphere. Observation of morphological traits showed that Cycas panzhihuaensis was more tolerant to unexpected freezing stress than C. bifida. Energy balance is crucial for plant tolerance to stress. Here, we aimed to determine whether the different responses of the two species to the unpredicted freezing stress were associated with the metabolism of energy and related substances. The effects of unexpected freezing temperatures on C. panzhihuaensis and C. bifida were studied by measuring chlorophyll fluorescence parameters, energy charge and the profile of nonstructural carbohydrates (NSC) and lipids. C. panzhihuaensis exhibited higher stability of photosynthetic machinery than C. bifida under unpredicted freezing events. Significant interaction between species and treatments were observed in the energy charge, the level of NSC and its most components and the amount of most lipid categories and lipid classes. The decrease of soluble sugar and the increase of neutral glycerolipids at the early freezing stage, the accumulation of membrane glycerolipids at the late freezing stage and the continuous decrease of energy charge during the freezing period were the characteristics of C. panzhihuaensis responding to unexpected freezing stress. The degradation of membrane glycerolipids and the continuous decrease of soluble sugar during the freezing period and the accumulation of neutral glycerolipids and energy charge at the late freezing stage represented the characteristics of C. bifida responses. The different freezing sensitivity between C. panzhihuaensis and C. bifida might be associated with the differential patterns of the metabolism of energy, NSC and lipids. C. panzhihuaensis possesses the potential to be introduced to the areas of higher latitudes and altitudes.

Cycad Regulation and Community Creation: South African Stakeholder Perspectives on Conservation

Cycads play a central role in Lobedu cultural mythology, with widespread acknowledgment of their cultural and spiritual values, as well as their instrumental use in rainmaking and coronation ceremonies. They are also widely prized as collectors’ items, both nationally and internationally, commanding high prices and placing them in the unenviable position of being among the world's most frequently trafficked plants. South African cycad species, most of which are endangered and all of which are protected, are heavily regulated, with the ownership, trade, and use of cycads requiring a permit. This article explores how regulations are understood by different stakeholders in cycad conservation. Traditional authorities, state institutions, and communities may collaborate in conservation, but also interpret and enact policies divergently. Processes of regulating cycad trade and propagation both reinforce and challenge certain aspects of community identity.

Comparative Analysis of the Complete Chloroplast Genomes of Six Endangered Cycas Species: Genomic Features, Comparative Analysis, and Phylogenetic Implications

Comparative Analysis of the Complete Chloroplast Genomes of Six Endangered Cycas Species: Genomic Features, Comparative Analysis, and Phylogenetic Implications

Conservation genomics of Dioon holmgrenii (Zamiaceae) reveals a history of range expansion, fragmentation, and isolation of populations

Many Cycad species may not survive the current extinction crisis, despite belonging to the oldest living seed plant lineage. Conservation of endangered and threatened species will require a combination of in situ and ex situ programs, both of which will benefit from better knowledge of species’ population genetic structure, as will assessments of threatened status. Here we develop a cost-effective method of obtaining population-level genomic data from across the range of the Mexican cycad, Dioon holmgreni, and use these data to characterize the genetic structure and diversity of the species. We also reconstruct aspects of the demographic history of the species and evaluate the taxonomic cohesion of populations across the range using genomic and morphological data. We find that D. holmgrenii harbors moderate genetic diversity across genetically and geographically isolated populations that each possess a substantial percentage of private alleles. We further find that the history of this species likely includes a widespread range expansion followed by fragmentation due to population contraction. These results argue for conservation of all populations and their unique alleles but also suggest an unexpected ability of this species to maintain genetic diversity despite dramatic reductions in population size.

Core Microbiome and Microbial Community Structure in Coralloid Roots of Cycas in Ex Situ Collection of Kunming Botanical Garden in China.

Endophytes are essential in plant succession and evolution, and essential for stress resistance. Coralloid root is a unique root structure found in cycads that has played a role in resisting adverse environments, yet the core taxa and microbial community of different Cycas species have not been thoroughly investigated. Using amplicon sequencing, we successfully elucidated the microbiomes present in coralloid roots of 10 Cycas species, representing all four sections of Cycas in China. We found that the endophytic bacteria in coralloid roots, i.e., Cyanobacteria, were mainly composed of Desmonostoc_PCC-7422, Nostoc_PCC-73102 and unclassified_f__Nostocaceae. Additionally, the Ascomycota fungi of Exophiala, Paraboeremia, Leptobacillium, Fusarium, Alternaria, and Diaporthe were identified as the core fungi taxa. The Ascomycota fungi of Nectriaceae, Herpotrichiellaceae, Cordycipitaceae, Helotiaceae, Diaporthaceae, Didymellaceae, Clavicipitaceae and Pleosporaceae were identified as the core family taxa in coralloid roots of four sections. High abundance but low diversity of bacterial community was detected in the coralloid roots, but no significant difference among species. The fungal community exhibited much higher complexity compared to bacteria, and diversity was noted among different species or sections. These core taxa, which were a subset of the microbiome that frequently occurred in all, or most, individuals of Cycas species, represent targets for the development of Cycas conservation.

Genetic Structure and Differentiation of Endangered Cycas Species Indicate a Southward Migration Associated with Historical Cooling Events

Understanding the genetic structure and differentiation in endangered species is of significance in detecting their phylogenetic relationships and prioritizing conservation. Here we sampled five endangered Cycas species endemic to southwest China and genotyped genetic structure and differentiation among them using the genotyping-by-sequencing (GBS) method. C. hongheensis showed high genetic diversity, but the other four species showed low genetic diversity. The genetic diversity between wild and cultivated populations was similar for C. debaoensis and C. guizhouensis, respectively. Low genetic differentiation and high gene flow were found among C. debaoensis, C. guizhouensis, and C. fairylakea, and C. hongheensis differentiated from them at ~1.74 Mya. TreeMix results showed historic migration events from C. guizhouensis to C. hongheensis, showing southward migration pathways. C. hongheensis showed increased effective population size with time, while the other four species underwent bottleneck events at ~1–5 Mya when continuous cooling events occurred. Our results indicate that the migration, differentiation, and speciation of Cycas species are associated with historical cooling events.

Impact of herbivory by Zerenopsis lepida (Lepidoptera: Geometridae) on the endangered Encephalartos eugene-maraisii under field conditions

Encephalartos eugene-maraisii is an endangered, endemic plant in the Waterberg Mountain range of South Africa. This is the first report of herbivory by Zerenopsis lepida (Lepidoptera: Geometridae) on natural populations of E. eugene-maraisii. The impact of herbivory by folivorous arthropods on this cycad species has not been studied before. This study aimed to determine the incidence and intensity of Z. lepida herbivory on E. eugene-maraisii under field conditions. Local plant dynamics were studied by recording the plant location, sex, size and phenological stage for each plant. Damage surveys were carried out over two consecutive seasons (2020–2021 and 2021–2022). Leaf damage was assessed on 227 plants comprising 692 stems. Approximately 40% of the stems had signs of leaf herbivory by Z. lepida and 10% of the total leaf area was removed by Z. lepida larvae. Less herbivory was recorded in areas where plants synchronously produced new leaf flushes compared to areas with asynchronous leaf flushes. Greater apparency of plants led to a greater incidence of herbivory and level of damage. Repeated damage to plants may delay future leaf and cone flushing events and contribute to the threat against this cycad species.