Evolutionary developmental biology in cycad phenology

We recently described lack of phenotypic plasticity in reproductive organ development and substantial plasticity in vegetative organ development for the cycad Cycas micronesica. Is there an evo-devo explanation for the disparity in phenotypic plasticity of vegetative vs. reproductive organs? Despite modularity, might evolution of cycad phenology be controlled more by drift than selection?

Application of game theory to the interface between militarization and environmental stewardship in the Mariana Islands

We recently described threats to the terrestrial biological resources on the Mariana islands of Guam and Tinian resulting from the large-scale buildup of military operations. Attitudes that view these military buildup plans in a zero sum context whereby the positives of greater security and improved local economy can be attained only with corresponding negatives of environmental destruction are prevalent. We argue these attitudes oversimplify the complicated interactions between military operations and environmental damage. Here we discuss aspects of our case study that would benefit from application of game theory. Declines in ecosystem health are not unavoidable forms of collateral damage of peace-time military operations. We repeat, conservation of environmental resources is not ancillary to national security, it is integral.

The aeta - pinatubo loop

The impact of Mount Pinatubo's 1991 eruption on the traditional use of natural resources by the indigenous Aeta was devastating. The damage resulted in the immediate and sustained disconnection of traditional knowledge from the biological resources integral to practice that knowledge. The relatively slow ecosystem recovery a full 20 years after the event hinders the transfer of traditional knowledge to younger generations of Aeta. Their traditional knowledge is at risk of disappearing from the cultural fabric of the Philippines. In seeking to adapt, decisions by the Aeta to accept the development of foreign-designed ecotourism enterprises may negatively affect natural ecosystem recovery. Alternatives to the existing ecotourism practices may be warranted to safeguard Aeta traditional knowledge.

Recovering plant biodiversity: Mount Pinatubo lessons to learn

Studying recovering plant biodiversity on Mount Pinatubo may provide valuable insights that improve our understanding of recovery of other ecosystems following disturbances of all types. Ongoing sheet and rill erosion coupled with mass waste events in the unstable pyroclastic flow deposits persist, effectively re-setting primary succession at micro-landscape scale without affecting habitat level diversity. Spatial factors and micro-habitat diversity may exert more control over continued succession as the riparian systems become more deeply dissected and complex. The number of taxa within functional groups and conservation concerns are botanical issues that deserve further research.

Rethinking cycad metabolite research

Cycads are among the most ancient of extant Spermatophytes, and are known for their numerous pharmacologically active compounds. One compound in particular, β-methylamino-L-alanine (BMAA), has been implicated as the cause of amyotrophic lateral sclerosis/Parkinson dementia complex (ALS/PDC) on Guam. Previous studies allege that BMAA is produced exclusively by cyanobacteria, and is transferred to cycads through the symbiotic relationship between these cyanobacteria and the roots of cycads. We recently published data showing that Cycas micronesica seedlings grown without endophytic cyanobacteria do in fact increase in BMAA, invalidating the foundation of the BMAA hypothesis. We use this example to suggest that the frenzy centered on BMAA and other single putative toxins has hindered progress. The long list of cycad-specific compounds may have important roles in signaling or communication, but these possibilities have been neglected during decades of attempts to force single metabolites into a supposed anti-herbivory function. We propose that an unbiased, comprehensive approach may be a more appropriate means of proceeding with cycad biochemistry research.

Novel tools for an old lineage: Population genomics for cycads

With a ca. 300 million year-old evolutionary history, cycads are often perceived as "living fossils," relicts of their previously widespread dominance. Patterns of genetic variation for a member of the most basal cycad genus, Cycas micronesica, support the notion that cycads are a dynamic group with ongoing diversification. Herein we hypothesize that cycad's hefty genomes enable rapid adaptive change and facilitate specific beneficial interactions with varying assemblages of symbionts. Characterizing population-level genomic patterns of cycads and their symbionts, pollinators in particular, will enlighten our understanding of these mechanisms and of adaptive variation that underlies cycad evolution. In light of rapid climate and landscape change, cycads are a beacon for understanding the ecological processes that ultimately enable species long-term survival.

Time-size trade-offs in responses of cycads to male cone herbivory

Plant-arthropod pollination mutualisms based on adults as pollinators and juveniles as predators of reproductive structures are understood to be successful by balancing the benefits of pollination with the antagonisms of herbivory. In a recent paper, I showed that Cycas micronesica male cone herbivory by larvae of the pollinator moth Anatrachyntis species hastened the plant's subsequent reproductive event. In this mutualism, both pollination and predation elicit distinct increases in plant fitness. The results support a resource tradeoff within an optimal-allocation model whereby cone disposal by the pollinator juveniles reduces reproductive costs. Many cycad species exhibit an annual coning season that is fixed by the environment, and in those cases the trade-off may be expressed as plasticity in cone size or cone number. Conservation plans would benefit from understanding the consequences of the lack of natural cone herbivory in ex situ germplasm management.

Cycad mutualist offers more than pollen transport

Specialist insects share obligate mutualisms with some contemporary cycad species whereby the insect's pollination services are rewarded with a nursery in which the insect's larvae consume the postdispersal male cone. I prevented visits of the pollinator moth Anatrachyntis sp. to male Cycas micronesica (Cycadaceae) cones to show that consumption of the cone tissue by the mutualist hastened initiation of the plant's subsequent reproductive event. This is the first documented case where removal of a postdispersal cycad pollination organ speeds up subsequent reproductive events, and the current paradigm that the offering of cone tissue as a nursery is a sacrifice by the plant in return for the pollination services is therefore inaccurate. In C. micronesica, the herbivory stage of pollination mutualism confers a cryptic benefit of cone tissue disposal, which translates into an increase in ultimate lifetime reproductive effort. The plant population relies on the pollinator for moving gametes, as well as for increasing the number of male coning events. The dual benefits afforded to the plant by associating with this pollinator shows that mutualism can operate simultaneously on very different traits.

Distribution of free and glycosylated sterols within Cycas micronesica plants

Flour derived from Cycas micronesica seeds was once the dominant source of starch for Guam's residents. Cycad consumption has been linked to high incidence of human neurodegenerative diseases. We determined the distribution of the sterols stigmasterol and β-sitosterol and their derived glucosides stigmasterol β-d-glucoside and β-sitosterol β-d-glucoside among various plant parts because they have been identified in cycad flour and have been shown to elicit neurodegenerative outcomes. All four compounds were common in seeds, sporophylls, pollen, leaves, stems, and roots. Roots contained the greatest concentration of both free sterols, and photosynthetic leaflet tissue contained the greatest concentration of both steryl glucosides. Concentration within the three stem tissue categories was low compared to other organs. Reproductive sporophyll tissue contained free sterols similar to seeds, but greater concentration of steryl glucosides than seeds. One of the glucosides was absent from pollen. Concentration in young seeds was higher than old seeds as reported earlier, but concentration did not differ among age categories of leaf, sporophyll, or vascular tissue. The profile differences among the various tissues within these organs may help clarify the physiological role of these compounds.

Free and glycosylated sterol bioaccumulation in developing Cycas micronesica seeds

The bioaccumulation of free and glycosylated forms of stigmasterol and β-sitosterol were determined from Cycas micronesica K.D. Hill seeds throughout seed ontogeny. Per-seed pool of the four compounds increased linearly from 2 to 24 months, indicating no developmental period elicited a major shift in the rate of bioaccumulation. The slopes were not homogeneous, signifying a change in relative sterol profile concomitant with seed maturation. This shift was in favour of the glucosides, as their rate of accumulation exceeded that of the free sterols. Stigmasterol content exceeded that of β-sitosterol, but ontogeny did not influence the ratio of these dominant sterols. The quantity and quality of sterol exposure during consumption of foods prepared from gametophytes by humans is strongly influenced by age of harvested seeds. Results are critical for a further understanding of the link between human neurodegenerative diseases and historical consumption of foods derived from the seed gametophyte tissue.

Phenotypic Characteristics as Predictors of Phytosterols in Mature Cycas micronesica Seeds

The relationship between mature Cycas micronesica K.D. Hill seed sterol concentration and content and plant or seed phenotypic characteristics was established by multiple regression. Combined models were significant for free but not glycosylated sterols. Reduced models revealed leaf number as the only significant predictor. Free and glycosylated sterol concentrations were unaffected throughout the range of several predictors: tree height (1.7 to 5.8 m), seed fresh weight (48 to 120 g), seed load (one to 76 seeds per plant), and estimated tree age (32 to 110 years). The free and glycosylated sterol phenotypes were also not dependent on the presence/absence of developed embryos in mature seeds. The significant response to leaf number was subtle with an increase of 43 leaves associated with a 0.1-mg increase in free sterol per gram seed fresh weight. This is the first report for any cycad that discusses reproductive or physiological traits in the context of allometric relations. Results indicate a highly constrained phenotypic plasticity of Cycas gametophyte sterol and steryl glucoside concentration and seed content in relation to whole plant and organ size variation.

Carica papaya (Caricaceae): a case study into the effects of domestication on plant vegetative growth and reproduction

Few studies have quantitatively evaluated the gender specific effects of cultivation on plant growth and reproduction. The availability of cultivated and wild populations of different genders of Carica papaya L. (Caricaceae) on Guam provided an opportunity to study these effects quantitatively. We compared the gender specific allometry of height vs. basal stem diameter (H vs. D), stem slenderness ratio (H/D), and the height at first flowering (H(fl)) of carpellate and staminate plants growing under natural conditions (N = 150 each) with those of carpellate and hermaphroditic plants (N = 250 each) from two cultivars (Sunrise and Tainung 2). These comparisons indicated that (1) wild carpellate and staminate plants are significantly taller than either gender of the two cultivars with equivalent D; (2) the scaling exponent governing the H vs. D relationship of both genders of wild plants is significantly higher than that of either cultivated gender; (3) cultivar type does not affect the H vs. D exponent, but gender expression does; (4) gender expression (but not cultivar-type) also affects H(fl) (cultivation substantially reduces carpellate plant H(fl)); and (5) the onset of sexual maturity is associated with a dramatic reversal in H/D ontogeny. Cultivation therefore has "condensed" patterns of vegetative growth in a gender specific manner, whereas gender expression alters both vegetative and reproductive growth significantly more so than does cultivar-type.

Steryl glucoside concentration declines with Cycas micronesica seed age

Neurotoxins contained in the seeds of Cycas micronesica K.D. Hill have been implicated in the Guam neurological disease cluster, amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS-PDC). Some of these neurotoxins remain in the washed cycad seed flour that was historically an important part of the Chamorro diet. Of these, variant steryl glucosides have been identified by us as a possible etiological factor in the disease. In vitro and in vivo animal studies have strongly supported a role for these molecules in some forms of neurodegeneration. As part of a series of studies, we have now determined the concentrations of several steryl glucosides and their sterol precursors as affected by the age of C. micronesica seeds. The concentration of these molecules declined with seed age from 2.0 to 30.5 months. Following log-transformation of both axes, the decline was linear. Similarly, concentration of all but one of the molecules declined with age when samples were restricted to gametophyte tissue. Factors suspected of influencing phenotypic plasticity must be addressed when interpreting plant physiology data. Our results confirm for the first time that tissue age must be documented and reported in cycad seed biochemistry studies to remove ambiguities from results. Past studies in this important area of research have failed to account for the potential impact of seed age, rendering previous outcomes and interpretations of cycad neurotoxins in their impact on ALS-PDC ambiguous.