Premise
Although maintaining the appropriate mid‐day timing of the diel thermogenic events of cones of the dioecious cycads Macrozamia lucida and M. macleayi is central to the survival of both plant ...and pollinator in this obligate pollination mutualism, the nature of the underlying mechanism remains obscure. We investigated whether it is under circadian control. Circadian mechanisms control the timing of many ecologically important processes in angiosperms, yet only a few gymnosperms have been studied in this regard.
Methods
We subjected cones to different ambient temperature and lighting regimens (constant temperature and darkness; stepwise cool/warm ambient temperatures in constant darkness; stepwise dark/light exposures at constant temperature) to determine whether the resulting timing of their thermogenic events was consistent with circadian control.
Results
Cones exposed to constant ambient temperature and darkness generated multiple temperature peaks endogenously, with an average interpeak‐temperature period of 20.7 (±0.20) h that is temperature‐compensated (Q10 = 1.02). Exposure to 24‐h ambient temperature cycles (12 h cool/12 h warm, constant darkness) yielded an interpeak‐temperature period of 24.0 (±0.05) h, accurately and precisely replicating the ambient temperature period. Exposure to 24‐h photo‐cycles (12 h light/12 h dark, constant ambient temperature) yielded a shorter, more variable interpeak‐temperature period of 23 (±0.23) h.
Conclusions
Our results indicate that cycad cone thermogenesis is under circadian clock control and differentially affected by ambient temperature and light cycles. Our data from cycads (an ancient gymnosperm lineage) adds to what little is known about circadian timing in gymnosperms, which have rarely been studied from the circadian perspective.
Plant–pollinator interaction research commonly focuses on more apparent traits, floral morphology and odor. A new study of a thermogenic gymnosperm brood-site pollination system via a specialist ...beetle reveals intricate long- and short-range multimodal signals are involved in host finding.
Plant–pollinator interaction research commonly focuses on more apparent traits, floral morphology and odor. A new study of a thermogenic gymnosperm brood-site pollination system via a specialist beetle reveals intricate long- and short-range multimodal signals are involved in host finding.
An important outcome of plant thermogenesis is increased emissions of volatiles that mediate pollinator behaviour. We investigated whether the large increase in emissions, mainly the monoterpene ...ß‐myrcene (>90%), during daily thermogenic events of Macrozamia macleayi and lucida cycad cones are due solely to the influence of high cone temperatures or are, instead, a result of increased respiratory rates during thermogenesis. We concurrently measured temperature, oxygen consumption and ß‐myrcene emission profiles during thermogenesis of pollen cones under typical environmental temperatures and during experimental manipulations of cone temperatures and aerobic conditions, all in the dark. The exponential rise in ß‐myrcene emissions never occurred without a prior, large increase in respiration, whereas an increase in cone temperature alone did not increase emissions. When respiration during thermogenesis was interrupted by anoxic conditions, ß‐myrcene emissions decreased. The increased emission rates are not a result of increased cone temperature per se (through increased enzyme activity or volatilization of stored volatiles) but are dependent on biosynthetic pathways associated with increased respiration during thermogenesis that provide the carbon, energy (ATP) and reducing compounds (NADPH) required for ß‐myrcene production through the methylerythritol phosphate (MEP) pathway. These findings establish the significant contribution of respiration to volatile production during thermogenesis.
Investigations of thermogenesis in plant reproductive organs have focused on the effects of increased temperature on the release of the volatiles (volatilization) that mediate pollinator behavior, but the possible role of the increased respiration rate underlying the increase in temperature on volatile production and release has never been thoroughly tested. We measured concurrently the respiration, temperature and volatile emissions during the daily thermogenic events of Macrozamia cycad cones. The large surges in monoterpene (mainly β‐myrcene) emission rates during thermogenesis are shown to be driven primarily by pathways that are dependent on high respiration rates that occur only during a thermogenic event and are clearly not a result of high cone temperature alone. We propose that the large daily respiratory burst during thermogenesis increases the availability of ATP, NADPH and carbon substrates required for production of the monoterpenes via the methylerythritol phosphate pathway.
Invasions of non-native species can threaten native biodiversity, and island ecosystems are ideal for studying these phenomena. In this article, first, we report on the invasive species that combine ...to threaten the island cycad
by reviewing the history of previously reported invasions and providing an update of recent invasions. Then, we prioritize the threat status of each herbivore and the interactions among them. Plant damage was initiated in 2003─2005 by the non-native
Takagi armored scale,
sp. Meyrick leaf miner, and
Horsfield butterfly, which elicited unprecedented irruptions of the native
Aurivillius stem borer and increased herbivory by feral pigs (
L.). The combined impact of these five consumers represents the greatest sustained threat to the cycad tree species. Mitigation of the damage caused by phytophagous non-native species is urgently needed to conserve this unique gymnosperm tree.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Aulacaspis yasumatsui Takagi invaded Guam in 2003 and caused the widespread mortality of the indigenous Cycas micronesica K.D. Hill population. The regeneration of the surviving tree population ...continues to be constrained 20 years later, and a look at the changes in megastrobili traits may inform future conservation management decisions concerning regeneration. We quantified megastrobilus reproductive effort and output from 2001 to 2022 to address this need. The reproductive effort of each megastrobilus was immediately reduced by the invasion, as the number of megasporophylls declined by 29%, and the number of ovules declined by 73% in 2006. Reproductive output was also damaged, as the percent seed set declined by 56% and the number of seeds per strobilus declined by 88%. These fecundity metrics have shown few signs of recovery through 2022. Our results reveal that chronic A. yasumatsui infestations, combined with other invasive herbivore threats, have damaged the host C. micronesica population through a sustained reduction in ovule production and the percent seed set for each megastrobilus, thereby impairing regeneration. This plant response to the biotic threats is distinct from the ongoing mortality of mature trees and emerging seedlings. Conservation interventions may be required to foster a return to adequate regeneration during future attempts to aid C. micronesica recovery.
Aulacaspis yasumatsui Takagi invaded Guam in 2003, and the influence on survival and demography of the host Cycas micronesica K.D. Hill population has been well-studied. To more fully understand how ...A. yasumatsui has threatened the host cycad species, we determined the microstrobilus size and number of pollinators per microstrobilus from 2001 to 2021. The microstrobilus height and diameter were measured directly, and the volume was calculated. Microstrobili were 58 cm in height, 13 cm in diameter, and 4740 cm3 in volume prior to direct A. yasumatsui infestations. Microstrobili decreased in size immediately after direct infestations by A. yasumatsui, and then began to slowly increase in size until 2021. For example, the volume was 24% of pre-invasion volume in 2007, and was 57% of pre-invasion volume in 2021. Microstrobili were harvested; then, the number of pollinator pupae were counted after an incubation period. Pollinator pupae counts per microstrobilus declined to 66% of pre-invasion levels by 2007 and have remained similarly constrained through 2021. Our results revealed that A. yasumatsui damage to the host C. micronesica population is not limited to attrition of the extant plant population, but also includes a loss in male reproductive effort and the risk of coextinction of the insular pollinator.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Odor-Mediated Push-Pull Pollination in Cycads Terry, Irene; Walter, Gimme H; Moore, Chris ...
Science (American Association for the Advancement of Science),
10/2007, Letnik:
318, Številka:
5847
Journal Article
Recenzirano
The reproductive organs of some plants self-heat, release scent, and attract pollinators. The relations among these processes are not well understood, especially in the more ancient, nonflowering ...gymnosperm lineages. We describe the influence of plant volatiles in an obligate pollination mutualism between an Australian Macrozamia cycad (a gymnosperm with male and female individuals) and its specialist thrips pollinator, Cycadothrips chadwicki. Pollen-laden thrips leave male cycad cones en masse during the daily thermogenic phase, when cone temperatures and volatile emissions increase dramatically and thrips are repelled. As thermogenesis declines, total volatile emissions diminish and cones attract thrips, resulting in pollination of female cones. Behavioral and electrophysiological tests on thrips reveal that variations in b-myrcene and ocimene emissions by male and female cones are sufficient to explain the observed sequential thrips' repellence (push) and attraction (pull). These dynamic interactions represent complex adaptations that enhance the likelihood of pollination and may reflect an intermediate state in the evolution of biotic pollination.
Guam's established population of non-native coconut rhinoceros beetle (CRB, Oryctes rhinoceros L.) began creating burrows in stem apices of several cycad species in a managed garden. We conducted an ...island-wide survey to determine the spatial patterns of CRB burrowing of stems of in situ Cycas micronesica. We also measured starch of healthy and unhealthy coconut leaf tissue and compared this with starch of cycad stem tissue. The starch concentration of the central unexpanded leaf in healthy Philippine coconut trees was ≈90 mg·g
−1
, and that of unhealthy Guam coconut trees was ≈40 mg·g
−1
. The starch concentration of the tissue within the CRB burrow locations on C. micronesica trees was 145 mg·g
−1
. Burrowing of C. micronesica was restricted to female CRB adults and was found throughout the full latitudinal gradient of Guam. Our findings indicate Guam's unhealthy coconut trees are no longer nutrient-dense, and the female CRB population may have exhibited a phylogenetically distant host shift to the abundant C. micronesica plants for a starch-rich diet within the concepts of the 'ecological fitting' hypothesis. We add proximity to coconut tree habitats as a new threat to Guam's endangered C. micronesica population.
Insect pollination of cycads Toon, Alicia; Terry, L. Irene; Tang, William ...
Austral ecology,
December 2020, 2020-12-00, 20201201, Letnik:
45, Številka:
8
Journal Article
Recenzirano
Most cycads have intimate associations with their insect pollinators that parallel those of well‐known flowering plants, such as sexually deceptive orchids and the male wasps and bees they deceive. ...Despite this, the mistaken belief that cycads are mostly wind‐pollinated is still commonly expressed. Perhaps as a consequence, cycad–pollinator systems are rarely exemplified in studies of the role of pollinators in plant evolution and diversification. Although first recognised more than a century ago, specialised associations between cycads and their insect pollinators have been elucidated experimentally only in the past few decades. This review covers the history of understanding pollination in cycads, the advances that have been made since the 1980s using field observations and experiments, and analyses of molecular data from the population to phylum level. We outline areas for future research to address how such interactions might have affected speciation and extinctions. We stress that inclusion of cycads in broader considerations of the role of pollinators in plant diversification is important because they are phylogenetically distant from flowering plants and their pollination systems might have evolved independently of one another. This review is timely because cycads are a globally threatened group that might be vulnerable to co‐extinction with pollinator loss.
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