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Molecular nitrogen (N2) constitutes the majority of Earth's modern atmosphere, contributing ~0.79 bar of partial pressure (pN2). However, fluctuations in pN2 may have occurred on 107–109 year timescales in Earth's past, perhaps altering the isotopic composition of atmospheric nitrogen. Here, we explore an archive that may record the isotopic composition of atmospheric N2 in deep time: the foliage of cycads. Cycads are ancient gymnosperms that host symbiotic N2‐fixing cyanobacteria in modified root structures known as coralloid roots. All extant species of cycads are known to host symbionts, suggesting that this N2‐fixing capacity is perhaps ancestral, reaching back to the early history of cycads in the late Paleozoic. Therefore, if the process of microbial N2 fixation records the δ15N value of atmospheric N2 in cycad foliage, the fossil record of cycads may provide an archive of atmospheric δ15N values. To explore this potential proxy, we conducted a survey of wild cycads growing in a range of modern environments to determine whether cycad foliage reliably records the isotopic composition of atmospheric N2. We find that neither biological nor environmental factors significantly influence the δ15N values of cycad foliage, suggesting that they provide a reasonably robust record of the δ15N of atmospheric N2. Application of this proxy to the record of carbonaceous cycad fossils may not only help to constrain changes in atmospheric nitrogen isotope ratios since the late Paleozoic, but also could shed light on the antiquity of the N2‐fixing symbiosis between cycads and cyanobacteria. [ABSTRACT FROM AUTHOR]

Most functions postulated for thermogenesis in plant reproductive organs are associated with pollination and pollinator activity. During thermogenesis other chemical changes occur, and these also may affect pollinator activity., We address how cone thermogenesis and the associated chemical emissions influence pollinator behaviour in the obligate mutualist Macrozamia lucida and M. macleayi cycad - Cycadothrips chadwicki thrips pollination system. Cones of these dioecious gymnosperms have a diel, mid-day metabolic burst that is associated with increased cone temperatures, volatile emissions (primarily β-myrcene), and CO2 and water vapour emissions. Concurrently, thrips leave cones en masse and then return to cones later in the day. We investigated the effects of these cues, individually and in combinations, on their potential to induce thrips to leave cones in the dark and light with a suite of Y-tube behavioural experiments., The results suggest that ambient light, and high cone temperatures, humidity, and β-myrcene levels, but not CO2, each induce Cycadothrips to leave cones. At typical overnight temperatures (14 °C) thrips were relatively inactive and negatively phototactic. At typical daytime ambient temperatures, 22-26 °C (lower than typical thermogenic temperatures), thrips were active and positively phototactic. Thrips moved away from or avoided thermogenic temperatures and high concentrations of β-myrcene, and they preferred dry (<8% RH) to humidified (~88% RH) air., Whereas several variables individually induce thrips to leave a cone's darker interior towards the daytime light, these signals are presented simultaneously during thermogenesis. There thus seems to be enhanced or redundant signalling that enforces thrips departure from pollen cones thus increasing the chances of vectoring pollen to ovulate cones. While high temperature appears necessary to mediate thrips movement, its concurrence with other plant signals that produce similar responses, suggests a dynamic multimodal signalling system that operates as a functional unit. [ABSTRACT FROM AUTHOR]

* Premise of the Study: Plants that invest in large, heavy seeds and colorful, fleshy fruits or analogous structures seem adapted for dispersal by large vertebrates. Some such plants, like Australian cycads in the genus Macrozamia, do not disperse well, which could be explained by seed-dispersal relationships with megafauna that are rare or extinct in contemporary ecosystems. Such plants provide an opportunity to investigate the ecological consequences of low seed-dispersal distances. * Methods: We investigated seed dispersal of Macrozamia miquelii in Central Queensland by tracking the fate of marked seeds, identifying the dispersal fauna and quantifying population demography and spatial structure. * Key Results: We found that 70-100% of marked seeds remained within 1 m of maternal females (cycads are dioecious). Of the 812 seeds recovered (from 840 originally marked) only 24 dispersed >1 m from maternal females, the greatest observed dispersal being 5 m. We found an average of 2.2 seedlings and 0.7 juveniles within 1.5 m of mature females, which suggests that most seeds that remain in the vicinity of maternal females perish. Within-stand densities ranged between 1000 and 5000 plants/ha. The brushtail possum Trichosurus vulpecula was the only animal observed to move the seeds. * Conclusions: Macrozamia are adapted for dispersal by megafauna that are rare or absent in contemporary ecosystems. We argue that Macrozamia are "grove forming" plants that derive ecological benefit from existing as high-density, spatially discrete populations, the function of megafaunal dispersal adaptations being the infrequent dispersal of seeds en masse to establish new such groves in the landscape. [ABSTRACT FROM AUTHOR]

Aim The geology and hydrology of the Central Ranges of Australia provide refuge for more mesic-adapted taxa unable to survive in the surrounding deserts. Whether this area has been a long-term refuge for mesic-adapted taxa is uncertain. Mesic-adapted taxa in the region have been argued as 'relicts', remnants of wet forests once covering the region. This scenario hypothesizes that 'relicts' survived in pockets of moist habitat in the Central Ranges as the Australian arid zone expanded. Here, we test an hypothesis of long-term occupancy in the Central Ranges for a cycad, Macrozamia macdonnellii, a taxon of conservation concern and also one frequently described as an 'ancient relict'. Location Australia. Methods A haplotype network, derived from DNA sequences of two chloroplast regions, was used to infer the biogeographical history of Macrozamia across Australia. Specifically, the question of long-term occupancy of the Central Australian Ranges is addressed. Results Macrozamia macdonnellii shares a haplotype with five eastern species. However, unique haplotypes restricted to only a part of the Mac Donnell Ranges Interim Biogeographic Regionalisation of Australia region are also present. Western Australian species of Macrozamia form a lineage distinct from those in the rest of Australia. Main conclusions The shared haplotype, nested within haplotypes from eastern Australia, indicates that M. macdonnellii is relatively recently derived from ancestral lineages of eastern Australia. This starkly contrasts with species of Macrozamia in Western Australia, which show long-term isolation from those in the east. Unique haplotypes in populations of M. macdonnellii indicate that the species has occupied the region for sufficient time to accumulate variation. Furthermore, this variation appears to be geographically structured. If so, it indicates that M. macdonnellii is undergoing population differentiation, and possible speciation, in different regions of the Mac Donnell Ranges. Isolated populations with unique haplotypes might be evolutionarily significant units that should be conserved. [ABSTRACT FROM AUTHOR]

Macrozamia seeds have long been considered an important economic resource to Australian hunter-gatherers. As a result of limited ecological data during the 1970's-1980's, seed production in Macrozamia spp. has been conceptualised as low yield and irregular, but easily stimulated through pyrogenic manipulation to produce high yield, regular resource gluts. This paper reviews and synthesises ecological data on Macrozamia ecology and seed production collated over the last few decades to argue that current archaeological conceptions of Macrozamia seed production and reproductive responses to fire are flawed, and to further consider how these resources were used in the past. [ABSTRACT FROM AUTHOR]

Influential arguments have been advanced in Australian archaeology concerning the origins and development of social and economic change in the mid-late Holocene (Lourandos 1997). One example used to support this claim is the perceived existence or ceremonial feasting events held in the semi-arid and rugged sandstone gorge systems of central Queensland, attended by large groups of people for extended periods, and underwritten by large quantities of kernels from the cycad Macrozamia moorei (Beaton 1977, 1982: see also Lourandos 1997). However the reexamination of the macrobotanical evidence from archaeological sites in this region using taphonomic analysis, replicative processing experiments, recalculations of seed density and estimations of the minimum numbers of seeds, does not support this model. This re-examination questions the role of Macrozamia seeds in the context of socio-economic change and suggests new interpretations of Macrozamia resource use. [ABSTRACT FROM AUTHOR]