Pollination ecology of the Australian cycad Lepidozamia peroffskyana (Zamiaceae)

Experiments carried out to investigate the reproductive ecology of the Australian cycad Lepidozamia peroffskyana (Regal, Bull. Soc. Imp. Nat. Mosc. 1857, 1: 184) revealed that this species is pollinated exclusively by host-specific Tranes weevils (Pascoe 1875). The weevils carry out their life cycle within the tissues of the male cones but also visit the female cones in large numbers. Female cones from which insects ( but not wind) were excluded had a pollination rate that was essentially zero. In contrast, female cones from which wind ( but not insects) were excluded had a pollination rate comparable with naturally pollinated cones. Assessment of Tranes weevil pollen load indicated that they are effective pollen-carriers. No other potential insect pollinators were observed on cones of L. peroffskyana. Sampling of airborne loads of cycad pollen indicated that wind-dispersed grains were not consistently recorded beyond a 2-m radius surrounding pollen-shedding male cones. The airborne load of cycad pollen in the vicinity of pollination-receptive female cones was minimal, and the spatial distribution of the coning population indicated that receptive female cones did not usually occur close enough to pollen-shedding male cones for airborne transfer of pollen to explain observed natural rates of seed set. These multiple lines of evidence suggest that wind-once considered the only pollination vector for cycads and other gymnosperms-plays only a minimal role in the pollination of L. peroffskyana, if any at all. The global diversity of insects associated with cycads suggests that some lineages of pollinating beetles may have been associated with cycad cones since Mesozoic times.

Pollination of Australian Macrozamia cycads (Zamiaceae): Effectiveness and behavior of specialist vectors in a dependent mutualism

Complementary field and laboratory tests confirmed and quantified the pollination abilities of Tranes sp. weevils and Cycadothrips chadwicki thrips, specialist insects of their respective cycad hosts, Macrozamia machinii and M. lucida. No agamospermous seeds were produced when both wind and insects were excluded from female cones; and the exclusion of wind-vectored pollen alone did not eliminate seed set, because insects were able to reach the cone. Based on enclosure pollination tests, each weevil pollinates an average 26.2 ovules per cone and each thrips 2.4 ovules per cone. These pollinators visited similar numbers of ovules per cone in fluorescent dye tests that traced insect movement through cones. Fluorescent dye granules deposited by Cycadothrips were concentrated around the micropyle of each visited ovule, the site of pollen droplet release, where pollen must be deposited to achieve pollination. In contrast, Tranes weevils left dye scattered on different areas of each visited ovule, indicating that chance plays a greater role in this system. Each weevil and 25 thrips delivered 6.2 and 5.2 pollen grains, respectively, on average, to each visited ovule per cone, based on examination of dissected pollen canals. In sum, the pollination potential of 25 Cycadothrips approximates that of one Tranes weevil.

Dioon Lindl. (Zamiaceae): Perspectives from phylogeny and a population genetic study of Dioon edule

Dioon Lindl. (Zamiaceae) is a small genus restricted to Mexico (12 species) and Honduras (one species). Previous systematic studies have been unable to fully resolve species relationships within the genus. Phylogenetic analyses were conducted with data from several sources, including Restriction Fragment Length Polymorphisms from the chloroplast genome, morphology, two introns of the low copy nuclear gene S-adenosyl-L-homocysteine hydrolase (SAHH) and the 5.8S/ITS2 regions of the nuclear ribosomal DNA. The goals of the study were to construct a total evidence species level phylogeny and to explore current biogeographical hypotheses. None of the analyses performed produced a fully resolved topology. Dioon is comprised of two main lineages (the Edule and Spinulosum Clades), which represents an ancient divergence within the genus. The two introns of the nuclear gene SAHH offer additional evidence for the split into two lineages. Intron 2 contains a 18 bp deletion in the Spinulosum Clade, providing a synapomorphy for that group. The 5.8S/ITS2 regions were highly polymorphic and subsequently omitted from the combined analyses. In order to visualize congruence between morphology and molecular data, morphological characters were mapped onto the combined molecular tree. Current biogeographical hypotheses of a general northward pattern of migration and speciation are supported here. However, sister relationships within the Edule Clade are not fully resolved. Seven DNA microsatellite markers were developed to investigate patterns of genetic variation of seven populations of D. edule, a species restricted to Eastern Mexico. We found that most of the genetic variation lies within populations (Ho = 0.2166–0.3657) and that levels of population differentiation are low (Fst = 0.088); this finding is congruent with the breeding system of this species, dioicy. Four of the populations deviate from Hardy Weinberg Equilibrium and have a high number of identical genotypes, we suggest that this unexpected pattern is due to the life-history strategy of the species coupled with the few number of polymorphic loci detected in these populations. Our results are not congruent with earlier evidence from morphology and allozyme markers that suggest that the two northernmost populations represent a distinct entity that is recognized by some taxonomists as D. angustifolium.

Association of cone thermogenesis and volatiles with pollinator specificity in Macrozamia cycads

Cone traits (volatile components and thermogenesis) of three cycad species in the genus Macrozamia were examined for differences related to their specific insect pollinators, the weevil, Tranes spp., or the thrips, Cycadothrips chadwicki. Linalool (>80% of emissions) dominated cone volatile components of M. machinii (Tranes-pollinated) and beta-myrcene was a minor component (