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Cycads: Their evolution, toxins, herbivores and insect pollinators
Abstract
Palaeobiological evidence indicates that gymnosperms were wind-pollinated and that insect pollination began in angiosperms in the Lower Cretaceous (ca. 135 mya) leading to close associations between higher plants and their pollinators. Cycads, which were widespread and pervasive throughout the Mesozoic (250-65 mya) are among the most primitive living seed-plants found today. Because pollination by beetles and by thrips has now been detected in several modern cycads, it is attractive to speculate that some insects and cycads had already developed similar mutualistic interactions in the Triassic (250-205 mya), long before the advent of angiosperms. We also draw attention to another key factor in this insect-plant relationship, namely secondary, defensive plant substances which must always have controlled interspecific interactions. Cycads mainly produce toxic azoglucosides and neurotoxic non-protein amino acids (e.g. BMAA), which apparently are crucial elements in the development and maintenance of mutualism (pollination) and parasitism (herbivory) by cycad-linked herbivores. We now add new results on the uptake and storage of the main toxin, cycasin, of the Mexican cycad Zamia furfuracea by its pollinator, the weevil Rhopalotria mollis, and by a specialist herbivore of Zamia integrifolia, the aposematic Atala butterfly Eumaeus atala.
... According to Rothschild (1992), the conspicuous scales are considered to provide an aposematic (warning) signal to potential predators. Atala butterflies store much of their cycasin (methylazoxymethanol glucoside), a protective chemical compound sequestered from their larval host plant, in their wings, but also a significant amount is found in the eggs (Schneider et al 2002). However, Schneider et al. (2002) were unable to find cycasin in the wing scales. ...
... Atala butterflies store much of their cycasin (methylazoxymethanol glucoside), a protective chemical compound sequestered from their larval host plant, in their wings, but also a significant amount is found in the eggs (Schneider et al 2002). However, Schneider et al. (2002) were unable to find cycasin in the wing scales. Cycasin is a toxin and carcinogen (Rothschild et al. 1986;Nash et al. 1992) and is classified as a β-glycoside of methylazoxymethanol (Rothschild et al. 1986;Nash et al. 1992;Yagi 2004). ...
... They court females by hovering in front of them while fanning the hair pencils with their wings (Opler and Krizek 1984;Scott 1986)-presumably wafting a courtship pheromone from the pencils to the females' antennae (Schneider 2001). Schneider et al. (2002) suggested that . Eumaeus atala Poey progression from prepupa to pupa. ...
This EDIS publication is an alternate version of a page published first on the Featured Creatures website. The Featured Creatures collection provides in-depth profiles of insects, nematodes, arachnids and other organisms relevant to Florida. These profiles are intended for the use of interested laypersons with some knowledge of biology as well as academic audiences. This revised 11-page fact sheet that discusses the Atala butterfly was written by Sandy Koi and Donald W. Hall, and published by the UF Entomology and Nematology Department, March 2016. EENY-641/IN326: Atala Butterfly, Atala Hairstreak, Coontie Hairstreak, Eumaeus atala Poey 1832 (Insecta: Lepidoptera: Lycaenidae) (ufl.edu)
... The genome of one cycad species in the genus Cycas was recently published, and with more than 10 Gbp, suggests a series of gene expansions as well as a whole genome duplication prior to divergence from its gingko sister taxa (Liu et al., 2022). These tropical gymnosperms harbor defensive chemicals in their leaves and other tissues, including the azoxyglycoside methylazoxymethanol (MAM), or cycasin, and the non-proteinogenic amino acid β-Methylamino-L-Alanine (BMAA), both of which are toxic to diverse organisms (Liu et al., 2009;Schneider et al., 2002). Previous studies have demonstrated that several insect herbivores are able to detoxify and even sequester the cycad-derived MAM glycoside, cycasin (Nash et al., 1992;Rothschild et al., 1986;Schneider et al., 2002;Teas, 1967), whereas mechanisms of BMAA resistance have not been described. ...
... These tropical gymnosperms harbor defensive chemicals in their leaves and other tissues, including the azoxyglycoside methylazoxymethanol (MAM), or cycasin, and the non-proteinogenic amino acid β-Methylamino-L-Alanine (BMAA), both of which are toxic to diverse organisms (Liu et al., 2009;Schneider et al., 2002). Previous studies have demonstrated that several insect herbivores are able to detoxify and even sequester the cycad-derived MAM glycoside, cycasin (Nash et al., 1992;Rothschild et al., 1986;Schneider et al., 2002;Teas, 1967), whereas mechanisms of BMAA resistance have not been described. BMAA is capable of blocking glutamate receptors (X. ...
Ingestion of the cycad toxins β-methylamino-L-alanine (BMAA) and azoxyglycosides is harmful to diverse organisms. However, some insects are specialized to feed on toxin-rich cycads with apparent immunity. Some cycad-feeding insects possess a common set of gut bacteria, which might play a role in detoxifying cycad toxins. Here, we investigated the composition of gut microbiota from a worldwide sample of cycadivorous insects and characterized the biosynthetic potential of bacteria isolated as putative keystone taxa. Cycadivorous insects shared a core gut microbiome consisting of six bacterial taxa, mainly belonging to the Proteobacteria, which we were able to isolate. To further investigate these potential keystone taxa from diverging lineages, we performed shotgun metagenomic sequencing of co-cultured bacterial sub-communities. We postulate and characterize four putative keystone bacteria from Serratia , Pantoea , and two different Stenotrophomonas lineages. The biosynthetic potential of these microorganisms includes a suite of biosynthetic gene clusters notably rich in siderophores and carotenoid-like aryl polyene pathways. Siderophore semi-untargeted metabolomics revealed a broad range of chemically related yet diverse iron-chelating metabolites, indicating a complex evolutionary landscape in which siderophores may have converged within the guts of cycadivorous insects. Among these, we provide evidence of the occurrence of an unprecedent desferrioxamine-like biosynthetic pathway that remains to be identified. These results provide a foundation for future investigations into how cycadivorous insects tolerate diets rich in azoxyglycosides, BMAA, and other cycad toxins, and highlight convergent evolution underlying chemical diversity.
... The adults of the majority of species also have red elements on the body and wings. Accordingly, toxic BMAM and MAMM compounds sequestered from cycads render all life stages (eggs, larvae, and adults) unpalatable to predators (Castillo-Guevara & Rico-Gray, 2002;Rothschild et al., 1986;Schneider et al., 2002). Caterpillars are able to detoxify these compounds from their host plants, as recent genomic evidence suggests that the rapid evolution of protein families related to autophagy and phagocytosis likely underlies these adaptations . ...
Eumaeus butterflies are obligate herbivores of Zamia, the most diverse neotropical genus of cycads. Eumaeus-Zamia interactions have been mainly characterized for species distributed in North and Central America. However, host plant use by the southern Eumaeus clade remains largely unknown, precluding a comprehensive study of co-evolution between the genera. Here, we combine fieldwork with museum and literature surveys to expand herbivory records for Eumaeus from 21 to 38 Zamia species. We inferred a time-calibrated phylogeny of Eumaeus to test for distinct macroevolutionary scenarios of host plant conservatism and co-evolution. We found remarkable coincidence between Eumaeus and Zamia diversification, with the butterfly stem group diverging at the same time as the most recent radiation of Zamia in the Miocene. Cophylogenetic reconciliation analyses show a strong cophylogenetic signal between cycads and their butterfly herbivores. Bipartite model-based approaches indicate that this is because closely related Zamia species are used by the same Eumaeus species, suggesting host plant resource tracking by the butterfly herbivores. Our results highlight a case of tight evolution between Eumaeus butterflies and cycads, pointing to the generality of correlated evolution and phylogenetic tracking in plant-herbivore interactions across seed plants.
... The Cycadales represent one the oldest extant groups of seed plants dating back to around 250 million years, with their peak of diversity during the Jurassic and Cretaceous (Norstog and Nicholls, 1997;Schneider et al., 2002;Wu and Chaw, 2015;Chang et al., 2020). The Cycadales consist of 10 genera within two families Cycadaceae and Zamiaceae, containing »368 extant species ( Fig. 1; Chang et al., 2020;Calonje et al., 2022), which have a wide distribution with the highest diversity within the tropical and subtropical regions (Grobbelaar, 2002;Whitelock, 2002). ...
The African endemic cycad genus Encephalartos consists of 68 extant taxa, that are of great conservation concern as 85% are threatened (CR, EN, or VU) and four, are extinct in the wild (EW). Due to there being no formally published monographs for the genus, there is lack of consensus on taxonomically significant characters. This lack of clarity regarding the species relationships and access to several taxa have made researching this group challenging. Nevertheless, numerous studies have proven that this genus has low levels of genetic variation over a wide distribution. The aim of this study was to produce the most robust phylogenetic reconstruction of Encephalartos to date. This was done by using markers from three different genomes – plastid (rbcL, matK-trnK, trnH-psbA, cab), mitochondrial (nad1) and nuclear (26S, AGAMOUS, NEEDLY, nrITS1) – for all currently accepted taxa. The results obtained show an increase in resolution for both the backbone and species level relationships compared to previous work. This genus can be separated into five new geographic groups – northern African, central African, eastern African, Mozambican-Zimbabwean, and southern African. There is also an indication that the evolution of the southern African group is driven by a form of reproductive isolation. Further studies on this group should be approached systematically based on the foundation provided by the linages that are shown in this study.
... Angiosperm Type 3-lobed 4 4 13 2 0 0 2 1 8 34 21 14 Angiosperm Type 6 3 3 3 0 1 1 2 1 0 14 9 6 Angiosperm Type 7 0 0 5 0 0 0 0 0 0 5 5 0 Angiosperm Type 8 0 herbivorous arthropods, rather than the more coriaceous foliage of pteridophytes and gymnosperms that possess more structural tissues (Ruhnke et al. 2009;Caldwell et al. 2016). Gymnosperms also likely to have had greater physical and chemical defenses than angiosperms, a condition that has been demonstrated for modern conifers (Moreira et al. 2012), cycads (Schneider et al. 2002), Ginkgo L. (Mohanta et al. 2012), and gnetaleans (González-Juárez et al. 2020). These differential herbivory values are consistent with other studies suggesting that the higher palatability of angiosperms results in higher herbivory pressure compared to gymnosperms (Chabot and Hicks 1982;Farrell 1998;Wardle et al. 2002;Augusto et al. 2014) Alternatively, although angiosperm origins remains a contentious issue (Wang 2010;Doyle 2012;Li et al. 2019), there is broad agreement regarding their pattern of early diversification and ecological extension into new environments. ...
Plants and insects are the two dominant groups in terrestrial ecosystems, and insect damage on fossil plants is the only direct evidence documenting the past ecological history between these two, hyperdiverse groups. We describe, analyze, and interpret plant–insect interactions of a lower Cenomanian paleoforest from western France – the Puy-Puy Quarry of the Nouvelle-Aquitaine Region. We examined 1605 fossil leaves, axes, and reproductive material of bennettitalean, pinalean, and ginkgoalean gymnosperms; lauralean and magnolialean angiosperms; and pteridophyte fronds. We identified functional feeding groups (FFGs) and insect damage types (DTs) preserved on this foliage and data were rarified to indicate sample completeness. By employing R, various statistical parameters were calculated. We established 71 DTs for the nine FFGs of hole feeding, margin feeding, skeletonization, surface feeding, oviposition, piercing and sucking, galling, mining, and pathogens, and 1292 feeding event occurrences. Of the specimens examined 22.2% exhibited one or more DT, with angiosperms the most affected plant group. The most diverse interactions were mining and galling, indicating a mosaic of humid and xeric habitats, respectively, for the Puy-Puy paleoforest, a conclusion consistent with previous paleontological and sedimentological interpretations. Elevated DT richness suggests long-standing ecological relationships between the plants and insects, representative of a mature forest.
... In our analysis, we include the Betulaceae related data as some wind-pollinated plant families may benefit from enhanced dispersal by insects, although the extent of this relationship is unknown 45 . Some recent studies reveal that some of the insect pollinators, particularly bees and syrphid fly species, collect pollen from a broad range of windpollinated plant species [46][47][48] , and also, some other studies [49][50][51][52][53][54][55][56][57] identified insect pollination in plant species which were presumed to be wind-pollinated. Our study may open some new horizons in the field of plant-pollinator interactions, a field with large gaps in knowledge. ...
Majority of the pollination related studies are based on the diurnal pollinators, and the nocturnal pollinators received less scientific attention. We reveal the significance of settling moths in pollination of angiosperm families in Himalayan ecosystem of North-East India. The refined and novel method of pollen extraction from the proboscides provides a more robust assessment of the pollen carrying capacity. The study is based on one of the largest data sets (140 pollen transporter moth species (PTMS)), with interpretation based on seasonal as well as altitudinal data. In the present study about 65% moths (91 species) carried sufficient quantities of pollen grains to be considered as potential pollinators (PPMS). Teliphasa sp. (Crambidae) and Cuculia sp. (Noctuidae) are found to carry the highest quantity of pollen. We found pollen grains of 21 plant families and the abundant pollen are from Betulaceae, Fabaceae, Rosaceae and Ericaceae. Species composition of PTMS and PPMS in pre-monsoon, monsoon, and post-monsoon revealed the dominance of Geometridae. Maximum diversity of PTMS and PPMS is found from 2000 to 2500 m altitude. The nocturnal pollen transfer network matrices exhibited high degree of selectivity (H2ʹ = 0.86).
... This characteristic makes reproductive synchronization essential for the reproductive success of the species in this group (Clugston et al., 2016;Heilbuth, 2000;Martínez-Domínguez et al., 2018;Morellato, 2004). Asynchronous phenological patterns can prevent successful reproductions in small and isolated cycad populations, negatively impacting their fitness and threatening their survival (Clugston et al., 2016;Laidlaw & Forster, 2012;Lopez-Gallego, 2007;Octavio-Aguilar, Rivera-Fern andez, et al., 2017;Okubamichael et al., 2016;Reed et al., 2012;Schneider et al., 2002;Segalla et al., 2019;Velasco García et al., 2016). ...
Dioecy, a character common to all cycads, requires obligatory outcrossing. The absence of potential reproductive mates of the opposite sex renders individuals effectively sterile. Therefore, reproductive synchrony is essential for the reproductive success of cycads. Here, we describe the reproductive phenology, morphology, and lifespan of strobili of Zamia boliviana (Cycadales, Zamiaceae), an endemic cycad in South America. We examined the variation in timing of maturation between polliniferous and ovuliferous individuals in two Z. boliviana populations. Lifespan of polliniferous and ovuliferous strobili was based on direct observations and systematic measurements of strobili development. Phenological study covered three reproductive cohorts in two distinct cycad populations. Lifespan of polliniferous strobili was comprised of four phases and lasted 50 days until the cycle's completion, while ovuliferous strobili underwent seven phases that extended over 330 days until seed dehiscence. Both sexes produced strobili during the dry season. We identified a seasonally synchronous pattern in the reproductive phenology of Z. boliviana, with a major overlap in the phases of emergence, pollen release, and strobili receptivity between sexes, populations, and subsequent years. Reproductive events of Z. boliviana followed the seasonality of the Cerrado vegetation and climate. Synchrony between the period of strobili production and reproductive activity peaks was found in both sexes, but seed dehiscence occurred in the dry season. Our study provides relevant and new biological data for Z. boliviana in its natural habitat, demonstrating a temporal distinction between the lifespan of polliniferous and ovuliferous strobili and the necessary overlap between the release and receptivity of pollen.
... Chemical defenses are well established for angiosperms (Mithöfer & Boland, 2012), where a variety of volatilized, inert, and penetrative substances are released by specialized tissues such as lactifers and conveyed through a system of secretory ducts (Picard, 2008). Such antiherbivore defenses have been documented for the four modern gymnosperm groups of conifers (Litvak & Monson, 1998;Mumm & Hilker, 2006;Moreira et al., 2012), cycads (Clark & Clark, 1991;Schneider et al., 2002;Castillo-Guevara & Rico-Gray, 2003), Ginkgo biloba L. (Matsumoto & Sei, 1987;Kwon et al., 1996;Mohanta et al., 2012), and gnetaleans (Boecklen & Hoffman, 1993;Caveny et al., 2001;González-Juárez et al., 2020). Physical defenses also are extensively reported for these extant gymnosperm groups that involve spines, trichomes (Hanley et al., 2007), sclerophylly as evidenced by thick cuticles (Clark & Clark, 1991), inordinate fibrovascular and other structural tissues concentrated in veins (Choong, 1996), and pronounced wound response from herbivory (Edwards & Wratten, 1983). ...
The Early Cretaceous terrestrial revolution involved global shifts from gymnosperm to angiosperm dominated floras. However, responses of insect herbivores to these changes remain unexamined. We evaluated 2176 highly sampled plant specimens representing 62 species/morphotypes from the 126 Ma Dawangzhangzi plant assemblage of Northeastern China. Our study consisted of horsetails, ferns, ginkgoaleans, czekanowskialeans, conifers, and an angiosperm. Their herbivory was evaluated by the functional feeding groups of hole feeding, margin feeding, and surface feeding (ectophytic feeders); piercer and suckers, and ovipositing insects (ectoendophytic feeders); mining, galling, and borings (endophytic feeders); and pathogens, collectively constituting 65 damage types (DTs). The plant assemblage was assessed for herbivory richness by DT richness, component community structure, and DT specialization on plant hosts; for herbivory intensity, it was evaluated for DT frequency, herbivorized surface area, and feeding event occurrences. Using feeding event occurrences, the data supported seven species/morphotypes as most intensely herbivorized: Liaoningocladus boii (76.6%), Czekanowskia sp. 1 (8.4%), Czekanowskia rigida (4.10%), Lindleycladus lanceolatus (3.5%), Ginkgoites sp. 2 (2.0%), Podozamites sp. 1 (1.1%), and Solenites sp. 1 (0.9%). The most herbivorized taxa were pinaleans (conifers), then czekanowskialeans, and lastly ginkgoaleans; the monodominant component community was the conifer Liaoningocladus. DT host specialization levels were low. The plant assemblage had an overall low 0.86% of foliage removed by herbivores, explained by physical and chemical antiherbivore defenses, and parasitoid attack. Although Paleozoic, gymnosperm-dominated assemblages had greater herbivory, component community structure of the three most herbivorized taxa are more similar to modern bracken fern and willow than modern gymnosperm taxa.
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β-methylamino-L-alanine (BMAA) is a neurotoxic non-protein amino acid found in the tissues of cycad plants. The demonstrated toxicity of BMAA to diverse organisms, including humans, is widely assumed to imply a defensive function of BMAA against herbivores; however, this hypothesis has not previously been tested in an ecologically relevant system. We investigated the effects of dietary BMAA, across a range of dosages matching and exceeding levels typically present in cycad leaves, on the feeding preferences and performance of a generalist lepidopteran herbivore (Spodoptera littoralis).We observed no effects of dietary BMAA on the survival or development of S. littoralis larvae, nor any larval preference between BMAA-laced and control diets. These findings suggest that BMAA in cycad tissues does not deter feeding by insect herbivores, raising questions about other potential physiological or ecological functions of this compound.
The processing of dietary pyrrolizidine alkaloids by larvae and adults of the arctiid moth Creatonotos transiens was studied in time-course experiments: In larvae, pyrrolizidine alkaloid uptake is quickly followed by the transformation of the alkaloids into their N-oxides. Furthermore, if 7 S-heliotrine is applied, a stereochemical inversion of the hydroxyl group at C7 to 7R-heliotrine can be observed within 48h of feeding. The rate of this biotransformation is substantially higher in males which use the 7R-form later as a precursor for the biosynthesis of 7R-hydroxydanaidal, a pheromone. The resorbed pyrrolizidine alkaloids are deposited in the integument within 48h, where they remain stored during the larval, pupal and partly also the imaginal stages. Virtually no alkaloids are lost during ecdysis. Some pyrrolizidine alkaloids can be recovered from the meconium which is released at eclosion by the imagines especially when disturbed. In the adults pyrrolizidine alkaloids are processed in different ways by the two sexes: In females, about 50-80% of total alkaloids are transferred from the integument to the ovaries and the eggs within 2-3 days after eclosion. If females mate with alkaloid-rich males they additionally receive with the spermatophore up to 290|ig pyrrolizidine alkaloid, which are further translocated to the eggs. A biparental endowment of eggs with acquired defence alkaloids is thus achieved. In males, 30-50% of pyrrolizidine alkaloids remain in the integument; about 10–30% are transferred to the scent organ, the corema, where they are converted into 7R-hydroxydanaidal. Another part (about 40%) is passed to the spermatophore. In the laboratory experiments, the sizes of the coremata and their respective 7R-hydroxydanaidal contents are strongly dependent on the availability of dietary pyrrolizidine alkaloids during L6 and especially L7 stages. In the L7 stage even short-term feeding (4-6h) on Senecio jacobaea is sufficient to induce large coremata.
Neither the insects nor the cycads are separately capable of long-term survival in nature, and unless both are protected and conserved, wild populations of Xamia are in jeopardy.
We investigated the effect of prescribed wet-season fire on the demography of Zamia pumila L. (Zamiaceae) in slash pine savanna of Everglades National Park, Florida. We monitored survival, coning, leaf production, and herbivore damage on two plots burned during the wet season of 1995 and on two unburned plots. Fire killed all leaves and promoted the flushing of new leaves but caused minimal mortality of adults and seedlings. Seeds within cones were killed, but some dispersed seeds survived. Coning, particularly of females, was enhanced in the plot that burned earlier and hotter. Larvae of Seirarctia echo appeared on new leaves within 1 mo postfire and were present at higher density on burned plots. Herbivore damage was significantly greater on burned plots for the first wet season following the fire, with many plants completely defoliated. This defoliation, which was more frequent in the plot burned late in the wet season, resulted in mortality of some adults but promoted greater leaf production in the remainder. Seirarctia echo consumed some Zamia cones, cancelling the positive effect of fire on reproduction. Overall, the combined direct and indirect effects of wet- season fires on Zamia was positive for the early wet-season fire but negative for the late wet-season fire because of reduced coning and increased mortality following herbivory.
Apinotropis Jordan is the only genus of the curculionoid family Anthribidae known to be exclusively associated with cycads, having been recorded only from certain species of Encephalartos in southern Africa. Recent surveys have produced the first records of these weevils from the Eastern Cape Province, South Africa, considerably extending the previously known range of the genus and the number of species. Three new species, A. brevis, A. robustus and A. nanus, are described, and the two previously known species, A. verdoornae Jordan and A. oberprieleri Frieser, as well as the genus Apinotropis are redescribed. These descriptions and redescriptions include several hitherto unused characters of the venter and male genitalia. In particular, the males of all species possess ventral abdominal setiferous sex patches of a location and structure so far unrecorded in Anthribidae. The adelphotaxon of Apinotropis is uncertain but is likely to include the southern African genus Holophloeus Jordan. A phylogenetic analysis of the five known species of Apinotropis indicates a monophyletic origin and a strictly dichotomous branching sequence of these species. The immature stages and life history of Apinotropis are still unknown but, based on the examination of pupal chambers in cycad sporophylls and other biological details, a putative reconstruction of the life cycle is presented. Fungal cultures of the gut contents and frass pellets of A. oberprieleri, A. verdoornae and A. brevis yielded several saprotrophic hyphomycetous fungi but no members of the wood-decaying Xylariaceae on which Anthribidae generally feed and develop. It therefore appears that Apinotropis is not mycetophagous but develops in cycad tissues, and that this lifestyle may represent the ancestral biological trait of the family (adapted only to a particular type of gymnosperm) rather than being a secondary specialization only in Apinotropis. The evolution of the genus is postulated to have been closely linked with that of the Encephalartos cycadifolius species group, including both cospeciation events and apparent secondary host shifts, and to have proceeded from an original development in trunk tissues to subsequent associations with female and later male cycad cones.
This paper deals with developments made in the area of toxins from lathyrus and vetch peas since our last review in 1964.1 The active principles, which include 3-amino-propionitrile (BAPN), 3-cyanoalanine (β-CNala), 2,4-diamino-butyric acid (DAB), and 3-N-(oxalyl)-2,3-diaminopropionic acid (OX-DAP), were isolated in free or bound form in our or other laboratories over the past twenty years, in studies relating to the neurological disease lathyrism in man.
In a published paper, a method for testing the correlation between two discrete characters was presented and applied to test whether in butterfly larvae origins of gregariousness are concentrated to lineages with aposematic coloration. The relationship was found to be nonsignificant. However, the butterfly data on which the test was applied had been compiled in another study to investigate evolutionary sequences and was biased, because there was an overrepresentation of aposematic, as compared to cryptic, branches in the sample. In the paper presented here, aposematic and cryptic clades of the original phylogeny were resolved to the same degree, and the resulting set of branches may be regarded as unbiased with respect to the hypothesis being tested. A method for testing the contingency of states in two characters was then applied to the new data set, resulting in a highly significant relationship between origins of gregariousness and aposematic coloration. I argue that when using statistical methods on phylogenetic data, it is crucial to resolve various parts of the phylogeny to the same comparable systematic unit in order not to get a distorted sample of taxa/branches.
Analysis of sequences of the chloroplast gene rbcL for
76 taxa of Podocarpaceae (representing all genera except
Parasitaxus) and five species of Phyllocladaceae were
undertaken with respect to their relationships to each other and to 28
coniferalean outgroup taxa from seven families. The results indicate that
Podocarpaceae are polyphyletic unless expanded to include Phyllocladaceae.
Within Podocarpaceae, Sundacarpus is placed in a clade
with Prumnopitys, and
Falcatifolium is paraphyletic as a basal grade to
Dacrydium. Phyllocladus is in an
unresloved clade with Halocarpus,
Manoao/Lagarostrobos and
Prumnopitys/Sundacarpus. The separation of
Afrocarpus from Podocarpus and its
placement instead as sister to Nageia and
Retrophyllum is supported.
Podocarpus s. str. is monophyletic, with both subgenera
identified, albeit poorly supported. The analysis placed
Lepidothamnus and Saxegothaea in
an unresolved basal polytomy within the family. There were no clear outgroup
relationships with the family. These results differ from the morphological
clades found by Kelch (1997), and disagree strongly with his
18S-sequence-based phylogeny (Kelch 1998). However, jackknife support values
indicate that although the genera are well supported, relationships both
within and between them are not, suggesting that intergeneric relationships in
the family require further study. There is also some congruence between our
results and those of the gymnosperm 18S study by Chaw
et al. (1997), although their study included only three
Podocarpaceae and one Phyllocladaceae species.