Linley K. Jesson

The biochemistry of Rubisco in Flaveria.

C(4) plants have been reported to have Rubiscos with higher maximum carboxylation rates (kcat(CO(2))) and Michaelis-Menten constants (K(m)) for CO(2) (K(c)) than the enzyme from C(3) species, but variation in other kinetic parameters between the two photosynthetic pathways has not been extensively examined. The CO(2)/O(2) specificity (S(C/O)), kcat(CO(2)), K(c), and the K(m) for O(2) (K(o)) and RuBP (K(m-RuBP)), were measured at 25 degrees C, in Rubisco purified from 16 species of Flaveria (Asteraceae). Our analysis included two C(3) species of Flaveria, four C(4) species, and ten C(3)-C(4) or C(4)-like species, in addition to other C(4) (Zea mays and Amaranthus edulis) and C(3) (Spinacea oleracea and Chenopodium album) plants. The S(C/O) of the C(4) Flaveria species was about 77 mol mol(-1), which was approximately 5% lower than the corresponding value in the C(3) species. For Rubisco from the C(4) Flaverias kcat(CO(2)) and K(c) were 23% and 45% higher, respectively, than for Rubisco from the C(3) plants. Interestingly, it was found that the K(o) for Rubisco from the C(4) species F. bidentis and F. trinervia were similar to the C(3) Flaveria Rubiscos (approximately 650 microM) while the K(o) for Rubisco in the C(4) species F. kochiana, F. australasica, Z. mays, and A. edulis was reduced more than 2-fold. There were no pathway-related differences in K(m-RuBP). In the C(3)-C(4) species kcat(CO(2)) and K(c) were generally similar to the C(3) Rubiscos, but the K(o) values were more variable. The typical negative relationships were observed between S(C/O) and both kcat(CO(2)) and K(c), and a strongly positive relationship was observed between kcat(CO(2)) and Kc. However, the statistical significance of these relationships was influenced by the phylogenetic relatedness of the species.

Correlated Evolution of Sexual System and Life-History Traits in Mosses

In mosses, separate and combined sexes are evolutionarily labile, yet factors selecting for this variation are unknown. In this study, we investigate phylogenetic correlations between sexual system and five life-history traits (asexual reproduction, chromosome number, gametophore length, spore size, and seta length). We assigned states to species on a large-scale phytogeny of mosses and used maximum likelihood analyses to test for the correlations and investigate the sequence of trait acquisition. Mosses in lineages with separate sexes were significantly more likely to be large, whereas those in lineages with combined sexes had higher chromosome numbers. Moreover, evolutionary transitions to separate sexes were more likely to occur in lineages with small spores. There was no support for a correlation between asexual reproduction and separate sexes. These results suggest that sexual system evolution is influenced by traits affecting mate availability and the dispersal of gametes and spores, and provides evidence for the existence of syndromes of life-history traits in mosses.

A test of simultaneous resource and pollen limitation in Stylidium armeria

This study tests the Haig-Westoby model, which predicts that seed output will be limited simultaneously by pollen and resources when plants optimally distribute their reproductive investment. The test was conducted over 2 yr using Stylidium armeria in a factorial design that fully crossed three pollination levels (small stigmatic loads, open pollination, and supplementation of natural loads) with three levels of resource availability (reduction through partial defoliation, unmanipulated resource conditions, and supplementation through nitrogen, phosphorus and potassium (NPK) addition). There was no evidence of pollen limitation from supplemental pollination; however, pollen reductions (to about half the normal mean stigmatic loads) sharply reduced seed output. There was no evidence of resource limitation, in that NPK addition did not, by itself, significantly elevate seed output in either year of the study, while resource reduction by defoliation lowered seed output in the second year. Simultaneous addition of both pollen and resources strongly and significantly increased seed production. These results match the direction of effects predicted by the Haig-Westoby model, and suggest that S. armeria plants at our site are at or near an equilibrium of joint limitation of seed production by pollen capture and resource availability.

Linking seed dispersal, germination and seedling recruitment in the invasive species Berberis darwinii (Darwin’s barberry)

Seedling recruitment is a multi-phased process involving seed production, dispersal, germination, seedling establishment and subsequent survival. Understanding the factors that determine success at each stage of this process is of particular interest to scientists and managers seeking to understand how invasive species spread and persist, and identify critical stages for management. To understand the factors and processes influencing recruitment of the invasive species Berberis darwinii Hook. (Darwin’s barberry), temporal and spatial patterns of seed dispersal, germination and seedling establishment were examined. Seed dispersal from a large source population was measured over two fruiting seasons, and subsequent patterns of seedling emergence and survival within each cohort were measured. Seed longevity was tested under both natural and artificial conditions. Seeds were widely dispersed by birds, up to 450xa0m from the source population. Dispersal was essential to seedling establishment, as few seedlings survived beneath the parent canopy. Seeds were relatively short-lived in the soil under both field and glasshouse conditions, with few surviving for more than 1xa0year. Patterns of newly emerged seedlings largely reflected patterns of seed rain, but seedling survival was significantly affected by distance from source population, seedling density and light environment. These results suggest that recruitment of B. darwinii is dependent on dispersal of seeds to favourable microsites. Management priorities should include the removal of fruiting plants, and seedling control in highlight areas.

Polyploidy influences sexual system and mating patterns in the moss Atrichum undulatum sensu lato

BACKGROUND AND AIMSnEvolutionary transitions between separate and combined sexes have frequently occurred across various plant lineages. In mosses, which are haploid-dominant, evolutionary transitions from separate to combined sexes are often associated with genome doubling. Polyploidy and hermaphroditism have strong effects on the inbreeding depression of a population, and are subsequently predicted to affect the mating system.nnnMETHODSnWe tested the association between ploidy (haploid, diploid or triploid gametophytes) and mating system in 21 populations of Atrichum undulatum sensu lato, where sex ratios vary widely. For each population, we measured the sex ratio, estimated selfing rates using allozyme markers and determined the level of ploidy through flow cytometry.nnnKEY RESULTSnHermaphrodites in A. undulatum were either diploid or triploid. However, many diploid populations were strictly separate-sexed, suggesting that hermaphroditism is not a necessary result of genome doubling. Levels of selfing were strongly supported as being greater than zero in one population with strictly separate-sexed individuals, and one-third of populations with hermaphrodites.nnnCONCLUSIONSnAlthough hermaphrodites are associated with triploidy, hermaphroditism is not a necessary outcome of genome duplication. Hermaphroditism, but not genome duplication alone, increased estimated selfing rates, probably due to the occurrence of selfing within a gametophyte. Thus, genome duplication can influence the mating system and the associated evolution and maintenance of reproductive traits.

Reproductive investment within inflorescences of Stylidium armeria varies with the strength of early resource commitment

BACKGROUND AND AIMSnResource allocation to flowers, fruits and seeds can vary greatly within an inflorescence. For example, distal fruits are often smaller and produce fewer and smaller fruits and seeds than more basal fruits. To assess the causes and functional significance of intra-inflorescence variation, pollen and resources were manipulated to test whether such patterns could be altered within racemes of Stylidum armeria, a perennial Australian herb.nnnMETHODSnPollen and resource levels were manipulated over two flowering seasons. How the number of ovules, fertilized ovules and seeds, the probability of fruit set, and the biomass of floral and fruiting structures varied with their position on the raceme were analysed.nnnKEY RESULTSnMost plants showed a decline in ovule and seed number toward the distal positions on the raceme, but plants differed in their pattern of intra-inflorescence allocation: racemes with greater investment in basal fruits displayed a stronger trade-off with distal investment than did racemes that made smaller initial investments. This trade-off was (a) much stronger for ovule number than for seed number, (b) ameliorated but not erased by resource addition, and (c) exacerbated by resource reduction. There was large and seemingly erratic variation across fruit positions in ovule fertilization and seed set following both natural and supplemental pollination.nnnCONCLUSIONSnIn S. armeria, allocation to reproductive traits within the inflorescence is influenced by dynamic trade-offs in resource allocation between early and late fruits, and may also be subject to inherent architectural effects. Large, unpredictable variation among fruits in fertilization success and seed set may influence the evolution of inflorescence size, ovule number and floral dimorphism.

Wing marker woes: a case study and meta-analysis of the impacts of wing and patagial tags

AbstractThe marking of individual birds has a long history in ornithology. This inexpensive and simple practice has been used to shed light on migration, behavior, and age-specific survival and recruitment. However, problems associated with markers and tags have often been overlooked. Wing tags have been used for over 40xa0years on frigatebirds, but their effects on this family of highly aerial seabirds have not been examined. Following higher than expected nest failure of treatment birds in the previous breeding season, we designed a study to test the impact of wing tagging and other standard capture and sampling methods on the nest success of Magnificent Frigatebirds (Fregata magnificens). Twelve nests were assigned to each of various band, measure, bleed, wing tag, and control treatments in the 2010/2011 breeding season on Barbuda, West Indies. We modeled nest fates using generalized linear models. Wing tags had a substantial negative effect on pre-fledging nest success, which was 42xa0% (10/24) for control nests, 39xa0% (14/36) for all non wing-tagged treatments, and 15xa0% (7/48) for wing-tagged treatments. We also conducted two meta-analyses, with different effect size calculations, to explore the general impact of wing and patagial tags on all birds. Our log odds ratio model showed a significant effect on survival and hatch and nest success, while our standardized mean difference model dealing largely with outcomes of behavioral, condition, and reproductive parameters (e.g., number of chicks and hatch date) showed no difference between marked and control birds. We consider possible mechanisms by which wing tags might contribute to lower nest success in frigatebirds, and propose that alternative markers be considered carefully before being applied to any species.ZusammenfassungFlügelmarkierungen sind möglicherweise problematisch: eine Fallstudie und Metaanalyse der Auswirkungen von Flügelmarkierungenn In der Ornithologie hat die Markierung einzelner Vögel eine lange Tradition. Als preiswerte und einfache Methode dient sie schon seit langem dazu, Erkenntnisse über den Vogelzug, das Verhalten und das Überleben und die Fortpflanzung zu gewinnen. Dabei sind aber Probleme, die aus den solchen Markierungen am Vogel resultierten, oft vernachlässigt worden. Seit mehr als 40 Jahren werden bei Fregattvögeln Flügelmarkierungen eingesetzt, aber deren Auswirkungen auf diese ausgesprochen flugintensiven Vögel wurden nie untersucht. Nachdem wir bei markierten Vögeln nach einer Brutsaison einen schlechteren Bruterfolg als erwartet beobachtet hatten, arbeiteten wir eine Studie aus zur Untersuchung der Auswirkungen von Flügelmarkierungen und anderer Fang- und Markierungsmethoden auf den Bruterfolg von Prachtfregattvögeln (Fregata magnificens). In der Brutsaison 2010/2011 wurden auf Barbuda, einer Insel der Kleine Antillen, zwölf Nester für je eine von mehreren Markierung- und Messmethoden sowie für Kontrollbehandlungen ausgewählt. Die weitere Entwicklung der einzelnen Nester wurde anhand linearer Modelle modelliert. Danach hatten Flügelmarkierungen einen substantiell negativen Effekt auf den Bruterfolg während der Zeit vor dem Flüggewerden: 42xa0% (10/24) bei den Kontrollnestern, 39 (14/36) bei allen Behandlungen außer Flügelmarkierung und 15xa0% (7/48) bei den Nestern mit Flügelmarkierungen. Außerdem führten wir zwei Metaanalysen für unterschiedliche Effektstärkenberechnungen durch, um den generellen Einfluss von Flügelmarkierungen zu untersuchen. Das von uns eingesetzte logarithmische Quotenverhältnis-Modell („log odds ratio model“) zeigte einen signifikanten Effekt auf den Überlebens- und Schlüpferfolg, während das standardisierte „mean difference“-Modell, das in erster Linie für Messungen von Verhaltens- und Fortpflanzungsparametern eingesetzt wird, keinen Unterschied zwischen den markierten und den Kontrollvögeln zeigte. Wir denken, dass es möglicherweise Mechanismen gibt, die bei an den Flügeln markierten Fregattvögeln zu einem geringeren Bruterfolg führen, und wir empfehlen, alternative Markierungen bei jeder Vogelart vor einer Anbringung sorgfältig zu prüfen.

Mitigation of pollen limitation in the lowbush blueberry agroecosystem: effect of augmenting natural pollinators

Growers of small fruit crops often supplement the natural pollinator community by introducing pollinators into commercial orchards and fields, but there are relatively few studies that test the extent to which such interventions increase fruit yield. To test whether plants are limited by pollen availability, inflorescences in 78 commercial lowbush blueberry fields during three years were hand-pollinated either with supplemental outcross pollen, or marked and left as controls (open-pollination). Maximum fruit set with supplemental pollination was in the range 50–65%, whereas with open-pollination, it was slightly, but significantly lower, in the range of 47–57%, suggesting that pollen limitation can affect fruit set. In a two-year experiment, we augmented native pollinators with introduced honey bees, bumble bees, and leaf cutter bees and all combinations in 48 fields. Stigmatic pollen loads were influenced by the total numbers of managed bees in a field in 2010 but not 2011. The presence of leaf cutter bees had a small but positive effect on seed set in 2010, and honey bees had a small but negative influence on seed set in 2011. There was a strong correlation between fruit set reproductive output of supplementally pollinated and open-pollinated plants, suggesting that plant health or plant resources influence reproductive success. Temperature variation among regional groupings of fields was minimal and is unlikely to have accounted for differences among fields in fruit set. We propose several reasons why, despite pollen-limitation of fruit and seed set of blueberry plants, augmentation of the pollinator community of lowbush blueberry did not significantly increase reproduction. These include pollinator-mediated transfer of self-pollen followed by subsequent fruit abortion due to inbreeding depression and resource limitation for fruit maturation. Management practices that focus on increasing outcross pollen receipt, or plant resources for fruit set may have greater overall benefit than pollinator augmentation alone.

Hybridization is associated with changes in sexual system in the bryophyte genus Atrichum

PREMISE OF THE STUDYnOver 50% of bryophytes have separate sexes, and numerous transitions have occurred between combined and separate sexes. Polyploidy and hybridization is one proximate mechanism hypothesized to cause evolutionary transitions to hermaphroditism in bryophytes because sex is expressed at the haploid stage and in nonpolyploid dioecious species males have a single V chromosome and females a U. Hermaphroditism can arise if gametophytes of allopolyploids have both U and V chromosomes. We examined the association between polyploidy and hermaphroditism in the bryophyte genus Atrichum, which has species where gametophytes can be haploid, diploid, or triploid, and some species have hermaphroditic individuals.nnnMETHODSnWe generated phylogenies of Atrichum from sequences of three plastid regions (rbcL, rps4, and trnL-trnF) and the second intron for the nuclear gene Leafy/Floricaula to further understand the relationships among haploid, diploid, and triploid species, and those with combined or separate sexes.nnnKEY RESULTSnThe existence of multiple sequences of Leafy/Floricaula in diploid and triploid, but not haploid, individuals is consistent with independent allopolyploid origins of the diploid and triploid species. Allopolyploidy was associated with a likely gain in hermaphroditism in triploid Atrichum undulatum and possibly diploid A. altecristatum, but not in the allopolyploid A. crispulum (diploid at the gametophyte level).nnnCONCLUSIONSnThese results highlight a role for hybridization and polyploidy in sexual system evolution, but the presence of diploid (allopolyploid) dioecious species suggest that other factors may influence the maintenance of sexual systems after an evolutionary transition.