Variation in pollen limitation and floral parasitism across a mating system transition in a Pacific coastal dune plant: evolutionary causes or ecological consequences?

Background and Aims Evolutionary transitions from outcrossing to self-fertilization are thought to occur because selfing provides reproductive assurance when pollinators or mates are scarce, but they could also occur via selection to reduce floral vulnerability to herbivores. This study investigated geographic covariation between floral morphology, fruit set, pollen limitation and florivory across the geographic range of Camissoniopsis cheiranthifolia, a Pacific coastal dune endemic that varies strikingly in flower size and mating system.Methods Fruit set was quantified in 75 populations, and in 41 of these floral herbivory by larvae of a specialized moth (Mompha sp.) that consumes anthers in developing buds was also quantified. Experimental pollen supplementation was performed to quantify pollen limitation in three large-flowered, outcrossing and two small-flowered, selfing populations. These parameters were also compared between large- and small-flowered phenotypes within three mixed populations.Key Results Fruit set was much lower in large-flowered populations, and also much lower among large- than small-flowered plants within populations. Pollen supplementation increased per flower seed production in large-flowered but not small-flowered populations, but fruit set was not pollen limited. Hence inadequate pollination cannot account for the low fruit set of large-flowered plants. Floral herbivory was much more frequent in large-flowered populations and correlated negatively with fruit set. However, florivores did not preferentially attack large-flowered plants in three large-flowered populations or in two of three mixed populations.Conclusions Selfing alleviated pollen limitation of seeds per fruit, but florivory better explains the marked variation in fruit set. Although florivory was more frequent in large-flowered populations, large-flowered individuals were not generally more vulnerable within populations. Rather than a causative selective factor, reduced florivory in small-flowered, selfing populations is probably an ecological consequence of mating system differentiation, with potentially significant effects on population demography and biotic interactions.     

Single mating type-specific genes and their 3′ UTRs control mating and fertility in Cochliobolus heterostrophus

To determine the number of proteins required for mating type (MAT) locus-regulated control of mating in Cochliobolus heterostrophus, MAT fragments of various sizes were expressed in MAT deletion strains. As little as 1.5?kb of MAT sequence, encoding a single unique protein in each mating type (MAT-1 and MAT-2), conferred mating ability, although an additional 160?bp of 3^′ UTR was needed for production of ascospores. No other mating type-specific genes involved in mating identity or fertility were found. Thus, although homologs of the C. heterostrophus MAT-1 and MAT-2 genes exist in the filamentous ascomycetes Neurospora crassa and Podospora anserina, C. heterostrophus does not appear to have mating type-specific homologs of two additional genes required by both N. crassa and P.?anserina for successful sexual reproduction. Three genes were identified in the common DNA flanking the MAT locus: a gene encoding a GTPase-activating protein and an ORF of unknown function lie 5^′ while a β-glucosidase encoding gene lies found 3^′. None of these genes appears to be involving in the mating process.     

Why does some pollen lack apertures? A review of inaperturate pollen in eudicots

Apertures are key characters of pollen grains with systematic importance in angiosperms. They function as sites for pollen tube exit, water uptake, transfer of recognition substances and accommodation of volume changes. Not all pollen has apertures; inaperturate pollen (lacking obvious apertures) characterizes many angiosperm groups, especially in early divergent angiosperms and monocots, but also eudicots. In order to expand our knowledge of the systematic distribution, possible functional significance and development of inaperturate pollen in angiosperms, this review focuses on inaperturate and cryptoaperturate (with hidden apertures) pollen in the large eudicot clade, which comprises about 75% of present‐day angiosperm species. It includes new TEM observations of inaperturate pollen from four exemplar taxa selected from different parts of the eudicot phylogeny. Two categories of inaperturate (including cryptoaperturate) pollen occur in eudicots. (1) Sterile attractant or feeding pollen associated with functional dioecy has evolved iteratively at least six times in conjunction with complex breeding systems in the core eudicots. (2) Fertile pollen has evolved numerous times independently throughout eudicots, though generally in a relatively small number of individual taxa. Notable exceptions are the petaliferous crotonoid Euphorbiaceae s.s., in which fertile inaperturate pollen occurs in c. 1500 species, and two subfamilies of Apocynaceae s.l. (Secamonoideae and Asclepiadoideae) with c. 2500 species with fertile inaperturate pollen in pollinia. Fertile inaperturate pollen is sometimes (but not always) associated with an aquatic habit, parasitism, insectivory, heterostyly, anemophily or pollinia. Most fertile inaperturate pollen has a thin exine, or the exine is largely restricted to isolated components (muri, protuberances, subunits) separated by thinner areas which probably function as apertures. In cryptoaperturate pollen, the aperture is covered by continuous exine which probably has a protective function, similar to an operculum. Developmentally, inaperturate pollen is not associated with any particular tetrad type or meiotic spindle orientation (unlike some apertures) due to the absence of a colpal shield of endoplasmic reticulum or other organelles and hence is independent of microsporogenesis type. The lack of a colpal shield during the tetrad stage of development permits complete deposition of first primexine and then exine around each microspore, possibly mediated by the action of the DEX1 protein. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 29–48.     

Airborne pollen in Bahía Blanca,Argentina: seasonal distribution of pollen types

The composition and seasonal distribution of airborne pollen grains in the atmosphere of Bahía Blanca, Argentina, has been studied between June 2001 and December 2003 using the Rotorod sampler (model 40). The results show that the main pollen types during this period were Cupressaceae, Fraxinus, Myrtaceae, Poaceae, Amaranthus/Chenopodiaceae, Pinus, Urticaceae, Ulmus, Olea and Styphnolobium. The highest concentrations occurred from August to December (end of winter and spring), accounting for 80% of the total annual pollen count. The greatest diversity was found in the spring, with the major of pollen coming from short-flowering plant types, such as Populus, Acer, Platanus, Juglans, Tamarix, Ailanthus and Typha. The potential sources of pollen from woody ornamental species are Cupressus sempervirens, Eucalyptus camaldulensis and Fraxinus pennsylvanica. whereas those from herbaceous species are the Chenopodiaceae and Poaceae, which are found within the city and also in the surrounding natural vegetation, and the Urticaceae, which are only present in the city. Marked annual differences were noted during the study period. The increase in 2002 may have been due to the abundant rainfall that occurred prior to the spring season, which would have favored the vegetative stage and flower development of plants. The decrease in pollen concentration in 2003 was mainly due to low rainfall throughout the year.     

Spatial variation in local pollen flow and mating success in a Picea abies clone archive and their implications for a novel ��breeding without breeding�� strategy

Currently, Norway spruce (Picea abies) breeding in Sweden is based on crosses between the best clones followed by clonal testing of the progenies to select for the long-term breeding population. An alternative breeding strategy called “Breeding without Breeding” (BwB) is proposed, which, in principle, relies on the DNA marker-based pedigree reconstruction from wind-pollinated progenies instead of controlled crosses. To test whether the pedigree structure could be established from progenies of clonal trials, we investigated the spatial pattern of local pollen flow and paternity assignment in a clone archive of Norway spruce. The results showed that 42% of the progeny can be assigned to fathers within 30-m distance with high confidence. Effective pollen dispersal decreased rapidly with distance and followed exponential distribution on local scale. The extent of close-neighbor (within 6 m) mating ranged from 0% to 48% among grafts with an average of 13%. Distance explained 25% deviance in mating success, and other factors such as phenology and spatial configuration of the clones should have contributed the rest. The success of parentage assignment in clone archive opens up the possibility to apply BwB in clonal trials of species that are easy to propagate vegetatively. This procedure could substantially shorten the breeding cycle and still give similar gain per year as the conventional breeding.     

How much pollen can thrips destroy?

ABSTRACT. 1. A laboratory technique for measuring the number of pollen grains consumed by thrips is described.
2. Thrips imaginis Bagnall and Thrips obscuratus (Crawford) (Thripidae) were studied particularly on pollen of the kiwifruit Actinidia deliciosa (A. Chevalier) Liang & Ferguson in New Zealand, and Echium plantagineum L. in Australia.
3. Mean daily feeding rates (in grains per thrips per day) ranged from 29 to 843, with an individual rate as high as 1626 for T.imaginis larvae II on E. plantagineum.
4. The time taken to feed on a single grain was proportional to grain volume, and decreased with temperature.
5. Daily feeding rates were significantly different between pollens, and were higher for smaller grains. The total volume of pollen contents consumed and the total time spent ingesting this volume per thrips per day may be constant with respect to pollen species.
6. Daily feeding rates were equivalent to 0.2–0.7% of the average total pollen production of a flower per thrips per day.
7. Extrapolation of the daily feeding rates suggests that pollen damage by thrips could sometimes be reducing crop yield or plant fitness.     

Single mating type-specific genes and their 3′ UTRs control mating and fertility in Cochliobolus heterostrophus

To determine the number of proteins required for mating type (MAT) locus-regulated control of mating in Cochliobolus heterostrophus, MAT fragments of various sizes were expressed in MAT deletion strains. As little as 1.5 kb of MAT sequence, encoding a single unique protein in each mating type (MAT-1 and MAT-2), conferred mating ability, although an additional 160 bp of 3^′ UTR was needed for production of ascospores. No other mating type-specific genes involved in mating identity or fertility were found. Thus, although homologs of the C. heterostrophus MAT-1 and MAT-2 genes exist in the filamentous ascomycetes Neurospora crassa and Podospora anserina, C. heterostrophus does not appear to have mating type-specific homologs of two additional genes required by both N. crassa and P.␣anserina for successful sexual reproduction. Three genes were identified in the common DNA flanking the MAT locus: a gene encoding a GTPase-activating protein and an ORF of unknown function lie 5^′ while a β-glucosidase encoding gene lies found 3^′. None of these genes appears to be involving in the mating process. Received: 21 November 1997 / Accepted: 28 April 1998     

Isolation and amino acid sequence of a mating pheromone produced by mating type α cells of Saccharomyces exiguus

A peptide, termed α^se pheromone, was isolated as a mating pheromone from culture filtrate of mating type a cells of Saccharomyces exiguus. The peptide showed both agglutinability-inducing activity to a cells of S. cerevisiae and shmoo-inducing action to a cells of S. cerevisiae, S. kluyveri and S. exiguus. The amino acid sequence of α^se pheromone was determined as H-Trp-His-Trp-Leu-Arg-Leu-Ser-Tyr-Gly-Gln-Pro-Ile-Tyr-OH by mass spectrometry, sequence analysis and enzymatic digestion.     

A practical approximation of pollen dispersal–deposition for calculation of pollen productivity and quantification of vegetation

We compared simple mathematical pollen dispersal–deposition models with Gaussian plume models. The simple mathematical models proved equal or better approximations of real world pollen dispersal–deposition. We concluded that for most standard applications, such as estimating pollen productivity or quantitative vegetation reconstructions, simple mathematical models would perform satisfactory. Such easy-to-use models may lower the threshold to employ quantitative tools to palaeoecological questions.     

Cyclic pollen production in Cedrus deodara

Based on a seven-year study of pollen production and release in two different natural populations of Cedrus deodara from Garhwal Himalaya, India, we determined that pollen output follows a two-year cycle. Pollen productivity determinations considered various sources of variability, including the number of pollen strobili per branch, strobili per tree, microsporophylls per tree and pollen grains per tree. Each of these parameters revealed significant year-to-year and population effects. Microsporangium dehiscence took from 2.5 to 3.5 days. Maximum dehiscence was observed between 12:00 and 14:00 h, which coincides with diurnal highest temperature and lowest relative humidity. Annual production of pollen per tree varied from averages of 4.7 × 10⁹, 7.2 × 10⁹ and 5.1 × 10⁹ in years of low production, with alternate high years, producing 12.6 × 10⁹, 14.1 × 10⁹, 13.3 × 10⁹ and 14.0 × 10⁹ pollen grains per tree. Annual pollen production in individual trees of C. deodara ranged from 1.4 × 10⁹ to 22.3 × 10⁹.     

The mating game: do opposites really attract?

When selecting a mate, females of many species face a complicated decision: choosing a very closely related mate will lead to inbreeding, while choosing a mate who is too genetically dissimilar risks breaking up beneficial gene complexes or local genetic adaptations. To ensure the best genetic quality of their offspring, the perfect compromise lies somewhere in between: an optimally genetically dissimilar partner. Empirical evidence demonstrating female preference for genetically dissimilar mates is proof of the adage 'opposites attract'. In stark contrast, Chandler & Zamudio (2008) show in this issue of Molecular Ecology that female spotted salamanders often choose males that are genetically more similar to themselves (although not if the males are small). Along with other recent work, these field studies highlight the broad spectrum of options available to females with respect to relatedness in their choice of mate that belies this rule of thumb.     

May random processes explain mating success in leks?

The object of this paper is to verify whether in specific cases the variance of mating success among lekking males may be due exclusively to a random mechanism, as opposed to the adaptive mechanisms of mate choice which are usually postulated in the literature in the framework of sexual selection theory. In fact, some studies attempted to compare observed distributions of male mating success with a Poisson ‘null’ distribution based on the conjecture of random mating; the conjecture is usually rejected. In this paper we construct a plausible model (the ‘null’ hypothesis) for a strictly random non-adaptive pattern of social behaviour of lekking males and females and we perform several simulations for reasonable choices of parameter values. It should be observed that some of the simulations based on our random model lead to a distribution of male mating success which is Poisson-like. However, contrary to predictions, in several simulations a random process of mate choice lead to non-Poissonian distributions. Accordingly, the fact that, when performing a statistical test on several sets of field data, we find both cases which are in agreement with Poisson distribution, or a normal one, and cases which are not, does not allow us to reject the assumption of random male reproductive success. Thus it is legitimate to conjecture that in many cases the inter-individual variability of male mating success might indeed be determined by random processes. If this conjecture were to be confirmed by further studies, the actual significance of sexual selection in the evolution of lekking species should be reassessed, and a novel approach in the analysis of field data would be called for.     

Variation in annual pollen accumulation rates of Fagus along a N–S transect in Europe based on pollen traps

Annual pollen-accumulation rates (PAR) of Fagus (beech) obtained within the framework of the Pollen Monitoring Programme (PMP) were analyzed in pollen traps along a N–S transect from the Baltic Sea to the Black Sea in different European vegetation units. The study regions are situated in the lowlands of northern Poland, the uplands of SE Poland, the Czech Krkono?e Mts, the Czech ?umava Mts, the Swiss Jura Mts, the Swiss Alps, the Bulgarian Rila Mts and the Bulgarian Strandzha Mts. Most time series are 10 or 11 years long, some are 5–16 years long. Inter-annual fluctuations in Fagus PAR were analyzed and compared with seed mast years. Years with high Fagus PAR and others with low Fagus PAR occurred most frequently in parallel within each region and often in two neighbouring regions. 2006 was exceptional as it had a very high Fagus sylvatica pollen deposition in all study regions and it was also a mast year. In Bulgaria, the trend in the 5 years of Fagus orientalis PAR in the Strandzha Mts differed from that of F. sylvatica PAR in the Rila Mts. Aiming at establishing the relationship between average Fagus PAR and tree cover, differences in Fagus PAR (averaged per pollen trap) were related in each region to the proportion of beech trees in the vegetation within 2 km of the pollen traps, the distance to the nearest pollinating Fagus tree, regional or local presence of beech forests, the degree of landscape openness, and the size of forest opening in which a trap is situated. Average Fagus PAR was found to track the regional abundance of beech trees in the vegetation, not the distance of the nearest Fagus tree. Regional occurrence of beech-dominated forests was reflected by a Fagus PAR of ca. 1,400 grains cm^?2 year^?1, local abundance very close to pollen traps by ca. 2,400 grains, small patches of forest with admixture of Fagus by ca. 170–220 grains, and scarcity or absence of Fagus by ca. 40 grains or less.