A New Microsporangial Protostelid,Microglomus paxillus gen. and sp. nov.*

SYNOPSIS. Microglomus paxillus is described as a new genus and species of the subclass Protosteliida (Class Eumyceto-zoa). It has been isolated only once from casuarina bark collected in Oahu, Hawaii. The new organism is characterized by a uninucleate ameboid trophic stage that feeds on bacteria and by sporocarps with spike-like stalks terminated by microspo-rangia containing tetrads of ameboid protoplasts or thin-walled spores. No flagellate cells are produced. The tetrads are typically formed by successive bipartition following conjugate nuclear divisions in the sporogen. The cells of the tetrad are at first binucleate but soon become uninucleate as a result of nuclear degeneration. Variations in the process of sporogenesis are described.     

Schizoplasmodium,a Mycetozoan Genus Intermediate Between Cavostelium and Protostelium; a New Order of Mycetozoa*

SYNOPSIS. Two new species of the simple mycetozoan genus Schizoplasmodium—S. ovatum and S. gracile—are described, the former having ovate spores and the latter spherical ones. All stages of the life cycle are multinucleate. At sporulation the holozoic plasmodium segments into prespore cells which develop directly into long-stalked, single-spored sporocarps. Sexual reproduction was not observed. A new order—the PROTOSTELIDA—is proposed for this and related genera, which are believed to comprise a phylogenetically linked series, beginning with the amoebo-flagellate genus Cavostelium and evolving through Schizoplasmodium to Protostelium. The two families Cavostelidae (Cavostelium) and Protostelidae (Schizoplasmodium, Protostelium) are recognized.     

Interactive influences of fire intensity and vertical distribution of seed banks on post‐fire recolonization of a tall‐tussock grassland in Argentina

Abstract Recolonization patterns of a tall‐tussock grassland differ between low‐frequency and high‐intensity fires. A series of laboratory and field experiments were performed on the seed bank and on seeds of the main colonizing species (Carduus acanthoides, Cirsium vulgare, Lotus glaber) to determine and compare the effects of fire frequency and fire intensity on their recolonization potential. Seed‐bank size of colonizing species did not show a significant variation with contrasting fire frequencies, so overall interval‐dependent effects do not seem to affect their propagule pool at the time of fire. However, frequency of fire modified the proportion of viable seeds and their dormancy state according to species. Accumulated emergence from experimentally buried soft‐seeds of Lotus was lower after high‐intensity fires (following wind direction) than after back‐fires (against wind direction), but no significant effects of fire‐front direction on seedling emergence were observed for hard‐seeds of Lotus nor Carduus and Cirsium. Seedling emergence from buried seeds of Cirsium was increased with doubling fuel loads, particularly from deepen soil layers, where Cirsium had most of their viable seeds after a low frequency of fire. Emergence from hard‐seeds of Lotus was less promoted than Cirsium by doubling fuel loads, and according to analysis of excavated seedlings, it was completely inhibited from upper soil layers of the seed bank. Integration of species‐specific and burial depth‐specific responses of Cirsium and Lotus seeds according to fuel load, vertical distribution of the seed banks, seed dormant states and mean emergence depths, resulted in expected emergence values which agree with their previously observed patterns of recolonization. Thus, event‐dependent mechanisms had a better predictive value on recolonization success of the studied species than the observed cumulative effects of fire history on their seed‐bank size.     

NOTOLIMEA CLANDESTINA A NEW SPECIES OF NEOTENOUS BIVALVE (BIVALVIA: LIMIDAE) ENDEMIC TO THE STRAIT OF GIBRALTAR

Notolimea clandestina new species (Bivalvia: Limidae) is describedfrom the littoral of the Strait of Gibraltar. The small size(1 mm) and the persistence of the larval hinge suggest a neotenousspecies. Its area of distribution is likely to be restrictedto the Strait of Gibraltar. (Received 7 July 1993; accepted 2 December 1993)     

Genetic structure and population dynamics of a heteroecious plant pathogen Melampsora larici-epitea in short-rotation coppice willow plantations

Complex life strategies are common among plant pathogens belonging to rust fungi ( Uredinales ). The heteroecious willow rust Melampsora larici-epitea produces five spore stages and alternates on larch ( Larix ). To shed light on the epidemiology of this pathogen, amplified fragment length polymorphisms (AFLPs) were used to determine the genetic diversity and genetic structure of rust samples collected from coppice willow ( Salix ) plantations at three UK sites (LA, CA and MC) over three sampling dates (September 2000, July 2001 and September 2001). Of the total of 819 isolates, 465 were unique AFLP phenotypes and there was a shift in genotype diversity between the two seasons (0.67 in 2000 and 0.87–0.89 in 2001). No phenotypes were common between the two seasons within a site, suggesting that the rust did not overwinter as an asexual stage within plantations. A temporal analysis detected large amounts of genetic drift ( F _S = 0.15–0.26) between the two seasons and very small effective population sizes ( N _e  =  2–3) within sites. These results all point to a new colonization of the plantations by the rust in the second season (2001). The F _ST-analogue values were Φ_CT = 0.121, Weir and Cockerham's θ = 0.086 and the Bayesian estimate θ^B = 0.087–0.096. The results suggest that the sources of inoculum were somewhat localized and the same sources were mainly responsible for disease epidemics in LA and CA over the two seasons. The relatively low F _ST-values among sites (0.055–0.13) suggest the existence of significant gene flow among the three sampled sites.     

Comparison Between the Effect of the Fruit and of Exogenous GA3-Applications on Source-Sink Relationships in Citrus Sprouts

Inflorescence leaves of citrus (Citrus sinensis L. Osbeck) accumulatecarbohydrate reserves at the beginning of the fruit set period.This effect is mimicked by exogenous GA₃ applications in deflorateinflorescences. The effect of the hormone on two processes thatcould result in carbohydrate accumulation, i.e. increased ribulosebisphosphate carboxylase (RuBPCase) activity and changes inthe import/export balance of assimilates in the sprouts, wasstudied. Neither RuBPCase activity nor respiration rates were affectedby the hormonal treatment. On the other hand, blocking of thephloem connections with the rest of the plant induced an increasein carbohydrate contents in the leaves that was proportionallylower in GA₃-treated sprouts than in control deflorate inflorescences.This increase was minimal in leaves from inflorescences at laterstages of fruit development. This was in spite of a lower fruitgrowth rate that, in turn, brought about a decrease in totaldry weight of the sprout. In contrast, total dry weight washigher in girdled deflorate inflorescences, whether or not theywere treated with the hormone. The presence of the fruit induceda thickening of the stems of intact inflorescences that wasalso seen in ungirdled GA₂-treated sprouts. This increase indry weight per unit length, however, had a different chemicalbasis depending upon whether it was caused by the fruit or thehormone. From these data, the possible causes for the enhancement ofcarbohydrate accumulation in inflorescence leaves, and the involvementof gibberellin in the effect of fruit on the sprouts is discussed. Carbohydrates, Citrus sinensis L. Osbeck, gibberellic acid, girdling, orange, ribulose bisphosphate carboxylase, source-sink     

Survival of caddis larvae in relation to their case material in a group of temporary and permanent pools

1. The occurrence of larvae of Limnephilus coenosus and L. vittatus (Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species. Limnephilus coenosus larvae were present in a higher proportion of pools that later dried out than in the permanent ones, while L. vittatus larvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.
2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full-grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought-resistant case material and a higher survival ability of the larvae themselves.
3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high-quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.
4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water-retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools.