Population biology of figs: Applications for conservation

Summary The flowering phenology typical of at least monoecious figs-intra-tree synchrony and inter-tree asynchrony-poses problems for persistence of the pollinator population, and hence of the fig population itself, when fig population size is small. Establishment and maintenance of a population of the short-lived, species-specific wasp pollinator require that the fig population include a critical minimum number of trees (critical population size: CPS). Below CPS, temporal gaps between flowering trees occur that are unbridgeable by the pollinator, leading to its local extinction. This has implications for conservation in two contexts: human-aided invasions of introduced fig/wasp pairs, in which initial populations of figs and/or wasps may be small, and the persistence of figs and wasps in fragmented forest, in which initially large populations may be drastically reduced. Long-distance range extension by fig/wasp pairs is problematical for two reasons: 1) the fig species must first attain CPS, most likely through repeated seed dispersal events, before the wasp can establish; and 2) long-distance transit should be difficult for the tiny, short-lived wasp pollinators. I review the biology of natural and human-aided range extension by figs and fig wasps, and show that in human-aided range extensions these two difficult steps are circumvented. Once introduced into an area where hosts are abundant, fig wasps should readily establish from a small number of initial colonists, since they mate before dispersal and are highly tolerant of inbreeding. They are thus less subject than many insects to the genetic and demographic hazards of small population size. Of 5–6 fig/wasp pairs that have performed human-aided long-distance range extensions, one Asian pair,Ficus microcarpa and its pollinatorParapristina verticillata, is established in numerous areas in the northern neotropics, and the plant may become a serious weed. In tropical forests, figs may provide keystone resources for frugivores, providing fruit during seasons when other resources are scarce. Figs pose difficult problems for conservation biology, since minimum viable populations appear to be large, and since many species of tropical rainforests occur at low densities. This means that minimum areas required for persistence of a fig population- and for those of other species that would be affected were figs to be removed from the system-may often be large.     

Seasonality in the reproductive phenology ofFicus: Its evolution and consequences

Summary Ficus can only reproduce if they are pollinated by mutualistic wasps that breed within the figs. Pollen-loaded wasps enter the figs when the female flowers are receptive. Several weeks later, their offspring load pollen within the fig and then emerge. As individual trees typically produce crops of synchronous figs at long intervals, the shortlived wasps have to move to another, receptive, tree. The wasp population can only survive, and hence the fig population reproduce, if there are trees fruiting all over the year. When only few trees are present within a population gaps in the flowering sequence may lead to the extinction of the local pollinator population. Two models are presented. One investigates the number of trees necessary in order to sustain a local pollinator population when the tree population has a seasonal pattern of fruiting. The second model investigates how such a seasonal pattern may evolve within a fig population as a result of individual selection on the trees. It is shown that pollinator populations are fragilized under seasonal conditions. Hence, the breeding system ofFicus limits their expansion into highly seasonal habitats. Seasonal habitats may also lead to seasonal adjustment of male versus female investments and to the evolution of dioecy.     

Zur Nahrungsaufnahme vonMegoura viciae Buckt., einer phloemsaugenden Aphide (Homoptera,Rhynchota)

Summary Problems connected with the food uptake of the aphidMegoura viciae Buckt., sucking in the phloem ofVicia faba, are studied by means of radioactive phosphate.Outside the phloem there is no intake of food by the stylets of the aphid. They are able to reach the phloem earliest 7 min after the beginning of the puncture. But only 3 h later all aphids have reached the phloem. The variability in time taken to reach the phloem is very high. The aphids seem not to be able to aim at the phloem, presumable this process is more or less incidentally. In plants, which do not belong to the host plants ofMegoura viciae, the aphid also pierces the phloem. Perhaps the aphids first in the phloem find out their host plant. The course of the ingestion of food is studied in relation to the time of sucking and shown in a diagram.     

Odour preference of a parasitic wasp depends on order of learning

FemaleLeptopilina boulardi wasps, larval parasites ofDrosophila melanogaster, can learn to respond to more than one odour by associating these odours with oviposition experience. These wasps can memorise and respond to at least two different odours, and prefer the last one learnt.     

Structure and function of the fig

Summary An overview is given of the functional anatomy of the fig. The fig is the site of pollination and oviposition, it produces wasps, seeds and pollen, and it is the unit of dispersal. Therefore the fig acts as both a flower and a fruit. When a flower is both fertilized and receives a wasp egg, it eventually produces a wasp. Fertilization in flowers that do not recieve a wasp egg initiates seed production. Wide variation exists in the structural features of figs among different subgenera and sections. Monoecious species and gynodioecious species have different strategies for maintaining the symbiosis with the pollinating fig wasps. Monoecious species produce wasps and seeds in a single fig type and show imperfect heterostyly. Gynodioecious species have specialized figs for wasp and for seed production and are characterized by perfect heterostyly.     

Host-plant oligosaccharins in the honeydew ofSchizaphis graminum (Rondani) (Insecta,Aphididae)

Summary The honeydew of the aphidSchizaphis graminum (Rondani) contains hetero-oligosaccharides (mol. wt>2200 D) having neutral sugar and uronic acid compositions similar to the pectic substances of the host plant,Sorghum biocolor (L.) Moench. These oligosaccharides are pectic fragments which result from the depolymerization of pectic substances in the phloem by aphid salivary polysaccharases.     

A peculiar fatty acid, (Z,Z)-9,12,17-octadecatrienoic acid,identified in the phospholipids of the pea aphid,Acyrthosiphon pisum (Harris) (homoptera: aphididae)

A peculiar fatty acid previously detected in the phospholipids of the pea aphid,Acyrthosiphon pisum, is identified as (Z,Z)-9,12,17-octadecatrienoic acid. It is the first report of this compound in the literature. Comparison of fatty acid profiles of phospholipids between normal and aposymbiotic pea aphids shows that aphid symbionts are not responsible for the biosynthesis of this unusual fatty acid.     

Classification and distribution ofFicus

Summary The classification of the genusFicus has changed considerably in the course of time and is still the subject of further research and discussion. The main subdivisions in the most recent classification by Corner¹² are presented together with the genera of pollinating fig wasps (Agaonidae) associated with them. These subdivisions are discussed and grouped according to morphological and functional traits, in particular in connection with the unique pollination system. Two main groups are recognized: one with only monoecious species and the other with predominantly (gyno)dioecious species. The former comprises two subgroups (Pharmacosycea andUrostigma) and the latter three, more profoundly different subgroups (Ficus, Sycidium andSycomorus). The neotropical representatives of the genus are discussed in somewhat more detail. In addition, the distribution of the genus is summarized for the three main regions of distribution; Africa, America, and Asia-Australasia. Finally the concordance between subdivisions ofFicus and those of the Agaonidae is briefly discussed.     

Genomic revelations of a mutualism: the pea aphid and its obligate bacterial symbiont

The symbiosis of the pea aphid Acyrthosphion pisum with the bacterium Buchnera aphidicola APS represents the best-studied insect obligate symbiosis. Here we present a refined picture of this symbiosis by linking pre-genomic observations to new genomic data that includes the complete genomes of the eukaryotic and prokaryotic symbiotic partners. In doing so, we address four issues central to understanding the patterns and processes operating at the A. pisum/Buchnera APS interface. These four issues include: (1) lateral gene transfer, (2) host immunity, (3) symbiotic metabolism, and (4) regulation.     

Starfish encounters: An experimental study of its advantages

Summary The predatory starfishCrossaster papposus exploits a chemically mediated escape response in another predatory starfishAsteria rubens when a common food resource is available to both species. Intraspecific avoidance amongC. papposus is strong and functions in dispersal. Responses to inter- and intraspecific encounters among starfish may be important to the predatory ecology of species in high positions in their food webs.I thank the MAFF. Fisheries Lab., Burnham-on-Crouch for hospitality and facilities, Prof. N.B. Marshall, F.R.S. and Dr A.C. Campbell for laboratory facilities at Q.M.C.     

Response to one point in Gingras’s review of Gravity’s shadow

Yves Gingras says of my book Gravity’s shadow that it is too long, the style is poor, and in its 870 pages there is nothing new that is not to be regretted. Gingras’s purity of vision would be a cause for congratulation were it not for the appalling implications of one of his claims. For the sake of the future of social science—indeed for the sake of the future of civilisation—it is impossible to leave unchallenged the idea that respondents, who don’t like to see their use of data questioned, are to be commended when they withhold those data from public scrutiny.     

Nachweis einer durch symbiontische Mikroorganismen bewirkten Sterinsynthese in künstlich ernährten Aphiden (Homoptera,Rhynchota, Insecta)

Summary Up to now the aphid,Neomyzus circumflexus Bckt., has been reared on a synthetic, sterile diet for 11 successive generations. The culture is still going. The defined diet contains no sterol or any other lipid. Nevertheless the sterol content of the artificially fed aphids remains constant over 8 generations. Ingestion of sodium acetate-1-C¹⁴ with the diet by the aphids leads to the appearance of a labelled sterol in the tissues of the insects. Incorporation of radioactivity into sterols was not found in aphids free of symbionts.     

The isolation,identification and synthesis of the alarm pheromone ofVespula squamosa (Drury) (Hymenoptera: Vespidae) and associated behavior

Summary A material that elicits alarm and attack behavior byVespula squamosa (Drury) workers was isolated from venom extracts and identified by spectroscopic methods as N-3-methylbutylacetamide. This compound elicited attack responses from worker wasps identical to those responses observed when venom was applied at the same dosage. This is the first behavioral role reported for this compound.The authors thank E. Adamak, R. Murphy and F. Takken for technical assistance. This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or the recommendation for its use by USDA.     

The largest known chromosome number for a mammal,in a South American desert rodent

Summary Tympanoctomys barrerae, a desert specialist member of the family Octodontidae, until now thought to be conservative, and ancestral to South American hystricognath rodents, presents the highest diploid chromosome number (2n=102) known in a mammal. Unexpectedly, its karyotype was found to be composed mainly of metacentric to sub-metacentric chromosomes. Mechanisms by which such a karyotype may have been derived are discussed.     

Protein level in the haemolymph of the waspPolistes gallicus L. at the beginning of imaginal life and during overwintering. Action of the strepsiterian parasiteXenos vesparum rossi

Summary During the imaginal life of malePolistes wasps, the protein concentration in the haemolymph remained constant. In females, there were 2 groups; one in which this concentration was also stable and another in which it increased. No difference was detected between the haemolymphatic protein level of stylopized males and normal ones. All parasitized females exhibited low haemolymph protein levels similar to those of the low level group.     

Geranyl acetate and 2-decen-1-ol in the cephalic secretion of the solitary waspSceliphron caementarium (Sphecidae; Hymenoptera)

Summary The cephalic secretion ofSceliphron caementarium contains a mixture of geranyl acetate and 2-decen-1-ol; the latter has not been described previously in arthropod secretions. The secretion is orally emitted when the wasps are handled, and may serve in defense or alternatively as an aid in roosting aggregation.Acknowledgment. We thank A. S. Menke and D. Vincent, Insect Identification and Beneficial Insect Introduction Institute, SEA, USDA, for taxonomic identification. We also thank Bedoukian Research, Inc., for kindly sending us samples of 2-decen-1-ol and decenyl acetate.     

Chemical and tactile communication between the root aphid parasitoidParalipsis enervis and trophobiotic ants: consequences for parasitoid survival

Females of the aphid parasitoidParalipsis enervis received liquid food by regurgitation (trophallaxis) from workers of the ant speciesLasius niger, but were not fed by workers ofMyrmica laevinodis andTetramorium caespitum. WhileP. enervis was not treated aggressively by workers of any of these species,Lasius flavus workers killed the parasitoid. This different ant behaviour resulted in a different parasitoid longevity. WhileP. enervis survived for only 10 min in the presence ofL. flavus (due to ant aggression) or for approximately one day in the presence ofT. caespitum andM. laevinodis (due to lack of trophallaxis), survival increased significantly to more than five days in the presence ofL. niger, which provided food regularly to the parasitoids. Our study suggests thatP. enervis mimics behavioural signals ofL. niger, as well as odor cues of its host aphidAnoecia corni, to avoid aggression byL. niger.     

Phenological studies of selected savanna mosses of south-western Nigeria

It was established that there is little diversity of bryophytes in the derived savanna. Mosses were found in the sampling sites, whereas liverworts were rarely observed. The reproductive methods of four dominant sexually reproducing savanna mosses —Archidium ohioense, Bryum coronatum, Fissidens minutifolius andTrachycarpidium tisserantii were monitored over two consecutive rainy seasons. Protonemal and gametophyte production were noticed in the field in March/April, and capsule dehiscence and spore dispersal occurred in September/October. The sequential stages of development, starting with gametangial production and ending with the falling of the dehisced capsules, occurred within the rainy season. However,A. ohioense andT. tisserantii did not discharge their spores easily (cleistocarpous), unlike the stegocarpous speciesB. coronatum andF. minutifolius. Water availability and possibly high humidity may have contributed to growth. The short period between sex organ formation and dehiscence of capsule seen in these studies, compared with the longer period in some temperate mosses, may be an advantage for bryophytes in a savanna environment.     

Natural and experimental interspecific hybridization between populations ofDolichopoda cave crickets

Summary Evidence of hybridization between 2 pairs of allopatricDolichopoda species is provided by electrophoretic analysis. Occurrence of hybrids was revealed by laboratory crosses and in nature both by occasional co-existence due to passive dispersal and by transplantation experiments.This research was supported by the National Research Council, Italy, grant No. 78.01441.04, and by funds of the Faculty of Sciences, University of Rome. Acknowledgments are due to Drs G. Carchini, M. Rampini and G. Sammuri for substantial help in collecting in caves and to Professor B. Baccetti for SEL micrographs.     

Elektronenmikroskopische Untersuchung der phäochromen (chromaffinen) Granula in den Markzellen der Nebenniere

Summary The catechol-containing granules in the adrenal medullary cells (mouse, guinea pig, cat) are true cell organells, clearly distinguished from mitochondria; their size varies over a fairly wide range, the mean diameter being calculated at about 175 mµ in the mouse (osmium-tetroxide-fixation). They have a surrounding membrane of 100 Å thickness; their internal structure is finely granular. On the thin sections, many granules are surrounded by spaces which appear empty under the electron microscope and which are limited by double-membranes; it is most likely thatintra vitam these spaces contain lipids.

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Ausgeführt mit Unterstützung der Friedrich-Baur-Stiftung und der Deutschen Forschungsgemeinschaft.