Reliability theory and foraging by ants

Reliability theory is used to explore the consequences of ant colony's foraging techniques for the evolution of individual competence. Five fundamental strategies are outlined according to Oster & Wilson (1978) and corresponding probabilities of food being returned to the nest are derived. The strategies differ in redundancy schemes and levels of worker reliability. Colony-level selection produces workers of imperfect competence. System reliability can be very high even when the workers are inept, if the foraging strategy is complex and redundant. Individual competence of foragers in a colony depends on diet breadth, caste polymorphism, and tempo. The implications of each variable for colony survival are discussed.     

Colony structure of a slavemaking ant. II. Frequency of slave raids and impact on the host population

The parasite pressure exerted by the slavemaker ant Protomognathus americanus on its host species Leptothorax longispinosus was analyzed demographically and genetically. The origin of slaves found in colonies of the obligate slavemaker was examined with nuclear and mitochondrial DNA markers to make inferences about the frequency and severity of slave raids. Relatedness of enslaved L. longispinosus workers in the same nest was very low, and our data suggest that, on average, each slavemaker nest raids six host colonies per season. Therefore, the influence of slavemaker species on their hosts is much stronger than simple numerical ratios suggest. We also found that slave relatedness was higher in small than in large slavemaker nests; thus, larger nests wield a much stronger influence on the host. We estimated that in the study population, on average, a host nest has a 50% chance of being attacked by a slavemaker colony per year. Free-living Leptothorax colonies in the vicinity of slavemaker nests did not represent the source of slaves working in P. americanus colonies, which suggests that raided nests either do not survive or migrate after being raided. Colony composition and intranest relatedness of free-living L. longispinosus colonies differed markedly between areas with slavemakers and those that are parasite-free. In the presence of slavemakers, host colonies were less likely to be polygynous and had fewer workers and a higher relatedness among worker brood. Host nests with slavemaker neighbors allocated more resources into sexuals, possibly caused by these shifts in nest demography. Finally, enslaved Leptothorax workers in P. americanus nests appeared to be less efficient than their counterparts in free-living colonies. Thus, slavemakers exert a much stronger impact on their hosts than had previously been suspected and represent an unique system to study parasite-host coevolution.     

High-level production of the non-cariogenic sucrose isomer palatinose in transgenic tobacco plants strongly impairs development

Palatinose (isomaltulose, 6-O-alpha-D-glucopyranosyl-D-fructose) is a structural isomer of sucrose which is produced from sucrose by some bacterial strains as a reserve material during periods of low carbon availability. The ability to synthesise palatinose is not only advantageous for the bacteria but is also of industrial interest since palatinose is used as a sucrose substitute in food production. To explore the possibility of palatinose production in plants a recently isolated sucrose isomerase gene (palI; EC 5.4.99.11) from Erwinia rhapontici [F. B?rnke et al. (2001) J Bacteriol 183: 2425-2430] was cloned into a plant expression vector between the constitutive 35S CaMV promoter and the octopine synthase polyadenylation signal. To allow secretion of the protein into the apoplast the signal peptide of the potato proteinase inhibitor II was N-terminally fused to the pall coding region. Expression of the protein was verified by northern and western blot analyses. Efficient secretion of the protein was demonstrated by palI detection in intercellular fluids. Transgenic plants expressing palI accumulated high levels of palatinose. As a consequence, transgenic plants showed severe phenotypic alterations. Young leaves were curled and developed bleached areas during maturation. Flowers were misshapen and sterile. Based on nonaqueous fractionation experiments palatinose was found in several subcellular compartments, indicating limited membrane transport of the sugar. In contrast to results obtained with short-term feeding experiments, no evidence for palatinose-mediated regulation of photosynthetic or defence genes could be obtained in the transgenic palI-expressing tobacco plants. Based on our results we conclude that plants can efficiently be used as bioreactors for the production of palatinose. Furthermore, tissue-specific expression of palI should allow carbon allocation to specific tissues and/or cell-types to be modulated.     

Molecular determinants of sink strength

The manipulation of sink to source relations has been subject to extensive plant breeding programs aiming to improve harvest index and thereby crop yield. The introduction of molecular and biochemical tools has enabled scientists to investigate the underlying principles. This has opened up the fascinating possibility of identifying molecular determinants of sink strength and to further increase yield on a rational basis. In the past, transgenic plants with alterations in the activity of only one putative molecular determinant have been created and this strategy has not resulted in substantial and reliable increases in yield. Yet, careful molecular and biochemical investigations have provided valuable insight about carbon flux into different metabolic pathways at different stages of sink development and it has become apparent that this metabolic channelling needs to be exploited by using stage- and cell-specific promoters in attempts to increase sink strength.     

Population genetics of the socially polymorphic ant <Emphasis Type="Italic">Formica podzolica</Emphasis>

Summary. We used microsatellite markers to analyze the hierarchical genetic structure of the North American mound building ant, Formica podzolica. About one-third of all colonies were headed by a single queen (monogynous) whose effective mating frequency was close to one (nestmate worker relatedness r = 0.70), while the remaining colonies were polygynous, with low average nestmate relatedness (r = 0.16). The low worker relatedness found in most polygynous colonies furthermore suggested that the numbers of queens in polygynous colonies of this ant are usually high. Contrary to what has been described from other ants with a queen number dichotomy, we did not find an effect of social form variation on the partitioning of genetic variation above the level of the colony. We found no significant differentiation between the sympatric social forms of F. podzolica, nor did differentiation among populations appear to be affected by colony social organization. These unexpected patterns of genetic structure may have resulted from differences either in the spatial distribution of the social forms or in their social flexibility.Received 12 January 2004; revised 23 February 2004; accepted 10 March 2004.     

Change in movement and subdivision of Myrmica punctiventris (Hymenoptera, Formicidae) colonies in north temperate forests is related to a long-term shift in social organization

We assessed temporal and spatial patterns of nest site use in the cavity dwelling ant, Myrmica punctiventris in a well-studied temperate forest site in central New York State. We evaluated changes in nest site use by repeatedly censusing the ants inhabiting artificial nests (hollow dowels) for three consecutive growing seasons. We confirm a shift towards more polydomy in this population of M. punctiventris, first reported by DeHeer et al. (2001), but extend these findings by demonstrating that this shift has occurred gradually over several years. We are unable to determine if this polydomy is seasonal or year round. We explore various explanations for the occurrence of polydomy and suggest that long-term changes in sex allocation are indirectly driving the shift in nesting strategies. Received 15 July 2004; revised 11 April and 19 October 2005; accepted 25 October.     

Technical enzymes produced in transgenic plants

Technical enzymes are used in many industrial applications. Nowadays technical enzymes are often produced in transgenic host organisms. The use of transgenic plants with respect to high level of expression at low costs as a prerequisite for successful commercial production of technical enzymes is discussed. This review summarises recently published examples for production of technical enzymes in plants. In addition, plastid transformation and viral vectors are discussed as methods which might be useful for obtaining high expression level of recombinant proteins in plants.     

COMPLEX COLONY STRUCTURE IN SOCIAL INSECTS: I. ECOLOGICAL DETERMINANTS AND GENETIC CONSEQUENCES

For social insect species, intraspecific variation in colony social structure provides an opportunity to relate the evolution of social behavior to ecological factors. The species Myrmica punctiventris is a cavity-dwelling forest ant that exhibits very different colony structures in two populations in the northeastern United States. Combined data from seasonal censuses, allozyme electrophoresis, and worker hostility tests showed that a population of M. punctiventris in Vermont was strictly monogynous and seasonally polydomous. The same procedures showed that a population of M. punctiventris in New York was facultatively polygynous and predominantly monodomous. Genetic relatedness among colony-mates was not different from Hamilton's expected values in the Vermont population and was consistent with little exchange of ants between colonies and single-mating of queens. In contrast, relatedness was lower in New York, and examination of nest-mate genotypes revealed exchange of ants between colonies, high rates of colony loss and replacement of queens, or multiple-mating of queens. The genetic structure of the Vermont population was consistent with no inbreeding, but in New York, the population genetic structure reflected microgeographic subdivision and inbreeding. Previous study of the ant communities at these sites implicates nest-site limitation in New York as a primary constraint on social structure.