Sex allocation in the solitary bee Osmia cornuta: do females behave in agreement with Fisher's theory?

Fisher's theory of sex allocation predicts that, in a panmictic population, parental investment will be equally distributed between male and female progeny. Most studies on parental investment in nesting solitary bees and wasps use offspring or provision weight as estimators of parental investment and do not corroborate Fisher's theory. The measurement of parental investment may be confounded by several factors. First, the use of offspring or provision size does not account for seasonal variation in foraging costs associated with aging of nesting females. Second, provision or offspring size do not reflect parental investment associated with nest construction. In this two-year study we measured parental investment in a solitary bee. We calculated sex allocation using both provision weight and foraging time as parental investment estimators. Investment in pollen-nectar provisions decreased, while investment in mud structures (nest construction) increased, as the nesting period progressed. Overall investment in provisions per nest was ∼25 times higher than investment in mud. Pollen-nectar foraging trips became longer as the season progressed, but mud trip duration did not vary. Due to weather differences between years, more offspring per female were produced in the first year, but progeny sex ratio and mean offspring size of both sexes were similar between years. Mortality did not differ between sexes. As predicted by Fisher's theory, production cost ratios did not differ from 1 in either year, irrespective of the currency used to estimate parental investment (provision weight or foraging time). Our results strongly support Fisher's theory.     

Genetic population structure and sociogenetic organisation in Formica truncorum (Hymenoptera; Formicidae)

Summary The genetic population structure and the sociogenetic organization of the red wood ant Formica truncorum were compared in two populations with monogynous colonies and two populations with polygynous colonies. The genetic population structure was analysed by measuring allele frequency differences among local subsets of the main study populations. The analysis of sociogenetic organisation included estimates of nestmate queen and nestmate worker relatedness, effective number of queens, effective number of matings per queen, relatedness among male mates of nestmate queens and relatedness between queens and their male mates. The monogynous populations showed no differentiation between subpopulations, whereas there were significant allele frequency differences among the subpopulations in the polygynous population. Workers, queens and males showed the same genetical population structure. The relatedness among nestmate workers and among nestmate queens was identical in the polygynous societies. In three of the four populations there was a significant heterozygote excess among queens. The queens were related to their male mates in the polygynous population analysed, but not in the monogynous ones. The data suggest limited dispersal and partial intranidal mating in the populations with polygynous colonies and outbreeding in the populations having monogynous colonies. Polyandry was common in both population types; about 50% of the females had mated at least twice. The males contributed unequally to the progeny, one male fathering on average 75% of the offspring with double mating and 45–80% with three or more matings. Correspondence to: L. Sundström     

Attraction,deterrence or intoxication of bees (Apis mellifera) by plant allelochemicals

The influence of 63 dietary allelochemicals (alkaloids, terpenes, glycosides,etc.) on the feeding behaviour of bees (Apis mellifera) was tested in terms of deterrency and attraction. For 39 compounds a deterrent (mostly alkaloids, coumarins and saponins) and for 3 compounds an attractive response (mostly terpenes) was obtained in choice tests, which allowed the calculation of respective ED₅₀-values. Under no-choice conditions, 17 out of 29 allelochemicals caused mortality at concentrations between 0.003 and 0.6%. Especially toxic were alkaloids, saponins, cardiac glycosides and cyanogenic glycosides. These data show that bees which are confronted with plant allelochemicals in nectar and pollen, are not especially adapted (i.e. insensitive) to the plants' defence chemistry. GLC and GLS-MS data are given on the alkaloid composition of nectar and pollen ofBrugmansia aurea, Atropa belladonna andLupinus polyphyllus.     

Labial gland marking secretion in males of two Scandinavian cuckoo bumblebee species (genusPsithyrus)

Summary Chemical components of the cephalic labial gland secretion, which most likely is used as a precopulatory attracting signal, were identified in males of the cuckoo bumblebeesPsithyrus vestalis (Geoffroy) andP. bohemicus (Seidl.) by gas chromatography-mass spectrometry (GC-MS). The former species has geranylcitronellyl acetate as main component, plus in decreasing amounts geranylcitronellol, an eicosadienal, an eicosenol, and an eicosenal. Another 17 fatty acid derivatives are present in minor amounts. The labial secretion ofP. vestalis differs distinctly in its chemistry from that of all of the 8 other ScandinavianPsithyrus species. In the taxonomically closely related (same subgenus)P. bohemicus, the labial gland secretion contains 16 fatty acid derivatives, of which 12 (75%) are present also in the secretion ofP. vestalis. Thus, both the labial gland secretions, and morphological traits lend support to the hypothesis that the two species share a common ancestor. The reproductive isolation between them is, at least in part, supported by the inclusion of a second biosynthetical pathway (the mevalonic acid pathway producing terpenoids) inP. vestalis, in addition to the pathway common to both species (the polyketide pathway producing fatty acid derivatives).     

The poison gland of the antMyrmicaria eumenoides and its role in recruitment communication

Summary The antMyrmicaria eumenoides is a significant arthropod predator. For rapid attraction of large numbers of nestmates to newly discovered food sources the ants use an efficient recruitment communication system based on the poison gland secretion. Workers exhibit age-based division of labour. Young workers perform brood-care; their poison gland reservoir develops and reaches its final size of 0.5 µl at an age of 6 weeks, when they become foragers. The secretion deposited during combat with enemies or prey is composed of equal amounts of both a high volatile and a low volatile fraction. Within the high volatile fraction (+)—limonene is the main component (97%) and is the only olfactory trigger to alert ants in the vicinity and to recruit them to places of combat, where they assemble. Ants respond to synthetic (+)—limonene in exactly the same way as to the poison gland secretion when applied at the same airborne concentrations. Further components of the high volatile fraction are four additional monoterpene hydrocarbons and hexanoic nitrile. The high volatile and the low volatile fraction of the poison gland secretion each have dual functions: The low volatiles, of which the main component is an alkaloid, serve as a fixative and extend the effective period of the limonene signal by modifying its evaporation kinetics. On the other hand the high volatile recruitment signal (+)—limonene is also the solvent for the alkaloid and enhances its spreading on the surface of the cuticle of arthropod enemies or prey.     

Social influence on the correlation between behaviours in young-of-the-year perch

The connection between risk-taking behaviour and exploratory behaviour in young-of-the-year perch (Perca fluviatilis) was studied in aquarium experiments to see whether individual behaviour patterns could be identified in this species and also to investigate how individual behaviour is influenced by their social environment. Risk-taking was defined as the time spent foraging in an open area vs hiding in the vegetation in the presence of a piscivore. Explorative behaviour was measured as latency to enter a passage leading to an unknown area. Groups of four fish were used for the observations, and both behaviours measured were positively correlated with the mean scores of these behaviours in the other group members. Risk-taking and explorative behaviours were correlated only when data was adjusted for the behaviour of the other group members. Individuals that spent more time in the open than their companions also tended to be faster than the others to enter the passage to the unknown area and vice versa. The results indicate that there are consistent individual differences in boldness in perch, but also that behaviour could be modified according to the behaviour of group members.     

Microgeographic heterogeneity in spatial distribution and mtDNA variability of gray mouse lemurs (<Emphasis Type="Italic">Microcebus murinus</Emphasis>, Primates: Cheirogaleidae)

The objective of our study was to investigate the spatial distribution and genetic structure of a solitary primate at the microgeographical scale of adjacent local populations. We obtained spatial data and tissue samples for mtDNA analysis from 205 gray mouse lemurs (Microcebus murinus) captured along transects and within 3 grid systems within a 12.3 km² area in Kirindy Forest, western Madagascar. Our capture data revealed that, even though the forest was continuous, gray mouse lemurs were not evenly distributed, and that daily and maximum dispersal distances were significantly greater in males. The frequency distribution of 22 mtDNA D-loop haplotypes was highly skewed. Nine haplotypes were unique to males, indicating male-mediated gene flow from surrounding areas. The geographic distribution of haplotypes revealed that males were also more dispersed than females. Females with the same haplotype showed a tendency towards spatial aggregation, and the correlation between genetic and geographic distances was higher in females. In several areas of the forest, however, spatially clustered females were not of the same haplotype, and females were not always found in clusters. Hence, in contrast to suggestions from previous studies, matrilineal clustering is not the only way females are socially organized. In addition, our study revealed heterogeneity and patterns in population structure that were not evident at smaller spatial scales, some of which may be relevant for designing conservation strategies.Communicated by C. Nunn     

On the sustainability of common property resources

We provide a model where a common property resource is managed by two types of agents, cooperators and non-cooperators, who adjust their extraction strategies in response to persistent differential payoffs. In our model, the social approval of cooperators works as a reward mechanism which, as we show, favors both the pervasiveness of cooperative behavior and the sustainable management of natural resources. Specifically, we show that in the presence of such a reward mechanism a stable equilibrium can be reached with both strategies being practiced simultaneously and a decentralized and sustainable management of common property resources is possible.     

The iridoid glycoside,catalpol, as a deterrent to the predatorCamponotus floridanus (Formicidae)

Summary We investigated the role of the iridoid glycoside, catalpol, as a deterrent to the predator,Camponotus floridanus. Four laboratory colonies of this ant were offered buckeye caterpillars (Junonia coenia: Nymphalidae) raised on diets with and without catalpol. The same colonies were offered sugar-water solutions containing varying concentrations of catalpol, in both no-choice and choice tests. Regardless of diet, buckeye caterpillars appeared to be morphologically protected from predation by the ants, possibly because of their large spines or tough cuticle. However, buckeyes raised on diets with catalpol had high concentrations of catalpol in their hemolymph; extracts of this high-catalpol hemolymph proved to be an effective deterrent to the ants. When starved ants were not given the choice of food items, they were more likely to consume sucrose solutions that contained 5 mg catalpol/ml or 10 mg catalpol/ml than they were to consume solutions with 20 mg catalpol/ml. When they were given a choice of sugar solution or a sugar solution containing catalpol, the ants avoided solutions with catalpol at any of these concentrations. Ant colony responses to catalpol in sucrose solutions varied considerably over time and among colonies.     

Form-specific fragances fromOphrys insectifera L. (Orchidaceae) attract species of different pollinator genera. Evidence of sympatric speciation?

Two closely related forms ofOphrys insectifera were observed in the field to attract different pollinator species selectively.O. i. ssp.insectifera attracted males of two species ofArgogorytes (Sphecidae, Hymenoptera Aculeata) andO. i. ssp.aymoninii attractedAndrena combinata males (Andrenidae, Apoidea, Hymenoptera Aculeata). A third form,O. aff.i. ssp.insectifera, attracted none of these three species. Volatile compounds from flowers and inflorescences of the three forms (originating from Öland, Sweden, and Aveyron, France) were collected, using entrainment, enfleurage, and solvent extraction techniques, and identified by gas chromatography — mass spectrometry. Scent differences between the three forms were confirmed in the amounts of aliphatic hydrocarbons (C₁₁–C₁₉), methyl esters (C₁₄–C₁₈), short chain aliphatic 1-alcohols (C₆–C₁₂), and monoterpene alcohols (C₁₀).