Networks and dominance hierarchies: does interspecific aggression explain flower partitioning among stingless bees?

1. The distribution of consumers among resources (trophic interaction network) may be shaped by asymmetric competition. Dominance hierarchy models predict that asymmetric interference competition leads to a domination of high quality resources by hierarchically superior species. 2. In order to determine the competitive dominance hierarchy and its effect on flower partitioning in a local stingless bee community in Borneo, interspecific aggressions were tested among eight species in arena experiments. 3. All species tested were strongly mutually aggressive in the arena, and the observed interactions were often lethal for one or both opponents. Aggression significantly increased with body size differences between fighting pairs and was asymmetric: larger aggressors were superior over smaller species. Additional aggression tests involved dummies with surface extracts, and results suggest that species‐ and colony‐specific surface profiles are important in triggering the aggressive behaviour. 4. Sixteen stingless bee species were observed foraging on 41 species of flowering plants. The resulting bee–flower interaction network showed a high degree of generalisation (network‐level specialisation H₂’ = 0.11), corresponding to a random, opportunistic distribution of bee species among available flower species. 5. Aggressions on flowers were rare and only occurred at a low level. The dominance hierarchy obtained in the arena experiments did not correlate significantly with plant quality, estimated as the number of flowers per plant or as total bee visitation rate. 6. Our findings suggest that asymmetries in interference competition do not necessarily translate into actual resource partitioning in the context of complex interacting communities.     

Are there geniuses among the apes?

We are often asked whether some apes are smarter than others. Here we used two individual-based datasets on cognitive abilities to answer this question and to elucidate the structure of individual differences. We identified some individuals who consistently scored well across multiple tasks, and even one individual who could be classified as exceptional when compared with her conspecifics. However, we found no general intelligence factor. Instead, we detected some clusters of certain abilities, including inferences, learning and perhaps a tool-use and quantities cluster. Thus, apes in general and chimpanzees in particular present a pattern characterized by the existence of some smart animals but no evidence of a general intelligence factor. This conclusion contrasts with previous studies that have found evidence of a g factor in primates. However, those studies have used group-based as opposed to the individual-based data used here, which means that the two sets of analyses are not directly comparable. We advocate an approach based on testing multiple individuals (of multiple species) on multiple tasks that capture cognitive, motivational and temperament factors affecting performance. One of the advantages of this approach is that it may contribute to reconcile the general and domain-specific views on primate intelligence.     

Are orientation mechanisms among migratory birds speciesospecific?

The mechanisms by which migratory birds find their way from breeding grounds to winter quarters and back have been the subject of intensive research during the past four decades. Birds are equipped with genetic information about the migratory direction, and they can use the earth's magnetic field, star patterns and the sun and/or skylight polarization patterns as compass references. Studies on a number of North American and European species have suggested possible species-specific differences in the relative role of the compass mechanisms. This may be largely the result of divergent experimental designs, which make results difficult to compare. Comparative studies with identical methods are needed to see how much species-specific variation exists in basic orientation mechanisms.     

Are predicted structures good enough to preserve functional sites?

BACKGROUND: A principal goal of structure prediction is the elucidation of function. We have studied the ability of computed models to preserve the microenvironments of functional sites. In particular, 653 model structures of a calcium-binding protein (generated using an ab initio folding protocol) were analyzed, and the degree to which calcium-binding sites were recognizable was assessed. RESULTS: While some model structures preserve the calcium-binding microenvironments, many others, including some with low root mean square deviations (rmsds) from the crystal structure of the native protein, do not. There is a very weak correlation between the overall rmsd of a structure and the preservation of calcium-binding sites. Only when the quality of the model structure is high (rmsd less than 2 A for atoms in the 7 A local neighborhood around calcium) does the modeling of the binding sites become reliable. CONCLUSIONS: Protein structure prediction methods need to be assessed in terms of their preservation of functional sites. High-resolution structures are necessary for identifying binding sites such as calcium-binding sites.     

Are we building enough bridges between paleolimnology and aquatic ecology?

Opening keynote lecture to the Aquatic Ecology and Palaeolimnological Interpretation session at the Vth International Symposium on Palaeolimnology, held at Ambleside, U.K., Sept. 1, 1989.     

Are Lithuanian eels fat enough to reach the spawning grounds?

Stocks of the European eel Anguilla anguilla have been in a steep decline since the 1980s. Stocking of water bodies with juvenile eels captured in the wild to establish or enhance local populations has been a common practise in Europe for many decades. However, the degree of contribution by stocked eels to natural spawning capacity is poorly known and extensively debated. There have been suggestions that eels derived from stocking are less likely to contribute to the spawning stock due to a lack of navigational capability and lower fitness related to insufficiency of energetic resources. Results of the current study indicated that eels translocated long distances from the point of capture and released into inland waters in Lithuania are successfully undergoing the silvering process. A proportion of 23.7% (N = 27) among all migrating eels were described to be at the yellow (SI, SFII or SFIII) eel stage and downstream movements of these eels should be attributed to local movements, rather than spawning migration; 76.3% were assigned to the silver eel stage. This study suggests that 36.8% (N = 32) of downstream migrating silver eels of stocked origin had accumulated sufficient energetic resources for spawning migration and gonadal development and should be able to traverse the 7900-km distance to the presumptive spawning grounds in the Sargasso Sea. The rest of migrating silver eels (63.2%, N = 55) had insufficient energetic resources; the average potential swimming range of these eels was estimated to be 6135 ± 683 km.     

Ribosomal DNA and resolution of branching order among the ascomycota: how many nucleotides are enough?

Molecular phylogenies for the fungi in the Ascomycota rely heavily on 18S rRNA gene sequences but this gene alone does not answer all questions about relationships. Particularly problematical are the relationships among the first ascomycetes to diverge, the Archiascomycetes, and the branching order among the basal filamentous ascomycetes, the Euascomycetes. Would more data resolve branching order? We used the jackknife and bootstrapping resampling approach that constitutes the "pattern of resolved nodes" method to address the relationship between number of variable sites in a DNA sequence alignment and support for taxonomic clusters. We graphed the effect of increasing sizes of subsamples of the 18S rRNA gene sequences on bootstrap support for nodes in the Ascomycota tree. Nodes responded differently to increasing data. Some nodes, those uniting the filamentous ascomycetes for example, would still have been well supported with only two thirds of the 18S rRNA gene. Other nodes, like the one uniting the Archiascomycetes as a monophyletic group, would require about double the number of variable sites available in the 18S gene for 95% neighbor-joining bootstrap support. Of the several groups emerging at the base of the filamentous ascomycetes, the Pezizales receive the most support as the first to diverge. Our analysis suggests that we would also need almost three times as much sequence data as that provided by the 18S gene to confirm the basal position for the Pezizales and more than seven times as much data to resolve the next group to diverge. If more data from other genes show the same pattern, the lack of resolution for the filamentous ascomycetes may indicate rapid radiation within this clade.     

Are human hemoglobin variants distributed randomly among the positions?

Summary The distribution of human hemoglobin variants has previously been studied by Vogel (1972) who concluded that the distribution was random although no statistical analysis was presented. This work points out that there are four biases in the data, one in the manner in which the number of variants is counted, another in the method by which they are detected and which favors charge changes, a third in the fact that for a few codons the same amino acid replacement may be brought about by two or three single nucleotide replacements, and a fourth in the non-random sampling procedure which favors variants producing clinical symptoms. Nevertheless, the distribution of beta hemoglobin variants is confirmed to be random as Vogel suggests. The alpha hemoglobin variants are distinctly non-randomly distributed, the best fit requiring that 69 of the alpha positions be considered invariable. The above biases could account for this result but other considerations combine to suggest the following: 1, about half of all alterations of alpha hemoglobin will not survive to sampling whereas nearly all beta variants can; 2, deleterious mutants that survive to sampling but are destined to be eliminated by selection are more likely to be observed in beta than in alpha hemoglobin; and 3, mutations destined to go to fixation are more likely to occur in beta than in alpha hemoglobin.     

Are human progestagens among the causes of amphibian extinction?

We hypothesised that massive elimination of human and animal progestagens through wastewater can be toxic for reproduction of amphibians. Several medical test using amphibian bioassays (i.e. Hogben test) have demonstrated that human chorionic gonadotropin is toxic for amphibians. Nowadays, a huge amount of sexual hormones from women, animal farms and aquaculture arrive to inland water systems and could be a cause of amphibians extinction.     

Competitive exclusion after invasion?

The ‘Competitive Exclusion Principle’ is a foundation stone in the understanding of interspecific competition and niche relationships between species. In spite of having the status of a biological law, the principle has limited empirical support. In this study, we document strong effects of competition from the invading fish species vendace Coregonus albula over a 14-year period in the sub-arctic Pasvik watercourse. The native d.r. whitefish, that shared food and habitat niche with the invader, was displaced from its original niche and showed a more than 90% decline in population density over the study period. The study thus provides a unique record of how an exotic fish species excludes a native species from its original niche. Our data support the competitive exclusion principle, but also indicate that the vulnerability of the inferior competitor depends on a lack of alternative resources and on indirect ecological interactions.