Biodiversity of Hymenoptera

From the Arctic to South Africa - one finds them everywhere: Ants. Making up nearly 15% of the entire terrestrial animal biomass, ants are impressive not only in quantitative terms, they also fascinate by their highly organized and complex social system. Their caste system, the division of labor, the origin of altruistic behavior and the complex forms of chemical communication makes them the most interesting group of social organisms and the main subject for sociobiologists. Not least is their ecological importance: Ants are the premier soil turners, channelers of energy and dominatrices of the insect fauna. TOC:The importance of ants.- Classification and origins.- The colony life cycle.- Altruism and the origin of the worker caste.- Colony odor and kin recognition.- Queen numbers and domination.- Communication.- Caste and division of labor.- Social homeostasis and flexibility.- Foraging and territorial strategies.- The organization of species communities.- Symbioses among ant species.- Symbioses with other animals.- Interaction with plants.- The specialized predators.- The army ants.- The fungus growers.- The harvesters.- The weaver ants.- Collecting and culturing ants.- Glossary.- Bibliography.- Index.

Phylogenies are usually dated by calibrating interior nodes against the fossil record. This relies on indirect methods that, in the worst case, misrepresent the fossil information. Here, we contrast such node dating with an approach that includes fossils along with the extant taxa in a Bayesian total-evidence analysis. As a test case, we focus on the early radiation of the Hymenoptera, mostly documented by poorly preserved impression fossils that are difficult to place phylogenetically. Specifically, we compare node dating using nine calibration points derived from the fossil record with total-evidence dating based on 343 morphological characters scored for 45 fossil (4--20 complete) and 68 extant taxa. In both cases we use molecular data from seven markers (∼5 kb) for the extant taxa. Because it is difficult to model speciation, extinction, sampling, and fossil preservation realistically, we develop a simple uniform prior for clock trees with fossils, and we use relaxed clock models to accommodate rate variation across the tree. Despite considerable uncertainty in the placement of most fossils, we find that they contribute significantly to the estimation of divergence times in the total-evidence analysis. In particular, the posterior distributions on divergence times are less sensitive to prior assumptions and tend to be more precise than in node dating. The total-evidence analysis also shows that four of the seven Hymenoptera calibration points used in node dating are likely to be based on erroneous or doubtful assumptions about the fossil placement. With respect to the early radiation of Hymenoptera, our results suggest that the crown group dates back to the Carboniferous, ∼309 Ma (95% interval: 291--347 Ma), and diversified into major extant lineages much earlier than previously thought, well before the Triassic. [Bayesian inference; fossil dating; morphological evolution; relaxed clock; statistical phylogenetics.]

Close relatedness has long been considered crucial to the evolution of eusociality. However, it has recently been suggested that close relatedness may be a consequence, rather than a cause, of eusociality. We tested this idea with a comparative analysis of female mating frequencies in 267 species of eusocial bees, wasps, and ants. We found that mating with a single male, which maximizes relatedness, is ancestral for all eight independent eusocial lineages that we investigated. Mating with multiple males is always derived. Furthermore, we found that high polyandry (>2 effective mates) occurs only in lineages whose workers have lost reproductive totipotency. These results provide the first evidence that monogamy was critical in the evolution of eusociality, strongly supporting the prediction of inclusive fitness theory.