Dispersal of first “workers” in social wasps: Causes and implications of an alternative reproductive strategy

Many “workers” in north temperate colonies of the eusocial paper wasp Polistes fuscatus disappear within a few days of eclosion. We provide evidence that these females are pursuing an alternative reproductive strategy, i.e., dispersing to overwinter and become nest foundresses the following spring, instead of helping to rear brood on their natal nests. A female is most likely to stay and help at the natal nest (i.e., least likely to disperse) when it is among the first workers to emerge and when it emerges on a nest with more pupae (even though worker-brood relatedness tends to be lower in such colonies). The latter cause may result from the fact that pupae-laden nests are especially likely to survive, and thus any direct or indirect reproductive payoffs for staying and working are less likely to be lost. Disappearing females are significantly smaller than predicted if dispersal tendency was independent of body size (emergence order-controlled), suggesting that the females likely to be most effective at challenging for reproductive rights within the natal colony (i.e., the largest females) are also most likely to stay. Thus, early dispersal is conditional on a female’s emergence order, the maturity of its natal nest, and its body size. Finally, we present evidence that foundresses may actively limit the sizes of first-emerging females, perhaps to decrease the probability that the latter can effectively challenge foundresses for reproductive rights. The degree to which foundresses limit the size of first-emerging females accords well with the predictions of the theory of staying incentives.

Social status regulates growth rate: Consequences for life-history strategies

The life-history strategies of organisms are sculpted over evolutionary time by the relative prospects of present and future reproductive success. As a consequence, animals of many species show flexible behavioral responses to environmental and social change. Here we show that disruption of the habitat of a colony of African cichlid fish, Haplochromis burtoni (Günther) caused males to switch social status more frequently than animals kept in a stable environment. H. burtoni males can be either reproductively active, guarding a territory, or reproductively inactive (nonterritorial). Although on average 25–50% of the males are territorial in both the stable and unstable environments, during the 20-week study, nearly two-thirds of the animals became territorial for at least 1 week. Moreover, many fish changed social status several times. Surprisingly, the induced changes in social status caused changes in somatic growth. Nonterritorial males and animals ascending in social rank showed an increased growth rate whereas territorial males and animals descending in social rank slowed their growth rate or even shrank. Similar behavioral and physiological changes are caused by social change in animals kept in stable environmental conditions, although at a lower rate. This suggests that differential growth, in interaction with environmental conditions, is a central mechanism underlying the changes in social status. Such reversible phenotypic plasticity in a crucial life-history trait may have evolved to enable animals to shift resources from reproduction to growth or vice versa, depending on present and future reproductive prospects.

Initiation process of earthquakes and its implications for seismic hazard reduction strategy.

For the average citizen and the public, "earthquake prediction" means "short-term prediction," a prediction of a specific earthquake on a relatively short time scale. Such prediction must specify the time, place, and magnitude of the earthquake in question with sufficiently high reliability. For this type of prediction, one must rely on some short-term precursors. Examinations of strain changes just before large earthquakes suggest that consistent detection of such precursory strain changes cannot be expected. Other precursory phenomena such as foreshocks and nonseismological anomalies do not occur consistently either. Thus, reliable short-term prediction would be very difficult. Although short-term predictions with large uncertainties could be useful for some areas if their social and economic environments can tolerate false alarms, such predictions would be impractical for most modern industrialized cities. A strategy for effective seismic hazard reduction is to take full advantage of the recent technical advancements in seismology, computers, and communication. In highly industrialized communities, rapid earthquake information is critically important for emergency services agencies, utilities, communications, financial companies, and media to make quick reports and damage estimates and to determine where emergency response is most needed. Long-term forecast, or prognosis, of earthquakes is important for development of realistic building codes, retrofitting existing structures, and land-use planning, but the distinction between short-term and long-term predictions needs to be clearly communicated to the public to avoid misunderstanding.