Impact of social dominance on the evolution of individual learning.

A major question in cultural-evolution studies is the phenotype of individual learners. Evidence suggests that social dominance is one influential factor, where socially subordinate individuals are more apt to learning of trial-and-error type than the dominants. Despite the accumulating evidence, the evolutionary dynamics leading to such outcomes remains largely elusive, partly because of the cost of individual learning. Here, we provide an evolutionary game framework to study the influence of social dominance on individual's learning decisions. We show that subordinates are indeed more apt to individual learning, because they gain a lot when individual learning is successful but lose little when it fails. We also predict that an evolutionary limit-cycle, in which dominants' and subordinates' behavior change over evolutionary time, may occur in such a case. We additionally showed that group-wide knowledge-gain is poor in egalitarian groups compared to moderately despotic ones. Our model sheds light onto the consequence of tactics played between dominants and subordinates for the evolution of individual learning.

Author Correction: Controlling invasive ant species: a theoretical strategy for efficient monitoring in the early stage of invasion.

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Controlling invasive ant species: a theoretical strategy for efficient monitoring in the early stage of invasion.

Invasion by the red imported fire ant, Solenopsis invicta Buren, has destructive effects on native biodiversity, agriculture and public health. This ant's aggressive foraging behaviour and high reproductive capability have enabled its establishment of wild populations in most regions into which it has been imported. An important aspect of eradication is thorough nest monitoring and destruction during early invasion to prevent range expansion. The question is: How intense must monitoring be on temporal and spatial scales to eradicate the fire ant? Assuming that the ant was introduced into a region and that monitoring was conducted immediately after nest detection in an effort to detect all other potentially established nests, we developed a mathematical model to investigate detection rates. Setting the monitoring limit to three years, the detection rate was maximized when monitoring was conducted shifting bait trap locations and setting them at intervals of 30 m for each monitoring. Monitoring should be conducted in a radius of at least 4 km around the source nest, or wider-depending on how late a nest is found. For ease of application, we also derived equations for finding the minimum bait interval required in an arbitrary ant species for thorough monitoring.

Assessing potential countermeasures against the dengue epidemic in non-tropical urban cities.

BACKGROUND: Dengue is a common mosquito-borne viral disease epidemic especially in tropical and sub-tropical regions where water sanitation is not substantially controlled. However, dengue epidemics sometimes occur in non-tropical urban cities with substantial water sanitary control. Using a mathematical model, we investigate what conditions can be important for a dengue epidemic to occur in an urban city such as Tokyo, where vectors are active only in summer and there are little number of vectors around hosts. METHODS: The model, which is a modified Ross-Macdonald model, consists of two sets of host-vector compartments. The two sets correspond to high-risk and low-risk areas, and only hosts can move between them. Assuming that mosquitoes have constant activity for only 90 days, we assess five potential countermeasures: (1) restricted movement between the two areas, (2) insecticide application, (3) use of repellents, (4) vector control, and (5) isolation of the infected. RESULTS: The basic reproduction number R 0 and the cumulative number of infected hosts for 90 days are evaluated for each of the five countermeasures. In the cases of Measures 2-5, the cumulative number of the infected for 90 days can be reduced substantially for small R 0 even if R 0>1. Although R 0 for Measure 1 monotonically decreases with the mobility rates, the cumulative number of the infected for 90 days has a maximum at a moderate mobility rate. If the mobility rate is sufficiently small, the restricted movement effectively increases the number density of vectors in the high-risk area, and the epidemic starts earlier in the high-risk area than in the low-risk one, while the growth of infections is slow. CONCLUSIONS: Measures 2-5 are more or less effective. However, Measure 1 can have the opposite effect, depending on the mobility rates. The restricted movement results in the formation of a kind of core population, which can promote the epidemic in the entire population.