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The obligate pollination mutualism between figs (Ficus, Moraceae) and pollinator wasps (Agaonidae, Hymenoptera) is a classic example of cospeciation. However, examples of phylogenetic incongruencies between figs and their pollinators suggest that pollinators may speciate by host shifting. To investigate the mechanism of speciation by host shifting, we examined the phylogenetic relationships and population genetic structures of six closely related fig species and their pollinators from southern China and Taiwan-Ryukyu islands using various molecular markers. The results revealed 1) an extraordinary case of pollinator sharing, in which five distinct fig species share a single pollinator species in southern China; 2) two types of copollination, namely, sympatric copollination by pollinator duplication or pollinator migration, and allopatric copollination by host migration and new pollinator acquisition; 3) fig species from southern China have colonized Taiwan repeatedly and one of these events has been followed by host shifting, reestablishment of host specificity, and pollinator speciation, in order. Based on our results, we propose a model for pollinator speciation by host shifting in which the reestablishment of host-specificity plays a central role in the speciation process. These findings provide important insights into understanding the mechanisms underlying pollinator speciation and host specificity in obligate pollination mutualism. Phylogenetic and population genetic analyses reveal mechanisms of pollinator sharing, copollination and speciation by host-shift in fig-wasp mutualism. [ABSTRACT FROM AUTHOR]

In this paper, a new default intensity model with dual frailties is proposed and an empirical evidence is provided to confirm the model's adequacy. In addition to the conventional explanatory variables, Duffie et al. introduces a time frailty and Chava et al. considers an industrial frailty to model the conditional default dependence. However, from an empirical study on Taiwan's public listed firms, Lin and Chen points out that the time frailty can only catch the default dependence along the time but not among the industries. On the other hand, the industrial frailty can only capture the default dependence from the industrial correlation but not from the time dependence. Hence, the default intensity model with time and industrial frailties is recommended. This paper introduces a dual frailty model to incorporate time and industrial frailties. Using the empirical data of Taiwan's public listed firms from January of 1995 to January of 2015, the dual frailty model is estimated and the Fisher's dispersion tests are conducted for bins from time and from industries. Our empirical findings indicate that the dual frailty model captures not only the time dependence of default clustering but also the industrial correlations. Therefore, our dual frailty model outperforms the intensity model with time frailty of Duffie et al. and the industrial frailty of Chava et al. [ABSTRACT FROM AUTHOR]