The innate immune system in insects is composed of a large variety of specific and non-specific responses that are activated in response to the presence of foreign agents. One important element in such responses is the enzyme phenoloxidase (PO). Here, we review recent progress in PO research and discuss new applications in the emerging field of ecological immunology. Phenoloxidase produces indole groups, which are subsequently polymerized to melanin. The enzymatic reactions in turn produce a set of intermediate products such as quinones, diphenols, superoxide, hydrogen peroxide, and reactive nitrogen intermediates, which are important during defense against bacterial (gram+ and )), fungal, and viral agents. Phenoloxidase requires a complex system of activation and inhibition that involves various cell types, PO zymogens, inhibitor enzymes, and signaling molecules. Finally, research in evolutionary ecology has studied the costs of PO in terms of resource use and pleiotropic relations with other key traits and functions. These studies indicate that PO is a costly trait, whose production and maintenance have fitness costs for hosts. Phenoloxidase does not seem to be an indicator of resistance but rather of host condition. Finally, we put forward some basic directions for future investigation of PO aimed at explaining its activating system, its substrates, its coordination with other immune components to fight off pathogens, and variation in PO in relation to gender, life stages, seasonality, and across different host species.

Over the last ten years, Oosterhof and Todorov's valence-dominance model has emerged as the most prominent account of how people evaluate faces on social dimensions. In this model, two dimensions (valence and dominance) underpin social judgments of faces. Because this model has primarily been developed and tested in Western regions, it is unclear whether these findings apply to other regions. We addressed this question by replicating Oosterhof and Todorov's methodology across 11 world regions, 41 countries, and 11,570 participants. When we used Oosterhof and Todorov's original analysis strategy, the valence-dominance model generalized across regions. When we used an alternative methodology to allow for correlated dimensions we observed much less generalization. Collectively, these results suggest that, while the valence-dominance model generalizes very well across regions when dimensions are forced to be orthogonal, regional differences are revealed when we use different extraction methods, correlate and rotate the dimension reduction solution.

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