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Examining physiological traits across large spatial scales can shed light on the environmental factors driving physiological variation. For endotherms, flexibility in aerobic metabolism is especially important for coping with thermally challenging environments and recent research has shown that aerobic metabolic scope [the difference between maximum thermogenic capacity (Msum) and basal metabolic rate (BMR)] increases with latitude in mammals. One explanation for this pattern is the climatic variability hypothesis, which predicts that flexibility in aerobic metabolism should increase as a function of local temperature variability. An alternative explanation is the cold adaptation hypothesis, which predicts that cold temperature extremes may also be an important driver of variation in metabolic scope. To determine the thermal drivers of aerobic metabolic flexibility in birds, we combined data on metabolic scope from 40 bird species sampled across a range of environments with several indices of local ambient temperature. Using phylogenetically‐informed analyses, we found that minimum winter temperature was the best predictor of variation in avian metabolic scope, outperforming all other thermal variables. Additionally, Msum was a better predictor of latitudinal patterns of metabolic scope than BMR, with species inhabiting colder environments exhibiting increased Msum over their counterparts in warmer environments. Taken together, these results suggest that cold temperature extremes drive latitudinal patterns of metabolic scope via selection for enhanced thermogenic performance in cold environments, supporting the cold adaptation hypothesis. Temperature extremes may therefore be an important selective pressure driving macrophysiological trends of aerobic performance in endotherms.

International audienceThis paper develops a model of cross-border M&A activity that features firm-level productivity shocks and endogenous export activity. We show that foreign firms will be relatively more attracted to targets in the domestic country that had high productivity levels that induced them to invest in large export networks several years prior to acquisition, but subsequently experienced a negative productivity shock (i.e., cherries for sale). From the theory we derive a dynamic panel binary choice empirical model to predict cross-border M&A activity, and find strong evidence for our hypotheses connecting the evolution of firm-level productivity to the ultimate targets of cross-border acquisitions using French firm-level data

With its large size, complex topography and high number of avian endemics, Hispaniola appears to be a likely candidate for the in situ speciation of its avifauna, despite the worldwide rarity of avian speciation within single islands. We used multilocus comparative phylogeography techniques to examine the pattern and history of divergence in 11 endemic birds representing potential within-island speciation events. Haplotype and allele networks from mitochondrial ND2 and nuclear intron loci reveal a consistent pattern: phylogeographic divergence within or between closely related species is correlated with the likely distribution of ancient sea barriers that once divided Hispaniola into several smaller paleo-islands. Coalescent and mitochondrial clock dating of divergences indicate species-specific response to different geological events over the wide span of the island's history. We found no evidence that ecological or topographical complexity generated diversity, either by creating open niches or by restricting long-term gene flow. Thus, no true within-island speciation appears to have occurred among the species sampled on Hispaniola. Divergence events predating the merging of Hispaniola's paleo-island blocks cannot be considered in situ divergence, and postmerging divergence in response to episodic island segmentation by marine flooding probably represents in situ vicariance or interarchipelago speciation by dispersal. Our work highlights the necessity of considering island geologic history while investigating the speciation-area relationship in birds and other taxa.

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Bilateral tax treaties (BTTs) are intended to promote foreign direct investment through double-taxation relief. Using BEA firm-level data, we find a positive effect of BTTs on FDI, which is larger for firms that use differentiated inputs. BTTs allow multinational firms to request assistance from treaty partners' governments if they have a grievance about how tax liabilities are determined. These provisions disproportionately benefit firms that use inputs for which an arm's-length price is difficult to observe, since allocation of earnings across countries is more complex. We find differential BTT effects for both sales by existing affiliates and entry of new affiliates. (JEL F23, H25, H87)

The Gray-crowned Palm-Tanager (Phaenicophilus poliocephalus), sometimes considered conspecific with its more widespread congener P. palmarum, is restricted to Haiti's Tiburon Peninsula, a biodiversity hotspot threatened by extensive habitat loss. We used a multilocus phylogeographic approach to identify evolutionarily distinct populations of Phaenicophilus. Mitochondrial haplotypes formed two reciprocally monophyletic groups separated by 5% uncorrected divergence. Genealogical patterns of differentiation at nuclear intron alleles were congruent with those of mtDNA, and the two species also differed in body size and shape. An ancient sea channel between the Tiburon Peninsula and mainland Haiti was likely a dispersal barrier that led to allopatric divergence, a hypothesis supported by our estimates of divergence times. Our results support the recognition of two Palm-Tanager species, confirming P. poliocephalus as Haiti's only endemic bird species and underscoring the need to protect the Tiburon Peninsula's single primary forest reserve.

Estimating the causal effect of offshoring on domestic employment is difficult because of the inherent simultaneity of multinational firms' domestic and foreign affiliate employment decisions. In this paper, we resolve this identification problem using variation in Bilateral Tax Treaties (BTTs), which reduce the effective cost of offshore activity by mitigating double taxation. We derive a panel difference-indifferences research design from a standard model of multinational firms, demonstrating the simultaneity problem and showing how to resolve it using BTTs as an instrument for offshore employment. We confirm that new treaty implementation is uncorrelated with existing employment trends, and use Bureau of Economic Analysis data on U.S. multinational firms to measure the domestic employment effects of offshore activity. Overall, we find modest positive effects of offshore activity on domestic employment. A 10 percent BTTinduced increase in affiliate employment drives a 1.8 percent increase in employment at the U.S. parent firm, with smaller effects at the industry and regional levels. Underlying these results is substantial heterogeneity based on offshoring margin and firm organizational structure. For example, increased foreign affiliate activity in vertically oriented multinational firms drives declining employment among non-multinationals in the same industry, and multinational firms opening new affiliates exhibit much smaller domestic employment growth than those expanding existing affiliates. Throughout the analysis, OLS estimates are much larger than the IV estimates, consistent with upward simultaneity bias. Overall, our results indicate that greater offshore activity raises net employment by U.S. firms, albeit with underlying job loss and reallocation of workers.