Background The limited neurobiological understanding of PTSD has been partially attributed to the need for improved animal models. Stress-enhanced fear learning (SEFL) in rodents recapitulates many PTSD-associated behaviors, including stress-susceptible (SS) and –resilient (SR) subgroups in outbred rats. Identification of subgroups requires additional behavioral phenotyping, a confound to mechanistic studies. Methods We employed a SEFL paradigm in inbred male and female C57BL/6 that combines acute stress with fear conditioning to precipitate “traumatic” memories. Extinction and long-term retention of extinction were examined after SEFL. Further characterization of SEFL effects on male mice was performed with additional behavioral tests, determination of regional activation by Fos immunofluorescence and RNA-sequencing of the basolateral amygdala (BLA). Results Stressed animals displayed persistently elevated freezing during extinction. While more uniform in females, SEFL produced male subgroups with differential susceptibility that were identified without post-training phenotyping. Additional phenotyping of males revealed PTSD-associated behaviors, including extinction-resistant fear memory, hyperarousal, generalization and dysregulated corticosterone in SS males. Altered Fos activation was also seen in the infralimbic cortex and BLA of SS males after remote memory retrieval. Key behavioral outcomes, including susceptibility, were replicated by two independent laboratories. RNA-sequencing of the BLA revealed transcriptional divergence between the male subgroups, including genes with reported polymorphic association to PTSD patients. Conclusions This SEFL model provides a tool for development of PTSD therapeutics that is compatible with the growing number of mouse-specific resources. Furthermore, use of an inbred strain allows for investigation into epigenetic mechanisms that are expected to critically regulate susceptibility and resilience.

The strategy of relying extensively on stored resources for reproduction has been termed capital breeding and is in contrast to income breeding, where needs of reproduction are satisfied by exogenous (dietary) resources. Most species likely fall somewhere between these two extremes, and the position of an organism along this gradient can influence several key life-history traits. Common eiders (Somateria mollissima) are the only flying birds that are still typically considered pure capital breeders, suggesting that they depend exclusively on endogenous reserves to form their eggs and incubate. We investigated the annual and seasonal variation in contributions of endogenous and exogenous resources to egg formation in eiders breeding at the East Bay colony in the Canadian Arctic. We collected prey items along with females and their eggs during various stages of breeding and used two complementary analytical approaches: body reserve dynamics and stable isotope [δ(13)C, δ(15)N] mixing models. Indices of protein reserves remained stable from pre-laying to post-laying stages, while lipid reserves declined significantly during laying. Similarly, stable isotope analyses indicated that (1) exogenous nutrients derived from marine invertebrates strongly contributed to the formation of lipid-free egg constituents, and (2) yolk lipids were constituted mostly from endogenous lipids. We also found evidence of seasonal variation in the use of body reserves, with early breeders using proportionally more exogenous proteins to form each egg than late breeders. Based on these results, we reject the hypothesis that eiders are pure capital layers. In these flying birds, the fitness costs of a strict capital breeding strategy, such as temporary loss of flight capability and limitation of clutch and egg size, may outweigh benefits such as a reduction in egg predation rate.

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Resumen. Hacer un desvío puede ser ventajoso para un ave migratoria si las tasas de abastecimiento de combustible en los sitios de parada a lo largo del desvío son considerablemente mayores que las de los sitios de parada a lo largo de una ruta más directa. Un ejemplo de un gran desvío migratorio es el de Calidris acuminata: un gran número de individuos jóvenes de esta especie se hallan en el oeste de Alaska durante la migración de otoño. Estas aves toman un desvío de 1500-3400 km de la ruta más directa entre sus áreas natales en el noreste de Siberia y las áreas no reproductivas en Australia. Estudiamos las tasas de abastecimiento otoñales y las cargas de combustible de 357 individuos de C. acuminata capturados en el oeste de Alaska. A principios de septiembre las aves aumentaron su masa a una tasa de sólo 0.5% de masa corporal magra por día. Más tarde en septiembre, la tasa de aumento de masa fue del 6% de masa corporal magra por día, que se ubica entre los valores más altos encontrados para aves playeras de tamaño similar alrededor del mundo. Algunos individuos aumentaron su masa corporal a más del doble debido al abastecimiento de combustible, permitiendo un vuelo sin escalas de entre 7100 y 9800 km, presumiblemente incluyendo un vuelo transoceánico al hemisferio sur. Nuestras observaciones indicaron que los ataques de depredadores fueron raros en nuestra área de estudio, agregando otro beneficio potencial al desvío. Concluimos que la razón más probable de los desvíos de Alaska es que le permite a los jóvenes de C. acuminata obtener reservas de combustible grandes a tasas excepcionalmente altas. A PUZZLING MIGRATORY DETOUR: ARE FUELING CONDITIONS IN ALASKA DRIVING THE MOVEMENT OF JUVENILE SHARP-TAILED SANDPIPERS? Un Desvío Migratorio Desconcertante: ¿Están las Condiciones de Abastecimiento en Alaska Conduciendo los Movimientos de los Jóvenes de Calidris acuminata?Abstract. Making a detour can be advantageous to a migrating bird if fuel-deposition rates at stopover sites along the detour are considerably higher than at stopover sites along a more direct route. One example of an extensive migratory detour is that of the Sharp-tailed Sandpiper (Calidris acuminata), of which large numbers of juveniles are found during fall migration in western Alaska. These birds take a detour of 1500-3400 km from the most direct route between their natal range in northeastern Siberia and nonbreeding areas in Australia. We studied the autumnal fueling rates and fuel loads of 357 Sharp-tailed Sandpipers captured in western Alaska. In early September the birds increased in mass at a rate of only 0.5% of lean body mass day −1. Later in September, the rate of mass increase was about 6% of lean body mass day −1 , among the highest values found among similar-sized shorebirds around the world. Some individuals more than doubled their body mass because of fuel deposition, allowing nonstop flight of between 7100 and 9800 km, presumably including a trans-oceanic flight to the southern hemisphere. Our observations indicated that predator a...