Growth patterns in male rats exposed to concurrent long-term environmental challenges

Abstract

SUMMARY.Growth is a key determinant of fitness in animals, and may be affected by the environmental challenges presented over the course of an individual's lifespan. When faced with limited resources and environmental challenges, organisms may prioritize the development and maintenance of particular processes over others. To expand our understanding of the consequences of organism exposure to a changing environment, we offer a long-term experiment to compare the growth patterns of young male rats exposed and not exposed to food limitation and social conflict. The patterns of growth of young rats were altered by the exposure to these environmental challenges, two of the most frequently faced by animals. As expected, scarcity of food resulted in a marked growth decline in animals exposed to nutritional stress. Interestingly, individuals exposed to an unstable social environment, but fed ad libitum, evidenced a growth rate 6% smaller than those under stable social conditions. An interaction between food limitation and social conflict was not observed. As a larger body size growth results in a competitive advantage in encounters, the detected divergence on growth patterns may represent significant consequences on the individual's life trajectory. RESUMEN. Patrones de crecimiento en ratas macho expuestas de manera prolongada a desafíos ambientales concurrentes. En animales, la eficacia biológica es influenciada por el crecimiento, que a su vez es afectado por los desafíos ambientales que el individuo enfrente a lo largo de su vida. Ante escasez de recursos u otros desafíos, los organismos priorizarían el desarrollo y mantenimiento de algunos procesos por sobre otros. Para profundizar nuestro conocimiento sobre las consecuencias de la exposición a un ambiente cambiante, desarrollamos un experimento de larga duración para comparar los patrones de crecimiento de ratas jóvenes expuestas y no expuestas a restricción alimentaria y conflicto social. La exposición a estos dos desafíos ambientales, comunes en la naturaleza, alteró los patrones de crecimiento de las ratas. La escasez de alimento ocasionó un descenso marcado del crecimiento en los animales bajo restricción alimentaria. Mientras que individuos expuestos a inestabilidad social, pero con alimento ad libitum, demostraron una tasa de crecimiento 6% menor que aquellos en condiciones sociales estables. Adicionalmente, no se encontró interacción significativa entre restricción alimentaria y conflicto social. Siendo que un mayor crecimiento corporal resulta ventajoso ante interacciones competitivas, la diferencia detectada entre los patrones de crecimiento tendría consecuencias de importancia en la trayectoria de vida de los individuos.

Chronic exposure to environmental stressors enhances production of natural and specific antibodies in rats

“…Individuals exposed to FR evidenced a much slower growth than those with free access to food (evidenced by the wBM and the wBMI; Tables and Supporting Information Tables S1 and S2; see Cuervo et al, ). The growth rate greatly differed among treatments, with FR+ animals gaining by week around 1/3 of the weight gained by the FR–SC– (Supporting Information Table S1).…”

“…The stress‐related changes observed (increased CORT levels and changes in the histoarchitecture of the adrenal glands) support the notion that FR+ animals perceived the scarcity of resources as threatening and thus elicited a stress response (Figure and Tables and and Supporting Information Table S3; this paper and Cuervo et al, ). Despite SC+ groups had CORT levels similar to those of controls (Figure and Tables and 6), their adrenal histoarchitecture was modified as expected under chronic stress (Supporting Information Table S3; see Cuervo et al, ; Ulrich‐Lai et al, ).…”

“…Males were selected because social interactions influence a wider range of behaviors in males than in females (Blanchard, McKittrick, & Blanchard, ). We selected pubertal rats to measure the immune responses while having growth as an additional physiological demand, as multiple demands are expected in real contexts (growth patterns of the same rats were analyzed and published in Cuervo, Racca, and Beldomenico ()). The rats were randomly selected and distributed into 11 groups (three animals in each of 10 polysulfona cages of 274 × 443 × 231 mm [+one cage with two rats] and a floor area of 800 cm 2 , Type III High Allentown Inc. [Allentown, NJ], with treated softwood as bedding material) in an experimental room with 24‐hr light–dark 12:12 cycle.…”

“…Growth pattern results of these same rats and stress induction were previously published (for details, see Cuervo et al, ), and a summary provided here with the only purpose of supporting the statements presented.…”

“…The induction of stress by the treatments applied was verified by comparing the adrenocortical histoarchitecture, the food intake, and the levels of plasmatic corticosterone (CORT) in a radioimmunoassay (Cuervo et al, ). CORT values were obtained in selected weeks of the experiment (0, 3, 6, 9, and 13) from diethyl ether extracted plasma aliquots (15 µl) using a radioimmunoassay, following Jahn, Moya, Jammes, and Rosato () and Valdez, Bonafede, Carreño, Deis, and Jahn ().…”