Investigation of seasonality and plasticity of daily activity patterns in a subterranean rodent (Ctenomys aff. knighti) using noninvasive methods of endocrine monitoring

Abstract

Tuco-tucos (Ctenomys aff. knighti) are solitary subterranean rodents that occur in the semi-arid northwest of Argentina. Their activity pattern is nocturnal in laboratory, but diurnal in field. Studies investigating the discrepancies between diurnal and nocturnal activity indicate that in nature the activity rhythm is plastic and influenced by a combination of biotic and abiotic factors, whose complexity is not reproducible in the laboratory, making field studies essential in the investigation of this subject. Noninvasive hormonal measurements may be excellent markers for certain physiological states, such as energetic and reproductive states, as well as for responses to stressful situations. Thus, this project has the general objective of tracing endocrine profiles using non-invasive techniques simultaneously with measurements of the daily rhythm of activity in tuco-tucos. We will explore, in the field and in the laboratory and throughout the year, the relationship between activity patterns and the reproductive, stress and energetic states through non-invasive measurements of hormone metabolites of sex steroids, glucocorticoids and thyroid hormones. Since noninvasive methods of hormonal dosages have never been used in C. aff. knighti, they will be validated analytically and physiologically. In addition, we will validate the use of faecal levels of thyroid hormone as a marker of energetic status, through comparison with traditional means of metabolic rate measurements. The establishment of these methods will also allow future and more detailed studies on the ecophysiological aspects related to the daily pattern of activity in tuco-tucos and will open doors to this type of investigation in other species of rodents. (AU)