Small mammal glucocorticoid concentrations vary with forest fragment size, trap type, and mammal taxa in the Interior Atlantic Forest

Abstract

Species that live in degraded habitats often show signs of physiological stress. Glucocorticoid hormones (e.g., corticosterone and cortisol) are often assessed as a proxy of the extent of physiological stress an animal has experienced. Our goal was to quantify glucocorticoids in free-ranging small mammals in fragments of Interior Atlantic Forest. We extracted glucocorticoids from fur samples of 106 small mammals (rodent genera Akodon and Oligoryzomys, and marsupial genera Gracilinanus and Marmosa) from six forest fragments (2–1200 ha) in the Reserva Natural Tapytá, Caazapá Department, Paraguay. To our knowledge, this is the first publication of corticosterone and cortisol levels for three of the four sampled genera (Akodon, Oligoryzomys, and Marmosa) in this forest system. We discovered three notable results. First, as predicted, glucocorticoid levels were higher in individuals living withing small forest fragments. Second, animals captured live using restraint trapping methods (Sherman traps) had higher glucocorticoid levels than those animals captured using kill traps (Victor traps), suggesting that hair glucocorticoid measures can reflect acute stress levels in addition to long-term glucocorticoid incorporation. These acute levels are likely due to urinary steroids diffusing into the hair shaft. This finding raises a concern about the use of certain trapping techniques in association with fur hormone analysis. Finally, as expected, we also detected genus-specific differences in glucocorticoid levels, as well as cortisol/corticosterone ratios.

Environmental Stress and the Primate Microbiome: Glucocorticoids Contribute to Structure Gut Bacterial Communities of Black Howler Monkeys in Anthropogenically Disturbed Forest Fragments

“…Interestingly, the interaction between a metric of food biomass (i.e., feeding tree basal area) and fGCMs significantly affected bacterial community shifts and diversity, supporting our hypothesis, although in a different direction than our prediction. Our findings show that the activation of the HPA-axis, which is a physiological response sensitive to environmental stressors such as forest disturbance (Martínez-Mota et al, 2007;Rangel-Negrín et al, 2014a;Boyle et al, 2021), contributes to some extent to structure the gut microbiome of arboreal primates in disturbed habitats.…”

“…While acute stress responses occur on a short-term scale (e.g., within minutes) and are characterized by the rapid rise and fall of hormones, suppressing functions that are not immediately needed like digestion or reproduction, a chronic stress response develops over a longer-term scale (e.g., weeks or months) with negative consequences for individuals, such as immunosuppression or reduced growth (Romero, 2004;Romero et al, 2009;Sapolsky, 2021). The reaction of the hypothalamicpituitary-adrenal (HPA) axis and the resulting release of glucocorticoids are often measured to assess the physiological response related to stressful environmental stimuli (Sheriff et al, 2011), and there is plenty of evidence indicating that animals inhabiting anthropogenically disturbed habitats tend to have increased glucocorticoid concentrations possibly reflecting higher stress levels (Creel et al, 2002;Martínez-Mota et al, 2007;Balestri et al, 2014;Rehnus et al, 2014;Formenti et al, 2018;Kleist et al, 2018;Messina et al, 2018;Boyle et al, 2021). However, determining the effects of stress due to anthropogenic impact on animal-symbiont associations is still a research area that needs to be explored in wildlife (Trevelline et al, 2019).…”

Bioindicators of edge effects within Atlantic Forest remnants: Conservation implications in a threatened biodiversity hotspot

“…An increase in edge is a direct effect of fragmentation and habitat loss (Pfeifer et al, 2017). In our sampling, larger forest remnants, especially their interiors, had low capture rates even with larger sampling efforts (de la Sancha, 2014;Hice & Velazco, 2012;Malcolm, 1997), compared with smaller forest remnants (Boyle et al, 2021). For example, trapping in Mbaracayú included several grids with <3 individuals.…”

“…We examined diversity along a forest remnant size gradient (~2 up to 95,758 ha). We capitalized on small mammal sampling conducted in five forest reserves distributed throughout eastern Paraguay (Boyle et al, 2021; de la Sancha, 2014): Mbaracayú Natural Forest Reserve, San Rafael Managed Resource Reserve, Morombí Natural Private Reserve, Limoy Biological Reserve and Tapytá Natural Reserve (Figure 1). Mbaracayú (64,000 ha) is among the largest forest remnants in Paraguay and is adjacent to other forests, totalling 95,758 ha.…”

“…We examined diversity along a forest remnant size gradient (~2 up to 95,758 ha). We capitalized on small mammal sampling conducted in five forest reserves distributed throughout eastern Paraguay (Boyle et al, 2021;de la Sancha, 2014) (17,507 and 1214 ha). Limoy (16,000 ha) is one of a series of reserves along the Parana River that was set aside by Itaipú Binational Hydroelectric Company for erosion control (de la Sancha, 2014).…”