Searching for the Physiological Mechanism of Density Dependence: Does Corticosterone Regulate Tadpole Responses to Density?

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press ABSTRACTDensity-dependent population regulation is important in many natural populations, and in those populations, high population density is a likely stressor. In amphibians, previous laboratory studies with tadpoles suggest that corticosterone, the main glucocorticoid stress hormone, is one of the key regulators of density-dependent growth. To test this relationship in natural settings, we manipulated wood frog (Rana sylvatica) tadpole density at three levels in outdoor mesocosms and used a capture stress protocol to examine the hormonal stress response. In addition, we used the same capture protocol in six natural ponds (three high density and three low density). In the mesocosms, there was an increase in corticosterone levels in tadpoles following 1 h of confinement at weeks 1, 2, and 5. However, while tadpoles maintained at higher densities were smaller after metamorphosis, density did not alter mean levels of corticosterone obtained during confinement, and baseline levels of corticosterone did not differ between the densities. Similarly, in natural ponds, density did not correlate with baseline corticosterone or mean corticosterone levels obtained during confinement. We suggest that the physiological response to density may vary across the range of natural densities and that the role of corticosterone may be limited to periods of extreme high density, such as during pond-drying events.

Parasitism in a community context: Trait-mediated interactions with competition and predation

“…Tadpoles from the highdensity tanks lacked changes in leukocytes that could account for increased susceptibility to infection, and neutrophil-to-lymphocyte ratios were higher in the highdensity mesocosms, opposite the effect predicted by stress-induced immunomodulation (Appendix D; Davis et al 2008). This result is consistent with previous studies, which have only found significant stress responses in tadpoles at much higher densities than used in this experiment (2-10 tadpoles/L; Hayes 1997, Glennemeier and Denver 2002, Belden et al 2007.…”

Stress hormones and the fitness consequences associated with the transition to a novel diet in larval amphibians

“…couchii, it is not entirely clear which causal pathways link these variables. Our multiple regression analysis indicated that CORT concentrations varied inversely with body mass (and to a lesser extent with C. C. Ledón-Rettig, D. W. Pfennig and E. J. Crespi (Belden et al, 2007) and other vertebrates (Kitaysky et al, 1999;Moore et al, 2000). However, the effect of diet on Sc.…”

Pond Acidification May Explain Differences in Corticosterone among Salamander Populations

“…Our field survey results show baseline corticosterone concentrations differing significantly among freeliving A. jeffersonianum populations. Belden et al (2007) have also shown variations in baseline corticosterone concentrations among tadpoles in free-living wood frog Rana sylvatica populations. Differing baseline corticosterone concentrations could suggest that these populations are experiencing varied environmental stressors in their aquatic systems, similar to what was proposed for adult Ambystoma maculatum by Homan et al (2003).…”

“…Wingfield 1994), and amphibians (Homan et al 2003;Belden et al 2007), although population-level variation in baseline glucocorticoid concentrations is not always found (Pravosudov et al 2004).…”

“…Baseline corticosterone concentrations were sampled by freezing larvae individually in a dry ice/ethanol slurry within 3 min of initial capture to reflect unstressed concentrations (Belden et al 2003). To induce the stress response, we held individual larvae in 120-mL cups filled with 80 mL of pond water for 30 min, with cups being gently agitated every 3 min (Belden et al 2007). After 30 min, larvae were frozen using a dry ice/ethanol slurry.…”