Effects of parasitic infection and reproduction on corticosterone plasma levels in Galápagos land iguanas,Conolophus marthaeandC. subcristatus

Abstract

In vertebrates, one main feature of stress response is the release of glucocorticoids (corticosterone in reptiles), steroid hormones whose synthesis is regulated by the hypothalamic–pituitary–adrenal axis (HPA). In the Galápagos Islands, populations of land iguanas are differentially impacted by a tick‐transmitted apicomplexan hemoparasite of genus Hepatozoon, which could cause diseases and ultimately reduce fitness. Using competitive enzyme‐linked immunosorbent assays (ELISA), we examined baseline plasma corticosterone levels of two syntopic and highly parasitized populations of the land iguana species Conolophus marthae and C. subcristatus in Wolf volcano (Isabela Island). We also used a poorly parasitized population of C. subcristatus from the same island (Bahia Urbina) as a reference. To better interpret the observed glucocorticoids patterns, we simultaneously performed the count of white blood cells (WBCs) in all individuals and investigated the reproductive status of females. We did not find evidence in support of either a positive or negative relationship between the tick load, hemoparasite infection, and glucocorticoid plasma concentration in C. marthae and C. subcristatus at Wolf volcano. The comparison between parasitized and non‐parasitized sites (V. Wolf and Bahia Urbina) would instead suggest an inverse relationship between corticosterone and parasites. Our findings support association between corticosterone plasma levels and reproduction.

Host sex, size, and hemoparasite infection influence the effects of ectoparasitic burdens on free‐ranging iguanas

“…Previous studies evaluating the effects of tick burden on glucocorticoid levels of lizards have yielded conflicting results. For example, as in this study, tick burden did not correlate with corticosterone levels in side‐blotched lizards ( U. stansburiana ; Spence et al, ) or in two iguana species, Conolophus marthae and C. subcristatus (Onorati et al, ). However, Hanley and Stamps () have reported a negative correlation between the intensity of ectoparasite burden and glucocorticoid plasma concentrations in black spiny‐tailed iguanas ( Ctenosaura similis ).…”

“…Iguanas (Conolophus spp.) with high hemoparasite loads from the Galápagos show significant alterations in heterophil-to-lymphocyte ratios (Onorati et al, 2017), while hemoparasites are uncorrelated with survival in the common lizard, (Lacerta vivipara; Sorci, Clobert, & Michalakis, 1996). In some reptile species, immunocompetence (i.e., bacterial killing ability) is only higher in individuals infected with both hemoparasites and ectoparasites (Spence et al, 2017).…”

Conservation of a flagship species: Health assessment of the pink land iguana, Conolophus marthae

“…Despite relatively high tick and hemogregarine burdens physical examination and diagnostic test results support our good health assessment. Hemogregarines are known to affect this species [ 31 ], and does not appear to produce any clinical signs, such as lethargy, open mouth breathing, weight loss, or dehydration that may be observed in immunocompromised animals [ 32 ]. In general, even though the C .…”

“…subcristatus from Wolf volcano did show significant alteration in some measures of immune function, significant correlation between corticosteroid levels (or body condition index) and the number of ticks or parasitemia were not found in C . marthae [ 31 ]. This supports the hypothesis that, in C .…”

Assessment of hematologic and corticosterone response in free‐living eastern box turtles (Terrapene carolina carolina) at capture and after handling

“…During acutely stressful periods, corticosterone can become elevated resulting in a decrease in absolute numbers of lymphocytes and monocytes whereas granulocyte numbers increase (Aguirre, Balazs, Spraker, & Gross, ; Cash et al, ; Deem et al, ; Dhabhar, ; Dhabhar, Miller, Stein, McEwen, & Spencer, ; French, DeNardo, Greives, Strand, & Demas, ; Hunt et al, ). Many factors influence the magnitude of corticosterone released across taxa, including environmental conditions, geographical location, season, nutrition, reproductive status, social dynamics, life stage, and disease (Cote, Clobert, Montes Poloni, Haussy, & Meylan, ; Dunlap & Wingfield, ; French et al, ; Gangloff et al, ; Hare & Cree, ; Jessop & Hamann, ; Jessop, Sumner, Limpus, & Whittier, ; Kahn et al, ; Klukowski, ; Onorati et al, ; Ott et al, ; Romero & Wikelski, ; Trompeter & Langkilde, ; Zachariah et al, ).…”