Haematology and plasma biochemistry reference intervals of Galapagos tortoises from Isabela Island

Abstract

Wildlife health assessments including haematology and biochemistry parameters are essential to evaluating the well-being of free-living species. In Galapagos, the iconic giant tortoises still thrive in the archipelago despite anthropogenic pressures, with up to 13 extant species distributed across most islands and ecosystems. In previous work conducted by our research group, we described for the first-time reference intervals of haematology and plasma biochemistry in four Galapagos tortoise species. With the aim of continuing to provide cutting-edge health data for Galapagos tortoises, here we report haematology and plasma biochemistry descriptive statistics, reference intervals and cell morphology of tortoises from four different tortoise populations (i.e. Alcedo Volcano, Cerro Azul Volcano, Cinco Cerros and Sierra Negra Volcano). Additionally, we compared values between sexes and applied a principal component analysis to explore differences in haematology and biochemistry parameters between tortoise populations, including those previously published by our research group. Females presented higher calcium, phosphorus and albumin, consistent with vitellogenesis, whereas males had higher packed cell volume and sodium than females. Blood cell morphology was consistent across species. The two main principal components of the multivariate statistical model were unable to explain >44.9% of the variance across tortoise populations. We suggest additional research to explore the correlation between anthropogenic factors (i.e. climate change, pesticides, plastics) and blood values, for a deeper understanding of tortoise physiology and ultimately improved diagnostics and management actions. In the anthropogenic era, understanding the health status of bioindicator species like Galapagos tortoises is mandatory to inform current and future conservation priorities and actions.

Keywords: Blood parameters; chelonians, Chelonoidis spp; reference values; wildlife health surveillance.

Figure 1

Sampling locations of Alcedo Volcano giant tortoises (C. vandenburghi), Sierra Negra Volcano tortoises (C. guntheri), Cerro Azul Volcano tortoises (C. vicina) and Cinco Cerros tortoises (C. vicina/C. guntheri) used to describe haematology and plasma biochemistry reference intervals in the Galapagos Islands.

Figure 2

Modified Wright–Giemsa-stained peripheral blood from Alcedo Volcano (C. vandenburghi) (a–d), Cerro Azul Volcano (C. vicina) (e–f), Cinco Cerros (C. vicina/C. guntheri) (g) and Sierra Negra Volcano giant tortoises (C. guntheri) (h–i). L, lymphocyte; RL, reactive lymphocyte; T, thrombocyte; H, heterophil; B, basophil; DB, degranulated basophil; M, monocyte; E, eosinophil. Erythrocyte from Alcedo Volcano giant tortoises with potential hemogregarine (d).

Figure 3

Graphical representation of Principal Components 1 (Axis 1) and 2 (Axis 2) with varimax rotation of Galapagos giant tortoise haematology and biochemistry parameters from eight different populations: (a) haematology parameters of all individuals; (b) biochemistry parameters of all individuals; (c) haematology parameters of females; (d) biochemistry parameters of females; (e) haematology parameters of males; and (f) biochemistry parameters of males. Haematological variables represented in (a), (c), and (e) are heterophils, lymphocytes, absolute white blood cell counts, and H:L ratio. Blood chemistry variables represented in (b) are total solids, total proteins, albumin, globulin and calcium. Variables represented in (d) are total solids, total proteins, calcium, globulin, uric acid and glucose. Variables represented in (f) are glucose, phosphorus, total proteins, globulin and sodium.