Effect of Trapping Method on Leukocyte Profiles of Black-Chested Spiny-Tailed Iguanas (Ctenosaura melanosterna): Implications for Zoologists in the Field

Andrew K Davis,John C Maerz,Leslie E Ruyle

doi:10.5402/2011/384825

Abstract

When wild animals are captured for zoological research, researchers must choose a method of capture, and often this can be some form of passive, baited cage trap, or a direct capture with nets or nooses. If information on basal levels of circulating leukocytes is a goal, these two methods may provide different information, since recent evidence indicates that animals that enter cage traps experience stress, and, elevated stress hormones are known to alter leukocyte numbers in circulation by lowering lymphocyte and raising heterophil numbers. We tested this idea using a study of Black-chested Spiny-tailed iguanas (Ctenosaura melanosterna), which were captured using cage traps () and noose (). Based on cell counts made from blood smears, iguanas caught with cage traps had significantly greater relative and absolute numbers of heterophils and higher heterophil-lymphocyte (H-L) ratios than those captured by noose. Cage-trapped animals also had a nonsignificant reduction in lymphocyte numbers. Similar trends were observed in animals captured with both methods. These patterns are consistent with the effects of stress hormones on white blood cell distributions and indicate that caution must be taken in interpreting leukocyte data from studies of wild animals captured with cage traps.

Highlights

Researchers of wild animals are increasingly conducting projects that include measures of circulating hormone levels or the distributions and abundances of white blood cells as a means to evaluate health or stress in animal populations
The central question in this study was whether estimated leukocyte counts of animals differed in directly captured animals or those captured with baited cage traps, and the results obtained are clear: the two methods do lead to at least some differences in the abundance of particular cell types in circulation
Given that the primary difference was in the relative and absolute counts of heterophils, which are known to increase with elevations in stress hormones, the higher average count among cagetrapped animals could be interpreted as a result of the stress induced by remaining in the cage trap

Summary

Introduction

Researchers of wild animals are increasingly conducting projects that include measures of circulating hormone levels or the distributions and abundances of white blood cells as a means to evaluate health or stress in animal populations. One of the most commonly assessed pieces of information in such projects is data on the numbers of circulating leukocytes (white blood cells) in the animals, which can be gathered from examination of stained blood smears on microscope slides. One aspect that investigators must consider in any research project involving capture of wild animals is the method of capture [12, 13]. This may be relevant when multiple capture techniques are used across studies

Methods

Results

Conclusion