Sex-specific ecophysiological responses to environmental fluctuations of free-ranging Hermann's tortoises: implication for conservation

Abstract

Physiological parameters provide indicators to evaluate how organisms respond to conservation actions. For example, individuals translocated during reinforcement programmes may not adapt to their novel host environment and may exhibit elevated chronic levels of stress hormones and/or decreasing body condition. Conversely, successful conservation actions should be associated with a lack of detrimental physiological perturbation. However, physiological references fluctuate over time and are influenced by various factors (e.g. sex, age, reproductive status). It is therefore necessary to determine the range of natural variations of the selected physiological metrics to establish useful baselines. This study focuses on endangered free-ranging Hermann's tortoises (Testudo hermanni hermanni), where conservation actions have been preconized to prevent extinction of French mainland populations. The influence of sex and of environmental factors (site, year and season) on eight physiological parameters (e.g. body condition, corticosterone concentrations) was assessed in 82 individuals from two populations living in different habitats. Daily displacements were monitored by radio-tracking. Most parameters varied between years and seasons and exhibited contrasting sex patterns but with no or limited effect of site. By combining behavioural and physiological traits, this study provides sex-specific seasonal baselines that can be used to monitor the health status of Hermann's tortoises facing environmental threats (e.g. habitat changes) or during conservation actions (e.g. translocation). These results might also assist in selection of the appropriate season for translocation.

Keywords: Body condition; corticosterone; population managment; reptile conservation; translocation methodology.

Figure 1:

Location of the two study sites. The black dots indicate the initial position of the radio-tracked tortoises (all years pooled).

Figure 2:

Effect of sex and season on the mean (+SEM) daily displacements of radio-tracked Hermann's tortoises. Two periods were considered: spring (left side), which corresponds to vitellogenesis and laying periods, and summer (right side), which corresponds to the main season of sexual activity in males. We found significant effects of sex and season, and a significant interaction between these factors (see Table 1).

Figure 3:

Relationship between body condition index and mean (±SEM) daily displacements of radio-tracked females (grey symbols; top panels) and males (black symbols; bottom panels). Individuals were monitored in spring (left panels) and in summer (right panels). Body condition index was calculated at the beginning of each season. The dashed line indicates a correlation close to statistical significance.

Figure 4:

Effect of sex and season (a) and sex, season and year (b) on the mean variations of body condition index (±SEM) in radio-tracked Hermann's tortoises. The numbers above or below the bars indicate sample size. We found significant effects of sex, season and their interactions (see Table 2).

Figure 5:

Annual and seasonal variations of plasma corticosterone concentration (shown as mean values + SEM) in Hermann's tortoises. We found significant effects of year and season, and significant interactions between sex and season and between year and season (see Table 2). The numbers above the bars indicate sample size.

Figure 6:

Effect of sex and season on glycaemia (shown as mean values + SEM) of radio-tracked Hermann's tortoises. Two periods were considered; spring corresponds to vitellogenesis and laying periods, whereas summer corresponds to intensive male sexual activity. The numbers above the bars indicate sample size.

Figure 7:

Effect of sex and season on Osmolarity (shown as mean values + SEM) of radio-tracked Hermann's tortoises. Two periods were considered; spring corresponds to vitellogenesis and laying periods, whereas summer corresponds to intensive male sexual activity. The numbers above the bars indicate sample size.