Oxidative stress and behavioral responses of moorish geckos (Tarentola mauritanica) submitted to the presence of an introduced potential predator (Hemorrhois hippocrepis)

Stressful situations induce an increase in the production of reactive oxygen species (ROS) which can lead to molecular damage and alteration of cell function. The introduction of new potential predators induces physiological stress in native fauna. However, behavioral responses have been reported in preys, demonstrating an induction of the defenses against alien species. Behavioral and antioxidant enzyme responses in the moorish gecko, Tarentola mauritanica, against the invasive predator horseshoe whip snake (Hemorrhois hippocrepis) were assessed. Behavior was recorded and a tissue sample from the tail was collected after placing the gecko in a terrarium with previous absence or presence of the snake in 'Control' and 'H. hippocrepis' groups, respectively. Fifteen behavioral variables were examined, including tongue flick (TF) and locomotion patterns. Antioxidant enzyme activities -catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR)-, and the levels of reduced (GSH) and oxidized glutathione (GSSG), glutathione/glutathione disulfide ratio (GSH/GSSG) and malondialdehyde (MDA) concentrations were measured in the tissue sampled. Geckos exposed to the snake's odor showed a higher number of TF, longer amounts of time remaining motionless or moving in slow motion and they spent less time on the ground in comparison to the 'Control' group. The presence of the snake produced a significant increase in the activities of CAT, SOD and GR and a decrease in the GSH/GSSG ratio in T. mauritanica individuals exposed to the snake's scent. Thus, both behavioral responses and oxidative stress biomarkers clearly showed that T. mauritanica is able to recognize H. hippocrepis as a potential predator, despite being a recently introduced snake at the Balearic Islands.

Tail breakage and predatory pressure upon two invasive snakes (Serpentes: Colubridae) at two islands in the Western Mediterranean

Tail breakage is an important anti-predator mechanism in snake populations, which can be used as a proxy for predation intensity as natural observations of predator-prey interactions are scarce. Frequency of tail breakage was calculated for two Iberian colubrids recently introduced in the Balearic Islands (Western Mediterranean, Spain): Hemorrhois hippocrepis (Linnaeus, 1758) in Eivissa and Zamenis scalaris (Schinz, 1812) in Formentera. The effect of sex, life-stage, dorsal coloration pattern, body length and body condition on frequency of tail breakage and on remaining subcaudal scale pairs (SBC) were analyzed and compared between the native range and the invaded islands. An increase of the frequency of tail breakage with body size was found, supporting a size-related effect, which also occurs in the native range. Frequency of tail breakage of H. hippocrepis was lower in Eivissa when compared with the original area, while in Formentera Z. scalaris showed a higher frequency, which could be related to the different predator community on each island compared with the mainland. The study of the main ecological aspects of these recent introduced species may allow to assess their potential impact on insular ecosystems and their native biodiversity as well as to promote future control actions in these areas previously free of snakes.

First report of heavy metal presence in muscular tissue of loggerhead turtles Caretta caretta (Linnaeus, 1758) from the Balearic Sea (Balearic Islands, Spain)

The concentrations of cadmium (Cd), mercury (Hg) and lead (Pb) were determined in muscular tissue of eleven loggerhead turtles (Caretta caretta) from the Balearic Islands (Spain, Western Mediterranean). The metal levels found in the present study were similar or lower than concentrations detected in Andalusia (mainland Spain), Italy, Canary Islands (Spain) or Japan. As the main source of metals in the loggerhead turtle is the diet, low metal burdens could be explained by its opportunistic feeding way. No significant differences were found in metal concentrations between juveniles and subadults in any of the heavy metals analysed. Furthermore, no significant correlation was detected between heavy metal concentrations and straight carapace length (SCL) of the studied individuals. These results could derive from the homogeneity in age and size of the turtles sampled, so further studies including adults are needed in order to assess the heavy metal accumulation with turtle growth.

Assessment of the invasion process of the common raccoon Procyon lotor (Carnivora: Procyonidae) on a Mediterranean island a decade after its introduction

The common raccoon, Procyon lotor was introduced at the Balearic Islands (Spain) in 2006. Since then, a colonization process has been carried out, with captures of specimens in 24.30% of the surface of the whole Mallorca Island. For the first time, information has been provided on the invasive process of P. lotor in an insular ecosystem. 257 specimens of P. lotor were captured during the period 2007-2018, of them 104 were analysed to estimate population parameters. Demographic data showed that the population had a sex ratio of 1.00:1.21 (males:females), high BMI values and up to 40% of females were lactating when captured. Related to diet data, the composition was mainly the same as previous studies around its natural and introduced distribution area. Plant residues represented the 53.25 ± 38.66% followed by invertebrates with 12.22 ± 22.54%, inorganic remains with 11.9 ± 22.07% and finally the vertebrates with 4.94 ± 18.27%. Thus, it is shown how an opportunistic omnivorous species has adapted to the resources provided by the island. Cultivated plants' remains and plastic content in diet evidence that P. lotor is entering in contact with human settlements and agricultural areas. As occurred in other islands where P. lotor was introduced, it is expected that it could become a future problem for the conservation biodiversity in insular ecosystems, as well as for agriculture and human activity. Due to the potential impact on native biodiversity it is necessary to reinforce the implementation of control actions and prevent its expansion to the rest of the island.