Suchergebnisse

Context Aggressive encounters, including those with venomous species, impose selective pressure on native species. Immediate lethal outcomes of these encounters have been the primary focus of research in this field. However, not all aggressive interactions result in immediate mortality, and indirect consequences of aggressive interactions may be an equally important but under-considered selective force. The red imported fire ant is a globally important venomous invader that imposes novel selective pressure on native communities. Aims We examined indirect effects of fire ant envenomation on native fence lizard growth rates and subsequent survival. Methods Fence lizards are subject to fire ant envenomation in the field when they eat fire ants (they are stung inside the mouth) and through fire ant attack (they are stung on the body). We quantified body sizes of adult lizards from fire ant-invaded and uninvaded sites. We then experimentally exposed hatchling fence lizards to the two modes of fire ant envenomation, and quantified their growth and survival over 1 year. Key results Lizards from fire ant-invaded sites were smaller than those from an uninvaded site, even at similar latitudes. However, in contrast to studies on other native taxa, we found no effect of fire ant venom on growth rates of lizards from naïve or fire ant-invaded populations. Lizards exposed to fire ant venom, through both eating and attack, experienced higher rates of delayed mortality, with 34% of lizards dying 1–11 weeks post-envenomation compared with 12% of lizards in the control treatment. These patterns were true for fire ant naïve populations as well as those exposed to fire ants for ~35 generations. Conclusions These results suggest that the smaller body sizes observed in fence lizards from fire ant-invaded sites are not a consequence of exposure to fire ant venom. However, fence lizards from both sites suffer delayed survival costs of fire ant envenomation. Implications The present study highlights the importance of considering indirect fitness consequences of aggressive encounters if we are to fully understand the ecological and evolutionary consequences of these interactions, and adequately manage and predict the impacts of invasive species.

Article published Nov 2021. Data are available at https://doi.org/10.5281/zenodo.5549751. This work was partly funded during writing and review by the European Union's Horizon 2020 research and innovation programme (Marie Skłodowska Curie grant no. 799025, to KJM). Abstract Reproduction is a critical part of an animal's life history, but one which incurs significant costs to survival and future reproductive potential. These physiological consequences are likely to be influenced by context – for example, if an individual is subject to environmental stressors, physiological and behavioral changes associated with reproduction may be altered. Glucocorticoids, hormones produced as part of the physiological response to stressors, may alter how reproduction affects female physiology and behavior, and therefore the outcomes of reproductive trade-offs. Glucocorticoids prioritize immediate survival over reproduction, for example through changes in immune function, metabolic rate, and foraging, which may reduce energy expenditure or increase energy gain. However, we previously found that female eastern fence lizards (Sceloporus undulatus) experiencing elevated glucocorticoid levels during gestation were nevertheless able to maintain reproductive output and body condition. Here we investigate compensatory mechanisms by which eastern fence lizard females may maintain reproduction under experimental increases in a glucocorticoid, corticosterone (CORT). We found that, although CORT-treated females had similar immune function and behavior, they had reduced metabolic rates 3-5 days post-parturition compared to control females. Given that CORT-treated females spent a similar time basking and had equal food intake compared to control females, we suggest that the reduced metabolic rate is a mechanism by which CORT-treated females maintain their energy balance and reduce the energetic costs of gestation during periods of stress. This study suggests that physiological responses to reproduction may be context-dependent and could act ...