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How climate change affect the “weakest links” of animal tolerance?

Final Report Summary - THE WEAKEST LINKS (How climate change affect the 'weakest links' of animal tolerance?)

Project context and objectives

The success of a species is strictly dependent on the capability of single individuals to sustain environmental conditions and to effectively cope with any fluctuations throughout their entire life. The scope for tolerance of a species to the variation of abiotic and biotic factors includes its adaptability and performance, but our understanding of this tolerance is very often restricted to the adaptability of adult individuals. In this view, it is remarkable that different phases of ontogenesis and specific life stages display higher vulnerability to climate effects, thus markedly reducing the overall range of scope tolerance. Moreover, the very same adult individuals do not have homogeneous responses to environmental factors during their entire life, but they are more susceptible to external changes during critical adult life phases, such as the reproductive period. Climate change poses additional challenges to animals, giving marked and stochastic fluctuation of the niche parameters. Consequently, the pressure of climate change on the 'weakest links' or the phases of lowest animal tolerance, represented by embryos, larvae and sub-adult individuals, as well as by reproducing, spawning and caring parents, is the strongest. Surprisingly enough, physiological, ecological, morphological, as well as behavioural traits of these weakest links and phases have been receiving modest consideration within current attempts to forecast the effects of climate change on ecosystems, species and communities.

The primary research objectives are:

Thermal tolerance in key species:
- to investigate the tolerance windows at two edges of their latitudinal distribution of two marine ectotherm model species ( Carcinus spp.);
- to compare the adaptive flexibility of a vertebrate and an invertebrate species to specific environmental solicitations;
- to investigate the tolerance windows, at the two latitudinal edges of species distribution, of sperm, eggs and developing embryos;
- to test the hypothesis of environmentally induced adaptive strategies of gamete production.

Physiological resilience to climate change:
- to investigate the physiological resilience and the adaptive flexibility of animals, from different latitudes, experimentally exposed and/or acclimatised to selective conditions (i.e. temperature, oxygen, CO2);
- to analyse the variability of expression and activity of selected proteins and enzymes in animals exposed and acclimatised to altered environmental conditions;
- to test the survival and the physiological responses of sperm, eggs and developing embryos in altered environmental conditions;
- to propose a rank of regional vulnerability to climate change in relation to the different tolerance windows;
- to re-define and adjust the tolerance windows of marine animals as a function of the adaptive flexibility of their gametes and early developmental stages.

Methodological objectives:
- to apply a multilevel approach to investigate the adaptive physiology, ranging from molecular to whole animal analyses;
- to extend the use of micro-sensors and micro-analyzers to investigate the physiology of sperm, eggs and early life stages.

Work performed and main results

1. I investigated and confirmed the pronounced thermal tolerance of a eurytherm model species, the green crab Carcinus maenas, through its high ability to sustain efficient oxygen transport to tissue. Similar to other eurytherms, C. maenas compensates for naturally occurring acute warming events via the integrated response of circulatory and respiratory systems. Furthermore, the amount of oxygen stored through binding to hemocyanin makes an emergency supply available when the acute warming increases severely. Thus, the thermal response of C. maenas occurs through the two following phases: during initial warming (between 10 ° to 16 °C), oxygen consumption and heart rate increase, while cardiac output and blood oxygenation decrease; during the second phase (between 16 °