International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.4, 197-207 http://ecoevopublisher.com/index.php/ijmeb 202 generations. Studies have shown that genetic changes often reverse plastic phenotypic changes to recover fitness after environmental shifts, indicating that plasticity serves as an emergency response rather than a stepping stone to genetic adaptation (Ho and Zhang, 2018). 5.3 Contribution of both mechanisms to avian survival in changing environments Both phenotypic plasticity and genetic adaptation play crucial roles in avian survival amidst rapid environmental changes. Phenotypic plasticity allows birds to quickly adjust to new conditions, providing an immediate buffer against environmental stressors. For instance, urban birds exhibit higher phenotypic variation in breeding phenology compared to their non-urban counterparts, which may result from plastic responses to the heterogeneous urban environment (Capilla-Lasheras et al., 2021). This plasticity can be vital for short-term survival and maintaining population viability. Genetic adaptation, while slower, ensures long-term survival by gradually optimizing phenotypes to the new environmental conditions. For example, in the Karoo scrub-robin, genetic variation underlying energy metabolic pathways and gut microbiome composition facilitates adaptation to arid conditions, highlighting the role of genetic adaptation in coping with extreme environments (Ribeiro et al., 2019). 6 Impact of Climate Change on Avian Genetic Adaptation 6.1 Detailed discussion on how climate change specifically drives genetic adaptation Climate change exerts significant pressure on avian species, driving genetic adaptation through various mechanisms. One primary way is by altering environmental conditions such as temperature, precipitation, and wind patterns, which in turn affect the availability of resources and habitat suitability. These changes can lead to shifts in phenotypic traits that are subject to natural selection. For instance, variations in weather conditions have been shown to impact nestling growth and development, which are critical for survival and reproductive success. Understanding how these environmental factors influence growth trajectories can help predict population changes and adaptive responses (Sauve et al., 2021). Moreover, climate change can impose evolutionary constraints by altering the selection pressures on morphological and phenological traits. For example, a meta-analysis revealed that while global warming has not systematically affected morphological traits in birds, it has advanced phenological traits such as breeding times. These phenological shifts are adaptive for some species but are often incomplete, indicating an evolutionary load that may threaten species persistence. Additionally, genetic correlations among traits can constrain the rate of adaptation, as seen in studies where multivariate constraints reduced the predicted rate of adaptation by 28% (Teplitsky et al., 2014). 6.2 Examples of avian species that have shown genetic adaptation to climate change Several avian species have demonstrated genetic adaptation to climate change. The great tit (Parus major) in the United Kingdom is a notable example. Over a 47-year study, this species exhibited phenotypic plasticity, allowing it to closely track environmental changes. This plasticity enabled the population to adjust behaviorally to the changing climate, although the response appeared to be fixed within the population. Another example is the collared flycatcher (Ficedula albicollis), where studies have shown that early environmental effects, rather than genetic heritability, significantly influence resting metabolic rate (RMR). This suggests that parental effects and early-life conditions play a crucial role in shaping adaptive responses to climate change (McFarlane et al., 2021). Additionally, North American migratory birds have shown a decline in body size over several decades, a phenotypic response correlated with increasing temperatures. This trend indicates that natural selection is favoring smaller body sizes, which may be an adaptive response to warmer climates (Buskirk et al., 2010).
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