International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.4, 162-173 http://ecoevopublisher.com/index.php/ijmeb 166 phenotypic plasticity. This plasticity allows organisms to adapt their phenotypes in response to environmental variations (Lema, 2014; Sharma et al., 2018). Additionally, the IGF1 pathway has been identified as being under increased evolutionary constraint in long-lived mammals, indicating its significant role in trait development related to longevity (Chen et al., 2018; Kowalczyk et al., 2020). 6.2 Metabolic pathways influencing physiological traits Metabolic pathways are integral to the physiological adaptations observed in mammals. For example, lipid metabolism pathways have been shown to undergo convergent evolutionary changes in marine mammals, facilitating their adaptation to aquatic environments. These changes include both adaptive evolution and loss of function in genes related to muscle physiology and sensory systems (Chikina et al., 2016). Furthermore, pathways related to cell cycle, DNA repair, and cell death are under increased evolutionary constraint in long-lived mammals, highlighting their importance in maintaining physiological traits that contribute to extended lifespan. 6.3 Pathways related to sensory adaptations Sensory adaptations in mammals are driven by specific molecular pathways that have undergone significant evolutionary changes. The phototransduction pathway, which is crucial for visual perception, has evolved under non-random selective pressures. Central proteins in this pathway, such as G proteins and retinoid cycle chaperones, are more evolutionarily constrained, while peripheral proteins like ion channels have experienced relaxed selective pressures. Positive selection signals have been detected in genes such as the short-wave opsin (OPN1SW) in hominids, indicating adaptive changes in vision (Invergo et al., 2013). Similarly, genes involved in the development and function of the mammalian inner ear have shown signatures of positive selection, contributing to the unique hearing capacities of mammals. For instance, the genes STRIP2 and ABLIM2 have been identified as crucial for auditory function, with mutations leading to cochlear neuropathy in mice (Pisciottano et al., 2019). Additionally, the loss of regulatory DNA sequences near genes involved in neural function has been linked to sensory adaptations in humans, such as the loss of sensory vibrissae and penile spines (McLean et al., 2011; Endo et al., 2020). 7 Case Studies of Trait Evolution 7.1 Evolution of fur and skin pigmentation The evolution of fur and skin pigmentation in mammals is a complex process influenced by both genetic and environmental factors. Mammalian colors and color patterns are among the most diverse traits in nature, driven by variations in pigment type and distribution. These variations have distinct developmental bases and are influenced by factors such as background matching, signaling, and physiological needs (Caro and Mallarino, 2020). Research on marine mammals has shown that genes related to skin and connective tissue have undergone adaptive evolution, further illustrating the genetic mechanisms behind pigmentation changes (Chikina et al., 2016). 7.2 Adaptations in mammalian teeth and diet Mammalian teeth and diet have co-evolved to meet the dietary needs of different species. The Peromyscus genus of rodents, for example, exhibits significant diversity in reproductive strategies and dietary adaptations, which are likely driven by local environmental conditions and plasticity in phenotypic traits (Wilsterman and Cunningham, 2022). Marine mammals also provide a compelling case for studying dietary adaptations. Genes associated with lipid metabolism and sensory systems have shown accelerated evolutionary rates, suggesting adaptations to a marine diet that includes high-fat content and different sensory requirements compared to terrestrial diets. These genetic changes are indicative of the broader evolutionary pressures that shape mammalian teeth and dietary adaptations. 7.3 Evolutionary rates and lifespan phenotypes Kowalczyk et al. (2020) proposed a novel approach to identify associations between protein evolutionary rates and continuous phenotypes across mammalian phylogeny (Figure 2). They treated absolute and relative lifespans as quantitative traits and demonstrated that these lifespan traits influence the evolutionary constraints of hundreds of genes. Specifically, the study found that genes associated with the cell cycle, DNA repair, cell death, the IGF1 pathway, and immunity are under increasing evolutionary constraint in large, long-lived mammals.
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