Echolocation is a sensory system whereby certain mammals navigate and forage using sound waves, usually in environments where visibility is limited. Curiously, echolocation has evolved independently in bats and whales, which occupy entirely different environments. Based on this phenotypic convergence, recent studies identified several echolocation-related genes with parallel sites at the protein sequence level among different echolocating mammals, and among these, prestin seems the most promising. Although previous studies analyzed the evolutionary mechanism of prestin, the functional roles of the parallel sites in the evolution of mammalian echolocation are not clear. By functional assays, we show that a key parameter of prestin function, 1/α, is increased in all echolocating mammals and that the N7T parallel substitution accounted for this functional convergence. Moreover, another parameter, V_1/2, was shifted toward the depolarization direction in a toothed whale, the bottlenose dolphin (Tursiops truncatus) and a constant-frequency (CF) bat, the Stoliczka’s trident bat (Aselliscus stoliczkanus). The parallel site of I384T between toothed whales and CF bats was responsible for this functional convergence. Furthermore, the two parameters (1/α and V_1/2) were correlated with mammalian high-frequency hearing, suggesting that the convergent changes of the prestin function in echolocating mammals may play important roles in mammalian echolocation. To our knowledge, these findings present the functional patterns of echolocation-related genes in echolocating mammals for the first time and rigorously demonstrate adaptive parallel evolution at the protein sequence level, paving the way to insights into the molecular mechanism underlying mammalian echolocation.

New echolocator: Echolocation is a well demonstrated convergent sensory mode in bats and toothed whales. These lineages are not closely related, and this sense might be more broadly distributed than we recognize. Using a suite of approaches, He et al. show that the lineage of soft-furred tree mice (genus Typhlomys ) includes multiple echolocators. Clear evidence of the behavioral use of echolocation under fully dark conditions was supported by the convergence of ear bone morphology and hearing-related genes with other echolocating mammals. Science , aay1513, this issue p. eaay1513

Echolocation allows toothed whales to adapt to underwater habitats where vision is ineffective. Because echolocation requires the ability to detect exceptional high-frequency sounds, fossils related to the auditory system can help to pinpoint the origin of echolocation in whales. However, because of conflicting interpretations of archaeocete fossils, when and how whales evolved the high-frequency hearing correlated with echolocation remain unclear. We address these questions at the molecular level by systematically investigating the convergent evolution of 7206 orthologs across 16 mammals and find that convergent genes between the last common ancestor of all whales (LCAW) and echolocating bats are not significantly enriched in functional categories related to hearing, and that convergence in hearing-related proteins between them is not stronger than that between nonecholocating mammalian lineages and echolocating bats. However, these results contrast with those of parallel analyses between the LCA of toothed whales (LCATW) and echolocating bats. Furthermore, we reconstruct the ancestral genes for the hearing protein prestin for the LCAW and LCATW; we show that the LCAW prestin exhibits the same function as that of nonecholocating mammals, but the LCATW prestin shows functional convergence with that of extant echolocating mammals. Mutagenesis shows that functional convergence of prestin is driven by convergent changes in the prestins S392A and L497M in the LCATW and echolocating bats. Our results provide genomic and functional evidence supporting the origin of high-frequency hearing in the LCATW, not the LCAW, and reveal molecular insights into the origin and evolutionary trajectories of echolocation in whales.

Molecular basis for mammalian echolocation has been receiving much concerns. Recent findings on the parallel evolution of prestin sequences among echolocating bats and toothed whales suggest that adaptations for high-frequency hearing have occurred during the evolution of echolocation. Here, we report that although the species tree for echolocating bats emitting echolocation calls with frequency modulated (FM) sweeps is paraphyletic, prestin exhibits similar functional changes between FM bats. Site-directed mutagenesis shows that the amino acid 308S in FM bats is responsible for the similar functional changes of prestin. We strongly support that the occurrence of serine at position 308 is a case of hemiplasy, caused by incomplete lineage sorting of an ancestral polymorphism. Our study not only reveals sophisticated molecular basis of echolocation in bats, but also calls for caution in the inference of molecular convergence in species experiencing rapid radiation.

Vertebrates display a vast array of morphological adaptations to ecological niches. These involve multiple large-scale changes of the appendages, such as evolving limbs from fins, wings (birds, bats), and even the loss of appendages (caecilians, lizards, snakes) during the transition from water to land. Reversals also exist, such as whales evolving back to having fins. This tremendous diversity of appendages leads to development of vertebrate appendage being a model for understanding the evolution and development of appendage morphologies. The development of appendages from buds is conserved among vertebrate. Appendage growth depends on cell proliferation and specializations along proximal-distal (PD), anterior-posterior (AP) and dorsal-ventral (DV) axes. Cell proliferation in lateral plate mesoderm relates to the initiation of buds. The growth of ectodermal cells forms an apical ectodermal ridge along the bud and secreted fibroblast growth factors (Fgfs) control outgrowth of the bud. Gene expression in a specific time and region and levels of expression determines if a bud becomes a fin, wing or limb. Several genes and regulation signal pathways have evolved during transition of fins to alternative types of limbs. Fgfs, Wnts, Shh, RA and Bmps signaling regulate the genes Tbx5, Tbx4, Fgf8, and Bmp and the Hox gene family, respectively, which are essential for appendage development and evolution. These genes associate with chondrocyte proliferation and differentiation. T-box, fgfs and wnts in lateral plate mesoderm are essential for lateral bud initiation, which relates to the transition of ancestral median fins to paired fins. The origin of appendages for the emergence onto land was depended on regions and levels of expression for such as Bmp4, Hoxd13 and hand2, which bmps and shh signals regulate, respectively. Hox13 is expressed on the distal margin of fins and limbs buds while the larger-scale region of expression in the limb bud constitutes the basis of the development of the PD axis in terrestrial vertebrates. Loss of Hand2 leads to the deficiency of hind-limbs in whales. High levels of expression of Bmps in the forelimb of bats lead the forelimb to be longer than the hind-one. Furthermore, not only signaling regulation, but also transcription factors, regions of genome regulation and some long non-coding RNAs (lncRNAs) play regulatory roles in gene expression during appendage development.

Introduction: The potential therapeutic role of nicotine in Alzheimer's disease (AD) remains controversial, particularly regarding its age-dependent effects and underlying mechanisms. Methods: This study investigated the impact of chronic nicotine administration on cognitive function and molecular pathways in Presenilin 1/2 double knockout (DKO) mice, an amyloid-β (Aβ)- independent model of AD. Three-month-old and eight-month-old DKO and wild-type (WT) mice received oral nicotine treatment (100 μg/ml) for three months. Behavioral assessments revealed that while the 6-month-old cohort showed no significant differences between nicotine-treated and control groups regardless of genotype, nicotine improved contextual fear memory in 11-month- old DKO mice but impaired nest-building ability and cued fear memory in age-matched WT controls. Transcriptome analysis of the prefrontal cortex identified distinct molecular responses to nicotine between genotypes. Results: In DKO mice, nicotine modulated neuropeptide signaling and reduced astrocyte activation, while in WT mice, it disrupted cytokine-cytokine receptor interaction and neuroactive ligand- receptor interaction pathways. Western blot analysis revealed that nicotine treatment significantly reduced tau hyperphosphorylation and Glial Fibrillary Acidic Protein (GFAP) expression in 11-month-old DKO mice, which was further confirmed by immunohistochemistry showing decreased astrocyte activation in multiple brain regions. Conclusion: These findings demonstrate that nicotine's effects on cognition and molecular pathways are both age- and genotype-dependent, suggesting its therapeutic potential may be limited to specific stages of neurodegeneration while potentially having adverse effects in healthy aging brains.