Baldwin, M. W. | bioRxiv Science

bioRxiv2024

Convergent and lineage-specific genomic changes contribute to adaptations in sugar-consuming birds

High-sugar diets cause human metabolic diseases, yet several bird lineages convergently adapted to feeding on sugar-rich nectar or fruits. We investigated the underlying molecular mechanisms in hummingbirds, parrots, honeyeaters, and sunbirds by generating nine new genomes and 90 tissue-specific transcriptomes. Comparative screens revealed an excess of repeated selection in both protein-coding and regulatory sequences in sugar-feeding birds, suggesting reuse of genetic elements. Sequence or expression changes in sugar-feeders affect genes involved in blood pressure regulation, lipid, amino acid and carbohydrate metabolism, with experiments showing functional changes in honeyeater hexokinase 3. MLXIPL, a key regulator of sugar and lipid homeostasis, showed convergent sequence and regulatory changes across all sugar-feeding clades; experiments revealed enhanced sugar-induced transcriptional activity of hummingbird MLXIPL, highlighting its adaptive role in high-sugar diets. Summary Figure: Our comparative screens across four independent sugar-feeding bird groups identified both repeated and lineage-specific targets of selection O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=65 SRC="FIGDIR/small/610474v2_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@148f5c8org.highwire.dtl.DTLVardef@1005dbaorg.highwire.dtl.DTLVardef@1097facorg.highwire.dtl.DTLVardef@9d365c_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2023

Evolution of novel sensory organs in fish with legs

How do animals evolve new traits? Sea robins are unusual "walking" fishes that use leg-like appendages to navigate the seafloor. Here, we show that legs are bona fide sense organs that mediate the unique ability to localize and uncover buried prey. We then probe the developmental and physiological basis of these novel sense organs as a striking example of a major trait gain in evolution. We find certain sea robin species have legs with unique end-organs called papillae that mediate enhanced mechanical and chemical sensitivity to enable predatory digging behavior. Papillae exhibit dense innervation from touch-sensitive neurons, noncanonical epithelial taste receptors, and chemical sensitivity that drives predatory digging behavior. Using a combination of developmental analyses, crosses between species with and without papillae, and interspecies comparisons of sea robins from around the world, we demonstrate that papillae represent a key evolutionary innovation associated with behavioral niche expansion on the seafloor. These discoveries provide a conceptual framework for understanding how molecular, cellular, and tissue-scale adaptations integrate to produce novel organismic traits and behavior.

evolutionary biology↗