Buttemer, W. A. | 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↗

bioRxiv2021

Experimental corticosterone manipulation increases mature feather corticosterone content: implications for inferring avian stress history from feather analyses

Feathers incorporate plasma corticosterone (CORT) during their development and, because feathers lack blood supply at maturity, the CORT content of feathers (CORTf) is presumed to represent an integrated average of plasma CORT levels during feather growth. We tested this assumption by quantifying CORTf in feathers of house sparrows (Passer domesticus) that were plucked before and after being implanted with either a corticosterone-filled, metyrapone-filled, or empty (sham) silastic capsule. Two of the seven flight feathers collected from each bird were fully grown when birds received implants. We found that CORTf of all seven feathers corresponded with treatment type, and with plasma CORT levels of non-moulting reference sparrows also given these implants. We also found that CORTf of the two mature feathers of each bird were 4 to 10-fold higher than values measured in new feathers. Given the avascular nature of mature feathers, and the fact that we did not wash the feathers prior to analysis, the most plausible explanation for our results is that CORT was externally deposited on feathers after implant. This outcome emphasises the need for follow-up studies to identify the external sources of CORT that may affect the CORTf of feathers. We hope this study will stimulate discussions and further much needed studies on the mechanism of CORT deposition in feathers and open exciting opportunities for application of such methods in ecological research, such as measuring multiple time scales in such a non-invasive manner.

physiology↗