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1. Genetic and ecological drivers of molt in a migratory bird

   https://doi.org/10.1038/s41598-022-26973-7  

   Contina, Andrea; Bossu, Christen M.; Allen, Daniel; Wunder, Michael B.; Ruegg, Kristen C. (January 2023, Scientific Reports)

   Abstract The ability of animals to sync the timing and location of molting (the replacement of hair, skin, exoskeletons or feathers) with peaks in resource availability has important implications for their ecology and evolution. In migratory birds, the timing and location of pre-migratory feather molting, a period when feathers are shed and replaced with newer, more aerodynamic feathers, can vary within and between species. While hypotheses to explain the evolution of intraspecific variation in the timing and location of molt have been proposed, little is known about the genetic basis of this trait or the specific environmental drivers that may result in natural selection for distinct molting phenotypes. Here we take advantage of intraspecific variation in the timing and location of molt in the iconic songbird, the Painted Bunting (Passerina ciris) to investigate the genetic and ecological drivers of distinct molting phenotypes. Specifically, we use genome-wide genetic sequencing in combination with stable isotope analysis to determine population genetic structure and molting phenotype across thirteen breeding sites. We then use genome-wide association analysis (GWAS) to identify a suite of genes associated with molting and pair this with gene-environment association analysis (GEA) to investigate potential environmental drivers of genetic variation in this trait. Associations between genetic variation in molt-linked genes and the environment are further tested via targeted SNP genotyping in 25 additional breeding populations across the range. Together, our integrative analysis suggests that molting is in part regulated by genes linked to feather development and structure (GLI2andCSPG4) and that genetic variation in these genes is associated with seasonal variation in precipitation and aridity. Overall, this work provides important insights into the genetic basis and potential selective forces behind phenotypic variation in what is arguably one of the most important fitness-linked traits in a migratory bird. 

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2. Sea ice concentration decline in an important Adélie penguin molt area

   https://doi.org/10.1073/pnas.2306840120  

   Schmidt, Annie E; Lescroël, Amélie; Lisovski, Simeon; Elrod, Megan; Jongsomjit, Dennis; Dugger, Katie M; Ballard, Grant (November 2023, Proceedings of the National Academy of Sciences)

   Unlike in many polar regions, the spatial extent and duration of the sea ice season have increased in the Ross Sea sector of the Southern Ocean during the satellite era. Simultaneously, populations of Adélie penguins, a sea ice obligate, have been stable or increasing in the region. Relationships between Adélie penguin population growth and sea ice concentration (SIC) are complex, with sea ice driving different, sometimes contrasting, demographic patterns. Adélie penguins undergo a complete molt annually, replacing all their feathers while fasting shortly after the breeding season. Unlike most penguin species, a majority of Adélies are thought to molt on sea ice, away from the breeding colonies, which makes this period particularly difficult to study. Here, we evaluate the hypothesis that persistent areas of high SIC provide an important molting habitat for Adélie penguins. We analyzed data from geolocating dive recorders deployed year-round on 195 adult penguins at two colonies in the Ross Sea from 2017 to 2019. We identified molt by detecting extended gaps in postbreeding diving activity and used associated locations to define two key molting areas. Remotely sensed data indicated that SIC during molt was anomalously low during the study and has declined in the primary molt area since 1980. Further, annual return rates of penguins to breeding colonies were positively correlated with SIC in the molt areas over 20 y. Together these results suggest that sea ice conditions during Adélie penguin molt may represent a previously underappreciated annual bottleneck for adult survival. 

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3. A Shellfish Journey: Characterizing an Inhibitory Receptor in the Crustacean Molt Cycle

   Madril, A; Perez-Moreno, J; Kozma, M; Gandhi, N; Hernandez_Jeppesen, L; Ventura, T; Mykles, DL (September 2024, Integrative and comparative biology)

   None (Ed.)

   Meeting abstract 

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4. A novel model for RTK mediated regulation of the molt cycle in the blackback land crab

   Collins, S.; Kozma, M.; Mykles, D. (March 2023, Integrative and comparative biology)
5. Lower survival of hybrid grosbeaks, but not towhees, suggests a molt divide disfavors hybrids

   https://doi.org/10.1093/evolut/qpad112  

   Rohwer, Vanya G.; Hagler, Samantha J.; Van Doren, Benjamin M.; Fuentes, Miguel; Billerman, Shawn M.; Linnen, ed., Catherine; Zelditch, ed., Miriam (June 2023, Evolution)

   Abstract Although avian hybrid zones in the Great Plains have been studied for almost 70 years, we know surprisingly little about the fitness costs to hybrids that keep these zones narrow. We compare age ratios in grosbeaks (Pheucticus ludovicianus and P. melanocephalus) and towhees (Pipilo erythropthalums and P. maculatus), two species pairs that differ in their life histories and molt schedules, to evaluate survival between hybrids and parentals. We then contrast molt and migratory divides as possible sources of selection against hybrids. Hybrid grosbeaks had 27%–33% lower survival relative to their parentals, whereas hybrid towhees had survival rates similar to parentals. Age ratio data for hybrid grosbeaks suggest high mortality in older birds, as expected if selection operates after the first year of life. This pattern is consistent with parental species of grosbeaks having contrasting molt schedules relative to migration, suggesting high mortality costs to hybrids driven by molt biology, which are expressed later in life. Contrasts in molt schedules are absent in towhees. While migratory divides may exist for towhees and grosbeaks, the low adult survival of hybrid grosbeaks suggest that molt may be an important and underappreciated source of selection maintaining this and other narrow avian hybrid zones. 

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