Browsing by Author "Vianna, Juliana A."

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    Adaptation and Cryptic Pseudogenization in Penguin Toll-Like Receptors
    (2022) Fiddaman, Steven R.; Vinkler, Michal; Spiro, Simon G.; Levy, Hila; Emerling, Christopher A.; Boyd, Amy C.; Dimopoulos, Evangelos A.; Vianna, Juliana A.; Cole, Theresa L.; Pan, Hailin; Fang, Miaoquan; Zhang, Guojie; Hart, Tom; Frantz, Laurent A. F.; Smith, Adrian L.
    Penguins (Sphenisciformes) are an iconic order of flightless, diving seabirds distributed across a large latitudinal range in the Southern Hemisphere. The extensive area over which penguins are endemic is likely to have fostered variation in pathogen pressure, which in turn will have imposed differential selective pressures on the penguin immune system. At the front line of pathogen detection and response, the Toll-like receptors (TLRs) provide insight into host evolution in the face of microbial challenge. TLRs respond to conserved pathogen-associated molecular patterns and are frequently found to be under positive selection, despite retaining specificity for defined agonist classes. We undertook a comparative immunogenetics analysis of TLRs for all penguin species and found evidence of adaptive evolution that was largely restricted to the cell surface-expressed TLRs, with evidence of positive selection at, or near, key agonist-binding sites in TLR1B, TLR4, and TLR5. Intriguingly, TLR15, which is activated by fungal products, appeared to have been pseudogenized multiple times in the Eudyptes spp., but a full-length form was present as a rare haplotype at the population level. However, in vitro analysis revealed that even the full-length form of Eudyptes TLR15 was nonfunctional, indicating an ancestral cryptic pseudogenization prior to its eventual disruption multiple times in the Eudyptes lineage. This unusual pseudogenization event could provide an insight into immune adaptation to fungal pathogens such as Aspergillus, which is responsible for significant mortality in wild and captive bird populations.
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    Are threatened seabird colonies of the pacific ocean genetically vulnerable? The case of the red-tailed tropicbird, Phaethon rubricauda, as a model species
    (2024) Varela, Andrea, I; Brokordt, Katherina; Vianna, Juliana A.; Frugone, Maria Jose; Ismar-Rebitz, Stefanie M. H.; Gaskin, Chris P.; Carlile, Nicholas; O'Dwyer, Terence; Adams, Josh; Vanderwerf, Eric A.; Luna-Jorquera, Guillermo
    Oceanic seabirds have suffered population declines and extirpations due to human disturbance and still face multiple threats. Here, we assessed the potential genetic vulnerability of the red-tailed tropicbird, Phaethon rubricauda, a seabird species threatened by human disturbance and listed as 'least concern' by the IUCN. Using Single Nucleotide Polymorphisms (SNPs) we evaluated the genetic population structure of the red-tailed tropicbird throughout the Pacific Ocean using samples from 132 individuals from six islands. We sampled individuals from islands without human-related disturbance (non-impacted islands) and with human-related disturbance (impacted islands). Results of genome-wide SNP analyses were consistent with previous results using mitochondrial DNA sequences analyses. Genetic diversity did not differ between impacted and non-impacted islands, and low inbreeding estimates were detected for all colonies. The SNPs analyses confirmed a pattern of isolation by distance and significant inter-regional (Chile, Australasia, and Hawai'i) genetic structure, but revealed greater differentiation of tropicbirds in Hawai'i compared with Chile and Australasia. Within regions, our results further indicated significant differentiation between Rapa Nui and Salas & G & oacute;mez Island (Chile), and between Meyer and Phillip islands (Australasia) that was not detected using mitochondrial DNA analyses. Within Hawai'i, we found a lack of significant genetic differentiation between O'ahu and Kaua'i, separated by 200 km. Our findings indicated that red-tailed tropicbird colonies are at genetic risk due to limited dispersal among colonies which may reduce the fitness of the species in the long-term. We suggest that red-tailed tropicbird colonies are vulnerable to future population declines because recovery through immigration from other islands may be limited by geographic distance. Conservation actions will help preserve genetic diversity and discrete populations for this native seabird at colonies throughout the Pacific.
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    Uncovering population structure in the Humboldt penguin (Spheniscus humboldti) along the Pacific coast at South America
    (2019) Dantas, Gisele P. M.; Oliveira, Larissa R.; Santos, Amanda M.; Flores, Mariana D.; de Melo, Daniella R.; Simeone, Alejandro; Gonzalez-Acuna, Daniel; Luna-Jorquera, Guillermo; Le Bohec, Celine; Valdes-Velasquez, Armando; Cardena, Marco; Morgante, Joao S.; Vianna, Juliana A.
    The upwelling hypothesis has been proposed to explain reduced or lack of population structure in seabird species specialized in food resources available at cold-water upwellings. However, population genetic structure may be challenging to detect in species with large population sizes, since variation in allele frequencies are more robust under genetic drift. High gene flow among populations, that can be constant or pulses of migration in a short period, may also decrease power of algorithms to detect genetic structure. Penguin species usually have large population sizes, high migratory ability but philopatric behavior, and recent investigations debate the existence of subtle population structure for some species not detected before. Previous study on Humboldt penguins found lack of population genetic structure for colonies of Punta San Juan and from South Chile. Here, we used mtDNA and nuclear markers (10 microsatellites and RAG1 intron) to evaluate population structure for 11 main breeding colonies of Humboldt penguins, covering the whole spatial distribution of this species. Although mtDNA failed to detect population structure, microsatellite loci and nuclear intron detected population structure along its latitudinal distribution. Microsatellite showed significant R-st values between most of pairwise locations (44 of 56 locations, R-st = 0.003 to 0.081) and 86% of individuals were assigned to their sampled colony, suggesting philopatry. STRUCTURE detected three main genetic clusters according to geographical locations: i) Peru; ii) North of Chile; and iii) Central-South of Chile. The Humboldt penguin shows signal population expansion after the Last Glacial Maximum (LGM), suggesting that the genetic structure of the species is a result of population dynamics and foraging colder water upwelling that favor gene flow and phylopatric rate. Our findings thus highlight that variable markers and wide sampling along the species distribution are crucial to better understand genetic population structure in animals with high dispersal ability.