Browsing by Author "Gaitan-Espitia, Juan Diego"

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    Do phytoplankton require oxygen to survive? A hypothesis and model synthesis from oxygen minimum zones
    (2023) Wong, Jane C. Y.; Raven, John A.; Aldunate, Montserrat; Silva, Sebastian; Gaitan-Espitia, Juan Diego; Vargas, Cristian A.; Ulloa, Osvaldo; von Dassow, Peter
    It is commonly known that phytoplankton have a pivotal role in marine biogeochemistry and ecosystems as carbon fixers and oxygen producers, but their response to deoxygenation has scarcely been studied. Nonetheless, in the major oceanic oxygen minimum zones (OMZs), all surface phytoplankton groups, regardless of size, disappear and are replaced by unique cyanobacteria lineages below the oxycline. To develop reasonable hypotheses to explain this pattern, we conduct a review of available information on OMZ phytoplankton, and we re-analyze previously published data (flow cytometric and hydrographic) on vertical structure of phytoplankton communities in relation to light and O-2 levels. We also review the physical constraints on O-2 acquisition as well as O-2-dependent metabolisms in phototrophs. These considerations, along with estimates of the photosynthetic capacity of phytoplankton along OMZ depth profiles using published data, suggest that top-down grazing, respiratory demand, and irradiance are insufficient to fully explain the vertical structure observed in the upper, more sunlit portions of OMZs. Photorespiration and water-water cycles are O-2-dependent pathways with low O-2 affinities. Although their metabolic roles are still poorly understood, a hypothetical dependence on such pathways by the phytoplankton adapted to the oxic ocean might explain vertical patterns in OMZs and results of laboratory experiments. This can be represented in a simple model in which the requirement for photorespiration in surface phytoplankton and O-2-inhibition of OMZ lineages reproduces the observed vertical fluorescence profiles and the replacement of phytoplankton adapted to O-2 by lineages restricted to the most O-2-deficient waters. A high O-2 requirement by modern phytoplankton would suggest a positive feedback that intensifies trends in OMZ extent and ocean oxygenation or deoxygenation, both in Earth's past and in response to current climate change.
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    Incomplete lineage sorting and phenotypic evolution in marsupials
    (2022) Feng, Shaohong; Bai, Ming; Rivas-Gonzalez, Iker; Li, Cai; Liu, Shiping; Tong, Yijie; Yang, Haidong; Chen, Guangji; Xie, Duo; Sears, Karen E.; Franco, Lida M.; Gaitan-Espitia, Juan Diego; Nespolo, Roberto F.; Johnson, Warren E.; Yang, Huanming; Brandies, Parice A.; Hogg, Carolyn J.; Belov, Katherine; Renfree, Marilyn B.; Helgen, Kristofer M.; Boomsma, Jacobus J.; Schierup, Mikkel Heide; Zhang, Guojie
    Incomplete lineage sorting (ILS) makes ancestral genetic polymorphisms persist during rapid speciation events, inducing incongruences between gene trees and species trees. ILS has complicated phylogenetic inference in many lineages, including hominids. However, we lack empirical evidence that ILS leads to incongruent phenotypic variation. Here, we performed phylogenomic analyses to show that the South American monito del monte is the sister lineage of all Australian marsupials, although over 31% of its genome is closer to the Diprotodontia than to other Australian groups due to ILS during ancient radiation. Pervasive conflicting phylogenetic signals across the whole genome are consistent with some of the morphological variation among extant marsupials. We detected hundreds of genes that experienced stochastic fixation during ILS, encoding the same amino acids in non-sister species. Using functional experiments, we confirm how ILS may have directly contributed to hemiplasy in morphological traits that were established during rapid marsupial speciation ca. 60 mya.
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    Local scale extreme low pH conditions and genetic differences shape phenotypic variation in a broad dispersal copepod species
    (2023) Aguilera, Victor M.; Sepulveda, Fabiola; von Dassow, Peter; Gaitan-Espitia, Juan Diego; Mesas, Andres; Vargas, Cristian A.
    Extreme low pH events in estuaries and upwelling areas can modulate the phenotypic and genetic diversity of natural populations. To test this hypothesis, we explored the linkage between local scale extreme low pH events, genetic diversity, and variation in fecundity-related traits (body size, egg size, and egg production rate) in the broad-dispersal copepod Acartia tonsa. We assessed genetic and phenotypic characteristics of populations by contrasting extreme low pH environments (upwelling and temperate estuary) in the coastal Southeast Pacific, under natural and experimental conditions. These populations showed significant genetic differentiation with higher diversity in mitochondrial and nuclear loci (encoding mtCOI and 18S rRNA) in the estuarine population. Copepods from this population are exposed to more frequent extreme low pH events (< 7.7), and the adult females exhibit consistent phenotypic variation in body size, egg size, and egg production rate across different cohorts. Experimental acclimation to extreme low pH conditions revealed no significant differences in fecundity-related traits between A. tonsa populations. Although these results partially support our hypothesis, the experimental findings suggest other drivers might also influence phenotypic differences in the local environments.
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    Upper environmental pCO2 drives sensitivity to ocean acidification in marine invertebrates
    (2022) Vargas, Cristian A.; Cuevas, L. Antonio; Broitman, Bernardo R.; San Martin, Valeska A.; Lagos, Nelson A.; Gaitan-Espitia, Juan Diego; Dupont, Sam
    The authors link the effects of pCO(2) on marine invertebrates to the localized pCO(2) conditions of their coastal habitats. They show that responses depend on the deviation from the locally experienced upper pCO(2) level, highlighting the importance of small-scale variability and adaptation.