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Data from: Divergent transcriptional patterns are related to differences in hypoxia tolerance between the intertidal and the subtidal sculpins
Mandic, Milica; Ramon, Marina L.; Gracey, Andrew Y.; Richards, Jeffrey G. — 2014-11-19 Transcriptionally mediated phenotypic plasticity as a mechanism of modifying traits in response to an environmental challenge remains an important area of study. We compared the transcriptional responses to low-oxygen (hypoxia) of the hypoxia tolerant intertidal fish, the tidepool sculpin (Oligocottus maculosus) with the closely related hypoxia intolerant subtidal fish, the silverspotted sculpin (Blepsias cirrhosus) to determine if these species use different mechanisms to cope with hypoxia. Individuals from each species were exposed to environmental O2 tensions chosen to yield a similar level of tissue hypoxia and gene transcription was assessed in the liver over time. There was an effect of time in hypoxia, where the greatest transcriptional change in the silverspotted sculpin occurred between 3 to 24 hours in contrast to the tidepool sculpin where the largest transcriptional change occurred between 24 and 72 hours of hypoxia. A number of genes showed similar hypoxia-induced transcription patterns in both species (e.g. genes associated with glycolysis and apoptosis) suggesting they are involved in a conserved hypoxia response. A large set of genes showed divergent transcriptional patterns in the two species, including fatty acid oxidation and oxidative phosphorylation, suggesting that these biological processes may contribute to explaining variation in hypoxia tolerance in these species. When both species were exposed to a single environmental O2 tension, large transcriptional responses were seen in the hypoxia intolerant silverspotted sculpin while almost no response was observed in the hypoxia tolerant tidepool sculpin. Overall, divergent transcription patterns in response to both magnitude and duration of hypoxia provide insights into the processes that may determine an animal's capacity to tolerate frequent bouts of hypoxia in the wild.
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Data from: Origins and functional diversification of salinity-responsive Na+, K+ ATPase α1 paralogs in salmonids
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Dalziel, Anne C.; Bittman, Jesse; Mandic, Milica; Ou, Michelle; Schulte, Patricia M. — 2014-06-05 The Salmoniform whole-genome duplication is hypothesized to have facilitated the evolution of anadromy, but little is known about the contribution of paralogs from this event to the physiological performance traits required for anadromy, such as salinity tolerance. Here, we determined when two candidate salinity-responsive paralogs of the Na+, K+ ATPase α subunit (α1a and α1b) evolved and studied their evolutionary trajectories and tissue-specific expression patterns. We found that these paralogs arose during a small scale duplication event prior to the Salmoniform, but after the teleost, whole-genome duplication. The ‘freshwater paralog’ (α1a) is primarily expressed in the gills of Salmoniformes and an unduplicated freshwater sister-species (Esox lucius), and experienced positive selection in the fresh-water ancestor of Salmoniformes and Esociformes. Contrary to our predictions, the ‘saltwater paralog’ (α1b), which is more widely expressed than α1a, did not experience positive selection during the evolution of anadromy in the Coregoninae and Salmonine. To determine if parallel mutations in Na+, K+ ATPase α1 may contribute to salinity tolerance in other fishes, we studied independently evolved salinity-responsive Na+, K+ ATPase α1 paralogs in Anabas testudineus and Oreochromis mossambicus. We found that a quarter of the mutations occurring between salmonid α1a and α1b in functionally important sites also evolved in parallel in at least one of these species. Together, these data argue that paralogs contributing to salinity tolerance evolved prior to the Salmoniform whole-genome duplication and that strong selection and/or functional constraints have led to parallel evolution in salinity-responsive Na+, K+ ATPase α1 paralogs in fishes.
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Data from: Migration, mitochondria, and the yellow-rumped warbler
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Toews, David P. L.; Mandic, Milica; Richards, Jeffrey G.; Irwin, Darren E. — 2013-08-19 Discordance between mitochondrial and nuclear DNA has been noted in many systems. Asymmetric introgression of mitochondria is a common cause of such discordances, although in most cases the drivers of introgression are unknown. In the yellow-rumped warbler, evidence suggests that mtDNA from the eastern, myrtle warbler, has introgressed across much of the range of the western form, the Audubon's warbler. Within the southwestern United States myrtle mtDNA comes into contact with another clade that occurs in the Mexican black-fronted warbler. Both northern forms exhibit seasonal migration, whereas black-fronted warblers are nonmigratory. We investigated the link between mitochondrial introgression, mitochondrial function, and migration using novel genetic, isotopic, biochemical, and phenotypic data obtained from populations in the transition zone. Isotopes suggest the zone is coincident with a shift in migration, with individuals in the south being resident and populations further north becoming increasingly more migratory. Mitochondrial respiration in flight muscles demonstrates that myrtle-type individuals have a significantly greater acceptor control ratio of mitochondria, suggesting it may be more metabolically efficient. To our knowledge this is the first time this type of intraspecific variation in mitochondrial respiration has been measured in wild birds and we discuss how such mitochondrial adaptations may have facilitated introgression.

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(Author: Mandic, Milica)

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