NEW YORK (GenomeWeb News) – Introduced, exotic species can affect the conduct and gene expression of other species, new research suggests.
In a paper appearing online today in PLoS ONE, Laval University biologist Louis Bernatchez led a team of researchers who mapped the transcription of Atlantic salmon before and after the fish were exposed to rainbow trout. The team discovered that salmon behavior and transcription are intimately linked: when invasive trout entered the water, gene expression — and behavior — became more similar in dominant and subordinate salmon.
Atlantic salmon maintain a social hierarchy in which some fish are dominant and others subordinate. But a growing body of evidence suggests that competition with other, invasive organisms — such as exotic rainbow trout — can disrupt this sort of dominance hierarchy. For instance, rainbow trout, native to Pacific Ocean tributaries in Asia and North America, have been introduced to many other areas, where they sometimes compete with native salmon and affect their interactions with one another.
“Identifying the genetic and molecular actors contributing to the plastic loss of dominance hierarchies previously reported in Atlantic salmon is of fundamental interest in behavioral ecology, behavioral physiology, and behavioral genetics,” Bernatchez and his colleagues wrote.
In an effort to get to the bottom of this, Bernatchez and his colleagues used salmonid cDNA microarrays to get a picture of the genome-wide transcription profiles at 16,006 sites in dominant and subordinate salmon brains either when trout were present or absent. They also measured salmon behavior in the presence or absence of competitors (either rainbow trout or other Atlantic salmon).
As expected, the team found that rainbow trout shook up the hierarchy between dominant and subordinate Atlantic salmon. When the salmon pairs were kept alone or in the presence of another salmon, dominant salmon were more active than subordinates, snagging spots closer to the food source. When the trout were around, though, dominant salmon acted more like subordinates. Not only were they less active, they also stayed further away from the food source.
Gene transcription also changed in the dominant fish when trout were around, becoming more similar to that of subordinate fish. Although the researchers cautioned that there was a great deal of variability between fish sampled and noted that at least some of the transcription differences may represent false positives, the overall trend was consistent.
Subsequent analysis suggested that transcriptional differences in some 27 genes could be used to distinguish between dominant and subordinate salmon — but only when there were no trout about.
“[T]he presence of the exotic competitor (rainbow trout) apparently suppressed most of the transcriptional differences between dominant and subordinate salmon,” the authors wrote. “Some of the suppressed differences might represent changes causing the loss of dominance hierarchy, whereas others might be a consequence of it.”
Dominant salmon did continue expressing a handful of genes differently than their subordinate counterparts, even when rainbow trout were around. In particular, they tended to over-express genes involved in processes such as protein turnover, neuronal structural change, and oxygen transport.
Along with changes in behavior and gene expression, the researchers found that the presence of rainbow trout also affected the interactions between salmon that could ultimately affect the dynamics of salmon mating and evolution.