Alternative life histories shape brain gene expression profiles in males of the same population

Abstract

Atlantic salmon (Salmo salar) undergo spectacular marine migrations before homing to spawn in natal rivers. However, males that grow fastest early in life can adopt an alternative 'sneaker' tactic by maturing earlier at greatly reduced size without leaving freshwater. While the ultimate evolutionary causes have been well studied, virtually nothing is known about the molecular bases of this developmental plasticity. We investigate the nature and extent of coordinated molecular changes that accompany such a fundamental transformation by comparing the brain transcription profiles of wild mature sneaker males to age-matched immature males (future large anadromous males) and immature females. Of the ca. 3000 genes surveyed, 15% are differentially expressed in the brains of the two male types. These genes are involved in a wide range of processes, including growth, reproduction and neural plasticity. Interestingly, despite the potential for wide variation in gene expression profiles among individuals sampled in nature, consistent patterns of gene expression were found for individuals of the same reproductive tactic. Notably, gene expression patterns in immature males were different both from immature females and sneakers, indicating that delayed maturation and sea migration by immature males, the 'default' life cycle, may actually result from an active inhibition of development into a sneaker.

The Phenomics and Expression Quantitative Trait Locus Mapping of Brain Transcriptomes Regulating Adaptive Divergence in Lake Whitefish Species Pairs (Coregonus sp.)

“…For example, Aubin-Horth et al (2005a) found that $15% of brain transcripts were significantly differently expressed in wild-caught salmon of two alternative life histories, and Aubin-Horth et al (2005b) found 10.5% were significantly differently expressed in a comparison of salmon of alternative life histories reared in either the wild or captivity.…”

“…Troponin is associated with actin and tropomyosin in the actin scaffold of muscle tissue (Roisen et al 1983). In neurons, these molecules are collectively associated with neural development and growth (Schevzov et al 1997;Aubin-Horth et al 2005a), thus potentially providing a link between troponin and behavioral differences between species pairs.…”

Agonistic encounters and cellular angst: social interactions induce heat shock proteins in juvenile salmonid fish

“…In the African cichlid, Astatotilapia burtoni, approximately 5 per cent of genes studied were differentially regulated in the brain according to male dominance phenotype (Renn et al 2008). Furthermore, distinct brain gene expression profiles were observed in male Atlantic salmon Salmo salar with alternative reproductive strategies (Aubin-Horth et al 2005a). Preliminary microarray analysis on the effects of social status on gene expression in rainbow trout Oncorhynchus mykiss observed more than 1000 gene differences in dominant, subdominant and subordinate fish including changes in stress-responsive genes (Sneddon et al 2005).…”

Rapid parallel evolution of standing variation in a single, complex, genomic region is associated with life history in steelhead/rainbow trout

“…In such cases, these parallel phenotypic changes may have the same underlying genetic basis [12 -17] or may involve different genetic changes that cause similar phenotypic responses [18,19]. While parallel adaptation may stem from novel mutations in the same gene or gene region, it is often attributed to concordant changes in the frequencies of existing alleles [14][15][16]20,21] or to parallel regulatory changes in gene expression [22,23]. However, the relative importance and frequency of these different underlying genomic responses to adaptive evolution in natural populations is largely unknown.…”