Understanding underlying genetic variation can elucidate how diversity in behavioral phenotypes evolves and is maintained.  Genes in the serotonergic signaling pathway, including the serotonin transporter gene (SERT), are candidates for affecting animal personality, cognition and fitness.  In a model species, the great tit (Parus major), we reevaluated previous findings suggesting relationships between SERT polymorphisms, neophobia, exploratory behavior and fitness parameters, and performed a first test of the relationship between single nucleotide polymorphisms (SNPs) in SERT and problem-solving in birds.  We found some evidence for associations between SERT SNPs and neophobia, exploratory behavior and laying date.  Furthermore, several SNPs were associated with behavioral patterns and success rates during obstacle removal problem-solving tests performed at nest boxes.  In females, minor allele homozygotes (AA) for nonsynonymous SNP226 in exon 1 made fewer incorrect attempts and were more likely to problem-solve.  In both sexes, there was some evidence that minor allele homozygotes (CC) for SNP84 in exon 9 were more likely to problem-solve.  Only one SNP-behavior relationship was statistically significant after correcting for multiple comparisons, but several were associated with substantial effect sizes.  Our study provides a foundation for future research on the genetic basis of behavioral and cognitive variation in wild animal populations.  

We genotyped SNPs in the 13 exons and promoter region of the great tit (Parus major) serotonin transporter gene (SERT) via directed sequencing.  We tested neophobia behavior, boldness and exploratory behavior using standardized behavioral tests performed on wild birds.  In addition, we tested novel problem-solving capacity using a obstacle removal test performed at nest boxes.  We also monitored nest boxes to determine fitness traits (lay date, fledgling numbers).  We related variation in behavioral (personality) traits, problem-solving performance and fitness traits to SERT polymorphisms.