Copy number variation in the melanocortin 4 receptor gene and alternative reproductive tactics the swordtail Xiphophorus multilineatus
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Alternative reproductive tactics are powerful examples of how variation in genetics and physiology among individuals can lead to striking diversity in phenotype. In the swordtails (genus Xiphophorus), copy number variation (CNV) at the melanocortin 4 receptor (mc4r) locus is correlated with male body size, which in turn is correlated with male mating behavior. We measured the relationship between mc4r CNV, behavior, and 11-ketotesterone (11-KT) in X. multilineatus to determine whether mc4r CNV was associated with other components of male tactics in addition to body size. We confirmed the results of previous studies, showing that male size increases with mc4r CNV and that mating behavior toward females was size-dependent. We also examined agonistic behavior by exposing males to their mirror image and found that male-male displays behavior were size-dependent. Small males were less likely to exhibit an agonistic response, suggesting that alternative reproductive tactics span intrasexual and intersexual contexts. There was no significant association between mc4r CNV and behavior or 11-KT hormone titer. Mc4r CNV is thus associated with the variation in male body size, but not with other traits independent of body size.
Keywords11-ketotestosterone Alternative reproductive tactics Copy number variation Melanocortin 4 receptor P-gene Xiphophorus
Ben Inbar and Rebecca Haning helped with the video analysis, processing the water samples and field work. Funding came from the Alfred P. Sloan Foundation Fellowship and a Dwight W. and Blanche Faye Reeder Centennial Fellowship in Systematic and Evolutionary Biology to HAH; by the Deutsche Forschungsgemeinschaft through SFB 487 to MS, and a Clark Hubbs Regents Professorship to MJR. Collecting permits were obtained from Secretaria Pesca of the government of Mexico (DGOPA.11319.031107.-4933). Fish maintenance and experiments were approved by the Institutional Animal Care and Use Committee at The University of Texas at Austin.
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