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The longer the better: evidence that narwhal tusks are sexually selected.

ABSTRACT: Once thought to be the magical horn of a unicorn, narwhal tusks are one of the most charismatic structures in biology. Despite years of speculation, little is known about the tusk's function, because narwhals spend most of their lives hidden underneath the Arctic ice. Some hypotheses propose that the tusk has sexual functions as a weapon or as a signal. By contrast, other hypotheses propose that the tusk functions as an environmental sensor. Since assessing the tusks function in nature is difficult, we can use the morphological relationships of tusk size with body size to understand this mysterious trait. To do so, we collected morphology data on 245 adult male narwhals over the course of 35 years. Based on the disproportional growth and large variation in tusk length we found, we provide the best evidence to date that narwhal tusks are indeed sexually selected. By combining our results on tusk scaling with known material properties of the tusk, we suggest that the narwhal tusk is a sexually selected signal that is used during male-male contests.

SUBMITTER: Graham ZA

PROVIDER: S-EPMC7115180 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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The longer the better: evidence that narwhal tusks are sexually selected.

Graham Zackary A ZA Garde Eva E Heide-Jørgensen Mads Peter MP Palaoro Alexandre V AV

Biology letters 20200318 3

Once thought to be the magical horn of a unicorn, narwhal tusks are one of the most charismatic structures in biology. Despite years of speculation, little is known about the tusk's function, because narwhals spend most of their lives hidden underneath the Arctic ice. Some hypotheses propose that the tusk has sexual functions as a weapon or as a signal. By contrast, other hypotheses propose that the tusk functions as an environmental sensor. Since assessing the tusks function in nature is diffic ...[more]

PMID: 32183636

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Project description:Transcript abundance was measured in whole-body virgin male Drosophila serrata from 41 inbred lines that had diverged through 27 generations of mutation accumulation that were sexually selected Sexual selection is predicted to have widespread effects on the genetic variation generated by new mutations as a consequence of the genic capture of condition by male sexual traits. We manipulated the opportunity for sexual selection on males during 27 generations of mutation accumulation in inbred lines of Drosophila serrata, and used a microarray platform to investigate the effect of sexual selection on the expression of 2685 genes, representing a broad coverage of biological function. Sexual selection had little effect on mean gene expression levels, with only 4 genes diverging significantly at a false discovery rate of 5% . In contrast, sexual selection impacted on both the magnitude and nature of mutational variance accumulating in these genes. The magnitude of mutational variance increased under sexual selection by an average of 29%. Mutational variance was less commonly generated by extreme phenotypes less commonly under sexual selection. Furthermore, analysis of random sets of five genes revealed that the mutational variance that accumulated under sexual selection was less pleiotropic in nature than that found in the absence of sexual selection. The generation of greater mutational variance without a general concomitant change in mean expression under sexual selection suggested that gene expression traits were be under apparent rather than direct sexual selection. We discuss two main explanations for the broad-based increase in mutational variance under sexual selection that both require extensive pleiotropy between traits affecting male mating success, standard metric traits represented here by gene expression traits, and general fitness. We measured gene expression of male Drosophila serrata from 41 mutation accumulation lines (whole-body) that were sexually selected. Data from two replicates for each line are presented.

Dataset Information

The longer the better: evidence that narwhal tusks are sexually selected.

Publications

The longer the better: evidence that narwhal tusks are sexually selected.

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