  Consider an advantageous allele that arises in a haploid population of size
$N$ evolving in continuous time according to a skewed reproduction mechanism,
which generates under neutrality genealogies lying in the domain of attraction
of a Beta$(2-\alpha, \alpha)$-coalescent for $\alpha \in (1,2)$. We prove in a
setting of moderate selection that the fixation probability $\pi_N$ of the
advantageous allele is asymptotically equal to $\alpha^{1/(\alpha-1)}
s_N^{1/(\alpha-1)}$ , where $s_N$ is the selection strength of the advantageous
allele. Our proof uses duality with a suitable $\Lambda$-ancestral selection
graph.
