Increased Fluctuating Asymmetry in a Naturally Occurring Hybrid Zone between the Stick InsectsBacillus Rossius RossiusandBacillus Rossius Redtenbacheri

Abstract

The impact of interracial hybridization on fluctuating asymmetry (FA) and phenotypic variability (σ²_p) in a presumed natural hybrid zone between the stick insects, Bacillus rossius rossius Rossi and Bacillus rossius redtenbacheri Nasceti & Bullini (Phasmatodea: Bacillidea), found on the Italian island Sardinia was investigated. The lengths of three bilateral traits and three unilateral traits were measured, and each individual was genotyped by five microsatellite loci. The genotypic data clearly confirmed the existence of the hybrid zone on Sardinia. A significantly increased FA was found in the hybrids when compared to both parental subspecies, which this study attributes to genetic incompatibilities in the hybrids. The increase in FA was not correlated with any increase in σ²p in the hybrids, which indicates that in this case σ²_p and FA originate from separate processes.