A “ghost” phasmid appearance: the male Bacillus atticus (Insecta: Phasmatodea)

Abstract

Bacillus atticus is an obligate parthenogen spread over the central/eastern Mediterranean basin, but males were also present about 1 million years ago (mya) in Sicily since they fertilized the parthenogenetic eggs of the hybrid B. whitei, originating the trihybrid parthenogen B. lynceorum. B. atticus females commonly reproduce through an altered meiotic process entraining the restitution of the first polar body; however, a small proportion of eggs, if inseminated by B. rossius or B. grandii males, can originate diploid or triploid hybrids. In the late 1980s, at Calagonone (eastern Sardinian coast), within a sample of diploid females, an adult male was found, which unfortunately died before karyological analyses could be done. Investigations on external and internal structures only evidenced male features: in addition to the slender bacilline body, clear male characters are the long antennae – realizing the heteromorphism of Bacillus males – and the terminalia, with typical sub-genital plate, vomer and cerci. Furthermore, by comparing the Calagonone male to the other Bacillus males and to B. atticus females, clear generic and specific features were ascertained, so that it could be definitely assigned to Bacillus atticus. The autosome:heterochromosome ratios of diploid Bacillus females and males are 1 and 1/2, respectively, while intermediate values give sterile intersexes. The analyzed specimen did not reveal intersexual traits, demonstrating that it had an AAX0 chromosome formula, which likely originated by the loss of one X chromosome from a female zygote. This had previously been observed to occur in B. rossius males of parthenogenetic origin. It could not be established whether this male was fertile. Neither additional syntopic males nor triploids were collected at Calagonone in the years following. Since this is the first known male of B. atticus, its accurate description/analysis will be of use for possible future comparisons.