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60 SCALI V., TINTI F., MANTOVANI B., MARESCALCHI O.
bisexuals as completely as commonly thought (Bell,
1982), but can reproductively interact with them and
evolve to some extent (Lynch, 1985;Hedges etal., 1992;
Quattro et al., 1992b; Mantovani &Scali, 1993a; Turgeon
& Hebert, 1993; Tinti & Scali, 1994).
Additionally, although rarely, hybridization may be in-
Downloaded by [31.185.101.124] at 08:47 23 March 2016 trogressive and lead to theformation of new bisexuals,
as, among fish, are the cases of Gila seminuda andofan
unnamed form arising from the Poeciliopsis monacha -
occidentalis complex through the breakdown of the
hybridogenetic mechanism (De Marais et al., 1992;
Vrijenhoek, 1989, 1993).
Therefore hybrid unisexuals cannot any longer be con-
sidered, as a whole, «dead ends» or «blind alleys»
(Maynard Smith, 1978; White, 1978), but all-female taxa
must be singly considered and carefully investigated.
When this has been done in depth, it always turned out
that each thelytokous hybrid is actually unique and can-
not be described just in general terms (Dawley & Bogart,
1989; Bullini & Nascetti, 1990;Hedges et al.,1992; Quat-
tro et al., 1992a, b; Turgeon & Hebert, 1993). We thus
here analyze in detail a single complex, thestick-insect of
the genus Bacillus, from which comparisons with other
complexes can be made and more general conclusions
drawn.
PARENTAL ANDHYBRID BACILLUS TAXA
The holomediterranean genus Bacillus comprises two
bisexual species, namely B. grandit Nascetti & Bullini
and B. rossius (Rossi).
Bacillus grandii, endemic to the Sicilian region (Fig.
1), is stricly bisexual, with a chromosome complement of
2n = 34, XXin thefemale and33.XO in themale. It is dif-
ferentiated into three formally recognized subspecies,
each found in very limited areas: B. g. grandii in spots of
southeastern Sicily; B. g. benazzii, in the northwestern
corner of the main island and on the Isle of Levanzo
(Egadi Archipelago); B. g. maretimi on the Isle of Maret-
timo (Egadi Archipelago) (Fig. 1A)(Marescalchi & Scali,
1990; Mantovani et al, 1991a; Scali, 1991;Mantovani &
Scali, 1993b).
Bacillus rossius (2n = 36,XX, female; 35.XO, male) is
to be found over a much wider range, covering most of
the western Mediterranean basin. Besides amphigonic
demes, it also shows several European all-female
populations, reproducing by facultative parthenogenesis
(reviews in Scali & Mantovani, 1989; Mantovani et al.,
1991b). Over its wide range B. rossius appears to be dif-
ferentiated into at least eight undescribed races on the
basis of ootaxonomy and allozyme characterization
(Gasperi et al., 1983; Nascetti & Bullini, 1983; Scali etal., Bullini, 1983; Mantovani &Scali, 1991; Tinti etal., 1992;
1987; Tinti etal., 1992;Tinti, 1993b); twoof them (B. r.
rossius and B. r. redtenbacheri) spread over Sardiniaand
Sicily, where they hybridized with theother members of
the genus, as explained below.
Bacillus atticus is a complex of parthenogenetic
Marcliimo I. Lovmizn K V
s. I. Favignana
Cuslonaci
Qistcllamarc
1: fl. grandii maretimi ¡Siracusa
2-7: 8. grandii benazzii
8-10 B. grandii grandii
11-18: fl. rossius
19-27: B. atticus
28-31: B. rossius-g. benazzii
32: B. rossius-g. grandii
33-43: a whitei
44-65: B. tynceorum
Fig. 1 - Map of Sicily showing the three collection areas of Bacillus
taxa. A, Egadi Archipelago; B, northwestern collection sites where
the hybridogenetic B. rossius-grandii benazzii are found in sym-
patry with B. rossius and B. grandii; C, Iblean area, where the
hybridogenetic B. rossius-grandii grandii, theclonal B. whiteiand
B. lynceorum aresympatric with B. grandii.
strains and includes both diploids (2n = 32-34,XX) and
triploids (3n = 48-51,XXX). Most likely they originated
from interracial crosses of a grandii-like taxon, and ap-
pear to be differentiated into three zymoraces: the
diploid B. a. atticus, comprising most of the Greek and
all Italian and Croatian populations; B. a. carius, em-
bodying diploid/triploid Turkish and triploid Greek
populations; B. a. cyprius (2n = 32,XX), till now known
as a distinct species, represented by Cyprian populations
(Tinti & Scali, 1991; Mantovani & Scali, 1993a;
Marescalchi & Scali, 1995a, b; Mantovani et al., 1955).
From allozyme analyses it has been shown that
bisexual populations of B. rossius can be highly
polymorphic, whereas parapatric unisexuals of both
Italian races aremuch less so,certainly influenced by the
diploidization mechanism of their facultatively par-
thenogenetic process (Gasperi et al., 1983; Nascetti &
Tinti, 1993b). Embryo diploidization actually entails
anaphase restitutions of dividing haploid egg nuclei