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Sister species within Triops cancriformis • M. Korn et al.

Patterns of genetic diversity and postglacial recolonization. areas. However, the lack of high diversification observed
Within the T. mauritanicus lineage, we observed several within T. cancriformis in the present study (see above) suggests
genetically highly divergent subclades indicating the occur- that, if such populations exist, they most likely did not have
rence of several subspecies (see above and Fig. 2). Our data an important contribution to the recolonization of Central
indicate that diversity is much lower among the haplotype and northern Europe after the last Ice Ages. Also, the single
groups of the T. c. cancriformis lineage, such that in this spe- literature report on a southern Greek T. cancriformis popula-
cies, all populations investigated (i.e. gonochoric as well as tion rather indicates the presence of a nongonochoric than of
nongonochoric populations) appear to have diverged rather a gonochoric population (the sample included seven females
recently from a common ancestor. There is no indication of and a single male; Colosi 1923). Furthermore, we have to
a differentiation into subspecies. The latter species clearly consider that even within these main refuges, most populations
has a more northerly distribution (Fig. 2), which may be may have become extinct due to repeated fast climatic oscil-
linked to its lower genetic diversity (see below). lations surely associated with changes in available habitats.
Our reconstruction of the possible maximum distribution Gonochoric populations often may have failed to follow
of Triops during the Ice Ages suggests that suitable refuges for fast climatic fluctuations and habitat changes since this mode
T. cancriformis within Europe may have existed in southern of reproduction has properties inherently less effective for
Iberia, Sardinia, Sicily as well as parts of mainland Italy and fast passive distribution (see above). They might thus have
Greece. The reported distribution of the former subspecies survived only in a few separated localities, promoting allo-
with their differing reproductive modes (see above; Fig. 2) patric diversification (Hewitt 1999). This might explain why
demonstrates that only nongonochoric populations have three highly divergent clades of T. mauritanicus could be found
been found to inhabit areas that had been depopulated during within a rather small area in the southern Iberian Peninsula.
the Ice Ages. Their high dispersal ability must have led to a The lack of diversity among the populations of the ‘Southern
rather fast recolonization of formerly depleted areas. This Spanish’ haplotype group compared to the high diversity
may explain the low genetic diversity found among populations among Moroccan populations of T. mauritanicus may be
inhabiting this area as compared to the high levels of diver- explained by recent recolonization events of formerly depopu-
gence found within North African lineages of T. mauritanicus. lated areas within the Iberian Peninsula. This may suggest
Populations of this species are expected not to have been that the only suitable refuges for T. mauritanicus may have
depleted by the Ice Ages, enabling ancient polymorphisms to been located in lowland plains at the southernmost edge of
be retained. This pattern of a latitudinal gradient in diversity the Iberian Peninsula.
agrees with that found in other animals (e.g. grasshopper, Future investigations should include further sources of
brown bear and hedgehog, Hewitt 1999, 2000; and a hawk- data, most importantly nuclear gene sequences, and specimens
moth, Hundsdoerfer et al. 2005). Parts of southern Europe from the Mediterranean islands, the Arabian Peninsula, Algeria,
(and northern Africa) appear to be more diverse in species’ Libya, Egypt and Sudan, as well as more specimens from the
haplotypes than Central and northern Europe. When the Iberian Peninsula, to gain broader insight into the biogeo-
latter areas were depopulated by the Ice Ages, the former acted graphical scenario and dispersal abilities of T. mauritanicus.
as refugia. Central and northern Europe appear to have been Also, future studies should investigate the status of southern
recolonized from these southern gene pools by leptokurtic African material.
dispersal (leading edge dispersal) resulting in low diversity.
Thus, we suppose that the present haplotype groups in Conclusion
T. cancriformis might reflect different refuge areas during the Within a group that is as difficult to handle morphologically
last Ice Age. The present distribution of reproductive modes as the Notostraca as a whole, molecular methods greatly
and haplotype groups suggests that there might have been improve the understanding of phylogenetic relationships. In
two separate refuges for gonochoric and nongonochoric this study, we suggest that the species Triops cancriformis, which
populations of the ‘Central European/Northern Spanish’ in the most recent classification comprises three subspecies,
haplotype group (these are identical, see Appendix 1). Thus, we actually divides into two distinct species, T. cancriformis and
hypothesize that Spain provided refuges for the gonochoric T. mauritanicus. The latter shows high substructuring and
populations of the ‘Central European/Northern Spanish’ may include at least five subspecies. Thus, the geographical
haplotype group and southern Italy gave refuge to nongono- distribution of some lineages of the former T. cancriformis is
choric ‘Central European’ as well as ‘Sicilian’ haplotype groups. much more restricted than previously thought.
For this study, no material was available from possible refuge Since we found only one locality for the T. mauritanicus
areas in Greece or Turkey, and notostracans of both areas haplotype ‘Gitanilla’ in Spain, in the pond Laguna de la Gitanilla
have not been well studied yet. Thus, further diversified (Extremadura), this haplotype may be highly endangered.
gonochoric populations might exist in these typical refuge This pond deserves formal protection. In south-western

318 Zoologica Scripta, 35, 4, July 2006, pp301–322 • © 2006 The Authors. Journal compilation © 2006 The Norwegian Academy of Science and Letters