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

and L. arcticus; 6.4% in 12S) or 3.3% (between L. lemmoni and number of apodous segments may vary greatly, even within
L. a. apus; 4.8% in 12S). It should be noted that despite low the same haplotype, as seen in the examples of northern
genetic divergences, two of these comparisons are among Spanish and typical T. cancriformis. We suggest that telson
morphologically most distinct species. Lepidurus lemmoni has morphology, including the size of furcal spines, represents the
much higher numbers of body segments and legs than the most useful source of morphological characters for determin-
other two taxa (e.g. there is no overlap in these characters among ing specimens of the T. cancriformis group. However, we do
L. lemmoni and L. arcticus referring to Rogers 2001). Thus, not know of a morphological character that clearly separates
the divergence into two taxa within the former T. cancriformis T. cancriformis and T. m. simplex.
by 2.9–3.3% (16S; and 4.1–4.3% 12S) as revealed by our
results is similar to that observed among other notostracan Biogeography of Triops cancriformis and T. mauritanicus
species. It is supported morphologically by the formation of Dispersal abilities and distribution. To understand present dis-
extraordinary long furcal spines in the T. mauritanicus lineage tribution patterns in both species, it is important to take into
(with the single exception of the T. m. simplex clade), a morpho- account the consequences that may arise from different
logical state unique among Notostraca in a character shown to reproductive modes. Nongonochoric modes of reproduction
have low variability within the haplotype groups (Fig. 5A). have properties inherently more effective for fast distribution.
In addition, the distance of 2.9–3.3% between the adel- One resting ‘egg’ (embryo in diapause) from a parthenogenetic
photaxa T. cancriformis and T. mauritanicus is higher than that female transported into a new habitat can rapidly form a new
observed in two other pairs of crustacean sister species in the population, whereas a minimum of two of these ‘eggs’, a male
genus Perisesarma (Sesarmidae; Gillikin & Schubart 2004). and a female (that of course also would have to hatch during
We estimate the latter to be 1.5–2.5% from the distance tree the same flooding event), are necessary for a gonochoric popu-
presented in their Fig. 3. A second pair of crustacean sister lation to colonize new habitats, which is much less probable
species, Aegla occidentalis and Aegla bahamondei (Aeglidae), (e.g. Dumont & Negrea 2002). In addition, a gonochoric
also has lower average divergences of 1.4–1.6% (Jara et al. population increases at a slower rate.
2003). However, higher sequence divergences can also occur We present the first record of T. c. cancriformis in northern
between sister species of Crustacea, e.g. Euchaeta marina and Africa (north-west Tunisia), where we found two unisexual
Euchaeta rimana (Copepoda; Braga et al. 1999), which diverged populations. The populations belong to two different haplo-
by 5.4% (recalculated from the divergence times presented type groups that also occur in Europe. One of these haplo-
and the molecular clock used). Therefore, compared to the type groups is shared only with northern Sicily and Ustica
variability observed among other taxa, the reclassification of Island, the other ranges throughout Western and Central
the former T. cancriformis into two species appears justified. Europe. The discovery of these two European haplotype
groups in northern Africa might be evidence for repeated
Validation of morphological characters long-distance passive dispersal events across the Mediterra-
As a high number of carina spines can be found in all of the nean Sea. The haplotypes have not yet diverged, so they
former T. c. mauritanicus, including the southern Spanish samples must have reached northern Africa long after the salinity
that are the sister group of the clade that includes T. m. simplex, crisis formed a land bridge between the two continents
this character state appears to be plesiomorphic, at least 5.6–5.3 million years ago (Mya) (Blondel & Aronson 1999).
within the T. mauritanicus lineage. Typical specimens of Similar evidence comes from the occurrence of ‘Central European’
T. m. simplex show an autapomorphic complete (or very strong) haplotypes on Sardinia and Malta. Furthermore, single
reduction of carina spines. Thus, for the intermediate popu- haplotype groups may have a vast distribution. For example,
lation from pond 063 (Kairouan) in Tunisia, this character the ‘Central European’ haplotype group occurs at least from
state seems to have reversed. The haplotype groups of eastern Spain to Serbia (and from Germany to Tunisia) and
T. cancriformis display different degrees of reduction of spines, populations belonging to the ‘Austrian’ haplotype group
including complete loss. The same is true for the reduction occur in Austria as well as in the United Arab Emirates. This
in the size of these spines within Moroccan T. m. mauritanicus. is in accordance with our hypothesis that nongonochoric
Also, statistics indicate that even population means may lack populations might disperse with a high probability.
significant differences among representatives of all three of For gonochoric populations, we could not find indications
the former subspecies (see Appendix 2C). This leads to the of long-distance dispersal in the present investigation. No
conclusion that the morphological character ‘size and North African haplotypes of T. mauritanicus were found in
number of carina spines’ is very plastic within the T. cancri- the Iberian Peninsula and vice versa (Fig. 4 and Appendix 1),
formis group and cannot be used to distinguish between indicating that dispersal of this lineage between Europe and
T. cancriformis and T. m. simplex, and sometimes even between Africa may be limited. However, the lack of evidence for
T. m. mauritanicus, T. m. simplex and T. cancriformis. Also, the passive dispersal across the Strait of Gibraltar in T. mauritanicus

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