Eremiadini, Shcherbak, 1975

Published, First, 2007, Systematics of the Palaearctic and Oriental lizard tribe Lacertini (Squamata: Lacertidae: Lacertinae), with descriptions of eight new genera, Zootaxa 1430, pp. 1-86 : 65-66

Relationships within Eremiadini

In the Eremiadini , recent independent phylogenetic analyses of mtDNA (data from Fu 2000 – Fig. 1) and nDNA sequence (Mayer & Pavličev 2005) show considerable resemblance to each other at some well-substantiated nodes. The analyses indicate that there are two Afrotropical groups: a South African one containing Tropidosaura , Pedioplanis , Meroles and Ichotropis; and another made up of Nucras of south and east Africa plus a clade consisting of Latastia , Heliobolus and Philochortus . This will be referred to as the Northeast African group, as it has most diversity in that region. In the nDNA tree (Mayer & Pavličev 2005) both these groups form a monophyletic unit which also includes the West African Poromer a. The remaining Eremiadini form a separate clade in the nDNA tree. Here, Adolfus and Holaspis are weakly associated, in agreement with their membership of the Equatorial African group of Eremiadini , which is characterised by several morphological synapomorphies and also includes Gastropholis ( Arnold 1989b) . Also present are the east Arabian Omanosaura and four genera mainly found in North Africa and southwest Asia, namely Acanthodactylus , Eremias , Ophisops and Mesalina .

The relationships of the Eremiadini have previously been estimated using 78 binary morphological characters ( Arnold 1989a), producing a tree in which many nodes have substantial heuristic support ( Harris et al. 1998, p. 1944). In contrast to the DNA trees, the morphological one is highly pectinate, with a main lineage from which most genera arise in sequence. The principal exception is the Equatorial African group of genera which arises relatively basally. When gross habitat is reconstructed on the morphological tree, there is one transition spread over more than one node from relatively mesic to increasingly xeric environments. This is associated with the appearance of many (more than 15) derived anatomical features that are widely distributed through the body and include aspects of the nostrils and nasal tract, frontal and quadratojugal bones, eye-size, xiphisternal ribs, body shape, limb, foot and kidney structure. A case can be made that they are functionally related to the problems of surviving in dry habitats with which they are associated ( Arnold 1989a, 1993, 2004).

In the DNA estimates of phylogeny, shift to xeric conditions may have occurred more than once, as noted by Mayer and Pavličev (2005). This applies to many of the extensive associated anatomical changes, and there may have been at least three shifts: in the South African group ( Meroles , Ichnotropis and Pedioplanis xeric), Northeast African group ( Latastia , Philochortus and Heliobolus xeric), and the North African-Eurasian assemblage ( Acanthodactylus , Eremias , Mesalina and Ophisops xeric). This would inevitably involve a great deal of morphological parallelism. A single shift to xeric conditions with this topology would be even less parsimonious in terms of morphological change, as several reversals to mesic habitats and morphology would be involved. If a multiple shift to xeric conditions and anatomy were accepted, the separate cases would be representatives of an ecomorph, a pattern of morphology that has been acquired independently by different ecological analogues (Williams 1972, 1983). Ecomorphs are a common phenomenon and resemblance may be very striking if the independent cases evolved from forms that, while separate, had similar anatomy. Such resemblance may extend even to the order in which different features are assembled in parallel (Arnold 1994).

Ecomorphs are sometimes detected in morphological data sets and many are already recognised in the Lacertidae on this basis ( Arnold 1989a, 1993, 2004). As here, such cases are often confirmed, or at least not refuted, by DNA-based phylogenies when these become available, and further cases may also be revealed. This has recently happened in Myotis bats (Ruedi 2001), Anolis lizards ( Losos et al. 1998), toad headed aga- mids (Phrynocephalus and Bufoniceps , on the phylogenetic evidence of Macey et al. 2006), and in skinks assigned to the genus Sphenops (Carranza & Arnold unpublished data). Such cases involve detailed morphological resemblances and contrast with ones where the lineages entering similar selective regimes are initially morphologically quite diverse. Here, anatomical and other solutions to problems may be different and they may be assembled in different orders (Arnold 1994).

The numerous examples of ecomorphs with detailed resemblance mentioned above make it more credible that Eremiadini could have become xeric at least three times. This is especially so as the relationships that indicate this possibility are supported independently by both mitochondrial and nuclear genes involving a total of no less than 6300 bp of sequence. If a tripartite shift into xeric conditions is accepted as a hypothesis, it can be tested further by improving taxon coverage for all available gene fragments and incorporating them into a single analysis of DNA sequence.

It is interesting to note that, although Eremiadini and Lacertini are sister groups and so the same age, branch lengths are generally much longer in the Eremiadini , in both the mtDNA and nDNA trees. This may possibly be because Eremiadini , being found in warmer areas, tend to breed sooner after hatching. They may consequently have had more generations in their history than most lineages of Lacertini , and so might evolve at a faster rate.

Relationships in the northeast African group. Distinctive non-molecular features are present in the Northeast African clade of Eremiadini , which have not been used in previous mainly morphological analyses. Firstly the hemipenis is often thin-walled with the stem inserting dorsal to the basal parts of the lobes, the sulcus often divides before the bifurcation of the organ and its outer lips in the lobes are frequently flap-like and cartilaginous ( Arnold 1986). The hemipenis of Pseuderemias , which is also found in northeastern Africa, is similar. Secondly, at least some Heliobolus , Philochortus and Pseuderemias have a distinctive way of digging burrows, in which only the forelimbs are used (S. Baha el Din & E. N. Arnold unpublished data). Finally, Pseuderemias and Heliobolus share additional morphological features ( Arnold 1989a). These characters suggest relationships in Nucras and the Northeast African group as a whole are:

Nucras ( Latastia ( Philochortus ( Heliobolus , Pseuderemias ))).