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DIAGNOSIS. Phrynobatrachus leveleve and P. dispar can be readily distinguished from each other in both sexes. Adult males are distinguished from Phrynobatrachus dispar by a lower jaw distinctly marked with vertical banding, a darkened vocal sac, the presence of minute spicules arranged in a U-shaped pattern along the anterior margin of the jaw and a proportionally smaller eye. Males of P. leveleve havefewer asperities, which are only faintly noticeable to the naked eye. By contrast, P. dispar males have distinct white-tipped conical asperities. Female P. leveleve are distinguished from female P. dispar by the absence of asperities in most individuals, smaller size and duller coloration. Although highly polymorphic, the overall coloration of both male and female P. leveleve is duller, generally lacking distinct vertical barring on the thigh and leg as found in P. dispar. Phrynobatrachus leveleve is distinguished from P. calcaratus and P. cornutus by the absence of an eyelid cornicle (although a small bump may be observed in the same location). Phrynobatrachus leveleve is further distinguished from P. parvulus and P. minutus of the mainland by larger size, stouter habitus and smaller femoral glands in males.
DESCRIPTION OF THE HOLOTYPE. CAS 218901 Male, 15.5mm SVL; total length of the leg is 1.5-2.0 times the SVL. Width of the head greater than 2.5 times the diameter of the eye. Dorsal asperities are indistinct to the naked eye and are most numerous between the posterior half of the eyelid and the tibio-fibula. However, a few asperities extend beneath the eye and onto the snout as well as the anterior portion of the eyelid. Tympanum indistinct, less than half the width of the eye. Two indistinct glandular ridges topped with 3 to 4 white-pointed asperities forming a broken X-shaped pattern are located on the mid-dorsum. The gular sac is darkened and appears as an inverted "U" shaped patch on the throat. The anterior border of the dark pigment contains numerous spicules that extend from the very tip of the lower jaw posterior to the corners of the mouth. These are found in 5-7 rows on the tip of the jaw and narrow to only 1-2 rows at the angle of the jaw. The medial lingual papilla on the tongue is present. Femoral glands, although indistinct, are present in the middle of the thigh; the glands extend about one-fourth the total length of the thigh. Webbing between fingers absent, webbing between toes reduced and deeply incised, existing mostly as a narrow fringe on the sides of the toes, webbing formula I2-3II3--3+III3+-4+IV5--4-V (Savage and Heyer 1997). Distal phalanx T-shaped, resulting in the appearance of dilated toe tips.
COLOR IN PRESERVATIVE.-Dorsum ground color a dark grayish-brown, lacking many distinctive markings. Two dark blotches over the front legs extend diagonally toward the eye. Faint light inter-orbital stripe followed by a faint dark patch in the center of the dorsum behind the eyes. Indistinct dark splotches are present on the dorsum. Only one or two faint dark bars are found on either the thigh or the tibio-fibula of the hind limb. Ventrum pale cream-colored and clear except for the throat and a few darkly pigmented spots extending along the flanks to just beyond the front legs. Seven distinct dark brown bars line the lower jaw. Undersides of the hind limbs clear, slight yellowish hue.
DISCUSSION.-Although we find no evidence for the existence of two taxa on Príncipe, it is intriguing that Boulenger describes Phrynobatrachus feae as having a throat that is dark brown or black, with uniform or round white spots (Boulenger 1906), which is a character we use to distinguish P. leveleve. All adult material we examined from Príncipe possessed a clear white throat. It is possible that Boulengers specimens, collected by L. Fea, may have been from São Tomé, but there are no existing records at the British Museum that suggest the specimens were collected elsewhere than Príncipe ("Princes Island") (B.T. Clarke, pers. comm.). Furthermore, the syntypes of P. feae examined (BMNH 19126.96.36.199, 91) appear to be juvenile P. dispar. Juvenile specimens tend to be darker overall and often have completely dark throats that fade at maturity. Although the coloration and presence of asperities on the syntypes were difficult to determine because of their state of preservation, we could find no reason to doubt that these are juvenile P. dispar collected from Príncipe Island.
Sequence data demonstrate considerable divergence between the two island species of Phrynobatrachus. Using a low estimate of divergence of 19% for the cytochrome b gene and a molecular clock estimate as high as 1.4% sequence divergence per million years, a value considerably higher than estimated divergence rates found in other amphibians (Caccone et al. 1997; Veith et al. 2003), suggests a time of divergence that predates the estimated origin for São Tomé of 13 million years ago (Lee et al. 1994). This would seem to suggest that the most likely scenario for the divergence of the two species would be independent colonizations from mainland Africa. After the recognition into two Phrynobatrachus species, each endemic to a single island, only one species of amphibian, Hyperolius molleri, appears to have successfully dispersed from one island to the other (or recently colonized both islands). However, it is difficult to make conclusions with any certainty given the unreliability of molecular clock estimates, the uncertainty of the sequence divergence, and the possibility that the estimated age of São Tomé may actually be much greater than 13 million years (orogeny dates were based upon the oldest lava flows, which only set a minimum age for the island). Analyses of 12S rRNA, valine-tRNA, and 16S rRNA-mtDNA further support the divergence between the two island species of Phrynobatrachus as intra-island variability was low in comparison to interspecific divergence.
Surprisingly, a number of recent molecular studies suggest that many of the endemic amphibians of the Gulf of Guinea islands may be more closely related to East African species than to their West African congeners; these studies include the fossorial caecilian, Schistometopum thomense (Wilkinson et al. 2003), Ptychadena newtoni (Measey et al. 2007) and, perhaps the treefrogs, Hyperolius molleri and H. thomensis. (Drewes and Wilkinson 2004, show the closest outgroup relative to be H. cinnamomeoventris, whose range includes East Africa). Similar claims have been made for the endemic terrestrial gastropod mollusk, Bocageia (Gascoigne 1994). Whereas this pattern may be a reflection of poor sampling in the intervening Congo Basin, the inclusion of the larger dataset (BMZ) in this study (12 Phrynobatrachus species) seems to support a Gulf of Guinea island-East Africa relationship. Phrynobatrachus dispar and P. leveleve consistently form a clade with Phrynobatrachus species from Ethiopia, Kenya, Malawi, and Tanzania (P. keniensis, P. inexpectatus, P. cf. minutus, P. parvulus, and P. rungwensis), rather than with the West African species P. calcaratus and P. cornutus. This curious pattern draws attention to the need for phylogenetic reconstruction of the Gulf of Guinea amphibians within the context of the African amphibian fauna, which may provide considerable data on the mechanisms and timing of colonization events. Currently such studies are limited by poor collections across Africa, especially the Congo Basin, and a paucity of researchers with an interest in African herpetofauna. We call attention to this deficit in the hopes that future researchers will take on the challenge of providing a comprehensive treatment of these species.
Excerpted with permission from:
The California Academy of Sciences Gulf of Guinea Expeditions (2001, 2006) VI. A new species of Phrynobatrachus from the Gulf of Guinea Islands and a reanalysis of Phrynobatrachus dispar and P. feae (Anura: Phrynobatrachidae) by Uyeda, J. C., Drewes, R. C., and Zimkus, B. M. (2007). Proceedings of the California Academy of Sciences, Vol. 58, pp. 367-385, 8 figs., Appendix (4 tables).