Makalata Husson, 1978

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 186-188

Makalata Husson, 1978 Red­nosed tree rats

Makalata is readily distinguished from all other echimyids from the Rio Juruá by the combination of bristly fur with a mixture of stiffened hairs and flattened but flexible spines, reddish­orange nose, and short (less than head­and­body length), naked, and scaly tail lacking a terminal tuft of hairs. Cranially (fig. 122), Makalata is similar to Isothrix Both genera have short, deep rostra and broad interorbital regions with overhanging supraorbital ledges that extend onto the parietals as distinct, but short ridges. The interorbital region of Makalata , however, diverges posteriorly, rather than being parallel as in Isothrix , and the rostrum is decidedly longer and narrower. The maxillary toothrows are parallel and separated by a narrow palate. The toothrows are longer than in Isothrix , making the teeth appear more massive since the overall skull length is similar. The palate is also longer, accommodating the longer toothrows, with the mesopterygoid fossa extending only to M3. The cheekteeth (fig 119B) are similar to those of Isothrix , with each tooth having three deep flexi on the labial side isolating four lophs, and a short medial flexus. In the unworn condition, these lophs form pairs of U­shaped anterior and posterior units joined on their medial side Each pair in all four cheekteeth may become connected labially with progressive wear Both lateral and medial flexi are narrow more so than the lophs, a condition opposite to that seen in Isothrix . The second lateral and medial flexi are joined and completely separate the anterior and posterior pair of Ushaped lophs in both M2 and M3. This condition differentiates the cheekteeth of Makalata from those of either Mesomys or Proechimys . Their relatively small size and parallel, as opposed to divergent, toothrows readily distinguish the teeth of Makalata from those of Dactylomys .

The genus was erected by Husson in 1978 to include the single species M. armata (I. Geoffroy St.­Hilaire) (= didelphoides Desmarest ; see Emmons, 1993), which had previously been included within the genus Echimys by most earlier workers (e.g., Ellerman 1940; Cabrera, 1961). The generic status of many of the species commonly listed within Echimys are under review by Louise H. Emmons, as is the complete species membership within Makalata . However, preliminary assessments indicate that the genus contains more than one species. Emmons (1993) limits the range of M. didelphoides to the Guiana region, including that part of Amazonian Brazil north of the Amazon and east of the Rio Negro and south of the Amazon from at least the Rio Xingu eastward. She suggested that specimens from the central Amazon belong to a second species, M. macrura (Wagner) . Finally, Emmons and Feer (1997) list grandis, occasius, and rhipidurus as valid species of Makalata , rather than of Echimys , in addition to didelphoides . Our preliminary mitochondrial DNA sequence data (da Silva and Patton, 1993) also suggested that Mak­

alata is composite, with at least two and possibly more entities replacing one another from west to east across Amazonia. We summarize the available molecular data below, again to emphasize the need for further geographic sampling and to help identify areas where critical samples would be especially beneficial.

We have examined individuals from only 11 geographic localities (20 individuals), but these are distributed across Amazonia from northern Perú to the Rio Xingu in eastern Brazil and south to eastern Bolivia (fig. 123, table 53). There is, however, extensive divergence among cytochrome­b haplotypes (798 bp), with two major geographic clades recognizable that differ by more than 16% (Kimura two­parameter distance). The first of these is from the Rio Xingu in Estado do Para´, Brazil, which, within itself, includes two quite divergent lineages that differ by an average of 10%. The Rio Xingu clade groups with strong bootstrap support (97%) to haplotypes from the Río Iténez in eastern Bolivia, but at an average divergence of 11.5%. The second major geographic clade is widespread, ranging from northern Perú east to at least the right bank of the lower Rio Negro north of Manaus and south to include samples from the Rio Juruá and the Rio Purus near its mouth. The groupings depicted in the tree (fig. 123) are generally concordant with the geographic distinction between morphs recognized by Patterson (1992) that differ in pelage characteristics, and recognized as separate species by Emmons (1993). These are the western M. macrura (Wagner) , characterized by a gray­brown venter, and the eastern and southern M. didelphoides , with a pale cream or buff venter. We follow Emmons’ guidance here, and allocate our specimens from the Rio Juruá to M. macrura However , we note that substantial geographic structure exists within both presumptive species. Within M. macrura , for example, three well­differentiated geographic units are evident that differ by an average of 6.0% and that exhibit a maximum pair­wise divergence of 9.7%. One of these includes specimens from northern Perú and the central portion of the Rio Jurua´, a second constitutes the single individual from the mouth of the Rio Juruá (locality 14), a third comprises specimens from the Rio Purus and the Arquipélago de Anavilhanas in the lower Rio Negro, and a fourth represents individuals from three adjacent localities on the Rio Jaú west of the Rio Negro. Similarly, as mentioned above specimens from the Rio Xingu divide into two sharply defined groups, one from the right bank and the second from a near­by but well­isolated island, and both differ substantially from the Bolivian specimens despite strong support for their phyletic linkage. Rats currently allocated to the genus Makalata offer a rich subject for systematic analysis, research that is currently being pursued by Louise H. Emmons.