Bedotia Regan, 1903

John S. Sparks & Leila M. R. Rush, 2005, A new rainbowfish (Teleostei: Melanotaenioidei: Bedotiidae) from the southeastern highlands of Madagascar, with comments on the biogeography of Bedotia., Zootaxa 1051, pp. 39-54 : 50-51

[[ Genus Bedotia Regan ]]

Biogeography. Sparks and Smith (2004a) demonstrated that Bedotiidae and Bedotia are monophyletic (Fig. 1). In that study, three essentially geographically distinct clades were recovered within Bedotia (Sparks & Smith, 2004a; Fig. 5). Clade A comprises species with distributions ranging from mid- to southeastern Madagascar. Members of clade A are characterized by a wide, continuous black midlateral stripe. Members of clade B, which lack a midlateral stripe and instead exhibit blotchy or speckled lateral pigmentation patterns, are restricted to eastern drainages north of the Masoala Peninsula. Members of clade C exhibit distributions extending from the Masoala Peninsula southward to the Ivoloina River basin, and possess either a heavily barred and mottled lateral pigmentation pattern (e.g., B. masoala ), or a continuous midlateral stripe (e.g., B. longianalis ).

Interestingly, the Ivoloina River drainage represents the only locality where distributional overlap has been reported for members of these three clades. Bedotia madagascariensis (clade A) and two recently discovered populations, B. sp. “ivoloina” and B. sp. “betampona” (both members of clade C), occur within the Ivoloina drainage; however, these taxa are not syntopically distributed (P. Loiselle, pers. comm.). Whereas both B. sp. “ivoloina” and B. sp. “betampona” are endemic to portions of the upper to middle reaches of the Ivoloina basin, this drainage represents the northern range limit for B. madagascariensis , which is restricted to its lower, coastal reaches. Bedotia madagascariensis exhibits a comparatively wide geographic range, which extends southward to the Mangoro River (Loiselle & Stiassny 2003; Fig. 5). Loiselle has suggested that expansion of the Pangalanes canal may have permitted B. madagascariensis to extend its range northward into the Ivoloina River drainage. This canal system, developed in French colonial times to increase commerce and spanning a large portion of eastern coastal Madagascar from about Tamatave in the north to near Farafangana in the south, effectively links the lower coastal reaches of eastern drainages throughout its range. Based on data from a number of recent expeditions to the region, there appears to be no distributional overlap between species belonging to clades B and C.

The hypothesis of relationships for Bedotia presented by Sparks and Smith (2004a; Fig. 1) reveals much undocumented intrageneric diversity, and also indicates that species of Bedotia exhibit a high degree of local endemism. Interestingly, the southern (clade A) and northern (clade B) clades are more closely related to each other than either is to the central eastern clade (clade C), which separates their distributional ranges. A pattern of geographically distinct northern and southern clades is consistent with biogeographic patterns recovered for other Malagasy freshwater fish lineages, including some cichlids (Sparks, 2003; Sparks & Smith, 2004b).

Unfortunately, not much is known about the intrarelationships of other Malagasy fish groups with similar geographic ranges (i.e., those which span most of the eastern escarpment of the island). Similarly, not enough is currently known about the paleogeographic history of eastern and northern Madagascar to relate these contemporaneous patterns to historical geological events (see Wells, 2003). Studies are ongoing to reconstruct the relationships of additional Malagasy freshwater fish clades (Sparks & Smith, unpubl. data), which will permit alternative biogeographic hypotheses to be evaluated. In conjunction with an increased understanding of the paleogeographic history of the region, these data may help to elucidate the historical processes that have shaped the current distributions of freshwater fishes in eastern and northern Madagascar.