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Multiple repeated patterns of adaptive radiation were revealed in cyprinid fish inhabiting the compact geographic region of the ethiopian Highlands. We found four independently evolved radiations in the evolutionary hexaploid (2n = 150) Labeobarbus lineage based on matrilineal relationships of >800 individuals. Each radiation displayed similar patterns of mouth phenotype diversification, and included ecomorphs/species of the generalized, lipped, scraping (one or two), and large-mouthed (one to three) types. All radiations were detected in geographically isolated rivers, and originated from different ancestral populations. This is the first documented case in which numerous parallel radiations of fishes occurred-via different ways-in a riverine environment. Some radiations are very recent and monophyletic, while others are older and include ecomorphs that originated in separate mini flocks and later combined into one. The diversification bursts among Ethiopian Labeobarbus were detected in the mid-upper reaches of rivers (1050-1550 m above sea level), which likely offer ecological opportunities that include diverse habitats yet poor fauna (i.e. lower competition and relaxed selection). this promising example of parallel evolution of adaptive radiation warrants further investigation.In the pioneering work on South African cichlids and catfishes, Joyce et al. 21 and Day et al. 19 suggested that the riverine flocks are remnants of radiations that emerged in a paleolake. This suggestion is corroborated by the finding of the Lake Tanganyika endemics beyond the lake basin 33 . While some riverine radiations clearly have lacustrine origins, it is likely that other riverine radiations originate from sources other than lakes. Hence, we aimed to test whether the same environmental factors that trigger lacustrine radiation can also act in rivers.In general, the main prerequisites for adaptive radiation are: (1) environmental stability for evolutionarily significant periods (starting from thousands of years ago); and (2) physical isolation from the river drainages harboring diverse fish faunas 15,20,31 . The latter serves a dual purpose: first, it provides the ecological opportunities for niche divergence at the initial stages of radiation, and later it prevents the extinction of diverged forms caused by competition with highly specialized species from other systematic groups. These processes can operate in specific and rather rare parts of the riverine network. For example, the segment of the Genale River that harbours the radiating assemblage of distinct forms of the Labeobarbus is situated in the apparently old canyon, isolated by the Baratieri Falls from the lower reaches of the river system and characterized by the depauperate fish fauna 20 .If the fish radiations in rivers are similar to the evolutionary phenomena experienced in lakes, they should display similar evolutionary patterns. It is well known that adaptive radiations are often repeatable in different organisms as exemplified from spiders 34 , fish 35 , and liz...

Large African barbs of the genus Labeobarbus constitute a hexaploid lineage (2n = 150). This group is widely distributed in African freshwaters, and exhibits profound phenotypic variation that could be a prerequisite for adaptive radiation. Using morphological, molecular, and stable isotope analyses, we investigated whether an adaptive radiation has occurred in a riverine assemblage of the Labeobarbus gananensis complex. This complex is composed of six phenotypically distinct sympatric forms inhabiting the Genale River (Ethiopian highlands, East Africa) in the Juba and Wabe–Shebelle drainages (Indian Ocean basin). Of the six forms, five were divergent in their mouth morphology, corresponding to generalised, lipped, scraping (two forms), and large‐mouthed phenotypes. One form had no mouth specialisation, but differed from the others in body shape (short and deep body; short form). Stable isotope analysis revealed differences in 15N among these forms, representing different foraging strategies (omnivorous, scraping, and piscivorous). Phylogenetic analysis of two mitochondrial DNA markers confirmed the monophyly of L. gananensis, suggesting an intra‐riverine radiation. However, the Genale assemblage appears to have originated through a combination of allopatric and sympatric events. Some of the specialised forms within the Juba and Wabe–Shebelle drainage originated independently from the local generalised forms in three different river regions. Each of these cases could be considered as a small species flock composed of two or three sympatric forms. Our study shows that adaptive radiation in rivers can be enhanced by a combination of sympatric speciation and temporal geographic isolation, leading to local sympatric speciation followed by migration.

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The ontogeny of the larvae and juveniles of the common roach, Rutilus rutilus, was accelerated and retarded via treatment with the thyroid hormone triiodothyronine (T 3 ), and thiourea. This treatment resulted in differential timing of scale formation. Development of squamation was earlier in accelerated fish but delayed in retarded fish compared with a control fish. A drastic shift in the number of lateral line scales (LL) resulted. Instead of a typical range of LL, retarded fish had an increased LL compared to the control as well as for the species as a whole, 47-71 vs 41-48, while accelerated fish had reduced LL: 38-44 vs 41-48. The mechanism of this drastic change in LL was related to developmental change in the timing of events, leading to changes in size and shape (heterochrony). The number of scales obtained experimentally was correlated to the body length at which scales first appeared.

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