Monsters with a shortened vertebral column: A population phenomenon in radiating fish Labeobarbus (Cyprinidae)

Abstract

The phenomenon of a massive vertebral deformity was recorded in the radiating Labeobarbus assemblage from the middle reaches of the Genale River (south-eastern Ethiopia, East Africa). Within this sympatric assemblage, five trophic morphs—generalized, lipped, piscivorous and two scraping feeders—were reported between 1993 and 2019. In 2009, a new morph with prevalence of ~10% was discovered. The new morph, termed ‘short’, had an abnormally shortened vertebral column and a significantly deeper body. This type of deformity is common in farmed Atlantic salmon and other artificially reared fish, but is rare in nature. In the Genale Labeobarbus assemblage, the deformity was present exclusively within the generalized and lipped morphs. The short morph had between seven and 36 deformed (compressed and/or fused) vertebrae. Their body depth was positively correlated with number of deformed vertebrae. In another collection in 2019, the short morph was still present at a frequency of 11%. Various environmental and genetic factors could contribute to the development of this deformity in the Genale Labeobarbus, but based on the available data, it is impossible to confidently identify the key factor(s). Whether the result of genetics, the environment, or both, this deep-bodied phenotype is assumed to be an anti-predator adaptation, as there is evidence of its selective advantage in the generalized morph. The Genale monstrosity is the first reported case of a massive deformity of the vertebral column in a natural population of African fishes.

Unexpected Diversity of Feeding Modes among Chisel-Mouthed Ethiopian Labeobarbus (Cyprinidae)

“…We have to note that the Varicorhinus-like forms in both the Genale and Gojeb rivers appear quite frequently in the catches; their prevalence is next to that of the omnivorous form with a generalized morphology. The smiling-like form is moderately prevalent in the Genale [14], while the smiling-like form is extremely rare in the Gojeb.…”

“…We consider the possibly lowered competition and relaxed natural selection in faunapoor mid-upper reaches of the rivers as a possible prerequisite for ongoing adaptive radiation of Labeobarbus in the waters of the Ethiopian Highlands [14][15][16]. In addition, the mid-upper reaches are characterized by the increased availability of ecological niches compared to the most-upper reach (i.e., more diverse ecotopes/habitats in this section offer more ecological opportunities, see [3]).…”

“…Ecological diversification is a cornerstone of the process of adaptive radiation, considered as one of the main sources of biodiversity emergence [1][2][3][4]. The Ethiopian Highlands appears to be a hotspot of adaptive radiation in the cyprinid genera Labeobarbus, Enteromius and Garra, in both lacustrine and riverine environments [5][6][7][8][9][10][11][12][13][14][15][16][17]. Based on fish morphology, it was suggested that trophic resource partitioning was the main driver for these cyprinid radiations, and this has been proven for some lacustrine and riverine Labeobarbus assemblages [11,15].…”

“…The other scraping forms from the Genale and Gojeb exhibit the head morphology that is seemingly unique for the African Torini (Figure 1): a rather rounded cutting edge to the lower jaw, elongated snout and shallow body. Both forms were designated as "scraper 2" by Levin et al [16], but such forms from the Genale were also designated as "smiling" by Levin et al [15] and Golubtsov et al [14]. The latter variant is accepted herein, and the morphologically similar form from the Gojeb is designated herein as "smiling-like" or S-like.…”

Adaptive radiation and burst speciation of hillstream cyprinid fish Garra in African river

“…Given that the same riverine segment is home for another riverine diversification of fishes represented by four phenotypically diverged ecomorphs of the genus Labeobarbus (Levin et al, 2020), we consider the Sore River to being a hot-spot of riverine diversification in the Ethiopian Highlands that requires conservation management. The Ethiopian Highlands are home for several young fish radiations -a large lacustrine diversification among cyprinids (15 species/morphotypes - Mina et al, 1996;Nagelkerke et al, 1994;Nagelkerke et al, 2015) as well as small-sized diversifications of Garra (three species - Stiassny & Getahun, 2007) and Enteromius (two species -de Graaf, Megens, Samallo, & Sibbing, 2007;Dejen et al, 2002) -all in Lake Tana, and five riverine adaptive radiations of cyprinids each including from four to seven species (Golubtsov, 2010;Golubtsov, Korostelev, & Levin, 2021;Levin et al, 2019;Mina, Mironovsky, Golubtsov, & Dgebuadze, 1998;current study), highlighting this region's importance as a hotspot for fish speciation that is in need of additional research on ecological speciation processes. Table 1.…”