Papyrus swamps, hypoxia, and faunal diversification: variation among populations of Barbus neumayeri

Abstract

To test whether patches of papyrus swamp contribute to diversification of populations of non-air-breathing fishes, the gill morphology of Barbus neumayeri was compared between a papyrus swamp and several tributaries which differed in oxygen regime. Total gill filament length differed among sites and was negatively related to dissolved oxygen availability, supporting strong selection pressure for low-oxygen tolerance in the swamp interior. Among recaptures of marked B. neumayeri over a 4·5-year period among the focal swamp and connected stream and river sites, 93% of fish were recovered at the site of capture. Some of the individuals that moved crossed physicochemical gradients and traversed long distances within the swamp/stream system. This movement rate would theoretically be sufficient to homogenize gene frequencies among populations. However, randomly amplified polymorphic DNA (RAPD) markers indicated significant genetic differentiation among sites and no relationship between genetic differences and geographical distances among sites suggesting habitat-specific selection pressures on dispersers, rather than insufficient dispersal. 1999 The Fisheries Society of the British Isles

Physiological tradeoffs may underlie the evolution of hypoxia tolerance and exercise performance in sunfish (Centrarchidae)

“…TGSA was one such trait (Fig. 4), consistent with the crucial role of the gills in oxygen uptake, as well as previous observations that the capacity of the gills for gas exchange increases in response to hypoxia exposure (Chapman et al, 1999;Sollid et al, 2003) and is greater in fish with greater hypoxia tolerance (Mandic et al, 2009). Larger gills are also characteristic of the high performance tunas and lamnid sharks (Bernal et al, 2001).…”

RAPD markers indicate the occurrence of structured populations in a migratory freshwater fish species

“…In Barbus neumayeri, genetic differentiation among sampling sites that presented different oxygen rates could represent the effects of selective pressure (Chapman et al, 1999). The well-developed homing instinct of salmonid fish seems to be a decisive factor leading to strong population subdivisions (Ryman, 1983).…”

Increase in Anoxia in Lake Victoria and Its Effects on the Fishery

“…They concluded that the adaptation to lifelong hypoxia is mainly due to improved oxygen transport. Some species like B. neumayeri survived extreme hypoxic conditions in the wetlands by combination of low metabolism, high haemoglobin, and very efficient use of aquatic surface respiration (Chapman & Liem, 1995;Olowo & Chapman, 1996;Chapman et al, 1999).…”