Diversity and Speciation of Semionotid Fishes in Mesozoic Rift Lakes

Abstract

Prolific speciation of fishes within lakes has long fascinated evolutionary biologists (e.g., Brooks 1950; Martens 1997), in part because of the difficulty in identifying extrinsic barriers to gene exchange that might permit allopatric speciation of vagile organisms such as fishes in lakes. The cichlid fishes of Lakes Victoria and Malawi (Fryer and Iles 1972; Greenwood 1981b) are the most celebrated examples of intralacustrine speciation, but its generality has been established by many other examples of endemic fishes, both extant (Kornfield and Carpenter 1984; Parenti 1984; Parker and Kornfield 1995; Strecker et al. 1996; Seegers et al. 1999) and fossil (McCune et al. 1984). Whether such intralacustrine speciation could be sympatric has engendered considerable debate (Worthington 1954; Kosswig 1963; Ribbink 1994; Turner 1994), despite previous theoretical arguments that the evolution of reproductive isolation is extremely unlikely without geographic separation (Tregenza and Butlin 1999). Empirical evidence that speciation in some of these fishes occurred in sympatry has been growing, however (Meyer et al. 1990; Schliewen et al. 1994; Johnson et al. 1996a; McCune and Lovejoy 1998), and recent theoretical results suggest that sympatric speciation is more plausible than previously believed (e.g., Dieckmann and Doebeli 1999; Kondrashov and Kondrashov 1999; Chapter 5). According to these latter theoretical studies, nonrandom mating and ecological interactions, like intraspecific competition for resources, can initiate sympatric speciation.