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Biogeographic and stratigraphic evidence for rapid speciation in semionotid fishes
- Amy R. McCune
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- Journal:
- Paleobiology / Volume 22 / Issue 1 / Winter 1996
- Published online by Cambridge University Press:
- 08 April 2016, pp. 34-48
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In this study I take advantage of an unusual system of fossil lakes in eastern North America to estimate the time for speciation of endemic semionotid fishes. Twenty-one species are all found in sedimentary cycle P4, the deposits of a single Early Jurassic lake, in the Towaco Formation of the Newark Basin in New Jersey. To determine the degree of endemism in the fauna from this fossil lake and estimate time for speciation, I surveyed more than 2000 museum specimens from 45 named localities in the Newark Basin and related basins of the Late Triassic to Early Jurassic Newark Supergroup. Six species not found in deposits equal in age to P4 or older are considered to be endemics, eight species occurring in older deposits presumably colonized Lake P4, and evidence for whether the remaining seven species were endemics or colonists is equivocal. The time for the formation, decline, and evaporation of Lake P4, in which P4 sediments were deposited, has been estimated at 21,000-24,000 years. Because all endemic Semionotus first occur in the first third of lake history, the estimated time for speciation of endemics is six species in 5000-8000 years. This rate is remarkably similar to that estimated for the five cichlids in Lake Nabugabo that diverged from Lake Victoria cichlids in about 4000 years.
18 - Diversity and Speciation of Semionotid Fishes in Mesozoic Rift Lakes
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- By Amy R. McCune, Cornell University
- Edited by Ulf Dieckmann, International Institute for Applied Systems Analysis, Austria, Michael Doebeli, University of British Columbia, Vancouver, Johan A. J. Metz, Rijksuniversiteit Leiden, The Netherlands, Diethard Tautz, Universität zu Köln
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- Book:
- Adaptive Speciation
- Published online:
- 05 July 2014
- Print publication:
- 02 September 2004, pp 362-379
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Summary
Introduction
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.
In this chapter, intralacustrine radiation of semionotid fishes during the Mesozoic is considered through a paleobiological perspective. While it is impossible to assess nonrandom mating in the fossil record, paleobiological studies do have the potential to illuminate pertinent aspects of ecology over a temporal scale impossible to study in extant organisms. First, some background on semionotid fishes and the ecological setting for their lives and preservation as fossils is given in Sections 18.2 and 18.3. In Section 18.4, parallel radiations of Semionotus in distinct lakes are described. These lacustrine radiations do, indeed, suggest an important role for ecology. Through detailed study of the history of a single lake (Section 18.5), it is shown that both intraspecific variation that subsequently became incorporated into new species and the first appearances of new species are concentrated in early lake history.