Palaeontological documentation of speciation in Cenozoic molluscs from Turkana Basin

Williamson, P. G.

doi:10.1038/293437a0

Cited by 318 publications

(170 citation statements)

References 21 publications

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“…If so, adaptive phenotypic plasticity may be important to emerging patterns of geographic variation and could enhance speciation in allopatric populations (58). Indeed, the magnitude and spatial scale of the induced changes seen in our experiments suggest that recent or fossil transitions in molluskan shell form are not unequivocal evidence of rapid selection (25,28,29) or speciation (59). Moreover, the discovery of plastic increases in the claw size and crushing force of a crab in response to diet (60) indicates that adaptive plasticity may inf luence both sides of the evolutionary arms race.…”

Section: Resultsmentioning

confidence: 71%

Induced defenses in response to an invading crab predator: An explanation of historical and geographic phenotypic change

Trussell

Smith²

2000

Proc. Natl. Acad. Sci. U.S.A.

233

222

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The expression of defensive morphologies in prey often is correlated with predator abundance or diversity over a range of temporal and spatial scales. These patterns are assumed to reflect natural selection via differential predation on genetically determined, fixed phenotypes. Phenotypic variation, however, also can reflect within-generation developmental responses to environmental cues (phenotypic plasticity). For example, water-borne effluents from predators can induce the production of defensive morphologies in many prey taxa. This phenomenon, however, has been examined only on narrow scales. Here, we demonstrate adaptive phenotypic plasticity in prey from geographically separated populations that were reared in the presence of an introduced predator. Marine snails exposed to predatory crab effluent in the field increased shell thickness rapidly compared with controls. Induced changes were comparable to (i) historical transitions in thickness previously attributed to selection by the invading predator and (ii) present-day clinal variation predicted from water temperature differences. Thus, predator-induced phenotypic plasticity may explain broad-scale geographic and temporal phenotypic variation. If inducible defenses are heritable, then selection on the reaction norm may influence coevolution between predator and prey. Trade-offs may explain why inducible rather than constitutive defenses have evolved in several gastropod species. P henotypic plasticity, the capacity of an organism to produce different phenotypes in response to environmental cues, can be an important adaptive strategy in variable or changing environments (1, 2). Inducible defenses are a ubiquitous form of plasticity that involve the production of chemicals, morphologies, or behaviors by prey species in response to predator cues (3). These changes reduce prey vulnerability to inducing predators or herbivores. Inducible defenses occur in diverse taxa and examples include: production of chemical defenses in plants (4, 5), formation of spines in rotifers (6) and marine bryozoans (7) and neck teeth and helmets in cladocerans (8), diel vertical migration in marine (9) and freshwater zooplankton (10), and changes in body shape in fish (11) and shell shape and thickness in mollusks and barnacles (12-15).Despite improved understanding of the cues inducing these defenses and their immediate adaptive value (3, 16), our understanding of how this phenomenon contributes to broader temporal and spatial patterns of phenotypic variation remains poor. To date, most studies have examined inducible defenses and their costs on very localized spatial scales (3-15). In doing so, there is limited consideration of environmental complexity and the interactive inf luences of others cues that are likely to occur across a broader scale. For example, many plant and animal species have wide altitudinal and latitudinal distributions where dramatic temperature gradients occur. Because temperature can profoundly inf luence developmental and metabolic rates (17, 18) and phen...

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Section: Resultsmentioning

confidence: 71%

Induced defenses in response to an invading crab predator: An explanation of historical and geographic phenotypic change

Trussell

Smith²

2000

Proc. Natl. Acad. Sci. U.S.A.

233

222

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“…Despite the commonness of stasis, there is little consensus about its cause or causes. Various forms of stabilizing natural selection have been invoked (2,8,20,24,25), and early suggestions of constraint (1,26) have been resuscitated by more sophisticated genetic perspectives (27). One factor recently advocated is spatially heterogeneous natural selection across semiisolated populations (9,23,28).…”

Section: Discussionmentioning

confidence: 99%

The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages

Hunt

2007

Proc. Natl. Acad. Sci. U.S.A.

265

315

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The nature of evolutionary changes recorded by the fossil record has long been controversial, with particular disagreement concerning the relative frequency of gradual change versus stasis within lineages. Here, I present a large-scale, statistical survey of evolutionary mode in fossil lineages. Over 250 sequences of evolving traits were fit by using maximum likelihood to three evolutionary models: directional change, random walk, and stasis. Evolution in these traits was rarely directional; in only 5% of fossil sequences was directional evolution the most strongly supported of the three modes of change. The remaining 95% of sequences were divided nearly equally between random walks and stasis. Variables related to body size were significantly less likely than shape traits to experience stasis. This finding is in accord with previous suggestions that size may be more evolutionarily labile than shape and is consistent with some but not all of the mechanisms proposed to explain evolutionary stasis. In general, similar evolutionary patterns are observed across other variables, such as clade membership and temporal resolution, but there is some evidence that directional change in planktonic organisms is more frequent than in benthic organisms. The rarity with which directional evolution was observed in this study corroborates a key claim of punctuated equilibria and suggests that truly directional evolution is infrequent or, perhaps more importantly, of short enough duration so as to rarely register in paleontological sampling.gradualism ͉ modes of evolution ͉ punctuated equilibria

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“…Nevertheless, a variety of studies have found evidence for evolution and adaptation occurring in a surprisingly effective manner in asexual populations (eg Parker, 1979a;Williamson, 1981;Glazier, 1992;Christensen et al, 1992;Toline and Lynch, 1994;Andrade and Roitberg, 1995;Sunnucks et al, 1998;Weeks and Hoffman, 1998;Wilson et al, 1999Wilson et al, , 2003. These works cite such evidence as diverse and closely adapted clonal arrays (eg Parker, 1979a-c;Weeks and Hoffman, 1998;Wilson et al, 1999), natural clonal assemblages shown to have high (comparable to sexual) heritabilities for life history, morphological, and fitness-related traits (Stratton, 1991(Stratton, , 1992, and parthenogenetic genotypes that seem to outcompete sympatric sexual forms (eg Browne, 1992;Christensen et al, 1992;Weeks and Hoffman, 1998).…”

Section: Conversion With Physical Limits On Recombination Chromosomalmentioning

confidence: 99%

The conversion of variance and the evolutionary potential of restricted recombination

Neiman

Linksvayer

2005

Heredity

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Genetic recombination is usually considered to facilitate adaptive evolution. However, recombination prevents the reliable cotransmission of interacting gene combinations and can disrupt complexes of coadapted genes. If interactions between genes have important fitness effects, restricted recombination may lead to evolutionary responses that are different from those predicted from a purely additive model and could even aid adaptation. Theory and data have demonstrated that phenomena that limit the effectiveness of recombination via increasing homozygosity, such as inbreeding and population subdivision and bottlenecks, can temporarily increase the additive genetic variance available to these populations. This effect has been attributed to the conversion of nonadditive to additive genetic variance.Analogously, phenomena such as chromosomal inversions and apomictic parthenogenesis that physically restrict recombination in part or all of the genome may also result in a release of additive variance. Here, we review and synthesize literature concerning the evolutionary potential of populations with effectively or physically restricted recombination. Our goal is to emphasize the common theme of increased short-term access to additive genetic variance in all of these situations and to motivate research directed towards a more complete characterization of the relevance of the conversion of variance to the evolutionary process.

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Palaeontological documentation of speciation in Cenozoic molluscs from Turkana Basin

Cited by 318 publications

References 21 publications

Induced defenses in response to an invading crab predator: An explanation of historical and geographic phenotypic change

Induced defenses in response to an invading crab predator: An explanation of historical and geographic phenotypic change

The relative importance of directional change, random walks, and stasis in the evolution of fossil lineages

The conversion of variance and the evolutionary potential of restricted recombination

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