Are natural hybrids fit or unfit relative to their parents?

Arnold, Michael L.; Hodges, Scott A.

doi:10.1016/s0169-5347(00)88979-x

Cited by 549 publications

(527 citation statements)

References 22 publications

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“…obs. ) The fact that hybrids may have higher fitness than their parents in certain habitats is now well documented (Arnold and Hodges 1995;Arnold 1997;Lexer et al 2003a). Moreover, it was recently demonstrated that transgressive segregation can be very important in generating hybrid genotypes that are adapted to novel habitats Lexer et al 2003b).…”

Section: Hybrid Origin Of Senecio Squalidusmentioning

confidence: 99%

Recent, Allopatric, Homoploid Hybrid Speciation: The Origin of Senecio Squalidus (Asteraceae) in the British Isles From a Hybrid Zone on Mount Etna, Sicily

2005

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Abstract. Homoploid hybrid speciation occurs through stabilization of a hybrid segregate (or segregates) isolated by premating and/or postmating barriers from parent taxa. Theory predicts that ecological and spatial isolation are of critical importance during homoploid hybrid speciation, and all confirmed homoploid hybrid species are ecologically isolated from their parents. Until recently, such species have been identified long after they originated, and consequently it has not been possible to determine the relative importance of spatial and ecological isolation during their origin. Here we present evidence for the recent origin (within the past 300 years) of a new homoploid hybrid species, Senecio squalidus (Asteraceae), in the British Isles, following long-distance dispersal of hybrid material from a hybrid zone between S. aethnensis and S. chrysanthemifolius on Mount Etna, Sicily, Italy. Historical records show that such hybrid material from Sicily was introduced to the Oxford Botanic Garden in Britain in the early part of the 18th century and that S. squalidus began to spread from there after approximately 90 years. A survey of randomly amplified polymorphic DNA/intersimple sequence repeats (RAPD/ISSR) marker variation demonstrated that S. squalidus is a diploid hybrid derivative of S. aethnensis and S. chrysanthemifolius that grow at high and low altitudes, respectively, on Mount Etna and that form a hybrid zone at intermediate altitudes. Senecio squalidus contained 11 of 13 RAPD/ISSR markers that were recorded at high frequency in S. chrysanthemifolius but were absent or occurred at low frequency in S. aethnensis, and 10 of 13 markers for which the reverse was true. Bayesian admixture analysis showed that all individuals of S. squalidus surveyed were of mixed ancestry with relatively high mean proportions of ancestry derived from both S. chrysanthemifolius and S. aethnensis (0.644 and 0.356, respectively). We argue that long-distance isolation of hybrid material from its parents on Mount Etna would have helped favor the origin and establishment of S. squalidus in the British Isles, regardless of whether the initial hybrid material introduced to Britain was preadapted to local conditions.

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Section: Hybrid Origin Of Senecio Squalidusmentioning

confidence: 99%

Recent, Allopatric, Homoploid Hybrid Speciation: The Origin of Senecio Squalidus (Asteraceae) in the British Isles From a Hybrid Zone on Mount Etna, Sicily

2005

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“…Although examples of superior performance of hybrids are rare, a growing number of studies show that hybrid fitness depends on genotype, generation, and environment (Campbell et al ., 1998;Hauser et al ., 2003;Lexer et al ., 2003). However, most studies involve only early generation hybrids that may display either heterosis, a transient condition that may overestimate the probability of persistence of crop genes within weed populations (reviewed in Arnold & Hodges, 1995;Arnold, 1997), or outbreeding depression, a transient condition that may underestimate the probability of persistence of crop genes within weed populations (Ellstrand, 1992).…”

Section: Introductionmentioning

confidence: 99%

Competition alters life history and increases the relative fecundity of crop–wild radish hybrids (Raphanusspp.)

2006

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Summary• The evolutionary impact of crop-to-wild gene flow depends on the fitness of hybrids under natural, competitive conditions. Here, we measured the performance of third-generation (F 3 ) radish hybrids ( Raphanus raphanistrum × Raphanus sativus ) and weedy R. raphanistrum to understand how competitive interactions affect life history and relative fecundity.• Three wild and three F 1 crop-wild hybrid radish populations were established in semi-natural, agricultural conditions in Michigan, USA. The effects of competition on life-history traits and fecundity of F 3 progeny were measured 2 yr later in a common garden experiment.• Third-generation hybrid plants generally produced fewer seeds per fruit and set fewer fruits per flower than wild plants, resulting in lower lifetime fecundity. With increasing competition, age at reproduction was delayed, the relative number of seeds per fruit was reduced in wild plants and differences between hybrid and wild fecundity diminished.• Competition may enhance the fecundity of advanced-generation hybrids relative to wild plants by reducing differences in life history, potentially promoting the introgression of crop alleles into weed populations.

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“…Since Darwin's time, many researchers have reported on the relative fitness of hybrids and have found that in many cases, hybrids are as fit, or fitter than their pure species counterparts (see Arnold and Hodges (1995); Arnold (2006Arnold ( , 2008 and for reviews). Many have debated what these estimates might mean with regard to the impact of genetic exchange on evolutionary pattern and process (Anderson, 1949;Anderson and Stebbins, 1954;Mayr, 1963;Lewontin and Birch, 1966;Grant, 1981;Barton and Hewitt, 1985;Arnold, 1992Arnold, , 1997Arnold, , 2006Arnold, , 2008Grant andGrant, 1992, 2010;Dowling and DeMarais, 1993;Rieseberg, 1997;Rieseberg et al, 2003;Seehausen, 2004;Seehausen et al, 2008;Anderson et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

“…These include: (1) hybrid genotypes with high relative fitness are produced more often than previously assumed (Arnold and Hodges, 1995); (2) even hybrids with low relative fitness may act as a conduit for genetic exchange, given that they have some level of fertility (Arnold and Hodges, 1995;Arnold, 1997Arnold, , 2006; and (3) for many taxonomic groups, allopatric divergence is not as frequent as divergence accompanied by some level of at least intermittent gene flow (that is, parapatric or sympatric divergence; Pinho and Hey (2010)). Numerous authors including Darwin himself-see above quote-contributed to the formulation of the first hypothesis (relating to the production of relatively fit hybrid genotypes).…”

Section: Introductionmentioning

confidence: 99%

Hybrid fitness, adaptation and evolutionary diversification: lessons learned from Louisiana Irises

2011

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Estimates of hybrid fitness have been used as either a platform for testing the potential role of natural hybridization in the evolution of species and species complexes or, alternatively, as a rationale for dismissing hybridization events as being of any evolutionary significance. From the time of Darwin's publication of The Origin, through the neo-Darwinian synthesis, to the present day, the observation of variability in hybrid fitness has remained a challenge for some models of speciation. Yet, Darwin and others have reported the elevated fitness of hybrid genotypes under certain environmental conditions. In modern scientific terminology, this observation reflects the fact that hybrid genotypes can demonstrate genotypeÂenvironment interactions. In the current review, we illustrate the development of one plant species complex, namely the Louisiana Irises, into a 'model system' for investigating hybrid fitness and the role of genetic exchange in adaptive evolution and diversification. In particular, we will argue that a multitude of approaches, involving both experimental and natural environments, and incorporating both manipulative analyses and surveys of natural populations, are necessary to adequately test for the evolutionary significance of introgressive hybridization. An appreciation of the variability of hybrid fitness leads to the conclusion that certain genetic signatures reflect adaptive evolution. Furthermore, tests of the frequency of allopatric versus sympatric/parapatric divergence (that is, divergence with ongoing gene flow) support hybrid genotypes as a mechanism of evolutionary diversification in numerous species complexes.

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Are natural hybrids fit or unfit relative to their parents?

Cited by 549 publications

References 22 publications

Recent, Allopatric, Homoploid Hybrid Speciation: The Origin of Senecio Squalidus (Asteraceae) in the British Isles From a Hybrid Zone on Mount Etna, Sicily

Recent, Allopatric, Homoploid Hybrid Speciation: The Origin of Senecio Squalidus (Asteraceae) in the British Isles From a Hybrid Zone on Mount Etna, Sicily

Competition alters life history and increases the relative fecundity of crop–wild radish hybrids (Raphanusspp.)

Hybrid fitness, adaptation and evolutionary diversification: lessons learned from Louisiana Irises

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