Abstract
There is growing attention given to gene flow between crops and the wild relatives as global landscapes have been rapidly converted into agricultural farm fields over the past century. Crop-to-wild introgression may advance the extinction risks of rare plants through demographic swamping and/or genetic swamping. Malus sieversii, the progenitor of the apple, is exclusively distributed along the Tien Shan mountains. Habitat fragmentation and hybridization between M. sieversii and the cultivated apples have been proposed to be the causal mechanism of the accelerated extinction risk. We examined the genetic diversity pattern of eleven wild and domesticated apple populations and assessed the gene flow between M. sieversii and the cultivated apples in Kazakhstan using thirteen nuclear microsatellite loci. On average, apple populations harbored fairly high within-population diversity, whereas population divergences were very low suggesting likely influence of human-mediated dispersal. Assignment results showed a split pattern between the cultivated and wild apples and frequent admixture among the apple populations. Coupled with the inflated contemporary migration rates, the admixture pattern might be the signature of increased human intervention within the recent past. Our study highlighted the prevalent crop to wild gene flow of apples occurring in Kazakhstan, proposing an accelerated risk of genetic swamping.
Highlights
Inter-specific gene flow between rare species and the allied taxa that are commonly distributed may result in the increased extinction risk at least locally for the rare species [1,2,3,4]
Hybridization may lead to increased extinction risk through demographic swamping, i.e., reduced population growth rate, driven by outbreeding depression and/or genetic swamping where the parental lineages are replaced by the hybrids [2,5]
Because we aimed to examine the level of crop to wild gene flow, both historical and contemporary migration rates among the wild apple populations and the cultivated apples were estimated as a proxy for the gene flow
Summary
Inter-specific gene flow between rare species and the allied taxa that are commonly distributed may result in the increased extinction risk at least locally for the rare species [1,2,3,4]. Gene flow among related taxa have become more frequent due to habitat destruction and translocation by anthropogenic influences [6]. Hybridization observed in Prunus fruticosa, a rare shrub distributed in Eurasia, with the widely cultivated cherries, P. avium and P. cerasus is one of the compelling examples showing likely risk of genetic swamping [9]. A recent review comprising over 350 hybridization-related studies proposed that genetic swamping resulting from interspecific hybridization causes local extinction more frequently than what has been expected [5]. With the advent of many advanced molecular tools, examining the rate of hybridization in rare plants is feasible. The extent of hybridization estimated from molecular methods might offer valuable insights for conservation practices
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