Clonal invasion: Kalanchoe ×houghtonii, a single genotype conquers the planet

Abstract

Invasive alien plant species pose a global challenge, and their impact is amplified by globalisation and the accelerating pace of climate change. In mild-climate regions, drought-tolerant invasive plants showing broad environmental tolerance have a competitive advantage. One example is Kalanchoe ×houghtonii (Crassulaceae), popularly known as “mother of millions”. It is a hybrid resulting from the interploid cross between K. daigremontiana and K. delagoensis, both native to Madagascar. Kalanchoe ×houghtonii, propagated as an ornamental plant, has emerged as a global invader in less than a century. Four morphotypes of this hybrid have been identified, with different ploidy levels and varying invasive capacities. Here we aim to investigate the genomic variability behind the invasion success of Kalanchoe ×houghtonii. We sampled 57 acces- sions of Kalanchoe ×houghtonii, K. daigremontiana, K. delagoensis and closely related taxa, including old herbarium materials, from all over the world. We analysed genome size, chromosome numbers, sequenced the whole genome, analysed the complete plastome sequence of each accession, and studied the diversity of the ribosomal RNA genes. We also performed a detailed phylogenomic study using nuclear BUSCO genes. Our study reveals the genetic and cytogenetic variability between morphotypes and shows that a single clonal tetraploid genotype (morphotype A) dominates all popula- tions, emerging as the first reported clonal hybrid capable of worldwide colonisation and invasion. Morphotype A shows a striking genetic uniformity, high phenotypic plasticity, and extremely high rates of vegetative reproduction, representing an example of a “general-purpose genotype”. The astonishing reproductive capacity, broad adaptability and the speed at which K. ×houghtonii is colonising new regions by clonal spread high- light the importance of understanding hybridisation and polyploidy in the invasion of ecosystems. Our findings call for the need for risk assessments before developing new hybrids for ornamental plant breeding that may exhibit invasive characteristics.

info:eu-repo/semantics/publishedVersion

Invasive alien plant species pose a global challenge, and their impact is amplified by globalisation and the accelerating pace of climate change. In mild-climate regions, drought-tolerant invasive plants showing broad environmental tolerance have a competitive advantage. One example is Kalanchoe ×houghtonii (Crassulaceae), popularly known as “mother of millions”. It is a hybrid resulting from the interploid cross between K. daigremontiana and K. delagoensis, both native to Madagascar. Kalanchoe ×houghtonii, propagated as an ornamental plant, has emerged as a global invader in less than a century. Four morphotypes of this hybrid have been identified, with different ploidy levels and varying invasive capacities. Here we aim to investigate the genomic variability behind the invasion success of Kalanchoe ×houghtonii. We sampled 57 acces- sions of Kalanchoe ×houghtonii, K. daigremontiana, K. delagoensis and closely related taxa, including old herbarium materials, from all over the world. We analysed genome size, chromosome numbers, sequenced the whole genome, analysed the complete plastome sequence of each accession, and studied the diversity of the ribosomal RNA genes. We also performed a detailed phylogenomic study using nuclear BUSCO genes. Our study reveals the genetic and cytogenetic variability between morphotypes and shows that a single clonal tetraploid genotype (morphotype A) dominates all popula- tions, emerging as the first reported clonal hybrid capable of worldwide colonisation and invasion. Morphotype A shows a striking genetic uniformity, high phenotypic plasticity, and extremely high rates of vegetative reproduction, representing an example of a “general-purpose genotype”. The astonishing reproductive capacity, broad adaptability and the speed at which K. ×houghtonii is colonising new regions by clonal spread high- light the importance of understanding hybridisation and polyploidy in the invasion of ecosystems. Our findings call for the need for risk assessments before developing new hybrids for ornamental plant breeding that may exhibit invasive characteristics.

info:eu-repo/semantics/publishedVersion

Invasive alien plant species pose a global challenge, and their impact is amplified by globalisation and the accelerating pace of climate change. In mild-climate regions, drought-tolerant invasive plants showing broad environmental tolerance have a competitive advantage. One example is Kalanchoe ×houghtonii (Crassulaceae), popularly known as “mother of millions”. It is a hybrid resulting from the interploid cross between K. daigremontiana and K. delagoensis, both native to Madagascar. Kalanchoe ×houghtonii, propagated as an ornamental plant, has emerged as a global invader in less than a century. Four morphotypes of this hybrid have been identified, with different ploidy levels and varying invasive capacities. Here we aim to investigate the genomic variability behind the invasion success of Kalanchoe ×houghtonii. We sampled 57 acces- sions of Kalanchoe ×houghtonii, K. daigremontiana, K. delagoensis and closely related taxa, including old herbarium materials, from all over the world. We analysed genome size, chromosome numbers, sequenced the whole genome, analysed the complete plastome sequence of each accession, and studied the diversity of the ribosomal RNA genes. We also performed a detailed phylogenomic study using nuclear BUSCO genes. Our study reveals the genetic and cytogenetic variability between morphotypes and shows that a single clonal tetraploid genotype (morphotype A) dominates all popula- tions, emerging as the first reported clonal hybrid capable of worldwide colonisation and invasion. Morphotype A shows a striking genetic uniformity, high phenotypic plasticity, and extremely high rates of vegetative reproduction, representing an example of a “general-purpose genotype”. The astonishing reproductive capacity, broad adaptability and the speed at which K. ×houghtonii is colonising new regions by clonal spread high- light the importance of understanding hybridisation and polyploidy in the invasion of ecosystems. Our findings call for the need for risk assessments before developing new hybrids for ornamental plant breeding that may exhibit invasive characteristics.

info:eu-repo/semantics/publishedVersion