Diversification of Aeonium Species Across Macaronesian Archipelagos: Correlations Between Genome-Size Variation and Their Conservation Status

Abstract

The rich endemic flora of the Macaronesian Islands places these oceanic archipelagos among the top biodiversity hotspots worldwide. The radiations that have determined the evolution of many of these insular lineages resulted in a wealth of endemic species, many of which occur in a wide range of ecological niches, but show small distribution areas in each of them. Aeonium (Crassulaceae) is the most speciose lineage in the Canary Islands (ca. 40 taxa), and as such can be considered a good model system to understand the diversification dynamics of oceanic endemic floras. The present study aims to assess the genome size variation within Aeonium distribution, i.e., the Macaronesian archipelagos of Madeira, Canaries and Cabo Verde, and analyse it together with information on distribution (i.e., geography and conservation status), taxonomy (i.e., sections), morphological traits (i.e., growth-form), geological data (i.e., island's geological age), and environmental variables (i.e., altitude, annual mean temperature, and precipitation). Based on extensive fieldwork, a cytogeographic screening of 24 Aeonium species was performed. The conservation status of these species was assessed based on IUCN criteria. 61% of the taxa were found to be threatened (4% Endangered and 57% Vulnerable). For the first time, the genome size of a comprehensive sample of Aeonium across the Macaronesian archipelagos was estimated, and considerable differences in Cx-values were found, ranging from 0.984 pg (A. dodrantale) to 2.768 pg (A. gorgoneum). An overall positive correlation between genome size and conservation status was found, with the more endangered species having the larger genomes on average. However, only slight relationships were found between genome size, morphological traits, and environmental variables. These results underscore the importance of characterizing the cytogenomic diversity and conservation status of endemic plants found in Macaronesian Islands, providing, therefore, new data to establish conservation priorities.

Genome size is positively correlated with extinction risk in herbaceous angiosperms

“…Nevertheless, in angiosperms, large genomes were found to be maladaptive, and associated with extinction risk (Vinogradov, 2003) and rarity (Pandit et al, 2011). These broad patterns in plants were also reported at lower taxonomic levels, as in the Crassulaceae genus Aeonium (Brilhante et al, 2021). However, the relationship between angiosperm genome size and extinction risk has not been explicitly tested to date within a comprehensive evolutionary framework at a global scale, despite the considerable phylogenetic clustering of genome size across the angiosperm evolutionary tree (Carta et al, 2022).…”

Genome size variation within Crithmum maritimum: Clues on the colonization of insular environments

“…Here, we present a comparative study of genome size among the mainland populations incorporating environmental variables. The relationships between genome size and both bioclimatic and geographic variables have been widely studied among various groups of plants (Bottini et al, 2000 ; Brilhante et al, 2021 ; Díez et al, 2013 ; Suda et al, 2003 , 2005 ). Hitherto, during the various studies carried out, no universal consistency was reached between them.…”

“…On the other hand, the opposite trend was observed in the Crambe and Sonchus genera. Brilhante et al ( 2021 ) found negative correlations between annual mean precipitation and GS for Aeonium in Tenerife.…”

Contribución al conocimiento de los híbridos naturales de los géneros Aeonium y Greenovia (crassulaceae) en La Gomera, Islas Canarias

“…has the largest number of species (Bramwell & Bramwell, 2001;Acebes-Ginovés et al, 2010;Schönfelder & Schönfelder, 2018;BIOTA, 2021;Sauerbier et al, 2023) and has undoubtedly generated the largest number of natural hybrids in the entire archipelago, with about 80 known nothotaxa. Although hybrids of the genus Aeonium usually disappear from nature in the first filial generation, they can produce gene dilution in the pure species with which they coexist since pollen viability in some hybrids is 80-90% (Liu, 1989), which compromises their reproduction and makes them more vulnerable to various threats in the wild (Levin et al, 1996;Francisco-Ortega et al, 2000;Brilhante et al, 2021). Therefore, it is important to recognize them in nature, describe them, and deposit material well-preserved in the herbarium collections since these can contribute to understanding the phylogeny and evolution of this group of plants.…”