Patterns of chromosomal variation in Mexican species of Aeschynomene (Fabaceae, Papilionoideae) and their evolutionary and taxonomic implications

Abstract

Citation: Tapia-Pastrana F, Delgado-Salinas A, Caballero J (2020) Patterns of chromosomal variation in Mexican species of Aeschynomene (Fabaceae, Papilionoideae) and their evolutionary and taxonomic implications. Comparative Cytogenetics 14(1): 157-182. https://doi. AbstractA cytogenetic analysis of sixteen taxa of the genus Aeschynomene Linnaeus, 1753, which includes species belonging to both subgenera Aeschynomene (Léonard, 1954) and Ochopodium (Vogel, 1838) J. Léonard, 1954, was performed. All studied species had the same chromosome number (2n = 20) but exhibited karyotype diversity originating in different combinations of metacentric, submetacentric and subtelocentric chromosomes, chromosome size and number of SAT chromosomes. The plasticity of the genomes included the observation in a taxon belonging to the subgenus Aeschynomene of an isolated spherical structure similar in appearance to the extra chromosomal circular DNA observed in other plant genera. By superimposing the karyotypes in a recent phylogenetic tree, a correspondence between morphology, phylogeny and cytogenetic characteristics of the taxa included in the subgenus Aeschynomene is observed. Unlike subgenus Aeschynomene, the species of Ochopodium exhibit notable karyotype heterogeneity. However the limited cytogenetic information recorded prevents us from supporting the proposal of their taxonomic separation and raise it to the genus category. It is shown that karyotype information is useful in the taxonomic delimitation of Aeschynomene and that the diversity in the diploid level preceded the hybridization/polyploidization demonstrated in the genus. The systematic implications of our results and their value can be extended to other Dalbergieae genera as knowledge about the chromosomal structure and its evolution increases.

Cytogenetics of Diphysa americana (Mill.) M.Sousa (Leguminosae-Papilionoideae-dalbergioid clade), a rare species from the coast of Oaxaca, Mexico

“…On the other hand, the values of THC, AC, Range, L/S and TF% (Table 2) are parameters obtained for the first time in the genus Diphysa and to demonstrate their taxonomic value, a greater number of species must be studied. However, with respect to THC (21.81 ± 3.14 µm) and AC (2.18 ± 0.21 µm), it can be stated that they differ little from the values obtained for species of the recently reestablished genus Ctenodon (Tapia-Pastrana et al 2020;Cardoso et al 2020) and Dalbergia spinosa (Jena et al 2004) also in the dalbergioid clade. Regarding the presence of small circular fragments, for the moment there is no information on their origin and function.…”

“…The karyotypic formula proposed here (5m + 5sm) shows that in the dalbergioid chromosome complements obtained so far, chromosomes with a medium (m) or slightly displaced (sm) centromere predominate (Table 1), and therefore they are symmetric or slightly asymmetric karyotypes (Tapia-Pastrana et al 2020). Likewise, the presence of secondary constrictions associated with microsatellites in short arms of sm chromosomes (SAT chromosomes) corroborates a trend in plant species where secondary constrictions are located preferentially in short arms (Lima de Faria 1976;Lim et al 2001), particularly in legumes (Biondo et al 2006;Tapia-Pastrana 2012;Tapia-Pastrana and Tapia-Aguirre 2018;Tapia-Pastrana et al 2020). Likewise, their role in the organization of the nucleolus is evident since they were observed associated with it in prometaphase cells (Fig.…”

“…3A) and considered nucleolar organizing regions (NOR) or at least part of them. In addition, its shape and behavior resemble those exhibited by species belonging to the genus Aeschynomene, Serie Americanae (Tapia-Pastrana et al 2020).…”

“…The genus Diphysa records a 2n = 16 chromosome count for Diphysa robinioides Benth., a synonymy of D. americana (Atchison 1951;Sousa 1990;WFO 2023). However, this number is far from the basic number x = 10 and the diploid number 2n = 20 that predominate in genera belonging to the dalbergiod clade of Papilionoide- ae (Goldblatt 1981;Lavin et al 2001;Tapia-Pastrana et al 2020) and therefore requires a cytogenetic reevaluation where, in addition to verifying its chromosome number, a detailed description of its karyotype is obtained.…”

Divergence time estimation and mapping of morphological and cytogenetical data in the southern South American geophyte genus Pterocactus (Cactaceae)

“…Cytological data contribute to clarifying the origin, speciation and the phylogenetic relationships of flowering plants (e.g., Weiss‐Schneeweiss & Schneeweiss, 2013; Chiarini & al., 2018; Tapia‐Pastrana & al., 2020), including Cactaceae (e.g., Majure & al., 2012; Moreno & al., 2015a; Las Peñas & al., 2019). Cacti are highly conservative in some chromosomal characteristics, such as the basic number ( x = 11) and highly symmetrical karyotypes (e.g., Ross, 1981; Pinkava & Parfitt, 1982; Cota & Wallace, 1995; Bandyopadhyay & Sharma, 2000; Las Peñas & al., 2008; Moreno & al., 2015a,b).…”