The Nature ofEspeletiaSpecies

Abstract

Species are often regarded as basic units of study in biology, following the presumption that they are real and discrete natural entities. But several biologists wonder if species are arbitrary divisions that do not correspond to discrete natural groups of organisms. Two issues must be addressed to solve this controversy, but few studies seem to do so. The first is whether organisms form sympatric and synchronic groups that are distinct in terms of phenotypes and genome-wide allele frequencies, often called "good species." Alternatives to "good species" include "cryptic species," syngameons and, more generally, cases in which phenotypes and genome-wide allele frequencies reflect contrasting evolutionary histories. The second issue is the degree to which species taxa (i.e., taxonomic classification at the species level) reflect natural groups of organisms or constitute arbitrary divisions of biological diversity. Here, we empirically addressed both issues by studying plants of the Andean genus Espeletia (Asteraceae). We collected a geographically dense sample of 538 specimens from the paramo de Sumapaz, in the Cordillera Oriental of Colombia. Additionally, we examined 165 herbarium specimens previously collected by other researchers in this region, or from taxa known to occur there. We tested for the existence of phenotypic groups using normal mixture models and data on 13 quantitative characters. Among 307 specimens with all 13 measurements, we found six distinct phenotypic groups in sympatry. We also tested for the existence of groups defined by genome-wide allele frequencies, using ancestry models and data on 2,098 single nucleotide polymorphisms. Among 77 specimens with complete genomic data, we found three groups in sympatry, with high levels of admixture. Concordance between groups defined by phenotype and genome-wide allele frequencies was low, suggesting that phenotypes and genome-wide allele frequencies reflect contrasting evolutionary histories. Moreover, the high levels of admixture suggest that Espeletia plants form a syngameon in the paramo de Sumapaz. To determine the extent to which species taxa corresponded to phenotypic and genomic groups, we used data on 12 phenotypic characters to assign 307 specimens to species taxa, according to descriptions of species taxa in the most recent monograph of Espeletia. This sample included 27 specimens cited in the monograph. Remarkably, only one out of 307 specimens in our sample fell inside any of the phenotypic ranges reported in the monograph for the species taxa known to occur in the paramo de Sumapaz. These results show that species taxa in Espeletia are delineations of largely empty phenotypic space that miss biological diversity.

An integrative genomic and phenomic analysis to investigate the nature of plant species in Escallonia (Escalloniaceae)

“…Our findings highlight the need of including specimen-level data in taxonomic descriptions and monographs in the future, and using probabilistic approaches that incorporate the variance and covariance among traits to define species in order to capture the shape of species in nature. Although our results are limited to Escallonia , we speculate this may be a widespread phenomenon in other groups 25 because plant species delimited and described with morphology are rarely based on explicit statistical analyses of phenotypic variation grounded on biological theory 26 , 27 . Therefore, we suggest that investigating the nature of plant species by relying on validating taxonomic species alone can be generally problematic.…”

Improving species delimitation for effective conservation: a case study in the endemic maple‐leaf oak (Quercus acerifolia)

“…While our sampling regime emphasizes sympatry, an alternative sampling method is to strive for a large geographic extent with sparsely distributed samples (Stevens, 1997; ter Steege et al ., 2011). In examining the species boundaries of a hypothesized endangered species, however, we argue that it is particularly critical to collect sympatric populations for a more stringent test of the species hypotheses (Pineda et al ., 2020). Sampling sympatric populations may show, as in our study, that phenotypic distinctions in morphological clusters from randomly sample individuals are often narrower than they appear in extant herbarium collections.…”

“…Another taxonomic problem is the imperfect concordance between traditional taxonomy and species supported by phenetic or genetic evidence (Cadena et al ., 2018; Pineda et al ., 2020). A previous study found only a c .…”