Biology subjects

Burquez, A.

Publications and source records attributed to Burquez, A..

4 recordsLinked to original sources

bioRxiv2023

An improved genome assembly of the saguaro cactus (Carnegiea gigantea (Engelm.) Britton & Rose).

We present an improved genome assembly of the saguaro cactus (Carnegiea gigantea (Engelm.) Britton & Rose), obtained by incorporating long-read PacBio data to the existing short reads. The assembly improves in terms of total size, contiguity, and accuracy, allowing to extend the range of sequence analyses beyond the single-gene scale. Consequently, the assembly is 16% larger and has 20% more genes, expanding the resources for a neglected yet very remarkable plant family such as Cactaceae. Species taxonomyEukaryota; Viridiplantae; Streptophyta; Streptophytina; Embryophyta; Tracheophyta; Euphyllophyta; Spermatophyta; Magnoliopsida; Mesangiospermae; eudicotyledons; Gunneridae; Pentapetalae; Caryophyllales; Cactineae; Cactaceae; Cactoideae; Echinocereeae; Carnegiea gigantea (Engelm.) Britton & Rose) (also known as saguaro cactus) (NCBI txid: 171969).

genomics↗

bioRxiv2023

Are 150 km of open sea enough? Gene flow and population differentiation in a bat-pollinated columnar cactus

Genetic differentiations and phylogeographical patterns are controlled by the interplay between spatial isolation and gene flow. To test the extent of gene flow across an oceanic barrier, we explored the effect of the separation of the peninsula of Baja California on the evolution of mainland and peninsular populations of the long-lived columnar cactus Stenocereus thurberi. We analyzed twelve populations throughout the OPC distribution range to assess genetic diversity and structure using chloroplast DNA sequences. Genetic diversity was higher (Hd=0.81), and genetic structure was lower (GST=0.143) in mainland populations vs peninsular populations (Hd=0.71, GST=0.358 respectively). Genetic diversity was negatively associated with elevation but positively with rainfall. Two mainland and one peninsular ancestral haplotypes were reconstructed. Peninsular populations were as isolated among them as with mainland populations. Peninsular haplotypes formed a group with one mainland coastal population, and populations across the gulf shared common haplotypes giving support to regular gene flow across the Gulf. Gene flow is likely mediated by bats, the main pollinators and seed dispersers. Niche modeling suggests that during the Last Glacial Maximum (c. 130 ka), OPC populations shrank to southern locations. Currently, Stenocereus thurberi populations are expanding, and the species is under population divergence despite ongoing gene flow. Ancestral populations are located on the mainland and although vicariant peninsular populations cannot be ruled out, they are likely the result of gene flow across the seemingly formidable barrier of the Gulf of California. Still, unique haplotypes occur in the peninsula and the mainland, and peninsular populations are more structured than these on the mainland.

evolutionary biology↗

bioRxiv2020

A new (old) approach to genotype-based phylogenomic inference within species, with an example from the saguaro cactus (Carnegiea gigantea)

AO_SCPLOWBSTRACTC_SCPLOWGenome sequence data are routinely being used to infer phylogenetic history within and between closely related diploid species, but few tree inference methods are specifically tailored to diploid genotype data. Here we re-examine the method of "polymorphism parsimony" (Inger 1967; Farris 1978; Felsenstein 1979), originally introduced to study morphological characters and chromosome inversion polymorphisms, to evaluate its utility for unphased diploid genotype data in large scale phylogenomic data sets. We show that it is equivalent to inferring species trees by minimizing deep coalescences--assuming an infinite sites model. Two potential advantages of this approach are scalability and estimation of a rooted tree. As with some other single nucleotide polymorphism (SNP) based methods, it requires thinning of data sets to statistically independent sites, and we describe a genotype-based test for phylogenetic independence. To evaluate this approach in genome scale data, we construct intraspecific phylogenies for 10 populations of the saguaro cactus using 200 Gbp of resequencing data, and then use these methods to test whether the population with highest genetic diversity corresponds to the root of the genotype trees. Results were highly congruent with the (unrooted) trees obtained using SVDquartets, a scalable alternative method of phylogenomic inference.

evolutionary biology↗

bioRxiv2020

Natural selection maintains species despite widespread hybridization in the desert shrub Encelia

Natural selection is an important driver of genetic and phenotypic differentiation between species. A powerful way to test the role of natural selection in the formation and maintenance of species is to study species complexes in which potential gene flow is high but realized gene flow is low. For a recent radiation of New World desert shrubs (Encelia: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions. After finding evidence for extremely strong selection at both hybrid zones, we use a combination of field experiments, high-resolution imaging, and physiological measurements to determine the ecological basis for selection at one of the hybrid zones. Our results identify multiple ecological mechanisms of selection (drought, salinity, herbivory, and burial) that together are sufficient to maintain species boundaries despite high rates of hybridization. Given that multiple pairs of species hybridize at ecologically divergent parapatric boundaries in the adaptive radiation of Encelia, such mechanisms may maintain species boundaries throughout this group. SIGNIFICANCE STATEMENTIn Baja California, the deserts meet the coastal dunes in a narrow transition visible even from satellite images. We study two species pairs of desert shrubs (Encelia) that occur across this transition. Although these species can interbreed, they remain distinct. Using a combination of genetics, field experiments, 3D-imaging, and physiological measurements, we show that natural selection counteracts the homogenizing effects of gene exchange. The different habitats of these species create multiple mechanisms of selection - drought, salinity, herbivory, and burial, which together maintain these species in their native habitats and their hybrids in intermediate habitats. This study illustrates how environmental factors influence traits and fitness and how this in turn maintain species, highlighting the importance of natural selection in speciation.

evolutionary biology↗