Biology subjects

Maddison, D. R.

Publications and source records attributed to Maddison, D. R..

3 recordsLinked to original sources

bioRxiv2020

Repetitive DNA profiles reveal evidence of rapid genome evolution and reflect species boundaries in ground beetles

AO_SCPLOWBSTRACTC_SCPLOWGenome architecture is a complex, multidimensional property of an organism defined by the content and spatial organization of the genomes component parts. Comparative study of entire genome architecture in model organisms is shedding light on mechanisms underlying genome regulation, evolution, and diversification; but such studies require costly analytical approaches which make extensive comparative study impractical for most groups. However, lower-cost methods that measure a single architectural component (e.g., distribution of one class of repeats) have potential as a new data source for evolutionary studies insofar as that measure correlates with more complex biological phenomena, and for which it could serve as part of an explanatory framework. We investigated copy number variation (CNV) profiles in ribosomal DNA (rDNA) as a simple measure reflecting the distribution of rDNA subcomponents across the genome. We find that signatures present in rDNA CNV profiles strongly correlate with species boundaries in the breve species group of Bembidion, and vary across broader taxonomic sampling in Bembidion subgenus Plataphus. Profiles of several species show evidence of re-patterning of rDNA-like sequences throughout the genome, revealing evidence of rapid genome evolution (including among sister pairs) not evident from analysis of traditional data sources such as multi-gene data sets. Major re-patterning of rDNA-like sequences has occurred frequently within the evolutionary history of Plataphus. We confirm that CNV profiles represent an aspect of genomic architecture (i.e., the linear distribution of rDNA components across the genome) via fluorescence in-situ hybridization. In at least one species, novel rDNA-like elements are spread throughout all chromosomes. We discuss the potential of copy number profiles of rDNA, or other repeats, as a low-cost tool for incorporating signal of genomic architecture variation in studies of species delimitation and genome evolution.

evolutionary biology↗

bioRxiv2019

Novelty and emergent patterns in sperm: morphological diversity and evolution of spermatozoa and sperm conjugation in ground beetles (Coleoptera: Carabidae)

1.The beetle family Carabidae, with about 40,000 species, exhibits enough diversity in sperm structure and behavior to be an excellent model system for studying patterns and processes of sperm evolution. We explore their potential, documenting sperm form in 177 species of ground beetles and collecting data on 1 qualitative and 7 quantitative sperm phenotypic traits. Our sampling captures 61% of the tribal-level diversity of ground beetles. These data highlight the notable morphological diversity of sperm in ground beetles and suggest that sperm in the group have dynamic evolutionary histories with much morphological innovation and convergence. Sperm vary among species in total length from 48-3,400m and in length and width of the sperm head. Most ground beetles make filamentous sperm with visually indistinct heads, but some or all studied members of the genus Omophron, genus Trachypachus, and tribe Dyschiriini make broad-headed sperm that show morphological differences between species. Most ground beetles package their sperm into groups of sperm, termed conjugates, and ground beetles show variation in conjugate form and in the number and arrangement of sperm in a conjugate. Most ground beetles make sperm conjugates by embedding their sperm in a non-cellular rod or spermatostyle, but some Trechitae make conjugates without a spermatostyle. The spermatostyle is remarkably variable among species and varies in length from 17-41,000m. Several unrelated groups of ground beetles make only singleton sperm, including Nebriinae, Cicindelinae, many Trechinae, and the tribe Paussini. Given current views about ground beetle relationships, we propose preliminary hypotheses on ground beetle sperm diversification. We hypothesize that spermatostyle and conjugate traits evolve faster than sperm traits and that head width evolves more slowly than head length and sperm length. We propose that conjugation with a spermatostyle evolved early within the history of Carabidae and that it has been lost independently at least three times.\n\nResearch highlightsO_LIGround beetle sperm is morphologically diverse.\nC_LIO_LIMost species make sperm conjugates with a spermatostyle, and there is variation in sperm, spermatostyles, and conjugates.\nC_LIO_LISperm have dynamic evolutionary histories.\nC_LI

evolutionary biology↗

bioRxiv2019

Measuring genome sizes using read-depth, k-mers, and flow cytometry: methodological comparisons in beetles (Coleoptera)

Measuring genome size across different species can yield important insights into evolution of the genome and allow for more informed decisions when designing next-generation genomic sequencing projects. New techniques for estimating genome size using shallow genomic sequence data have emerged which have the potential to augment our knowledge of genome sizes, yet these methods have only been used in a limited number of empirical studies. In this project, we compare estimation methods using next-generation sequencing (k-mer methods and average read depth of single-copy genes) to measurements from flow cytometry, the gold standard for genome size measures, using ground beetles (Carabidae) and other members of the beetle suborder Adephaga as our test system. We also present a new protocol for using read-depth of single-copy genes to estimate genome size. Additionally, we report flow cytometry measurements for five previously unmeasured carabid species, as well as 21 new draft genomes and six new draft transcriptomes across eight species of adephagan beetles. No single sequence-based method performed well on all species, and all tended to underestimate the genome sizes, although only slightly in most samples. For one species, Bembidion haplogonum, most sequence-based methods yielded estimates half the size suggested by flow cytometry. This discrepancy for k-mer methods can be explained by a large number of repetitive sequences, but we have no explanation for why read-depth methods yielded results that were also strikingly low.

genomics↗