Biology subjects

Markow, T. A.

Publications and source records attributed to Markow, T. A..

3 recordsLinked to original sources

bioRxiv2026

Widespread occurrence of XXY females in Drosophila mojavensis and related species

Bridges first reported that XXY individuals are fertile females in Drosophila melanogaster, arising at low frequency (~1/2000) through errors in chromosome segregation (BRIDGES 1914; BRIDGES 1916). Although widely used in genetic studies, XXY females are seldom found in wild-type strains or natural populations, presumably because natural selection keeps them at very low frequency. Here we show that many wild-type strains of D. mojavensis and its close relatives D. arizonae, D. navojoa, and D. wheeleri carry XXY and XXYY females at frequencies of up to 88%; males from these strains are frequently XYY or XYYY. Although field collections were hampered by population declines and safety concerns, we found one XXY female (out of 87) and one XYY male (out of 36) in a natural population of D. mojavensis, indicating that these genotypes also occur at appreciable frequencies in nature. XXY females are expected to produce XY-bearing and X-bearing eggs in equal proportions; instead, we found a 57:43 ratio. Mathematical modeling shows that this meiotic-drive advantage is sufficient to explain high frequencies of XXY females. It is universally accepted that Y evolution responds exclusively to male selection, yet in XXY-bearing species it also responds to female fitness.

evolutionary biology↗

bioRxiv2020

A De Novo Genome Assembly, Gene Annotation, And Expression Atlas For The Monarch Butterfly Danaus plexippus

The monarch butterfly epitomizes insect biodiversity decline. Understanding the genetic basis of the adaptation of the monarch to a changing environment requires genomic and transcriptomic resources that better reflect its genetic diversity while being informative about gene functionality during life cycle. We report a reference-quality genome assembly from an individual resident at a nonmigratory colony in Mexico, and a new gene annotation and expression atlas for 14,865 genes, including 492 unreported long noncoding RNA (lncRNA) genes, based on RNA-seq data from 14 larval and pupal stages, plus adult morphological sections. Two thirds of the genes show significant expression changes associated with a life stage or section, with lncRNAs being more finely regulated during adulthood than protein-coding genes, and male-biased expression being four times more common than female-biased. The two portions of the heterochromosome Z display distinct patterns of differential expression between the sexes, reflecting that dosage compensation is either absent or incomplete -depending on the sample- in the ancestral but not in the novel portion of the Z. This study represents a major advance in the genomic and transcriptome resources available for D. plexippus while providing the first systematic analysis of its transcriptional program across most of its life cycle.

genomics↗

bioRxiv2020

Differential gene expression reflects larval development and survival of monarch butterflies on different milkweed hosts

Second instar larvae of the monarch butterfly, Danaus plexippus, from a nonmigratory population in Irapuato, Mexico, were reared for twenty-four hours on three species of milkweed hosts: Asclepias curassavica, A. linaria, and Gomphocarpus physocarpus. We then measured larval growth and differential expression of coding genes and of microRNAs. Larval growth was similar on the two Asclepias species, while little growth was observed on G. physocarpus. The greatest differences in coding gene expression occurred in genes controlling growth and detoxification and were most extreme in comparisons between G. physocarpus and the two Asclepias. MicroRNAs are predicted to be involved as regulators of many of these processes, in particular miR-278, differentially expressed here, could be an important regulator of growth through Hippo signaling. The implications for survival of the monarch, especially in the context of environmental factors altering the availability of their favored milkweed species, are discussed.

genomics↗