The origin and evolution of stereotyped patterns of macrochaetes on the nota of cyclorraphous Diptera

Abstract

A long-standing problem in evolutionary biology is how genetic variation arises within populations and evolves to make species anatomically different. Many of the morphological differences in body plans between animal groups are thought to result from changes in gene expression during development. The rules governing the structure and evolution of cis-regulatory gene sequences are unknown, however, and the evolution of traits between closely related species remains relatively unexplored at a molecular level. To study the evolution of gene regulation, it is necessary to find a tractable trait that varies between species and for which the genetic regulation is well known in at least one of the species. The stereotyped, two-dimensional pattern of bristles on the thorax of Drosophila has been intensively investigated and is due to a precise spatial expression of proneural genes. Other species of flies have different bristle patterns and so comparisons between them provide a good paradigm for the study of changes in gene regulation. Here, we review the current state of understanding of these changes.

Revision of Drusinae subfamily (Trichoptera, Limnephilidae): divergence by paraproct and paramere: speciation in isolation by integration

“…The development of sensory setal structures and possibly also other cuticular surface processes of spines, spinules, pits, ridges, plates or any noncellular processes or outgrowths is organised by a prepattern of field centres of morphogenes and substrate concentration (Maynard Smith & Sondhi 1961, Simpson & Marcellini 2006. Sensory setal structures, like macrochaetes of Drosophila on mesonotum are species specific, usually constant in number and distributed with stereotyped pattern for a species.…”

“…The tertiary spines are most probably noncellular processes of cuticular origin. The development of sensory setal structures is organised by a prepattern of field centres of mophogenes and substrate concentration (Maynard Smith & Sondhi 1961, Simpson & Marcellini 2006. Sensory setal structures of bristle typed macrochates are usually constant in number and distributed with stereotyped pattern for a species.…”

“…Noncellular processes of cuticular structures, minute scobinate points, nodules or small irritant spicules, spines, thorns, irregularly shaped knobs, microplates of various shapes, spatulates fixed and confluent with exosceleton may exhibit organised spacing offering another taxonomic alternative for fine phenomics. The patterns of small groups of cells in proneural cluster responsible for structure spacing are regulated by the genes of achaete-scute complex and mediated by lateral inhibition and Notch-signalling pathway (Simpson & Marcellini 2006).…”

The kinase Sgg modulates temporal development of macrochaetes inDrosophilaby phosphorylation of Scute and Pannier

“…First, in species of Nematocera, such as Anopheles gambiae, duration of development of the imaginal thorax is very short and sensory organ precursors arise from a single phase of expression of the proneural genes that regulate bristle development (Wulbeck and Simpson, 2002;Simpson and Marcellini, 2006). In cyclorraphous flies there are two temporally separate phases of proneural gene expression during the protracted development of the thoracic imaginal epithelium, an early one for macrochaetes and a later one for microchaetes Simpson and Marcellini, 2006). Second, microchaete precursors arise from ubiquitous or very broad domains of proneural gene expression, as do the sensory organ precursors in Anopheles gambiae (Sato et al, 1999;Wülbeck and Simpson, 2000;Pistillo et al, 2002;Wulbeck and Simpson, 2002).…”

Development vs. behavior: a role for neural adaptation in evolution?

“…In most vertebrates, mechanosensory organs of various types are randomly distributed over the body surface, unlike in insects, where sensory bristles are often arranged in reproducible, species-specific patterns, facilitating the genetic analysis of pattern formation and pattern evolution (Simpson and Marcellini, 2006). In the lateral line system of fish, however, individual mechanosensory organs form specific patterns much as in invertebrates, allowing for a detailed analysis of pattern formation and evolution.…”