Biology Reference
In-Depth Information
4.12.7 Aphid Symbionts 146
4.12.8 Tsetse Fly Symbionts
148
4.13 Insect Development 149
4.13.1 Oocyte Formation in
D. melanogaster
149
4.13.2 Embryogenesis in
D. melanogaster
151
4.13.3 Postembryonic Development 153
4.14 Dissecting Development with
D. melanogaster
Mutants
154
4.14.1 Maternal-Effect Genes 155
4.14.2 Zygotic-Segmentation Genes
157
4.14.2.1
Gap Genes
158
4.14.2.2
Pair-Rule Genes
159
4.14.2.3
Segment-Polarity Genes
159
4.14.2.4
Homeotic Genes
159
4.14.3 Insect Metamorphosis 161
4.15 Interactions During Development 162
4.16 Similarities and Differences in Development in Other Insects
162
4.17 Evo-Devo and the Revolution in Developmental Studies
164
References Cited
166
4.1 Overview
Molecular genetics has revolutionized our understanding of insect gene struc-
ture, organization, regulation, and development. One surprise has been the dis-
covery that genomes are very dynamic over evolutionary time. For example, large
portions of the insect genome may consist of multiple families of transposable
elements (TEs) that can alter gene structure and function, chromosomal organiza-
tion, and transfer horizontally between species. The discovery that gene amplifi-
cation can be involved in resistance to insecticides in aphids and mosquitoes has
opened new avenues for understanding this evolutionary and economic problem.
Research also suggests that the genetic information contained in microbial sym-
bionts such as
Wolbachia
may play an essential role in speciation and evolution
of some insects. Other symbionts provide essential nutrients or other physiologi-
cal services. Many insects contain three or four (or more) genomes: nuclear, mito-
chondrial, one or more gut symbionts, and
Wolbachia
, raising questions about the
definition of the “biological individual.” Perhaps we should consider insects to be
a biome that contains multiple genomes (species) living together. Our knowledge
of the diversity of organisms associated with arthropods as symbionts and the role
these play in the biology of their arthropod hosts is expanding, in large part due
to our ability to use molecular tools, including whole-genome sequencing of sym-
biont and host.
Insect nuclear genomes can be diverse. Although many species have diploid
males and females, some have haploid males and diploid females (arrhenotoky)
