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Biomedical subjects

H F Nijhout

Publications and source records attributed to H F Nijhout.

At least 19 recordsLinked to original sources
PubMed2000

The development and evolution of exaggerated morphologies in insects.

We discuss a framework for studying the evolution of morphology in insects, based on the concepts of "phenotypic plasticity" and "reaction norms." We illustrate this approach with the evolution of some of the most extreme morphologies in insects: exaggerated, sexually selected male ornaments and weapons, and elaborate social insect soldier castes. Most of these traits scale with body size, and these scaling relationships are often nonlinear. We argue that scaling relationships are best viewed as reaction norms, and that the evolution of exaggerated morphological traits results from genetic changes in the slope and/or shape of these scaling relationships. After reviewing literature on sexually selected and caste-specific structures, we suggest two possible routes to the evolution of exaggerated trait dimensions: (a) the evolution of steeper scaling relationship slopes and (b) the evolution of sigmoid or discontinuous scaling relationship shapes. We discuss evolutionary implications of these two routes to exaggeration and suggest why so many of the most exaggerated insect structures scale nonlinearly with body size. Finally, we review literature on insect development to provide a comprehensive picture of how scaling relationships arise and to suggest how they may be modified through evolution.

Animals↗
PubMed1999

Ultrabithorax function in butterfly wings and the evolution of insect wing patterns.

BACKGROUND: . The morphological and functional evolution of appendages has played a critical role in animal evolution, but the developmental genetic mechanisms underlying appendage diversity are not understood. Given that homologous appendage development is controlled by the same Hox gene in different organisms, and that Hox genes are transcription factors, diversity may evolve from changes in the regulation of Hox target genes. Two impediments to understanding the role of Hox genes in morphological evolution have been the limited number of organisms in which Hox gene function can be studied and the paucity of known Hox-regulated target genes. We have therefore analyzed a butterfly homeotic mutant 'Hindsight', in which portions of the ventral hindwing pattern are transformed to ventral forewing identity, and we have compared the regulation of target genes by the Ultrabithorax (Ubx) gene product in Lepidopteran and Dipteran hindwings. RESULTS: . We show that Ubx gene expression is lost from patches of cells in developing Hindsight hindwings, correlating with changes in wing pigmentation, color pattern elements, and scale morphology. We use this mutant to study how regulation of target genes by Ubx protein differs between species. We find that several Ubx-regulated genes in the Drosophila haltere are not repressed by Ubx in butterfly hindwings, but that Distal-less (Dll) expression is regulated by Ubx in a unique manner in butterflies. CONCLUSIONS: . The morphological diversification of insect hindwings has involved the acquisition of different sets of target genes by Ubx in different lineages. Changes in Hox-regulated target gene sets are, in general, likely to underlie the morphological divergence of homologous structures between animals.

Animals↗
PubMed1998

Competition among body parts in the development and evolution of insect morphology.

Changes in form during ontogeny and evolution depend in large measure on changes in the relative growth of the various parts of the body. The current consensus in developmental biology is that the final size of appendages and internal organs is regulated autonomously, within the structure itself. Size regulation of body parts typically requires no external control and is thought to be relatively insensitive to signals from the developmental environment. We show in two very different systems, butterfly wings and beetle horns, that experimentally induced changes in the allocation of developmental resources to one trait produces compensatory changes in the relative sizes of other traits. These findings illustrate that interaction among body parts in development is part of the mechanism of size regulation of those parts. Furthermore, in the case of beetle horns, we show that the tradeoff in size is manifest as a significant negative genetic correlation among the involved body parts and, therefore, constitutes a developmental source of genetic constraint on the evolution of body form.

Animals↗
PubMed1990

Metaphors and the role of genes in development.

In describing the flawless regularity of developmental processes and the correlation between changes at certain genetic loci and changes in morphology, biologists frequently employ two metaphors: that genes 'control' development, and that genomes embody 'programs' for development. Although these metaphors have an admirable sharpness and punch, they lead, when taken literally, to highly distorted pictures of developmental processes. A more balanced, and useful, view of the role of genes in development is that they act as suppliers of the material needs of development and, in some instances, as context-dependent catalysts of cellular changes, rather than as 'controllers' of developmental progress and direction. The consequences of adopting this alternative view of development are discussed.

Animals↗
PubMed1985

Independent development of homologous pattern elements in the wing patterns of butterflies.

Rank correlation analyses demonstrate that the degree of color pattern development in each wing cell of Cercyonis pegala (Satyridae) and Smyrna blomfildia (Nymphalidae) is either weakly or not at all correlated with that in other wing cells. There is much greater individual variability in pattern development in different wing cells than there is in homologous wing cells on opposite wings. This finding indicates that differences in pattern development in adjacent wing cells are not due to developmental noise, but are programmed, and that pattern development in each wing cell is in large measure independent of that in other wing cells.

Animals↗
PubMed1985

Cautery-induced colour patterns in Precis coenia (Lepidoptera: Nymphalidae).

Cautery of the dorsal hindwing in the butterfly, Precis coenia, induces the formation of a concentric colour pattern around the site of injury. The induced pattern is identical in pigmentation to the eyespots that normally develop on this wing surface. This response to cautery also occurs, though much less dramatically, on the ventral forewing. In addition to the peculiar response to cautery, the dorsal hindwing of Precis also develops a series of unique pattern aberrations in response to coldshock. These consist of irregular elongation of the anterior eyespot along the proximodistal axis of the wing. In the most dramatic aberrations the eyespot field covers the entire anterior half of the wing surface. An analysis is presented that attempts to reconcile the effects of cautery on the Precis hindwing with the very different morphological effects of cautery on the colour pattern of Ephestia kühniella, described by Kühn & Von Engelhardt. Computer simulations reveal that the finding presented in this paper, as well as the classical work on Ephestia, can both be explained by assuming that the site of cautery becomes a sink for one of the morphogens involved in colour pattern determination. The experimental findings furthermore indicate that minor perturbations of the wing epidermis can evoke the physiological conditions that attend normal eyespot determination. It is shown that this interpretation also helps to explain the unusual pattern modifications following coldshock.

Animals↗
PubMed1984

Colour pattern modification by coldshock in Lepidoptera.

When young pupae of Vanessa cardui, V. virginiensis and Precis coenia (Lepidoptera: Nymphalidae) are exposed to severe coldshock many develop aberrant adult wing patterns. For each species, a synchronous cohort of experimental animals always develops a broad range of aberrant pattern morphologies but these can always be arranged in a single unbranched morphological series. When such phenotypic series are compared, between species and between wing surfaces within a species (each wing surface usually bears a different colour pattern), many parallel modifications and trends become evident. These parallelisms reveal certain homologies of pattern elements and suggest that a common physiology underlies the development of a considerable diversity of normal and aberrant colour patterns. The case is made that the phenotypic series produced may represent either a series of sequential stages in colour pattern determination or, a series of quantitatively different 'interpretations' of an established gradient system. Colour pattern morphoclines reveal which patterns are developmentally 'adjacent' to one another and may therefore prove useful in elucidating the evolution of patterns.

Animals↗
PubMed1982

Ultrastructural changes accompanying secretion and cell death in the molting glands of an insect (Oncopeltus).

During the fifth (last) larval instar of Oncopeltus fasciatus, morphological changes in the molting glands associated with ecdysone secretion include a increase in cytoplasmic volume relative to that of the nucleus, increased amounts of rough endoplasmic reticulum and mitochondria, and the formation of deep infoldings of the plasma membrane. On the sixth day of the fifth instar large electron-lucent areas become apparent beneath the basement membrane; however, the glands remain intact until the seventh (last) day of the instar when a dramatic fragmentation of the cytoplasm, and condensation and fragmentation of the nucleus are observed. It is likely that such changes occur rapidly, just prior to the time of ecdysis to an adult. Cell death in the molting glands of Oncopeltus is markedly different from that described for the molting glands of other insect species in that autophagic vacuoles are not observed prior to a complete loss of cellular integrity.

Animals↗
PubMed1979

Antennal hair erection in male mosquitoes: a new mechanical effector in insects.

Male Anopheles mosquitoes erect their antennal hairs prior to mating. The erectile mechanism resides in a unique annulus at the base of each hair whorl. It appears that the insect regulates the degree of hydration of this annulus. When the annulus is made to swell the attached hairs are pushed to their erect position.

Animals↗
PubMed1975

Excretory role of the midgut in larvae of the tobacco hornworm, Manduca sexta (L.).

Caterpillars of Manduca sexta use two distinct transport mechanisms for the excretion of dyes. One pump (Type A) has a high affinity for acid (anionic) dyes and occurs in the midgut and medial Malpighian tubules. Acid dyes accumulate rapidly in the lumen of the midgut while the Malpighian tubules appear to play only a minor role in the excretion of these dyes. The other pump (Type B) excretes basic (cationic) dyes and is located primarily in the proximal Malpighian tubules. Evidence is presented that hippuric acid competes with acid dyes for excretion by both midgut and Malpighian tubules. After the final-instar larva purges its gut the ability of the midgut and Malpighian tubules to excrete dyes gradually decreases. Sixty hours after the purge only the Malpighian tubules retain some dye excreting activity.

Amaranth Dye↗