The cause of reduced growth of Manduca sexta larvae on a low-water diet: Increased metabolic processing costs or nutrient limitation?

Relative growth rates and nitrogen accumulation rates are lower for third-instar Manduca sexta larvae on an artificial diet containing 65% water than on one containing 82% water, due to reduced efficiencies of conversion of digested food and digested nitrogen into larval biomass. Uric acid production is 2.0-2.5-fold greater, and non-feeding respiration rates 16.0% higher in the larvae on the low-water diet. Food is the major source of water for the larvae, with metabolic water making only a minor contribution to water input. Faecal excretion is the major avenue of water loss, although a significant amount of water is also lost by transpiration. Larvae from the low-water diet retain and use a higher percentage of the water they gain than larvae from the high-2ater diet (49.4% vs 41.9%). They produce much drier faeces (48.1% water vs 77.3% water), and, because their tissues are less hydrated (81.3% water vs 88.1% water), they synthesize 70% more new, fully hydrated tissue from a given amount of water than larvae from the high-water diet. We discuss problems involved in the use of determinations of efficiency of conversion of digested food in establishing causal links between diet, growth, and metabolic maintenance costs, and also offer a definition of food processing costs that distinguishes them from metabolic costs attributable to other processes, such as food acquisition, growth, and moulting. We conclude that reduced growth and reduced efficiency of conversion of digested food on low-water diets are due to limitation in the amount of water available for the synthesis of new hydrated tissue, and not to the imposition of higher food processing costs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27572/1/0000616.pd

A high-coverage draft genome of the mycalesine butterfly <i>Bicyclus anynana</i>

The mycalesine butterfly Bicyclus anynana, the "Squinting bush brown," is a model organism in the study of lepidopteran ecology, development, and evolution. Here, we present a draft genome sequence for B. anynana to serve as a genomics resource for current and future studies of this important model species. Seven libraries with insert sizes ranging from 350 bp to 20 kb were constructed using DNA from an inbred female and sequenced using both Illumina and PacBio technology; 128 Gb of raw Illumina data was filtered to 124 Gb and assembled to a final size of 475 Mb (∼×260 assembly coverage). Contigs were scaffolded using mate-pair, transcriptome, and PacBio data into 10 800 sequences with an N50 of 638 kb (longest scaffold 5 Mb). The genome is comprised of 26% repetitive elements and encodes a total of 22 642 predicted protein-coding genes. Recovery of a BUSCO set of core metazoan genes was almost complete (98%). Overall, these metrics compare well with other recently published lepidopteran genomes. We report a high-quality draft genome sequence for Bicyclus anynana. The genome assembly and annotated gene models are available at LepBase (http://ensembl.lepbase.org/index.html)

Acute Multiple Organ Failure in Adult Mice Deleted for the Developmental Regulator Wt1

There is much interest in the mechanisms that regulate adult tissue homeostasis and their relationship to processes governing foetal development. Mice deleted for the Wilms' tumour gene, Wt1, lack kidneys, gonads, and spleen and die at mid-gestation due to defective coronary vasculature. Wt1 is vital for maintaining the mesenchymal–epithelial balance in these tissues and is required for the epithelial-to-mesenchyme transition (EMT) that generates coronary vascular progenitors. Although Wt1 is only expressed in rare cell populations in adults including glomerular podocytes, 1% of bone marrow cells, and mesothelium, we hypothesised that this might be important for homeostasis of adult tissues; hence, we deleted the gene ubiquitously in young and adult mice. Within just a few days, the mice suffered glomerulosclerosis, atrophy of the exocrine pancreas and spleen, severe reduction in bone and fat, and failure of erythropoiesis. FACS and culture experiments showed that Wt1 has an intrinsic role in both haematopoietic and mesenchymal stem cell lineages and suggest that defects within these contribute to the phenotypes we observe. We propose that glomerulosclerosis arises in part through down regulation of nephrin, a known Wt1 target gene. Protein profiling in mutant serum showed that there was no systemic inflammatory or nutritional response in the mutant mice. However, there was a dramatic reduction in circulating IGF-1 levels, which is likely to contribute to the bone and fat phenotypes. The reduction of IGF-1 did not result from a decrease in circulating GH, and there is no apparent pathology of the pituitary and adrenal glands. These findings 1) suggest that Wt1 is a major regulator of the homeostasis of some adult tissues, through both local and systemic actions; 2) highlight the differences between foetal and adult tissue regulation; 3) point to the importance of adult mesenchyme in tissue turnover

Performance of the tree-feeder Orgyia leucostigma (Lepidoptera: Liparidae) on artificial diets of different water content: A comparison with the forb-feeder Manduca sexta (Lepidoptera: Sphingidae)

The egg-to-pupa growth rate of Orgyia leucostigma, which normally feeds on tree foliage, is an order of magnitude smaller than that of Manduca sexta, which normally feeds on herbaceous foliage, on four different nutrient-rich artificial diets. Relative growth rates of fifth-instar female O. leucostigma are only 37-53%, and relative consumption rates only 40-50%, of those of comparably sized third-instar M. sexta larvae. Similarly, respiration rates of O. leucostigma larvae are only 57-68% those of M. sexta larvae of equal size. The water budgets of the two species are very similar, and the two physiological adaptations contributing most to the efficient retention and use of water by larvae of both species on low-water diets are the resorption of water from the hindgut and the tolerance of reduced levels of tissue hydration. These results are consistent with the prediction of Mattson and Scriber that folivores adapted to feeding on nutrient-poor plants have inherently lower growth rates and lower metabolic rates than folivores adapted primarily to nutrient-rich plants, but it is not clear whether the differences reside primarily in behavioural or physiological processes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28216/1/0000669.pd

The effect of diet water content on energy expenditure by third-instar Manduca sexta larvae (Lepidoptera: Sphingidae)

The total energy expenditure during the third instar of Manduca sexta larvae on a diet containing 65% water is substantially higher than that of larvae on a diet containing 82% water. The higher energy expenditure of larvae on the low-water diet is due to (1) a greater amount of time spent in the feeding stage of the instar and (2) to a higher respiration rate throughout the instar. We discuss problems in establishing causal links between diet, water content, growth and energy expenditure, and emphasize that the higher energy expenditure of larvae on a low-water diet is a consequence rather than a cause of reduced growth rate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28194/1/0000646.pd