Developmental stages and durations of Drosophila
Stages Times after egg laying Duration
Larva 1st instar 22 hours day
2nd instar 46 hours day
3rd instar 70 hours ^2 days
Pupa 120 hours ^5 days on strain and environment. Under standard conditions, wild-type flies live up to 2-3 months.
Characteristics of aging Finch (1990) has identified three major patterns of aging in animals: rapid, which is typified by semelparous organisms such as Atlantic salmon and mayflies (Ephemeroptera); negligible, which is typified by colonial invertebrates and some turtles and fish; and gradual, which is found in most birds and mammals, including humans (Finch, 1990). Unlike many insects, Drosophila aging is gradual, an important feature for an organism serving as a model for human aging. However, unlike humans, Drosophila does not have a very long postreproductive lifespan. Some examples of manifestations of senescence are shown in Table 22.2 (Rockstein and Miquel, 1973).
In general, marked degenerative changes occur in Drosophila tissues with advancing age. It is perhaps
TABLE 22.2 Manifestation of aging in Drosophila
• Formation of giant mitochondria by fusing, "swirls" in matrix
• Decrease in glycogen content, almost absent in very old individuals
• Decrease in oxidative phosphorylation enzyme activity
• Myofibrillar degeneration
• Inability to fly in very old individuals Reproductive system
• In male testis, decreases in the number of spermatogonia and spermatocytes
• Decrease in numbers of egg production in females Digestive system
• Accumulation of numerous large lamellated cytoplasmic inclusions in the midgut
• Increases in lipid droplets and vacuoles Fat body
• Decrease in fat content
• Decrease in cell size and shrunken appearance
• Uneven distribution of glycogen within a cell Nervous system
• Nerve-cell degeneration in brain
• Decrease in the amount of cytoplasm and ribosomes in neurosecretory cells
• Decrease in negative geotaxis ability Others
• Decrease in heart rate
• Structural and functional alterations in Malpighian tubules in excretory system due to the fact that cells in Drosophila are mostly postmitotic and are not replaced except for a small part of the reproductive tissues. Causes of death in Drosophila are not well established. Suggestions include starvation, fat body degeneration, failure of the digestive system, failure of the excretory organs, and failure of the nervous system, among others (Rockstein and Miquel, 1973).
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