BIOL 312 Lecture Notes - Lecture 16: Polyphenism, Aphid, Hemimetabolism
14 Nov 2017
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Document Summary
Final: weighted towards second half of the course. Common themes: importance of trade-offs (negative associations between traits e. g. growth vs reproduction, survival vs reproduction). Polyphenisms (response to enviro change) are very common and (often) under hormonal control. Focus on how insects respond to stress and change. Evolutionary trend towards fewer instars: ametabolous > hemimetabolous > holometabolous. Juveniles: growth: determinate growth (except primitively wingless hexapods) in discrete stages (moults). Number of instars can be fixed (genetically determined) or variable and may depend on growth conditions (e. g. crowding) and optimal size for metamorphosis. Key determinant of fitness in insects: body size (bigger females = more eggs). Size at last moult (and size is the main trigger for hormonal changes driving moulting and metamorphosis). Dealing with environmental changes and extremes: dispersal, diapause, tolerance (physiology and behaviour). Dispersal: means of escape in space and time.
