14. Escaping Adversity

14 Escaping - Lecture 14 Lecture Mechanisms for Escaping Adversity Lecture Goals Lecture • How do insects adapt to allow them to escape adversity

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Unformatted text preview: Lecture 14 Lecture Mechanisms for Escaping Adversity Lecture Goals Lecture • How do insects adapt to allow them to escape adversity? • What choices do insects have when their environment becomes unsuitable? • Adapt • Migrate • Die • Think back to your notes on insect development, metamorphosis, and what insects do (in particular what they eat). What is adversity in the insect world? • Abiotic (Physical) – Temperature extremes – Moisture extremes – Light & Photoperiod – Shelter • Biotic – Food – Enemies – Mates What adaptations would be useful in overcoming or escaping from adversity? • Developmental Escape: – Metamorphosis – Polymorphism/Polyphenism – Diapause • Ecological Escape: – Host Relationships • Physical Escape: – Foraging/Commuting – Ranging – Migration Adaptations That Allow Escape From Adversity • Developmental-– How does complete metamorphosis serve as an escape from adversity? • Different environments • Pupal stage non-feeding • Pupal stage may be extended Adaptations That Allow Escape From Adversity • Developmental-– What is polyphenism? The occurrence of several phenotypes in a population which are not due to different genetic types. A type of polymorphism (variation in body form or color within a species) that is a product of the environment in which an insect lives. Adaptations That Allow Escape From Adversity • Developmental-– When does polyphenism occur? • Crowding • Food quality and quantity Brachypterous Short-winged form Planthopper Macropterous Long-winged form Planthopper What is polyphenism? What – Castes of social insects – Aphid morphs (variety of colors, winged, not winged, asexual and sexual reproduction) – Brachyptery (short-winged forms) vs. macroptery (long-winged form) – Color and form (e.g. locusts) Adaptations That Allow Escape From Adversity (Developmental/Host Relationships) Spring Summer Winter Fall Adaptations That Allow Escape From Adversity • Developmental-– Diapause • A delay in development evolved in response to recurring periods of adverse environmental conditions. • Arrested physiological development. • A long-term response to environmental change. Oxygen consumption (μl.egg-1.h-1) What happens during diapause? What Adaptations That Allow Escape From Adversity • Developmental-– What does diapause facilitate? • Winter survival • Survival through dry seasons • Synchronization of adult emergence for mate finding – What initiates diapause? Adaptations That Allow Escape Adaptations From Adversity • Developmental-– What initiates diapause? Immediate response usually too late. – Trigger needs to be some reliable preceding cue • Photoperiod • Interaction between photoperiod & temperature • May affect “sensitive” stage well before diapause stage • Different insects diapause in different developmental stages. Types of Diapause • Facultative diapause • Obligate diapause Hormones and Diapause • Various hormones affect diapause – Role of PTTH (prothoracicotrophic hormone) – Role of juvenile hormone • Diapause hormone – – – – Silkworm adult Subesophageal ganglion Eggs affected Exposure to cold – chilling Adaptations That Allow Escape From Adversity (Ecological) • Host relationships – Hardships insects face relative to their food sources (hosts). • Patchiness in space and/or time • Competition • Transient hosts (e.g., annual plants) – What could help insects escape these hardships? • Host switching • Movements to track resources Adaptations That Allow Escape From Adversity • Foraging, Commuting, Ranging vs. Migration – Foraging: Movement to seek food (honey bee scouts finding pollen and nectar sources). – Commuting: Honey bees moving between pollen and nectar sources and the hive (Central Place Foraging). – Ranging: Adult water beetles and diving beetles may fly from one pond to another if the original pond begins to dry. Adaptations That Allow Escape From Adversity • Foraging, Commuting, Ranging vs. Migration – Foraging – Commuting – Ranging – Migration: Insects often require specific host plants and climatic conditions to survive. Migration is a response to specific “triggers” or “signals” (e.g. day length). Migrating insects move for “programmed” distances--not stopping even when appropriate resources seem evident, e.g. Monarch butterflies. Adaptations That Allow Escape From Adversity •Migration •Migration distances vary, but often over large geographic expanses. •Why do so many insects have migratory behaviors? •How do migratory insects ‘know’ where to go? •Why do so many migratory insects stop and roost at the same places, at the same time each year? What are the evolutionary What advantages of migration? •Migration gets insects out of harsh environments •Migration allows insects to track resources and synchronize their location with availability of their specific food plants. What are the risks associated What with migration? •What risks occur for a migrating insect? •Weather •Blown off course •Rainstorm, hail •Physical barriers •Predation •Changes in habitats in path of migration •Construction, agriculture (pesticides), logging, burning •Highway (vehicles) •Habitat destruction at final destination Some Examples Some •The Jersey Tiger Moth: Migrates to a deep valley on the island of Rhodes, to avoid extremes of heat and drought. They migrate and congregate in the millions each summer, causing local people to call this place the Valley of the Butterflies. Some Examples Some In California, a ladybird beetle species migrates in late spring from the hot, dry Central Valley to the cool Sierra Nevada mountains. To do this, the beetles fly one mile high and are carried on the seasonally prevailing winds to the mountains. They aggregate and assemble by the millions on tree trunks, spend the winter and return to the Valley in the spring when the prevailing winds are conveniently in the opposite direction. The Monarch Butterfly The •Regular migrations across the North American Continent. •Managed to find its way to such distant parts as Australia, New Zealand and Hawaii, where it is now established. •Occasionally turns up in Britain, but does not survive due to lack of food. The Monarch Butterfly The •Monarchs have complete metamorphosis. •They require a specific host plant to complete their development (milkweed). •They can’t tolerate extremes of climate. Important concept: Recall the of role the milkweed plant in the Monarch’s evolutionary success Monarch Butterfly Migration Monarch Two populations: eastern and western WESTERN POPULATION •In summer, it is in Canada and N.W. USA •In autumn this population migrates to California (45 roosting sites) •The migrating butterflies cover 80 miles/day, flying as much as 3,000 miles before roosting. **How do the butterflies know where to go?** Monarch Butterfly Migration Two populations: eastern and western EASTERN EASTERN POPULATION: •Butterflies from S.E. Canada and N.E. USA (approx. 100 million) fly to the volcanic mountains of central Mexico. •They use 11 roosting sites. •From November to January they enter diapause as adults. Overwintering Populations Overwintering Butterflies often cluster in such large numbers that their weight can break branches. As the spring nears they emerge from diapause and mate. Monarch Butterfly Migration Monarch Spring Migration Northward: •Butterflies move a few hundred miles and die after laying eggs on milkweed plants. •The next generation flies further north, again dying after laying eggs on milkweed plants. •In this fashion they leapfrog their way north. ...
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This note was uploaded on 12/07/2009 for the course ECON 19993 taught by Professor Helms during the Spring '09 term at UC Davis.

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