“Duality of natural history:

- richness in particularities,

- potential union in underlying explanations.”

- Stephen Jay Gould

Quotation of the DayQuotation of the Day

Seasonal Adaptation – Seasonal Adaptation – Diapause and DormancyDiapause and Dormancy

• Seasonal Adaptations– Escaping seasonal extremes of the

environment – Categories

• dormancy - escape in time• migration - escape in space• polymorphism - change in phenotype to better

cope with situation or in conjunction with other strategies

I. IntroductionI. Introduction

• Timing– Duration - short vs. long term

environmental change– Predictability - cyclic (seasonal) vs acyclic

(aseasonal)

• Response to Variables

II. Environmental ChangesII. Environmental Changes

  Predictability

Duration acyclic cyclic

short nervous system biological clock

long genetic neurohormonal

• Adaptations– Quiescence - reversible state of suppressed

metabolism imposed by conditions beyond certain thresholds in temperature, moisture, or nutrition

– Aseasonal migration - a movement out of an unfavorable area to find more favorable site

– Aseasonal polyphenism – environmentally induced changes in color or structure for protection or movement

III. AseasonalIII. Aseasonal

• Definitions– Dormancy - seasonally recurring period in

the life cycle of an organism during which growth, development, and reproduction are suppressed. 

• aestivation - summer• autumnal dormancy - fall • hibernation - winter• vernal dormancy – spring

IV. SeasonalIV. Seasonal

• Definitions– Diapause - neurohormonally mediated

dynamic state of low metabolic activity.  Occurs in genetically determined stages. Species specific in response to token stimuli.  Once diapause is initiated, it does not terminate with immediate return to favorable conditions

• diapause syndrome - species specific, dynamic process

IV. SeasonalIV. Seasonal

• Definitions– Diapause

• token stimuli - environmental factors, not of themselves unfavorable, that signal changes in environmental conditions (usually photoperiod but also temperature, moisture, etc.)

IV. SeasonalIV. Seasonal

• Habitat Deterioration– Non-diapause

• seasonal alteration with decreased metabolism or

• environmentally imposed reduction in metabolism

• includes: – seasonal polyphenism– seasonal migration– dormancy

IV. SeasonalIV. Seasonal

• Habitat Deterioration– Diapause

• diapause mediated phenomena– dormancy– seasonal migration– seasonal polyphenism

• stage-specific trigger (genetically determined) but may not be diapausing stage; diapause may include >1 stage,

– e.g. Aedes sierreusis 1 yr life cycle.  2 stage diapause (egg aestivation and larval hibernation)

IV. SeasonalIV. Seasonal

• Habitat Deterioration– Diapause

• diapause phenology (1-3 regulated by token stimuli, 4-5 by non-token stimuli and may include quiescence)

– 1. prediapause– 2. diapause induction– 3. diapause maintenance– 4. post diapause transitional period– 5. non-diapause period

IV. SeasonalIV. Seasonal

• Habitat Deterioration– Diapause

• diapause syndrome (includes prediapause)– hormonal mediation - mechanisms differ by stage, also

variation between species– behavioral expression - different responsiveness to

feeding and reproductive stimuli, movement to dormancy sites (very short to long range movement, e.g. Monarch), phototactic and geotactic responses

– physiological adaptations - accumulation of metabolic reserves (fat body changes from synthesis to storage), reduced metabolism

IV. SeasonalIV. Seasonal

• Habitat Deterioration– Diapause

• diapause syndrome (includes prediapause)– morphological expression - functions:

» crypsis or physical protection from predators or injury (abiotic stressors)

» wing polymorphenism - adjust allocations for dispersal and movement vs hibernation and reproduction

» color or size changes may be associated with pre or post diapause development

» no function» post diapause

IV. SeasonalIV. Seasonal

• Habitat Deterioration– Diapause

• diapause syndrome (includes prediapause)– for most temperate-zone species no specific

diapause terminating stimulus identified, probably insects cease responding to diapause maintaining factors and gradually diapause ends

– for a few species may be terminating stimuli usually maintained by photoperiod and altered thermal responses

IV. SeasonalIV. Seasonal

• Environmental Regulation of Seasonal Cycles– Facultative vs obligatory responses– Photoperiod

• may regulate entire life cycle for some species, in other species responses vary (may decrease after diapause)

• most important single factor

IV. SeasonalIV. Seasonal

• Environmental Regulation of Seasonal Cycles– Temperature

• may induce diapause (but this is relatively rare)• may modify photoperiodic response

– Food • may induce diapause (especially important in

tropics) • more often modifies effects of photoperiod and

temperature

IV. SeasonalIV. Seasonal

• Environmental Regulation of Seasonal Cycles– Moisture

• role is obscure, but probably important for some species

IV. SeasonalIV. Seasonal

• Accommodation of Environmental Extremes– Particularly important basis for

physiological adaptations– Allows species to exploit more habitats

V. Ecological Implications of V. Ecological Implications of Seasonal AdaptationsSeasonal Adaptations

• Difference Among Regions– Clearly diapause important in temperate

zones - best studied here– Tropics - still have seasonal cycles

(typically wet and dry rather than hot and cold)

• photoperiod not adequate predictor• often cycles associated with synchrony with

host plants

V. Ecological Implications of V. Ecological Implications of Seasonal AdaptationsSeasonal Adaptations

• Variation & Spreading the Risk Theory– Considerable intraspecific variability in life

history traits; may even see differences in generation numbers or nature of diapause in different populations

– Relates to the evolutionary value of intraspecific variability in phenotypes (and therefore associated genotypes)

V. Ecological Implications of V. Ecological Implications of Seasonal AdaptationsSeasonal Adaptations

• Variation & Spreading the Risk Theory– Spreading the risk theory - formal statement

of the evolutionary value of variability; theory argues that:

• the longevity of a natural population is an expression of a low probability that all local populations fluctuate to extinction either by low or high densities

• stability can be indicated by the range in maximum and minimum population densities

V. Ecological Implications of V. Ecological Implications of Seasonal AdaptationsSeasonal Adaptations

• Evolution– Tauber et al. argue:

• first, time measurement system (oscillatory or hourglass) (e.g. circadian) evolved

• next, evolution of environmentally controlled neuroendocrinological responses adaptive for some environmental conditions

• finally, neuroendocrinologically controlled responses are coupled to a seasonally reliable indicator (token stimulus)

V. Ecological Implications of V. Ecological Implications of Seasonal AdaptationsSeasonal Adaptations