Age-Structure by wuxiangyu

VIEWS: 19 PAGES: 36

									     Quotation of the Day

“I prefer the errors of enthusiasm to the
   indifference of wisdom.”
     - Anatole France
Population Age Structure
        I. Age Distribution
• Introduction
  – Definition
     • the relative abundance of individuals of various ages in
       the population
  – Importance - relates to natality and mortality
    thereby influencing fluctuations in population
    numbers
     • Mortality - age specific (e.g. immatures)
     • Natality - reproduction restricted to specific age groups
     • Behavior - e.g. migratory behaviors, dormancy, host
       finding, and others age specific
       I. Age Distribution
• Age Pyramids
  – Used to indicate population age structure
  – Stylized types:
    • type I - young population; e.g. new introduction
       I. Age Distribution
• Age Pyramids
    • type II - stable population; population in
      equilibrium with births and deaths;
      characteristic of long lived animals in stable
      environment
       I. Age Distribution
• Age Pyramids
    • type III- senescent (senile) population;
      population declining
       I. Age Distribution
• Age Pyramids
    • type IV- population nearing extinction; many old
      individuals
I. Age Distribution




             Pedigo, L. P. 1989. Entomology and Pest Management.
             McMillan, NY
        I. Age Distribution
• Age Pyramids
  – Lotka - stated age structure in a population
    tends to reach a stable form; with
    catastrophes, age structure may change
    temporarily but should return to a stable
    form
    • probably true for many vertebrate populations
         I. Age Distribution
• Age Pyramids
  – Lotka - stated age structure in a population tends
    to reach a stable form; with catastrophes, age
    structure may change temporarily but should
    return to a stable form
     • probably not true for insects in temperate climates; stable
       insect environments might be in tropics, certain urban
       habitats, but even these have substantial fluctuations
       (e.g. drought)
     • Andrewartha and Birch stated they don't know any
       experimental population with stable age structure
        I. Age Distribution
• Age Classes
  – Immature vs. adult
  – Immatures (differentiation)
    • apolysis vs. ecdysis
       – apolysis - the separation of the old cuticle from the
         underlying epidermis
       – ecdysis - molting, emerging from the old cuticle
        I. Age Distribution
• Age Classes
  – Immature vs. adult
  – Immatures (differentiation)
    • puparium vs. pupa
       – puparium - sclerotized skin of the last (3rd) instar
         (Diptera: Muscomorpha)
       – pupa – the intermediate stage between the larva and
         the adult in holometabolous insects
         I. Age Distribution
• Age Classes
  – Immature vs. adult
  – Immatures (differentiation)
     • definitions
         – instar - stage between molts, the first instar is the stage
           between egg and the first molt
         – stage - a distinct period in the life of an insect, typically
           defined between molts
         – stadium - the time interval between two molts
         – eclosion - escape of adult insect from the cuticle of the
           pupa, cocoon, puparium, or last nymphal stage (not
           hatching)
         – hatching - breaking of the eggshell by an insect in the
           process of emergence
         – pharate - inside the cuticle of the preceding stage
         – teneral - condition of adults after eclosion before cuticle is
           completely sclerotized
       I. Age Distribution
• Age Classes
  – Adults
    • reproductive status
       – pre reproductive
       – reproductive
       – post reproductive
           Species            Pre        Reproductive       Post
                          Reproductive                  Reproductive
       migratory locust       52             28             20
       American               72             24              4
       cockroach
       mayfly                 99              1              0
       cadelle beetle         30             45             25
       D. melanogaster        30             45             25
       human                  30             44             26
       Norway rat             32             23             45
       I. Age Distribution
• Age Classes
  – Adults
    • other terms
       – parity - degree of egg development
           » nulliparous - no egg development having
             occurred
           » parous - egg development having occurred
           » senescent - after all egg development has
             concluded
       I. Age Distribution
• Age Classes
  – Adults
    • other terms
       – also virgin, preovipositional, ovipositional, and
         postovipositional
           II. Age Grading
• Introduction
  – Needed for establishing age structure, also
    marker for some migrants, indication of
    overwintering, used to establish age bias in
    sampling technique
  – Especially important for discriminating
    generations in populations with overlapping
    generations
     • consequently recognizing newly emerged
       individuals especially important
           II. Age Grading
• Introduction
  – Most important for adults
     • immatures relatively easy to age
  – Used principally for medically important
    insects (Diptera)
     • information crucial for epidemiological studies
       (Detinora 1968 review of medical insects,
       Tyndale-Biscoe 1984 review of others, lots on
       techniques)
           II. Age Grading
• Immatures
  – Body size and weight commonly used to
    indicate instars, but this is not necessarily
    precise
     • supernumary instars - extra instars, typically
       occur from inadequate nutrition
          II. Age Grading
• Immatures
  – Body measurements
    • Dyar's Law - states (assumes) linear
      dimensions of insect increase geometrically at
      each molt with rates constant for given stage
      and species
       – used with head capsule measurements
       – not true, but useful nevertheless
          II. Age Grading
• Immatures
  – Body measurements
    • Przibram's Rule - observation that weight of an
      insect is doubled during each molt and at each
      molt all linear dimensions are increased by the
      ratio 1.26
       – not true (but sometimes an acceptable
         approximation)
       – not used much
          II. Age Grading
• Immatures
  – Other techniques
    • # eye facets with some hemipterous nymphs
      (e.g. Tingidae, Corixidae)
    • pupal age - pigmentation of eyes & parts of
      body
           II. Age Grading
• Adults
  – Requirements (Tyndale-Biscoe)
    • technique simple and rapid
       – many techniques are neither
       – ideally allows reasonable samples of population at
         regular intervals
    • should distinguish adults into specific age
      classes:
       – by physiological age (reproductive condition, somatic
         change)
       – by chronological age (cuticular bands - but even
         these influenced by temperature)
                II. Age Grading
• Adults
   – Techniques for adults
      • changes in reproductive system
           – female
               » follicular relics (Tyndale-Biscoe)
               » (i) ovarian structure - follicle, pedicel
               » (ii) contracted follicular epithelium pushed to anterior of
                 pedicel. (Indicates parity - distinguishes nulliparous from
                 parous and can subdivide class by yolk deposition in egg)
               » (iii) can occur in both polytrophic & telotrophic ovaries
               » (iv) differs among species, may or may not be able to
                 distinguish individual relics; some species may eventually
                 reabsorb relics
               » (v) follicular dilatation - bead-like swelling in pedicel, single or
                 multiple (many mosquito species multiple, can count
                 ovipositions); yellow body- relic may be yellow colored; very
                 distinctive; sometimes newer dilatation & yellow body
               » (vi) can subdivide nulliparous - parous classes by degree of
                 oocyte development (e.g. amount of yolk deposition or # of
                 nurse cells)
II. Age Grading
           II. Age Grading
• Adults
  – Techniques for adults
    • changes in reproductive system -
       – female
           » tracheolar skeins - tracheoles around ovary in
             very tight bundles prior to oviposition; become
             very loose (a loose net) after oviposition; used
             only in Diptera
           » declining fecundity - indication of age for some
             females, fewer eggs indicates older females (e.g.
             used in Lepidoptera, black flies (Simulium
             damnosum))
           II. Age Grading
• Adults
  – Techniques for adults
    • changes in reproductive system -
       – female
           » other criteria
           » (i) granular material in accessory gland (=
             nulliparous) - used for one species,
             phletobomine sand fly.
           » (ii) shape of bursa copulatrix - (undisturbed
             nulliparous) used with Coslelytra zealandica
             (phlebetomine sand fly)
           II. Age Grading
• Adults
  – Techniques for adults
    • changes in reproductive system -
       – male
          » changes in width of seminal vesicle - narrow
            newly emerged, wide in unmated, narrow after
            mating (phlebotomine sand flies)
          » size of testes used for some beetles
               II. Age Grading
• Adults
  – Somatic changes - (somatic - relating to the body);
    must work for males and females
     • cuticle growth
           – endocuticle deposited daily in some structures (cuticle)
             and internal cuticular projections
           – can count growth bands (layers)
           – used in various groups - grasshoppers, rhinoceros beetle
             (pronotum, horn, femora)
           – rate of deposition a function of temperature
           – layers deposited only for a short period after pupal eclosion
               II. Age Grading
• Adults
  – Somatic changes - (somatic - relating to the body);
    must work for males and females
     • fluorescence
           – fluorescent age pigment, lipofuscin, accumulates in post-
             mitotic cells of some tissues of many animals including
             insects
                » deposition based on physiological age
                » e.g. "heart", fat body, brain of Musca domestica
           – fluorescent eye pigment (pteridines) accumulate in
             Stomoxys calcitrans
           – measure with spectrophotometer
           – fat body
           – decreases in adult, especially useful when adult does not
             feed
           II. Age Grading
• Adults
  – Somatic changes - (somatic - relating to
    the body); must work for males and
    females
    • various other (minor) approaches also available
           II. Age Grading
• Adults
  – Changes associated with wear and tear
    • useful for males & females, but very dependent
      on environmental conditions
    • wing fraying - used for many species,
      Lepidoptera & Diptera
    • cuticular wear - used for migratory locust, some
      dung beetles, and a few others
           II. Age Grading
• Adults
  – Changes associated with wear and tear
              II. Age Grading
• Limitations to Age Grading Methods for
  Adults
  – Often measure physiological time not
    chronological time; but for insects this is
    appropriate (can convert to chronological time with
    degree days); however must calculate degree
    days associated with different adult age classes
    (this is rarely done)
     • depend on temperature
     • may depend on other factors such as:
        –   protein meal-mating
        –   availability of oviposition sites
        –   diapause (dormancy)
        –   microclimate (solar radiation)
             II. Age Grading
• Limitations to Age Grading Methods for
  Adults
  – Once some physiological processes start,
    subsequently they may depend only on
    temperature
     • essentially true for accumulation of fluorescent pigments
     • may be true for fat body depletion
             II. Age Grading
• Limitations to Age Grading Methods for
  Adults
  – Methods may be too specific
     • specific for only a given sex (usually females)
     • some approaches are specific for a given species; may
       need to adapt or develop approach for a species of
       research interest
  – Refining estimates
     • use multiple techniques to better define portion of life
       cycle
     • use different techniques for different portions of life cycle
       (e.g. one technique for nulliparous vs. parous & another
       for senescent)

								
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