Schultz lab research topics

Birth, growth, sex and death in surfperch

 

  1. The daily otolith age record as research tool
  2. Natural history of the dwarf surfperch
    1. (Mm with penny)
    2. embioticidae
    3. Mm ecology
      1. shallow, grassbeds
      2. Baja CA to N CA
    4. mm repro bio (use slide)
    5. pregnant females in aquarium
    6. cutaway mother
  3. Validation of the daily age record
    1. Otolith pix
      1. (slide of earstones in embryo)
      2. (microstructure)
      3. (yoy otolith)
    2. If daily record, then can determine conception date, birth date
    3. Validation: chemical marking of otoliths (slide of tet-tagged otolith)
      1. otolith marked on known date, individual sacrificed on known date.
      2. What is relationship between days and increments?

      (validation results transparency)
      I've plotted the results of both groups here. Counted the number of increments beyond the mark, in each fish. Plotted means against the number of days between treatment and end of the expt, on x axis. Line describes best fit. The lines for the two groups are different. The line for the wild fish has a slope of 1; for every day of experiment, one increment was formed.

    4. Conclusion: dwarf surfperch have a daily age record
  4. Variation in breeding time
    1. Female conception date varies with size
      1. collect females regularly in the spring
        1. net haul slide
      2. measure their length, age from scales
      3. take out their embryos and age them
      4. fig: breeding schedule against size and age
      5. small females of each age class breed later than the larger females.
      6. More than three months of variation in breeding schedule in this population.
      7. This is seen in many fishes, and other animals. I wanted to know why.
    2. Physiological explanation
      1. Energy reserves influence time of conception
        1. analyze fat content of pregnant females
        2. plot fat content against conception date
        3. figure: clear relationship
      2. Why? Small fish wait until later in the spring, wait until more food available
    3. Implication: it's better to breed early than later
  5. fitness vs. birth date in female offspring
    1. Prediction: early-born daughters should have the highest fitness
    2. Method:
      1. sample population over year
      2. follow cohorts through the year (cohorts: e.g. a week-class, all the individuals born in a particular week)
        1. requires daily ageing
      3. do early-born daughters survive better? reproduce better?
    3. Female fecundity
      1. Collect yearling females in 1997 (1996 yearclass)
      2. Count embryos
      3. Determine female's birth date
      4. plot: bx vs. birth date
      5. Early-born females have more young
      6. Reason: they are larger at time of reproduction
    4. Female survival
      1. determine abundance of each cohort at birth (e.g. how many individuals born first week in May?)
      2. determine abundance of these cohorts next spring
      3. difference is survival
      4. plot survival vs. birth date
      5. early born and late-born have poor survival
    5. Female fitness vs. birth date
      1. combine fecundity and survival analyses
      2. what is lifetime production of offspring in relation to birth date?
      3. net reproductive rate vs birth date shows that daughters born mid-season have highest fitness
        1. small fecundity advantage of early birth not enough to overcome big survival disadvantage.
  6. Male fitness vs. birth date
    1. Situation may be very different for males
      1. maturity at birth
      2. do early-born males have more chances to mate?
    2. Indications that early birth is a good strategy for males
      1. males leave mother earlier than females
        1. from yoy otoliths, days in mother: males = xx, females = xx.
        2. from embryos: dropoff in sex ratio near the end of gestation
      2. early born males have big testes, late born males don't (gsi figures)
        1. having big testes is important in this species, males have to produce lots of sperm
      3. Males born early may mate more, grow less
        1. (courtship mark) One sign that males are mating a lot right after birth: very fine lines in some males, for 3-4 weeks, after birth.
        2. not all males have the mark; are they skipping spawning and growing instead?
        3. Early born males have the 'mating' pattern, late-born males have the 'grow' pattern.
    3. Conclusion: early birth is good for males, not good for females
    4. So is it good for mothers to breed early?
      1. Still working on this one