larval period

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The influence of larval growth history and exogenous thyroid hormone on life history allocation patterns in the axolotl ( Ambystoma mexicanum ) Pamela M. Clarkson and Christopher K. Beachy Minot State University. metamorphic size. larval period. Wilbur and Collins, 1973. - PowerPoint PPT Presentation

Text of larval period

  • The influence of larval growth history and exogenous thyroid hormone on life history allocation patterns in the axolotl (Ambystoma mexicanum)

    Pamela M. Clarkson and Christopher K. BeachyMinot State University

  • Lab manipulations of growth almost never confirm this.This pattern is uncommonly observed in nature.Wilbur and Collins, 1973

  • larvalgrowthstoragesexualmaturation

  • Ambystoma mexicanumAmbystoma mexicanum+ 5 nM TH

  • TIMELINEin dayshatchinginitiate foodtreatmentsfirst metamorphlast metamorphinitiate THtreatmentsswitch foodtreatmentsfirstweighingsecondweighingthirdweighingfourthweighing14 March200721 January2008Metamorphic(and control)weightsmetamorphic timing (TH)gonad massfat body massmetamorphic massTwo-factor MANOVA

  • control5 nM TH5 nM TH

  • Big GonadsBig fat bodies

  • switched tolow foodswitched tohigh foodmetamorphic mass (g)Metamorphs (TH treated animals)

  • switched tohigh foodfat body mass (mg)

  • PAEDOMORPHSMETAMORPHSfat body mass (mg)fat body mass (mg)

  • Our ResultsIn the low-high group, metamorphosis was delayed similar to the Wilbur-Collins hypothesis

  • Final AnalysisSuggests storage and metamorphic development interact classic Wilbur-Collins modelStorage rather than growth may be an indicator of environmental quality or deterioration

  • ACKNOWLEDGMENTS

    Heather Modrow (MSU)Leah Crites (MSU)Charles Crites (MSU)Sharon Denks (FBCC)Dwight Blackhawk (FBCC)Karen Pocha-Melby (MSU)

    Nature is supposed to be about trade-offs, e.g. sexual maturity OR fat storage. In laboratory experiments we have not been able to reproduce strong trade-offs. Note here that there is a significant trade-off. The lo-high food group has a steep negative correlation.

    *The Wilbur and Collins model does not take into account other endocrine-mediated factors that may influence metamorphic timing, such as sexual maturation and storage. These are all complex interacting systems. Energy can lead to growth, and metamorphic development, which interact. If they do, this is the graph we should see. However, storage and sexual maturation are also affected by energy intake, which interact with growth and metamorphic development. Taking all of these factors into account, we could also see this graph.

    *By using paedomorphic salamanders, we take away variable metamorphic timing.

    *No one has ever tested the Wilbur-Collins model with paedomorphs, because they dont morph. However, we can induce metamorphosis by using thyroxine.

    This is our experimental design. Immediately after hatching, we begin two food treatments, high and low. We first weigh them at about 120 days. As you can see, there is an immediate difference in weight (size). We also weigh them right before we switch food treatments at 150 days. The size difference remains. We take half the high food treatments, and switch them to low. The other half does not change. Half of the low food treated salamanders are switched to high, and the other half remains unchanged. We weigh them at about 200 days. As you can see, the low-high and high-low groups are now identical. A couple days later, we began TH treatments to induce metamorphosis in half of each food treatment group. The first salamander morphed at about 225 days, with the last one morphing at about 310 days. The sister control (not TH-induced) salamander was also removed at the same time as each salamander metamorphosed. Note how the low-high group has outgrown the high-low group.

    *These are examples of what we look for in metamorphosed salamanders. The guy on the top has all larval features, with long gills with filaments on them, and a tail fin. The guy on the left has begun metamorphosis, with reduced gill length. The guy on the right has undergone metamorphosis, with fully reabsorbed gills and no tail fin. Also note his pigmentation is like that of an adult tiger salamander.

    The top picture is a female salamander. The top right arrow points to the pigmented eggs. The left arrow points to the very large oviduct. The bottom is a male, the left arrow pointing to the testis lobe. The right arrow is pointing to a fat body.

    None of these are significantly different from zero.

    Nature is supposed to be about trade-offs, e.g. sexual maturity OR fat storage. In laboratory experiments we have not been able to reproduce strong trade-offs. Note here that there is a significant trade-off. The lo-high food group has a steep negative correlation.

    The paedomorphic high-high and low-high treatment groups are virtually identical. The metamorphic low-high group significantly differs.

    *It needs to be said that this kind of work requires a lot of hands and a lot of time and a lot of care. As such, it cant be done by a single individual, and the persons listed here were involved in many stages of the work, from obtaining embryos, to husbandry, to dissection, experimental design and statistical analysis.Because this work requires a lot of bodies, it also can require money, and this work benefits greatly from the financial support of the North Dakota INBRE.