FOLLOWING THE FUEL: EXPLORING RESOURCE USE AND ALLOCATION

144 Pages·2010·1.17 MB·English

FOLLOWING THE FUEL: EXPLORING RESOURCE USE AND ALLOCATION
DURING LIFE-HISTORY TRANSITIONS IN THE FLESH FLY, SARCOPHAGA
CRASSIPALPIS

By

FRANK J. WESSELS

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2010
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© 2010 Frank J. Wessels

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To Erin, for your love and support

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ACKNOWLEDGMENTS
This dissertation represents my work compiled as part of a group mentoring
process with the ultimate goal of teaching me how to become a successful scientist. As
such, a number of individuals have contributed their advice, technical expertise,
constructive criticism and comments on a number of aspects of this research, and l
thank you all. In particular, I would like to thank my doctoral committee, Mike Scharf,
Peter Teal and Bruce MacFadden. I also thank my collaborator and mentor John Hatle
for his guidance. Finally, and most importantly, I thank my major advisor Dan Hahn for
his mentorship, his candor and his down to earth philosophy of science, which will
continue to guide me throughout my career.

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TABLE OF CONTENTS

page
ACKNOWLEDGMENTS ...................................................................................................... 4
LIST OF TABLES ................................................................................................................ 8
LIST OF FIGURES .............................................................................................................. 9
ABSTRACT........................................................................................................................ 11
CHAPTER
1 INTRODUCTION ........................................................................................................ 13
Insect Physiological Ecology ...................................................................................... 13
Scavenging Insects: an Interesting Evolutionary Model............................................ 14
Resource Allocation and Trade-offs ........................................................................... 15
Stable Isotopes in Entomology ................................................................................... 18
Aims and Scope .......................................................................................................... 21
Aim 1: Stable Isotope Chemistry and Metabolism .............................................. 22
Aim 2: Reproductive Allocation and Plasticity ..................................................... 22
Aim 3: Diapause Metabolism and Substrate Use ............................................... 22
2 CARBON 13 DISCRIMINATION DURING LIPID BIOSYNTHESIS VARIES
WITH DIETARY CONCENTRATION OF STABLE ISOTOPES: IMPLICATIONS
FOR STABLE ISOTOPE ANALYSES........................................................................ 23
Introduction ................................................................................................................. 23
Materials and Methods ............................................................................................... 26
Culturing B. subtilis .............................................................................................. 26
Lipid Extraction ..................................................................................................... 27
Whole Bacterial Tissue Samples ......................................................................... 28
Stable Isotope Analysis........................................................................................ 28
Calculation of Discrimination Factors .................................................................. 28
Statistical Analyses .............................................................................................. 29
Results ........................................................................................................................ 29
Discussion ................................................................................................................... 29
Acknowledgements..................................................................................................... 34
3 ALLOCATION FROM CAPITAL AND INCOME SOURCES TO
REPRODUCTION SHIFT FROM FIRST TO SECOND CLUTCH IN THE FLESH
FLY, SARCOPHAGA CRASSIPALPIS ...................................................................... 37
Introduction ................................................................................................................. 37
Materials and Methods ............................................................................................... 41
Insect Rearing ...................................................................................................... 41
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Experimental Diets ............................................................................................... 41
Sample Preparation ............................................................................................. 43
Stable Isotope Analysis........................................................................................ 44
Mixing Model ........................................................................................................ 45
Results ........................................................................................................................ 46
Discussion ................................................................................................................... 47
Acknowledgements..................................................................................................... 52
4 DOES IT PAY TO DELAY? BENEFITS OF DELAYING REPRODUCTION IN
THE FLESH FLY SARCOPHAGA CRASSIPALPIS.................................................. 57
Introduction ................................................................................................................. 57
Materials and Methods ............................................................................................... 61
Animal Rearing and Experimental Design .......................................................... 61
Stable Isotope Analysis........................................................................................ 63
Stable Isotope Incorporation – Mixing Model ...................................................... 65
Results ........................................................................................................................ 66
Discussion ................................................................................................................... 68
Acknowledgements..................................................................................................... 74
5 RESOURCE AVAILABILITY AFFECTS REPRODUCTIVE ALLOTMENT AND
TIMING, BUT NOT THE RATE OF OOCYTE DEVELOPMENT IN THE FLESH
FLY, SARCOPHAGA CRASSIPALPIS. ..................................................................... 80
Introduction ................................................................................................................. 80
Materials and Methods ............................................................................................... 83
Insect Rearing ...................................................................................................... 83
Experimental Design ............................................................................................ 84
Rate and Magnitude of Reproductive Allotment ................................................. 84
Protein Allocation ................................................................................................. 85
Stable Isotope Analysis........................................................................................ 86
Results ........................................................................................................................ 87
Discussion ................................................................................................................... 88
Acknowledgements..................................................................................................... 93
6 BIOCHEMICAL DISSECTION OF THE METABOLIC RESERVES AND FUEL
USE IN THE OVERWINTERING DIAPAUSE OF THE FLESH FLY,
SARCOPHAGA CRASSIPALPIS. ............................................................................ 101
Introduction ............................................................................................................... 101
Materials and Methods ............................................................................................. 105
Insect Rearing and Diapause Initiation ............................................................. 105
Monitoring the Diapause Response .................................................................. 106
Micro-Separation and Quantification ................................................................. 106
Weight Loss and Indirect Calorimetry ............................................................... 107
Analysis of 13C in Respired CO ........................................................................ 108
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Statistical Analyses ............................................................................................ 109
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Results ...................................................................................................................... 109
Characteristics of Diapause in S. crassipalpis .................................................. 109
Fuel Use during Diapause ................................................................................. 110
Discussion ................................................................................................................. 111
Acknowledgements................................................................................................... 117
7 OVERALL DISCUSSION AND CONCLUSIONS .................................................... 123
LIST OF REFERENCES ................................................................................................. 130
BIOGRAPHICAL SKETCH.............................................................................................. 144

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LIST OF TABLES
Table page

2-1 Bacillus subtilis experimental broth treatments. .................................................... 35
2-2 A) ANCOVA model for δ13C profiles of B. subtilis diet and tissue fractions. B)
Regression data for sampled tissue classes. ........................................................ 35
4-1 Quantification of 13C discrimination of egg and somatic tissue from female S.
crassipalpis raised on high and low 13C artificial diets. ......................................... 75
4-2 Multivariable general linear model for the effects of treatment and timing on
egg development. ................................................................................................... 75
5-1 A multivariable general linear model for the rate of reproductive development.
. ............................................................................................................................... 94
6-1 ANCOVA tables for the effects of pupal weight and time in diapause on lipid,
protein and glycogen stores, stars indicate statistical significance. ................... 118

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LIST OF FIGURES
Figure page

2-1 Relationship between isotopic values of diet, bacterial tissue, lipid-extracted
tissue, and lipids. .................................................................................................... 36
3-1 Flesh fly A) egg and B) somatic whole tissue contain less carbon from adult-
acquired income sources at the first clutch compared to the second clutch. . .... 54
3-2 A) Neutral and B) polar lipids extracted from eggs across two reproductive
clutches in the flesh fly. ......................................................................................... 55
3-3 A) Neutral and B) polar lipid fractions extracted from flesh fly somatic tissue. .... 56
4-1 A) Predictive model for adaptive reproductive plasticity in S. crassipalpis. B)
Experimental design outlining the timing of resources during the delay period... 76
4-2 Egg development over time across feeding treatments, A) non-pulsed control
treatments. B) Pulsed feeding treatments. ........................................................... 77
4-3 A) The relationship between reproductive timing and fecundity and B) the
relationship between timing and egg size. ............................................................ 78
4-4 A) The amount of carbon allocated to eggs from resources provided during
the reproductive delay and B) the amount of carbon allocated to somatic
tissue....................................................................................................................... 79
5-1 A) Incomplete egg development in females that were protein-restricted as
adults. B) Female flesh flies that are denied a protein meal ............................... 95
5-2 Average number of eggs in the first clutch across treatments. ............................ 96
5-3 Average egg length, width and estimated volume. ............................................... 97
5-4 Total egg allotment ................................................................................................. 98
5-5 Stable isotope profiles for whole egg tissue. ......................................................... 99
5-6 Stable isotope profiles for the protein fraction of egg tissue. .............................. 100
6-1 A) Eclosion histogram diapausing flesh flies. B) Metabolism depicted as
respired CO for non-diapausing and diapausing pupae .................................... 119
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6-2 Wet mass of diapausing S. crassipalpis pupae .................................................. 120
6-3 Metabolic reserves during diapause and post diapause development (A)
neutral lipids (B) protein C) glycogen and D) glycerol. ....................................... 121
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6-4 Concentration of 13C isotopes in the respired CO of diapausing S.
2
crassipalpis. .......................................................................................................... 122

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