The Impeccable Timing of the Apple Maggot Fly, Rhagoletis pomonella

156 Pages·2017·4.95 MB·English

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Dissertations and Theses Dissertations and Theses
Fall 11-24-2015
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Monte Arthur Mattsson
Portland State University
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Mattsson, Monte Arthur, "The Impeccable Timing of the Apple Maggot Fly, Rhagoletis pomonella
(Dipetera: Tephritidae), and its Implications for Ecological Speciation" (2015). Dissertations and Theses.
Paper 2627.
https://doi.org/10.15760/etd.2623
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The Impeccable Timing of the Apple Maggot Fly, Rhagoletis pomonella
(Diptera: Tephritidae), and its Implications for Ecological Speciation

by
Monte Arthur Mattsson

A thesis submitted in partial fulfillment of the
requirements for the degree of

Master of Science
in
Biology

Thesis Committee:
Luis A. Ruedas, Chair
Deborah I. Lutterschmidt
Jason E. Podrabsky
Wee L. Yee

Portland State University
2015
© 2015 Monte Arthur Mattsson
Abstract

Speciation is the process by which life diversifies into discrete forms, and
understanding its underlying mechanisms remains a primary focus for biologists.
Increasingly, empirical studies are helping explain the role of ecology in generating
biodiversity. Adaptive radiations are often propelled by selective fitness tradeoffs
experienced by individuals that invade new habitats, resulting in reproductive isolation
from ancestral conspecifics and potentially cladogenesis. Host specialist insects are
among the most speciose organisms known and serve as highly useful models for
studying adaptive radiations. We are just beginning to understand the pace and degree
with which these insects diversify. The apple maggot, Rhagoletis pomonella, is a well-
studied insect whose eastern and southern populations are models for ecological
speciation. Recently (40–65 ya), the fly has invaded the Pacific Northwestern United
States through human-transported apples infested with larvae. There, populations of R.
pomonella have rapidly colonized two novel hawthorn hosts whose fruiting times bracket
apple’s (early-season native Crataegus douglasii and introduced C. monogyna, which
fruits late in the season). The recent introduction might initiate host shifts, providing
opportunities to examine the pace and mechanistic means with which host races (an
evolutionary stage preceding speciation) become established. Here, I demonstrate that
host-associated populations at a site in southwest Washington are partially allochronically
isolated from one another, and life cycles temporally match with natal host fruit ripening
times in sympatry. If spatially widespread, these temporal barriers could result in
reproductive isolation and possibly cladogenesis. Implications of these findings reach
i
beyond academic import, as R. pomonella is expanding not only its host range, but its
geographic range is encroaching upon central Washington, the site of a multi-billion
dollar per year apple-growing industry.
ii
For my parents, Jim & Laura Mattsson, whose charisma to explore the world and listen
to music was the greatest heirloom.
iii
Acknowledgements

I thank:
My wife and kids for their loving support, labor, curiosity, and hilarity;

Luis Ruedas for telling me when I was blowing it, as well as killing it;

My committee: Jason Podrabsky, Deborah Lutterschmidt, and Wee Yee, who have
supported and steered me when I occasionally went off-roading;

Jeff Feder and Glen Hood for their pointed insights, suggestions, and influence;

Robert Richardson for his unwavering support and encouragement;

Forbes-Lea Endowed Fund for Student Research and the Theodore Roosevelt Memorial
Grant from the American Museum of Natural History.

Ernest Hemingway and John Steinbeck for their refreshing approaches to writing.

iv
Table of Contents
Abstract ............................................................................................................................... i

Dedication ..........................................................................................................................iii

Acknowledgements ............................................................................................................iv

List of Tables ....................................................................................................................vii

List of Figures ..................................................................................................................viii

Chapter 1:
Introduction..........................................................................................................................1

Chapter 2:
Rapid and Repeatable Shifts in Life History Timing of Rhagoletis pomonella (Diptera:
Tephritidae) Following Colonization of Novel Host Plants in the Pacific Northwestern
United States

Abstract..................................................................................................................17

Introduction............................................................................................................19

Materials and Methods...........................................................................................24

Results....................................................................................................................31

Discussion..............................................................................................................36

Tables.....................................................................................................................42

Figures....................................................................................................................46

Chapter 3:
Effects of Pre-winter Conditions on Mortality Rates and Diapause Phenologies of Host-
associated Populations of Rhagoletis pomonella (Diptera: Tephritidae) in Southwest
Washington State

Abstract..................................................................................................................52

Introduction............................................................................................................54

v
Materials and Methods...........................................................................................62

Results....................................................................................................................67

Discussion..............................................................................................................72

Tables.....................................................................................................................78

Figures....................................................................................................................81

Chapter 4:
Life History Adaptations Traverse Trophic Levels

Abstract..................................................................................................................91

Introduction............................................................................................................93

Materials and Methods...........................................................................................97

Results..................................................................................................................100

Discussion............................................................................................................103

Tables...................................................................................................................105

Figures..................................................................................................................109

Chapter 5:
Summary, Conclusions, and Future Directions...............................................................114
Table....................................................................................................................121
Bibliography....................................................................................................................122

Appendix: Supplementary data for Chapter 2................................................................ 141
Table A.1 Specific dates of fruit data collection.................................................141
Table A.2 Data describing mean dates of eclosion for individual replicates.......142
Table A.3 Soil temperature data..........................................................................143
Fig. A.1 Fruit firmness and diameter, showing interquartile ranges
and standard errors, respectively..........................................................................144
vi
List of Tables

Table 2.1 Larval infestation times of alternative hosts in 2013 42
Table 2.2 Statistical tests of alternative host fruit ripening times 43
Table 2.3 Pairwise post hoc tests of host-associated eclosion times 44
Table 2.4 Estimates of reproductive isolation among host-associated populations 45

Table 3.1 Numbers of R. pomonella pupae reared from host fruits during times
of peak activity 78
Table 3.2 Estimates of prewinter intervals experienced by alternative host
populations in nature 79
Table 3.3 Numbers of pupae entering pre-winter treatments 80

Table 4.1 Parasitoid wasps that attack Rhagoletis spp. and the plant hosts that are
infested by the Rhagoletis spp. 105
Table 4.2 Fruit collection dates, numbers of R. pomonella pupae reared and total
wasp infestation rates 108

Table 5.1 Estimates of total reproductive isolation as a result of the combined effects of
allochronic and behavioral isolation 121
vii