Eastern Illinois University The Keep Masters Theses Student Theses & Publications 1993 The Relationship between Lifespan and Reproduction in the Giant Waterbug (Belostoma flumineum) Wendy Nixdorf This research is a product of the graduate program in Zoology at Eastern Illinois University. Find out more about the program. Recommended Citation Nixdorf, Wendy, "The Relationship between Lifespan and Reproduction in the Giant Waterbug (Belostoma flumineum)" (1993). Masters Theses. 2139. https://thekeep.eiu.edu/theses/2139 This is brought to you for free and open access by the Student Theses & Publications at The Keep. It has been accepted for inclusion in Masters Theses by an authorized administrator of The Keep. For more information, please contact [email protected]. THESIS REPRODUCTION CERTIFICATE TO: Gradua~e Degree Candidates who have written formal theses. SUBJECT: Perrpission to reproduce theses. 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(TITLE) BY Wendy Nixdorf THESIS SUBMITIED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science IN THE GRADUATE SCHOOL, EASTERN ILLINOIS UNIVERSITY CHARLESTON, ILLINOIS 1993 YEAR I HEREBY RECOMMEND THIS THESIS BE ACCEPTED AS FULFILLING THIS PART OF THE GRADUATE DEGREE CITED ABOVE DATE ABSTRACT The evolutionary significance of senescence and death is poorly understood. Life history theory suggests that the allocation of energy to growth or reproduction is necessarily associated with a decrease in energy available for maintenance of the soma. This study attempted to determine if an investment in reproduction would decrease longevity in the giant waterbug (Belostoma flumineum). Male and female waterbugs were collected from the field as last instar stage nymphs and maintained under controlled laboratory conditions. Individuals were randomly assigned to mating effort treatments, (virgins or breeders with breeding efforts ranging from 1 to >5 times). Following breeding, one half of the males had their egg pads artificially removed whereas the other half were allowed to brood eggs pads through hatching. Female waterbugs lived, on average, longer than males; though when considered by level of mating effort the difference was statistically indistinguishable. Neither breeding nor number of breeding efforts had a detrimental effect on lifespan; virgins and breeders lived for approximately the same length of time. There was no significant difference between the lifespan of brooding and non-brooding males. Both male and female waterbugs that were paired with the opposite sex, yet i yet failed to breed, died significantly sooner than either virgins or breeders; casual factors for this decreased longevity are uncertain. There was a significant positive relationship between age at first reproduction and age at death in both male and female waterbugs; those bugs that bred early in life died sooner than those that bred for the first time late in life. These results suggest that male and female waterbugs pay a longevity cost by reproducing early in life. ii ACKNOWLEDGMENTS I would first like to thank Dr. Kipp Kruse for serving as my graduate advisor. I could always count on him for help when problems developed, advice when I needed it, motivation when I got lazy and, most importantly, a good laugh when things got boring. I would like to thank Dr. Eric Bollinger and Dr. Michael Goodrich for comments on the thesis and for serving on my graduate committee. Thanks also go to Dr. Charles Costa for the use of his computer and for help with the figures. I have to thank Colin Smith for sweating it out with me in the "bug house"; I couldn't have done it without his help. Thanks also to Jimmie Griffiths, Nancy Johnson, Lori Davis and Roger Jansen for wading into the mud to collect bugs with me. Thanks to my friends and especially to my family for supporting me. No matter where I go, I always have a great place to go home to (even if I don't have a bed to sleep in!). iii TABLE OF CONTENTS Cover Page Abstract i Acknowledgments iii Table of Contents iv Introduction 1 Materials and Methods 7 Results 11 Discussion 15 Literature Cited 22 Table 1 29 Table 2A&B 30 Figure lA,B,C,D Legend 31 Figure 2A,B,C,D Legend 32 Figure 3 Legend 33 Figure 4A,B,C,D Legend 34 Figure 5 Legend 35 Figure 6A,B,C Legend 36 iv INTRODUCTION No organism survives indefinitely even when maintained under "ideal conditions" where resources are readily available and the threat of predation, competition and disease are removed. In this situation, individuals continue to experience a persistent decline in age-specific fitness components due to some internal physiological decline (Rose 1991). The decrease in the likelihood of survival with increasing chronological age has been termed senescence (Comfort 1954; Medewar 1955). The evolutionary explanation of senescence has been ascribed to the decline in the force of natural selection with age (Rose 1984, 1991; Finch 1991). Prior to the onset of sexual maturity, lethal mutations are selected against because affected individuals do not bear offspring. Lethal or deleterious alleles that do not exert their effects until late in life may not be selected against and could persist within the population (Medewar 1955). Williams (1957) was the first to speculate how pleiotropic genes may play a role in senescence by suggesting that alleles with detrimental effects occurring, after reproduction, could actually be selected for if they also carried effects that improved fitness early in life. This theory, known as "antagonistic pleiotropy," is considered a likely candidate for explaining senescence (Charlesworth 1980; 1 Rose and Charlesworth 1980; Rose 1984, 1991; Finch 1991). Senescence may play an important role in the evolution of life history characteristics. According to the "principle of allocation," natural selection optimally allocates resources among growth, maintenance and reproduction (Gadgill and Bossert 1970; Pianka 1988). When resources become limited, competition occurs for the allocation of these resources; resources allocated to one area is thought to be associated with a decrease in resources available to other areas (Bell 1984; Reznick 1985). If, for example, environmental hazards (e.g., predation, disease) are likely to kill an individual early in its life, natural selection should favor individuals who invest more energy in reproduction than in maintenance. In contrast, species that are likely to survive longer should divert relatively more energy into maintenance. Known as the "disposable soma" theory, this suggests that energy should be invested to maintain the soma for only the expected period of vigor whereas the remainder should be used for reproduction (Kirkwood 1985, 1987). It is generally assumed that there is a inverse relationship between reproduction and longevity (Bell 1984; Reznick 1985). organisms that reproduce are faced with costs that may decrease their longevity. For example, individuals may encounter ecological costs 2 which include exposure to predators during oviposition or while guarding eggs or young (Bell 1984; Tallamy 1984). Physiological costs may also be incurred when energy used for egg production or other reproductive activities is not available for maintenance. Furthermore, the increases in the size of reproductive organs that occur during breeding may constrict and reduce the effectiveness of other organs that are essential for normal maintenance. (Calow 1954; Tallamy and Denno 1982). Some research has shown that individuals that breed die sooner than their virgin counterparts (Tinkle 1969; Snell and King 1977; Law 1979; Tallamy and Denno 1982; Feifarek, Wyngaard and Allen 1983; Partridge, Green and Fowler 1987; Fowler and Partridge 1989; Reznick 1992); there has, however, been evidence to the contrary (Haukioja and Hakala 1978; Dean 1981; svard and Wiklund 1988). Most research dealing with the relationship between longevity and reproduction has been devoted to females, since they generally have the greater parental investment than males (Trivers 1972). The cost of reproduction to males has generally been thought to be minimal (Partridge and Andrew 1985; Hayashi 1993). Recently, work with the nematode~ elegans suggested that males may also pay a longevity cost associated with sperm production (VanVoorhies 1992) • Insects have been utilized extensively in aging 3 research for several reasons: (1) the lifespan of insects is relatively short so several generations can be investigated in a relatively short period of time; (2) insects are often available in large numbers, and can be generally easily maintained and will breed in captivity; and (3) though insect physiology can be complex, it is well known for several species (Lints 1985). There has not been