David B. Mertz

Senescent Decline in Flour Beetle Strains Selected for Early Adult Fitness

1Robert Taylor (University of Minnesota), D. A. Cawthon, Mrs. Joyce Reed, Mrs. Carol Mooney, Wayne Landerholm, and John Moy provided technical assistance at various times during the course of this study. I am grateful as well to Joseph Connell and William Murdoch (University of California, Santa Barbara), F. A. Lints (Catholic University of Louvain), Monte Lloyd and Thomas Park (University of Chicago), Richard Lewontin (Harvard University), William Heinze (University of Illinois Medical Center), Peter Frank (University of Oregon), J. S. F. Barker (University of Sydney), John Maynard Smith (University of Sussex), and George Sacher (Argonne National Laboratories) for discussions and advice during the conduct of the research and preparation of the manuscript. The manuscript benefited from critical readings by Thomas Park and Michael Wade (University of Chicago) and John Lussenhop (University of Illinois, Chicago Circle). This study was supported by National Science Foundation grants GB-7280, GB-17028, and GB-24818 and by a general research grant from the University of California, Santa Barbara. Medawar (1952) set forth an evolutionary theory of senescence based on concepts of adaptive demography; later, Hamilton (1966) and Charlesworth (1973) corrected and clarified mathematical aspects of Medawars theory. Variants of the theory, based on similar demographic considerations but invoking different genetic explanations, have been proposed by Williams (1957, 1966), Edney and Gill (1968), and Guthrie (1969). The virtue of the approach used by all of these authors is that it views senescence not as a pathological condition but, rather, as just one component of an organisms life history. Insofar as life-history attributes are adaptive, senescence may be an integral part of an adapted constellation of characters.

Some Developmental Consequences of Handling, Egg‐eating, and Population Density for Flour Beetle Larvae

Unhandled larvae of Tribolium castaneum (genetic strain cIV—a) were reared in a whole—wheat flour medium (Fortified with dried powdered brewers yeast, 5% by weight) in a climate of 29°C and 70% RH at three levels of crowding: 100, 200, and 400 per 8 g of flour. At all three densities the median time for pupation was about 18.15 days. Mortality of the developing stages was 3—4% at the 2 lowest densities and about 8% for 400 larvae. Larvae which were subjected to daily handling and reared at the same densities developed more slowly, the prolongation of the larval stage being greatest at density 400. Handling also induced increased mortality at this density but not at lower densities. Handled larvae which were fed eggs of their own kind grew more rapidly than those not fed eggs, and, at the highest egg—feeding rates, the effects of handling and density were almost completely compensated. Evidence is presented that egg—eating would also accelerate the development of unhandled larvae. This is one of the most ...

Mortality Patterns in Eight Strains of Flour Beetles

Male and female flour beetles are described in terms of one mortality characteristic: adult age at death. Four strains of Triboliurn ccnfusum and four strains of Tribolium castaneum were studied. The actual data are reported in two Appendix tables. Death rates were found to depend upon the species, strain, sex, and age of the individuals concerned. Differences between the mortality patterns of the two sexes were especially striking and seemed to have a common character for all strains and both species.

Genetic stability of cannibalism inTribolium confusum

This study reports the stability of genetically controlled cannibalistic behavior in four strains of flour beetles. The strains were derived from Thomas Parks “Chicago Standard” strain ofTribolium confusum using only three or four generations of brother-sister matings in the mid-1950s. Their cannibalistic attributes, as well as their fecundity, egg hatchability, developmental time, and adult longevity, were assayed shortly thereafter and strong interstrain cannibalistic differences were reported. However, other aspects of their demography were remarkably similar. Using the same strains, the cannibalism assays, originally performed during 1959–1962, were repeated. After some 60 generations of husbandry in identical abiotic environments, the strains are essentially unchanged. Different environments were generated, however, by the social and antisocial behaviors of the beetles themselves. The stability is discussed with regard to three possibilities: (1) there are only a few genes which account for the observed differences in cannibalism, (2) cannibalism is selectively neutral, and (3) each strain is at a different local adaptive peak with respect to cannibalism.

Flour beetles: responses to extracts of their own pupae.

Two species of flour beetles, Tribolium confusum and Tribolium castaneum, respond to neutral pith disks impregnated with aqueous extracts of their pupae in such a way that the adults and larvae tend to select the extract of the other species. These findings have implications for the population ecology of Tribolium.

The Domain of Laboratory Ecology

Ecologists often divide their field into three parts: theoretical, laboratory, and field studies. These approaches are directed toward many of the same concepts and, ideally, may have the same ultimate goals, but they are also distinct, not only in the scientific tools they use, but even in the types of questions best addressed by each one. This paper is concerned in particular with laboratory ecology and the relations, and distinctions, between it and field ecology.

Sex Differences in the Cannibalistic Roles of Adult Flour Beetles

Adult males of the flour beetles Tribolium confusum and T. castaneum were found to be several times more voracious than were females as cannibals of pupae. This is exactly the reverse of the sex differences reported earlier with regard to egg—eating; as egg cannibals, females excel males by 7 to 19 times. This is a remarkable division of labor between the two sexes with respect to cannibalistic self—regulation of numbers. See full-text article at JSTOR

Factors Affecting the Susceptibility of Flour Beetle Pupae to Cannibalism by Adults

Knowledge about the cannibalistic behavior of flour beetles (Tribolium confusum Duval and T. castaneum Herbst) continues to grow. The reason for studying this phenomenon so industriously has been explained, and justified, in a series of prior publications. Suffice it to say that the pattern of consumption of eggs and pupae (prey) by larvae and adult beetles (predators) is the primary factor in understanding how these populations regulate their numbers. For contemporary treatments of this subject, Park et al. (1965), Mertz and Davies (1968), and Park et al. (1974) provide an introduction to the literature and give some insight into both the nature of the experimental approach and the interpretation of the derived data. The present paper is devoted to yet another exploration of cannibalistic 1 The research conducted at the University of Chicago was supported by grants to T. P. from the National Science Foundation (GB 212X2) and by the Dr. Wallace C. and Clara A. Abbott Memorial Fund of the University of Chicago. The research conducted at the University of Illinois at Chicago Circle was supported by a grant to D. B. M. from the National Science Foundation (GB 24818). We express our appreciation to Mr. D. A. Cawthon (Illinois) for technical assistance and to Mrs. Mary G. Haynes (Chicago) for assistance in the preparation of the manuscript. 2 Hull Biological Laboratories, University of Chicago, Chicago, Illinois 60637. 3 Department of Biological Sciences, University of Illinois at Chicago Circle, Chicago, Illinois 60680. predation in populations of flour beetles. In a sense, it takes its lead from the recent report of Mertz and Cawthon (1973), who showed that adult males, when eating pupae, are significantly more voracious than females. Specifically, male T. confusum consumed pupae of their own species at 14 times the rate exhibited by females, while T. castaneum males exceeded the female cannibalism rate by nearly four times. This is not necessarily a remarkable discovery in itself. But it does become remarkable, perhaps paradoxical, when taken in conjunction with the earlier work of Rich (1956) and Sonleitner (1961). These investigators studied the cannibalism of eggs by adults and reported exactly the opposite sexual trend from that demonstrated for pupae by Mertz and Cawthon. Rich showed that female T. confusum cannibalized eggs at a rate some seven times greater than males, while Sonleitner, using T. castaneum, showed that females were some 19 times more voracious! Thus, to the extent that these findings can be extrapolated to continuously breeding populations, we infer that eggs suffer greater depletion from female predation while pupae find the presence of males more hazardous. The Mertz-Cawthon study asks, What is the relation between the sex of the adults and their voracity? Alternatively, the present study asks, What is the relation between the sex of the pupae and their risk of being eaten by a

Identification of Tribolium Species by Pupal Characteristics

Two species of flour beetles, Tribolium confusum Du Val and Tribolium castaneum (Herbst), are widely used as laboratory organisms in the field of population ecology. Today, they are also becoming established in laboratories studying artificial and natural selection. In such work it is frequently advantageous, if not even mandatory, to distinguish between the species. For the imaginal stage this is readily accomplished by using the eye and antennal characters given in Hintons key to the species of Triboliumn (Hinton 1948). However, there is no published account of a technique for distinguishing species in their immature stages. A method is described herewith by which the pupae of Tribolium confusum can be differentiated from those of T. castaneum. Figure 1 is drawn as a dorsal view to show 6 tergites of the pupae of each species. Several differences in the

Inbreeding Effects on Competition in Tribolium

When replicate cultures ofT. confusum andT. castaneum are husbanded together under identical treatment conditions, sometimesT. confusum eliminatesT. castaneum, and other times,T. castaneum wins (i.e., competitive indeterminacy occurs). While several plausible explanations were advanced, the results of Mertz et al. (1976) implicated demographic stochasticity and not classical genetic founder effect as the predominant factor influencing the identity of the winning species. They also observed, however, that the size of the founding population had an influence on the competitive strength ofT. castaneum. The present study shows that the decline in competitive strength that accompanied decreasing founder size inT. castaneum can be amply explained by simple inbreeding depression. The eggs of inbred adults showed an approximate 15% reduction in hatchability when compared to outbred adults. No evidence was found that the decrease in competitive strength was due either to prior history differences or reduced genetic heterogeneity of the founding adults.