Stephen T. Trumbo

Reproductive Benefits and the Duration of Paternal Care in a Biparental Burying Beetle, Necrophorus Orbicollis

A monogamous pair of burying beetles (Necrophorus spp.) prepares a vertebrate carcass as a food source for their young and then protects the carcass and young from aggressive congeners. It was estimated that N. orbicollis males received four times the reproductive benefit on large (27-33 g) as opposed to small carcasses (10-18 g) in the field. Large carcasses were more likely to be taken over by free-flying intruders than small carcasses and the presence of a male parent reduced the probability of such takeovers. A male also decreased the time that a large carcass was vulnerable to a takeover. The presence of a male did not affect the number of larvae produced in field or laboratory experiments or the size of larvae reared in the laboratory. Males provided a longer duration of care when on a large carcass, when larval development was slow, or when the female was removed experimentally. The number of larvae, the number of days spent on the carcass, the mass of the carcass remaining at the end of the trial, female size, male size, burial depth and prior reproduction were not found to have independent effects on the probability of fin-ding the male on the carcass. In addition, males that were allowed to provide care prior to being placed in the field did not show a subsequent decline in reproductive success as compared to males that did not provide prior care.

Interference competition among burying beetles (Silphidae, Nicrophorus)

Abstract. 1. This study investigated the impact of intraspecific and interspecific competition on the reproductive success of a biparental burying beetle, Nicrophorus defodiens Mannerheim.

Reproductive benefits of infanticide in a biparental burying beetle Nicrophorus orbicollis

SummarySingle females and pairs of Nicrophorus orbicollis Say were established as residents on carcasses to investigate interactions with intruders under natural conditions. When carcasses were exhumed 10–12 days later, one or more intruders were found on 19% of nests. Intruders expelled one or both of the residents and sometimes paired with a resident or another intruder of the opposite sex. An intruder tended to be larger than the same-sex adult it replaced on a carcass. A male intruder that joined a single female, on the other hand, was not necessarily larger than the resident female. There was indirect evident that intruders committed infanticide and then started their own reproductive attempt on the carcass. Follow-up experiments in the laboratory indicated that interactions between intruders and residents were agonistic and that infanticide regularly occurred as a consequence of a takeover. Use of a genetic marker demonstrated that male and female intruders obtained reproductive benefits from infanticide. However, intruders sometimes cared for mixed broods consisting of their own young and young of a prior resident.

Rapid elevation of juvenile hormone titer during behavioral assessment of the breeding resource by the burying beetle, Nicrophorus orbicollis

Female burying beetles (Nicrophorus orbicollis) rapidly complete ovarian maturation upon discovering a suitable carrion resource for breeding. In this study, we examined changes in hemolymph titers of juvenile hormone (JH) over the first 30 days of adult female life, and in response to the discovery of a mouse carcass. Levels of JH were found to increase gradually over the first 20 days, and then increased abruptly within 24 h of discovery of a carcass. Changes in JH titer were correlated with increases in ovarian mass and length of terminal oocytes. To more precisely determine the timing of the endocrine response to a carcass, hemolymph titers of JH were measured 2, 10, 20 and 60 min after carcass discovery. Titers of JH were significantly elevated (112% over controls) in just 10 min. To confirm this resource discovery-related increase in JH, hemolymph samples were taken from the same individuals both 2 days before, and 10 min after, discovery of a carcass. Again, JH titers rose significantly (170%) in beetles 10 min after carcass discovery. Prominent behaviors observed during the 10-min period following discovery included palpating, lifting, walking around the carcass and making forays into the surrounding soil. Feeding did not occur. These results suggest that the rapid JH surge in female burying beetles is triggered by information obtained during behavioral assessment of a breeding resource, and not by mating or feeding cues. The association between ovarian development and JH titer further suggests a role for JH in co-ordinating reproduction in a temporally and spatially unpredictable environment.

Interspecific competition, brood parasitism and the evolution of biparental cooperation in burying beetles

The potential impact of interspecific competition on mating systems has received limited attention. In this study, I examine the ability of single females and pairs of burying beetles (Nicrophorus spp.) to secure and prepare carrion resources for their brood when matched against two very different types of competitors. In the first set of experiments, I presented N. defodiens small and large rodent carcasses which previously had been exposed in the field to oviposition by carrion flies. Pairs experienced significantly fewer brood failures than single females (25% vs 51%). In successful reproductive attempts (at least one beetle larva produced), the presence of a male marginally increased the number and mass of the brood on,small, but not large, carcasses

Parental Care in Invertebrates

Publisher Summary Ecological and physiological analyses of invertebrate parental care need to be integrated. This chapter reviews the physiological and behavioral mechanisms that control the onset, intensity, and termination of parental care; and the use of invertebrates to address parental care theory. This approach is taken to demonstrate that mechanistic studies of invertebrate parental behavior will provide insight as well as experimental tools for ecologists, to fill gaps in the coverage of invertebrates, and to reveal the potential for the use of invertebrate models in tests of parental care theory. Broad phylogenetic comparisons have the potential to address how physiology constrains the expression of parental care. Parental care in numerous independent phylogenetic lines of insects is regulated by the same neural and endocrine structures. Individuals from selected genetic lines can be employed to examine the physiological differences between individuals with varying tendencies to express parental behavior; genetic lines also will be useful in field experiments investigating the ecological trade-offs of adopting alternative patterns of investment. The effects of development on the expression of care have been neglected as well. The ease with which the developmental environment of many immature invertebrates can be manipulated suggests that the lack of understanding is caused by neglect and not by experimental barriers.

Division of labor between undertaker specialists and other middle-aged workers in honey bee colonies

Abstract A primary determinant of colony organization in temporally polyethic insect societies is inter-individual variation in behavior that is independent of worker age. We examined behavioral repertoires, behavioral correlates of adult development, and spatial distributions within the hive to explore the mechanisms that produce behavioral variation among middle-age honey bees (Apis mellifera). Individually labeled undertakers, guards, food storers, and wax workers exhibited a broad range of task-related behavior, but bees tagged as undertakers were more likely to subsequently remove a corpse from the hive and handle a corpse compared to other middle-aged bees. The activity level of undertakers was similar to other task groups, suggesting that undertaking specialists were neither hyper-active “elites” nor quiescent “reserves” that become active only when a dead bee stimulus is present. Undertakers also were more likely to remove debris and to remain in the lower region of the hive or near the entrance, even when not engaged in corpse removal; both preferences may promote colony efficiency by reducing inter-task travel times. Guards and undertakers were less likely to perform behavior normally associated with young bees compared to food storers and wax workers. Undertakers and guards also initiated foraging at earlier ages than the other task groups. These results suggest that undertakers and guards may be slightly developmentally advanced compared to food storers and wax workers. There also was evidence for lifetime differences in behavioral preferences which could not be explained by differences in adult development. Bees tagged as undertakers were more likely to subsequently remove a dead bee during their entire pre-foraging career compared to other task groups or members of their general age cohort. Differences in both the rate of adult development and individual behavioral preferences, both of which may be subject to genetic and environmental influences, are important determinants of inter-individual variation among honey bees of middle age.

Juvenile hormone‐mediated reproduction in burying beetles: From behavior to physiology

The burying beetle, Nicrophorus orbicollis, is the first beetle exhibiting parental care for which endocrinological studies have been initiated. Burying beetles bury and prepare small vertebrate carcasses as a breeding resource for their offspring. After emergence as an adult, hemolymph titers of juvenile hormone and ovarian size increase in concert for 2–3 weeks, and both plateau until an appropriate resource is discovered. Upon finding a suitable carcass, titers of juvenile hormone increase extremely rapidly (<20 min), and within 18 h ovarian mass increases threefold and oviposition begins. This rapid reproductive development is hypothesized to be selected by the intense competition for these protein-rich but quickly deteriorating resources. Burying beetle females exhibit an additional juvenile hormone surge at the time young hatch. This peak in juvenile hormone is hypothesized to be associated with either the considerable behavioral demands which accompany care of young larvae or with a females willingness to oviposit a replacement clutch should brood failure occur early in the care-giving phase. Parental care has evolved in at least 16 additional families within the Coleoptera. Comparative studies of nonparental and parental groups will be important for understanding how the physiology of ancestral groups affects the evolution of complex social behavior. Arch. Insect Biochem. Physiol. 35:479–490, 1997.

Regulation of brood size in a burying beetle, Nicrophorus tomentosus (silphidae)

Regulation of brood size in a biparental burying beetle, Nicrophorus tomentosusWeber, was studied by providing pairs with one of two sizes of mouse carcasses in the laboratory. For a given carcass size, there was an inverse relationship between number and mass offspring in a brood. The requirement for regulation was that brood size was adjusted such that mean mass of individual larvae was constant for carcasses of different size. Brood size was regulated if parents were present but regulation did not occur if parents were removed prior to hatching of larvae. Pairs bred in quick succession on two carcasses raised fewer than the regulated number of young in the second reproductive attempt. Reasons for regulation of brood size in this genus are discussed.

Changes in biosynthesis and degradation of juvenile hormone during breeding by burying beetles: a reproductive or social role?

Burying beetles, Nicrophorus orbicollis, depend on the location of an unpredictable resource, a small vertebrate carcass, for reproduction. When they discover a carcass, they undergo a correlated rapid rise in titers of juvenile hormone (JH) in the hemolymph and ovarian development. This study investigates the regulation of the changes in JH during breeding in both male and female burying beetles and the role of JH in ovarian development. JH biosynthesis by the corpora allata (CA), measured in vitro, increased in females within an hour of their discovery of a carcass and increased later in males. After returning to low rates as oviposition began, JH biosynthesis rose again 3 days later in females but not in males. Neither the ovaries nor testes synthesized JH. There was a concomitant fall in JH esterase activity within 12 h of discovery of the carcass in both males and females. Although the rise in JH titers and biosynthesis and the fall in JH esterase is correlated with ovarian development, application of methoprene or JH III in the absence of a carcass did not result in vitellogenin uptake by the oocytes. Therefore, we conclude that, in spite of the rapid rise in JH before oviposition, it is not sufficient to regulate vitellogenin synthesis and/or its uptake by the ovaries. We suggest that its role has been preempted to organize social behavior and coordinate parental behavior between mates.