Terminal Investment Research Articles

Spontaneous male death during copulation in an orb-weaving spider

Males of some cannibalistic species of spiders and insects appear to sacrifice themselves by allowing the female to eat them, and the adaptive significance of such drastic terminal reproductive investment has recently been demonstrated for a spider. Typically, the female has to kill the male, but it has been suggested that males of some species in the cannibalistic orb-weaving spider genus Argiope may die in copula without female 'collaboration'. Here, we provide the first experimental evidence to our knowledge of programmed sudden death after onset of copulation in males of the spider Argiope aurantia. Our observations reveal that males invariably die during the insertion of their second pedipalp, regardless of whether they mate with newly moulted, defenceless females or with older mature females that often attack them. We determined experimentally that the death of males is triggered immediately upon insertion of the second palp, when males become unresponsive, and heartbeat ceases within minutes of insertion. We discuss the possible adaptive significance of programmed death during copulation, and argue that male death has evolved in a context other than sexual cannibalism.

Age-related decline in humoral immune function in Collared Flycatchers.

Although immune function usually declines with age in humans and captive animals, little is known about whether immune function deteriorates with age in natural populations. Here we present evidence for such an age-related deterioration in humoral immune function from a wild population of the Collared Flycatcher (Ficedula albicollis). In this study, young (1-year old), mid-age (3-year old) and old (5-6-year old) females were challenged with a nonpathogenic antigen, sheep red blood cells (SRBC), while provisioning their nestlings. The level of antibodies against SRBC was measured thereafter. Old females showed markedly lower humoral immune response and produced fledglings of lower body mass in comparison with the other two age classes. Moreover, the age classes differed in the relationship between immune response and fledgling body mass with mid-age females showing a significant positive relationship while the relationship was negative but nonsignificant among young and old females. The results are discussed in light of existing theories of optimal resource allocation, ageing and the theory of terminal investment.

Risky mate search and male self-sacrifice in redback spiders

Male redback spiders twist their abdomens onto the fangs of their mates during copulation and, if cannibalized (65% of matings), increase their paternity relative to males that are not cannibalized. The adaptive male sacrifice hypothesis proposes that this increased reproductive payoff from a single mating outweighs the residual reproductive value of a cannibalized male, because high mortality during mate searching restricts alternative mating opportunities. It has been reported that redback male residual reproductive value is low because males are functionally sterile after one mating—a putative intrinsic constraint that could arguably favor self-sacrifice in the absence of ecological restrictions on multiple mating. However, sterility and self-sacrifice may both arise as aspects of a terminal investment strategy if the probability of multiple mating is sufficiently low. Here I report field data that support the adaptive male sacrifice hypothesis. More than 80% of redback males die without finding a potential mate in nature. Data from two observational field studies and one release experiment suggest that in the absence of cannibalism, male redbacks would expect fewer than one mating opportunity in a lifetime. This expectation was not significantly higher for a large male or one in good condition. A simple quantitative analysis confirms that even if males are assumed to be fertile throughout life, the measured mortality rate during mate search in combination with previously documented paternity benefits of cannibalism is sufficient to ensure that self-sacrifice is adaptive for male redback spiders.

The somatic cost of reproduction: what determines reproductive effort in prime-aged fallow bucks?

The somatic costs of reproduction are important for understanding the relationship between sexual selection and life-history evolution, and there are two main hypotheses used to explain the pattern of reproductive effort in ungulates. The terminal investment hypothesis predicts that reproductive effort should increase with age, because the value of each offspring increases as the number of future potential offspring decreases over the lifetime of an individual. In contrast, the mating strategy-effort hypothesis predicts that reproductive effort should be highest in prime-aged males, and lower in both younger and older males, since prime-aged males are most active in trying to gain matings. We examined reproductive effort among prime-aged (5–8 years old) fallow bucks (Dama dama) by comparing mass loss during the breeding season with mating success and activities associated with mating. Males lost about 26% of their body mass during the breeding season and mating success was strongly positively related to the time spent moving and in vocal display. However, mass loss was not related to either mating success or the behaviours associated with mating success. This indicates that males of higher quality were more efficient at converting energy into reproductive success, and is consistent with our earlier results showing phenotypic quality differences between males in our study population. Mass loss was positively correlated with initial mass. Therefore, body condition at the start of the breeding season was the most important determinant of reproductive effort. Mass loss was not related to age, in that it neither increased with age nor peaked in males that are usually the most reproductively active (ages 6 and 7). Thus, for reproductive effort in prime-aged males, our results do not support either the terminal investment hypothesis or the mating strategy-effort hypothesis.

Age– and density–dependent reproductive effort in male red deer

Reproductive effort in female ungulates originates from gestation and lactation and has been studied extensively; however, no comparable studies of reproductive effort in males (due to fighting for access to mates) have, to our knowledge, previously been reported. Here, we report on weight loss of male red deer during the annual mating season--a direct measure of male reproductive effort (or somatic reproductive costs). The 'terminal investment' hypothesis predicts that reproductive effort should increase with age, given that costs remain stable. We also propose the 'mating strategy-effort' hypothesis, which predicts that reproductive effort peaks in prime-aged males, since they are most often the harem holders. Consistent with the mating strategy-effort hypothesis, relative weight loss during the rutting season peaked at prime age and was lower in younger and senescent males. Weight loss during the rut was relatively smaller as density increased and more so for older males. This is probably primarily due to males (particularly senescent males) starting their rut in poorer condition at high density. The pattern of reproductive effort in males with regard to age and density therefore differs markedly from the pattern reported for females.

Value of male remating and functional sterility in redback spiders

In the Australian redback spider, Latrodectus hasselti, males typically use their paired copulatory organs (palps) to copulate twice with a single female then sacrifice themselves to their cannibalistic mates in a strategy that increases their paternity in that one mating, but leads to death. This type of terminal investment in one mating is predicted only if the expected value of future matings is low for males relative to the value of repeated mating with the same female. In this laboratory study, we quantified the reproductive value of mating more than once with the same female (repeated mating) and mating with more than one female (multiple mating) for male redback spiders. We tested two natural selection hypotheses for repeated mating, sperm limitation and reproductive insurance, but found no support for either hypothesis. We show that, in the absence of sperm competition or cannibalism, male lifetime reproductive output is the same whether a male copulates once, twice, or several times with a given female. Repeated mating does not increase the probability of successful fertilization, nor does it increase the number of offspring produced in successful matings. Although male repeated mating is not favoured because of increased fertility of mates, other studies suggest it may be important in sperm competition. Here we show that the relative reproductive value of the first two copulations is very high for redback males because they are functionally sterile after each palp has been used once; nonvirgin males are unable to father offspring. Functional sterility and repeated mating by male redbacks may be favoured by the same factors that lead to male sacrifice behaviour: ecological constraints on multiple mating combined with competitive benefits of maximal investment in the first mating. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Age-related reproductive effort in reindeer (Rangifer tarandus): evidence of senescence.

Age-specific rates of survival and reproduction in iteroparous organisms remain a key issue in population ecology. How patterns of survival vary with age in large herbivores is well known; much less is known regarding age-specific patterns of reproduction. The senescence hypothesis predicts a progressive loss of function accompanied by decreased performance with age. The terminal investment hypothesis predicts that the proportion of resources a mother invests (i.e. effort relative to costs) is expected to increase toward the end of her life-span, when the number of offspring she can expect to rear in the future is low. Assuming that the costs remain stable, the terminal investment hypothesis predicts increased reproductive effort with age. We used data on body weight of 1,956 semi-domestic reindeer (Rangifer tarandus) calves from females with known age and weight to test these two (not mutually exclusive) hypotheses. Body weight of calves clearly decreased after 7years of age was reached (also after controlling for female body weight), which was in support of the senescence hypothesis. We can conclude that either the terminal investment hypothesis is wrong, and/or the reproductive costs increase with age in female reindeer.

Temperature-Dependent Parental Investment in the Giant Waterbug <I>Belostoma flumineum</I> (Heteroptera: Belostomatidae)

We examined the effects of ambient temperature on the brooding behavior of male waterbugs, Belostoma flumineum Say. Male waterbugs are more likely to prematurely terminate care for small egg-pads than for larger egg-pads. Because embryogenesis and breeding season are both associated with ambient temperature, males in warmer environments may respond differently than those in cooler conditions. We studied the effects of temperature on male parental behavior by housing groups of completely and partially egg-encumbered males under different thermal regimes. Completely encumbered males rarely discarded egg-pads, regardless of ambient temperature. Partially encumbered males housed under warm ambient temperatures, however, were significantly more likely to discard the eggs than those housed under cooler conditions. These results are consistent with the hypothesis that cool ambient temperatures at the end of the breeding season elicit a terminal investment strategy.

Empirical evidence of a trade–off between reproductive effort and expectation of future reproduction in female three-spined sticklebacks

Optimal life-history models generally predict that the reproductive effort of iteroparous organisms may increase with age, as their expectation of future reproduction decreases. The population of three–spined sticklebacks ( Gasterosteus aculeatus ) in the Camargue (Rhone River Delta, France) is annual, all adults dying after their first breeding season. As the three–spined stickleback is a multiple spawner, we tested the hypothesis that reproductive effort may increase during the breeding season on field data. From 1987 to 1998, 653 female sticklebacks were collected in the field during the breeding seasons. The body size, body weight and weights of the liver, gonads and carcass were measured for these individuals. Only gravid females with mature eggs (176 fish) were included in the analysis. Considering the female three–spined stickleback as a capital breeder, the energetic resources available for allocation between soma and gonads were estimated by its body weight. Somatic condition decreased during the breeding season and reproductive effort (gonad weight relative to body weight) increased. These patterns did not vary significantly between years. These observed variations in reproductive effort during the breeding season can be interpreted as empirical evidence of a trade–off between reproductive effort and expectation of future reproduction.

Does reproductive investment change with age in tsetse flies, Glossina morsitans morsitans (Diptera: Glossinidae)?

1. Viviparous insects such as tsetse (Glossina spp.) provide unusual opportunities to compare age-related changes in the proportion of maternal resources transferred to offspring. 2. In laboratory populations of Glossina morsitans morsitans the survival of females was high for the first 60 days of adult life but declined rapidly thereafter. 3. Average longevity did not differ significantly between mated and unmated females (93·6 and 90 days, respectively). 4. Nutritional state in terms of fat content and residual dry mass did not decline with adult female age. 5. The fecundity of mated females was constant for the first 60 days of adult life and declined only slightly thereafter. 6. Offspring size did not change towards the end of the adult female lifespan and there was no evidence of an increase in the allocation of resources to reproduction in older females. 7. Results contrast with those obtained recently for vertebrates and may indicate that age-related changes in offspring size in Glossina are not adaptive, or that so few females reach old age under natural conditions that there is no selection for a strategy of terminal investment.

Reproductive senescence and terminal investment in female Barbary macaques (Macaca sylvanus) at Salem

The reproductive history of 207 female Barbary macaques, living in a large outdoor enclosure in Southwest Germany, was studied during an 11-year period. The results yielded a significant relationship between female age and fecundity, with fertility rates lower than expected among young and old females. Analysis of the reproductive history of individual females revealed a significant decline in fertility from prime age (7–12 years) to mid age (13–19 years), and from mid age to old age (20–25 years). The proportion of long interbirth intervals increased steadily among aging females. Infant survival was not significantly related to maternal age, but offspring of old females showed the highest survivorship. Behavioral observations revealed that old mothers weaned their offspring significantly later than younger mothers, suggesting that prolongation of interbirth intervals is due not only to deteriorating physical condition but also to increased maternal investment, as life history theory predicts. Reproduction ceased during the middle of the third decade of life. Final cessation of estrous cycling invariably occurred 3 or 4 years after the birth of the last offspring, but a postreproductive life span of ≥5 years appears to be common in this population. Available data suggest that reproductive senescence and menopause are more common among nonhuman primates than widely believed and that both traits are part of an adaptive life history strategy.

Predation Risk Affects Mate Choice in a Gobiid Fish

Predation Risk Affects Mate Choice in a Gobiid Fish

"Terminal Investment" and a Sexual Conflict in the Collared Flycatcher (Ficedula albicollis)

When the expectation of future reproduction is reduced by senescence, life-history theory predicts that reproductive effort will increase with increasing age. This idea was examined in the collared flycatcher by estimating whether reproductive costs increase with female age, comparing feeding rates and weight losses of old, "senescent" females (i.e., >=5 yr old) and middle-aged females (2-3 yr old) with the same breeding phenology and the same brood size, and testing whether feeding rate was correlated with daily energy expenditure and with weight loss of females during the nestling period. There was a negative relationship between fledgling production and subsequent survival among old females (>=5 yr old), but not among younger age classes, which suggests that reproductive effort increases with age. Also, old females fed their nestlings more often and lost more weight during the nestling period than did middle-aged females Observed feeding rates were positively correlated with daily energy expenditure and weight loss. Since there was no evidence that individuals that survived to old ages were better at all ages, the results strongly suggest that old collared flycatcher females increase their reproductive effort at the cost of a decreased probability of surviving to the next year. However, the payoff of the increased reproductive effort of old females seemed to be small. We suggest that this is a consequence of a conflict between the sexes over the division of work, because old females generally are mated to younger males that probably have better future prospects. Data on male feeding rates in relation to female feeding rates support this idea.

Measuring performance of airport passenger terminals

Performance of an airport passenger terminal generally has something to do with moving travelers and their bags between aircraft and ground transportation, but airport operators, travelers, airlines, and other users of the terminal have a range of concerns about comfort, convenience, costs, and ambiance that should accompany this movement and will assess performance in terms of such factors. Statistics are available for a few airports and limited periods of time, but there is no comprehensive base of information on how airport terminal buildings operate or the conditions their users experience. Neither is there a generally accepted definition of what is adequate performance. The principal factors comprising a framework for describing performance are presented, focusing primarily on passengers, airlines, and the airport operator. Specific measures that may be used to assess performance within this framework are considered, along with computational tools that might be developed to support more systematic assessment of airport terminal investments and operating strategies.

Reproductive Effort and Terminal Investment in Iteroparous Animals

Though it has been widely predicted that in animals in which reproductive value declines with age, reproductive effort should increase toward the end of the lifespan, analysis of changes in reproductive effort are impeded by fundamental difficulties in measuring the costs of reproduction. Energetic measures may not reflect the effects of breeding on subsequent survival and breeding success, especially in organisms in which body size increases with age, while attempts to estimate reproductive costs directly are complicated by positive correlations between breeding success and parental survival. Though the long-lived birds and mammals are among the most promising organisms on which to test the theory that reproductive effort increases with age, measures of fecundity commonly decline with increasing maternal age. Some recent evidence suggests, however, that offspring survival may improve toward the end of the lifespan.

On the Diffusion of Computer Terminals in an Established Engineering Environment

The introduction of new technologies in existing administrative and technical organizations usually represents a significant investment in equipment and training. A prudent manager will attempt to acquire the equipment needed fast enough to encourage its use while avoiding the inefficiencies of under-utilization. This paper presents a method of applying a mathematical model to the specific problem of predicting the approximate rate at which additional computer terminals should be acquired. The model used is in the form of a “logistics” or “diffusion” function. To apply the model to the Aerospace division of a company, a “calibration” of that organization was required. A questionnaire on the use of hand calculators was submitted to a sample group. At the time of the study, hand calculators had virtually displaced slide rules and desk top adding machines, and about 15 percent of the organization was competing for available terminals of the central computer system. Increased use of terminals and on-line computing was anticipated. The response of the organization to the hand calculator innovation was established by determining a “logistics” or “diffusion” function to fit the sample data. The function was modified to accommodate the additional complexity of the more sophisticated computational capability and then used to predict terminal requirements. This study was undertaken to satisfy a management need to plan for its investment in terminals. At the introduction of an interactive computing system, terminals were requested for individuals or projects. As the number of terminals increased, the number of qualifed users increased faster, and requests for terminals became more numerous. Justifications frequently appeared to be overlapping or duplicative. At this point, a better perspective of the money needed was required, and the study was initiated. The results of the study, together with user requirements data, have been used to expedite the acquisition of terminals.

Natural Selection, the Costs of Reproduction, and a Refinement of Lack's Principle

Natural Selection, the Costs of Reproduction, and a Refinement of Lack's Principle

Aspects of Synchronous Communication Satellites

Abstract : Before 1980, satellites will probably be a wellestablished means for point-to-point communication on earth. A wide variety of passive and active satellite systems are being studied, and some studies are supplemented by experimental programs. The active systems seem more promising because of their larger capacity for a given weight in orbit with a given investment in ground terminals. Of the active systems, that which offers the greatest capacity is the geocentric stabilized station-keeping satellite in a synchronous equatorial orbit. This satellite is in direct line of sight of almost half of the earth's surface. The orbit is unique in that the satellite may have little motion about the line of sight; this may permit the use of large stationary ground antennas, in addition to the directive antennas on the satellite which cover the visible earth. This report concerns the satellite design and payload weight required to provide a given channel capacity. It is oriented toward commercial point-to-point communication, where costs dictate conservative techniques. (Author)