Patterns Of Parental Investment Research Articles

Partitioning of Parental Care in the Leaden Flycatcher

SummaryLeaden Flycatchers Myiagra rubecula are sexually dichromatic spring and summer visitors to south-eastern Australia. Twelve pairs were observed for 661 hours throughout the 1993–94 breeding season. These pairs made repeated nesting attempts, due to a high failure rate (young fledged from only 23% of nests that received eggs). Investment by male and female parents was very similar at all stages of nesting, though females contributed slightly more to incubation (55% of time) and brooding of nestlings (58% of time) and incubated eggs and brooded nestlings overnight. The pattern of parental investment is similar to that shown by the Willie Wagtail Rhipidura leucophrys, a sedentary, sexually monochromatic flycatcher. We suggest that parental investment is so similar between the sexes in these flycatchers because the very low breeding success means that the potential benefits of seeking extra-pair copulations by males will be lower than the benefits of investing in the few nests that reach the later stages of breeding.

Sex ratios and sexual selection in socially monogamous zebra finches

An experiment was performed in which adult sex ratios of zebra finches, Taeniopygyia guttata castanotis, were varied to test possible effects of adult population sex ratios on sexual selection intensity and mating system dynamics in species with biparental care. The possibility that sex ratio influences the success of social mating patterns (leading to polygyny when males are rare and polyandry when females are rare) was not supported. Results did support the prediction of the differential allocation hypothesis that individuals of the abundant sex would increase their relative parental expenditure (PE). Although total (male + female) PE did not vary between treatments, relative male PE was significantly higher in the male-biased treatment (MBT; sex ratio 64% male) than in the female-biased treatment (FBT; sex ratio 36% male). In both treatments, male PE contributions contributed to female reproductive rate. Results also supported the prediction of the differential access hypothesis that individuals of the abundant sex would experience greater intensity of selection on sexually selected attributes. Male beak color, a sexually selected trait, influenced male social parentage in the MBT but not in the FBT. Finally, broods in the FBT displayed higher hatching asynchrony and lower hatching success; we believe this was caused by early onset of incubation, a tactic used as a defense against intraspecific brood parasitism, which was much higher in the FBT. Population sex ratios may be an important factor affecting female ability to influence male parental investment patterns.

Behavioural ecology in managed reserves: gender‐based asymmetries in interspecific dominance in African elephants and rhinos

AbstractAs large‐bodied mammals become restricted to progressively smaller fragments of former habitat, competitive interactions and interspecies aggression are likely to intensify. Data on the outcomes of 159 encounters between endangered African pachyderms revealed that: (1) female elephants (Loxodonta africana) dominated both sexes of black rhinos (Diceros bicornis); and (2) rhino males but not females displaced elephant bulls. The results of an additional 127 interactions involving pachyderms and 12 additional mammals ranging in size from cheetahs (Acinonyx jubatus) to giraffe (Giraffa camelopardalis) indicates that females of either pachyderm deny immediate access to limited resources. Although the evolution of gender‐specific asymmetries in interspecific dominance has received little formal study, it may best be explained by understanding patterns of parental investment; however, from a conservation perspective, one consequence of size‐related dominance is that with continued containment of elephants and rhinos in managed reserves, the most handicapped species are likely to be the smaller ones.

Behavioural ecology in managed reserves: gender-based asymmetries in interspecific dominance in African elephants and rhinos

As large-bodied mammals become restricted to progressively smaller fragments of former habitat, competitive interactions and interspecies aggression are likely to intensify. Data on the outcomes of 159 encounters between endangered African pachyderms revealed that: (1) female elephants (Loxodonta africana) dominated both sexes of black rhinos (Diceros bicornis); and (2) rhino males but not females displaced elephant bulls. The results of an additional 127 interactions involving pachyderms and 12 additional mammals ranging in size from cheetahs (Acinonyx jubatus) to giraffe (Giraffa camelopardalis) indicates that females of either pachyderm deny immediate access to limited resources. Although the evolution of gender-specific asymmetries in interspecific dominance has received little formal study, it may best be explained by understanding patterns of parental investment; however, from a conservation perspective, one consequence of size-related dominance is that with continued containment of elephants and rhinos in managed reserves, the most handicapped species are likely to be the smaller ones.

Unit pricing: Economics and the evolution of litter size

Variability in litter size and the concept of optimality are central to our current understanding of parental investment patterns and life histories. A fundamental component of most models of optimum litter size is an apparently inescapable trade-off between litter size and size of offspring. Most previous models of litter size have focused on the evolution of an optimum litter size rather than variability in litter size. Because variability provides the raw material from which numerous optimal litter sizes are fashioned to meet prevailing conditions, approaches that specifically address adaptive patterns of variability might provide new insights into the evolution of litter size. A model based on a non-linear relationship between total parental effort and litter size reduces trade-offs between offspring size and offspring number to simple reproductive economics, and illustrates how litter size variability might be predictable under certain environmental conditions.

Human Neonatal Cry Quality as an honest signal of fitness

Care soliciting vocalizations are common in the young of many bird and mammal species. As parents are expected to assess individual offspring's potential contributions to parental fitness when partitioning resources between young, I propose that offspring solicitation displays are evolved demonstrations of phenotypic quality with which offspring compete with current and future siblings for access to parental resources. This hypothesis should apply to human neonatal crying as well as offspring solicitation in other species. In this review of the scientific literature, I test three predictions derived from this hypothesis: (1) that crying is relatively more costly for low phenotypic quality infants than infants of higher phenotypic quality; (2) that the acoustic structure of cries correlates with infant condition; and (3) that the aspects of cry structure that trigger parental emotions likely to affect investment behaviors will be those that communicate offspring condition. All predictions were supported. Acoustic characteristics tied to the neurophysiological production of cries (particularly fundamental frequency, or pitch) constitute a reliable signal of infant phenotypic quality. I conclude that in addition to asserting need, an evolved function of the human neonatal cry is to communicate phenotypic quality (and hence, likely contributions to parental fitness) to parents. The study of offspring solicitation vocalizations may contribute importantly to our understanding of animal communication systems, patterns of parental investment, and the etiology of human child abuse.

Trivers-willard rules for sex allocation

We present a quantitative model of sex allocation to investigate whether the simple "rules of thumb" suggested by Trivers and Willard (1973) would really maximize numbers of grandchildren in human populations. Using demographic data from the !Kung of southern Africa and the basic assumptions of the Trivers-Willard hypothesis, we calculate expected numbers of grandchildren based on age- and sex-specific reproductive value. Patterns of parental investment that would maximize numbers of expected grandchildren often differ from the Trivers-Willard rules. In particular, the optimum parental behavior is sensitive to population dynamics, type of parental investment, and, most important, relative ages of sons and daughters. It is doubtful whether a parent blindly following the simple Trivers-Willard rules would maximize numbers of expected grandchildren, on average. In addition, we show that sex-specific infanticide will almost never achieve the goal of maximizing expected numbers of grandchildren.

Breeding territoriality and pair formation in the convict cichlid (Cichlasoma nigrofasciatum; Pisces, Cichlidae)

In many biparental species a sex difference in parental investment in a brood before fertilization, such as establishing a breeding territory or preparing a nest, may be an important component of the overall pattern of parental investment. Prefertilization investment patterns have been described for several species of biparental cichlid fishes, but there are discrepancies in the descriptions for the convict cichlid, Cichlasoma nigrofasciatum. This study describes quantitatively the prespawning behaviour of male and female convict cichlids and examines the influence on their behaviour of limiting the number of available spawning sites. The results indicate that pair formation begins several days before spawning when the female begins to follow a male and chase other females away from him. The pair then begins to spend more time in a smaller area where spawning eventually occurs. The breeding territory is usually established by the pair on the day of spawning. There was little difference in the pattern of prespawning behaviour offish with abundant versus limited spawning sites. It appears that neither sex will establish a territory until the female is ready to spawn and the pair has formed.

Comparison of parental behavior in male and female prairie voles (Microtus ochrogaster)

A comparison of male and female parental investment patterns is needed before predictions can be generated from parental investment theory. One aspect of parental investment is parental care, therefore behavioral observations were conducted to compare the parental behavior of male and female prairie voles. Females brooded pups more frequently than did males during the first week of pup life and, in the absence of their mates in the nest, brooded pups more frequently throughout the preseparation period (between birth and separation from parents on day 20). Females also licked pups more frequently than did males during the entire preseparation period. Conversely, males spent more time outside the nest throughout the preseparation period. There were no differences between the sexes in the proportion of time spent in indirect parental behaviors such as nest building, food caching, or runway maintenance. These differences in direct parental care combined with a female's energetic investment in gestation and lactation result in greater total parental investment for female than for male prairie voles.

Sex-Biased Parent-Offspring Conflict

AbstractIn species showing sexual dimorphism, parents may obtain different fitness returns per unit of parental expenditure from sons and daughters. Under these circumstances, parents are expected to invest extra resources in offspring of the most profitable sex. However, it is unclear whether sex-biased expenditure is the result of selection acting on parents, their offspring, or both. Current parent-offspring conflict theory is used to investigate whether sex biases in parental expenditure should be accompanied by sex biases in parent-offspring conflict. It is suggested that, in general, greater conflict should be expected between parents and offspring of the favoured sex. Specifically, greater conflict is predicted among mother-son dyads than among mother-daughter dyads in most polygynous birds and mammals. Data on domestic sheep, as well as empirical evidence available for other species (mainly ungulates), lends support to the prediction. The prediction is further extended to cercopithecine primates, a group which lacks clear sex-biases in parental investment. In this case, differences in fitness returns per unit of parental expenditure between the daughters of dominant and subordinate mothers are positively related to differences in the extent of mother-daughter conflict. The results from this study highlight the important role that selective pressures acting on the offspring phenotype may have played in the evolution of sex-biased patterns of parental investment.

Autocrine control in milk secretion

The mammary gland is controlled at two levels in the body. The genetically controlled pattern of parental investment during lactation is modified by nutritional status and signalled to the mammary gland by the endocrine system (see Peaker 1989). The response to this strategic control of the rate of milk secretion is modulated by a tactical control mechanism operating within each mammary gland. The local intramammary mechanism responds to changes in the frequency or completeness of milk removal and acts to match the rate of milk secretion to the rate of milk removal by the young or, in dairy animals, by the milker. It is the local control of milk secretion by milk removal which has been uncovered in recent years, following the realization of the physiological significance of unilateral effects of frequent milking in goats (Linzell & Peaker 1971) and cows (Morag 1973) that is the subject of this brief review.

The effects of nesting stage, sex, and type of predator on parental defense by killdeer (Charadrius vociferous): testing models of avian parental defense

Two models predicting the temporal patterns of parental investment in offspring defense over the nesting cycle were tested. The first is based on offspring age, the other on the vulnerability of offspring to predation. Both models make very similar predictions for altricial species after eggs have hatched, i.e., increases in intensity of parental defense until fledging. For precocial species, however, the post-hatching predictions of each model are different: the offspring age model predicts a continued increase in defense intensity, while the vulnerability model predicts a decline. I examined the temporal patterns of parental defense of a precocial shorebird, the killdeer (Charadrius vociferus), and determined which model was supported. Killdeer responses to human and natural predators were observed. Killdeer were less willing to leave the nest, responded most intensely, and displayed closest to a potential predator around hatching. Defense intensity increased from early to late incubation as predicted by the offspring age model. However, after hatching killdeer parental defense declined for both males and females, thus supporting the vulnerability model for this stage. Males and females responded significantly differently to all types of predators. Males took greater risks, remained on the nest longer, defended offspring more intensely, and displayed closer to the predator than females at the approach of a potential predator. Responses to natural predators depended on the type of predator and the approach made by the predator; a greater range of defense behavior was used for predators approaching on the ground compared to aerial predators. In general, killdeer responses to humans were more intense and less variable than their responses to natural predators. This was most likely because the human intruder approached nests and chicks more directly and closer than natural predators.

An Analysis of Demographic Tactics in Birds and Mammals

Using field data on fecundity, age at first reproduction and adult life expectancy, we reconsider the so-called r-K gradient by analyzing relationships between these three demographic parameters in 80 mammal species and 114 bird species. After the allometric effect of adult body weight is removed, the three variables remain correlated. The existence of demographic tactics which are independent of adult body weight is demonstrated by multivariate analyses of these variables. These analyses confirm the importance of ecological and phylogenetic constraints. The main structure is a time-scale gradient ranking species according to turn-over, both in birds and mammals. A second gradient ranking species according to iteroparity level appears significantly both in birds and mammals. In mammals, this pattern is related to patterns of parental investment.

Biochemical determination of parental uncertainty in white-fronted bee-eaters

Maternity and paternity uncertainty represent important costs to breeders among white-fronted bee-eaters (Merops bullockoides) in Kenya. Analysis of enzyme polymorphisms reveals that between 9% and 12% of all offspring are genetically unrelated to one or both of their putative parents. These ‘bastards’ are the result of three different sources of parental uncertainty: Extrapair copulation, intraspecific egg parasitism, and quasi-parasitism (parasitism by a female who was fertilized by the male attending the parasitized nest). The first two represent costs to males, who rear offspring that are not genetically their own; the latter two produce the same costs for females. Genetic relatedness plays an important role in defining the social structure of M. bullockoides populations. In order to predict patterns of parental investment and the choice of recipients for helping behavior, one would like to know the relative frequency of maternity vs paternity uncertainty. The possible use of maximum likelihood techniques to separate the sources of non-kin is discussed. Unfortunately, the sample size of detected non-kin in the present study was not large enough to allow constructive use of the technique for bee-eaters. A comparison of estimates from biochemical and behavioral analyses indicates that both methods can produce misleading results. Behavioral data can be used to test underlying assumptions of biochemical analyses, and vice-versa. Used together, the two approaches reinforce one another and strengthen the reliability of conclusions drawn from either one alone.

The Effect of Formalin Fixation on Weight of Lizard Eggs

Central to an understanding of life history and reproductive tactics (Stearns, 1976, 1977; Tinkle, 1969; Tinkle et al., 1970) and patterns of parental investment in animals (Smith and Fretwell, 1974; Brockleman, 1975; Congdon et al., 1978, 1981) is the accurate measurement of relevant reproductive characteristics. Offspring size is one such characteristic. A large number of studies have presented various kinds of data on egg size in reptiles as a relative measure of offspring size. Egg size data for reptiles are generally presented as length by width (often then used to calculate volume), egg wet weight, or egg dry weight. In many instances, wet weights of preserved eggs are presented, with no attendant information regarding time of eggs in fixative, and more importantly, correlations between weights of fixed eggs and fresh eggs. In this study, we demonstrate the effect of formalin (10% solution of 39% formaldehyde) fixation on weights of lizard eggs. The only similar comparison we know of is that of Martin (1978) where it was shown that clutch weight/total body weight ratios of lizards were significantly affected by preservation. Small samples of females of three species of lizards, Cnemidophorus septemvittatus, Sceloporus merriami and Urosaurus ornatus, were collected in or near Big Bend National Park, Brewster Co., Texas during early summer of 1981. Lizards were killed, and oviductal eggs were removed, weighed to 0.001 g, and preserved in 10% formalin, a fixative commonly used for reptiles. At three time intervals, 1 wk, 2 wk, and 24 wk, eggs were removed from fixative and reweighed. After 24 wk in formalin, the eggs were freeze dried (-60?C) to constant weight, and dry weights were taken to 0.0001 g. This allowed approximation of water content as well as dry weight. In all cases, means are presented + one standard error of the mean.

A comparison of the reproductive strategies of three species of Dysdercus from Africa (Hemiptera, Pyrrhocoridae).

Reproductive strategies have been investigated for three species of Dysdercus from Africa, D. intermedius, D. cardinalis and D. nigrofasciatus. Reproductive parameters were measured for each species on individuals cultured in the laboratory. D. cardinalis is associated more with herbaceous than with arboreal host plants and is intermediate in body size. It tended to have the least age at first reproduction, reproduced most frequently, and layed the smallest clutches on average, spreading relatively high amounts of parental investment in more clutches than the other two species. It also laid the greatest number of clutches and eggs in a lifetime. D. intermedius specializes on arboreal host plants, and is the largest of the three species. It had the greatest age at first reproduction, reproduced less frequently than D. cardinalis, and layed the largest clutches. Its parental investment over time declined earlier than that of D. cardinalis. D. intermedius layed the least number of clutches in a lifetime, but its lifetime gross reproduction was intermediate in magnitude. D. nigrofasciatus has the widest diet breadth, and is the smallest in body size. Its age at first reproduction was similar to that of D. cardinalis, but D. nigrofasciatus reproduced least frequently, laying relatively large clutches. It was similar to D. intermedius in its pattern of parental investment over time, and essentially layed the same number of clutches in a lifetime as the latter species, although its lifetime gross reproduction was the smallest.It is suggested that the reproductive strategies of the three species might have evolved as adaptations to selection events in the niches of the immature stages.

An Embryo-Dyeing Technique for Identification Through Hatching

The clutches of many birds tend to hatch synchronously (Lack 1968) and may also hatch at night (pers. observ.). Thus, it is difficult to determine which young hatched from which egg, even with frequent nest visits (e.g., Fiala 1981). The ability to easily assign nestlings to specific eggs would aid in accumulating the large samples that are needed to elucidate the effects of different patterns of parental investment. Precise relationships of egg-laying order, egg size, hatching order and clutch size to hatchling quality (e.g., probability of fledging) could be determined. In this paper we present a method of dyeing embryos while still in the egg, thus permitting such questions to be examined directly.

Patterns of parental care and parental investment in marsupials.

Patterns of parental care and parental investment in marsupials.

SEX RATIO AND PARENTAL INVESTMENT IN AN ANT POPULATION.

Sex ratios and patterns of parental investment of eusocial Hymenoptera have recently been the subject of considerable debate. Trivers and Hare (1976) initiated a controversy by claiming that in monogynous (single queen) ant colonies the workers control the ratio of investment, biasing it towards female reproductives. Their conclusion has been cited by Wilson (1975) and other sociobiologists as evidence that kin selection acting on workers takes precedence over selection for queen control of the sex ratio of parental investment. Trivers and Hare (1976) have been criticized by Alexander and Sherman (1977), who argued that Hamilton's (1967) concept of local mate competition is a better explanation of observed female-biased patterns of investment. However, for monogynous ants little empirical evidence exists for local mate competition, a process whereby reproductive competition acts to devalue the contribution of the competitors to the inclusive fitness of their parents. Theoretical studies by Oster et al. (1977), Benford (1978) and Charnov (1978) have produced predictions supporting Trivers and Hare's (1976) argument that in monogynous colonies the queen will benefit if the sex ratio of investment is 1:1 while workers will benefit if the ratio is biased 3:1 in favor of females. However, Trivers and Hare's (1976) empirical evidence for worker control of the ratio of investment in ants is statistically weak (Alexander and Sherman, 1977). The effects of sample biases on such compilations may be considerable as this report attempts to demonstrate. The purpose of this paper is to report on the effects which queen mortality and production of males by laying workers appear to exert on the sex ratio of investment in queen-right (containing a fertile queen) colonies of the ant Apterostigma dentigerum Mayr (Hymenoptera: Formicidae).

Patterns of parental investment, dispersal and size among coral-reef fishes

Patterns of parental investment, dispersal and size among coral-reef fishes