Parental Care Strategies Research Articles

Reproductive consequences for males of paternal vs territorial strategies in the polygynous spotless starling under variable ecological

Abstract The males' trade-off between caring for the offspring or investing in attracting additional mates is well established in the theory of mating systems. The reproductive consequences for males of alternative strategies adopted by them in response to these conflicting demands should depend on several ecological and social factors that may strongly vary among years. This variation, however, has been rarely addressed in field studies despite it being essential to understand the evolution of parental care in facultatively polygynous species. In the present paper, we examine the reproductive consequences of paternal vs. territorial strategies in the polygynous spotless starling (Sturnus unicolor) during four consecutive breeding seasons (1996-1999) in which the number of male defending nest boxes and several population variables such as nestling starvation rates, nest predation rates and fledgling production varied markedly. In 1996 we manipulated the propensity of males to feed their offspring by means of androgens and antiadrogens, and examined the consequences of male behaviour on reproductive success during the subsequent four breeding seasons. Males implanted in1996 with the antiandrogen cyproterone acetate (Cy-males) fed more frequently than males implanted with testosterone (T-males) or control males (C-males) both during the season in which they were implanted and in the next season. The number of nest boxes defended influenced total breeding success mainly in the years when male feeding frequency was less important for breeding success per nest. A lower proportion of Cy-males than T- or C-males still held at least a nest box in 1999, three years after they were implanted. As a result, the number of fledglings produced over the four years studied was smaller for Cy-males than for T- or C-males. These results suggest that the oscillating selective forces acting on breeding male starlings seem to operate more frequently against the development of parental care strategies, while the polygynous strategy seems to be favoured under a wide array of ecological conditions. Although increased density of potential breeders may constrain territorial expansion and polygyny, the high cost of losing a minimum breeding site may select for the maintenance of aggressive behaviour and low parental investment.

APPLICATIONS AND SEXUAL VERSION OF A SIMPLE MODEL FOR BIOLOGICAL AGING

We use a simple model for biological aging to study the mortality of the population, obtaining a good agreement with the Gompertz law. We also simulate the same model on a square lattice, considering different strategies of parental care. The results are in agreement with those obtained earlier with the more complicated Penna model for biological aging. Finally, we present the sexual version of this simple model.

Effects of Supplemental Food on Parental-Care Strategies and Juvenile Survival of Northern Goshawks

Abstract Using food supplementation, we tested whether food limits juvenile survival in a population of Northern Goshawks (Accipiter gentilis) in northeastern Utah. The influence of additional food on female nest attendance also was investigated because those strategies may influence predation mortality rates of juveniles. We provided supplemental food near 13 nests from close to hatching until close to independence during the 1996 and 1997 breeding seasons. Thirteen additional nests served as controls and received no supplemental food. We compared the following variables at treatment and control nests: (1) adult female mass, (2) nestling mass and size, (3) female nest attendance, and (4) juvenile survival. Following supplemental feeding, adult females from treatment nests were heavier than their control counterparts, and remained closer to the nest during the latter part of the nestling period and throughout the postfledging period. Nestlings from supplemented nests were significantly heavier than those from unsupplemented nests, but results for size measurements were equivocal. Survival rates for treatment nestlings were significantly higher than controls in 1997, but not in 1996. Those results support the hypothesis that food does not limit avian reproductive success on an annual basis. Most deaths in 1997 were the result of starvation or sibling competition. That observation, and the fact that fed nestlings were heavier, is consistent with the idea that treatment nestlings were in improved nutritional condition. Overall patterns of mass and nest-attendance for adult female goshawks supports the hypothesis that female condition and behavior are adjusted in response to food supplies. However, it is less clear what role the females' presence in the nest stand plays in mediating juvenile deaths, because we did not document predation as a primary mortality factor during the two years of this study. The apparent flexibility in female nest attendance behavior suggests that such plasticity may be an adaptation to lower the risk of predation.

Effects of Supplemental Food on Parental-Care Strategies and Juvenile Survival of Northern Goshawks

Effects of Supplemental Food on Parental-Care Strategies and Juvenile Survival of Northern Goshawks

Consequences of parental care on population dynamics

We review the results obtained using the Penna model for biological ageing (T.J.P. Penna, J. Stat. Phys. 78 (1995) 1629) when different strategies of parental care are introduced into evolving populations. These results concern to: longevity of semelparous populations; self-organization of female menopause; the spatial distribution of the populations and finally, sexual fidelity.

Parental and predatory behaviour of Scytodes sp., an araneophagic spitting spider (Araneae: Scytodidae) from the Philippines

AbstractParental care, especially as it relates to our understanding of sociality, is a topic that has received considerable recent attention in research on spiders (Aviles, 1997). Predatory strategies, including foraging decisions, prey preferences and predatory versatility, have also been emphasized in the recent literature. The present paper is concerned with both of these areas, parental care and predatory strategies. Scytodes sp. indet. is a versatile predator that captures prey either in its web or away from webs, and prey capture may be either by ambush or by active pursuit regardless of whether in the presence and absence of webs. The web is a sparsely woven sheet across a concave upper leaf surface, with a three‐dimensional tubular nest linked to the sheet via a small opening. Leaves may be green and living or brown and dead. In the field, a wide range of insects and spiders is taken, but jumping spiders (Salticidae) are the dominant prey. Predatory attacks are by spitting, with large prey being spat at repeatedly before being subdued. After spitting, the scytodid wraps prey in silk before feeding. Eggs are enclosed in a silk egg sac. The female uses her chelicerae to hold her eggs until hatching. After hatching, there is an extended mother–offspring association, with juveniles tending to remain in their mother's web until after the third moult. Females take prey to their juveniles and either feed alongside the juveniles or leave the juveniles to feed alone.

Orange-Tufted Sunbirds Do Not Feed Nectar to Their Chicks

In most bird species, parents eat the same types of food that they deliver to their nestlings (Ydenberg 1994). Many frugivorous and granivorous species supplement chick diets with arthropod prey that contains essential nutrients such as proteins (Gill 1990), but parents may also eat this food themselves. Several studies have shown that single-prey-loading parents selectively transport large prey to their nestlings and eat smaller prey themselves (Carlson 1985, Krebs and Avery 1985, Sonerud 1989). This may lead to different ranges of prey types being consumed by parents and chicks, but rarely does it lead to exclusive food types for parents versus chicks. Adult Orange-tufted Sunbirds (Nectarinia osea; body mass 6 to 7 g) feed on flower nectar and arthropods, but all observed cases of parental provisioning appear to involve only arthropod prey (Markman et al. 1995, 1996). Therefore, we hypothesized that adult Orange-tufted Sunbirds would feed on flower nectar but would not feed it to their chicks. If so, this would provide us with an experimental tool to manipulate parental self feeding independent of chick feeding and enable us to address questions pertaining to the evolution of parental-care strategies (e.g. Kacelnik and Cuthill 1990, Martins and Wright 1993, Ydenberg 1994). We tested our hypothesis using free-living sunbirds at Sede Boqer in the Negev Desert, Israel, by placing artificial nectar sources in the territories of breeding pairs and using a food dye marker to see whether the young received this nectar from their parents. Methods and results.-In the first experiment, we addressed the question of whether parent sunbirds feed sugar solution to their chicks. We used feeders filled with a 0.25-mol sucrose solution colored red with 0.004 g of food coloring (Maimon Spicesf') per g of water. In a pilot study, we found this to be the highest dye concentration that the parent birds would accept and drink in the same quantities as a clear sugar solution. In order to encourage unbiased use, feeders were covered with brown paper bags, a red artificial flower was stuck in the feeder opening, and a perch was provided in front of each feeder. Each feeder was suspended from a tree 5 m from the nest to enable an observer to watch the nest and the feeder simulta-

Evolution of parental care inPhodopus: Conflict between adaptations for survival and adaptations for rapid reproduction

SYNOPSIS. Two species of dwarf hamsters are used to develop a model of the proximate and ultimate selective forces leading to the evolution of parental care strategies. One species, Phodopus campbelli , has been studied extensively as a socially monogamous, biparental species; the other, P. sungorus , rears its young withoutmale assistance. The cold, arid habitat occupied by both species has selected for shape, insulation, and physiology that provide tolerance of extremely cold ambient temperatures and enhance survival when water availability is limited. At the same time, the small body size and highly seasonal environment have selected for rapid maturation and the most compressed reproductive cycle known in a mammal. Rapid reproduction increases water demands for milk production and further stresses water balance because maternal hyperthermia demands increased evaporative heat loss. Thus, in Phodopus habitat, rapid reproduction requires heat tolerance and water availability, which conflict with adaptations for survival. In the habitat of P. sungorus , predictable rains allow a breeding season and females rear litters alone. In P. campbelli , water availability is insufficient for solitary reproduction. Instead, male presence alleviates thermoregulatory, and thus water balance, stresses on the female. The result is improved pup survival and growth. Therefore, an ‘ultimate’ reason for biparental care in P. campbelli is its harsh environment, and a ‘proximate’ reason is a need to reduce maternal water demand. Results confirm that independent physiological constraints, in addition to constraints on energy or time investment, can be essential selective pressures in the evolution of mammalian social organization and behavior.

Relative reproductive success of female moorhens using conditional strategies of brood parasitism and parental care

In a population of moorhens (GaOinula chloropus), at least 27% of netting females laid one or more eggs in a neighbor's nest Females laid parasitically under three conditions: 56% of parasitic eggs were from nesting females that preceded laying a dutch in their own nest by a parasitic laying bout, 19% were from females whose nests were depredated before clutch completion and that laid the following egg parasiticaDy, and 25% were from a small number of females without territories, non-nesting parasites, that each laid a series of parasitic eggs. Clutch sizes varied greatly between females, but nesting females each laid a consistent clutch size both within and between seasons for a given mate and territory. Nesting females that employed a dual strategy of brood parasitism and parental care produced extra eggs that they laid in the nests of neighbors before laying a dutch in their own nests. Two out of ten females whose dutches I experimentally removed during the laying period were successfully induced to lay their next egg in the nest of a neighbor. Nesting females that laid parasitically selected their hosts opportunistically from among the nests dosest to their territories. An experiment in which parasitic eggs were removed and hosts left to rear only their own young showed that parasites did not choose hosts that were better parents than pairs with contemporary nests that were not parasitized. Females that only laid parasiticaDy within a given season timed their parasitic laying bouts poorly and achieved no reproductive success. Parasitic young rarely fledged, and the mean seasonal reproductive success of nesting brood parasites did not differ from that of nonparasitic females. However, the variance in reproductive success of nesting brood parasites was significantly higher than that of nonparasitic females.

An Evolutionary Model of Parental Care in St. Peter's Fish

Galilee St. Peter's fish shows unusual lability in caring patterns; male-only, female-only and biparental care all occur in the same population. We present a game-theoretical model and investigate the evolutionary stability of the care frequencies observed. Using mean values for each of the model's parameters (estimated previously for the Lake Kinneret population of St. Peter's fish) we find that the current care frequencies are unstable and male-only care is the only evolutionarily stable parental care strategy. However, two key model parameters have significant dispersions: the operational sex ratio (OSR) varies both temporally and spatially, and the advantage of biparental care relative to uniparental care depends critically on clutch size, which can vary dramatically. Within the full ranges of observed OSRs and clutch sizes, there are regions in which each of male-only, female-only and biparental care is an evolutionary stable strategy; there is also a region where no evolutionarily stable strategy exists. Thus natural variations in OSR and clutch size may account for the observed care frequencies.

Parental-care strategies among muskrats in a female-biased population

In mammals, parental care is primarily maternal, male participation being influenced by access to mates. We studied parental behaviours of muskrats (Ondatra zibethicus) in a female-biased free-ranging population over two breeding seasons, with the objective of assessing the plasticity of parental care under differing mating strategies (monogamy versus polygyny). Weaned juveniles received predominantly paternal rather than maternal care, and the care provided was both direct (i.e., food harvesting) and indirect (i.e., burrow maintenance). Parental care appeared to be affected by the multiple mating opportunities available to some males. Polygynous males provided less parental care, presumably because they devoted extra time to pursuing a multiple-mating strategy. However, polygynous males provided care only to the offspring of their first mate (i.e., a mixed reproductive strategy). Females that were secondary mates of polygynous males appeared to compensate for the lack of male assistance by increasing their level of parental care compared with primary females. These results support the view that monogamy constitutes the fundamental social system in muskrats.

Successful surf-riding on size spectra: the secret of survival in the sea

All ecosystems require constituent species to survive against a backcloth of biotic and abiotic scenery. How this scenery shapes the life-history strategies of the players and how they in turn shape the scenery are important themes of the play of life. Species surviving in temperate and Arctic shelf seas do so against a scenery dominated by seasonal changes in the size-spectrum of other players. Successful survival in such an environment requires species to ride the big wave of annual productivity as it rolls through the extended size spectrum from phytoplankton to large fish. This wave flattens and broadens as it moves towards higher sizes. We speculate that in a seasonal shelf seas environment the wave shape is such that the Sheldon-Sutcliffe spectrum of equal biomass per log size interval is approximately true as an annual average although it may not be true at any particular moment in the year. Such spectra are structured by biomass being moved up the size spectrum mainly by predation processes, with growth of individuals being a second order process. However, the problem for an individual is to grow up through a size spectrum from its size at birth to its size at reproduction. Hence species need to find survival paths through the fluctuating scenery. This scenery is composed of the biomass of the prey, that of animals of a similar size, and larger predators. The paths followed dictate the life-history strategies of the species. This central problem for sea dwellers in temperate and Arctic shelf seas generates a broad similarity in the choice of life-history strategy for many key players over quite wide geographic areas of the globe. In these seas, strategies of high fecundity, high mortality and high growth rate are particularly common while strategies of low fecundity and parental care are rare for much of the size range. These seas also seem to favour longer trophic chains than terrestrial systems and either several generations per year or multiannual life cycles rather than annual cycles.

Effect of restricted grazing area on the normal behaviour of horses

Individual recognition in gregarious species is fundamental in order to avoid misdirected parental investment. In ungulates, two very different parental care strategies have been identified: ‘hider’ offspring usually lie concealed in vegetation whereas offspring of ‘follower’ species remain with their mothers while they forage. These two strategies have been suggested to impact on mother–offspring vocal recognition, with unidirectional recognition of the mother by offspring occurring in hiders and bidirectional recognition in followers. In domestic cattle, Bos taurus, a facultative hider species, vocal communication and recognition have not been studied in detail under free-ranging conditions, where cows and calves can graze freely and where hiding behaviour can occur. We hypothesized that, as a hider species, cattle under these circumstances would display unidirectional vocal recognition. To test this hypothesis, we conducted playback experiments using mother–offspring contact calls. We found that cows were more likely to respond, by moving their ears and/or looking, turning or walking towards the loudspeaker, to calls of their own calves than to calls from other calves. Similarly, calves responded more rapidly, and were more likely to move their ears and/or look, turn or walk towards the loudspeaker, and to call back and/or meet their mothers, in response to calls from their own mothers than to calls from other females. Contrary to our predictions, our results suggest that mother–offspring vocal individual recognition is bidirectional in cattle. Additionally, mothers of younger calves tended to respond more strongly to playbacks than mothers of older calves. Therefore, mother responses to calf vocalizations are at least partially influenced by calf age.

Parental response to brood size in a cichlid fish

This paper reports on an experiment designed to investigate whether guarding females of the cichlid Aequidens coeruleopunctatus adjust their parental behaviour in response to changes in brood size. It was found that females were easier to scare away from their broods when threatened, and stayed away for longer, after some of their fry had been removed, and that the reverse occurred when broods were experimentally augmented with foreign fry. Brood size manipulations change the expected benefits of future investment. These results therefore indicate that parental care strategies in A. coeruleopunctatus reflect future prospects for reproductive success rather than past investment.

Phylogenetical Constraints in the Evolution of Parental Care Strategies in Birds

In species with internal fertilization, but without parental care, an evolution of 'maternal care' is fundamentally different from an evolution of 'paternal care'. Maternal care should be a pure EES. Paternal care should always be superimposed on a mixed ESS to stay (or not to stay) and to establish some kind of a pair-bond with the female from copulation until egg-laying. This implies that paternal care is less reliable than maternal care. This could have led to the evolution of female strategies and properties which raise the chances for male care. The above considerations offer a framework for the evolutionary pathways between the various parental care strategies and between their associated mating systems. Both paternal and maternal care might directly evolve towards biparental care. For the evolution from paternal towards biparental care it is more likely, however, that a transitional stage of 'uniparental care' will be passed. That stage is characterized by paternal care in most cases, but by maternal care if the male deserts. It is probable that the biparental care system with similar roles for both sexes evolved along this route. Since such similar role systems are widely distributed among birds, and since monogamous paternal care systems can easily evolve towards all recent mating systems in birds, it is advocated that the evolution of parental care in birds was primarily based on a monogamous paternal care system.

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