The costs and benefits of kin

Human Nature - In this paper data from a Tanzanian horticultural population are used to assess whether mother’s kin network size predicts several measures of children’s health and...     

The costs and benefits of fast living

Growth rates play a fundamental role in many areas of biology (Q. Rev. Biol., 67, 1992, 283; Life History Invariants. Some Explorations of Symmetry in Evolutionary Biology, 1993; Philos. Trans. R. Soc. Lond. B Biol. Sci., 351, 1996, 1341; Plant Strategies, Vegetation Processes, and Ecosystem Properties, 2002; Trends Ecol. Evol., 18, 2003, 471; Q. Rev. Biol., 78, 2003, 23; J. Ecol., 95, 2007, 926.) but the cost and benefits of different growth rates are notoriously difficult to quantify (Q. Rev. Biol., 72, 1997, 149; Funct. Ecol., 17, 2003, 328). This is because (1) growth rate typically declines with size and yet the most widely used growth measure – relative growth rate or RGR (conventionally measured as the log of the ratio of successive sizes divided by the time interval) – is not size-corrected and so confounds growth and size, (2) organisms have access to different amounts of resource and (3) it is essential to allow for the long-term benefits of larger size. Here we experimentally demonstrate delayed costs and benefits of rapid growth in seven plant species using a novel method to calculate size-corrected RGR. In control treatments, fast-growing plants benefited from increased reproduction the following year; however, fast-growing plants subjected to an experimental stress treatment (defoliation) showed strongly reduced survival and reproduction the following year. Importantly, when growth was estimated using the classical RGR measure, no costs or benefits were found. These results support the idea that life-history trade-offs have a dominant role in life-history and ecological theory and that the widespread failure to detect them is partly due to methodological shortcomings.     

Evolution of cooperation with shared costs and benefits

The quest to determine how cooperation evolves can be based on evolutionary game theory, in spite of the fact that evolutionarily stable strategies (ESS) for most non-zero-sum games are not cooperative. We analyse the evolution of cooperation for a family of evolutionary games involving shared costs and benefits with a continuum of strategies from non-cooperation to total cooperation. This cost-benefit game allows the cooperator to share in the benefit of a cooperative act, and the recipient to be burdened with a share of the cooperator's cost. The cost-benefit game encompasses the Prisoner's Dilemma, Snowdrift game and Partial Altruism. The models produce ESS solutions of total cooperation, partial cooperation, non-cooperation and coexistence between cooperation and non-cooperation. Cooperation emerges from an interplay between the nonlinearities in the cost and benefit functions. If benefits increase at a decelerating rate and costs increase at an accelerating rate with the degree of cooperation, then the ESS has an intermediate level of cooperation. The game also exhibits non-ESS points such as unstable minima, convergent-stable minima and unstable maxima. The emergence of cooperative behaviour in this game represents enlightened self-interest, whereas non-cooperative solutions illustrate the Tragedy of the Commons. Games having either a stable maximum or a stable minimum have the property that small changes in the incentive structure (model parameter values) or culture (starting frequencies of strategies) result in correspondingly small changes in the degree of cooperation. Conversely, with unstable maxima or unstable minima, small changes in the incentive structure or culture can result in a switch from non-cooperation to total cooperation (and vice versa). These solutions identify when human or animal societies have the potential for cooperation and whether cooperation is robust or fragile.     

Mating in aphidophagous ladybirds: costs and benefits

Abstract:  Mating costs and benefits were studied in three aphidophagous ladybirds, viz. Cheilomenes sexmaculata , Coccinella septempunctata and Propylea dissecta by subjecting them to different numbers of matings. Longevity, fecundity and percent egg viability were regressed with number of matings to determine the costs and trade-offs, if any. Longevity decreased with increasing number of matings in both C. sexmaculata and P. dissecta indicating a cost of mating. The lack of such a cost in C. septempunctata has been ascribed to spermatophore consumption by females of this ladybird. Both fecundity and percent egg viability increased with increasing number of matings and are probably indicative of the benefits. Short-lived females distributed their reproduction uniformly in their lifetime while long-lived females showed a high burst of reproductive activity followed by a gradual decline. Percent egg viability decreased after the completion of the requisite number of matings.     

Direct benefits and costs for hybridizing Ficedula flycatchers

It is well understood that females may gain direct benefits from breeding with attractive males. However, the direct fitness effects of mate-choice are rarely considered with respect to mating between different species (hybridization), a field dominated by discussion of indirect costs of producing unfit hybrid offspring. Hybridizing females may also gain by the types of direct benefits that are important for intraspecific mate choice, and in addition may have access to certain benefits that are restricted to mating with males of an ecologically diverged sister-taxon. We investigate possible direct benefits and costs female Ficedula flycatchers gain from breeding with a heterospecific male, and demonstrate that hybridizing female collared flycatchers (F. albicollis) breed in territories that do not suffer the seasonal decline in habitat quality experienced by females breeding with conspecifics. We exclude the hypotheses that heterospecific males provide alternative food-types or assume a greater amount of the parental workload. In fact, the diets of the two species (F. albicollis and F. hypoleuca) were highly similar, suggesting possible interspecific competition over food resources in sympatry. We discuss the implications of direct fitness effects of hybridization, and why there has been such a disparity in the attention paid to such benefits and costs with regard to intraspecific and interspecific mate-choice.     

Artificial weaning of calves: benefits and costs

Evidence indicates that allowing beef calves to stay in the maternal herd beyond the age of natural weaning promotes animal welfare and may enhance the cows' natural reproductive potential.     

Fitness costs and benefits of personality disorder traits

Extreme personality traits in humans often have detrimental life consequences, so they have long been supposed to be diseases. However, many other species display personality variants that are maintained due to their fitness advantages; in this case, they are construed as strategies. To examine the fitness costs and benefits of pathological personality traits in humans, we measured features of the A (socially odd, distrustful), B (incentive-seeking, selfish) and C (fearful, inhibited) clusters with the Personality Diagnostic Questionnaire-4 + (PDQ-4 +) in a sample of 738 outpatients. Fitness relevant parameters like mating success, reproductive output, self preservation, and access to status were assessed with the Life Outcome Questionnaire. No fitness advantages were found for high-A subjects. In contrast, high-B subjects tripled low-B subjects with regard to mating success and had 39% more offspring. Further, high-C subjects outperformed low-C subjects in attaining status and avoiding risks. These findings help explain the commonness of some extreme personality traits in humans, and suggest that they should be seen as evolutionary strategies rather than as diseases.     

Mapping the economic costs and benefits of conservation

Resources for biodiversity conservation are severely limited, requiring strategic investment. Understanding both the economic benefits and costs of conserving ecosystems will help to allocate scarce dollars most efficiently. However, although cost-benefit analyses are common in many areas of policy, they are not typically used in conservation planning. We conducted a spatial evaluation of the costs and benefits of conservation for a landscape in the Atlantic forests of Paraguay. We considered five ecosystem services (i.e., sustainable bushmeat harvest, sustainable timber harvest, bioprospecting for pharmaceutical products, existence value, and carbon storage in aboveground biomass) and compared them to estimates of the opportunity costs of conservation. We found a high degree of spatial variability in both costs and benefits over this relatively small (~3,000 km²) landscape. Benefits exceeded costs in some areas, with carbon storage dominating the ecosystem service values and swamping opportunity costs. Other benefits associated with conservation were more modest and exceeded costs only in protected areas and indigenous reserves. We used this cost-benefit information to show that one potential corridor between two large forest patches had net benefits that were three times greater than two otherwise similar alternatives. Spatial cost-benefit analysis can powerfully inform conservation planning, even though the availability of relevant data may be limited, as was the case in our study area. It can help us understand the synergies between biodiversity conservation and economic development when the two are indeed aligned and to clearly understand the trade-offs when they are not.     

The costs and benefits of being a chimera

Most multicellular organisms are uniclonal. This is hypothesized to be because uniclonal organisms function better than chimeras (non-clonal organisms), owing to reduced levels of internal genetic conflict. We tested this idea using the social amoeba or slime mold Dictyostelium discoideum. When starving, the normally solitary amoebae aggregate to form a differentiated multicellular slug that migrates towards light and forms a fruiting body, facilitating the dispersal of spores. We added 10(7) amoebae to Petri plates containing 1, 2, 5 or 10 clones mixed together. We found an intrinsic cost to chimerism: chimeric slugs moved significantly less far than uniclonal slugs of the same size. However, in nature, joining with other clones to form a chimera should increase slug size, and larger slugs travel further. We incorporated this size effect into a second experiment by giving chimeras more cells than single clones (single clones had 10(6) cells, two-clone chimeras had 2 x 10(6) cells and so on). The uniclonal treatments then simulated a clone in a mixture that refuses to form chimeras. In this experiment, chimeras moved significantly further than the uniclonal slugs, in spite of the intrinsic cost. Thus, chimerism is costly, which may be why it evolves so seldom, but in D. discoideum the benefits of large size appear to compensate.     

Wives' and husbands' expected costs and benefits of childbearing as predictors of pregnancy.

This paper examines the usefulness of 1-sex and 2-sex utility models of reproductive behavior in predicting births as consequences of wives' and husbands' perceptions of the costs and benefits of another child. We used longitudinal data on a sample of 280 white and 69 black young urban American couples. For whites, the female models proved more useful than the male models. 2-sex models generally predict more variance than do female models. It was shown that the white wife's utility considerations dominate the predictions, with husband as a junior partner and partial redundancy in female and male models. We conclude that neither sex incorporates completely the spouse's utility considerations into its own utility structure. Because some male models are surprisingly strong, researchers cannot omit males without running the risk of excluding an important component of the determinants of fertility.     

Marginal habitats provide unexpected survival benefits to the alpine marmot

Age-specific survival trajectories can vary significantly among wild populations. Identifying the environmental conditions associated with such variability is of primary importance to understand the dynamics of free-ranging populations. In this study, we investigated survival variations among alpine marmot (Marmota marmota) families living in areas with opposite environmental characteristics: the typical habitat of the species (alpine meadow) and a marginal area bordering the forest. We used data collected during an 11-year study in the Gran Paradiso National Park (Italy) and performed a Bayesian survival trajectory analysis on marked individuals. Furthermore, we investigated, at a territorial level, the relationships among demographic parameters and habitat variables by using a path analysis approach. Contrary to our expectations, for most of the marmot's lifespan, survival rate was higher in the marginal site closer to the forest and with lower visibility than in the alpine meadow site. Path analysis indicated that the number of families living close to each other negatively affected the stability of the dominant couple, which in turn affected both juvenile survival and reproduction. Given the lower number of neighboring families which inhabited the marginal site and the potentially different predation pressure by the most effective predator in the area (Aquila chrysaetos), our results suggest that species adapted to live in open habitats may benefit from living in a marginal habitat. This study highlights the importance of habitats bordering the forest in the conservation of alpine marmots.     

Parabiotic ants: the costs and benefits of symbiosis

1. Mutualisms are important drivers of co‐evolution and speciation. However, they typically imply costs for one or both partners. Each partner consequently tries to maximise benefits and minimise costs. Mutualisms can therefore develop towards commensalism or parasitism if one partner fails to provide sufficient benefits. This is particularly likely in diffuse interactions, where multiple species can associate with each other. If costs and benefits of a species vary with the identity of the partner species, this may result in a geographical mosaic of co‐evolution. 2. In the present study, inter‐specific interactions in two parabiotic associations of ants were studied (Hymenoptera: Formicidae). One Crematogaster species was associated with one of two closely related Camponotus species. We assessed cost and benefits by studying behavioural interactions, foraging behaviour, and nest defence in the associations. 3. While parabioses had been shown to be mutualistic, evidence was found for exploitation and aggressive competition between species. In spite of apparent costs of being exploited, we found no benefits for one partner (Crematogaster). The magnitude of potential costs to Crematogaster varied between the two Camponotus species. 4. We conclude that the cost/benefit ratio for Crematogaster varies between the two Camponotus partners, and between environmental conditions. Parabiosis can thus fluctuate between mutualism, commensalism, and parasitism, with Crematogaster being the species that may have higher costs than benefits. 5. We suggest that geneflow in the Crematogaster population hinders local adaptation to the resulting mosaic of locally varying selection pressures. This study demonstrates how diffuse interactions and environmental variation can result in a complex of local selection pressures.