Predictions Of Evolutionary Theory Research Articles

Pregnancy is linked to faster epigenetic aging in young women

A central prediction of evolutionary theory is that energy invested into reproduction comes at the expense of somatic maintenance and repair, accelerating biological aging. Supporting this prediction are findings that high fertility among women predicts shorter lifespan and poorer health later in life. However, biological aging is thought to begin before age-related health declines, limiting the applicability of morbidity and mortality for studying the aging process earlier in life. Here, we examine the relationship between reproductive history and biological aging in a sample of young (20 to 22yo) men and women from the Cebu Longitudinal Health and Nutrition Survey, located in the Philippines (n = 1,735). We quantify biological aging using six measures, collectively known as epigenetic clocks, reflecting various facets of cellular aging, health, and mortality risk. In a subset of women, we test whether longitudinal changes in gravidity between young and early-middle adulthood (25 to 31yo) are associated with changes in epigenetic aging during that time. Cross-sectionally, gravidity was associated with all six measures of accelerated epigenetic aging in women (n = 825). Furthermore, longitudinal increases in gravidity were linked to accelerated epigenetic aging in two epigenetic clocks (n = 331). In contrast, the number of pregnancies a man reported fathering was not associated with epigenetic aging among same-aged cohort men (n = 910). These effects were robust to socioecological, environmental, and immunological factors, consistent with the hypothesis that pregnancy accelerates biological aging and that these effects can be detected in young women in a high-fertility context.

The correlated evolution of foraging mode and reproductive effort in lizards.

Life-history theory suggests that the optimal reproductive effort of an organism is affected by factors such as energy acquisition and predation risk. The observation that some organisms actively search for their prey and others ambush them creates the expectation of different energy needs and predation risk associated with each foraging behaviour, the so-called 'foraging-mode paradigm'. Although this paradigm has been around for decades, the empirical evidence consists of conflicting results derived from competing models based on different mechanisms. For instance, models within the foraging-mode paradigm suggest that widely foraging females have evolved low reproductive effort, because a heavy reproductive load decreases their ability to escape from predators. By contrast, a long-standing prediction of evolutionary theory indicates that organisms subject to high extrinsic mortality, should invest more in reproduction. Here, we present the first partial evidence that widely foraging species have evolved greater reproductive effort than have sit-and-wait species, which we attribute to a larger body size and greater mortality among mobile foragers. According to our findings, we propose a theoretical model that could explain the observed pattern in lizards, suggesting ways for evolutionary ecologists to test mechanistic hypotheses at the intraspecific level.

The Nuclear Hormone Receptor NHR-40 Acts Downstream of the Sulfatase EUD-1 as Part of a Developmental Plasticity Switch in Pristionchus

Developmental plasticity, the ability of one genotype to produce distinct phenotypes in different environments, has been suggested to facilitate phenotypic diversification, and several examples in plants and animals support its macroevolutionary potential [1-8]. However, little is known about associated molecular mechanisms, because environmental effects on development are difficult to study by laboratory approaches. One promising system is the mouth dimorphism of the nematode Pristionchus pacificus [9-12]. Following an irreversible decision in larval development, these nematodes form moveable teeth that occur in either of two discrete morphs. The "eurystomatous" (Eu) form has a wide mouth and two teeth, allowing predatory feeding on other nematodes. In contrast, the alternative ("stenostomatous"; St) form has diminutive mouthparts that largely constrain its diet to microbes. The sulfatase EUD-1 was previously discovered to execute a polyphenism switch based on dosage of functional alleles [13] and confirmed a prediction of evolutionary theory about how developmental switches control plasticity [1, 3]. However, the genetic context of this single gene, and hence the molecular complexity of switch mechanisms, was previously unknown. Here we use a suppressor screen to identify factors downstream of eud-1 in mouth-form regulation. We isolated three dominant, X-linked mutants in the nuclear hormone receptor gene nhr-40 that are haploinsufficient. Both eud-1 nhr-40 double and nhr-40 single mutants are all Eu, whereas transgenic overexpression of nhr-40 does not restore the wild-type phenotype but instead results in nearly all-St lines. Thus, NHR-40 is part of a developmental switch, suggesting that switch mechanisms controlling plasticity consist of multi-component hormonal signaling systems.

Reputation, a universal currency for human social interactions.

Decision rules of reciprocity include ‘I help those who helped me’ (direct reciprocity) and ‘I help those who have helped others’ (indirect reciprocity), i.e. I help those who have a reputation to care for others. A person's reputation is a score that members of a social group update whenever they see the person interacting or hear at best multiple gossip about the person's social interactions. Reputation is the current standing the person has gained from previous investments or refusal of investments in helping others. Is he a good guy, can I trust him or should I better avoid him as a social partner? A good reputation pays off by attracting help from others, even from strangers or members from another group, if the recipient's reputation is known. Any costly investment in others, i.e. direct help, donations to charity, investment in averting climate change, etc. increases a person's reputation. I shall argue and illustrate with examples that a person's known reputation functions like money that can be used whenever the person needs help. Whenever possible I will present tests of predictions of evolutionary theory, i.e. fitness maximizing strategies, mostly by economic experiments with humans.

Molecular evolution patterns reveal life history features of mycoplasma-related endobacteria associated with arbuscular mycorrhizal fungi.

The mycoplasma-related endobacteria (MRE), representing a recently discovered lineage of Mollicutes, are widely distributed across arbuscular mycorrhizal fungi (AMF, Glomeromycota). AMF colonize roots of most terrestrial plants and improve plant mineral nutrient uptake in return for plant-assimilated carbon. The role of MRE in the biology of their fungal hosts is unknown. To start characterizing this association, we assessed partitioning of MRE genetic diversity within AMF individuals and across the AMF phylogeographic range. We further used molecular evolution patterns to make inferences about MRE codivergence with AMF, their lifestyle and antiquity of the Glomeromycota-MRE association. While we did not detect differentiation between MRE derived from different continents, high levels of diversity were apparent in MRE populations within AMF host individuals. MRE exhibited significant codiversification with AMF over ecological time and the absence of codivergence over evolutionary time. Moreover, genetic recombination was evident in MRE. These patterns indicate that, while MRE transmission is predominantly vertical, their complex intrahost populations are likely generated by horizontal transmission and recombination. Based on predictions of evolutionary theory, we interpreted these observations as a suggestion that MRE may be antagonists of AMF. Finally, we detected a marginally significant signature of codivergence of MRE with Glomeromycota and the Endogone lineage of Mucoromycotina, implying that the symbiosis between MRE and fungi may predate the divergence between these two groups of fungi.

Phenotypic engineering of sperm-production rate confirms evolutionary predictions of sperm competition theory

Sperm production is a key male reproductive trait and an important parameter in sperm competition theory. Under sperm competition, paternity success is predicted to depend strongly on male allocation to sperm production. Furthermore, because sperm production is inherently costly, individuals should economize in sperm expenditure, and conditional adjustment of the copulation frequency according to their sperm availability may be expected. However, experimental studies showing effects of sperm production on mating behaviour and paternity success have so far been scarce, mainly because sperm production is difficult to manipulate directly in animals. Here, we used phenotypic engineering to manipulate sperm-production rate, by employing dose-dependent RNA interference (RNAi) of a spermatogenesis-specific gene, macbol1, in the free-living flatworm Macrostomum lignano. We demonstrate (i) that our novel dose-dependent RNAi approach allows us to induce high variability in sperm-production rate; (ii) that a reduced sperm-production rate is associated with a decreased copulation frequency, suggesting conditional adjustment of mating behaviour; and (iii) that both sperm production and copulation frequency are important determinants of paternity success in a competitive situation, as predicted by sperm competition theory. Our study clearly documents the potential of phenotypic engineering via dose-dependent RNAi to test quantitative predictions of evolutionary theory.

Comparative Demography of an At-Risk African Elephant Population

Knowledge of population processes across various ecological and management settings offers important insights for species conservation and life history. In regard to its ecological role, charisma and threats from human impacts, African elephants are of high conservation concern and, as a result, are the focus of numerous studies across various contexts. Here, demographic data from an individually based study of 934 African elephants in Samburu, Kenya were summarized, providing detailed inspection of the population processes experienced by the population over a fourteen year period (including the repercussions of recent increases in illegal killing). These data were compared with those from populations inhabiting a spectrum of xeric to mesic ecosystems with variable human impacts. In relation to variability in climate and human impacts (causing up to 50% of recorded deaths among adults), annual mortality in Samburu fluctuated between 1 and 14% and, unrelatedly, natality between 2 and 14% driving annual population increases and decreases. Survivorship in Samburu was significantly lower than other populations with age-specific data even during periods of low illegal killing by humans, resulting in relatively low life expectancy of males (18.9 years) and females (21.8 years). Fecundity (primiparous age and inter-calf interval) were similar to those reported in other human impacted or recovering populations, and significantly greater than that of comparable stable populations. This suggests reproductive effort of African savanna elephants increases in relation to increased mortality (and resulting ecological ramifications) as predicted by life history theory. Further comparison across populations indicated that elongated inter-calf intervals and older ages of reproductive onset were related to age structure and density, and likely influenced by ecological conditions. This study provides detailed empirical data on elephant population dynamics strongly influenced by human impacts (laying the foundation for modeling approaches), supporting predictions of evolutionary theory regarding demographic responses to ecological processes.

Sex differences in friendship expectations: A meta-analysis

Friendship expectations are prescriptive normative behaviors and highly valued qualities in ideal same-sex friends. This paper reports the results of five meta-analyses of sex differences from 37 manuscripts (36 samples, N = 8825). A small difference favoring females was detected in overall friendship expectations ( d = .17). Friendship expectations were higher for females in three of four categories: symmetrical reciprocity (e.g., loyalty, genuineness; d = .17), communion (e.g., self-disclosure, intimacy; d = .39), solidarity (e.g., mutual activities, companionship; d = .03), but agency (e.g., physical fitness, status; d = -.34) was higher in males. Overall expectations and symmetrical reciprocity showed small effect sizes. Medium effect sizes for communion favoring females and for agency favoring males support predictions of evolutionary theory.

Adaptive misbeliefs are pervasive, but the case for positive illusions is weak

AbstractIt is a foundational prediction of evolutionary theory that human beliefs accurately approximate reality only insofar as accurate beliefs enhance fitness. Otherwise, adaptive misbeliefs will prevail. Unlike McKay & Dennett (M&D), we think that adaptive belief systems rely heavily upon misbeliefs. However, the case for positive illusions as an example of adaptive misbelief is weak.

How can evolutionary theory accommodate recent empirical results on organismal senescence?

According to a prominent recent report, guppies collected from sites lacking predators are inferior in every aspect of their life history profile to those evolved in other, nearby sites with predators present. This is an exception to two classical predictions of evolutionary theory: that low extrinsic mortality should be associated with longer life span, and that higher fertility should be associated with shorter life span. Some theorists have tried to accommodate this and other anomalous results within the standard framework, but we argue that the exceptions they carve out do not explain the results at hand. In fact, the findings suggest that population regulation has been selected at the group level, though this is a mechanism that most theorists regard with suspicion. We conclude by relating the present result to other experiments that seem to point in the same direction.

Resurrecting the Ghost of Competition Past with Dormant Zooplankton Eggs

A common prediction of evolutionary theory is that the strength of interspecific competition should decline over time among sympatric populations of competing species. Here we provide experimental evidence of historical declines in competition effects among competing zooplankton populations. Using diapausing eggs, we resurrected clones of three species of zooplankton obtained from different periods of community assembly in a single lake. We show that clones of Daphnia ambigua obtained from early in assembly when D. ambigua was dominant became extinct in competition with clones of Daphnia pulicaria and Daphnia dentifera (the current lake dominants). In contrast, D. ambigua clones obtained from later in the lake's history experienced weaker competition effects and persisted with D. dentifera. While we cannot rule out the role of intraspecific competition within D. ambigua, our results are in line with the view that natural selection favors reduced interaction strength among co-occurring species, facilitating coexistence and population persistence.

Resurrecting the Ghost of Competition past with Dormant Zooplankton Eggs

A common prediction of evolutionary theory is that the strength of interspecific competition should decline over time among sympatric populations of competing species. Here we provide experimental evidence of historical declines in competition effects among competing zooplankton populations. Using diapausing eggs, we resurrected clones of three species of zooplankton obtained from different periods of community assembly in a single lake. We show that clones of Daphnia ambigua obtained from early in assembly when D. ambigua was dominant became extinct in competition with clones of Daphnia pulicaria and Daphnia dentifera (the current lake dominants). In contrast, D. ambigua clones obtained from later in the lake’s history experienced weaker competition effects and persisted with D. dentifera. While we cannot rule out the role of intraspecific competition within D. ambigua, our results are in line with the view that natural selection favors reduced interaction strength among co‐occurring species, facilitating coexistence and population persistence.

You don't need a weatherman: famines, evolution, and intervention into aging

Calorie restriction (CR) is the most robust available intervention into biological aging. Efforts are underway to develop pharmaceuticals that would replicate CR's anti-aging effects in humans ("CR mimetics"), on the assumption that the life- and healthspan-extending effects of CR in lower organisms will be proportionally extrapolable to humans (the "proportionality principle" (PP)). A recent argument from evolutionary theory (the "weather hypothesis" (WH)) suggests that CR (or its mimetics) will only provide 2-3years of extended healthy lifespan in humans. The extension of healthy human lifespan that would be afforded by intervention into aging makes it crucial that resources for therapeutic development be optimally allocated; CR mimetics being the main direction being pursued for interventive biogerontology, this paper evaluates the challenge to the potential efficacy of CR mimetics posed by the WH, on a theoretical level and by reference to the available interspecies data on CR. Rodent data suggest that the anti-aging effects of CR continue to increase in inverse proportion to the degree of energy restriction imposed, well below the level that would be expected to be survivable under the conditions under which the mechanisms of CR evolved and are maintained in the wild. Moreover, the same increase in anti-aging effects continues well below the point at which it interferes with reproductive function. Both of these facts are in accordance with the predictions of evolutionary theory. Granted these facts, the interspecies data-including data available in humans-are consistent with the predictions of PP rather than those of the WH. This suggests that humans will respond to a high degree of CR (or its pharmaceutical simulation) with a proportional deceleration of aging, so that CR mimetics should be as effective in humans as CR itself is in the rodent model. Despite this fact, CR mimetics should not be the focus of biomedical gerontology, as strategies based on the direct targeting of the molecular lesions of aging are likely to lead to more rapidly developable and far more effective anti-aging biomedicines.

Mitochondrial Gene Fragments Suggest Paraphyly of the Genus Panorpa (Mecoptera, Panorpidae)

Life history studies of scorpionfly species have been used to test predictions of evolutionary theory, but comparative analysis has been hampered by a lacking phylogeny of scorpionflies. We present a molecular phylogeny of selected panorpid scorpionflies inferred from mitochondrial 12S, 16S rRNA, and COI gene fragments, using parsimony and maximum-likelihood methods. Maximum-likelihood reconstructions depend on an explicit evolutionary substitution model; therefore, we estimated fit of substitution models to our data and used an optimal evolutionary substitution model in subsequent reconstructions. Both reconstruction methods converge on compatible trees with considerable statistical support for a majority of nodes. We performed parametric tests of most important phylogenetic conclusions employing the fitted GTR + %I + Γ substitution model. Parametric bootstrapping allowed rejection of alternative explanations of the data set, where classical tests, like the KHY test, failed. Parametric bootstrapping confirmed that the association of Neopanorpa sp. with Asian Panorpa species is currently the superior explanation of the data set. Therefore, it is concluded that the genus Panorpa is most likely paraphyletic to the representative of the genus Neopanorpa. We conclude that the sequenced mitochondrial gene fragments appear to be well suited for future more comprehensive phylogenetic investigations of panorpid scorpionflies.

Fertility‐related changes in maternal body composition among the au of Papua New Guinea

Evolutionary theory predicts that organisms make trade-offs between their somatic and reproductive energy budgets. Thus every round of reproduction should result in a concomitant decline in the parents' total energy reserves. Among humans this prediction was corroborated more than 25 years ago when fertility-related nutritional depletion was reported among mothers in the Highlands of New Guinea (Jelliffe and Maddocks, 1964). More recently, however, a number of studies of fertility and maternal nutritional status in both developed and developing nations have reported fertility-related increases in various indices of adiposity and lean body mass. Such findings have called the so-called "maternal depletion syndrome" into question, and have raised serious doubts as to whether the phenomenon is widely generalizable to all populations. In light of this recent controversy, data are presented here on fertility-related changes in maternal adiposity and lean body mass among the Au, a lowland forager-horticulturalist population in Papua New Guinea. While both a short-term decline in adiposity following childbirth, and a long-term fertility-related decline are seen among more traditional Au, individuals with a regular source of wage-income show only the former. There are no significant changes in lean body mass with increasing fertility in either group. The finding of significant socioeconomic variation in the capacity to withstand the stress of repeated reproduction even within this one extremely rural area of Papua New Guinea may lend insight into why previous studies have been unable to find evidence of maternal depletion. The fertility-related decline in adiposity that is reported for the more traditional Au is consistent with the predictions of evolutionary theory.

Gas in globular clusters. I - Time-independent flow models

A search for H..cap alpha.. emission in five globular clusters has yielded upper-limit ionized hydrogen masses within the core radii of M/sub H+/ = 0.1-0.7M/sub sun/. This augments the findings of previous searches for ionized hydrogen (both radio and optical) that clusters are gas deficient with respect to the mass loss predictions of evolutionary theory, if the gas remains in the cluster. Time-independent gas flow models have been constructed for globular clusters of 10/sup 5/ M/sub sun/ and 10/sup 6/ M/sub sun/, with physical assumptions chosen to maximize the predicted gas content. Ionization by electron impact was assumed, and the ionization state of both hydrogen and helium was calculated throughout the flow; the radiative cooling of the gas under these conditions was treated with considerable care. For the 10/sup 5/ M/sub sun/ cluster, steady-state flows were obtained for all gas input energies, ..beta.., down to (2..beta..)/sup 1///sup 2/ = 17 km s/sup -1/, and it seems certain that gas outflow will occur for all plausible stellar mass loss mechanisms. For the 10/sup 6/ M/sub sun/ cluster, radiative cooling prevented gas outflows for input energies less than (2..beta..)/sup 1///sup 2/ < 120 km s/sup -1/, and it appears that red-giant-branch massmore » loss will result in the gradual accumulation of gas.Integrated surface brightness and flux values for the flow models showed no clear conflict with the presently observed upper limits for the 21 cm line, the radio free-free, and H..cap alpha... In the 21 cm line case, however, the observations are on the threshold of the predicted emission for 10/sup 5/ M/sub sun/ cluster flow models with no photoionization and with very low gas ejection energy, and further attempts to detect neutral hydrogen seem well worthwhile. (AIP)« less

Falsifiable Predictions of Evolutionary Theory

Many philosophers have asserted that evolutionary theory is unfalsifiable. In this paper I refute these assertions by detailing some falsifiable predictions of the theory and the evidence used to test them. I then analyze both these predictions and evidence cited to support assertions of unfalsifiability in order to show both what type of predictions are possible and why it has been so difficult to spot them. The conclusion is that the apparent logical peculiarity of evolutionary theory is not a property of evolutionary theory; it is a property of our human-sized perspective on evolutionary theory.