Evolution of Complexity. Molecular Aspects of Preassembly

An extension of neo-Darwinism, termed preassembly, states that genetic material required for many complex traits, such as echolocation, was present long before emergence of the traits. Assembly of genes and gene segments had occurred over protracted time-periods within large libraries of non-coding genes. Epigenetic factors ultimately promoted transfers from noncoding to coding genes, leading to abrupt formation of the trait via de novo genes. This preassembly model explains many observations that to this present day still puzzle biologists: formation of super-complexity in the absence of multiple fossil precursors, as with bat echolocation and flowering plants; major genetic and physical alterations occurring in just a few thousand years, as with housecat evolution; lack of precursors preceding lush periods of species expansion, as in the Cambrian explosion; and evolution of costly traits that exceed their need during evolutionary times, as with human intelligence. What follows in this paper is a mechanism that is not meant to supplant neo-Darwinism; instead, preassembly aims to supplement current ideas when complexity issues leave them struggling.

Predictive evolution of metabolic phenotypes using model-designed selection niches

Traits lacking fitness benefit cannot be directly selected for under Darwinian evolution. Thus, features such as metabolite secretion are currently inaccessible to adaptive laboratory evolution. Here, we utilize environment-dependency of trait correlations to enable Darwinian selection of fitness-neutral or costly traits. We use metabolic models to design selection niches and to identify surrogate traits that are genetically correlated with cell fitness in the selection niche but coupled to the desired trait in the target niche. Adaptive evolution in the selection niche and subsequent return to the target niche is thereby predicted to enhance the desired trait. We experimentally validate the theory by evolving Saccharomyces cerevisiae for increased secretion of aroma compounds in wine fermentation. Genomic, transcriptomic, and proteomic changes in the evolved strains confirmed the predicted flux re-routing to aroma biosynthesis. The use of model-designed selection niches facilitates the predictive evolution of fitness-costly traits for ecological and biotechnological applications.

Long-term Exposure to Predation Threat Can Modulate the Expression of Sexually Selected Traits in Male Guppy (Poecilia reticulata)

The expression of sexual traits can be affected by different environmental factors among which predation may be particularly important life-history traits. This study investigated the effects of predation risk on courtship behavior, growth and sexual color patterns in male guppy (Poecilia reticulata). In the study, juvenile male guppies were randomly assigned to two treatments, namely T1 (predation threat) and T2 (no predation threat). The courtship performances were visually observed and recorded, while color patterns and morphological traits were measured by using the ImageJ software from the captured photos. The courtship behavioral trials revealed that predation threatened males performed significantly lower number of sigmoid displays than those of no-predation group. Further, the predation scared group had significantly shorter standard length, body area and a reduced number and area of orange spots than their counter group. However, the predation threat did not affect significantly the gonopodial thrusts, and black and iridescent color components (spot number and area). The reduction of costly traits (e.g. behavior, color patterns and body size) is common anti-predator response which presumably reduces predation risks. Male guppies are probably using this form of defence in response to the increased predation risk. The overall result suggests that growth and sexually selected trait expression are sensitive to predation risk and thereby aid in our understanding to predict the evolution of phenotypic variation in natural systems.

Pre- and post-copulatory traits working in concert: sexual dichromatism in passerines is associated with sperm morphology

Passerine birds produce costly traits under intense sexual selection, including elaborate sexually dichromatic plumage and sperm morphologies, to compete for fertilizations. Plumage and sperm traits vary markedly among species, but it is unknown if this reflects a trade-off between pre- and post-copulatory investment under strong sexual selection producing negative trait covariance, or variation in the strength of sexual selection among species producing positive covariance. Using phylogenetic regression, we analysed datasets describing plumage and sperm morphological traits for 278 passerine species. We found a significant positive relationship between sperm midpiece length and male plumage elaboration and sexual dichromatism. We did not find a relationship between plumage elaboration and testes mass. Our results do not support a trade-off between plumage and sperm traits, but may be indicative of variance among species in the strength of sexual selection to produce both brightly coloured plumage and costly sperm traits.

Adiposity signals predict vocal effort in Alston's singing mice

Advertisement displays often seem extravagant and expensive, and are thought to depend on the body condition of a signaller. Nevertheless, we know little about how signallers adjust effort based on condition, and few studies find a strong relationship between natural variation in condition and display. To examine the relationship between body condition and signal elaboration more fully, we characterized physiological condition and acoustic displays in a wild rodent with elaborate vocalizations, Alston's singing mouse, Scotinomys teguina . We found two major axes of variation in condition—one defined by short-term fluctuations in caloric nutrients, and a second by longer-term variation in adiposity. Among acoustic parameters, song effort was characterized by high rates of display and longer songs. Song effort was highly correlated with measures of adiposity. We found that leptin was a particularly strong predictor of display effort. Leptin is known to influence investment in other costly traits, such as immune function and reproduction. Plasma hormone levels convey somatic state to a variety of tissues, and may govern trait investment across vertebrates. Such measures offer new insights into how animals translate body condition into behavioural and life-history decisions.

Mobility can promote the evolution of cooperation via emergent self-assortment dynamics

The evolution of costly cooperation, where cooperators pay a personal cost to benefit others, requires that cooperators interact more frequently with other cooperators. This condition, called positive assortment, is known to occur in spatially-structured viscous populations, where individuals typically have low mobility and limited dispersal. However many social organisms across taxa, from cells and bacteria, to birds, fish and ungulates, are mobile, and live in populations with considerable inter-group mixing. In the absence of information regarding others’ traits or conditional strategies, such mixing may inhibit assortment and limit the potential for cooperation to evolve. Here we employ spatially-explicit individual-based evolutionary simulations to incorporate costs and benefits of two coevolving costly traits: cooperative and local cohesive tendencies. We demonstrate that, despite possessing no information about others’ traits or payoffs, mobility (via self-propulsion or environmental forcing) facilitates assortment of cooperators via a dynamically evolving difference in the cohesive tendencies of cooperators and defectors. We show analytically that this assortment can also be viewed in a multilevel selection framework, where selection for cooperation among emergent groups can overcome selection against cooperators within the groups. As a result of these dynamics, we find an oscillatory pattern of cooperation and defection that maintains cooperation even in the absence of well known mechanisms such as kin interactions, reciprocity, local dispersal or conditional strategies that require information on others’ strategies or payoffs. Our results offer insights into differential adhesion based mechanisms for positive assortment and reveal the possibility of cooperative aggregations in dynamic fission-fusion populations.Author SummaryCooperation among animals is ubiquitous. In a cooperative interaction, the cooperator confers a benefit to its partner at a personal cost. How does natural selection favour such a costly behaviour? Classical theories argue that cooperative interactions among genetic relatives, reciprocal cooperators, or among individuals within groups in viscous population structures are necessary to maintain cooperation. However, many organisms are mobile, and live in dynamic (fission-fusion) groups that constantly merge and split. In such populations, the above mechanisms may be inadequate to explain cooperation. Here, we develop a minimal model that explicitly accounts for mobility and cohesion among organisms. We find that mobility can support cooperation via emergent dynamic groups, even in the absence of previously known mechanisms. Our results may offer insights into the evolution of cooperation in animals that live in fission fusion groups, such as birds, fish or mammals, or microbes living in turbulent media, such as in oceans or in the bloodstreams of animal hosts.

Flight behaviour attenuates the trade-off between flight capability and reproduction in a wing polymorphic cricket

Flight-dimorphic insects have been used extensively to study trade-offs between energetically costly traits. Individuals may develop and maintain structures required for flight, or alternatively they may invest in reproduction. Previous experiments have not examined whether flight itself might affect investment into reproduction. As in other Gryllus species, flight-capable individuals of the wing polymorphic cricket, Gryllus texensis , incur an apparent reproductive penalty for being able to fly, expressed as smaller ovaries in females and lower courtship propensity in males, than their flight-incapable counterparts. We find that a short bout of flight eliminates the trade-off. Two days after the flight, the ovaries of flight-capable females were comparable with those of short-winged females. Similarly, flight markedly increased the probability of courtship behaviour. Our results suggest that the impact of the flight–reproduction trade-off described in earlier studies may have been overestimated.

The evolution of aggression: can selection generate variability?

Three models - the war of attrition, the size game and the badges of dominance game - are described, in which natural selection can maintain genetic variability for aggression. The models differ in whether or not the traits that settle contests are costly in contexts other than fighting, and also in whether signals are used. It is concluded that contests will be settled by non-costly traits only if the value of the contested resource is small relative to the cost of fighting, and that ‘honest’ signalling of aggressiveness is stable only if individuals giving signals that are inconsistent with their behaviour suffer costs. The literature on ‘badges of dominance’ in birds is reviewed. New data on great tits, greenfinches and corn buntings show that there is plumage variability within age and sex that sometimes serves to settle contests, and that, in the first two species but not the third, the badges are uncorrelated with size, and settle contests only over trivial resources.