R. Craig Sargent

MATE DENSITY, PREDATION RISK, AND THE SEASONAL SEQUENCE OF MATE CHOICES: A DYNAMIC GAME

We describe and analyze a computer-simulation model of mate choice, featuring two different quality groups (based on offspring per mating) in each sex. Mating between quality groups results from two-dimensional random encounter and mutual assent, where assent reflects an attempt to maximize expected lifetime reproductive success, E(LRS). Premating predation (via random encounter with predators) and other mortality also influence E(LRS). Given potentially conflicting optimal choices, the model finds the evolutionarily stable patterns of choosiness for the four quality groups. When there are multiple mating episodes by individuals through the season, the resulting dynamic game is solved to obtain a seasonal pattern of mate choice and reproduction. The model generates seven different mating patterns among quality groups. These patterns imply different opportunities for selection, as indicated by the variance components of normalized lifetime reproductive success, var(LRS). The changes in E(LRS), var(LRS), and mating patterns in response to different densities of predators and of potential mates are explored in detail. Decreasing predation risk or increasing mate availability tends to increase E(LRS), choosiness, and assortative mating. Var(LRS) and thus the opportunity for selection for mate quality is highest at intermediate densities of predators and of potential mates. When density remains constant throughout the mating season, choosiness increases late in the season, a time at which less of the potential E(LRS) is jeopardized by the greater predation risk associated with choosiness. Reproductive success of the low-quality group of the less choosy sex is particularly sensitive to changes in density and other parameters. When seasonal density patterns of predators and potential mates are predictable, these low-quality individuals should do better and may thus be more numerous when mate densities are high and predator densities are low, or when predator densities are high and mate densities are low, than for other combinations of relative densities.

Sex and parenting: the effects of sexual conflict and parentage on parental strategies

There is perhaps no more popularized aspect of animal behavior than the things parents do for offspring. Yet our understanding of the evolution of care is only rudimentary, perhaps because parental behavior is one of the most variable behavioral traits we know. Sexual reproduction, particularly in anisogamous species, has a major impact on variable patterns of care. Recent work on conflicts between the sexes over care and the consequences of variable paternity on paternal care has generated fascinating new ideas about the evolutionary forces acting on parenting.

Food access, brood size and filial cannibalism in the fantail darter, Etheostoma flabellare

Abstract We compared the occurrence of filial cannibalism in fed and starved male fantail darters (Etheostoma flabellare). All males in the experiment consumed eggs, and 56% ate all of their eggs. A males initial body condition did not explain the number of eggs that he ate. Neither did non-fed males eat more eggs than fed males. Fed males were able to maintain better body condition during the experiment, but the change in body condition also depended on the number of eggs eaten. Thus, males who ate more eggs were able to maintain better body condition.The most important determinant of whether or not a male ate all of his eggs was his initial egg number. Males with small egg masses ate all of their eggs whereas males with large egg masses were only partial cannibals. There was, however, no difference in the total number of eggs eaten by total and partial cannibals. We conclude that eggs are only partially eaten for energetic reasons. We also suggest that small egg masses are completely consumed because the costs of caring for a small egg mass may exceed the expected reproductive benefits of a small egg mass.

Female fitness declines with increasing female density but not male harassment in the western mosquitofish, Gambusia affinis

Sexual conflict occurs when individuals of one sex express traits that reduce the fitness of individuals of the other sex. In many poeciliid fish, males harass females for copulations, which is thought to reduce female fitness by lowering foraging efficiency and increasing predation risk, energetic expenditure and the likelihood of disease transmission. Mating may also be costly for males, who often engage in aggressive interactions with other males in addition to expending energy pursuing females. We examined the effects of three operational sex ratios on male behaviour, female fitness and male body condition in the western mosquitofish, Gambusia affinis, during a 10-week experiment. Despite a significant reduction in male harassment, female growth and reproductive success decreased as the proportion of females increased. Results suggest that increases in female density had a strong, negative effect on female fitness, overwhelming any potential costs of male harassment. Aggressive behaviour between males increased and male copulation rate decreased as the proportion of males increased, suggesting that operational sex ratio influences the number of copulations that a male attempts by altering the frequency of agonistic interactions with other males and the number of females available to mate. We did not detect a difference in male body condition between treatments. Sources of female density dependence and consequences of variation in operational sex ratio on male fitness are discussed.

Meditation acutely improves psychomotor vigilance, and may decrease sleep need

BackgroundA number of benefits from meditation have been claimed by those who practice various traditions, but few have been well tested in scientifically controlled studies. Among these claims are improved performance and decreased sleep need. Therefore, in these studies we assess whether meditation leads to an immediate performance improvement on a well validated psychomotor vigilance task (PVT), and second, whether longer bouts of meditation may alter sleep need.MethodsThe primary study assessed PVT reaction times before and after 40 minute periods of mediation, nap, or a control activity using a within subject cross-over design.This study utilized novice meditators who were current university students (n = 10). Novice meditators completed 40 minutes of meditation, nap, or control activities on six different days (two separate days for each condition), plus one night of total sleep deprivation on a different night, followed by 40 minutes of meditation.A second study examined sleep times in long term experienced meditators (n = 7) vs. non-meditators (n = 23). Experienced meditators and controls were age and sex matched and living in the Delhi region of India at the time of the study. Both groups continued their normal activities while monitoring their sleep and meditation times.ResultsNovice meditators were tested on the PVT before each activity, 10 minutes after each activity and one hour later. All ten novice meditators improved their PVT reaction times immediately following periods of meditation, and all but one got worse immediately following naps. Sleep deprivation produced a slower baseline reaction time (RT) on the PVT that still improved significantly following a period of meditation. In experiments with long-term experienced meditators, sleep duration was measured using both sleep journals and actigraphy. Sleep duration in these subjects was lower than control non-meditators and general population norms, with no apparent decrements in PVT scores.ConclusionsThese results suggest that meditation provides at least a short-term performance improvement even in novice meditators. In long term meditators, multiple hours spent in meditation are associated with a significant decrease in total sleep time when compared with age and sex matched controls who did not meditate. Whether meditation can actually replace a portion of sleep or pay-off sleep debt is under further investigation.

Reflectance spectra from free-swimming sticklebacks (Gasterosteus): Social context and eye-jaw contrast

Summary The color patterns of many organisms change rapidly with social context but such dynamic signals have been little studied with current methods. In this study we applied objective spectrophotometry techniques to the color displays of unrestrained male threespine sticklebacks, to assess the ine uence of social context on coloration. Analyzing our data with a color space model based on stickleback visual physiology, we found that unrestrained males enhanced saturation of both their blue eye and red jaw color in response to the presence of a mature male or female conspecie c. Divergence between the eye and the jaw lead to enhanced contrast, likely increasing conspicuousness. We found little relationship between measures of color saturation and condition, but the color of males in better condition varied more with social context. This study is the e rst to evaluate contrast between stickleback color pattern elements quantitatively and the e rst in which ree ectance spectra were collected from freeswimming e sh. The methods presented here could be used in future studies of sticklebacks and could potentially be adapted to other animals.

Whence tit-for-tat?

SummaryIn theoretical and empirical studies of the evolution of cooperation, the tit-for-tat strategy (i.e. cooperate unless your partner did not cooperate in the previous interaction) is widely considered to be of central importance. Nevertheless, surprisingly little is known about the conditions in which tit-for-tat appears and disappears across generations in a population of interacting individuals. Here, we apply a newly developed classifier-system model (EvA) in addressing this issue when the key features of interactions are caricatured using the iterated prisoners dilemma game. Our simple representation of behavioural strategies as algorithms composed of two interacting rules allowed us to determine conditions in which tit-for-tat can replace noncooperative strategies and vice versa. Using direct game-theoretic analysis and simulations with the EvA model, we determined that no strategy is evolutionarily stable, but larger population sizes and longer sequences of interactions between individuals can yield transient dominance by tit-for-tat. Genetic drift among behaviourally equivalent strategies is the key mechanism underlying this dominance. Our analysis suggests that tit-for-tat could be important in nature for cognitively simple organisms of limited memory capacity, in strongly kin-selected or group-selected populations, when interaction sequences between individuals are relatively short, in moderate-sized populations of widely interacting individuals and when defectors appear in the population with moderate frequency.