Does nocturnal activity prolong gecko longevity?

The majority of lizard clades are ancestrally and predominantly diurnal. The only major taxon in which most species are nocturnal is the Gekkota (geckos and pygopodids). As ectothermic thermoregulators, lizard metabolic rates are highly temperature dependent, and diurnal lizards therefore demonstrate higher metabolic rates than nocturnal ones. Furthermore, exposure to solar radiation is thought to reduce ectothermic longevity by increasing both metabolic costs and the rate of accumulating harmful mutations through UV radiation (UVC specifically). In being nocturnal, ectothermic species may reduce their intrinsic mortality rates and thus live longer. To test this hypothesis, we collected literature data on the maximum longevities of 740 lizard species, of which 185 are geckos. We examined whether geckos live longer than other lizards, and whether activity time affects gecko longevity. While geckos live relatively long for lizards of their size, their activity time was found to be unrelated to longevity, contradicting our predictions. We suggest that diurnal species may have evolved higher resistance to UV radiation via thicker, more keratinized skin. Elevated metabolic rates do not automatically equate with faster aging. Mortality through extrinsic causes (e.g., predation) may impose much stronger selective pressures than intrinsic causes.

Death and Progress: How Evolvability is Influenced by Intrinsic Mortality

Many factors influence the evolvability of populations, and this article illustrates how intrinsic mortality (death induced through internal factors) in an evolving population contributes favorably to evolvability on a fixed deceptive fitness landscape. We test for evolvability using the hierarchical if-and-only-if (h-iff) function as a deceptive fitness landscape together with a steady state genetic algorithm (SSGA) with a variable mutation rate and indiscriminate intrinsic mortality rate. The mutation rate and the intrinsic mortality rate display a relationship for finding the global maximum. This relationship was also found when implementing the same deceptive fitness landscape in a spatial model consisting of an evolving population. We also compared the performance of the optimal mutation and mortality rate with a state-of-the-art evolutionary algorithm called age-fitness Pareto optimization (AFPO) and show how the two approaches traverse the h-iff landscape differently. Our results indicate that the intrinsic mortality rate and mutation rate induce random genetic drift that allows a population to efficiently traverse a deceptive fitness landscape. This article gives an overview of how intrinsic mortality influences the evolvability of a population. It thereby supports the premise that programmed death of individuals could have a beneficial effect on the evolvability of the entire population.

Perceived extrinsic mortality risk and reported effort in looking after health: Testing a behavioural ecological prediction

Socioeconomic gradients in health behaviour are pervasive and well documented. Yet, there is little consensus on their causes. Behavioural ecological theory predicts that, if people of lower socioeconomic position (SEP) perceive greater personal extrinsic mortality risk than those of higher SEP, they should disinvest in their future health. We surveyed North American adults for reported effort in looking after health, perceived extrinsic and intrinsic mortality risks, and measures of SEP. We examined the relationships between these variables and found that lower subjective SEP predicted lower reported health effort. Lower subjective SEP was also associated with higher perceived extrinsic mortality risk, which in turn predicted lower reported health effort. The effect of subjective SEP on reported health effort was completely mediated by perceived extrinsic mortality risk. Our findings indicate that perceived extrinsic mortality risk may be a key factor underlying SEP gradients in motivation to invest in future health.

Perceived extrinsic mortality risk and reported effort in looking after health: Testing a behavioural ecological prediction

Socioeconomic gradients in health behaviour are pervasive and well documented. Yet, there is little consensus on their causes. Behavioural ecological theory predicts that, if people of lower socioeconomic position (SEP) perceive greater personal extrinsic mortality risk than those of higher SEP, they should disinvest in their future health. We surveyed North American adults for reported effort in looking after health, perceived extrinsic and intrinsic mortality risks, and measures of SEP. We examined the relationships between these variables and found that lower subjective SEP predicted lower reported health effort. Lower subjective SEP was also associated with higher perceived extrinsic mortality risk, which in turn predicted lower reported health effort. The effect of subjective SEP on reported health effort was completely mediated by perceived extrinsic mortality risk. Our findings indicate that perceived extrinsic mortality risk may be a key factor underlying SEP gradients in motivation to invest in future health.

Perceived extrinsic mortality risk and health behaviour: Testing a behavioural ecological model

Purpose: Socioeconomic gradients in health behaviour are pervasive and well documented. Yet, outside the evolutionary literature, there is no consensus on their causes. Our previously presented theoretical behavioural ecological model predicted that people of low socioeconomic position (SEP) should perceive greater personal extrinsic mortality risk than those of higher SEP, leading them to disinvest in their future health. We collected data to test this prediction. Methods: We surveyed North American adults for measures of SEP, effort in looking after health and perceived extrinsic and intrinsic mortality risks. We examined the relationships between SEP, perceived mortality risks and effort in looking after health. We then tested whether the association between SEP and effort in looking after health was mediated by perceived extrinsic mortality risk. Results: SEP was associated with effort in looking after health. Lower SEP was also associated with higher perceived extrinsic mortality risk, which in turn predicted effort in looking after health. The effect of SEP on effort in looking after health was completely mediated by perceived extrinsic mortality risk. Conclusions: Our findings support the predictions of our previously presented theoretical model. They show that SEP gradients in perceptions of extrinsic mortality risk mirror known SEP gradients in actual extrinsic mortality risk. The large effect size for the relationship between perceived extrinsic mortality risk and health effort in our sample indicates that perceived extrinsic mortality risk may be a key predictor of health behaviour.

Empirical Evidence for Various Evolutionary Hypotheses on Species Demonstrating Increasing Mortality with Increasing Chronological Age in the Wild

Many species show a significant increase in mortality with increasing chronological age in the wild. For this phenomenon, three possible general hypotheses are proposed, namely that: (1) it has no adaptive meaning; (2) it has an adaptive meaning; (3) the ancestry is the pivotal determinant. These hypotheses are evaluated according to their consistency with the empirical evidence. In particular, (1) the existence of many species with a constant, or almost constant, mortality rate, especially the so-called “animals with negligible senescence”; (2) the inverse correlation, observed in mammals and birds in the wild, between extrinsic mortality and the proportion of deaths due to intrinsic mortality; (3) the existence of highly sophisticated, genetically determined, and regulated mechanisms that limit and modulate cell duplication capacities and overall cell functionality. On the whole, the hypothesis of an adaptive meaning appears to be consistent with the empirical evidence, while the other two hypotheses hardly appear compatible.

To avoid or eliminate: cestode infections in copepods

The outcome of a parasite infection is the result of the interaction between the host and the parasite. In the system we studied, there are 3 critical stages for the outcome of infection of the (intermediate) host, the copepod Macrocyclops albidus, with the cestode Schistocephalus solidus. During the establishment phase of the parasite, the host may firstly avoid ingesting the parasite and, secondly, may prevent the parasite from entering the body cavity and, thirdly, during the growth phase of the parasite, the host's immune system may eliminate the parasite from the body cavity. We were able to study the growth phase separately from the establishment phase. The establishment phase was influenced by characteristics of the host as well as characteristics of the parasites. Small copepods and males performed poorly; they were more often infected and had a lower survival. Parasites from different sib-groups differed in infectivity. During the growth phase some disappearance of parasites was observed. However, this could not be related to any of the studied characteristics of the host, and the sib-groups of parasites did not seem to differ in their likelihood to disappear. Instead, we suggest that disappearance of parasites, once they have entered the body cavity, may be due to intrinsic mortality of the parasites, independent of the host or the sib-group that the parasites belong to. This indicates that the crucial interactions between host and parasite determining the outcome of infection takes place in the short time-period between ingestion and penetration of the gut-wall.