Changes In Life-history Strategies Research Articles

The phenotype of recovery VI: The association between life-history strategies, delay discounting, and maladaptive health and financial behaviors among individuals in recovery from alcohol use disorders.

The life-history theory is a well-established framework that predicts behaviors and explains how and why organisms allocate effort and resources to different life goals. Delay discounting (DD) is associated with risky behaviors and has been suggested as a candidate behavioral marker of addiction. Thus, we investigated the relationship between DD, life-history strategies, and engagement in risky behaviors among individuals in recovery from alcohol use disorder (AUD). Data from 110 individuals in recovery from addiction from The International Quit & Recovery Registry, an ongoing online registry designed to understand recovery phenotype, were included in the analysis. The association between life-history strategies, DD, engagement in risky behaviors, and remission status were assessed. Life-history strategy scores were significantly associated with DD rates and finance, health, and personal development behaviors after controlling for age, sex, race, ethnicity, years of education, marital status, smoking status, and history of other substance use. Remission status was significantly associated with life-history strategy, DD, drug use, fitness, health, and safe driving after controlling for age, sex, race, years of education, marital status, and smoking status. In addition, a mediation analysis using Hayes' methods revealed that the discounting rates partially mediated the association between remission status and life-history strategy scores. Life-history strategies and remission status are both significantly associated with DD and various health and finance behaviors among individuals in recovery from AUD. This finding supports the characterizations of DD as a candidate behavioral marker of addiction that could help differentiate subgroups needing special attention or specific interventions to improve the outcomes of their recovery. Future longitudinal studies are warranted to understand the relationships between changes in life-history strategies, DD, maladaptive health behaviors, and remission status over time.

Persistently warmer temperatures lead to life history changes in bluegill sunfish (Lepomis macrochirus)

Life history strategies shape many aspects of species’ ecological importance and population demographics. For ectotherms, life history strategies are highly dependent on temperature, among other environmental conditions. With projected increases in global temperatures, understanding the success of organisms under warmer conditions is critical. Due to the difficulty of establishing long-term heating studies on whole lake systems, there is little empirical evidence addressing the potential changes in life history strategies of fish in situ in response to future climate warming predictions. Here, we study early growth rates, size-at-maturation, maximum adult size, and lifespan of bluegill sunfish in three lakes in Illinois from 2013 to 2017 that experience above-ambient temperatures year-round due to artificial heating by electrical power plant cooling systems and compare these to populations in three nearby ambient lakes. Temperature changes in the heated lakes are within the range of temperature increases predicted by the year 2100. We find evidence that life history strategies and population demographics are substantially affected by warmer environments. Heated populations showed 22% faster first-year growth, 23% shorter lifespans, greater rates of maturation at small body sizes, and over a 4-fold reduction in the relative number of individuals that reach large sizes. Changes in life history strategies, including lifespan and maximum sizes, will be evident across many fish species under warmer conditions in the future and further research should aim to address how these changes will affect trophic interactions.

Plant populations of three threatened species experience rapid evolution under ex situ cultivation

Many botanic gardens keep ex situ collections of rare species to prevent their extinction and to enable their reintroduction into the wild. A potential problem with ex situ collections is that relaxed selection, genetic drift, novel selection and inbreeding may cause rapid loss of adaptation to natural conditions and therefore may hamper success of reintroductions. Here, we investigated whether cultivation in ex situ collections of three threatened species—Trifolium spadiceum, Sisymbrium austriacum and Bromus grossus—influenced trait differentiation. Using plant material from the original source populations and from the ex situ collections, we compared germination characteristics, growth and phenology under different environmental treatments. Trifolium spadiceum showed reduced seed dormancy in the ex situ collection compared to the wild population, whereas germination temperature requirements changed for S. austriacum. Trifolium spadiceum also showed reduced seed viability in the ex situ collection compared to the wild population. All species showed differences in plant growth between the plants from nature and from the botanic garden. Additionally, B. grossus showed advanced flowering time in plants from the botanic garden. These differences may reflect reduced performance or changes in life-history strategies. We conclude that all three species have rapidly differentiated between wild and ex situ origins and that effects of relaxed selection, genetic drift, inbreeding depression and adaptation to cultivation conditions in the botanic garden may have played a role in population differentiation, which may be unfavourable for reintroduction into nature. To explore this further we suggest broader studies across more species, populations and gardens, involving common garden, reciprocal transplant and molecular studies.

Sex bias in ability to cope with cancer: Tasmanian devils and facial tumour disease.

Knowledge of the ecological dynamics between hosts and pathogens during the initial stages of disease emergence is crucial to understanding the potential for evolution of new interspecific interactions. Tasmanian devil (Sarcophilus harrisii) populations have declined precipitously owing to infection by a transmissible cancer (devil facial tumour disease, DFTD) that emerged approximately 20 years ago. Since the emergence of DFTD, and as the disease spreads across Tasmania, the number of devils has dropped up to 90% across 80% of the species's distributional range. As a result, the disease is expected to act as a strong selective force on hosts to develop mechanisms of tolerance and/or resistance to the infection. We assessed the ability of infected devils to cope with infection, which translates into host tolerance to the cancer, by using the reaction norm of the individual body condition by tumour burden. We found that body condition of infected hosts is negatively affected by cancer progression. Males and females presented significant differences in their tolerance levels to infection, with males suffering declines of up to 25% of their body condition, in contrast to less than 5% in females. Sex-related differences in tolerance to cancer progression may select for changes in life-history strategies of the host and could also alter the selective environment for the tumours.

Butterflies Do Not Alter Conspecific Avoidance in Response to Variation in Density.

High conspecific densities are associated with increased levels of intraspecific competition and a variety of negative effects on performance. However, changes in life history strategy could compensate for some of these effects. For instance, females in crowded conditions often have fewer total offspring, but they may invest more in each one. Such investment could include the production of larger offspring, more time spent engaging in parental care, or more choosy decisions about where offspring are placed. For animals that have a relatively immobile juvenile stage, the costs of competition can be particularly high. Females may be able to avoid such costs by investing more in individual reproductive decisions, rearing young or laying eggs in locations away from other females. We tested the hypothesis that conspecific density cues during juvenile and adult life stages lead to changes in life history strategy, including both reproduction and oviposition choices. We predicted that high-density cues during the larval and adult stages of female Pieris rapae butterflies lead to lower fecundity but higher conspecific avoidance during oviposition, compared to similar low-density cues. We used a 2×2 factorial design to examine the effects of low and high conspecific density during the larval and adult stages of butterflies on avoidance behavior and fecundity. We found that past information about conspecific density did not matter; all butterflies exhibited similar levels of fecundity and a low level of conspecific avoidance during oviposition regardless of their previous experience as larvae and adults. These results suggest that P. rapae females use a fixed, rather than flexible, conspecific avoidance strategy when making oviposition decisions, and past information about conspecific density has no effect on life history and current reproductive investment. We speculate that this may be partially because past conspecific density per se is not a reliable cue for predicting current density and levels of competition, and thus it does not affect the development of life history strategies in this system.

Daphnia magna's sense of competition: intra-specific interactions (ISI) alter life history strategies and increase metals toxicity.

This work investigates whether the scale-up to multi-animal exposures that is commonly applied in genomics studies provides equivalent toxicity outcomes to single-animal experiments of standard Daphnia magna toxicity assays. Specifically, we tested the null hypothesis that intraspecific interactions (ISI) among D. magna have neither effect on the life history strategies of this species, nor impact toxicological outcomes in exposure experiments with Cu and Pb. The results show that ISI significantly increased mortality of D. magna in both Cu and Pb exposure experiments, decreasing 14 day LC50 s and 95 % confidence intervals from 14.5 (10.9–148.3) to 8.4 (8.2–8.7) µg Cu/L and from 232 (156–4810) to 68 (63–73) µg Pb/L. Additionally, ISI potentiated Pb impacts on reproduction eliciting a nearly 10-fold decrease in the no-observed effect concentration (from 236 to 25 µg/L). As an indication of environmental relevance, the effects of ISI on both mortality and reproduction in Pb exposures were sustained at both high and low food rations. Furthermore, even with a single pair of Daphnia, ISI significantly increased (p < 0.05) neonate production in control conditions, demonstrating that ISI can affect life history strategy. Given these results we reject the null hypothesis and conclude that results from scale-up assays cannot be directly applied to observations from single-animal assessments in D. magna. We postulate that D. magna senses chemical signatures of conspecifics which elicits changes in life history strategies that ultimately increase susceptibility to metal toxicity.Electronic supplementary materialThe online version of this article (doi:10.1007/s10646-016-1667-1) contains supplementary material, which is available to authorized users.

Breeding Young as a Survival Strategy during Earth's Greatest Mass Extinction.

Studies of the effects of mass extinctions on ancient ecosystems have focused on changes in taxic diversity, morphological disparity, abundance, behaviour and resource availability as key determinants of group survival. Crucially, the contribution of life history traits to survival during terrestrial mass extinctions has not been investigated, despite the critical role of such traits for population viability. We use bone microstructure and body size data to investigate the palaeoecological implications of changes in life history strategies in the therapsid forerunners of mammals before and after the Permo-Triassic Mass Extinction (PTME), the most catastrophic crisis in Phanerozoic history. Our results are consistent with truncated development, shortened life expectancies, elevated mortality rates and higher extinction risks amongst post-extinction species. Various simulations of ecological dynamics indicate that an earlier onset of reproduction leading to shortened generation times could explain the persistence of therapsids in the unpredictable, resource-limited Early Triassic environments, and help explain observed body size distributions of some disaster taxa (e.g., Lystrosaurus). Our study accounts for differential survival in mammal ancestors after the PTME and provides a methodological framework for quantifying survival strategies in other vertebrates during major biotic crises.

Invader population speeds up life history during colonization

We explore the long-term developments in population biology and life history during the invasion and establishment of the fish species vendace Coregonus albula in a subarctic watercourse by comparing life-history traits and molecular genetic estimates between the source and the colonist population. The two populations exhibited highly contrasting life-history strategies. Relative to the source population, the colonist population was characterized by slower somatic growth rates, earlier sexual maturation at smaller individual size, higher mortality rates and a shorter life span. The two populations could also be significantly discriminated by the genetic markers. Limited founder effects were detected from heterozygote deficit and reduced allelic richness in the colonist population, but both populations were associated with relatively high genetic diversity. The study reveals that the invasion into a new environment induced large changes in life-history strategy, with typical r-selected traits being more prominent in the colonist than in the source population. We discuss the mechanisms that may explain the observed life-history differences between the source and the colonist population, and argue that the accelerated life history of the colonist population represents an adaptive pioneer strategy aimed at fast population increase during colonization and establishment.

Which demographic traits determine population growth in the invasive brown seaweed Sargassum muticum?

Summary 1 Life-history traits commonly associated with plant invasiveness are vegetative reproduction or r-selected traits such as short generation times and high rates of reproduction and individual growth. 2 We used matrix modelling to assess which demographic traits are important for the population growth of an invasive seaweed lacking vegetative reproduction and whether demographic and life-history strategies shift with increased dominance of the invader. The vital rates of one of the most successful invading seaweeds, Sargassum muticum, were investigated monthly for 2 years in intertidal pools dominated by the native brown seaweed Cystoseira humilis and by S. muticum, respectively. In order to speculate about the demographic mechanisms that determine invasiveness of S. muticum, and as the study sites were recently colonized, we assumed that C. humilis and S. muticum pools are proxies for early and late phases of invasion, respectively. 3 Both deterministic and stochastic matrix models showed positive rates of population growth, and rates were significantly higher in the pools dominated by S. muticum than in the ones dominated by C. humilis, indicating demographic changes with invader dominance. The variability of population growth rates and of reproductive and elasticity values of S. muticum was higher in the pools dominated by C. humilis, suggesting invader-driven stabilization of environmental conditions. Generation times of the species increased with invader dominance, supporting invader-stabilized environmental conditions. 4 Elasticity analyses revealed that the most important demographic trait for population growth rate at both levels of invader dominance was the persistence of the non-fertile adult fronds rather than reproduction or growth. No major shifts in the life-history strategy of S. muticum between levels of invader dominance were detected. 5 Synthesis. This study suggests that the invasiveness of S. muticum, a perennial invader without vegetative reproduction, relies on K- rather than r-selected traits and without drastic changes in life-history strategy between phases of invasion.

Echinoderms

Echinoderms

The effects of ecology on life history strategies and metabolic disturbances during development: an example from the African bovids

Life history theory predicts environmental factors to affect changes in life history strategies. However, owing to the interrelationships between body mass and life history variables, it is difficult to discern causal relationships, especially in large-bodied mammals and using a comparative approach. The situation is exacerbated in palaeobiological studies, where many of the variables cannot be observed directly. Specifically, mortality risk has been identified as one of the most important factors determining life history strategies, but its assessment is difficult. This hampers analyses of life history evolution. This study thus explored the possibility to extract previously untapped information from hard tissue, i.e. teeth, which may be useful for life history reconstruction. Histological sections of 25 molars of bovids, representing all subfamilies and spanning a wide range of body masses, were analysed with regard to: (i) molar crown formation times in relation to female body mass and gestation length, and (ii) metabolic disturbances from early to late forming teeth in relation to habitat type occupied, diet consumed and habitual walking style employed. It was found that molar crown formation times in bovids are highly correlated with gestation length once the effects of body mass have been removed. This differs from primates and indicates similarities in pre- and postnatal growth rates in these mammals. Closed-habitat species exhibit relatively fewer disturbances during development than open-country species, but the reverse holds for adult specimens. This accords with what is known about the ecological and behavioural adaptations of the species and is predicted by life history theory. It could thus be confirmed that teeth may provide vital information about life history variables. Exploitation of this information will allow hypotheses to be tested regarding the evolutionary changes in life history strategies of extinct species. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75, 271–279.

Variation in mating system among birds: ecological basis revealed by hierarchical comparative analysis of mate desertion

Since most bird species are socially monogamous, variation among species in social mating systems is determined largely by variation in the frequency of mate desertion. Mate desertion is expected to occur when the benefits, in terms of additional reproductive opportunities, outweigh the costs, in terms of reduced reproductive success from the present brood. However, despite much research, the relative importance of costs and benefits in explaining mating system variation is not well understood. Here, we investigate this problem using a comparative method. We analyse changes in the frequency of mate desertion at different phylogenetic levels. Differences between orders and families in the frequency of desertion are negatively associated with changes in the potential costs of desertion, but are not associated with changes in the potential benefits of desertion. Conversely, differences among genera and species in the frequency of desertion are positively associated with increases in the potential benefits of desertion, but not with changes in the potential costs of desertion. Hence, we suggest that mate desertion in birds originates through a combination of evolutionary predisposition and ecological facilitation. In particular, ancient changes in life-history strategy determine the costs of desertion and predispose certain lineages to polygamy, while contemporary changes in the distribution of resources determine the benefits of desertion and thereby the likelihood that polygamy will be viable within these lineages. Thus, monogamy can arise via two very different evolutionary pathways. Groups such as albatrosses (Procellariidae) are constrained to social monogamy by the high cost to desertion, irrespective of the potential benefits. However, in groups such as the accentors (Prunellidae), which are predisposed to desertion, monogamy occurs only when the benefits of desertion are very limited. These conclusions emphasise the additional power which a hierarchical approach contributes to the modern comparative method.

A Non-Swimming Ascidian Larva: Protostyela longicauda (Styelidae)

The ascidian Protostyela longicauda broods larvae that have a unique, non-locomotory tail. In hatched larvae, the tail is a simple strand of tunic without cellular components or external fins, extremely elongated and anteriorly directed. Before hatching, the tail consists of a mass of secretory cells that release fibrillar material to the tunic. Notochord, neural tube, and muscle cells are absent, but presumptive chordal cells are found at earlier embryonic stages. The anterior part of the trunk bears three conical adhesive papillae and five pairs of ampullae, which elongate at metamorphosis. The tunic of the trunk and tail is sticky from the first moment after hatching and adheres readily to any object; the papillae make contact later. This species attaches to algal fronds in wave-swept, rocky intertidal habitats. Field observations on adult populations revealed a strongly aggregated, philopatric pattern of distribution, as well as within-patch patterns of colonization of some algal species as substrate. Restricted dispersal of short-lived larvae in these communities diminishes the risk of being swept away and is consistent with the aggregated pattern found. We suggest that, upon release of the larva, the sticky tail rapidly becomes entangled with algae, thereby allowing the papillae, oriented at about 30? to the tail, to contact the substrate and achieve permanent fixation. We therefore interpret these non-swimming larvae as facilitating philopatry. Additional key words: tunicate larvae, caudal complex, dispersal, distribution, philopatry Structural and morphological variations in invertebrate larval forms, driven by strong selective pressures, reflect profound differences in the biology of the species-in duration of larval period, in feeding mode, dispersal ability, and mortality-even in taxonomically close groups (reviewed in Giangrande et al. 1994). A vast literature is concerned with debating the adaptive value of diverse larval strategies (reviewed in McEdward 1995). Indeed, major developmental and morphological changes in larval forms may accompany corresponding changes in life-history strategies of the species (Wray 1995). Among ascidians, the typical tadpole larva has a locomotory tail, sensory structures (ocellus, otolith) for orientation, and papillae and ampullae for anchoring. Adult organs are present in a rudimentary state (Cloney & Torrence 1984; Svane & Young 1989). In some species, adult features develop precociously (a phenomenon called adultation by Jeffery & Swalla 1992); in others, the locomotor tail system is enhanced (caudalization, Jeffery & Swalla 1992); and in some a To whom correspondence should be addressed. cases, the free-swimming larval stage is completely suppressed (anural development). In general, larvae of solitary ascidians tend to be simpler than those of colonial species, which more often feature adultation and/or caudalization. While some biologists focus on the developmental mechanisms (Jeffery & Swalla 1990, 1992; Satoh 1994), these phenomena also have life-history consequences. Adultation reduces the interval between hatching and metamorphosis, while caudalization enhances swimming and hence dispersal. For dispersal, the most drastic dichotomy is between urodele and anural modes of development (Bates 1993; Satoh 1994). Anural forms have been reported in some members of the family Molgulidae and in two species of Styelidae (Pelonaia corrugata MILLAR 1954 and Polycarpa tinctor MILLAR 1962). Most anural species are unattached inhabitants of sand-flat substrates, which are far more homogeneous than hard substrates (Berrill 1931, 1975). But some anural species inhabit high-energy habitats, such as shallow subtidal communities along rocky shores, and appear specifically adapted to such environments (Young et al. 1988). Recently, another anural species has also been reported to inhabit rocky, This content downloaded from 157.55.39.58 on Sun, 11 Dec 2016 04:28:38 UTC All use subject to http://about.jstor.org/terms

Causes and Consequences in Human Evolution

Explanations for both the origins of humans and the pattern of human evolution have been diverse, imaginative and often erroneous. The problems associated with both single factor or trigger models and multifactorial models are discussed. It is suggested that in order to explain events in hominid evolution it is necessary to recognize that such events are produced by the interaction of factors acting as conditions, causes (selective pressures), constraints (often phylogenetic) and consequences. Within this framework a number of explanatory strategies are proposed. First, that the pattern of evolution can throw light on process; second, that the relationship between the pattern of hominid evolution and the context in which it occurs can be significant; third, that assessing general models in terms of the feasibility of the detailed biological parameters can be a powerful tool; fourth, that the selective advantages of hominid characteristics should consider both costs and benefits; and fifth, that the consequences of humans having evolved may help us to assess the underlying causes. These strategies lead to the conclusion that the pattern of human evolution is similar to that of other animals in consisting of a series of adaptive radiations. Climate influences hominid evolution, but does not lead to the appearance of new species. The primary effect is through extinction, implying that evolutionary novelty amongst hominids derives from local competitive conditions. The evolution of high levels of encephalization, whatever the proximate selective pressures, was only possible in the context of major changes in life history strategy and foraging behaviour. Finally, when the development of food production is linked to long-term evolutionary patterns, it can be seen that humans have been part of the most significant ecological change for 280 million years.