Low-condition Individuals Research Articles

Ageing desexualizes the Drosophila brain transcriptome.

General evolutionary theory predicts that individuals in low condition should invest less in sexual traits compared to individuals in high condition. Whether this positive association between condition and investment also holds between young (high condition) and senesced (low condition) individuals is however less clear, since elevated investment into reproduction may be beneficial when individuals approach the end of their life. To address how investment into sexual traits changes with age, we study genes with sex-biased expression in the brain, the tissue from which sexual behaviours are directed. Across two distinct populations of Drosophila melanogaster, we find that old brains display fewer sex-biased genes, and that expression of both male-biased and female-biased genes converges towards a sexually intermediate phenotype owing to changes in both sexes with age. We further find that sex-biased genes in general show heightened age-dependent expression in comparison to unbiased genes and that age-related changes in the sexual brain transcriptome are commonly larger in males than females. Our results hence show that ageing causes a desexualization of the fruit fly brain transcriptome and that this change mirrors the general prediction that low condition individuals should invest less in sexual phenotypes.

PARASITIC FAUNA OF MALAPTERURUS ELECTRICUS AND PARACHANNA OBSCURA FROM LEKKI LAGOON, LAGOS, NIGERIA

Host condition factor and gastrointestinal parasites in Malapterurus electricus and Parachanna obscura in Lekki lagoon, Lagos, Nigeria were investigated from September, 2014 to February, 2015. Eighty (80) fishes of Malapterurus electricus and eighty (80) of Parachanna obscura were caught and dissected for intestinal helminth parasites and protozoa. Condition factors of all individuals were determined. Median condition (K < 2.17 and K > 2.17) for Malapterurus electricus, (K < 1.02 and K > 1.02) for Parachanna obscura were used in grouping the individuals. Protozoa infection in the gut includes; myxosporidia and coccidians. Heterogeneous infection of these protozoa in low condition Parachanna obscura were; Myxosporidia, 0.20, Coccidia, 0.10 and high condition individuals, 0.10, 0.15 respectively. There were no coccidian infection in M. electricus, but myxosporidia in low and high condition individuals were 0.15 and 0.10. The rate of infection of Electrotaenia malopteruri, a cestode, specific to M. electricus was higher among high condition individuals, 0.15, compared low condition individuals, 0.10. Procamallanus sp, had the highest prevalence among the high condition individuals of Parachanna obscura, the trend was; High Condition M.electricus (0.10) < Low Condition P.obscura (0.15) < Low Condition M.electricus (0.20) < High Condition P.obscura (0.25). Infected individuals of low condition factor (K < 2.17) of Malapterurus electricus had a greater histopathological alteration index (HAI, 18.0) compared to the high condition individuals (HAI, 8.0). These individuals had from mild to severe ulceration of the mucosa and congestion of the blood vessels. In infected individuals of low condition factor (K < 1.02) of Parachanna obscura, there were mucosal edema and haemorrhage in their intestinal walls. They also had greater histopathological alteration index (HAI, 22.0) compared to the high condition individuals (HAI, 6.0). Prevalence of gastrointestinal parasitic fauna in low condition host could be an indicator of stress in fish

Condition-dependent mortality exacerbates male (but not female) reproductive senescence and the potential for sexual conflict.

Disentangling the relationship between age and reproduction is central to understand life-history evolution, and recent evidence shows that considering condition-dependent mortality is a crucial piece of this puzzle. For example, nonrandom mortality of 'low-condition' individuals can lead to an increase in average lifespan. However, selective disappearance of such low-condition individuals may also affect reproductive senescence at the population level due to trade-offs between physiological functions related to survival/lifespan and the maintenance of reproductive functions. Here, we address the idea that condition-dependent extrinsic mortality (i.e. simulated predation) may increase the age-related decline in male reproductive success and with it the potential for sexual conflict, by comparing reproductive ageing in Drosophila melanogaster male/female cohorts exposed (or not) to condition-dependent simulated predation across time. Although female reproductive senescence was not affected by predation, male reproductive senescence was considerably higher under predation, due mainly to an accelerated decline in offspring viability of 'surviving' males with age. This sex-specific effect suggests that condition-dependent extrinsic mortality can exacerbate survival-reproduction trade-offs in males, which are typically under stronger condition-dependent selection than females. Interestingly, condition-dependent extrinsic mortality did not affect mating success, hinting that accelerated reproductive senescence is due to a decrease in male post-copulatory fitness components. Our results support the recent proposal that male ageing can be an important source of sexual conflict, further suggesting this effect could be exacerbated under more natural conditions.

Condition dependence of advertisement calls in male African clawed frogs

Variations in the costs or benefits of signaling may result in variations in signaling strategies. The adverse conditions hypothesis suggests that reliable signaling can be improved under stress or adverse environmental conditions, but the empirical cases are limited. In the present study, we manipulated food availability in male Xenopus laevis in order to determine whether certain characteristics of advertisement call in X. laevis are condition-dependent and how food depletion modulates the association between individual condition and signaling performance. The results showed that although frogs tend to decrease their within-bout call rate compared to other call characteristics (calling effort and dominant frequency) under food constraint, none of them was statistically significantly affected by food restriction. However, within-bout call rate was positively coupled with adaptive immunocompetence in starved frogs, and the correlation was decoupled in those with free access to food. These results support that within-bout call rate is a condition-dependent characteristic of advertisement call and even mild adverse conditions may enhance reliable signaling in X. laevis, probably due to enlarging the relative fitness difference between high- and low-condition individuals.

Epigenetic paternal effects as costly, condition-dependent traits.

It is now recognized that post-copulatory traits, such as sperm and ejaculate production can impose metabolic costs, and such traits are therefore expected to exhibit condition-dependent expression, whereby, low condition individuals experience a greater marginal cost of investment compared to high condition individuals. Ejaculates are especially costly in species where males invest in offspring quality through nutrient-rich spermatophores or other seminal nuptial gifts. However, recent evidence shows that, in species where males do not provision females or offspring, males can still influence offspring development through paternal effects mediated by epigenetic factors, such as non-coding RNAs, DNA methylation and chromatin structure. Because such epigenetic paternal effects do not involve the transfer of substantial quantities of resources, such as nutrients, the costs of conferring such effects have not been considered. Here we argue that if selection favours paternal investment in offspring quality through epigenetic factors, then the epigenetic machinery required to bring about such effects may also be expected to evolve strongly condition-dependent expression. We outline indirect evidence suggesting that epigenetic paternal effects could impose substantial metabolic costs, consider the conditions under which selection may act on such effects, and suggest ways to test for differential costs and condition-dependence of these effects. Incorporating epigenetic paternal effects into condition-dependent life history theory will further our understanding of the heritability of fitness and the evolution of paternal investment strategies.

Sexual competition and the evolution of condition-dependent ageing

Increased individual resources (condition) can be correlated with either increased or decreased longevity. While variation in resource acquisition and allocation can account for some of this variation, the general conditions that select for either pattern remain unclear. Previous models suggest that nonlinearity of payoffs from investment in reproduction (e.g., male secondary sexual traits) can select for high‐condition individuals that sacrifice longevity to increase reproductive opportunity. However, it remains unclear what mating systems or patterns of sexual competition might select for such life‐history strategies. We used a model of condition‐dependent investment to explore how expected payoffs from increased expression of secondary sexual traits affect optimal investment in lifespan. We find that nonlinearity of these payoffs results in a negative relationship between condition and lifespan under two general conditions: first, when there are accelerating marginal benefits from increasing investment; second, when individuals that invest minimally in secondary sexual trait expression can still achieve matings. In the second scenario, the negative relationship occurs due to selection on low‐condition individuals to extend lifespan at the cost of secondary sexual trait expression. Our findings clarify the potential role of sexual selection in shaping patterns of condition‐dependent ageing, and highlight the importance of considering the strategies of both low‐ and high‐condition individuals when investigating patterns of condition‐dependent ageing.

Temperature effects on life-history trade-offs, germline maintenance and mutation rate under simulated climate warming

Mutation has a fundamental influence over evolutionary processes, but how evolutionary processes shape mutation rate remains less clear. In asexual unicellular organism, increased mutation rates have been observed in stressful environments and the reigning paradigm ascribes this increase to selection for evolvability. However, this explanation does not apply in sexually reproducing species, where little is known about how the environment affects mutation rate. Here we challenged experimental lines of seed beetle, evolved at ancestral temperature or under simulated climate warming, to repair induced mutations at ancestral and stressful temperature. Results show that temperature stress causes individuals to pass on a greater mutation load to their grand-offspring. This suggests that stress-induced mutation rates, in unicellular and multicellular organisms alike, can result from compromised germline DNA repair in low condition individuals. Moreover, lines adapted to simulated climate warming had evolved increased longevity at the cost of reproduction, and this allocation decision improved germline repair. These results suggest that mutation rates can be modulated by resource allocation trade-offs encompassing life-history traits and the germline and have important implications for rates of adaptation and extinction as well as our understanding of genetic diversity in multicellular organisms.

Condition-Dependent Trade-Off Between Weapon Size and Immunity in Males of the European Earwig

Investigating the expression of trade-offs between key life-history functions is central to our understanding of how these functions evolved and are maintained. However, detecting trade-offs can be challenging due to variation in resource availability, which masks trade-offs at the population level. Here, we investigated in the European earwig Forficula auricularia whether (1) weapon size trades off with three key immune parameters – hemocyte concentration, phenoloxidase and prophenoloxidase activity - and whether (2) expression and strength of these trade-offs depend on male body condition (body size) and/or change after an immune challenge. Our results partially confirmed condition dependent trade-offs between weapon size and immunity in male earwigs. Specifically, we found that after an immune challenge, weapon size trades off with hemocyte concentrations in low-condition, but not in good-condition males. Contrastingly, weapon size was independent of pre-challenge hemocyte concentration. We also found no trade-off between weapon size and phenoloxidase activity, independent of body condition and immune challenge. Overall, our study reveals that trade-offs with sexual traits may weaken or disappear in good-condition individuals. Given the importance of weapon size for male reproductive success, our results highlight how low-condition individuals may employ alternative life-history investment strategies to cope with resource limitation.

Host condition, parasite interaction and metal accumulation in Tilapia guineensis from Iddo area of Lagos lagoon, Nigeria

This paper investigates host condition factor, parasite interaction and metal accumulation in Tilapia guineesis and Host-Parasite system in Iddo Area of Lagos Lagoon, Nigeria. Eighty specimens of T. guineensis from the Lagoon were caught and dissected for intestinal helminth parasites. Condition factors of all individuals were determined. Median condition (K 2.62) were used in grouping the individuals. Sediment, water samples, livers and intestinal parasites were analyzed for heavy metals using atomic absorption spectrophotometer. Metal concentrations in the water medium were below detectable limits, but those in sediments were; cadmium (Cd) (mg/l), 11.29±22.59, Manganese (Mn)(mg/l), 0.02±0.02, Iron (Fe) (mg/l), 141.09±15.09, P 2.62) accumulated more metals than the low condition infested individuals (<2.62), but irregular trend was found among the non-infested individuals. Parasite prevalence among infested individual of low condition factor were; Heterostomum sp., a trematode; 0.25, Procamallanus sp., a nematode; 0.75, Acanthogyrus tilapae , an acanthocephalan, 0.05 and Proteocephalanus sp., a cestode was absent. High condition individuals had parasite load; Heterostomum sp.; 0.45, Procamallanus sp., 0.05, Proteocephalanus sp., 0.05 and Acanthogyrus sp.; 0.25. Generally, the host liver accumulated more metals than their parasites except iron among parasites of high condition individuals. Relative abundance and diversity in intestinal parasites with varying metal bioaccumulation potentials in high and low condition individuals could have been responsible for the difference in metal accumulation in their host tissue. Therefore, it is recommended that environmental monitoring studies involving the use of fish could be improved upon by including the macro-parasites, considering the significant effect they could have in the fish biology, behaviour and ecology.

DNA Repair Pathway Choice Is Influenced by the Health of Drosophila melanogaster

In nature, individuals vary tremendously in condition and this may be an important source of variation in mutation rate. Condition is likely to affect cell state and thereby impact the amount of DNA damage sustained and/or the way it is repaired. Here, we focus on DNA repair. If low-condition individuals are less capable of devoting the same level of resources to accurate repair, they may suffer higher mutation rates. However, repair decisions are also governed by various aspects of cell physiology, which may render the prediction that "higher-condition individuals use better repair mechanisms" too simplistic. We use a larval diet manipulation in Drosophila melanogaster to create high- and low-condition individuals and then contrast their relative usage of three repair pathways [homologous recombination (HR), single-strand annealing (SSA), and nonhomologous end joining (NHEJ)] that differ in their mechanistic requirements and their mutational consequences. We find that low-condition flies are more likely than high-condition flies to use the most conservative of these three repair pathways, suggesting that physiological constraints on repair pathway usage may be more important than energetic costs. We also show that the repair differences between high- and low-condition flies resemble those between young and old flies, suggesting the underlying mechanisms may be similar. Finally, we observe that the effect of larval diet on adult repair increases as flies age, indicating that developmental differences early in life can have long-lasting consequences.

An Experimental Test of Condition-Dependent Male and Female Mate Choice in Zebra Finches

In mating systems with social monogamy and obligatory bi-parental care, such as found in many songbird species, male and female fitness depends on the combined parental investment. Hence, both sexes should gain from choosing mates in high rather than low condition. However, theory also predicts that an individual's phenotypic quality can constrain choice, if low condition individuals cannot afford prolonged search efforts and/or face higher risk of rejection. In systems with mutual mate choice, the interaction between male and female condition should thus be a better predictor of choice than either factor in isolation. To address this prediction experimentally, we manipulated male and female condition and subsequently tested male and female mating preferences in zebra finches Taeniopygia guttata, a songbird species with mutual mate choice and obligatory bi-parental care. We experimentally altered phenotypic quality by manipulating the brood size in which the birds were reared. Patterns of association for high- or low-condition individuals of the opposite sex differed for male and female focal birds when tested in an 8-way choice arena. Females showed repeatable condition-assortative preferences for males matching their own rearing background. Male preferences were also repeatable, but not predicted by their own or females' rearing background. In combination with a brief review of the literature on condition-dependent mate choice in the zebra finch we discuss whether the observed sex differences and between-studies differences arise because males and females differ in context sensitivity (e.g. male-male competition suppressing male mating preferences), sampling strategies or susceptibility to rearing conditions (e.g. sex-specific effect on physiology). While a picture emerges that juvenile and current state indeed affect preferences, the development and context-dependency of mutual state-dependent mate choice warrants further study.

Condition Dependence of a Multicomponent Sexual Display Trait in Drosophila serrata

Theory predicts that costly sexual displays should evolve condition dependence if the marginal fitness gain from trait exaggeration is greater for high- than for low-condition individuals and that the strength of condition dependence should increase with the strength of directional selection. While there is substantial support for the first prediction, evidence for the latter is much weaker. We undertook a quantitative test of this prediction for a multivariate sexual display consisting of a suite of contact pheromones termed "cuticular hydrocarbons" (CHCs) in Drosophila serrata. We performed a dietary manipulation of condition (i.e., the pool of metabolic resources available for allocation to fitness-enhancing traits) within a half-sibling breeding design, thereby also providing insight into the genetic basis of condition dependence. As predicted, the linear combination of CHCs under the strongest sexual selection from female mate preferences was unusually condition dependent relative to other CHC combinations within the population ([Formula: see text]). A significant positive correlation also existed between the strengths of condition dependence and sexual selection among different CHC blends ([Formula: see text], [Formula: see text]). Finally, sires varied in their response to the dietary manipulation, demonstrating significant genetic variance in condition dependence. Our results are consistent with the evolution of heightened condition dependence of sexual displays in response to persistent sexual selection.

Increased Transmission of Mutations by Low-Condition Females: Evidence for Condition-Dependent DNA Repair

Evidence is mounting that mutation rates are sufficiently high for deleterious alleles to be a major evolutionary force affecting the evolution of sex, the maintenance of genetic variation, and many other evolutionary phenomena. Though point estimates of mutation rates are improving, we remain largely ignorant of the biological factors affecting these rates at the individual level. Of special importance is the possibility that mutation rates are condition-dependent with low-condition individuals experiencing more mutation. Theory predicts that such condition dependence would dramatically increase the rate at which populations adapt to new environments and the extent to which populations suffer from mutation load. Despite its importance, there has been little study of this phenomenon in multicellular organisms. Here, we examine whether DNA repair processes are condition-dependent in Drosophila melanogaster. In this species, damaged DNA in sperm can be repaired by maternal repair processes after fertilization. We exposed high- and low-condition females to sperm containing damaged DNA and then assessed the frequency of lethal mutations on paternally derived X chromosomes transmitted by these females. The rate of lethal mutations transmitted by low-condition females was 30% greater than that of high-condition females, indicating reduced repair capacity of low-condition females. A separate experiment provided no support for an alternative hypothesis based on sperm selection.

Wandering in male fiddler crabs (Uca tangeri): alternative reproductive tactic or a functional constraint?

AbstractThe 'aggressive wandering' behaviour of male fiddler crabs is well documented in several species and is usually described as an apparently random movement through a population, punctuated by threats and combat directed at displaying males, and superficial burrow explorations. It has been suggested that wandering males are mainly low condition individuals with a regenerating major claw, unsuccessful at attracting mates, wandering through the population seeking surface copulations as an alternative to burrow copulations, which may be considered an alternative reproductive tactic. In order to test this hypothesis we have made several predictions. We observed several focal wandering males, compared sizes of wandering and resource holder individuals, and monitored their abundance across the lunar cycle. We did not observe any surface copulation attempts in any of our focal subjects. The number of burrows explored by wandering males was highly variable and not dependent on the subject's size although larger males do spend more time superficially exploring burrows. Wandering males are significantly larger than burrow-holder males and there was a peak in wandering in the first moon quarter. We conclude that it is important to dissociate wandering from surface copulations and that wandering is not an alternative reproductive tactic for lower condition males. The number of wandering males across the lunar cycle still suggests that wandering may be related to mating and we discuss several ways in which it could be possible.