Individuals In Poor Condition Research Articles

Condition‐Dependent Sex and the Rate of Adaptation

Recent modeling has shown that condition-dependent sex can evolve much more readily than sex that occurs at a uniform rate, even in the face of substantial costs of sex. Specifically, evolution favors genes that cause organisms to allocate more resources to sexual reproduction when they are in poor condition and to asexual reproduction--including increased life span--when they are in good condition. This form of fitness-associated sex (FAS) evolves because modifier genes that promote their own escape from low-fitness genetic backgrounds and that remain longer in high-fitness genetic backgrounds rise in frequency alongside the spread of high-fitness genotypes due to selection. Importantly, FAS does not evolve because it is good for the individual or good for the species but because it is in the selfish interest of modifier genes that promote FAS to move from low- to high-fitness genetic backgrounds. Even though FAS does not evolve for the good of its descendants, we show here that FAS often hastens the rate of adaptation. Ironically, the rate of adaptation is most likely to be accelerated by FAS when sex is costly, because FAS makes it more likely that individuals in poor condition will suffer the costs of sex, improving the efficiency with which less fit alleles are eliminated.

The vicious circle and infection intensity: The case of Trypanosoma microti in field vole populations

ObjectiveIn natural populations, infection and condition may act synergistically to trigger a vicious circle: poor condition predisposes to host infections, which further reduce condition, and so on. If this vicious circle originates from a reduced resistance to infection, it will not only result in greater proneness to becoming infected of those that are in poorer condition, but it may also cause infections of higher intensity. Here, we investigate the temporal relationship between host condition and intensity of infection by a specific pathogen using as a system the dynamics of the protozoan Trypanosoma microti in field vole (Microtus agrestis) populations. Methods and resultsWith two years of longitudinal data from three monthly-sampled populations, we evaluated if individuals acquiring a high intensity of infection previously had lower haematological indicators of condition (red blood cells [RBCs] and lymphocyte counts) than those that acquired lower infection intensities. Also, the association of these indicators with past and present trypanosome blood levels was investigated. The individuals that developed high levels of parasitaemia were those that previously had low lymphocyte counts. Greater intensity of infection corresponded with lower RBCs only in low to moderate weight females, and no effect of intensity of infection on lymphocyte counts was observed. However, delayed effects of high trypanosome intensity were seen on both RBCs and lymphocytes. ConclusionsThe vicious circle may also result in high infection intensity: individuals in poor condition are not only more likely to become infected by one pathogen; they may also be the most important source of infection for that and for other pathogens, and thus key protagonists for parasite dynamics.

Beak colouration as a possible sexual ornament in gentoo penguins: sexual dichromatism and relationship to body condition

Gentoo penguins (Pygoscelis papua) have conspicuous red beak spots, the function of which is currently unknown. We hypothesized that beak spots might be sexual ornaments and investigated sexual dichromatism, assortative mating and the possible relationship between beak spot colouration and body condition. Beak colouration was measured with a portable spectroradiometer in 19 breeding pairs of gentoo penguin. Body mass and body mass relative to structural body size were used as estimates of body condition. We found that beak spots were sexually dichromatic, as they were more UV in males and more violet in females, but males and females did not mate assortatively in relation to beak spot colouration. Body condition was strongly related to red colouration in males, with individuals in good condition having redder beaks and individuals in poor condition more orange beaks. The beaks of males in good condition were also brighter. Body condition was not significantly related to beak spot colouration in females, so females might show red beak spots because of genetic correlation with the male trait. These results suggest that the red colour of the beak spot has the potential to be a secondary sexual character in males. Interpretation of the sexual dichromatism in the UV colour will require further knowledge of the capability of gentoo penguins to discriminate small differences in UV wavelengths. In any case, experimental manipulation of beak colouration will be needed to ascertain the role of this trait.

Condition‐dependent mutation rates and sexual selection

'Good genes' models of sexual selection show that females can gain indirect benefits for their offspring if male ornaments are condition-dependent signals of genetic quality. Recurrent deleterious mutation is viewed as a major contributor to variance in genetic quality, and previous theoretical treatments of 'good genes' processes have assumed that the influx of new mutations is constant. I propose that this assumption is too simplistic, and that mutation rates vary in ways that are important for sexual selection. Recent data have shown that individuals in poor condition can have higher mutation rates, and I argue that if both male sexual ornaments and mutation rates are condition-dependent, then females can use male ornamentation to evaluate their mate's mutation rate. As most mutations are deleterious, females benefit from choosing well-ornamented mates, as they are less likely to contribute germline-derived mutations to offspring. I discuss some of the evolutionary ramifications of condition-dependent mutation rates and sexual selection.

Host condition and individual risk of cowpox virus infection in natural animal populations: cause or effect?

Recent studies have provided evidence that endemic pathogens may affect dynamics in animals. However, such studies have not typically considered that infected individuals might have a preceding underlying poor condition. We examined whether individuals in poor condition are more likely to become infected by an endemic pathogen, using as a system the dynamics of cowpox virus in field voles. With data from monthly sampled vole populations, a nested case-control study evaluated whether susceptible individuals with poorer condition had higher probabilities of contracting cowpox. The influence of condition was found to be considerable, especially for males. At times when a susceptible male with good body condition had a relatively low probability of becoming infected, a susceptible male with poor body condition was twice as likely to contract cowpox; if this male was also anaemic, the chances were almost quadrupled. We discuss the care needed when interpreting the findings of wildlife disease studies.

What Makes a Host Profitable? Parasites Balance Host Nutritive Resources against Immunity

Numerous host qualities can modulate parasite fitness, and among these, host nutritive resources and immunity are of prime importance. Indeed, parasite fitness increases with the amount of nutritive resources extracted from the host body and decreases with host immune response. To maximize fitness, parasites have therefore to balance these two host components. Yet, because host nutritive resources and immunity both increase with host body condition, it is unclear whether parasites perform better on hosts in prime, intermediate, or poor condition. We investigated blood meal size and survival of the ectoparasitic louse fly Crataerina melbae in relation to body condition and cutaneous immune response of their Alpine swift (Apus melba) nestling hosts. Louse flies took a smaller blood meal and lived a shorter period of time when feeding on nestlings that were experimentally food deprived or had their cutaneous immune response boosted with methionine. Consistent with these results, louse fly survival was the highest when feeding on nonexperimental nestlings in intermediate body condition. Our findings emphasize that although hosts in poor condition had a reduced immunocompetence, parasites may have avoided them because individuals in poor condition did not provide adequate resources. These findings highlight the fact that giving host immunocompetence primary consideration can result in a biased appraisal of host-parasite interactions.

Early body condition, time budgets and the acquisition of foraging skills in meerkats

Early body condition commonly has important downstream effects on fitness. One, as yet unexplored, mechanism behind these effects may be that condition in early life affects time budgets and hence opportunities to learn critical skills. Meerkat, Suricata suricatta, pups must choose between begging for food from helpers and foraging for themselves. I found that pups in good condition early in life invested more time in foraging than individuals in poor condition and subsequently developed greater foraging efficiency, which was maintained in later life. Young pups spent an average of 18% of their time foraging, even though all pups were initially incompetent foragers and gained few direct benefits from their attempts. Pups whose hunger was reduced through experimental provisioning increased their investment in foraging. This suggests that investment in foraging is mediated by available energy reserves and raises the possibility that, although foraging is energetically costly, pups may gain long-term benefits by practising. Surprisingly, manipulating body weight through long-term experimental provisioning did not result in increased investment in foraging or improved foraging efficiency. Possible explanations for this result are considered. The findings presented here provide some support for the hypothesis that high body condition allows individuals to invest time in costly foraging practice, leading to the development of skills. These effects, acting in tandem with other processes such as differential neural development, may help to explain common links between early condition and future fitness.

Body condition and clutch desertion in penduline tit Remiz pendulinus

AbstractParental care is costly since it takes time and energy, and whilst caring the parent may be predated. The benefits of care (i.e., viable offspring) however, are shared equally between the genetic parents: the male and the female. Thus a conflict occurs between the parents over care in many multiple-brooding animals, since each parent prefers the other to do the hard work of raising young ('sexual conflict over care'). One of the most striking examples of this conflict occurs in a small passerine bird, the penduline tit Remiz pendulinus in which both the male and the female may sequentially mate with several mates within a single breeding season. Incubation and brood-rearing are carried out by a single parent (either the male or the female). However, about 30% of clutches are abandoned by both parents. We investigated how body condition may influence parental behaviour of male and female penduline tits. We show that three measures of body condition (body mass, fat reserves and haematocrit value) are consistent with each other for males, although not for females. Nest building appears to be energetically more demanding than incubation in both sexes. In line with this, we found that males and females in good condition deserted their clutch more often than males and females in poor condition. Individuals in poor condition may care because incubation is energetically less expensive than nest building, and they cannot afford the energy requirement of building a new nest. We argue that understanding body condition in the context of parental care is both challenging and essential, since mathematical models (single-parent optimisation models and game-theory models) provide conflicting predictions. Future work, preferably by experimentally manipulating the body condition of penduline tits, is needed to test how body condition influences caring/deserting decisions in this puzzling avian system.

Dynamics of an immune response in house sparrowsPasser domesticusin relation to time of day, body condition and blood parasite infection

The T‐cell mediated response to a challenge of the immune system with phytohemagglutinin (PHA) is a common measure used in ecological studies of host‐parasite interactions or parasite‐mediated selection. We investigated the temporal dynamics of this response in house sparrowsPasser domesticusin order to determine factors that contribute to temporal and individual variation in PHA response. After an initial significant increase in response from injection to six hours post‐injection, there was no further significant change in mean response after 12, 24, 36, 48 and 72 hours. Responses at night were consistently stronger than during daytime. Individuals may benefit from producing both a strong and a quick immune response to parasite attacks, although this may be impossible because of the observed positive relationship between maximum response and latency to maximum response. House sparrows withHaemoproteusinfections had lower PHA responses and smaller maximum responses than individuals without infections. Individuals in prime body condition had stronger PHA responses than individuals in poor condition. House sparrows with large diurnal fluctuations in body mass had a weaker maximum response than individuals with small fluctuations. Since individuals withHaemoproteusinfections have large fluctuations in body mass, this result suggests that infected individuals with large fluctuations in mass are unable to mount a strong immune response.

Annual Migration Density and Stopover Patterns of Northern Saw-whet Owls (Aegolius acadicus)

Abstract Northern Saw-whet Owls (Aegolius acadicus) exhibit large fluctuations in annual number of individuals migrating in eastern United States. Underlying large differences in the magnitude of the migration may be important density-dependent effects on body condition and stopover patterns. We investigated such effects using data from saw-whet owls that were trapped and banded during autumn migration at the southern tip of the Delmarva Peninsula (near Cape Charles, Virginia) from 1994 to 2000. Irruptive migration events occurred in 1995 and 1999 when 1,002 and 700 owls were captured, respectively. Capture totals ranged from 22 to 105 owls during five nonirruptive years. Irruptive migration years were dominated by immature owls (82% of captures) and were characterized by low recapture rates (13%) and shorter minimum stopover lengths (median = 5 nights) for all owls. Body masses and body-condition index scores were significantly lower for both immature and adult age classes during years when owl density was very high. During such years, a smaller percentage of owls elected to stopover and, among those that did, individuals in good condition departed sooner than individuals in poor condition. Conversely, during nonirruptive years, adults constituted 67% of captures, recapture rates were nearly 3× higher (35%), and stopover lengths were twice as long (median = 10 nights). Recapture rates were significantly higher for adults (43%) than for immature owls (23%) and initial body condition of adults was positively correlated with their length of stopover. During light migration years, conditions may be conducive for extended residency, particularly for adult owls in good condition. Our results suggest that density-dependence is an important mechanism driving migration and stopover patterns of saw-whet owls.

Variation in fish condition between Atlantic cod ( Gadus morhua) stocks, the effect on their productivity and management implications

A comparative analysis of the fish condition (Fulton’s K) of 10 cod stocks in the north Atlantic in relation to the temperature of their habitat, growth rates and their reproductive potential is presented. It is shown that the cod stocks in the north Atlantic display different levels of mean condition, which is partly due to the different temperature regimes of their habitats. Cod living in colder waters, e.g. Greenland, Labrador and Grand Bank stocks, were found to be in poorer condition than cod living in warmer waters, e.g. North Sea and Irish Sea stocks. Poor condition causes reduced productivity in terms of slow growth and low recruitment potential. Stocks in better condition display significantly higher weights at age 4 than stocks in poor condition. The a coefficients (function’s slopes) obtained from standardised Ricker’s recruitment–spawning stock biomass (SSB) relationships were defined as indicators for the recruitment potential of stocks. These a coefficients were found to be positively correlated with the mean condition factor of the 10 stocks analysed. This indicates that stocks consisting of individuals in poor condition appear to be very susceptible to reduced recruitment at low SSB, while the stocks that consist of fish in good condition seem to behave more robustly with a higher probability of good recruitment at low SSB. The positive effect of the cod condition on their reproductive potential generally implies that the stocks in good condition in the temperate regions of the northeast and west Atlantic can sustain higher exploitation rates than stocks in poor condition in the colder regimes of the northwest Atlantic (Greenland, Labrador and Grand Bank). This is confirmed by the positive relationship established between the estimated biological management reference points F med and the mean cod condition factors, as well as by the recent status of these stocks.

Costs of sexual traits: a mismatch between theoretical considerations and empirical evidence.

Costs of sexual traits are of central importance to the theory of sexual selection. To qualify as a cost in line with theoretical models, empirical studies must demonstrate that sexual traits cause negative effects on one component of fitness of the trait bearer. Moreover, it must be demonstrated that the costs are differential such that negative effects on fitness are more severe for individuals in poor condition than for individuals in good condition. However, in the current literature, there is confusion over what qualifies as a cost, and costs are often anticipated based on findings of increased expenditure. Consequently, it seems that the generally accepted notion that sexual traits are costly is in fact based almost exclusively on indirect evidence and that direct empirical evidence is very scarce.

Asymmetry in antler size in roe deer (Capreolus capreolus ): an index of individual and population conditions.

Fluctuating asymmetry (FA) refers to small random differences that occur between the right and the left sides of bilateral characters. Under the hypothesis that the degree of FA in secondary sex traits reflects the ability of males to cope with environmental stress, and consequently reflects individual quality, a negative relationship is expected between FA and the trait size. Additionally, selective mortality acting preferentially on individuals in poor condition, presumably more asymmetric, should lead to a decrease in FA with age. We tested these hypotheses on roe deer (Capreolus capreolus) antlers, analysing the FA pattern in antler size from individuals culled over 18 years in a single population. Absolute asymmetry significantly decreased with age, and tended to decrease with antler size, at constant carcass mass, within age classes. Moreover, increase in the population density negatively affected carcass mass and antler size, and resulted in a significant increase in the degree of asymmetry in antlers. These results suggest that antler development in roe deer represents a reliable signalling of individual quality. Moreover, due to the deciduous nature of antlers, asymmetry in antler size appears to be a valuable indicator of the current environmental conditions encountered by populations.

Age, sex, and condition as predictors of moult and the efficacy of a novel fur‐clip technique for individual marking of the European badger (Meles meles)

The European badger (Meles meles) moults once a year. In our study site in lowland England, pelage replacement of the guard hairs and a protracted period of fur growth (follicular anagen) occur between May and early November, with a peak in July. The precise timing of the moult depends on the age and condition of the badger. Yearling badgers undergo moult significantly earlier than adults. Adult females that have lactated, moult significantly later than other classes of adult, delaying the moult until autumn which corresponds to an annual period of food abundance. Lactation was significantly associated with poor condition in these badgers. It was not possible to determine whether delayed moult was due to poor condition per se, or due to some other physiological consequence of lactation, e.g. hormonal changes. We hypothesize that delay of moult in laclating/poor condition individuals has the adaptive consequence of delaying the metabolic costs of pelage replacement from a time of energy deficit until a time of relative plenty.These findings are of practical importance to a novel solution to the problem of individually marking badgers during observational studies. The technique involves clipping the dark band near the tips of the badger's guard hairs to reveal the white under‐fur and produce patterning of the coat. The highly contrasting marks were well suited to visual identification during observations under low light and infra‐red illumination, and they allowed a large number of individuals (over 80 in our study) to be distinctively marked. The mark persists until the badger undergoes its single annual moult, or until three months of the active phase of fur growth have passed. Clip marks on adults made in late August had the greatest longevity, with 80% still visible after nine months. Though clipping had no significant effect on body condition in our study site, it should be cautiously applied with individuals in poor condition or in cold climates.

Lipid class composition as a measure of nutritional condition in individual larval Atlantic cod (Gadus morhua)

Atlantic cod (Gadus morhua) larvae were reared under various feeding environments to assess their lipid class composition and survival during development. Lipids were assessed in individual larvae. Triacylglycerol (TAG), phospholipids (PL), and defatted dry weight (DDW) all fell during yolk absorption. TAG increased after initiation of exogenous feeding in different feeding treatments but did not increase in starved larvae. The percentage of individuals greater than 8 d old with high TAG or PL increased with increasing prey concentration. Survivorship was low in all feeding trials, but groups with a larger percentage of individuals in poor condition tended to exhibit a higher risk of death. We suggest a condition index based on a discriminant function using TAG, PL, and DDW. We assessed the condition of field-collected larvae based on this index.

Physiological Condition of Autumn-Banded Mallards and Its Relationship to Hunting Vulnerability

An important topic of waterfowl ecology concerns the relationship between the physiological condition of ducks during the nonbreeding season and fitness; i.e., survival and future reproductive success. We investigated this subject using direct band recovery records of mallards (Anas platyrhynchos) banded in autumn (1 Oct-15 Dec) 1981-83 in the Mississippi Alluvial Valley (MAV). A condition index, weight (g)/ wing length (mm), was calculated for each duck, and we tested whether condition of mallards at time of banding was related to their probability of recovery during the hunting season. In 3 years, 5,610 mallards were banded and there were 234 direct recoveries. Three binary regression models were used to test the relationship between recovery probability and condition. Likelihood-ratio tests were conducted to determine the most suitable model. For mallards banded in autumn there was a negative relationship between physical condition and the probability of recovery. Mallards in poor condition at the time of banding had a greater probability of being recovered during the hunting season. In general, this was true for all age and sex classes; however, the strongest relationship occurred for adult males. J. WILDL. MANAGE. 50(2):177-183 In recent years many studies have focused on documenting the physiological condition of waterfowl, where condition often is defined poorly but generally refers to the quantity of energy reserves. This interest in condition results primarily from the assumption that individuals in good relative condition (i.e., those with high levels of energy reserves) exhibit greater probabilities of surviving and reproducing than individuals in poor condition. Investigations of waterfowl condition primarily have concentrated on: (1) estimating physical condition (Bailey 1979, Wishart 1979, Chappell and Titman 1983, Piersma 1984, Whyte and Bolen 1984b, and others); (2) documenting changes in physical condition in relation to various energetic costs such as reproduction (Harris 1970, Raveling 1979, Drobney 1982, Tome 1984), molt (Ankney 1979, 1984; Young and Boag 1982), and weather (Owen and Cook 1977, Bennett and Bolen 1978); and (3) relating physical condition to some measure of fitness such as breeding success (Ankney and MacInnes 1978, Krapu 1981, Cowardin et al. 1985) and time of pairing (Wishart 1983). There are relatively few empirical results, however, that support the assumption that being in good physical condition is advantageous. A noted exception occurs for waterfowl during the breeding season. Studies show that females of some waterfowl species depend on the accumulation of energy reserves (lipids, calcium, and protein) to breed successfully. For example, development of nutrient reserves before arriving at breeding areas (McLandress and Raveling 1981a,b; Gauthier et al. 1984) is important for the reproductive success of arcticn sting geese (Newton 1977, Raveling 1978). In some species of ducks fat reserves also are critical for development of initial clutches, but protein demands can be satisfied through exogenous sources (Siegfried et al. 1976, Krapu 1981, Drobney 1982). Winter generally is considered to be energetically stressful for waterfowl (Reinecke et al. 1982) and other species of birds that overwinter in temperate regions. Individuals often are faced with reduced food availability (Jorde et al. 1984) and severe weather conditions (Bennett and Bolen 1978) which may cause a negative energy balance (Whyte and Bolen 1984a). It seems reasonable, therefore, that individuals entering 'Present address: Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29801.