Live animal radiography to measure developmental instability in populations of small mammals after a natural disaster

Stress placed on individuals in a population from natural and anthropogenic disturbances can elevate developmental instability. We studied the result of a natural disaster when one-third of a forested nature preserve was destroyed by an F3 tornado. Populations of two abundant species of small mammals, Peromyscus maniculatus and P. leucopus, were monitored in both disturbed and undisturbed habitats. We used an X-ray technique to measure developmental instability as indicated by fluctuating asymmetry (FA) in cranial and skeletal features of live animals. FA in femur length was higher in disturbed habitat for P. leucopus but was higher in undisturbed habitat for P. maniculatus. This difference in developmental instability mirrors differences in habitat preference between these species: P. leucopus prefers forest habitat and P. maniculatus prefers open, herbaceous habitat. These results were not explained by either food availability or body condition, both of which were higher in the disturbed habitat suggesting higher quality for this habitat. Thus, the FA response may be related to other indicators of habitat quality, e.g., vertical stratification, coarse-woody debris, or population density, which may differ between undisturbed and disturbed habitats.     

The relationships between habitat suitability,population size and body condition in a pond-breeding amphibian

The ecological niche of a species determines whether a species can persist and reproduce in a patch or not. The niche of a species is often described using habitat suitability models and indices. Accordingly, one may expect tight links between demography, phenotypes of individuals, population size, and habitat suitability. However, such links are not always found. Here, we study the relationship between a habitat suitability index that is commonly used for conservation assessments and metrics describing the performance at the level of populations and individuals. Using data from a metapopulation of a pond-breeding amphibian, the Great Crested Newt (Triturus cristatus), we show that habitat suitability predicts population size but not body condition. Ponds with higher suitability had a higher population size of newts, whereas population size correlated negatively with body condition of individuals. Our results are in line with previous studies showing no straightforward relationship between habitat suitability and body condition (a measure of individual performance) and the performance of populations. We suggest that a population size-dependent reduction of body condition may be a regulatory mechanism in newt populations.     

Sex, diet and feeding method-related differences in body condition in the Oystercatcher Haematopus ostralegus

Measurements were made of Oystercatcher corpses to find the most reliable measure of body condition in live birds. Total body weight was as accurate as muscle thickness in assessing the weight of the pectoral muscles, a major store of protein reserves. Total body weight was also a good indicator of fat reserves. Wing‐length was the most reliable measure of body size. Body condition in live birds was measured as an individual's residual weight derived from a general linear model of (loge) body weight against age, month, (loge) wing‐length and time since capture. On the Exe estuary in autumn, there was no significant difference in body condition between same‐age Oystercatchers of different diets and feeding methods. In the winter months, however, body condition differed significantly between mussel feeders using different feeding methods, and between mussel feeders and birds that fed on worms and clams. Differences between diet/feeding methods were not the same for each age group. Birds with the highest mean body condition index in adults were mussel hammerers, in immatures mussel stabbers and in juveniles, worm/clam feeders. No significant difference in body condition was found between the sexes in any age group in autumn. In winter, when birds with the same diet/feeding method were considered, females were significantly heavier than males. However, when birds of all diets and feeding methods were combined, weight differences between the sexes were not apparent. We examine reasons why birds with certain diets and feeding methods may be heavier than others in winter, and why females are sometimes heavier than males. We conclude that, in most cases, it is due to differences between birds in their ability to achieve a common target weight. However, we conclude that adult females try to achieve a higher target weight than males, probably as a premigratory and prebreeding strategy. In the light of this, we consider the consequences for adult females, in terms of reproductive success and survival, of specializing in diets and feeding methods associated with lower body weights in winter.     

The costs of immunological challenge to developing mountain chickadees, Poecile gambeli, in the wild

The tradeoff between immunocompetence and development in avian species could have long-term consequences relating to fitness. This study investigated the developmental cost of mounting a humoral immune response in growing mountain chickadees, Poecile gambeli . We immunologically challenged nestling chickadees using nonpathogenic antigens of either Newcastle disease virus vaccine or sheep red blood cells. Body mass, tarsal length, haematocrit, total plasma protein, and survival did not vary significantly between antigen treatment groups and control groups. Developmental stability was assessed using fluctuating asymmetry (FA) between the right and left ninth primary feather length. FA was increased significantly in the antigen-challenged birds. This result indicates that the up-regulation of the humoral immune response was developmentally costly to the nestlings by causing an increase in FA.     

Variations in body weight, wing length and condition of Mallard Anas platyrhynchos platyrhynchos and their relationship to environmental changes

This paper describes the analysis of over 15,000 weights of Mallard caught for ringing at Borough Fen Decoy, Northamptonshire, during a 13 year period. Weights are corrected to give condition indices by using wing length to give an indication of body size. The weight of pectoral muscles varies with body weight but as the fat stores increase in weight the proportion of body weight made up of flight muscles decreases. Body weight corrected for size gives a better indication of the bird's condition (defined as its fitness for its present and future needs) than the relative weight of the pectoral muscles or the shape of the breast.
The relationships between food availability and weather, and condition are examined. Only occasionally can a drop in condition following hard weather be detected; the birds normally emigrate to the coast after a few days of adverse conditions. There is a relationship between the condition of Mallard in autumn and the amount of grain left on their stubble feeding grounds after harvest. The implications of variations in winter condition on survival and breeding success are briefly discussed.     

Dimorphisms and fluctuating asymmetry in the forceps of male earwigs

Male dimorphisms are particularly conspicuous examples of the alternative reproductive strategies employed within some species. Such dimorphisms are thought to exist as genetic polymorphisms under ESS conditions, or to be conditional strategies where exogenous conditions determine the adult body plan. Fluctuating asymmetry (FA) is currently considered to be a fitness correlate of significant use in interpreting the functional significance of secondary sexual characteristics. In particular, negative slopes of FA on trait size are thought to arise in traits whose expression is dependent on condition. We measured forceps lengths and asymmetries in 2 island populations of the European earwig Forficula auricularia and Museum specimens of 5 other earwig (Dermaptera, Forficulidae) species from different genera, that appeared to be dimorphic. In a detailed study of Forficula auricularia we found a significant fit to a statistical model for the identification of dimorphisms and, for all species examined, morphs differed in the slope and/or elevation of the allometric relationship between body size and forcep length. Possible determinates of male dimorphisms are suggested from the data. Contrary to expectation, FA was not found to be greater in the minor morphs. Negative relationships between FA and forceps length were absent in both morphs of species examined from museum collections. Of the two island populations of Forficula auricularia, the smaller and more isolated population had higher FA and a negative relationship between FA and forceps length in the major morph. We discuss these patterns in the light of recent theories of FA and honest signalling.     

Body Condition Indices Predict Reproductive Success but Not Survival in a Sedentary,Tropical Bird

Body condition may predict individual fitness because those in better condition have more resources to allocate towards improving their fitness. However, the hypothesis that condition indices are meaningful proxies for fitness has been questioned. Here, we ask if intraspecific variation in condition indices predicts annual reproductive success and survival. We monitored a population of Neochmia phaeton (crimson finch), a sedentary, tropical passerine, for reproductive success and survival over four breeding seasons, and sampled them for commonly used condition indices: mass adjusted for body size, muscle and fat scores, packed cell volume, hemoglobin concentration, total plasma protein, and heterophil to lymphocyte ratio. Our study population is well suited for this research because individuals forage in common areas and do not hold territories such that variation in condition between individuals is not confounded by differences in habitat quality. Furthermore, we controlled for factors that are known to impact condition indices in our study population (e.g., breeding stage) such that we assessed individual condition relative to others in the same context. Condition indices that reflect energy reserves predicted both the probability of an individual fledging young and the number of young produced that survived to independence, but only during some years. Those that were relatively heavy for their body size produced about three times more independent young compared to light individuals. That energy reserves are a meaningful predictor of reproductive success in a sedentary passerine supports the idea that energy reserves are at least sometimes predictors of fitness. However, hematological indices failed to predict reproductive success and none of the indices predicted survival. Therefore, some but not all condition indices may be informative, but because we found that most indices did not predict any component of fitness, we question the ubiquitous interpretation of condition indices as surrogates for individual quality and fitness.     

Reindeer antlers: visual indicators of individual quality?

Fluctuating asymmetry (FA) in ornamental characters may reflect developmental stability in the translation from genotype to phenotype. Antlers of reindeer show FA, are visually conspicuous ornaments and are important in intraspecific assessment. We show that there is a negative relationship between size and asymmetry in visual antler characteristics (i.e., antler length and number of tines) among free-ranging male reindeer in rut. This indicates that individuals that develop large ornaments are better able to buffer developmental stress than individuals that develop small ornaments. There is no relationship between asymmetry in antler length and asymmetry in jaw length, suggesting that symmetry in antlers does not reflect overall body symmetry. This difference may be caused by trait-specific sensitivity to developmental stress. Such stress may partly be caused by parasites, which show a positive association with asymmetry in antlers, but no relationship to asymmetry in jaws. Our results indicate that antlers may be exposed to directional selection in a visual signaler-receiver system and that information about parasite burden may be obtained from evaluation of asymmetry in antlers developed under exposure to a multitude of environmental stresses. Received: 8 October 1996 / Accepted: 13 January 1997     

Relationship between Fulton's condition factor and proximate body composition in three freshwater fish species

Morphometric‐based condition indices are widely used to assess proximate body composition and, collaterally, feeding and living conditions of fish. However, the exact relationship between condition indices and proximate body composition of fish and its relatedness to life history traits and seasonality has yet to be fully explored. Therefore, the aim of this study was to examine how the Fulton's condition factor (K‐factor) is related to the chemical composition (i.e. lipid, protein, water and carbon content, and molar carbon : nitrogen ratio), length and gonadal development of fish, and how these relationships are influenced by gender and seasonality in three freshwater fish species: Amur sleeper (Perccottus glenii), pumpkinseed (Lepomis gibbosus) and rudd (Scardinius erythrophthalmus). It was found that the strength and direction of association between the K‐factor and proximate body composition can vary markedly among fish species. The K‐factor correlated positively with gonadal development in pumpkinseed and Amur sleeper, while no such relationship existed in rudd. Condition factor can be a reliable measure of lipid content; however, the relationship was stronger in species with higher and more variable lipid contents. Moreover, a striking and consistently negative linkage was found between the K‐factor and water content of the fish body, which corresponds to the findings of several other studies. In turn, any relationship between the K‐factor and the protein content of fish was not detected. Gender seemed to exert a negligible effect on the relationship between the K‐factor and proximate body composition, while seasonal variance was obvious in most relationships.     

The effect of body condition on the cost of reproduction in female Collared Flycatchers Ficedula albicollis

Survival of females in relation to their body condition was investigated in the Collared Flycatcher Ficedula albicollis on Gotland, Sweden. The brood size was manipulated by enlarging or reducing the number of nestlings by one or two chicks. We found a positive relationship between experimental treatment and the condition of the female in the year of the experiment. Among females which disappeared (had apparently died) between years, the relationship was negative but not significant. When the effect of brood manipulation on the probability of survival was analysed separately for females in poor and good body condition, a negative relationship between experimental treatment and probability of survival among females in poor condition was found. This result indicates the existence of a cost of reproduction in terms of survival in low quality females. There was no effect of brood manipulation on the survival of females in good body condition. Our analyses suggest that individuals have different costs of reproduction, depending on their conditional state.