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Fluctuating asymmetry in antlers of fallow deer (Dama dama): the relative roles of environmental stress and sexual selection
Abstract
Antler lengths were recorded of a total of 250 male fallow deer (Dama dama (L)). Animals sampled were from marked populations where the majority of individuals were of known age. Asymmetry in antler length was normally distributed with a mean not significantly different from zero, confirming that differences in length between the antler pair constitute a true fluctuating asymmetry (FA). We found no clear relationship between the degree of asymmetry in antler length of an individual male and either population density or actual body mass. We did, however, detect a significant relationship between asymmetry and deviation from maximum cohort bodyweight. If deviation from maximum weight within a cohort may be considered some index of competitive success or increasing environmental stress, this may suggest that asymmetry in antler length relates in some way to developmental stress suffered by the individual concerned. The degree of asymmetry recorded in antler length also showed a significant decline with animal age, with antlers of animals of 2 years or older showing significantly greater symmetry. This is consistent with a hypothesis that despite continued competition for resources, there is a changing balance of selection pressure as animals reach maturity, with increased pressure from sexual selection requiring males to produce significantly more symmetrical ornaments
Red deer hinds play a significant role in selecting stags for mating. We tested the hypotheses that in red deer (Cervus elaphus) the probability of becoming a harem holder (and hence achieving reproductive success) occurs in stags bearing larger, branched antlers and showing low fluctuating asymmetry (FA). Eleven antler characteristics were measured; absolute and relative FA were calculated on 51 cast antler sets from 19 individually recognized stags. Probability of becoming a harem holder (PBHH) was originally analysed separately, i.e. for antler size and FA of each antler characteristic and calculated factors for both antler size and FA. If analysed separately, large antler size and low relative but high absolute FA increased PBHH. When we combined antler size and FA of antler characteristics in one model using antler size and FA factors, however, PBHH and achieving reproductive success were mainly dependent on increasing antler size and enhanced antler branching rather than on FA. We conclude that in contrast to antler size, FA is unlikely to play any significant role in sexual selection as an indicator of individual quality. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87, 59–68.
Fluctuating asymmetry (FA) has been suggested as a measure of the sensitivity of development to a wide array of genetic and environmental stresses. It has been also suggested that antlers in red deer could be important during social and rutting displays. We used antler measurements of 51 males that were measured over subsequent seasons, from 3–8 years of age, and analysed three antler traits: antler weight, length, and the number of antler tines (antler size). We calculated absolute and relative FA. All three size traits were highly significantly intercorrelated. By contrast to this, the FA of the three traits, did not show such relationships. With increasing age, antler size and FA also increased. When testing the repeatability of FA and antler size, there was a principal difference in the pattern between FA and antler size, with the latter being much more consistent than the former. This suggests that antler size, not FA, may be a good predictor of the bearer’s quality in mate selection. This fits well with the good-genes hypothesis that the development of extravagant secondary sexual characters can be an honest advertisement of heritable male quality. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 215–226.
Senescence can be defined as accelerating phenotypic deterioration with old age. For traits that grow throughout life, such as the horns of some ungulates, senescence may be expressed as a decrease in annual growth rates, or an increase in asymmetry, in the years preceding death. Age-specific yearly horn-growth segments of 378 male Alpine ibex Capra ibex L. that died from natural causes were analysed in the Gran Paradiso National Park (Italian Alps). Horn annuli displayed fluctuating asymmetry. The hypothesis that asymmetry and size of the annuli of the horns could predict annual survival probability was tested. It was found that between 5 and 11 years of age, male ibex that grew shorter annuli than the average for the population had a greater probability of mortality over the following years than those with greater rates of horn growth. Horn asymmetry and mortality rates were not significantly correlated. Annulus size, reflecting the onset of senescence, seemed to be a better indicator of individual q
Competitive interactions between mature male fallow deer were investigated to determine whether antler length, body weight, age or dominance rank were related to the number of fights between individuals. Four different hypotheses were tested; the first predicted that body weight and antler length indicate individual quality and, therefore, as the difference between competitors in body weight and antler length increases, there should be a corresponding decrease in fight rate. The second and third hypotheses predicted that, as difference in dominance rank increased there would be a decrease in fight rate between males either, as a risk reduction measure or because of inhibitory control by dominant males. A fourth hypothesis predicted that, where dominance rank does not mediate fight rate, that similarity between contestants based on age might be important. If this is the case, then as the difference in age between competitors increased there should be a decrease in fight rate. Our results show that when dominance rank is controlled for, there was no relation between body weight, antler length or age with fight rate. There was a negative relation between dominance rank difference and fight rate, a result that supports both the risk reduction and inhibitory hypotheses. There was an increasing tendency to fight with closely ranked males as cohorts reached peak reproductive age; males aged 5 yr fought with other 5-yr-old males based on rank difference and males aged 6 yr fought with other males aged six and across all age groups based on rank difference. This trend was not observed in 4 or 7-yr-old males. Our results suggest that males in prime breeding condition limit potential costs of fighting (such as time and energy) by only interacting with other males of similar rank.
A central aim of the study of animal communication is to identify the mode and content of information transferred between individuals. The lateral presentation of the antler palm between male fallow deer has been described as either a signal of individual quality or an attempt to avoid fighting. In the first case two phenotypic features have been proposed by which transmission of individual quality may be facilitated. These are antler size and antler symmetry. The alternative hypothesis proposes that the lateral presentation of antlers occurs as a consequence of averting a threatening posture and may signify a reluctance to fight. We examined whether mature fallow deer use lateral palm presentation as a display during fights to indicate antler size and symmetry. We found no relationship between presentation rate of the antler and antler size and symmetry. Furthermore, males did not preferentially present their larger antler to their opponent. We also investigated whether the rate at which males presented antlers laterally during a fight was related to their ability to win the fight. Our results show that the male who performed more presentations during a fight was more likely to lose it. There were behavioural differences in the way in which a bout of presentation ended; subsequent losers tended to turn their body away from their opponent and subsequent winners tended to lower their antlers to an opponent which we interpret as an invitation to continue fighting. We conclude that the lateral palm presentation serves to de-escalate fighting between mature fallow deer. It is not a mechanism by which to communicate individual quality but rather an indication that a male is less committed to continuing investment in the current contest.
There is currently no agreement about the suitability of fluctuating asymmetry (FA) as an estimate of individual quality. We investigated the relationship between FA and health, a proxy for individual quality, in captive populations of three endangered gazelle species: Gazella cuvieri, G. dama, and G. dorcas. FA indices including information from sexual (horns) and/or non-sexual ordinary traits were calculated for each individual. Health was assessed using 15 blood parameters, and inbreeding coefficient was also included in the analyses. In the three species, the FA index was significantly related to at least one blood parameter (platelets, mean platelet cell volume, albumin, and lactate dehydrogenase), with levels indicating unhealthy condition in more asymmetric individuals. The exception was the negative relationship between FA and aspartate aminotransferase in ordinary traits of G. cuvieri and G. dama. FA was related to different blood parameters in every species and type of trait. As a large number of diseases can cause abnormal blood parameter levels in humans, we assumed that this also might be the case in gazelles. In general, the results suggest that FA is related to health in the three gazelle species studied, and thus, we concluded that FA can provide useful information about individual quality.
After about 50 years of research on fluctuating asymmetry (FA) as a reliable indicator of both individual quality and environmental stress, the enthusiasm is beginning to decline. The findings of many studies are inconsistent and the relationship between FA and stress appears both weaker and more complex than first thought. To provide clarification of the debate, new studies should use more efficient and unified statistical protocols, large sample sizes and joint analysis of several related traits. In addition, fitness–FA associations should be tested at the individual level, in different populations and under different environmental conditions. To achieve these criteria, we describe a 9-year study in which we measured six antler traits of 3 000 Iberian red deer, Cervus elaphus hispanicus, from three study areas in southwest Spain. Males were harvested during hunting activities and measured, weighed and aged post mortem. We found evidence of correlations between traits in FA, an association between asymmetry and stress conditions and a weak but significant negative relationship between FA and fitness surrogates (body mass and antler size), thus supporting some assumptions of the FA hypothesis. As also predicted by theory, antler traits of less functional importance were more asymmetric and more sensitive to stress than those directly used in fighting behaviour. The relationship between age and antler asymmetry was U-shaped, suggesting an effect of sexual selection on antler development in favour of larger and more symmetrical antlers during prime age.
Fluctuating asymmetry occurs when an individual is unable to undergo identical development on both sides of a bilaterally
symmetrical trait. Fluctuating asymmetry measures the sensitivity of development to a wide array of genetic and environmental
stresses. We propose that fluctuating asymmetry is used in many signalling contexts for assessment of an individual's ability
to cope with its environment. We hypothesize that fluctuating asymmetry is used in sexual selection, both in fighting and
mate choice, and in competition for access to resources. Evidence is reviewed showing that the patterns of fluctuating asymmetry
in secondary sexual characters differ from those seen in other morphological traits. Secondary sexual characters show much
higher levels of fluctuating asymmetry. Also, there is often a negative relationship between fluctuating asymmetry and the
absolute size of ornaments, whereas the relationship is typically U-shaped in other morphological traits. The common negative
relationship between fluctuating asymmetry and ornament size suggests that many ornaments reliably reflect 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.
Behavioral ecologists are being attracted to the study of within-individual morphological variability, manifested in random deviations from bilateral symmetry, as a means of ascertaining the stress susceptibility of developmental regulatory mechanisms. Several early successes Indicate that incorporating measures of symmetry into sexual-selection studies may help link individual sexual success to a basic component of viability - developmental stability.
We studied the behavior and copulatory success of fallow deer ( Cervus dama ) males at a lek. We recorded 471 copulations in 3 years. Most males did not copulate. The top three males accounted for between 60 and 90% of copulations each year. Lek attendance time was the major determinant of male copulatory success, but territory location also affected the number of copulations achieved. Copulatory success was correlated with the number of females in a male's territory and possibly with dominance status, but not with fighting success or fighting rate. All males that defended lek territories were 5 years of age or older. Copulatory success may improve with age. Body condition appears to be an important determinant of male copulatory success, because only males in superior condition could defend a lek territory for up to 2 weeks. Males do not feed while defending lek territories. Foraging ability during the year probably determines condition at the onset of the rut. Females appear to choose mates at least partially on the basis of location, preferring males located near traditional routes. Females may ultimately select mates in the best body condition.
p>This thesis investigates the effects of various population parameters, together with other factors such as climate and management intervention, on performance and behaviour of fallow deer, Dama dama . British deer parks were chosen for study as they provide a wide range of accurately measurable population densities, and animals within them can be observed and caught relatively easily in comparison to wild deer. The populations present fully mixed-sex herds which are entirely free-ranging within the boundaries of each park throughout the year, and thus offer a model system where population processes may be studied. Live capture of fallow deer in 15 parks enabled collection of data on body weights and skeletal size in relation to age and sex on 3740 individuals, many of these being recaptured in a number of years. Intensive field observations focused on marked individuals in 9 populations, to determine fawning success, birth dates and weights, and variation in maternal and mating behaviour. Additional data on natural mortalities, culled carcases, food availability, climate and habitat characteristics were collected over the extended set of parks. Wide variation occurred between parks in winter live weights, population means ranging from, for example 19.5 to 32.3 kg for male fawns, and 32.1 to 42.6 kg for yearling females. In contrast, such variation within sites between years rarely exceeded 10%. Within some populations changes in mean body weights between years could be explained directly by changes in stocking density, associations being strongest with density measured in the year of birth. Variation in body weights and skeletal sizes between populations showed density-independent associations with summer pasture productivity and winter climate; after accounting for these factors, density-dependent effects, acting through forage availability and supplementary feed obtained per deer in winter, were also apparent. Reproductive rates of adult does (≥2 years old at rut) were very high in all the sites where age-specific data were collected. Fecundity of younger does (< 2 years at rut) was consistently lower than that of adults, with differences greater in parks offering most restricted resources. The winter body-weight threshold for yearlings, at which 50% produced fawns the next summer, was determined as 32 kg. Yearlings produced lighter offspring than adults, and mated and fawned an average of 11 days later. Near maximum reproduction was attained even in parks holding up to 6 deer/ha, as long as at high densities adequate supplementary feeding and shelter were offered. Marked differences in mating behaviour occurred during the rut. High territorial systems ranging from single rutting stands to leks occurred in some parks, while non-territorial systems based on defense of mobile female groups by dominant males were observed in others. Variation in the systems observed is fully described, and was found to relate in particular to buck density, total number of bucks, and doe density. Individual male mating success was highly skewed in all systems. Costs and benefits of variation and timing of mating behaviour are discussed. Juvenile mortality in summer, as well as other natural mortality was very low in the most parks and years. Higher mortality was associated with low body weights in years of cold late winter temperatures. Survival rates were highest where supplementary winter feeding was extensive and commenced before December.</p
Previous analysis has suggested that inter-year variation in mortality of adult red deer in Scotland is principally affected by summer weather conditions. Data collected over 14 yr on the Isle of Rhum (Inner Hebrides) show that mortality was negatively correlated with winter temperatures and positively with rainfall in late winter. In conjunction, these 2 factors accounted for 82% of observed variation between years.-Authors
While the effects of age and condition on female reproductive success have been widely reported in a number of deer species, they have received little study in fallow deer (Dama dama). Beginning in 1986,we established in many British deer parks marked fallow populations with a range of densities and resource availabilities. Annual live capture of the deer provided physical data in relation to age and sex, and subsequent observations were made of marked animals to assess individual fawning and rearing success, as well as mating and parturition dates.
Despite wide variation in mean live body weights between parks, reproductive rates of adult does were very high at all sites;however, fecundity of yearling does wasa consistently lower than taht of adults, with differences greatest at parks offering restricted resources. The winter body-weight threshold, at which 50% of yearling produced fawns, was determined as 32 kg. Yearlings which did reproduce were shown to produce were shown to produce lighter offring than adults, and to fawn an average of 11 days later. Near maximum reproduction was attained in park populations kept at 6 deer/ha or less, as long as at high densities animals were offered adequate supplementary feeding and access to shelter during winter.
Patterns of mortality were studied in 15 park populations of red (Cervus elaphus) and fallow deer (Dama dama) in England in an attempt to determine relationships between levels of overwinter mortality and various characteristics of population structure or management. Our data show that high levels of mortality may be expected among animals of poor condition (low body weight) at the end of cold winters (especially in years where late-winter temperatures in January and/or February are particularly low). Lower mortalities are experienced where stocking densities remain at or below two stock units per hectare of good grazing, where feeding of supplementary fodder overwinter commences in November rather than later in the winter, and when that winter supplement provides the equivalent of 12 MJ or more ME per stock unit per day.
Extravagant secondary sexual characters, i.e. sexual ornaments, are exaggerated, often bilaterally symmetrical traits of great intricacy of design. The full expression of such traits is likely to be very costly and close to the limits of production. Any kind of environmental stress is therefore more likely to affect the expression of ornaments than that of any other morphological trait not subjected to strong directional selection. One measure of the ability of individuals to produce extravagant sexual traits is their degree of fluctuating asymmetry. This occurs when symmetry is the normal state and there is no tendency for the trait on one side of the body to have larger character values than that on the other. The degree of fluctuating asymmetry has been shown to reflect the ability of individuals to cope with a wide array of environmental stress (review in Parsons (1990)). We predicted that sexual ornaments should show a larger degree of fluctuating asymmetry than other morphological traits or than homologous traits in non-ornamented species. If ornaments honestly indicate the quality of individuals, high quality individuals should develop little asymmetry and large traits. Thus, we predicted a general negative relation between the degree of asymmetry and the size of ornaments. This should not be the case for other traits or for homologous traits in conspecific females or in either sex of monomorphic species. We tested these predictions on elaborate feather ornaments in birds, as these have been shown to be used as cues during female choice. We made pairwise comparisons between males and females of ornamented species and between males of ornamented and of non-ornamented, confamilial species. Sexual ornaments showed both a larger absolute and relative degree of fluctuating asymmetry than did wing length or did traits homologous to the feather ornament in females and in males of non-ornamented species. The degree of fluctuating asymmetry for tail ornaments generally showed a negative relation with the size of the ornament, whereas that was not the case for wing length or for traits homologous to the feather ornament in females and in males of non-ornamented species. The large degree of fluctuating asymmetry in ornaments and the negative relation between ornament size and degree of asymmetry suggest that fluctuating asymmetry in ornaments reliably reflects male phenotypic quality.
The developmental stability of an organism is reflected in its ability to produce an ‘ideal’ form under a particular set of conditions (Zakharov, 1992). The lower its stability, the greater the likelihood it will depart from this ‘ideal’ form. Ideal forms are rarely known a priori. However, bilateral structures in bilaterally symmetrical organisms offer a precise ideal, perfect symmetry, against which departures may be compared (Palmer & Strobeck, 1986). Thus they provide a very convenient method for assessing deviations from the norm, and studying the factors that might influence such deviations.
1. Fluctuating asymmetry (FA) of birch leaves collected along four pollution gradients in NW Europe was assessed by measuring the difference in width between right and left halves of the leaf. 2. FA of leaves was not related to tree diameter, and values for long and short shoots of the same tree were correlated. 3. FA of silver birch Betula pendula and two subspecies of B. pubescens, white birch B. pubescens ssp. pubescens and mountain birch B. pubescens ssp. tortuosa, decreased hyperbolically with distance away from four sources of aerial emission which differed in amounts and composition of pollutants. 4. The extent of the zone of increased FA was higher around polluters which produced more emissions. 5. FA of leaves sampled around two copper-nickel smelters was positively related to foliar nickel concentrations, and regressions from these two sites had similar slopes and intercepts. 6. The data suggest that FA of birch leaves may represent a convenient indicator for rapid assessment of environmental quality.
The correlations between the fluctuating asymmetries of different characters were investigated in three species (chaetae and wings of Drosophila melanogaster, cheek teeth of Peromyscus leucopus, and cheek teeth of the fossil horse Griphippus gratus). A mean correlation of 0 was found for the two former species, but a mean positive correlation of +0.046 was found for the horse. Reasons are given why this exception may be only apparent. The intensities of some morphological differences in Drosophila have a general component even though they may be bilaterally independent. The lack of variation for a general buffering capacity against minor developmental accidents was not expected. This and related matters are discussed.
Reviews evidence for 5 functional explanations of the evolution of antlers in male cervids. 1) There is extensive evidence that antlers are used in fights between competing males. Fights are regular during the breeding season and can be damaging. Antlers have proved to be effective weapons of defence and offense, and there is no systematic evidence to support the suggestion that antler-less males (hummels) are more successful in competition for females than antlered stags. 2) Though male deer sometimes use their antlers in defence against predators, the absence of antlers in females of most species suggests that this is not their principal function. 3) Nor does it seem likely that antlers evolved as heat-regulating mechanisms. 4) There is no conclusive evidence that males assess each other by their relative antler size, most measures of antler size and shape are not closely correlated with dominance or fighting ability. 5) Nor is there firm evidence that females selectively mate with large-antlered males. Antlers thus evolved as weapons and are retained by selection because of their function in intra-specific combat. -from Author
Measurements of tail and wing length in swallows suggest that length in males was a reliable advertisement of male quality. Since females use tail length as a cue during mate choice, they will prefer males with symmetrical tails, who have proven their ability to pay the costs of producing the most costly ornament. Fluctuating asymmetry in secondary sexual traits may signal the ability of males to cope with environmental conditions during growth and development of the ornament. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Extravagant secondary sexual characters are assumed to have arisen and be maintained by sexual selection. While traits like horns, antlers and spurs can be ascribed to intrasexual competition, other traits such as extravagant feather ornaments, displays and pheromones have to be ascribed to mate choice. A number of studies have tested whether females exert selection on the size of male ornaments, but only some of these have recorded female preferences for the most extravagantly ornamented males. Here I demonstrate that female choice can be directly predicted from the relationship between the degree of fluctuating asymmetry and the size of a secondary sexual character. Fluctuating asymmetry is an epigenetic measure of the ability of individuals to cope with stress, and it occurs when an individual is unable to undergo identical development of an otherwise bilaterally symmetric trait on both sides of its body. There is a negative relationship between the degree of fluctuating asymmetry and the absolute size of an ornament in those bird species with a female preference for the largest male sex trait, while there is a flat or U-shaped relationship among species without a female preference. These results suggest that females prefer exaggerated secondary sexual characters if they reliably demonstrate the ability of males to cope with genetic and environmental stress. Some species may demonstrate a flat or U-shaped relationship between the degree of fluctuating asymmetry and the absolute size of an ornament because (i) the genetic variance in viability signalled by the secondary sex trait has been depleted; (ii) the secondary sex trait is not particularly costly and therefore does not demonstrate condition dependence; or because (iii) the sex traits can be considered arbitrary traits rather than characters reflecting good genes.
Male fallow deer Dama dama, in a free-ranging population in the New Forest, southern England, either defend territories on a lek, defend single territories or are non-territorial. Mating success is highest on the lek, but unsuccessful lek males get fewer matings than some single territory males off the lek. The mating success of non-territorial behaviour, which is adopted by most males at some time during the rut, is uncertain. Non-lek matings in this population are higher than those reported in other lekking ungulate populations. Male fallow deer are not specialists; individuals commonly change strategies as mating opportunities dictate.
In fallow deer (Dama dama), as well as in other lek-breeding ungulates, receptive females arriving at leks commonly join males that are defending large harems. This tendency enhances differences in harem size and mating success between males. It could occur because females independently move to the same males, because females are attracted to males with females, or because females are attracted to each other. Using controlled experiments with estrous female fallow deer, we show that, although females are more attracted to males with harems than to those without, they are as frequently attracted to groups of females without a male as to female groups with males. We conclude that female fallow deer joining leks are attracted to each other and copy each other's movements. As yet, there is no firm evidence in fallow deer or in other lek-breeding ungulates that females copy each other's choice of mating partners.
We studied fluctuating asymmetry (FA) in the number of antler points from a total of 2126 moose (Alces alces) bulls killed during the hunting season in central Norway over a period of 23 years. All age groups showed a positive relation between FA and the number of antler points on the largest antler (antler size, AS). Based on the assumption that only the highest-quality individuals can produce the largest and most symmetrical sexual traits, the results did not support the hypothesis that FA in sexual traits signals the quality of the possessor. However, a partial correlation analysis revealed a negative relation between FA and carcass mass when controlling for AS. Thus relatively larger bulls in relation to their antler size produce more symmetrical antlers compared with relatively smaller bulls. Similarly, a regression analysis between FA and AS in the different age groups revealed a significant age-dependent decrease in the regression coefficients. This suggests that older bulls are more able to cope with environmental stress during the development of the antlers than younger bulls. Thus, for a given antler size, the age of the bull can be signalled through the FA. We therefore suggest that quality signalling by antler size and FA could be an additional component of sexual selection on moose antlers.
(1) The paper investigates the factors affecting calf survival between 1971 and 1976 in the red deer population of the North Block of the Isle of Rhum, Scotland. (2) On average, 18% of all calves born in the study area died before the end of September and a further 11% died during the winter and early spring. (3) There was no overall difference in mortality between stag and hind calves. However, light-born hind calves were more likely to die than light-born stag calves whereas heavy-born stag calves were more likely to die than heavy-born hind calves. (4) Mortality during the first 6 months of life was higher among the offspring of young and old hinds than among those of 7-10-year-olds. (5) Overall mortality did not differ between calves born to milk and yeld hinds. However, medium weight calves born to yeld hinds were more likely to die than similar calves born to milk hinds. (6) Winter mortality was higher among the offspring of hinds using the part of the study area where population density was highest. (7) Very light calves were more likely to die in summer than heavier calves. (8) Late-born calves showed higher mortality than those born early or within the main birth period. (9) Changes in winter (but not summer) mortality were correlated with increasing population density of hinds in the study area.
The right antlers of fallow deer are significantly more developed than the left antlers with respect to the lengths of the beam, trez tine and palm, as well as antler weight and number of points. The cross-section at the base is also more elliptical in the right antler. The size difference is correlated with the more intense use of right antlers in fighting, and with the greater breadth of the areas of insertion of the neck muscles in the skull's nuchal region.
Males of many animals have more than a single exaggerated secondary sexual character, but inter-specific variability in the number of ornaments has never been explained. We examine three hypotheses that may account for the presence of multiple ornaments. First, the multiple message hypothesis proposes that each display reflects a single property of the overall quality of an animal. This is likely to be the case for ornaments that respond to condition on different time scales. Second, the redundant signal hypothesis suggests that each ornament gives a partial indication of condition. Females pay attention to several sex traits because in combination they provide a better estimate of general condition than does any single ornament. The redundant signal hypothesis predicts that (i) multiple ornaments should be particularly common among taxa with relatively uncostly and fine-tuned female choice, and (ii) females pay equal attention to the expression of all the secondary sex traits in order to obtain an estimate of overall male condition. Finally, the unreliable signal hypothesis argues that some ornaments are unreliable indicators of overall condition and are only maintained because they are relatively uncostly to produce and there is a weak female preference for them. This predicts that (i) multiple sexual ornaments should be particularly common in taxa with the most intense sexual selection (i.e. lekking and other polygynous taxa), and (ii) there should be more evidence for condition dependence in ornaments of species with single as opposed to multiple ornaments. Both the latter predictions are supported by data on feather ornaments in birds.
Extinction can be attributed broadly to environmental or genetic stress. The ability to detect such stresses before they seriously affect a population can enhance the effectiveness of conservation programs. Recent studies have shown that within-individual morphological variability may provide a valuable early indicator of environmental and genetic stress.
We used DNA fingerprinting to determine paternity of 80 calves born into the individually monitored population of red deer ( Cervus elaphus ) on the Isle of Rum, Scotland. Using the paternity information, we investigated the assumptions and predictions of behavioral estimates of male mating success, on which previous studies in this population have relied. Over an 11- day interval in the rut centered on a female's estimated date of conception, the probability that a male fathers a calf is closely related to the number of days he holds the female in his harem, increasing from 0.12 for 1 day to 1.0 for 6 days or more. We compared three methods for estimating the reproductive success of individual males from field observations of harem membership with true success revealed by DNA fingerprinting. All three methods accurately identified the relative success of individual males but were poor predictors of absolute success: the behavioral methods underestimate the true success of successful males and overestimate the success of many males who, in fact, fail to father any calves. In consequence, variance in male mating success is greater than previous behavioral estimates for this population suggested. Both harem membership data and observations of mating and other estrous behavior can be used to identify males most likely to father a specific calf.
(1) Fluctuating asymmetry (FA) is a useful trait for monitoring stress in the laboratory and in natural environments.
(2) Both genomic and environmental changes can increase FA which represents a deterioration in developmental homeostasis apparent in adult morphology. Genetic perturbations include intense directional selection and certain specific genes. Environmental perturbations include temperature extremes in particular, protein deprivation, audiogenic stress, and exposure to pollutants.
(3) There is a negative association between FA and heterozygosity in a range of taxa especially fish, a result consistent with FA being a measure of fitness.
(4) Scattered reports on non-experimental populations are consistent with experiments under controlled laboratory conditions. FA tends to increase as habitats become ecologically marginal; this includes exposure to environmental toxicants.
(5) In our own species, FA of an increasing range of traits has been related to both environmental and genomic stress.
(6) Domestication increases FA of the strength of homologous long bones of vertebrate species due to a relaxation of natural selection.
(7) FA levels are paralleled by the incidence of skeletal abnormalities in stressful environments.
(8) Increased FA is a reflection of poorer developmental homeostasis at the molecular, chromosomal and epigenetic levels.
Leks, on which males defend small clustered mating territories, may have evolved because of the unusual opportunities they provide for female choice of mating partners, and several studies of lek-breeding animals have demonstrated correlations between the mating success of males and their phenotype or behaviour. However, these could arise because (1) females select mates on the basis of male phenotypic traits; (2) males interfere with each other's mating attempts; or (3) females show preferences for particular mating territories, and larger or stronger males are more likely to win access to these territories. Here we report that when fallow bucks on a traditional lek were experimentally induced to change their territories, differences in the mating success of bucks persisted, whereas differences in the position of their territories relative to the centre of the lek did not. The observation that bucks rarely interfered with their neighbours' harems and females moved freely between bucks suggests that females choose their mates on the basis of male phenotype rather than territory type or location. In this population, the immediate factor affecting the movements of females between males was the size of a buck's harem.
Fluctuating asymmetry (FA) of populations of the shrimp, Palaemon elegans, and the blood worm, Chironomus salinarius, was used to assess the environmental impact of a fertilizer manufacturing facility on the surrounding marine and freshwater ecosystems, respectively. Populations of both species were found to have elevated levels of asymmetry compared with control populations, indicating that the facility was having a significant impact on organism development. The use of FA of invertebrate populations as a simple, sensitive and cost-effective biomonitoring system for the detection of environmental stress is discussed.
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