F. E. Guinness

Red deer : behavior and ecology of two sexes

Red Deer: Behavior and Ecology of Two Sexes is the most extensive study yet available of reproduction in wild vertebrate. The authors synthesize data collected over ten years on a population of individually recognizable red deer, usually regarded as conspecific with the American elk. Their results reveal the extent of sex differences in behavior, reproduction, and ecology and make a substantial contribution to our understanding of sexual selection.

The logical stag: Adaptive aspects of fighting in red deer (Cervus elaphus L.)

For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6 % of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed. Anitn. Behav., 1979. 27, 21 I-225 THE LOGICAL STAG: ADAPTIVE ASPECTS OF FIGHTING IN RED DEER (CER VUS ELAPHUS L.) BY T. H. CLUTTON-BROCK, S. D. ALBON, R. M. GIBSON* & F. E. GUINNESS King’s College Research Centre, King’s College, Cambridge Abstract. For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6 % of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed. For red deer stags, fighting both has appreciable costs and yields considerable benefits. Up to 6 % of rutting stags are permanently injured each year, while fighting success and reproductive success are closely related, within age groups as well as across them. Fighting behaviour is sensitive to changes in the potential benefits of fighting: stags fight most frequently and most intensely where potential benefits are high and tend to avoid fighting with individuals they are unlikely to beat. The relevance of these findings to theoretical models of fighting behaviour is discussed.

Microsatellites reveal heterosis in red deer

The fitness consequences of inbreeding and outbreeding are poorly understood in natural populations. We explore two microsatellite–based variables, individual heterozygosity (likely to correlate with recent inbreeding) and a new individual–specific internal distance measure, meand2 (focusing on events deeper in the pedigree), in relation to two measures of fitness expressed early in life, birth weight and neonatal survival, in 670 red deer calves (Cervus elaphus) born on the Isle of Rum between 1982 and 1996. For comparison, we also analyse inbreeding coefficients derived from pedigrees in which paternity was inferred by molecular methods.Only 14 out of 231 calves (6.1%) had non–zero inbreeding coefficients, and neither inbreeding coefficient nor individual heterozygosity was consistently related to birth weight or neonatal survival. However, meand2 was consistently related to both fitness measures. Low meand2 was associated with low birth weight, especially following cold Aprils, in which foetal growth is reduced. Low meand2 was also associated with low neonatal survival, but this effect was probably mediated by birth weight because fitting birth weight to the neonatal survival model displaced meand2 as an explanatory variable. We conclude that in the deer population fitness measures expressed early in life do not show evidence of inbreeding depression, but they do show evidence of heterosis, possibly as a result of population mixing. We also demonstrate the practical problems of estimating inbreeding via pedigrees compared with a direct marker–based estimate of individual heterozygosity. We suggest that, together, individual heterozygosity and meand2, estimated using microsatellites, are useful tools for exploring inbreeding and outbreeding in natural populations.

ANTLER SIZE IN RED DEER: HERITABILITY AND SELECTION BUT NO EVOLUTION

Abstract We present estimates of the selection on and the heritability of a male secondary sexual weapon in a wild population: antler size in red deer. Male red deer with large antlers had increased lifetime breeding success, both before and after correcting for body size, generating a standardized selection gradient of 0.44 (±0.18 SE). Despite substantial age- and environment-related variation, antler size was also heritable (heritability of antler mass = 0.33 ± 0.12). However the observed selection did not generate an evolutionary response in antler size over the study period of nearly 30 years, and there was no evidence of a positive genetic correlation between antler size and fitness nor of a positive association between breeding values for antler size and fitness. Our results are consistent with the hypothesis that a heritable trait under directional selection will not evolve if associations between the measured trait and fitness are determined by environmental covariances: In red deer males, for example, both antler size and success in the fights for mates may be heavily dependent on an individuals nutritional state.

Population density affects sex ratio variation in red deer.

Many mammal populations show significant deviations from an equal sex ratio at birth, but these effects are notoriously inconsistent. This may be because more than one mechanism affects the sex ratio and the action of these mechanisms depends on environmental conditions. Here we show that the adaptive relationship between maternal dominance and offspring sex ratio previously demonstrated in red deer (Cervus elaphus),, where dominant females produced more males, disappeared at high population density. The proportion of males born each year declined with increasing population density and with winter rainfall, both of which are environmental variables associated with nutritional stress during pregnancy. These changes in the sex ratio corresponded to reductions in fecundity, suggesting that they were caused by differential fetal loss. In contrast, the earlier association with maternal dominance is presumed to have been generated pre-implantation. The effects of one source of variation superseded the other within about two generations. Comparison with other ungulate studies indicates that positive associations between maternal quality and the proportion of male offspring born have only been documented in populations below carrying capacity.

Great expectations: dominance, breeding success and offspring sex ratios in red deer

Differences in dominance rank among red deer (Cervus elaphus) females (hinds) on Rhum were related to their breeding success as well as to the comparative success of male and female offspring. Males (stags) born to mothers above median rank were more successful than hinds, while hinds born to subordinate mothers were more successful than stags. The ratio of male to female calves produced by dominant mothers was significantly higher than that produced by subordinates. Since dominance rank among hinds is related to their body weight as adults and to their birth weight, these results suggest that the birth sex ratio may be affected by environmental factors operating during a females early development.

Early development and population dynamics in red deer. I: Density-dependent effects on juvenile survival

(1) The paper investigates the effects of density-dependent changes in early development on population dynamics in red deer (Cervus elaphus) on Rhum. (2) The survival of calves through their first year of life was related to their birth weight and birth date. (3) As population density increased, the average date of parturition became later. Mean birth weight did not change, but at high density, its influence on over-winter calf survival intensified. (4) An extension of key factor analysis showed that these two effects were responsible for much of the increase in over-winter calf mortality at high population density.

Early determinants of lifetime reproductive success differ between the sexes in red deer.

In polygynous, sexually dimorphic species, sexual selection should be stronger in males than in females. Although this prediction extends to the effects of early development on fitness, few studies have documented early determinants of lifetime reproductive success in a natural mammal population. In this paper, we describe factors affecting the reproductive success of male and female red deer (Cervus elaphus) on the island of Rum, Scotland. Birthweight was a significant determinant of total lifetime reproductive success in males, with heavier–born males being more successful than lighter ones. In contrast, birthweight did not affect female reproductive success. High population density and cold spring temperatures in the year of birth decreased several components of fitness in females, but did not affect the breeding success of males. The results confirm the prediction that selection on a sexually dimorphic trait should be greater in males than in females, and explain the differential maternal expenditure between sons and daughters observed in red deer. Differences between the sexes in the effects of environmental and phenotypic variation on fitness may generate differences in the amount of heritable genetic variation underlying traits such as birthweight.

Factors Affecting Calf Mortality in Red Deer (Cervus elaphus)

(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.

POPULATION SUBSTRUCTURE, LOCAL DENSITY, AND CALF WINTER SURVIVAL IN RED DEER (CERVUS ELAPHUS)

Population substructure and the effects of scale have recently received much theoretical attention, but few studies have examined these factors in free-living populations of vertebrates. We used > 200 000 sightings of recognized females recorded over a con- tinuous 20-yr period to explore population substructure and spatial heterogeneity in red deer on the Isle of Rum, Scotland. We used hierarchical cluster analysis to group individuals together by their proximities in space, and we explored the influence of scale, considering scales ranging between the whole population and groups of one or two individuals. Inter- mediate scales were isolated as being the best at describing calf winter survival, the key factor in determining future population density. The most statistically explanatory scale isolated a population substructure related to vegetation, with higher local densities occurring around herb-rich Festuca-Agrostis grassland. Calves at high local density were most likely to die. Patterns of local population density varied between seasons in relation to food availability. High-resolution scales were the best descriptors of calf winter survival in summer; coarser scales were better in winter. In both summer and winter, local population density was more important than total population density in influencing calf winter survival. The effects on calf survival of local population density during the summer interacted significantly with calf sex and the mothers reproductive status. In this study, the technique of grouping animals by their proximity in space was more realistic and informative than discrete spatial divisions of the study area.