Do female roe deer in good condition produce more sons than daughters

In polygynous roe deer Capreolus capreolus, males are only slightly heavier than females and the overall sex ratio at birth is close to unity. We studied offspring sex ratio and litter size (range 1–4, n = 74) of culled females, in utero, which provided an opportunity to examine responses of sex ratio to maternal condition. Male embryos were heavier than their sisters, and male fawns (9 months old) heavier than female fawns, suggesting a higher growth rate in males. There was no evidence for differential mortality between the sexes from birth to 9 months old. Heavier adult females produced larger embryos than lighter, or primiparous females. The overall sex ratio of embryos did not differ from unity, but adult does had more male embryos (55%) than primiparous does (32%), and the proportion of male embryos in a litter increased with the mother's body mass. Litter size also tended to increase with maternal age and body mass. We argue that this pattern reflects adaptive variation in offspring sex ratio.     

Contest behaviour in the speckled wood butterfly (Pararge aegeria): seasonal phenotypic plasticity and the functional significance of flight performance

Although contemporary animal contest theory emphasises the importance of physical asymmetries in resolving disputes, such asymmetries do not obviously settle fights in all groups. Territorial male butterflies, for example, compete via elaborate non-contact aerial interactions in which success is determined by relative persistence. Prior research suggests that the resolution of these contests is not clearly related to physical variables such as body size or energy reserves. However, given that the contests involve elaborate aerial manoeuvres, one long-standing suggestion is that asymmetries in flight performance, and thus flight morphology, may be important. We addressed this hypothesis via a manipulative investigation into the biophysical correlates of contest success in the speckled wood butterfly, Pararge aegeria. This species possesses the ability for significant adaptive phenotypic plasticity in relevant flight morphological parameters. We took advantage of this plasticity to rear 90 individuals of markedly varying flight morphologies, which we then pitted against each other in a semi-controlled experimental fashion. Multiple logistic and lognormal analyses provided little evidence for the relevance of morphological parameters, including relative flight musculature, wing loading and wing aspect ratio (wing length relative to area), to the outcome and/or duration of experimental contests. Instead, we found a positive effect of age upon contest success. Given that ability for high acceleration is strongly linked to variation in these morphological parameters, our findings suggest that flight performance is not a strong determinant of resource-holding potential in this notably territorial butterfly.     

A dynamic model of mating behavior in digger wasps: the energetics of male-male competition mimic size-dependent thermal constraints

I develop a state-based dynamic model of behavior to demonstrate that size-dependent differences in temperature tolerances are not necessary to account for the activity of small male digger wasps late in the day. In the model, males defend or patrol the nesting area, wait near nests, or feed away from the nesting area depending on time of day, energy reserves and size rank. I assume a large male competitive advantage, so mating opportunities decrease with size rank for territorial or patrolling males and are rare for all waiting males; the costs of patrolling or defense are higher than the costs of waiting. If energy reserves of all males are initially small, all males alternate feeding and territorial or patrolling behavior. If energy reserves are initially large, large males patrol or maintain territories until they risk starvation and leave the area to feed. At this time, smaller males that have conserved their resources by waiting and feeding may defend territories or patrol. I simulate the behavior of three populations representing two species of Microbembex by assuming large initial energy reserves for populations in which males were territorial and small initial reserves for populations in which males patrolled, and then convert the predicted time of activity to temperature using local regressions from field studies. Temporal patterns in the activity of large and small males were similar to those actually observed, and relationships between size and temperature predicted by the model corresponded to most observations and were sometimes positive. Thus, the delayed activity of smaller males does not correspond to activity at higher temperatures and is probably not attributable to size-dependent thermal tolerances, but may represent a temporal displacement of mating activity due to intra-sexual competition and mediated by energetics. The model makes testable predictions on the timing of feeding and depletion of energy reserves in relation to size and initial energy state, and suggests how differences among species may influence the temporal and spatial organization of male mating behavior. Received: 27 February 1997 / Accepted after revision: 26 July 1997     

Pair and extra-pair mating success relative to male quality in red-winged blackbirds

We tested whether the reproductive success of male red-winged blackbirds (Agelaius phoeniceus) varied with male secondary sexual traits or with haematozoa prevalence, and whether these patterns were consistent with females preferring genetically superior males. We also determined whether the traits that correlated with male success on their own territories were also correlated with male success at siring young on other males territories. Our analysis included data from a 6-year study involving 617 nestlings for which paternity was determined by DNA profiling. Larger males sired more young on their territories, principally because they obtained larger harems. The success of larger males at acquiring more mates did not appear to be a consequence of larger males holding larger or better-quality territories. Older and longer-lived males sired more young by extra-pair fertilizations. Larger males sired the most offspring overall (on territory + off territory). Variation in epaulet size and color, responses to male and female models, nest defence and parasitism was not correlated with male success either on or off their territories or overall. Male success in a given year was significantly correlated with success the previous year, as expected if females were selecting genetically superior males. The male that was by far the most successful individual in this study was highly consistent from year to year. Because male body size is positively correlated with survival in this population (although not within the sample of males included in this study), female preference for larger males may have reflected a general preference for males with superior Survival ability. We propose that the direct advantage realized by older males in extra-pair matings might indicate that experience is important, such that experienced males are better at creating or exploiting the opportunities for extra-pair mating. This hypothesis is consistent with a pairwise analysis of cuckoldry that showed that cuckolders were most often older than the males they cuckolded.     

A field test of the Hamilton–Zuk hypothesis in the Trinidadian guppy (<Emphasis Type="Italic">Poecilia reticulata</Emphasis>)

The Hamilton–Zuk hypothesis proposes that females prefer male secondary sexual traits because they are honest indicators of parasite resistance. Despite the attention that this hypothesis has received, its role in sexual selection remains equivocal. This study presents the first field test in guppies of two key predictions of the Hamilton–Zuk hypothesis: (1) that within populations, the most highly ornamented males have the fewest parasites and (2) that among populations, males in high parasite populations have the most conspicuous ornaments. Five hundred male guppies from 19 distinct populations in the Northern Range of Trinidad were inspected for Gyrodactylus parasites and photographed. Eight measures of orange spot ornamentation were used to test the predictions: hue, saturation, lightness, relative area, number, and area-weighted hue, saturation, and lightness. Parasite load had no significant effect on any of these measures. There was also no relationship between orange spot ornamentation and parasite abundance among populations. Guppies from high-predation environments had significantly more parasites, and their orange coloration was lighter and less saturated than that in guppies from low-predation environments. Despite previous lab results, this study found no relationship between parasite load and male orange spot ornamentation.     

Determinants of male territorial behavior in a Hungarian collared flycatcher population: plumage traits of residents and challengers

In intrasexual conflicts, contestants can rely on relative or absolute size of status badges to mediate aggressive behavior. Most studies focus on the response of focal animals to variation in status badges of their competitors; few have simultaneously considered the traits of both participants under experimental conditions. By simulating territorial intrusions, we tested the importance of two sexual traits [forehead patch size (FPS) and wing patch size (WPS)] in territorial behavior of males in a Hungarian population of the collared flycatcher, Ficedula albicollis. We presented a stimulus male to an unpaired resident male to examine whether the characteristics of the territory owner or those of the challenger were associated with the latency of the first attack of the owner, which is a good predictor of the territorial behavior in general. WPS of the stimulus male was a significant determinant of the latency of the first attack, as males with a larger WPS elicited quicker attacks from the residents than males with a small WPS. From the residents’ perspective, age appeared to influence their territorial behavior, as yearlings had shorter attack latencies than older males. Additionally, latency could be considered an individual-specific attribute because it varied consistently among males, even when the WPS of the stimulus male was controlled, and it was associated with pairing success. Contrary to findings in a Swedish population, FPS seemed to be unimportant in male–male competition in our population, which suggests population differences in the role of the two plumage traits. Our results indicate that in a territorial conflict, the characteristics of both participants are important.     

The efficacy of female choice in chimpanzees of the Taï Forest, Côte d’Ivoire

Male–male competition has historically been considered the major force driving sexual selection. However, female choice and inter-sexual conflict are increasingly recognized as important influences affecting differential mating and reproductive success. Many females exhibit preferences for particular males; however, male strategies may conflict with females’ ability to obtain their mate preferences. To influence paternity, females must affect both (1) whether or not sexual interactions occur, particularly during the periovulatory period (POP) and (2) the outcome of sexual interactions. This study focuses on the effectiveness of female choice in wild chimpanzees (Pan troglodytes verus). Over 2,600 h of data were collected on two habituated chimpanzee communities in the Taï National Park, Côte d’Ivoire. Female mate preferences were measured by quantifying proceptive and resistance behavior toward males in both the periovulatory period and non-POP phases of estrus. The efficacy of female preference was measured both (1) by measuring success rates of female proceptivity and resistance behaviors and (2) by determining how well measures of female mate preference (proceptivity and resistance rates) predict male mating success. Though male chimpanzees are clearly dominant to females, the results indicate that females could effectively resist male solicitations and, in most cases, unwanted copulations were averted. Both female proceptivity and resistance rates correlate (positively and inversely, respectively) with male mating success in POP. Outside POP, female proceptivity rates corresponded with male mating success, but resistance rates did not. Males (irrespective of rank) that were preferred by females obtained higher mating success compared to other males during the POP, suggesting that females were effective in their mate choice and that, despite clear male dominance, female choice influences paternity in wild chimpanzees.     

Male coloration and chick condition in blue-footed booby: a cross-fostering experiment

Sexual selection models suggest that female choice is based on male traits that indicate their genetic or environmental condition, consequently enhancing her reproductive success by direct or indirect benefits. We investigated the relationship between male foot colour and offspring condition in the blue-footed booby, a socially monogamous seabird, with conspicuous and variably condition-dependent coloured feet that are selected by females. In a cross-fostering experiment, we found that chick condition was related to the foot colour of the foster father and, to some extent, to the foot colour of the genetic father; thus overall, the fathers sexual ornamentation (genetic and foster) explained 32% of variance of chick condition. These data suggest that foot colour, a dynamic sexually selected trait, is mostly a signal of parental contribution. In species in which males provide parental care, females may choose mates with higher parental ability. Overall, our data suggest that colourful integuments are honest signals of parental ability.Communicated by J. Graves     

Sexual conflict over sperm ejection in monogamous pairs of kittiwakes<Emphasis Type="Italic"> Rissa tridactyla</Emphasis>

Socially monogamous partners suffer conflicting interests concerning various aspects of reproduction such as parental care, copulation and fertilization. Female black-legged kittiwakes commonly eject their mates' sperm immediately following copulations. Because sperm ejection reduces male sperm competitiveness and paternity assurance, males and females have conflicting interests as regards sperm ejection. Males whose mates ejected their sperm at least once remained longer on their mates' backs after the last insemination which apparently prevented the females from ejecting sperm. These results suggest that compelling females to retain their sperm may be a previously unidentified tactic employed by males to assure their paternity. Females tried to prevent their mates from witnessing sperm ejection by ejecting sperm after their mates departed from the nest. Females were more likely to eject sperm when they terminated the copulations by unbalancing the male. The conflict over sperm ejection was related to the ability of the females to end the copulations which covaried with the body mass of their mates. These findings suggest that conflicts in monogamous pairs also exist over the disposition of sperm.Communicated by C.R. Brown     

The tactics of mutual mate choice and competitive search

A model of mutual mate choice is described, formulated as a dynamic game, which yields predictions about mating behaviour under the influence of time constraints, choice costs and competition for mates. These variables were examined because they may result in a change in the distribution of qualities among unmated individuals of both sexes over the course of the breeding season. The model predicts that mutual choice gives rise to assortative mating, although high costs of choice and/or inaccurate assessment both lead to lower overall correlations between the qualities (or the attractiveness) of mates. When all individuals are present from the start of the breeding season, the correlation between the qualities of individuals pairing at a given time declines throughout the season, so that mates are more closely matched among individuals who pair early than among those who pair late (and extra-pair copulation may thus be more common among the latter). Delayed arrival of lower-quality individuals may, however, lead to an increase in this correlation with time during the early part of the season. The mean quality of unmated males and females declines over time, because more attractive individuals tend to mate sooner. As a result of this decline, and because of time constraints, superior individuals become less choosy as the season progresses. If choice is costly, however, then inferior individuals become more selective with time during the early part of the season, and the level of choosiness peaks later for such individuals. Received: 28 March 1996 / Accepted after revision: 21 September 1996