scholarly journals Function of weaponry in females: the use of horns in intrasexual competition for resources in female Soay sheep

2007 ◽  
Vol 3 (6) ◽  
pp. 651-654 ◽  
Author(s):  
Matthew R Robinson ◽  
Loeske E.B Kruuk
Keyword(s):  
Local Density ◽  
Intrasexual Competition ◽  
Genetic Associations ◽  
Aggressive Interactions ◽  
Soay Sheep ◽  
Male Phenotype ◽  
Feral Population ◽  
Males And Females ◽  
Competition For Resources ◽  
Horn Development

In many species, females show reduced expression of a trait that is under sexual selection in males, and this expression is thought to be maintained through genetic associations with the male phenotype. However, there is also the potential for the female trait to convey an advantage in intrasexual conflicts over resources. We tested this hypothesis in a feral population of Soay sheep, in which males and females have a polymorphism for horn development, producing either full (normal horned), reduced (scurred) or no (polled, females only) horns. During the lambing period, females who possessed horns were more likely to initiate and win aggressive interactions, independent of age, weight and birthing status. The occurrence of aggression was also context dependent, decreasing over the lambing period and associated with local density. Our results demonstrate that a trait that confers benefits to males during intrasexual competition for mates may also be used by females in intrasexual competition over resources: males use weaponry to gain mates, whereas females use weaponry to gain food.

scholarly journals Sex ratio and the evolution of aggression in fruit flies

2021 ◽  
Vol 288 (1947) ◽  
Author(s):  
Eleanor Bath ◽  
Danielle Edmunds ◽  
Jessica Norman ◽  
Charlotte Atkins ◽  
Lucy Harper ◽  
...  
Keyword(s):  
Social Environment ◽  
Experimental Evolution ◽  
Genetic Basis ◽  
Female Aggression ◽  
Female Competition ◽  
Sexual Competition ◽  
The Social ◽  
Males And Females ◽  
Competition For Resources ◽  
Shared Genetic

Aggressive behaviours are among the most striking displayed by animals, and aggression strongly impacts fitness in many species. Aggression varies plastically in response to the social environment, but we lack direct tests of how aggression evolves in response to intra-sexual competition. We investigated how aggression in both sexes evolves in response to the competitive environment, using populations of Drosophila melanogaster that we experimentally evolved under female-biased, equal, and male-biased sex ratios. We found that after evolution in a female-biased environment—with less male competition for mates—males fought less often on food patches, although the total frequency and duration of aggressive behaviour did not change. In females, evolution in a female-biased environment—where female competition for resources is higher—resulted in more frequent aggressive interactions among mated females, along with a greater increase in post-mating aggression. These changes in female aggression could not be attributed solely to evolution either in females or in male stimulation of female aggression, suggesting that coevolved interactions between the sexes determine female post-mating aggression. We found evidence consistent with a positive genetic correlation for aggression between males and females, suggesting a shared genetic basis. This study demonstrates the experimental evolution of a behaviour strongly linked to fitness, and the potential for the social environment to shape the evolution of contest behaviours.

Social influences on intergroup transfer by pine voles (Microtus pinetorum)

1998 ◽  
Vol 76 (12) ◽  
pp. 2131-2136 ◽  
Author(s):  
Nancy G Solomon ◽  
John G Vandenbergh ◽  
William T Sullivan, Jr.
Keyword(s):  
Social Influences ◽  
Same Sex ◽  
Control Groups ◽  
Intergroup Transfer ◽  
Mating Opportunities ◽  
Microtus Pinetorum ◽  
Group A ◽  
Opposite Sex ◽  
Males And Females ◽  
Competition For Resources

Selection to obtain mating opportunities is hypothesized to be a major factor in dispersal. Thus, if individuals move to another group or switch nests to maximize their reproductive opportunities, they should move to groups or sites where they minimize competition for resources or mates and where they can find potential mates. We examined movement of pine voles (Microtus pinetorum) in an orchard habitat. Males dispersed later than females, but the two sexes showed similar patterns of movement with respect to conspecifics. Males and females immigrated to territories that contained some opposite-sex conspecifics; they also immigrated to territories without same-sex conspecifics. The latter suggests that they may avoid competitors and move to territories where an opening exists. When female breeders were removed from a social group, a replacement female arrived and began to breed relatively rapidly. In control groups where breeding females were not removed, no replacement females appeared. These results suggest that pine voles, at least females, may monitor vacancies and immigrate if a vacancy appears.

scholarly journals Sexual conflict in twins: male co-twins reduce fitness of female Soay sheep

2009 ◽  
Vol 5 (5) ◽  
pp. 663-666 ◽  
Author(s):  
Peter Korsten ◽  
Tim Clutton-Brock ◽  
Jill G. Pilkington ◽  
Josephine M. Pemberton ◽  
Loeske E. B. Kruuk
Keyword(s):  
Sex Allocation ◽  
Limited Resources ◽  
First Year ◽  
Specific Interactions ◽  
Soay Sheep ◽  
Sibling Interactions ◽  
Survival And Reproduction ◽  
Males And Females ◽  
Long Term Consequences

Males and females often have different requirements during early development, leading to sex-specific interactions between developing offspring. In polytocous mammals, competition for limited resources in utero may be asymmetrical between the sexes, and androgens produced by male foetuses could have adverse effects on the development of females, with potentially long-lasting consequences. We show here, in an unmanaged population of Soay sheep, that female lambs with a male co-twin have reduced birth weight relative to those with a female co-twin, while there was no such effect in male twins. In addition, females with a male co-twin had lower lifetime breeding success, which appeared to be mainly driven by differences in first-year survival. These results show that sex-specific sibling interactions can have long-term consequences for survival and reproduction, with potentially important implications for optimal sex allocation.

Reversed Sexual Size Dimorphism: Effect on Resource Defense and Foraging Behaviors of Nonbreeding Northern Harriers

The Auk ◽  
1986 ◽  
Vol 103 (1) ◽  
pp. 70-78 ◽  
Author(s):  
Ethan J. Temeles
Keyword(s):  
Sexual Size Dimorphism ◽  
Sexual Differences ◽  
Foraging Strategies ◽  
Resource Defense ◽  
Aggressive Interactions ◽  
Nonbreeding Season ◽  
Males And Females ◽  
Circus Cyaneus ◽  
Reversed Sexual Size Dimorphism

Abstract Sexual differences in resource defense and foraging behaviors during the nonbreeding season are detailed for Northern Harriers (Circus cyaneus) in California. Female harriers hunted more frequently in high (>0.5 m) vegetation than males. In addition, females hunted at slower speeds and used different hunting behaviors than males. Females in high vegetation showed a significantly greater response (i.e. attack) rate to approaching harriers than males, and females won nearly all (28/29) aggressive interactions with males. These results suggest that sexual differences in harrier foraging behavior during the nonbreeding season result from females excluding males from preferred foraging areas and males adopting alternative foraging strategies. Foraging strategies of harrier sexes are compared with foraging strategies of sexes of birds in which males are larger than females to examine the role of body size in determining sexual foraging strategies.

Pilot Study of Relationship between Fertility Risk and Bargaining

2007 ◽  
Vol 101 (1) ◽  
pp. 302-310 ◽  
Author(s):  
Margery M. Lucas ◽  
Elissa Koff ◽  
Susan Skeath
Keyword(s):  
Pilot Study ◽  
Intrasexual Competition ◽  
Bargaining Games ◽  
Ultimatum Games ◽  
Healthy Pregnancy ◽  
Competition For Resources

Competition for resources to support a healthy pregnancy and later offspring was likely very important for ancestral women. Therefore, it was predicted that women evolved a propensity for intrasexual competition over resources during times of their highest conception risk. To investigate this hypothesis, women played a series of ultimatum games, bargaining games that test participants' willingness to share a monetary stake. During periods of high conception risk, intrasexual competition increased as evidenced by lower offers to share a stake with others as well as higher rates of rejection of offers.

scholarly journals A model of sexual selection and female use of refuge in a coercive mating system

2012 ◽  
Vol 279 (1741) ◽  
pp. 3209-3216
Author(s):  
Dessa Bokides ◽  
Yuan Lou ◽  
Ian M. Hamilton
Keyword(s):  
Total Population ◽  
Relative Number ◽  
Threshold Level ◽  
Male Harassment ◽  
Male Phenotype ◽  
Males And Females ◽  
Selection For ◽  
Coercive Mating ◽  
The Relationship ◽  
Number Of Males

In many non-monogamous systems, males invest less in progeny than do females. This leaves males with higher potential rates of reproduction, and a likelihood of sexual conflict, including, in some systems, coercive matings. If coercive matings are costly, the best female strategy may be to avoid male interaction. We present a model that demonstrates female movement in response to male harassment as a mechanism to lower the costs associated with male coercion, and the effect that female movement has on selection in males for male harassment. We found that, when females can move from a habitat patch to a refuge to which males do not have access, there may be a selection for either high, or low harassment male phenotype, or both, depending on the relationship between the harassment level of male types in the population and a threshold level of male harassment. This threshold harassment level depends on the relative number of males and females in the population, and the relative resource values of the habitat; the threshold increases as the sex ratio favours females, and decreases with the value of the refuge patch or total population. Our model predicts that selection will favour the harassment level that lies closest to this threshold level of harassment, and differing harassment levels will coexist within the population only if they lie on the opposite sides of the threshold harassment. Our model is consistent with empirical results suggesting that an intermediate harassment level provides maximum reproductive fitness to males when females are mobile.

scholarly journals Predictors of early survival in Soay sheep: cohort-, maternal- and individual-level variation

2005 ◽  
Vol 272 (1581) ◽  
pp. 2619-2625 ◽  
Author(s):  
Owen R Jones ◽  
Michael J Crawley ◽  
Jill G Pilkington ◽  
Josephine M Pemberton
Keyword(s):  
Maternal Age ◽  
Ovis Aries ◽  
Relative Importance ◽  
Level Variation ◽  
Individual Level ◽  
Soay Sheep ◽  
Individual Based Models ◽  
Feral Population ◽  
Early Survival ◽  
The Individual

A demographic understanding of population dynamics requires an appreciation of the processes influencing survival—a demographic rate influenced by parameters varying at the individual, maternal and cohort level. There have been few attempts to partition the variance in demography contributed by each of these parameter types. Here, we use data from a feral population of Soay sheep ( Ovis aries ), from the island of St Kilda, to explore the relative importance of these parameter types on early survival. We demonstrate that the importance of variation occurring at the level of the individual, and maternally, far outweighs that occurring at the cohort level. The most important variables within the individual and maternal levels were birth weight and maternal age class, respectively. This work underlines the importance of using individual based models in ecological demography and we, therefore, caution against studies that focus solely on population processes.

THE SOAY SHEEP OF THE ISLAND OF HIRTA, ST. KILDA. A STUDY OF A FERAL POPULATION

2009 ◽  
Vol 142 (1) ◽  
pp. 129-164 ◽  
Author(s):  
J. MORTON BOYD ◽  
J. MACKAY DONEY ◽  
R. GRAHAM GUNN ◽  
PETER A. JEWELL
Keyword(s):  
Soay Sheep ◽  
Feral Population

scholarly journals Can outcomes of dyadic interactions be consistent across contexts among wild zebrafish?

2015 ◽  
Vol 2 (11) ◽  
pp. 150282 ◽  
Author(s):  
Tamal Roy ◽  
Anuradha Bhat
Keyword(s):  
Reproductive Success ◽  
Resource Availability ◽  
Food Resource ◽  
Group Living ◽  
Dyadic Interactions ◽  
Agonistic Interactions ◽  
Aggressive Interactions ◽  
Probable Role ◽  
Competition For Resources

Winner–loser relations among group-living individuals are often measured by the levels of aggressive interactions between them. These interactions are typically driven by competition for resources such as food and mates. It has been observed in recent studies on zebrafish that dominant males generally have higher total reproductive success than their less aggressive subordinate counterparts. This study aimed to test whether males who monopolized a food resource (winners) also displayed higher levels of aggression than the males who were unsuccessful (losers). Further, the study also tested whether the same ‘winner’ males were also able to monopolize interactions with females during courtship. The results from these experiments showed that while males monopolizing food resources (winners) demonstrated higher levels of agonistic interactions than the losers, the average number of courtship interactions initiated by either of the males (i.e. winners/losers) with a female was not significantly different. A significant relationship was obtained between the number of aggressive interactions and feeding latencies of males in the context of food monopolization. This indicated that there could be a linkage between boldness defined by feeding latency in a novel environment and agonistic responses. The probable role of nature of resources, resource availability and distribution in determining the outcomes of dyadic contests is discussed.

Disrupting information alters the behavioral response to a mutual signal trait in both sexes of Nicrophorus (Coleoptera: Silphidae) burying beetles

2019 ◽  
Vol 30 (4) ◽  
pp. 960-967
Author(s):  
Jillian D Wormington ◽  
Barney Luttbeg
Keyword(s):  
Body Size ◽  
Behavioral Responses ◽  
Reproductive Investment ◽  
Sexually Dimorphic ◽  
Burying Beetles ◽  
Signaling Function ◽  
Opposite Sex ◽  
Nicrophorus Orbicollis ◽  
Males And Females ◽  
Competition For Resources

AbstractEffective signals transfer information in a way that enhances the fitness of the sender. Signal traits are often sexually dimorphic. However, in some species, males and females display similar signals, and these mutual signals are less often studied. Competition for resources occurs in both males and females, and mate choice is likely to occur whenever mates vary in quality and reproductive investment is high. Nicrophorus burying beetles compete intrasexually over the carrion resources on which they biparentally raise their young. Nicrophorus species also often have clypeal membranes which scale hyperallometrically with body size, exaggerating the apparent body size of larger individuals. To examine the potential signaling function of clypeal membranes, we examined the behavioral responses of male and female Nicrophorus orbicollis and Nicrophorus pustulatus burying beetles to same- and opposite-sex social partners which had their membranes painted black or clear. We found evidence that blocking the information in clypeal membranes affected intrasexual aggressive interactions for both sexes of both species. Blocking a female’s signal reduced the likelihood of mating attempts for male N. pustulatus, whereas blocking a male’s signal influenced female rejection behaviors in N. orbicollis. Our results show that males and females can experience similar selection pressures, and suggest that examining mutual signals in a broader range of systems will expand our understanding of evolutionary differences and similarities between the sexes.

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