Female calls in lek-mating birds: indirect mate choice, female competition for mates, or direct mate choice?

I tested predictions from ultimate hypotheses of why femalegreat snipe Gallinago media give loud calls when visiting leks,using observational data and playback experiments. One hypothesisis that calls might be used in female—female competitionfor popular males, either (1) in an aggressive context towarda specific female, or (2) toward females in general to defendthe male. It has also been suggested that female calls (3) may not have an adaptive function, the capability of vocalizingbeing explained as a correlated response to selection on malesinging. Further, calls might function as (4) a copulationsolicitation toward a specific male. Finally, calls might havea function in mate choice, either (5) in indirect mate choiceas a fertility advertisement to incite male fighting, or (6)in direct mate choice as a mate-sampling aid to provoke quality-revealing responses from males. Disproportionately many female calls wereuttered when no other females were present on a male's territoryand in territories of males without mating success, contradictinghypotheses 1 and 2. Female calls were not associated with copulation;calls generally occurred several days before copulations, contradictinghypotheses 4 and 5. Playback of female calls attracted malesand increased fighting among males, even if females were presentnearby, contradicting hypothesis 3. Males changed their ownsongs in response to playback, and the response was relatedto their mating success. Taken together, the results are onlyconsistent with one of the hypotheses considered—femalecalls may function as a mate-sampling aid used in direct matechoice.     

Social rank,feeding and winter weight loss in red deer: any evidence of interference competition?

During winter at northern latitudes, large herbivores often exploit patches of concentrated, relatively high quality forage, which may lead to interference competition. The factors affecting success in contests and subsequent dominance rank, such as age and body weight, remain key issues in ungulate behavioural ecology. Maternal effects on offspring body weight are well known, but few studies have investigated if mothers social rank influence offspring rank. Moreover, no study has related dominance rank in ungulates to weight loss during winter. Outcomes of social interactions (n=7,609), feeding time and spatial position in red deer (Cervus elaphus) hinds and calves, and weight loss of calves, were registered from 1981 to 1996 at six winter-feeding sites within the county of Sør-Trøndelag in Norway. The level of aggressiveness was higher among calves than among adult hinds, and the factors determining the outcome of contests also differed. The initiator won the majority of interactions (more than 90% in both hinds and calves). Social rank was related to both age and body weight in adult hinds, and related to body weight and mother rank in calves. The relationship between feeding time and rank was non-linear. Feeding time was correlated with rank only among high ranked hinds, while there was no such relationship among low ranked hinds or calves. There was no correlation between winter weight loss and social rank in calves. Our study therefore underlines that, although frequent aggression is observed at artificial feeding sites of northern herbivores, this is not necessarily sufficient to give rise to interference competition.     

Does environmental stochasticity matter? Analysis of red deer life-histories on Rum

Summary Most life-history theory assumes that short-term variation in an organism's environment does not affect the survivorships and fecundities of the organisms. This assumption is rarely met. Here we investigate the population and evolutionary biology of red deer,Cervus elephas, to see if relaxation of this assumption is likely to make significant differences to the predicted evolutionary biology of this species. To do this we used 21 years of data from a population of deer on Rum, Western Isles, Scotland. Population growth rates in a stochastic environment were estimated using Tuljapurkar's small noise approximation, confirmed by bootstrap simulation. Numerical differentiation was used to see if the selection pressures (i.e. sensitivities of population growth rate to changes in the vital rates) differ between the stochastic and deterministic cases. The data also allow the costs of reproduction to be estimated. These costs, incorporated as trade-offs into the sensitivity analysis, allow investigation of evolutionary benefits of different life-history tactics. Environmentally induced stochastic variation in the red deer vital rates causes a slight reduction ( 1%) in the predicted population growth rate and has little impact on the estimated selection pressures on the deer's life-history. We thus conclude that, even though density-independent stochastic effects on the population are marked, the deer's fitness is not markedly affected by these and they are adapted to the average conditions they experience. However, the selected life-history is sensitive to the trade-offs between current fecundity, survivorship and future fecundity and it is likely that the environmental variance will affect these trade-offs and, thus, affect the life-history favoured by selection. We also show that the current average life-history is non-optimal and suggest this is a result of selection pressures exerted by culling and predation, now much reduced. As the use of stochastic or deterministic methods provide similar estimates in this case, the use of the latter is justified. Thus,r (the annual per capita rate of population growth) is an appropriate measure of fitness in a population with stochastic numerical fluctuations. In a population of constant size lifetime reproductive success is the obvious measure of fitness to use.     

Is competition needed for ecological character displacement? Does displacement decrease competition?

Interspecific competition for resources is generally considered to be the selective force driving ecological character displacement, and displacement is assumed to reduce competition. Skeptics of the prevalence of character displacement often cite lack of evidence of competition. The present article uses a simple model to examine whether competition is needed for character displacement and whether displacement reduces competition. It treats systems with competing resources, and considers cases when only one consumer evolves. It quantifies competition using several different measures. The analysis shows that selection for divergence of consumers occurs regardless of the level of between‐resource competition or whether the indirect interaction between the consumers is competition (?,?), mutualism (+,+), or contramensalism (+,?). Also, divergent evolution always decreases the equilibrium population size of the evolving consumer. Whether divergence of one consumer reduces or increases the impact of a subsequent perturbation of the other consumer depends on the parameters and the method chosen for measuring competition. Divergence in mutualistic interactions may reduce beneficial effects of subsequent increases in the other consumer's population. The evolutionary response is driven by an increase in the relative abundance of the resource the consumer catches more rapidly. Such an increase can occur under several types of interaction.     

Female Copulation Calls in Guinea Baboons: Evidence for Postcopulatory Female Choice?

We tested the hypothesis that primate female copulation calls are a form of postcopulatory female choice. We collected data on female sexual swellings, sexual and agonistic behavior, copulation calls and postcopulatory behavioral interactions in a multimale-multifemale captive group of Guinea baboons over a 3-mo period. Males copulated with only a few females, and females copulated with only 1 or 2 different males in the group, suggesting a harem-like mating system similar to that of hamadryas and gelada baboons. Female copulations were most likely to occur at peak sexual swellings and male copulatory success was accounted for by dominance rank and age. Variation in female tendencies to call after copulation is best explained by the copulatory success of the male with which each female copulated the most and by the number of copulating partners. The findings are consistent with predictions that calls are likely to be associated with copulation with preferred males and the risk of sperm competition. The prediction that copulation calls increased the probability of postcopulatory mate guarding is also supported. Taken together, the findings suggest that female copulation calls may play an important role in postcopulatory sexual selection and in particular in the expression of postcopulatory female choice in primate species in which females have little opportunity to choose their mates or female mate choice is costly or both.     

Isolation effect in mice (Mus musculus): (i) Does it really induce aggression?

In previous studies, isolated mice are found to be extremely more aggressive than group-reared mice. In most of those studies, however, the pairings of the group-reared mice were randomly determined, without attention to individuals' ranks in their home cages. In this study, the effect of isolation was analyzed by comparing isolated mice with dominants of group-reared mice. In experiment 1 the group-reared mice were randomly chosen as in previous studies. Isolated mice were significantly more aggressive, but the pairings of the group-reared mice were found to be all dominant vs. subordinate. In experiment 2, the group-reared dominants encountered unfamiliar dominants in an unfamiliar place. Dominant mice were found to be less aggressive than the isolated mice. This result was inconsistent with the “territorial dominant hypothesis” on the hyperaggressiveness of the isolated mice. Sequential analysis of behavior clarified that the isolated mice had a sequential pattern quite different from the group-reared mice, and provided an illustrative figure for the “escalation hypothesis”. The lack of aggression in the group-reared mice, however, left a question about the sequence similarity of aggressive behavior in isolaed and group-reared mice.     

Sperm selection and genetic incompatibility: does relatedness of mates affect male success in sperm competition?

Sperm selection may be said to occur if females influence the relative success of ejaculates competing to fertilize their ova. Most evidence that female animals or their ova are capable of sperm selection relates to male genetic incompatibility, although relatively few studies focus on competition between conspecific males. Here I look for evidence of sperm selection with respect to relatedness of mates. Reduced fitness or inbreeding effects in offspring resulting from copulations between close relatives are well documented. If females are capable of sperm selection, they might therefore be expected to discriminate against the sperm of sibling males during sperm competition. I describe an experimental protocol designed to test for evidence of sperm selection while controlling for inbreeding effects. Using decorated field crickets (Gryllodes supplicans), I found that sibling males achieved lower fertilization success in competition with a male unrelated to the female than in competition with another sibling more frequently than expected by chance, although the mean paternity values did not differ significantly between treatments. The tendancy for sibling males to achieve relatively lower fertilization success in competition with males unrelated to the female could not be explained by the effects of increased ejaculate allocation, female control of sperm transfer or inbreeding. This study therefore provides some evidence in support of the idea that female insects (or their ova) may be capable of selection against sperm on the basis of genetic similarity of conspecific males.     

Intrasexual competition in females: evidence for sexual selection?

In spite of recent interest in sexual selection in females, debate exists over whether traits that influence female-female competition are sexually selected. This review uses female-female aggressive behavior as a model behavioral trait for understanding the evolutionary mechanisms promoting intrasexual competition, focusing especially on sexual selection. I employ a broad definition of sexual selection, whereby traits that influence competition for mates are sexually selected, whereas those that directly influence fecundity or offspring survival are naturally selected. Drawing examples from across animal taxa, including humans, I examine 4 predictions about female intrasexual competition based on the abundance of resources, the availability of males, and the direct or indirect benefits those males provide. These patterns reveal a key sex difference in sexual selection: Although females may compete for the number of mates, they appear to compete more so for access to high-quality mates that provide direct and indirect (genetic) benefits. As is the case in males, intrasexual selection in females also includes competition for essential resources required for access to mates. If mate quality affects the magnitude of mating success, then restricting sexual selection to competition for quantity of mates may ignore important components of fitness in females and underestimate the role of sexual selection in shaping female phenotype. In the future, understanding sex differences in sexual selection will require further exploration of the extent of mutual intrasexual competition and the incorporation of quality of mating success into the study of sexual selection in both sexes.     

Does competition for nests affect genetic monogamy in Cory's shearwater Calonectris diomedea?

Most bird species are socially monogamous. However, extra‐pair copulations (EPCs), resulting in extra‐pair paternity (EPP), commonly occur. EPCs should allow females to adjust social mate choice and allow males that fail to obtain a nest a chance to avoid missing a breeding season, especially when poor nest supply constrains social mate choice. Procellariiformes (albatrosses and petrels) are socially monogamous seabirds which seldom divorce, even when nest availability constrains social mate choice. In Cory's shearwater Calonectris diomedea, a burrow‐nesting petrel, two studies conducted in the Mediterranean, where competition for nests is weak, detected no EPP. EPP remains to be investigated at localities where competition for nests is much stronger, such as Vila islet, Azores archipelago, Atlantic Ocean. We conducted a genetic (microsatellites) study over two successive years on Vila, involving the breeding pairs of the same 65 nests each year and their single chick. EPPs occurred each year, the overall rate being 11.6%. Coupling genetic analyses to a 7‐year demographic survey provided additional data on pair bonds and competition for nests. Overall, cuckoldry was unrelated to divorce, nest density and inbreeding avoidance, but was more frequent when the social male was small. Nest changes were more costly for males than for females, and some apparently unpaired males attempted to dislodge social males during within‐pair copulations. These results are compatible with the existence of a link between poor nest availability and EPP and confirm that even species considered strongly monogamous can adopt flexible mating strategies.     

Molecular phylogeny of Megaloceros giganteus--the giant deer or just a giant red deer?

Two fragments of mitochondrial DNA (mtDNA) of the cytochrome b gene (137 bp and 167 bp) were successfully isolated and sequenced from antlers and bones of five specimens of the Giant Deer (Megaloceros giganteus) to examine the phylogenetic position of Megaloceros giganteus within the family Cervidae. This is the first report on ancient DNA (aDNA) sequences from Megaloceros giganteus. A phylogenetic analysis based on parameter-rich models describes the evolutionary relationships between five individuals of fossil Megaloceros giganteus and 37 individuals of 11 extant species of the family Cervidae. The results support a "Cervus-Megaloceros" clade. The phylogenetic positions of sympatric Megaloceros and Cervus elaphus specimens in particular indicate either that the Megaloceros mtDNA gene pool did not evolve for a substantial time period as an entity distinct from Cervus elaphus until its extinction, or that Megaloceros contributed mtDNA to Cervus elaphus or vice versa. The results of this study allow the conclusion that the European Megaloceros giganteus is more related to its modern regional counterparts of the species of Cervus elaphus than recent claims have suggested.     

Female mate choice and male–male competition in Tonkean macaques: Who decides?

The theory of sexual selection predicts that females should be discriminatory in the choice of sexual partners. Females can express their choice in two ways. In direct mate choice, they show preferences for certain partners. In indirect mate choice, they select partners by displaying sexually attractive traits, thus eliciting contest competition between males. We focused on a primate species in which females advertise the timing of their ovulation and studied the balance between these two choice strategies. We tested predictions related to three hypotheses about direct and indirect female choice, namely the best‐male, graded‐signal and weak‐selectivity hypotheses. We investigated the sexual and agonistic interactions occurring during oestrous periods in five captive groups of Tonkean macaques (Macaca tonkeana). The results showed that dominant males used mate guarding to monopolise sexual access to parous females that were in the fertile stage of their reproductive cycle, while lower‐ranking males monitored only nulliparous females. The distribution of sexual presentations indicated that females accepted different types of partners, supporting the weak‐selectivity hypothesis regarding direct mate choice. The analysis of behavioural sequences revealed that mate‐guarding males used mild coercive behaviours to prevent females from mating with other males at conception time. The distribution of mounts showed that females mainly mated with dominant males, which leads us to argue that the best‐male hypothesis provides the most parsimonious explanation regarding indirect mate choice in Tonkean macaques. At the individual level, it may be concluded that male competitive strategies prevented females from exercising direct mate choice. At the evolutionary level, however, female sexual advertising and thus indirect choice promoted competition between males. The outcome is that indirect mate choice appears more important than direct mate choice in female Tonkean macaques.     

Does genetic diversity reduce intraspecific competition in rotifer populations?

As a result of reduced intraspecific competition, genetically diverse populations may have higher relative fitness than genetically uniform populations. To test this hypothesis, we compared polyclonal (i.e., genetically diverse) versus monoclonal (i.e., composed of a single clonal genotype) experimental populations of the rotifer Brachionus plicatilis (Müller, 1786) growing separately and in competition. We estimated the following fitness components: intrinsic growth rate; carrying capacity; proportion of sexual females; diapausing egg production per sexual female and total egg production. Polyclonal populations showed similar dynamics to monoclonal populations and no statistical difference between their fitness components was detected. Therefore, results do not support the hypothesis that genetically diverse populations reduce competition through diversification in resource use. Instead, results suggest that B. plicatilis is a generalist consumer whose polyphagy does not depend on genetic differences, but on the broad diet of each genotype. However, clones showed significant differences in almost all fitness components demonstrating among-clone variation in life-history traits. We found a trade-off between sexual ratio and carrying capacity, highlighting the cost of sex in cyclical parthenogenetic rotifers. We discuss the mechanisms that could maintain the observed among-clone genetic variation in natural populations, and speculate on results implication for sex maintenance in rotifers.     

Spotlight surveys for white-tailed deer: Monitoring panacea or exercise in futility?

Many monitoring programs for white-tailed deer (Odocoileus virginianus) on both private and public lands across the United States have long relied on the use of road-based spotlight surveys for monitoring population size and trends. Research has suggested spotlight surveys are ineffective and that road-based surveys for deer are biased because of highly variable detection rates. To evaluate variability in detection rates relative to the assumption that repeated surveys along roads will provide reliable trend data for use in calculating deer density estimates, we collected 5 years of thermal-imager and spotlight survey data using a multiple-observer, closed-capture approach. Using a Huggin's closed capture model, data bootstrapping, and variance components analyses, our results suggest that density estimates for white-tailed deer generated from data collected during road-based spotlight surveys are likely not reflective of the standing deer population. Detection probabilities during individual spotlight surveys ranged from 0.00 to 0.80 (median = 0.45) across all surveys, and differed by observer, survey, management unit, and survey transect replicate. Mean spotlight detection probability (0.41) and process standard deviation (0.12) estimates indicated considerable variability across surveys, observers, transects, and years, which precludes the generation of a correction factor or use of spotlight data to evaluate long-term trends at any scale. Although recommended by many state, federal, and non-governmental agencies, our results suggest that the benefit of spotlight survey data for monitoring deer populations is limited and likely represents a waste of resources with no appreciable management information gained. © 2012 The Wildlife Society.     

Partial migration in expanding red deer populations at northern latitudes – a role for density dependence?

Partial migration is common in ungulates living in highly seasonal environments. Typically, at higher latitudes, this involves movement between high elevation summer areas used during breeding and lowland areas with less snow used during winter. Snow depth is regarded the main cause of migration to low elevation, but it is less clear why deer migrate to high elevation in spring. The forage maturation hypothesis explains the upward migration due to plant phenology. We here present also an alternative and non‐exclusive hypothesis, that deer migrate uphill in summer to escape competition due to the high density in winter areas (the competition avoidance hypothesis). We also suggest that social fences may play a role at high population density. Based on a unique study of 141 GPS‐marked red deer from seven regions covering the main distribution in Norway, we found that the proportion of migrants in the populations varied from 38% to 100%. Migration was more common in areas with a diverse topography, i.e. for areas with access to high elevation. Further, we found evidence that migration was negatively density dependent, and that fall migration was delayed at high density. We suggest that a combination of avoidance of competition in high density winter ranges, social fencing during summer in addition to the forage maturation and predation risk avoidance hypotheses, is needed to explain migration patterns of northern ungulates.     

QTL for live weight traits in Père David's x red deer interspecies hybrids

Interspecies hybrids between Père David's deer (Elaphurus davidianus) and red deer (Cervus elaphus) have proved to be a powerful resource in the search for quantitative trait loci (QTL) in deer. Several regions of the genome with significant effects on live weight and growth rates in backcross hybrids were detected. These include putative QTL for 6-month live weight (LOD 3.90) on linkage group 12, for 14-month live weight (LOD 3.19) on linkage group 1, three putative QTL for growth rate from 3 to 6 months (LOD 4.19 on linkage group 12, LOD 3.92 on linkage group 12, and LOD 3.34 on linkage group 5). In addition, linkage groups 20 and 1 appear to be associated with live weight traits between 9 and 16 months. The variance in traits explained by these QTL ranged between 5.3% and 11.2%. Allele substitution with Père David's alleles at different loci had both positive and negative effects on live weights and growth rates.     

Sulfation pattern in glycosaminoglycan: Does it have a code?

Heparan sulfate chains (HS) are initially synthesized on core proteins as linear polysaccharides composed of glucuronic acid--N-acetylglucosamine repeating units and subjected to marked structural modification by sulfation (N-, 2-O-, 6-O-, 3-O-sulfotransferases) and epimerization (C5-epimerase) at the Golgi lumen and further by desulfation (6-O- endosulfatase) at the cell surface, after which divergent fine structures are generated. The expression patterns and specificity of the modifying enzymes are, at least partly, responsible for the elaboration of these fine structures of heparan sulfate. HS interacts with many proteins including growth factors (GF) and morphogens through specific fine structures. Recent biochemical and genetic studies have presented evidence that HS plays important roles in cell behavior and organogenesis. In knock-down experiments of heparan sulfate 6-O-sulfotransferase, 6-O-sulfated units in HS have been shown to act as a stimulator or suppressor according to individual GF/morphogen signaling systems.     

Does quasi-local competition lead to pattern formation in metapopulations? An explicit resource competition model

In metapopulations, competitive interactions may extend beyond the confines of the local population such that members of neighbouring habitat patches affect each other adversely (quasi-local competition). We derive a model for quasi-local competition from first principles, assuming that individuals compete for shared resources and members of a population spend a certain fraction of their foraging time in the adjacent populations. Contrary to the results of Doebeli and Killingback [2003. Theor. Popul. Biol. 64, 397-416], our model does not produce spatial patterns of population densities in homogeneous environments. Quasi-local competition nevertheless contributes to pattern formation by amplifying the effect of heterogeneities in the external environment, and this amplification can be extremely strong when dispersal is absent. We discuss why apparently similar models lead to contrasting results.