Establishment success and resulting fitness consequences for vole dispersers

Dispersal is one of the most important, yet least understood phenomena of evolutionary ecology. Triggers and consequences of dispersal are difficult to study in natural populations since dispersers can typically only be identified a posteriori. Therefore, a lot of work on dispersal is either of a theoretical nature or based on anecdotal observation. This is especially true for cryptic species such as small mammals. We conducted an experiment on the common vole, Microtus arvalis, in semi‐natural enclosures and investigated the spatial and genetic establishment success of residents and dispersers in their natal and new populations. Our study uses genetic data on the reproductive success of 1255 individuals to measure the fitness trajectories of the residents and dispersing individuals. In agreement with past studies, we found that dispersal was highly male‐biased, and was most probably induced by the agonistic encounters with conspecifics, suggesting it could act as an inbreeding avoidance mechanism. There was low breeding success of dispersers into new populations. Although nearly 26% of identified dispersers reproduced in their natal populations, only seven percent reproduced in the new populations. Settlement appeared to be a pre‐requisite for reproduction in both sexes, and animals that did not spatially settle into a new population dispersed again, usually on the same day of immigration. In the event that dispersers reproduced in the new population, they did so at relatively low population densities. We also found age‐related differences between the sexes in breeding success, and male dispersers that subsequently established in the new population were young individuals that had not reproduced in their natal population, whereas successful females had already reproduced in their natal population. In conclusion, with our detailed field data on establishment and substantial parentage assignments to understand breeding success, we were able to gain an insight into the fitness of dispersers, and how the two sexes optimise their fitness. Taken together, our results help to further understand the relative advantages and costs of dispersal in the common vole.     

Increased lifetime reproductive success for Siberian jay (Perisoreus infaustus) males with delayed dispersal

In a crowded environment the natal territory could serve as a haven for young and inexperienced offspring until a breeding vacancy emerges. Delayed dispersal and association with kin could then offer adaptive benefits through an individual fitness gain. Here we report that delayed dispersal is associated with a higher lifetime individual fitness in Siberian jay (Perisoreus infaustus) males. Sons bred more successfully and had more reproductive events in life when they delayed dispersal. The higher lifetime reproductive success when sons disperse later in life is sufficient to promote postponement of natal dispersal, suggesting that dispersal is delayed due to ecological constraints on access to high-quality habitats. We argue that the maintenance of this variation in the timing of dispersal and reproductive success can be reconciled with non-genetic mechanisms driving dispersal. Social dominance within broods reflecting environmental conditions during growth is such a mechanism.     

Banded mongooses avoid inbreeding when mating with members of the same natal group

Inbreeding and inbreeding avoidance are key factors in the evolution of animal societies, influencing dispersal and reproductive strategies which can affect relatedness structure and helping behaviours. In cooperative breeding systems, individuals typically avoid inbreeding through reproductive restraint and/or dispersing to breed outside their natal group. However, where groups contain multiple potential mates of varying relatedness, strategies of kin recognition and mate choice may be favoured. Here, we investigate male mate choice and female control of paternity in the banded mongoose (Mungos mungo), a cooperatively breeding mammal where both sexes are often philopatric and mating between relatives is known to occur. We find evidence suggestive of inbreeding depression in banded mongooses, indicating a benefit to avoiding breeding with relatives. Successfully breeding pairs were less related than expected under random mating, which appeared to be driven by both male choice and female control of paternity. Male banded mongooses actively guard females to gain access to mating opportunities, and this guarding behaviour is preferentially directed towards less closely related females. Guard–female relatedness did not affect the guard's probability of gaining reproductive success. However, where mate‐guards are unsuccessful, they lose paternity to males that are less related to the females than themselves. Together, our results suggest that both sexes of banded mongoose use kin discrimination to avoid inbreeding. Although this strategy appears to be rare among cooperative breeders, it may be more prominent in species where relatedness to potential mates is variable, and/or where opportunities for dispersal and mating outside of the group are limited.     

Bateman's Principle in Cooperatively Breeding Vertebrates: The Effects of Non-breeding Alloparents on Variability in Female and Male Reproductive Success

The sex-specific slopes of Bateman's gradients have importantimplications for understanding animal mating systems, includingpatterns of sexual selection and reproductive competition. Intersexualdifferences in the fitness benefits derived from mating withmultiple partners are expected to yield distinct patterns ofreproductive success for males and females, with variance indirect fitness predicted to be greater among males. These analysesassume that typically all adults are reproductive and that failureto produce offspring is non-adaptive. Among some species ofcooperatively breeding birds and mammals, however, non-breedingadult alloparents are common and may comprise the majority ofindividuals in social groups. The presence of a large numberof non-breeding adults, particularly when coupled with greatersocial suppression of reproduction among females, may alterthe relative variance in direct fitness between the sexes, therebygenerating an apparent contradiction to Bateman's Paradigm.To explore quantitatively the effects of non-breeding alloparentson variance in reproductive success, we used genetic estimatesof parentage and reproductive success drawn from the literatureto calculate the relative variability in direct fitness forfemales and males in alloparental and "other" societies of birdsand mammals. Our analyses indicate that in mammals and, to alesser extent, in birds, variability in direct fitness is greateramong females in species characterized by the presence of non-breedingalloparents. These data suggest that social interactions, includingsocial suppression of reproduction, are powerful determinantsof individual direct fitness that may modify sex-specific patternsof reproductive variance from those described by Bateman.     

Invasion fitness,inclusive fitness,and reproductive numbers in heterogeneous populations

How should fitness be measured to determine which phenotype or “strategy” is uninvadable when evolution occurs in a group‐structured population subject to local demographic and environmental heterogeneity? Several fitness measures, such as basic reproductive number, lifetime dispersal success of a local lineage, or inclusive fitness have been proposed to address this question, but the relationships between them and their generality remains unclear. Here, we ascertain uninvadability (all mutant strategies always go extinct) in terms of the asymptotic per capita number of mutant copies produced by a mutant lineage arising as a single copy in a resident population (“invasion fitness”). We show that from invasion fitness uninvadability is equivalently characterized by at least three conceptually distinct fitness measures: (i) lineage fitness, giving the average individual fitness of a randomly sampled mutant lineage member; (ii) inclusive fitness, giving a reproductive value weighted average of the direct fitness costs and relatedness weighted indirect fitness benefits accruing to a randomly sampled mutant lineage member; and (iii) basic reproductive number (and variations thereof) giving lifetime success of a lineage in a single group, and which is an invasion fitness proxy. Our analysis connects approaches that have been deemed different, generalizes the exact version of inclusive fitness to class‐structured populations, and provides a biological interpretation of natural selection on a mutant allele under arbitrary strength of selection.     

Estimating fitness consequences of dispersal: a road to 'know-where'? Non-random dispersal and the underestimation of dispersers' fitness

1. Many studies investigating fitness correlates of dispersal in vertebrates report dispersers to have lower fitness than philopatric individuals. However, if dispersers are more likely to produce dispersing young or are more likely to disperse again in the next year(s) than philopatric individuals, there is a risk that fitness estimates based on local adult survival and local recruitment will be underestimated for dispersers. 2. We review the available empirical evidence on parent-offspring resemblance and individual lifelong consistency in dispersal behaviour, and relate these studies to recent studies of fitness correlates of dispersal in vertebrates. 3. Of the 12 studies testing directly for parent-offspring resemblance in dispersal propensity, five report a significant resemblance. The average effect size (r) of parent-offspring resemblance in dispersal was 0.15 [95% confidence interval (CI) = 0.07-0.22], with no difference between the sexes (average weighted effect size of 0.12 (0.08-0.16) and 0.16 (0.11-0.20) for females and males, respectively). Only three studies report data on within-individual consistency in dispersal propensity, of which two suggest dispersers to be more likely to disperse again. 4. To assess the magnitude of fitness underestimation expected for dispersing individuals depending on the heritability of dispersal distance and study area size, we used a simulation approach. Even when study area size is 10 times the mean dispersal distance, local recruitment per breeding event may be underestimated by 4-10%, generating a potential difference of 4-60% in average lifetime production of recruits between dispersing and philopatric individuals, with larger differences in long-lived species. 5. Estimates of both fitness correlates of dispersal and parent-offspring resemblance or within-individual consistency in dispersal behaviour have been reported for 11 species. Although some comparisons suggest genuine differences in fitness components between philopatric and dispersing individuals, others, based on adult and juvenile survival, are open to the alternative explanation of biased fitness estimates. 6. We list three potential ways of reducing the risk of making wrong inferences on biased fitness estimates due to such non-random dispersal behaviour between dispersing and philopatric individuals: (a) diagnosing effects of non-random dispersal, (b) reducing the effects of spatially limited study area and (c) performing controlled experiments.     

Investment and relatedness: A cost/benefit analysis of breeding and helping in the pied kingfisher (Ceryle rudis)

Helping at the nest in birds is often termed altruism. However, so far, no study has ever demonstrated high costs to a helper's own lifetime reproductive success (=direct fitness), nor its compensation through benefits from relatives other than its own offspring (=indirect fitness). In this paper on pied kingfishers (Ceryle rudis) the relationship between investment, relatedness and inclusive fitness (expressed in terms of genetic equivalents) is investigated for breeding males, and males that help either relatives (=primary helpers) or strangers (=secondary helpers). With respect to guarding nests against predators and feeding young, primary helpers invest as much as breeders, but secondary helpers contribute significantly less. These differences in status and investment (measured in energy expenditure) affect the birds' future to such an extent that primary helpers have a lower chance of surviving and mating than secondary helpers. However, their costs in direct fitness are compensated by pronounced benefits to indirect fitness, resulting from improved survival of siblings and parents. An attempt is made to calculate the inclusive fitness of birds following different strategies over a 2-year period. It is concluded that (a) breeding is superior to helping and helping superior to doing nothing and (b) that kin-selection must be invoked to explain why surplus males choose the more costly primary helper strategy instead of the cheaper secondary helper strategy. Alternative explanations, including group selection, parental manipulation and reciprocity, are discussed.     

Male‐induced costs of mating for females compensated by offspring viability benefits in an insect

Sexual conflict facilitates the evolution of traits that increase the reproductive success of males at the expense of components of female fitness. Theory suggests that indirect benefits are unlikely to offset the direct costs to females from antagonistic male adaptations, but empirical studies examining the net fitness pay‐offs of the interaction between the sexes are scarce. Here, we investigate whether matings with males that invest intrinsically more into accessory gland tissue undermine female lifetime reproductive success (LRS) in the cricket Teleogryllus oceanicus. We found that females incur a longevity cost of mating that is proportional to the partner’s absolute investment into the production of accessory gland products. However, male accessory gland weight positively influences embryo survival, and harmful ejaculate‐induced effects are cancelled out when these are put in the context of female LRS. The direct costs of mating with males that sire offspring with higher viability are thus compensated by direct and possibly indirect genetic benefits in this species.     

Dispersal and extra-territorial prospecting by slender-tailed meerkats (Suricata suricatta) in the south-western Kalahari

Dispersal in slender-tailed meerkats or suricates, Suricata suricatta, in the south-western Kalahari occurred mainly during the early breeding season, and was age- and sex-dependent. Among yearlings, more males than females were immigrants, but more females than males disappeared. There were no sex differences in dispersal among two-year-olds, but among animals aged three years or older, more males than females emigrated. Most dispersers moved into adjacent bands or joined other transients, and females apparently suffered higher rates of mortality than males. Kinship with the same-sex or opposite-sex breeder had no discernible effect on the likelihood of dispersing. Both males and females made prospecting forays to other groups, apparently to assess dispersal and breeding opportunities. Males made frequent and repeated forays, often in coalitions with other band members or transients, whereas prospecting by females was generally solitary, and they were not known to make multiple forays. Prospecting males successfully took over dominance of two bands, and attempted to take over bands on three other occasions. Animals attempting to join or follow a band ( trailers ) behaved submissively and were readily chased by residents, whereas those attempting a dominance takeover ( invaders ) scent-marked at a high rate and showed no submissive behaviours. Dispersing meerkats maximized reproductive success by increasing their mating opportunities, while animals which delayed dispersal received indirect benefits by helping to raise kin.     

No evidence for divergence in male harmfulness or female resistance in response to changes in the opportunity for dispersal

The outcome of sexual conflict can depend on the social environment, as males respond to changes in the inclusive fitness payoffs of harmfulness and harm females less when they compete with familiar relatives. Theoretical models also predict that if limited male dispersal predictably enhances local relatedness while maintaining global competition, kin selection can produce evolutionary divergences in male harmfulness among populations. Experimental tests of these predictions, however, are rare. We assessed rates of dispersal in female and male seed beetles Callosobruchus maculatus, a model species for studies of sexual conflict, in an experimental setting. Females dispersed significantly more often than males, but dispersing males travelled just as far as dispersing females. Next, we used experimental evolution to test whether limiting dispersal allowed the action of kin selection to affect divergence in male harmfulness and female resistance. Populations of C. maculatus were evolved for 20 and 25 generations under one of three dispersal regimens: completely free dispersal, limited dispersal and no dispersal. There was no divergence among treatments in female reproductive tract scarring, ejaculate size, mating behaviour, fitness of experimental females mated to stock males or fitness of stock females mated to experimental males. We suggest that this is likely due to insufficient strength of kin selection rather than a lack of genetic variation or time for selection. Limited dispersal alone is therefore not sufficient for kin selection to reduce male harmfulness in this species, consistent with general predictions that limited dispersal will only allow kin selection if local relatedness is independent of the intensity of competition among kin.     

Age-specific mating strategies and reproductive senescence

While males gain obvious direct advantages from multiple mating, the reproductive capacity of females is more constrained. The reason why polyandry evolved in females is therefore open to many conjectures. One hypothesis postulates that females gain indirect benefits by increasing the probability of siring young from high quality males. To explore this hypothesis, we used the natural variation of the reproductive value that males and females undergo through age. The age-related variation of phenotypic performance might then induce variations in mating strategies in males and females. Using the common lizard (Lacerta vivipara) as our model system, we showed that reproductive immaturity and senescence created variability in both male and female reproductive success (including survival of offspring). Consistent with theory, males at their best-performing phenotype adopted a polygynous strategy. These males were of an intermediate age and they produced offspring of higher viability than younger and older males. In contrast, females at their best performing phenotype, also of an intermediate age, were less polyandrous than other less-performing females. Middle-aged females tended to mate with males of an intermediate age and produced litters with higher viability independently from their reproductive strategy. Males of an intermediate age enhanced their fitness by additional matings with young or old females. Young and old females increased their fitness by being more polyandrous. Polyandry therefore appears as means to seek for good males. A positive correlation between males and their partners' fitness disagree with the idea that polyandry is the result of a sexual conflict in this species.     

Male-biased Adult Sex Ratios and their Significance for Cooperative Breeding in Dhole,Cuon alpinus,Packs

Two free-ranging packs of dholes (Asiatic wild dog, Cuon alpinus) were monitored for a period of 6 yr (Sep. 1990-Sep. 1996) in the Mudumalai sanctuary, southern India. Demographic data on age structure, litter-size, sex ratio and age and sex specific dispersal were collected. Behavioural data on social interactions and reproductive behaviour among pack members were obtained to determine the frequencies of dominant and subordinate behaviours shown by male and female pack members and a measure of each male's reproductive access to females. Behaviours displayed by pack members at dens were recorded to determine whether any age- or sex-specific role specialization existed during pup care. Tenures for dominant males and females within the pack were calculated to ascertain the rate of breeding vacancies occurring within packs. Approximate levels of genetic relatedness within packs were determined by studying pedigrees. In most years one study pack had a male-biased adult sex ratio. This was caused by almost two-fold higher dispersal of adult females over adult males. A considerable variance existed in the percentage of sub-adults dispersing from the two packs. Differences existed in the frequencies of dominant and subordinate behaviours shown by males. For males, dominance ranks and ranks based on submissive behaviours were not correlated with frequencies of reproductive behaviours. Subordinate males also displayed reproductive behaviours. In packs, dominant males had lower tenures than dominant females indicating that among males breeding vacancies arose more quickly. The litter size was found to be negatively correlated with the age of the breeding female. There were no significant differences across individuals of varying age or sex classes in the display of pup care behaviours. Significant differences did exist among individual adults. Genetic relatedness among packs tended to vary temporally as a consequence of possible mating by subordinate animals and immigration of new males into the pack. In conclusion, it appears that males delay dispersal and cooperate within their natal packs because of the variety of reproductive strategies they could pursue within. A combination of ecological constraints and the difficulties of achieving breeding status within non-natal packs may make early dispersal and independent breeding less beneficial.     

Correlates and Consequences of Dominance in a Social Rodent

In harem‐polygynous societies, body condition is often correlated with dominance rank. However, the consequences of dominance are less clear. High‐ranking males do not inevitably have the highest reproductive success, especially in systems where females mate with multiple males. In such societies, we expect male reproductive success to be more highly skewed than female reproductive success, but reproductive skew in females can still arise from rankings established within matrilineal societies. Dominance can also impact life‐history decisions by influencing dispersal patterns in yearlings. To better understand the function of dominance in harem‐polygynous societies, we studied the causes and consequences of dominance in yellow‐bellied marmots (Marmota flaviventris), a social rodent with skewed male reproductive success and female reproductive suppression. Specifically, we examined body condition as a predictor and the probability of breeding, number of offspring, and dispersal as outcomes of dominance. Additionally, we looked at variation in dominance between males and females and adults and yearlings, because marmots can engage in distinct interactions depending on the type of individuals involved. We found that marmots in better body condition have higher dominance rank than those in poorer condition. In addition, adults are dominant over yearlings. Within yearlings, dominance does not influence dispersal, but those in better body condition are less likely to disperse. Within all adults, individuals in better condition produce more offspring per year. Within adult males, more dominant males have greater reproductive success. Despite previous evidence of reproductive suppression in females, we found no effects of dominance rank on female reproductive success in the current study. The function of dominance in female marmots remains enigmatic.     

Substantial direct fitness gains of workers in a highly eusocial ant

Hamilton's theory of inclusive fitness suggests that helpers in animal societies gain fitness indirectly by increasing the reproductive performance of a related beneficiary. Helpers in cooperatively breeding birds, mammals and primitively eusocial wasps may additionally obtain direct fitness through inheriting the nest or mating partner of the former reproductive. Here, we show that also workers of a highly eusocial ant may achieve considerable direct fitness by producing males in both queenless and queenright colonies. We investigated the reproductive success of workers of the ant Temnothorax crassispinus in nature and the laboratory by dissecting workers and determining the origin of males by microsatellite analysis. We show that workers are capable of activating their ovaries and successfully producing their sons independently of the presence of a queen. Genotypes revealed that at least one fifth of the males in natural queenright colonies were not offspring of the queen. Most worker‐produced males could be assigned to workers that were unrelated to the queen, suggesting egg‐laying by drifting workers.     

Lifetime fitness of short- and long-distance dispersing great reed warblers

Dispersal is of prime importance for many evolutionary processes and has been studied for decades. The reproductive consequences of dispersal have proven difficult to study, simply because it is difficult to keep track of dispersing individuals. In most previous studies evaluating the fitness effects of dispersal, immigrants at a study locality have been lumped into one category and compared to philopatric individuals. This is unfortunate, because there are reasons to believe that immigrants with long and short dispersal distances may differ substantially in reproductive success. In the present study, we used a combination of capture-recapturing and multilocus microsatellite genotyping to categorize great reed warblers at our Swedish study site as philopatric individuals or short- or long-distance dispersing immigrants. We then performed novel comparisons of lifetime reproductive success (LRS) and survival rates of these three dispersal categories. The birds belonged to cohorts 1987-1996, and data for their LRS were gathered between 1988 and 2003. The analyses showed that philopatric males attracted more females, produced more fledglings and recruits throughout their lives, and survived better than immigrants. Among the immigrant males, those categorized as long-distance dispersers had lowest LRS and survival probability. Models that included covariates of potential importance showed that the difference in LRS between dispersal categories was partly caused by corresponding variation in number of breeding years at our study site. These results indicate that short- and, in particular, long-distance dispersers were of poor phenotypic quality, but it may also be proposed that immigrants attracted few females because they were poorly adapted to the local social environment. In females, the number of local recruits corrected for the number of breeding years (as well as for number of fledglings) differed between dispersal categories in a pattern that suggests an intermediate optimal dispersal distance. Short-distance dispersers recruited more offspring per year (and per fledgling) than both philopatric individuals and long-distance dispersers. Data suggest that the low LRS of philopatric females was related to costs of inbreeding. The low LRS of long-distance dispersing females may have resulted from their offspring being especially prone to disperse outside the study area, but also other potential explanations exist, such as local maladaptation. Our study highlights the importance of separating immigrant birds on the basis of their genetic similarity to the local study population when analyzing variation in LRS and inferring realized gene flow.     

Genetic population structure and relatedness in the narrow‐striped mongoose (Mungotictis decemlineata), a social Malagasy carnivore with sexual segregation

Information on the genetic structure of animal populations can allow inferences about mechanisms shaping their social organization, dispersal, and mating system. The mongooses (Herpestidae) include some of the best‐studied mammalian systems in this respect, but much less is known about their closest relatives, the Malagasy carnivores (Eupleridae), even though some of them exhibit unusual association patterns. We investigated the genetic structure of the Malagasy narrow‐striped mongoose (Mungotictis decemlineata), a small forest‐dwelling gregarious carnivore exhibiting sexual segregation. Based on mtDNA and microsatellite analyses, we determined population‐wide haplotype structure and sex‐specific and within‐group relatedness. Furthermore, we analyzed parentage and sibship relationships and the level of reproductive skew. We found a matrilinear population structure, with several neighboring female units sharing identical haplotypes. Within‐group female relatedness was significantly higher than expected by chance in the majority of units. Haplotype diversity of males was significantly higher than in females, indicating male‐biased dispersal. Relatedness within the majority of male associations did not differ from random, not proving any kin‐directed benefits of male sociality in this case. We found indications for a mildly promiscuous mating system without monopolization of females by males, and low levels of reproductive skew in both sexes based on parentages of emergent young. Low relatedness within breeding pairs confirmed immigration by males and suggested similarities with patterns in social mongooses, providing a starting point for further investigations of mate choice and female control of reproduction and the connected behavioral mechanisms. Our study contributes to the understanding of the determinants of male sociality in carnivores as well as the mechanisms of female competition in species with small social units.     

Lifetime fitness and age‐related female ornament signalling: evidence for survival and fecundity selection in the pied flycatcher

Ornaments displayed by females have often been denied evolutionary interest due to their frequently reduced expression relative to males, habitually attributed to a genetic correlation between the sexes. We estimated annual and lifetime reproductive success of female pied flycatchers (Ficedula hypoleuca) and applied capture–mark–recapture models to analyse annual survival rates in relation to the patterns of expression (absence/presence) of an ornament displayed by all males and a fraction of females. Overall, the likelihood of expressing the ornament increased nonlinearly with female age and was due to within‐individual variation, not to the selective appearance or disappearance of ornament‐related expression of phenotypes in the population. Accordingly, expressing the forehead patch in a given year did not influence survival probability. However, those females expressing the ornament at early ages (1–2 years old) enjoyed survival advantages throughout lifetime. Although ornamented females had higher lifetime fecundity and fledging success, their yearly reproductive performance, in terms of fledging productivity, decreased as they aged so that, late in life, ornamented females reared fewer offspring than nonexpressing females of the same age. In addition, both strategies (expressing vs. not expressing the trait) returned similar fitness payoffs in terms of recruited offspring. Our results support the hypothesis that fecundity and survival selection are involved in the displaying of this ‘male’ ornament by females.     

Genetic and environmental influences on natal dispersal distance in a resident bird species

We analyzed more than 1,600 dispersal events from two populations of a North American cooperatively breeding woodpecker species to determine what factors influence natal dispersal distance and whether distance traveled affects reproduction later in life. We found significant heritability of natal dispersal distance, in both males and females, indicating substantial additive genetic variance for this behavioral trait. Natal dispersal distance additionally was affected by social and ecological factors: individuals dispersing in their first year of life moved longer distances than those staying on their natal site as helpers for a prolonged time prior to dispersal, and increasing territory isolation led to longer dispersal distances. Successful dispersers incurred fitness costs, with lifetime fledgling production (in both sexes) and lifetime production of recruits to the breeding population (in females only) decreasing with increasing natal dispersal distance. We conclude that natal dispersal distance has a genetic basis but is modulated by environmental and social factors and that natal dispersal distance in this species is (currently) under selection.     

Early growth,dominance acquisition and lifetime reproductive success in male and female cooperative meerkats

In polygynous species, variance in reproductive success is higher in males than females. There is consequently stronger selection for competitive traits in males and early growth can have a greater influence on later fitness in males than in females. As yet, little is known about sex differences in the effect of early growth on subsequent breeding success in species where variance in reproductive success is higher in females than males, and competitive traits are under stronger selection in females. Greater variance in reproductive success has been documented in several singular cooperative breeders. Here, we investigated consequences of early growth for later reproductive success in wild meerkats. We found that, despite the absence of dimorphism, females who exhibited faster growth until nutritional independence were more likely to become dominant, whereas early growth did not affect dominance acquisition in males. Among those individuals who attained dominance, there was no further influence of early growth on dominance tenure or lifetime reproductive success in males or females. These findings suggest that early growth effects on competitive abilities and fitness may reflect the intensity of intrasexual competition even in sexually monomorphic species.     

Risky movements? Natal dispersal does not decrease survival of a large herbivore

Natal dispersal is assumed to be a particularly risky movement behavior as individuals transfer, often long distances, from birth site to site of potential first reproduction. Though, because this behavior persists in populations, it is assumed that dispersal increases the fitness of individuals despite the potential for increased risk of mortality. The extent of dispersal risk, however, has rarely been tested, especially for large mammals. Therefore, we aimed to test the relationship between dispersal and survival for both males and females in a large herbivore. Using a radio‐transmittered sample of 398 juvenile male and 276 juvenile female white‐tailed deer (Odocoileus virginianus), we compared survival rates of dispersers and nondispersers. We predicted that dispersing deer would experience greater overall mortality than philopatric deer due to direct transfer‐related risks (e.g., vehicular collision), indirect immigration‐related mortality attributable to colonization of unfamiliar habitat, and increased overwinter mortality associated with energetic costs of movement and unfamiliarity with recently colonized habitat. For both male and female yearlings, survival rates of dispersers (male = 49.9%, female = 64.0%) did not differ from nondispersers (male = 51.6%, female = 70.7%). Only two individuals (both female) were killed by vehicular collision during transfer, and overwinter survival patterns were similar between the two groups. Although dispersal movement likely incurs energetic costs on dispersers, these costs do not necessarily translate to decreased survival. In many species, including white‐tailed deer, dispersal is likely condition‐dependent, such that larger and healthier individuals are more likely to disperse; therefore, costs associated with dispersal are more likely to be borne successfully by those individuals that do disperse. Whether low‐risk dispersal of large mammals is the rule or the exception will require additional research. Further, future research is needed to evaluate nonsurvival fitness‐related costs and benefits of dispersal (e.g., increased reproductive opportunities for dispersers).