Costs of delayed dispersal and alloparental care in the fungus-cultivating ambrosia beetle <Emphasis Type="Italic">Xyleborus affinis</Emphasis> Eichhoff (Scolytinae: Curculionidae)

Body reserves may determine the reproductive output of animals, depending on their resource allocation strategy. In insects, an accumulation of reserves for reproduction is often obtained before dispersal by pre-emergence (or maturation) feeding. This has been assumed to be an important cause of delayed dispersal from the natal nest in scolytine beetles. In the cooperatively breeding ambrosia beetles, this is of special interest because in this group delayed dispersal could serve two alternative purposes: “selfish” maturation feeding or “altruistic” alloparental care. To distinguish between these two possibilities, we have experimentally studied the effect of delayed dispersal on future reproductive output in the xyleborine ambrosia beetle Xyleborus affinis. Females experimentally induced to disperse and delayed dispersing females did not differ in their body condition at dispersal and in their founding success afterwards, which indicates that females disperse independently of condition, and staying adult females are fully mature and would be able to breed. However, induced dispersers produced more offspring than delayed dispersers within a test period of 40 days. This suggests that delayed dispersal comes at a cost to females, which may result primarily from alloparental care and leads to a reduced reproductive output. Alternatively, females might have reproduced prior to dispersal. This is unlikely, however, for the majority of dispersing females because of the small numbers of offspring present in the gallery when females dispersed, suggesting that mainly the foundress had reproduced. In addition, “gallery of origin” was a strong predictor of the reproductive success of females, which may reflect variation in the microbial complex transmitted vertically from the natal nest to the daughter colony, or variation of genetic quality. These results have important implications for the understanding of proximate mechanisms selecting for philopatry and alloparental care in highly social ambrosia beetles and other cooperatively breeding arthropods.     

Synergism between sib-rearing and sex ratio in Hymenoptera

Summary In many bees and wasps, solitary females produce offspring without help from other females. The transition from lone mothers producing offspring to situations in which females often help to rear siblings is an important step in the origins of complex sociality and nonreproductive castes. Recent work on Hymenoptera has stressed the role of sex ratio variation in this transition; when a mother's brood is more female biased than average, older daughters are favored to help rear their younger siblings because they are more closely related to sisters than to their own offspring. Here the direction of causality is from biased sex ratios, which arise by some extrinsic mechanism, to the origins of sib-rearing (eusociality). We present a model in which there is a synergism between sib-rearing and female-biased sex ratios, which may either complement the sex ratio variation idea by increasing the rate at which helping spreads or be an alternative hypothesis about the origins of eusociality. The synergism in our model depends on three conditions. 1) Daughters that help cause more food to be provisioned per offspring, which in turn causes larger offspring. 2) Females gain more than males by being large, which favors mothers with helpers to produce a higher proportion of daughters. 3) A helper's inclusive fitness rises as her mother's brood becomes increasingly female biased because a female helper is more closely related to her sisters than to her brothers. A female helper may also be more closely related to her sisters than to her own offspring, but this particular sibling-offspring relatedness asymmetry is not required by the synergism model. These three conditions create a synergism which favors a rapid transition from solitary (subsocial) to eusocial. Demographic and ecological factors that facilitate the evolution of eusociality reduce the stringency of the relatedness asymmetry condition (3) required by our idea. The synergism model therefore complements factors other than relatedness that may have been important during the evolution of eusociality.     

Joint breeding in female burying beetles

Summary Burying beetles (Nicrophorus) exhibit advanced parental care, by feeding and guarding their offspring on buried vertebrate carrion. Till now, interactions between two conspecific females on a carcass have been thought to be mostly competitive, and parental care was thought to be provided by single females or male-female pairs exclusively. Here we demonstrate that cooperative brood care occurs in this species, and that its incidence is contingent on carcass size. Small carcasses are usually monopolized by one female; typically the larger of two female combatants secures the carcass for her offspring (Figs. 1 and 2). On large carcasses fights still occur, but in most cases both females stay on the carcass long enough to provide care for the brood. The use of genetic markers revealed that the maternity of offspring is shared evenly among joint breeders (Figs. 3, 4). We hypothesize that cooperative breeding is an adaptive response to a situation that arises partly as a consequence of a physical constraint. Correspondence to: J.K. Müller     

Sociality reduces individual direct fitness in a communally breeding rodent,the colonial tuco-tuco (<Emphasis Type="Italic">Ctenomys sociabilis</Emphasis>)

In many social vertebrates, remaining in the natal group leads to at least short-term reductions in the direct fitness of philopatric animals. Among communally breeding rodents, the direct fitness costs of philopatry appear to increase as the frequency of successful natal dispersal decreases, suggesting a functional link between constraints on natal dispersal and the reproductive consequences of sociality. To explore this relationship empirically, I documented patterns of direct fitness among female colonial tuco-tucos (Ctenomys sociabilis), which are group-living subterranean rodents from southwestern Argentina. Demographic data suggest that successful natal dispersal is rare in this species, leading to the prediction that natal philopatry in C. sociabilis is associated with significant reductions in individual direct fitness. Using data obtained during 1996–2001, I compared the direct fitness of females that dispersed from their natal group and bred alone as yearlings to that of females that lived and bred in their natal group as yearlings. Philopatric yearlings reared significantly fewer young to weaning than did disperser (lone) yearlings. Although neither survival to a second breeding season nor the estimated lifetime number of pups reared to weaning differed between dispersal strategies, the annual direct fitness of group-living females was 23–40% less than expected, suggesting that philopatric animals experienced a substantial direct fitness cost by remaining in their natal group. These data yield important insights into the adaptive bases for group living in C. sociabilis and suggest that constraints on natal dispersal are an important factor favoring group living in this species.Communicated by J. Wilkinson     

Movements of dispersing flying squirrels in relation to siblings and parents

Knowledge of kin interactions can be informative in explaining the processes underlying dispersal. By dispersing, relatives can avoid kin competition for resources or mates and prevent inbreeding. We investigated sibling movements in relation to each other and parents before and after dispersal in radio-collared juvenile flying squirrels (Pteromys volans L.). Before dispersal, most siblings moved in different areas and were not in contact while exploring the surroundings of natal area. After dispersal, all siblings settled far away from each other, as they dispersed different distances and to random directions compared to each other. No clear effect of litter size or presence of same-sex siblings was observed on dispersal. Time spent in the same nest with the mother did not differ between dispersing sons and daughters. Mother did not force dispersers to leave the natal nest; instead, the mother often moved away from the nest before offspring. Father and offspring were not observed to be in contact before dispersal. Dispersal direction was unaffected by the location of fathers’ home range. We conclude that after dispersal interaction between relatives is limited in flying squirrels, but we did not find any indication that interaction between relatives before dispersal is determining dispersal decision. Siblings’ settlement far away from each other was already indicated by the movement within the natal home range, but, interestingly, the latter could not be used to predict dispersal patterns of sexes.     

Home range shifts by breeding female Townsend's voles (Microtus townsendii ): a test of the territory bequeathal hypothesis

Numerous accounts of partial or complete breeding dispersal by adult females reported in the literature on microtines have been interpreted as maternal bequeathal. However, for most species, no causal relationship between a female's movements between successive litters and the settlement of her offspring in the natal range has been demonstrated. I tested predictions from the bequeathal hypothesis using data from an intensive study of Townsend's voles where genetical relationship had been determined by marking most pups in the maternal nest before weaning. After correcting statistically for temporal changes in the distance moved between successive litters I rejected the following predictions: (1) that females with one or several daughters of reproductive age should be more likely to disperse or disperse farther between successive births than females without such daughters; (2) that mothers should be more likely to bequeath their range to their daughters in spring when the latter would gain most from having ready access to a breeding range; (3) that daughters benefit from their mother abandoning the natal range through an increase in their probability of recruitment; and (4) that daughters actually use the home range vacated by their mother. I critically reassess the empirical studies quoted as evidence that breeding dispersal is a form of parental investment in microtines and other mammals. Most empirical studies cited in support of the bequeathal hypothesis often only contain anecdotal reports of movements by breeding females or do not mention it as one of its possible adaptive functions. Some studies contain evidence only consistent with the bequeathal hypothesis whereas others are incompatible with this explanation. Documented evidence of bequeathal comes exclusively from species which rely on a semi-permanent resource such as a midden, mound or burrow. I conclude that there is no indication from Townsend's voles or any other microtines that females abandon their breeding range to their female offspring as a form of parental investment. Received: 27 February 1996 / Accepted after revision: 1 March 1997     

The habitat saturation hypothesis and sociality in an allodapine bee: cooperative nesting is not “making the best of a bad situation”

Several factors thought to be important for the evolution of cooperative breeding in vertebrates have received little attention in facultatively social insects. One of these, the “habitat saturation hypothesis” of Selander (1964), predicts that colony sizes will be greater in breeding units where dispersal opportunities are limited, suggesting that group living is a secondary option to independent reproduction. The Australian allodapine bee Exoneura bicolor exhibits a number of traits that occur in cooperatively breeding bird species, including long life-span, repeated opportunities for reproduction, and vulnerability to brood predation and parasitism. We experimentally examined the effect of a potentially limiting environmental factor, nesting substrate availability, as an agent influencing sociality in E. bicolor. We manipulated nesting substrate availability in two separate locations during a time when foundress dispersal is common. No significant difference was found between colony sizes in cases where dispersal options were abundant and cases where dispersal options were limited. An increase in opportunities for dispersal did not lead to higher rates of independent nesting, suggesting that cooperative nesting is a preferred strategy regardless of distance-related costs of dispersal. Reproductivity per female and brood survival were examined as factors selecting for group living. Low survival of brood in single-female nests has the potential to select for cooperative nesting in this bee. Received: 29 September 1995/Accepted after revision: 24 June 1996     

Parental facilitation: parent-offspring relations in communally breeding birds

Summary A view of parent-offspring relations is developed that stresses an increased role for mutualism and tolerance rather than conflict in evolutionary trends toward sociality. For example, in Aphelocoma jays, parental tolerance of offspring increases from asocial to social species, contrary to what parental manipulation or parent-offspring conflict models have suggested. A simple model is presented in which parents can leave more grand-offspring while having fewer offspring through a mutualistic relationship between parent and offspring. Consistent with the model are the following observations: (1) At the extreme of sociality, in Mexican jays, A. ultramarina, both sexes commonly inherit their natal territory, thus retaining productive territories largely under control of genotypes that tolerate persistence of young in the territory. Sons and daughters may breed on their natal territory in the presence of their mothers and presumed fathers. (2) Jays banded as nestlings in the study area achieved higher reproductive success when breeding on their natal territory than those that moved to other territories. It is hypothesized that plural breeding can evolve as an extension of the trend leading to singular breeding via a non-altruistic reduction in the number of offspring per parent. The concept of parental facilitation may prove to be important for many highly social types of animals, including insects, birds and mammals.     

Parental condition, brood sex ratio and differential young survival: an experimental study in gulls (Larus fuscus)

Empirical evidence is growing that the offspring sex ratio in birds can be biased in relation to the body condition of parents during breeding. The sex ratio bias may come about because (1) the actual production of the two sexes may be skewed and/or (2) there may be a sex bias in early nestling mortality contingent on parental condition. By manipulating parental condition and giving them a control brood to rear, thereby eliminating effects operating via the eggs, we examined the extent to which parental condition influences the post-hatching survival of male and female lesser black-backed gulls, Larus fuscus. We found that the pre-fledging survival of male chicks was strongly reduced in all-male broods reared by parents in poor condition. Pre-fledging survival of female chicks was, however, unaffected by parental condition or brood sex composition. Thus, independently of any production biases, sex differences in nestling mortality alone can bias the offspring sex ratio at fledging in relation to the prevailing rearing conditions. In other studies on gulls we have, however, also shown that females in poor condition at laying preferentially produce female eggs. Clearly a bias in fledging sex ratio can occur within the same species due to a combination of differential production and differential post-laying mortality; the latter can involve a differential effect of poor egg quality on male and female offspring, differential effects of brood sex composition on their survival and a difference in the capacity of parents to rear males and females. All of these processes need to be taken into account in attempting to understand offspring sex ratios. Received: 15 February 2000 / Revised: 7 August 2000 / Accepted: 26 August 2000     

Ecological correlates of duckling adoption among white-winged scoters Melanitta fusca: strategy, epiphenomenon, or combination?

Young waterfowl can frequently join foster females shortly after hatch, resulting in post-hatch brood amalgamation. Much uncertainty remains about physiological or ecological factors that motivate adoption including potential costs and benefits to fostered offspring as well as to females that either lose or accept young. Several hypotheses have been put forth to explain adoption. In this paper, we examine the salvage strategy (SSH) and accidental-mixing (AMH) hypotheses. According to the SSH, females abandon or lose their young due to substantial energetic constraints from incubation and brood rearing. The AMH posits that adoption results from local ecological conditions on breeding areas (i.e., adverse weather conditions, high brood densities) which act to separate offspring and mothers. We used multistate modeling to estimate relationships between probabilities of adoption by white-winged scoter (Melanitta fusca) ducklings from natal to foster females and a set of hypothesized ecological covariates. Results showed that most adoption occurred within 6 days of hatch; additionally, likelihood of adoption was positively related to inclement weather and negatively related to hatch date, size, and condition of natal females, and duckling condition. We conclude that adoption in this population is consistent with both the salvage strategy and accidental-mixing hypotheses. Ultimately, we suggest that adoption in our study population was foremost an outcome of intense gull predation but also of local environmental conditions.     

Socially induced delayed primiparity in brown bears Ursus arctos

Reproductive suppression through behavioral or physiological means is common in group-living and cooperative breeding mammals, but to our knowledge it has not been shown in wild large carnivores other than those with a clear form of social organization. Brown bear (Ursus arctos) females form matrilinear assemblages with related females using a common and largely exclusive area. Behavioral reproductive suppression might develop due to a hierarchical system among females within a matrilinear assemblage or due to inbreeding avoidance, because male brown bears can overlap with their daughters. We tested whether natal dispersal influenced the age of primiparity. We predicted that emigrant females, geographically removed from maternal or paternal influence, would reproduce earlier than philopatric females. The average age of primiparity was 4.3 years in females that dispersed outside their mother’s home range (n=8) and 5.2 years in philopatric females (n=10). Only the overlap with the mother’s home range, and not body size, body mass, growth, local population density, or overlap with the father’s home range, had a significant influence on the age of primiparity. The ultimate role of reproductive suppression for brown bears is likely to avoid inbreeding or to minimize resource competition. Due to the low risk of inbreeding and frequent exposure of young females to unrelated males, we conclude that resource competition within female hierarchies causes reproductive suppression in young females.     

The dynamics of brood desertion among communally breeding females in the treehopper, Publilia concava

In species that exhibit extended parental care, females sometimes lay eggs communally in order to redistribute the costs of offspring care. Communal egg-laying often involves redundancy in female effort, such that the number of females contributing to reproduction is more than is needed to provide adequate parental care. As a result, a subset of females will often abandon the communal brood, with the time of departure ranging from immediate abandonment after egg-laying (brood parasitism) to delayed abandonment with prolonged care (cooperative breeding). In this paper I approach the parental care dynamics of female-female broods as a desertion game similar to that of mate desertion in species with bi-parental care. I describe a field study of the insect Publilia concava (Hemiptera: Membracidae), a species that exhibits communal oviposition and a full range of egg guarding. This species exhibits full redundancy in female care, with no difference in survival between singly and doubly guarded broods. I find that double guarding is extremely rare in the population, with most communal broods having only one female guard. While this guard was usually the female that initiated the brood, these same females were more likely to abandon when secondary females arrived and when secondary females exhibited longer guarding durations. Paradoxically, the secondary females usually abandoned the broods they visited, resulting in up to 50% of broods with double abandonment. These unguarded broods suffered a 50% reduction in hatching success, reflecting an important risk for primary females that abandon egg masses to secondary females. Overall, P. concava exhibits desertion dynamics similar to mate desertion in vertebrates and it is likely that the theoretical work in this area will be useful for future work that addresses the allocation of parental care among communal breeders.     

Why do female Belding's ground squirrels disperse away from food resources?

We examined the effects of food provisioning on the natal dispersal behavior of Belding's ground squirrels (Spermophilus beldingi). We provided extra food to adult and yearling females in their maternal territories during pregnancy and lactation, and to offspring of these females in their natal areas for 6 weeks after weaning. We used unprovisioned young of unprovisioned mothers as controls. Provisioning influenced the probability of dispersal from the natal area by female but not male S. beldingi. All surviving male S.␣beldingi dispersed by 55 weeks of age, regardless of whether they and their mothers received extra food. By contrast, we observed a significant trend, beginning 3 weeks after weaning and continuing through the yearling year, for a greater proportion of provisioned than control female S. beldingi to emigrate from the natal area. Competition for food did not appear to influence natal dispersal of females. However, overall population density, density of females weaning litters, and rates of aggression and vigilance among these females, were higher in provisioned than control areas, suggesting that competition for non-food resources was unusually intense in provisioned areas. We propose that juvenile female, but not juvenile male, S. beldingi may emigrate from the natal site to increase access to areas with low densities of conspecifics. Together with findings of earlier workers, our results suggest that spatial and temporal distributions of environmental resources are important influences on the dispersal behavior of female ground squirrels. Received: 28 February 1996 / Accepted after revision: 16 October 1996     

The effect of maternal body size on embryo survivorship in the broods of pregnant male pipefish

The occurrence of male pregnancy in the family Syngnathidae (seahorses, pipefishes, and sea dragons) provides an exceptionally fertile system in which to investigate issues related to the evolution of parental care. Here, we take advantage of this unique reproductive system to study the influence of maternal body size on embryo survivorship in the brood pouches of pregnant males of the broad-nosed pipefish, Syngnathus typhle. Males were mated with either two large females, two small females, a large then a small female, or a small then a large female. Our results show that offspring survivorship depends on an interaction between female body size and the number of eggs transferred by the female. Eggs of larger females deposited in large numbers are more likely to result in viable offspring than eggs of smaller females laid in large numbers. However, when females deposited smaller numbers of eggs, the eggs from smaller females were more likely to produce viable offspring compared to those from larger females. We found no evidence that this result was based on mating order, the relative sizes of competing females, or egg characteristics such as dry weight of eggs. Additionally, male body size did not significantly influence the survivorship of offspring during brooding. Our results suggest that the factors underlying offspring survivorship in pipefish may be more complex than previously believed, with multiple factors interacting to determine the fitness of individual offspring within the broods of pregnant males.     

Cooperatively breeding carrion crows adjust offspring sex ratio according to group composition

In cooperatively breeding species, parents should bias offspring sex ratio towards the philopatric sex to obtain new helpers (helper repayment hypothesis). However, philopatric offspring might increase within-group competition for resources (local resource competition hypothesis), diluting the benefits of helper acquisition. Furthermore, benefits of offspring sex bias on parents’ fitness may depend on different costs of production and/or different breeding opportunities of sons and daughters. Because of these counteracting factors, strategies of offspring sex allocation in cooperative species are often difficult to investigate. In carrion crows Corvus corone corone in northern Spain, sons are more philopatric and more helpful at the nest than daughters, which disperse earlier and have higher chances to find a breeding vacancy. Consistent with the helper repayment hypothesis, we found that crows fledged more sons in groups short of subordinate males than in groups with sufficient helper contingent, where daughters were preferred. Crow females also proved able to bias primary sex ratio, allocating offspring sex along the hatching sequence in a way that provided the highest fledging probability to sons in the first breeding attempt and to daughters in the following ones. The higher cost of producing male offspring may explain this pattern, with breeding females shifting to the cheapest sex (female) as a response to the costs generated by previous reproductive attempts. Our results suggest complex adjustments of offspring sex ratio that allowed crows to maximize the value of daughters and sons.     

Philopatry and mother-daughter associations in bushy-tailed woodrats: space use and reproductive success

Social groups in mammals are often based on overlapping generations of philopatric females, yet few researchers have examined fitness consequences of associations between females and their daughters. We examined survival and reproductive consequences of sharing a natal site with one's mother or daughter in wild bushy-tailed woodrats (Neotoma cinerea). Bushy-tailed woodrats reside on discrete rocky outcrops, and females tend to spend their entire reproductive life on their natal outcrop. Mothers and daughters that co-existed on the natal outcrop were closely associated in space. Juvenile females were more likely to survive their first winter to become breeding yearlings at their natal site if their mother was also present at the natal site during the winter. Juveniles survived equally well with or without their mother where densities of adult females were experimentally reduced, suggesting that females enhance their daughter's survival by facilitating their access to limited resources. Yearling females exhibited no reproductive costs from association with their mothers at the natal site during the breeding season; in fact, yearlings that bred at the natal site simultaneously with their adult mothers tended (P = 0.07) to experience fewer reproductive failures than did those that bred in the absence of their mothers. Mothers did not experience any detectable costs when sharing a natal site with a daughter. We conclude that bushy-tailed woodrats exhibit stable, fitness-enhancing associations among mothers and their philopatric daughters.     

Paternity and paternal care in the polygynandrous Smith's longspur

In species where females copulate with more than one male during a single breeding attempt, males risk investing in offspring that are not their own. In the polygynandrous Smith's longspur (Calcarius pictus), females copulate sequentially with one to three males for each clutch of eggs and most of these males later assist in feeding the young. Using multilocus DNA profiling, we determined that there was mixed paternity in >75% of broods (n=31) but that few offspring (<1% of 114 nestlings) were sired by males outside the polygynandrous group. Male feeding rate increased significantly with the number of young sired, with males siring four nestlings feeding the brood at double the frequency of males siring only a single nestling. However, male Smith's longspurs appear to show a graded adjustment of paternal care in response to paternity only when other males are available to compensate for reduced care: feeding rate did not vary in relation to paternity when only one male provisioned young at the nest. There was no evidence that males could recognise their own offspring within a brood and feed them preferentially. The number of offspring sired by each male was significantly correlated with the number of days spent copulating with the attending female: on average, a male sired one offspring for every 2 days of copulatory access. If males use their access to females to estimate paternity (and thereby decide on their subsequent level of parental investment), a positive relationship is expected between the amount of female access and the subsequent feeding rate to the nestlings. Nonetheless, male feeding effort was only weakly correlated with female access and more study is needed to determine how males estimate their paternity in a brood. Received: 1 June 1997 / Accepted after revision: 1 April 1998     

Reproductive success increases with degree of kinship in cooperative coalitions of female red howler monkeys (Alouatta seniculus)

Evaluation of evolutionary mechanisms proposed to promote cooperative behavior depends on the relative influence of the behavior on the reproductive success of individuals, the reproductive success of the group in which they interact behaviorally, and the degree of gene correlation among cooperators. The genetic relationship within cooperative coalitions of female red howler monkeys was examined for three populations with different densities and growth rates. Patterns of gene correlation change within coalitions is documented using data from the mitochondrial and nuclear genomes, and long-term census monitoring. Differences in fecundity and infant survivorship within and between groups of unrelated (rˉ=0) and related (rˉ≥ 0.25) females are compared. Females that emigrate from their natal groups form coalitions with other migrant females. These coalitions attempt to establish a territory and, once successful in producing offspring, exclude other females from feeding resources. Females in these coalitions had different mtDNA haplotypes and a genetically estimated mean r of 0, supporting demographic data on emigration patterns indicating that these females rarely have the opportunity to form coalitions with kin. Patterns of recruitment and rate of matriline development within social groups supported behavioral data indicating that females actively attempt to promote their own matriline as breeders over that of other females, and that some matrilines are more successful at this than others. Mean r among females was significantly higher in coalitions established as social groups for several generations (rˉ=0.44). In these groups, females all shared the same mtDNA haplotype, and mtDNA haplotype divergence was significantly higher between than within groups. Females in coalitions with kin had significantly higher reproductive success than females in unrelated coalitions in all populations. This difference was not a function of coalition size, number of males, socionomic sex ratio, or primiparity, although anecdotal evidence suggests that allomothering may compensate for inept new mothers in related coalitions more often than in unrelated ones. Differences in territory quality could not be ruled out as a potential causal factor in the saturated populations, but were unlikely in the low-density, growing population. There were substantial differences among long-established coalitions in overall reproductive output in all three populations, and this was significantly correlated with the number of breeding females. Increase in coalition size was a function of both group age and the behavioral tolerance among females. Regardless of the underlying reasons for the patterns observed, reproductive success clearly increases with degree of gene correlation among females within cooperative coalitions, and coalitions that recruit more daughters produce more offspring. The nature of the cooperative relationship among group females directly influences both of these outcomes. This is associated with substantial genetic differentiation among social groups within populations, creating conditions in which genetic tendencies towards cooperative behavior can become tightly associated with group reproductive success. Received: 15 September 1999 / Revised: 27 April 2000 / Accepted: 27 May 2000     

Genetic relatedness and space use in a behaviorally flexible species of marmot, the woodchuck (Marmota monax)

Solitary species show several patterns of space use and relatedness. Individuals may associate randomly or may live near female or male kin, often as a result of natal philopatry or dispersal patterns. Although usually described as solitary or asocial, woodchucks (Marmota monax) are behaviorally flexible marmots that exhibit greater sociality in some populations than others. I examined relationships between kinship, geographic distance, and home range overlap, as well as dispersal and philopatry, to determine the extent to which kin associated spatially. I used a combination of microsatellite DNA analysis, long-term behavioral observations, and radiotelemetry to test predictions that females, but not males, would associate with kin. Indeed, woodchucks lived closer and shared a greater proportion of their home range with more closely related animals. Overlap of females' and males' home ranges was positively correlated with kinship, and male–female dyads shared more area with closer kin. Most juveniles delayed dispersal beyond their first summer. Females often remained philopatric and settled near their natal range. Although males often dispersed as yearlings, some males also established territories within or immediately adjacent to their natal home ranges. A combination of factors can explain these spatial patterns, including high population density associated with the study site's location within a suburban environment, high dispersal costs, and abundant food. Thus, despite their asocial and solitary reputation, woodchucks displayed spatial patterns seen in other, more social species of ground-dwelling sciurids.