Sex-biased dispersal in a long-lived polygynous reptile (Crocodylus johnstoni )

We compared natal dispersals of freshwater crocodiles (Crocodylus johnstoni) against the prediction of male dispersal bias for a polygynous mating system. The crocodiles inhabited a linear series of pools and we calculated the net distances from natal pools to recapture locations some 12–18 years later, at maturity. Philopatry was assessed in terms of adult social distances. A female social distance was 0.46 pools and a male social distance was 1.0 pool. By these criteria, both sexes showed low levels of philopatry (7–12%). However, individuals of both sexes dispersed from the natal site long before they were sexually mature. Divergence in dispersal patterns by sex occurred after the maturity threshold, as males dispersed two to three times farther than females. Intrasexual competition by males is resolved by a size-based hierarchy. The displacement of small males from local mating access is a probable cause of the longer dispersals undertaken by males. Competition, rather than inbreeding avoidance, is driving dispersal in this population of freshwater crocodiles. Received: 8 May 1998 / Accepted after revision: 26 June 1998     

Correlates of extra-pair fertilization success in hooded warblers

We examined correlates of extra-pair fertilization (EPF) success in the hooded warbler (Wilsonia citrina), a species where females pursue extra-pair matings. The good genes hypothesis predicts that females choose extra-pair mates with morphological or behavioral traits that reflect differences in male genetic quality. EPFs were common, as 35.3% (42/119) of broods contained extra-pair young (EPY) and 26.7% (95/356) of nestlings were the result of EPFs. There was a strong skew in male EPF success which increased the variance in annual male mating success 2–3 fold. However, male morphology did not predict EPF success, as extra-pair males were not older or larger than the males they cuckolded. Likewise, there were no significant correlations between the proportion of extra-pair young in a brood and male size or age. The good genes hypothesis predicts that high-quality males will be consistently preferred as genetic mates, but the number of young sired by a male with his social mate was not consistent from one year to the next. There was a significant negative correlation between female age and proportion of EPY produced, which could result if older females obtain higher-quality social mates. We found no strong evidence that females choose extra-pair mates for good genes, but females may use behavioral rather than morphological cues to assess relative male quality. Received: 31 May 1996 / Accepted after revision: 17 October 1996     

A same-sex stepparent shortens a prebreeder's duration on the natal territory: tests of two hypotheses in Florida scrub-jays

Prebreeders of the Florida scrub-jay (Aphelocoma coerulescens) are less likely to be found on their natal territories with a same-sex stepparent than with parents or an opposite-sex stepparent. We tested two models that had been proposed to account for this sexual asymmetry. The dominance hypothesis states that stepparents perceive same-sex prebreeders as competitors, primarily for a mate, so behave aggressively toward them. The pair-formation hypothesis states that prebreeders remain home to pair eventually with the opposite-sex stepparent. Predictions from these two models were tested by analyses from a quarter-century of records on a study population at Archbold Biological Station and by new behavioral field observations at the Station. Results clearly rejected the latter and strongly supported the former hypothesis. No prediction from the pair-formation hypothesis was confirmed: no pairing by a prebreeder of either sex has ever occurred with a stepparent; remaining home was equally frequent in age-one males with stepmothers and genetic mothers, and in females with stepfathers and genetic fathers; and the same results were found in age-two prebreeders. By contrast, the data strongly supported the dominance hypothesis. Field data showed higher aggression rates by stepfathers to male prebreeders and stepmothers to female prebreeders than by parents to their same-sex genetic offspring. Fewer age-one males remained home with a stepfather than with the genetic father, and the same was found for age-one females with a stepmother and genetic mother; at age two, the effect occurred only in female prebreeders. The two hypotheses make different predictions about prebreeders with two stepparents versus with both parents, thus providing a critical test. The dominance hypothesis correctly predicted decreased duration at home by age-one males and females; data for age-two females were in the direction of predicted difference but not significant; and, as in other tests, no effect was found for age-two males. We propose that age-two male prebreeders remain home despite elevated aggression from stepfathers because these prebreeders retain the possibility of budding from or inheriting the natal territory. Received: 16 July 1997 / Accepted after revision: 26 June 1998     

Parentage and sex allocation in the facultatively polygynous ant Myrmicatahoensis

Most social groups have the potential for reproductive conflict among group members. Within insect societies, reproduction can be divided among multiple fertile individuals, leading to potential conflicts between these individuals over the parentage of sexual offspring. Colonies of the facultatively polygynous ant Myrmicatahoensis contain from one to several mated queens. In this species, female sexuals were produced almost exclusively by one queen. The parentage of male sexuals was more complex. In accordance with predictions based on worker sex-allocation preferences, male-producing colonies tended to have low levels of genetic relatedness (i.e., high queen numbers). Correspondingly, males were often reared from the eggs of two or more queens in the nest. Further, over half of the males produced appeared to be the progeny of fertile workers, not of queens. Overall investment ratios were substantially more male biased than those predicted by genetic relatedness, suggesting hidden costs associated with the production of female sexuals. These costs are likely to include local resource competition among females, most notably when these individuals are adopted by their maternal nest. Received: 3 March 1998 / Accepted after revision: 20 June 1998     

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     

Brood sex ratio is dependent on female mating status in polygynous great reed warblers

Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females, females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we would predict that females which start breeding first within harems might produce more sons than those which start breeding later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably stronger than the latter factor. Received: 11 March 1998 / Accepted after revision: 23 May 1998     

Estimating paternity with spatial behaviour and DNA fingerprinting in the striped plateau lizard, Sceloporus virgatus (Phrynosomatidae)

The association between spatial proximity and paternity was studied in a population of the striped plateau lizard, Sceloporus virgatus. The relationship between estimated mating success and male phenotypic traits was examined for a sample of 55 males. DNA samples were obtained from 13 female-offspring families. The males with the closest spatial proximity to each female were tested as possible sires within each family. Fingerprinting with two multilocus hypervariable minisatellite probes revealed a strong correspondence between male-female spatial proximity and actual paternity. Paternity could be assigned for 72 of the 100 hatchlings. Most hatchlings with identifiable sires were attributed to a male with the highest category of spatial proximity to the mother. However, there was a low to moderate level of multiple paternity within clutches, and for some clutches probable sires could not be identified even though the most likely behavioural candidates were tested. Thus, nonterritorial males or other males lacking strong social and spatial relationships with females may achieve some degree of reproductive success. Analysis of mating success revealed that male success increased with body size, up to a point beyond which larger size conferred no advantage. Received: 7 January 1997 / Accepted after revision: 16 June 1997     

The influence of kinship on foraging competition in Siberian jays

Foraging competition in Siberian jay groups was examined in relation to dominance and kinship to determine whether juvenile offspring, by associating with adults, gained in food acquisition relative to juvenile immigrants. Members of the adult pair were dominant over juvenile cohort members and males were dominant to females, although an inter-sexual hierarchy, with male juveniles occasionally overlapping adult females, was suggested. Few competitive asymmetries were found between adults and retained offspring or adults and immigrant juveniles when they were competing for food together, but in kin and non-kin foraging groups, respectively. Male offspring visited the bait site more frequently than adult males, and female immigrants spent less time at the bait site than adult females. Under these circumstances, hoarding activities may limit the ability of alpha members to control resources. In mixed groups containing both juvenile offspring and juvenile immigrants, no difference was found in the number of visits made to the bait site, although load sizes and foraging rates were lower for immigrant birds. Retained juveniles obtained greater load sizes and foraging rates when associating with adults. The social dominance of parents suggests that they control juvenile foraging. Although offspring benefit in the presence of adults, adults may incur a cost to their restraint by spending more time at the bait site when competing with immigrants. These results extend conclusions from previous work describing the role of selective tolerance by adults which relaxes competition with retained offspring in Siberian jay winter groups. The present findings suggest that offspring benefit in both immediate and future energy gains, which may have a direct influence on survival. Received: 18 September 1996 / Accepted after revision: 26 January 1997     

Coalitionary mate guarding by male chimpanzees at Ngogo, Kibale National Park, Uganda

Cooperative mate guarding by males is unusual in mammals and birds, largely because fertilizations are non-shareable. Chimpanzees live in fission-fusion communities that have cores of philopatric males who cooperate in inter-group aggression and in defending access to the females in their community. Male contest mating competition is restrained within communities, but single high-ranking males sometimes try to mate guard estrous females. Data from an unusually large chimpanzee commmunity at Ngogo, Kibale National Park, Uganda, that contains more males than any previously studied community show new variation in chimpanzee mate-guarding behavior. Contrary to expectation given the large number of males, mate guarding was as common as, or more common than, at other sites, and males other than the alpha male guarded more often. More strikingly, pairs or trios of top-ranking males sometimes engaged in cooperative aggression to prevent estrous females from mating with other males, but tolerated each other's mating activities. Both single males and coalitions mostly guarded periovulatory females. Mate-guarding coalitions were previously unknown in chimpanzees. Coalitions occurred in large mating parties, seemingly because these often contained too many males for single males to maintain exclusive access to estrous females. Coalition members gained higher shares of copulations than they could have expected from solo mate guarding, and suffered lower per capita costs of guarding (as inferred from aggression rates). Two males who most often participated in coalitions formed two-male coalitions at about the point where the number of males present made it unlikely that either could get 50% or more of total copulations on his own, and formed trios when this value dropped below 33%. Kin selection could be a factor in cooperation among male chimpanzees, but coalition members were not necessarily close relatives and the apparent structure of payoffs fit that of mutualism. Furthermore, reliance of male chimpanzees on support from allies to maintain high rank could have led to trading of mating exclusivity for support against mating competitors. Received: 28 May 1997 / Accepted after revision: 16 May 1998     

Altered responses to female odors in parasitized male mice: neuromodulatory mechanisms and relations to female choice

There is accumulating evidence that females may preferentially select parasite-free or -resistant males. Minimal attention has, however, been paid to the mate preferences and responses of the parasitized male hosts themselves. Here, we considered the effects of parasitic infection on male host mate responses, the neuromodulatory correlates of these responses, and the relations of these responses to female mate choice. Using an odor “preference” test, we examined the effects of different stages of an acute, sub-clinical infection with the naturally occurring, enteric, single host, protozoan parasite, Eimeria vermiformis, on the responses of male mice, Mus musculus domesticus, to the odors of estrous females along with the responses of uninfected females to the parasitized males. At 4 days post-infection (non-infective, pre-patent stage) E. vermiformis-infected male mice showed a significantly decreased preference for the odors of estrous females, whereas at 10 days post-infection (infective, patent stage) infected males showed a significantly increased preference for the odors of estrous females. Parasitized males displayed no significant changes in their responses to the odors of non-estrous females, supporting effects on the reproductively related responses of the host. In parallel, estrous females displayed a reduced interest in the odors of infected males. Least interest was expressed in the odors of the patent, infective males, consistent with the avoidance of contagion. Using selective opioid peptide receptor agonists and antagonists we found evidence that enhanced kappa opioid peptide (e.g., dynorphin) activity was related to the decreased sexual interest of the pre-infective males, while augmented delta opioid peptide (e.g., enkephalin) activity was associated with the enhanced responses of the infective males to females. We further showed that acute kappa opiate administration reduced the responses of uninfected males to females and that uninfected females displayed modified responses to the odors of uninfected males subject to acute modifications of opioid activity. We suggest that these differential shifts in endogenous opioid activity in the parasitized males are associated with and, or related to alterations in neuro-immune and endocrine functions. These findings show that parasitic infection can have, depending on the stage of infection and associated neuromodulatory changes, either significant facilitatory or inhibitory effects on male host preferences for and responses to females. Received: 22 April 1996 / Accepted after revision: 15 March 1997     

Changes in male guppy courting distance in response to a fluctuating light environment

In the guppy (Poecilia reticulata), effective courting by a male requires visual contact with the female. Therefore, environmental light intensity may affect male display behavior, particularly initial courtship distance. We found that male guppies courted at exact and predictable distances from the female given a particular light level, both in field and laboratory studies. In lower light levels (<0.1 μmol m⁻² s⁻¹), for example at dawn, dusk, or under heavy canopy, males court females at closer and less variable distances (<3 cm). At higher light levels, which occur during most of the day and with less canopy cover, males often court from twice or three times further out. Light levels over guppy streams change over relatively short time periods and ranges, correlating with variation in courtship distances. Laboratory manipulations of irradiance confirmed that courtship distance depends on illumination. Hence, courtship distances may be set by the effect of lighting on signal efficiency, minimization of energy or time expenditures, or predation risk. Received: 16 December 1997 / Accepted after revision: 8 August 1998     

Parentage and paternal care: consequences of intersexual selection in Savannah sparrows?

Empirical relationships between parentage and male parental care are commonly interpreted in the context of life-history models that consider increased offspring survivorship as the only benefit of paternal effort. However, indirect benefits associated with male care can also influence a male's response to cuckoldry: if females allocate paternity according to their prior experience with male parental care, it may pay for males to provision extra-pair young in early broods. Here, I assess the relationship between first-brood parentage and paternal care in a population of Savannah sparrows (Passerculussandwichensis) where a male's fertilization success in the second brood appears to be influenced by his prior parental performance. Based on the multi-locus DNA fingerprinting of 17 first broods, male feeding effort was influenced by parentage (percent of brood resulting from within-pair fertilizations) but not by brood size, male mating status (monogamous versus polygynous), timing of breeding (hatching date), structural size (wing length) or condition (mass). Males provided more care to broods that contained few within-pair young. This result supports the idea that males provision young to increase their future mating success, but alternative hypotheses involving male quality and timing of breeding cannot be excluded. Received: 13 August 1996 / Accepted after revision: 22 February 1997     

Food access, brood size and filial cannibalism in the fantail darter, Etheostoma flabellare

We compared the occurrence of filial cannibalism in fed and starved male fantail darters (Etheostoma flabellare). All males in the experiment consumed eggs, and 56% ate all of their eggs. A male's initial body condition did not explain the number of eggs that he ate. Neither did non-fed males eat more eggs than fed males. Fed males were able to maintain better body condition during the experiment, but the change in body condition also depended on the number of eggs eaten. Thus, males who ate more eggs were able to maintain better body condition.The most important determinant of whether or not a male ate all of his eggs was his initial egg number. Males with small egg masses ate all of their eggs whereas males with large egg masses were only partial cannibals. There was, however, no difference in the total number of eggs eaten by total and partial cannibals. We conclude that eggs are only partially eaten for energetic reasons. We also suggest that small egg masses are completely consumed because the costs of caring for a small egg mass may exceed the expected reproductive benefits of a small egg mass. Received: 26 January 1996 / Accepted after revision: 2 November 1996     

Maternal investment in Antarctic fur seals: evidence for equality in the sexes?

Studies of the otariids (fur seals and sea lions), a highly sexually dimorphic group, have provided conflicting evidence of differential maternal expenditure in male and female offspring and, thus, suggestions that they conform to predictions of investment theory are equivocal. Since the mid-1970s, a diversity of research on Antarctic fur seals (Arctocephalus gazella) including studies of their reproductive ecology, lactation energetics, and foraging behaviour have been conducted at Bird Island, South Georgia that have resulted in one of the more complete and diverse data sets for any species of otariid. These long-term data were reviewed to determine whether there was any evidence to support that differential maternal expenditure occurred in Antarctic fur seals. Most of the data examined were collected during five consecutive austral summers from 1988 through 1992 and included years in which local food resources were abundant and scarce. We were unable to detect differences in the sex ratios of pups at birth or sex-biased differences in growth rates estimated from serial data, the number of foraging trips made, the duration of attendance ashore, diving behaviour, suckling behaviour, or milk consumption in any year and in the duration of foraging trips or age at weaning in 2 of 3 years. In addition, we found no evidence of greater reproductive costs between mothers with sons or daughters relative to their reproductive performance the following year. In contrast, sex-biased differences were only found in the duration of foraging trips in 1990, the age at weaning in 1988, and consistently in growth rates estimated from cross-sectional data. We suggest that differential maternal expenditure does not occur in Antarctic fur seals because male pups probably do not gain greater benefit from additional maternal expenditure than female pups. After weaning, males experience a period of rapid juvenile growth over 3–4 years during which time body mass nearly trebles. This growth will almost certainly be dependent upon available food resources then rather than on any maternal expenditure received over the first 4 months of life and, thus, the assumptions of the Trivers and Willard hypothesis are probably invalid for Antarctic fur seals. Received: 10 July 1996 / Accepted after revision: 3 March 1997     

Disease resistance: a benefit of sociality in the dampwood termite Zootermopsis angusticollis (Isoptera: Termopsidae)

The benefit of sociality in relation to disease susceptibility was studied in the dampwood termite Zootermopsis angusticollis. Although contact with high concentrations of fungal conidia is lethal, the survivorship of nymphs exposed to spore suspensions ranging from 6 × 10⁶ to 2 × 10⁸ spores/ml of the fungus Metarhizium anisopliae increased with group size. The survivorship (measured as LT₅₀) of isolated individuals ranged from 3.0 to 4.8 days, but infected nymphs living in groups of 10 and 25 individuals survived significantly longer (5.6–8.3 and 5.6–9.1 days, respectively). In most cases, there were no significant differences in the survival distributions of the 10- and 25-termite groups. When nymphs were infected with concentrations of 7 × 10¹–7 × 10⁴ spores/ml and allowed to interact with healthy nestmates, fungal infections were not contracted by the unexposed termites. Moreover, infected termites benefitted from social contact with unexposed nestmates: their survival rates were significantly higher than those of infected termites living with similarly infected nestmates. Allogrooming, which increased in frequency during and after exposure to conidia, appeared to remove potentially infectious spores from the cuticle, thus increasing termite survivorship. These results suggest that allogrooming plays a crucial role in the control of disease and its death hazard in termites. The infection-reducing advantage of group living may have been significant in the evolution of social behavior in the Isoptera. Received: 18 March 1998 / Accepted after revision: 31 May 1998     

Queen control of egg fertilization in the honey bee

The study investigated the precision with which honey bee queens can control the fertilization of the eggs they lay. Because males and workers are reared in different-sized cells, the honey bee is one of the few Hymenoptera in which it is possible for the experimenter to know which type of egg a queen “intends” to lay. Eggs were collected from both worker and drone (male) cells from four honey bee colonies. Ploidy of the embryo was determined using polymorphic DNA microsatellites. All 169 eggs taken from worker cells were heterozygous at at least one microsatellite locus showing that the egg was fertilized. All 129 eggs taken from drone cells gave a single band at the B124 locus, strongly suggesting haploidy. These data show that honey bee queens have great, and quite possibly complete, ability to control the fertilization of the eggs they lay. Data from the literature suggest that in two species of parasitoid Hymenoptera (Copidosoma floridanum, Colpoclypeus florus) females have great, but not complete, ability to control fertilization. Received: 23 December 1997 / Accepted after revision: 17 May 1998     

Mating patterns and reproductive success in the bushy-tailed woodrat (Neotoma cinerea), as revealed by DNA fingerprinting

The mating patterns and reproductive success of the bushy-tailed woodrat (Neotoma cinerea) were investigated over a 3-year period (1992–1994) using DNA fingerprinting. Paternity was determined by genetic analysis of 58 juveniles of known maternity from 35 litters. Analysis of DNA fingerprints revealed that all offspring within a litter were fathered by a single male; the statistical probability of detecting multiple males mating with a female was high, indicating that multiple paternity would have been detected had it occurred. However, individual males did not father more than one litter from a given female either within or between years. At least 75% of females and 57% of males successfully produced offspring each year. The finding that all littermates are first-order relatives may contribute to the high level of female cooperation in this species. Received: 28 May 1997 / Accepted after revision: 22 March 1998     

A molecular genetic analysis of social structure, dispersal, and interpack relationships of the African wild dog (Lycaon pictus )

The African wild dog is a highly social, pack-living predator of the African woodland and savannah. The archetypal wild dog pack consists of a single dominant breeding pair, their offspring, and non-breeding adults who are either offspring or siblings of one of the breeding pair. Non-breeding adults cooperate in hunting, provisioning and the protection of young. From these observations follows the prediction that the genetic structure of wild dogs packs should resemble that of a multigenerational family, with all same-sexed adults and offspring within a pack related as sibs or half-sibs. Additionally, a higher kinship between females from neighboring packs should be evident if females tend to have small dispersal distances relative to males. We test these predictions through analysis of mitochondrial DNA control region sequences and 14 microsatellite loci in nine wild dog packs from Kruger National Park, Republic of South Africa. We show that as predicted, African wild dog packs generally consist of an unrelated alpha male and female, subdominant close relatives, and offspring of the breeding pair. Sub-dominant wild dogs occasionally reproduce but their offspring rarely survive to 1 year of age. Relatedness influences the timing and location of dispersal events as dispersal events frequently coincide with a change in pack dominance hierarchy and dispersers often move to areas with a high proportion of close relatives. Received: 22 February 1996 / Accepted after revision: 16 November 1996     

Female mate choice in the non-territorial lizard Ameiva plei (Teiidae)

Mate choice by females has been documented in a variety of taxa. Female mate choice in species lacking male resource control or paternal care might occur if preferred males provide protection from harassment. Female mate choice was investigated in a natural population of the non-territorial lizard Ameiva plei (Teiidae). Consort pairs were allowed to form naturally. Consort males were significantly larger than non-consort males. After removal of consort males, the “abandoned” female's reaction to the first male who approached her was recorded. Females rejected all small males. Female preference for large males was significantly higher than preference for small males. Large males may be better equipped to guard the females from harassment and behavior of large males is less harassing than behavior of small males, thereby affording the female increased foraging time. Received: 21 June 1996 / Accepted after revision: 28 December 1996     

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