Mechanisms of kin discrimination inferred from pedigrees and the spatial distribution of mates

Where animals avoid inbreeding, different mechanisms of kin discrimination can leave different 'signatures' in the patterns of observed mate relationship. For example, consider a species with no paternal care. If a female avoids mating with familiar individuals, one would expect a deficit of offspring whose parents are maternal half-siblings, but paternal half-siblings would be unfamiliar with each other and thus have offspring at the frequency expected by chance. If spatial cues are used to avoid inbreeding, a female would be expected to produce few offspring with males (even unrelated males) living near her birth site. We searched for these and other signatures with data from a long-term study of banner-tailed kangaroo rats, Dipodomys spectabilis, in Arizona, USA, using a combination of intensive censusing, mapping of available dens, microsatellite-based parentage determination, and a randomization routine that determines the numbers of offspring expected if females in the population mate indiscriminately among the males available to them. The data are consistent with the hypothesis that kangaroo rats discriminate kin by familiarity developed via association early in life, rather than by using spatial cues or self-referential phenotype matching. Our approach should be widely applicable as a means of assessing the degree to which kin discrimination exists (in contexts like nepotism as well as inbreeding avoidance) and in inferring what cues animals use to assess categories of relationship.     

Site selection by swans wintering in Britain and Ireland; the importance of habitat and geographic location

Monthly surveys of Bewick's Swans Cygnus columbianus bewickii , Whooper Swans Cygnus cygnus and Mute Swans Cygnus olor in Britain and Ireland were made during the 1990–1991 winter to determine factors affecting the swans' selection of feeding sites. Geographic location and habitat both influenced site selection. Whooper Swans occurred in greatest numbers at sites in Scotland, northeastern England and Northern Ireland, whereas Bewick's Swans had a more southerly distribution, reflecting differences in the migratory routes used by these two species. The resident Mute Swans were more widespread, with large flocks occurring in southeastern England and in parts of Scotland. Whooper and Mute Swans were found mainly on permanent inland waters (68% and 61%, respectively), but the majority of Bewick's Swans (60%) were on arable land. The percentage of Bewick's Swan flocks found on permanent inland waters (42%) was higher than that found on arable fields (23%), indicating that the large number recorded on arable land was a result of the birds congregating at a comparatively small number of sites. Overall, less than 15% of Whooper Swans and 3% of Mute Swans were on arable crops during the winter, but the largest flocks were associated with arable land for all three species. Thus, although the occurrence of large flocks at particular arable sites may give an impression that swans feed mainly on farmland, the swans are in fact more widely dispersed. Regional variation in the percentage of juveniles present was recorded for all three species. Changes during the winter in the distribution of juveniles, and of the swans as a whole, are considered in relation to food supply and to migratory routes for the Bewick's and Whooper Swans.     

Burial depth distribution of fennel pondweed tubers (Potamogeton pectinatus) in relation to foraging by Bewick's swans

Deep burial in the sediment of tubers of fennel pondweed (Potamogeton pectinatus) has been explained in terms of avoidance by escape against consumption by Bewick's swans (Cygnus columbianus bewickii) in autumn. We therefore expected changes in foraging pressure to ultimately result in a change in the tuber distribution across sediment depth. A trade-off underlies this idea: deep tubers are less accessible to swans but must be larger to meet the higher energy demands of sprouting in spring. To test this prediction, we compared tuber burial depth over a gradient of foraging pressure both across space and across time. Tuber samples were obtained after aboveground plant senescence but before arrival of Bewick's swans. First, we compared the current tuber bank depth profile in a shallow lake with high foraging pressure, the Lauwersmeer, with that in two wetlands with moderate and low foraging pressure. Second, we compared the current tuber burial in the Lauwersmeer with that in the early 1980s when exploitation by swans had just started there. In accordance with our hypothesis, we found significantly deeper burial of tubers under high consumption risk compared to low consumption risk, both when comparing sites and comparing time periods. Since tubers in effect only survive to the next spring, the observed differences in burial depth among sites and over time cannot be a direct result of tuber losses due to consumption by swans. Rather, these observations suggest adaptive responses in tuber burial related to foraging pressure from Bewick's swans in the recent past. We thus propose that fennel pondweed exhibits flexible avoidance by escape, of a kind rarely described for plants, where both phenotypic plasticity and genotype sorting may contribute to the observed differences in tuber burial.     

Functional aspects of prolonged parental care in Bewick's swans

In Bewick's swans prolonged parental care is important in protecting offspring from feeding competition with other individuals in winter flocks. When separated from their parents, cygnets were less successful in aggressive encounters, were frequently displaced and spent less time feeding than when close to their parents. parents protected their offspring by intervening in encounters on their behalf. They were able to do so because of their high dominance rank within the flock. Differences in dominance rank among families were correlated with differences in dominance of cygnets both with and away from their parents, and preliminary evidence suggested that cygnets may assume their parents' dominance, the effect continuing into the second winter. Parental care involved measurable costs to both parents at the beginning of the winter.     

银鲫两个雌核发育克隆间两性生殖子代的遗传多样性分析

Based on the discovery of gonochoristic reproductive mode in silver crucian carp (Carassius auratus gibelio), 18 individuals from the mated offspring between clone F and clone D and their parents were analyzed using 11 RAPD primers. The mated offspring differentiated into three phenotypes. One phenotype is similar to that of clone F (SF). The second is similar to that of clone D (SD). The third shows a novel longer and thinner body type (NL). Electrophoretogram results show abundant polymorhic DNA fragments among individuals in the FD mated offspring. Obviously, the polymorphic DNA fragments originate from the genome recombination owing to the gonochoristic reproductive mode. The FD mated offspring amplify different fingerprints from maternal, and their fingerprints are different from each other. These different DNA fragments can be divided into four groups according to their origin. The average genetic distance among individuals from the FD offspring (0.23 +/- 0.123) is much higher than that of allogynogenetic offspring, which is only about 0.01. Of the three phenotypes in the FD offspring, the average distances among SD is the highest (0.235 +/- 0.097). The next is SF phenotype, in which the average distances is 0.148 +/- 0.073. The average distances among NL is the lowest (0.094 +/- 0.083). The gonochoristic reproductive mode introduces high genotypic variability and underlines genetic diversity. A dendrogram was constructed by NJTREE cluster analysis based on a total of 2320 distinguishable fragments (116 per individual). NL3 and maternal are most closely related, and SD3 and paternal are most closely related. The average genetic distances between SD and SF or NL (> 0.31) is higher than that of between SF and NL (0.124). Consistent with previous study, the genetic distance between maternal and paternal is 0.35. The average genetic distances between FD offspring and parents are both about 0. 32. But the similarities among the three phenotypes in mated group FD offspring and parents are different. The similarity between SF and maternal (71%) is higher than similarities among other phenotypes and maternal. The similarity between SD and paternal (70%) is higher than similarities among other phenotypes and paternal. The results suggest the similarities among three phenotypes in the FD offspring and parents are related with their phenotypes because some DNA fragments specific for phenotypes were amplified in this study. The revelation about reproductive diversity will be able to open the door in which complicated mechanism has been locked in unisexual organisms for long time, and establish the important roles of silver crucian carp in the studies on evolutionary genetics in unisexual or polyploid vertebrates.     

Complete mitochondrial genome of the Bewick's swan Cygnus columbianus bewickii (Aves, Anseriformes, Anatidae)

The mitochondrial genome of Bewick's swan Cygnus columbianus bewickii was completely sequenced and then the resultant data were compared with those of the whistling swan Cygnus columbianus columbianus. The complete mitochondrial genome sequence of C. c. bewickii was 16,727?bp in length and its gene arrangement pattern, gene content, and genome organization were identical to those of Cygnus species. The similarities of nucleotide and amino acid sequences between the two swans were 99.1% and 99.6%, respectively. Out of the 13 protein-coding genes and 2 rRNA genes, COIII showed the lowest nucleotide sequence similarity with 98.0%. On the other hand, in amino acid sequence similarities, both COII and ATP6 showed the lowest with 98.7% in common. The control region has the 97.8% nucleotide sequence similarity.     

Prediction of bird-day carrying capacity on a staging site: a test of depletion models

1. The carrying capacity of a site for migratory water birds, expressed in bird-days, can be of particular conservation value. Several attempts have been made to model this carrying capacity using ideal free distribution models such as, for instance, depletion models, in which the distribution is fully determined by exploitative competition. 2. In the tests of depletion models carried out so far, no alternative models were compared; rather, one specific model was tested. We tested whether bird-days were more in accordance with birds depleting the food resource (a1) until a critical food density which just enabled survival or (a2) until a threshold food density which renders the site as profitable as an alternative site; and birds (b1) satisfying their daily requirements or (b2) maximizing daily intake. 3. We studied Bewick's swans feeding on below-ground tubers of fennel pondweed in one part of an autumn staging site. In most years between 1995 and 2005, we measured tuber biomass densities around September, November and March, and counted swans daily during their stopover in October. 4. The best fit between observed and predicted bird-days was obtained by assuming that the swans were maximizing their daily intake and depleting the tubers until a threshold biomass density (which yielded the same energetic return as the alternative food source after accounting for a small part of the initial tuber biomass being out of reach of the swans). Also in line with daily intake maximization, the daily feeding time did not differ from 10 h day(-1), the value predicted for Bewick's swans based on their feeding costs. 5. Our results suggests that the applicable model to calculate carrying capacity may depend strongly on whether birds use a site to stopover or to winter, because it determines whether the birds are more likely to use a threshold or critical food density, and to behave as energy maximizers or satisficers.     

The risks of parenthood. I. General theory and applications

Summary We use contemporary life history theory to analyze parental decisions concerned with the defense of offspring, and with the provisioning of offspring in the presence of risk. In achieving the optimal level of parental investment, the parent faces a tradeoff between present and future reproductive success. Our models, which are based on stochastic dynamic programming, lead to predictions of the following kind: (i) offspring will be defended more vigorously as they grow older; (ii) long-lived species will accept fewer risks in caring for offspring than short-lived species; (iii) parents living in permanently riskier environments will defend their offspring more vigorously than parents in less risky environments; (iv) however, temporary increases in risk will result in temporarily less vigorous defense and provisioning of offspring. The models also show that parents and their offspring have different conceptions of the optimal level of parental investment. The flexibility of our modeling approach as a method of analyzing facultative behavior is also emphasized. Finally, we apply the methods of this paper to analyze fledging behavior of Atlantic puffins.     

Hampered foraging and migratory performance in swans infected with low-pathogenic avian influenza A virus

It is increasingly acknowledged that migratory birds, notably waterfowl, play a critical role in the maintenance and spread of influenza A viruses. In order to elucidate the epidemiology of influenza A viruses in their natural hosts, a better understanding of the pathological effects in these hosts is required. Here we report on the feeding and migratory performance of wild migratory Bewick's swans (Cygnus columbianus bewickii Yarrell) naturally infected with low-pathogenic avian influenza (LPAI) A viruses of subtypes H6N2 and H6N8. Using information on geolocation data collected from Global Positioning Systems fitted to neck-collars, we show that infected swans experienced delayed migration, leaving their wintering site more than a month after uninfected animals. This was correlated with infected birds travelling shorter distances and fuelling and feeding at reduced rates. The data suggest that LPAI virus infections in wild migratory birds may have higher clinical and ecological impacts than previously recognised.     

Sex differences in biparental care as offspring develop: a field study of convict cichlids (<Emphasis Type="Italic">Amatitlania siquia</Emphasis>)

Parental investment theory states that parents should contribute more to older offspring. Differences between the sexes also influence how each parent contributes to offspring in biparental species. Here, we examined a naturally occurring population of biparental convict cichlids in Costa Rica to determine how each parent cared for offspring during two distinct offspring development stages. Consistent with the predictions of the reproductive value hypothesis, we hypothesized that the levels of parental contribution would be relative to the value that each parent places on a brood. We predicted that female parents would contribute more than male parents because female convict cichlids have lower future reproductive success than males. Additionally, we predicted that both parents should contribute more to older offspring, either due to the young’s increased susceptibility to predation (i.e., the vulnerability hypothesis) or because of the longer period of time parents have been interacting with older offspring (i.e., feedback hypotheses). This increase in investment by males should coincide with a change in the coordination of care between parents. Detailed observations of parental pairs in their natural habitat supported these predictions. Females contributed more to broods than males and were relatively unaffected by offspring age while males spent significantly more time with older, free-swimming fry. Additionally, males tended to leave younger offspring more than females did, and were more likely to do so consecutively with younger offspring. This suggests that the coordination of duties between parents changes as parental investment changes. Overall, these data support both the reproductive value and the vulnerability hypotheses, but not necessarily the feedback hypothesis.     

Segregation of HLA A,B haplotypes and the distribution of antigen mismatches between mother and offspring in Hutterite families

Segregation of HLA haplotypes and offspring genotype distributions were analyzed in families from an inbred Caucasoid population, the Dariusleut Hutterite Brethren. Both parents and from one to 12 offspring were typed for HLA-A and -B antigens in 108 families. Segregation of paternal haplotypes was analyzed conditional on sibship size in 95 sibships (a total of 547 offspring), and segregation of maternal haplotypes, in 90 sibships (a total of 515 offspring). The distribution of the number of different genotypes among the offspring was analyzed conditional on sibship size in 90 families (515 offspring) where four equiprobable genotypes were expected. The distribution of the number of antigenic differences or mismatches for broad specificities between mother and offspring was analyzed in pooled family data consisting of a total of 377 offspring comprising 68 families. Compared with the multinomial distribution of segregation classes of haplotypes, there was no significant departure (probability .05 or less) from the expected segregation ratio for either paternal or maternal haplotypes. Compared with the multinomial distribution of the number of genotypes among the offspring, only two of the 11 sibship sizes had configurations that exceeded the 5% level of significance. Given the number of statistical tests performed, it is likely that these results could be explained by chance variation. Finally, there was no relative deficiency of offspring who were less mismatched with their mother for HLA-A and -B broad specificities. Therefore, if HLA-A,B region variation does have a major effect on the differential survival of fetuses in some families, it is an uncommon factor among fertile couples from this inbred population.     

Adaptive Offspring Sex Ratio Depends on Male Tail Length in the Guppy

A biased sex ratio in a brood is considered to be an adaptive strategy under certain circumstances. For example, if the expected reproductive success of one sex is greater than that of the other, parents should produce more offspring of the former sex than the latter. A previous study has documented that in the guppy, Poecilia reticulata, the female offspring of males possessing proportionally longer tails exhibit smaller body sizes and show decreased reproductive outputs than those of males having shorter tails. On the other hand, the total lengths of the male offspring of the long‐tailed males are larger because of their longer tails; consequently, they exhibit greater sexual attractiveness to females. Therefore, it has been hypothesized that this asymmetry in the expected reproductive success between the male and female offspring of long‐tailed males may result in a biased sex ratio that is dependent on the tail lengths of their fathers. This hypothesis was tested in the present study. The results showed that the females that mated with long‐tailed males produced more male offspring than those that mated with short‐tailed males. Logistic regression analysis showed that the ratio of tail length to the standard length of the fathers is a determinant factor of the sex of their offspring. These results suggest that the manipulation of the offspring sex ratios by parents enhances the overall fitness of the offspring.     

Retrodicting patch use by foraging swans in a heterogeneous environment using a set of functional responses

Effective conservation of important bird areas requires insight in the number of birds an area can support, and how this carrying capacity changes with habitat modifications. When food depletion is the dominant mechanism of competition, it should in principle be possible to calculate the total time foragers can spend per patch from their functional response (intake rate as a function of food density). However, in the field there are likely to be factors modulating the functional response. In this study previously published results of experiments on captive Bewick's swans were used to obtain functional responses of swans digging for tubers of Fennel pondweed on different foraging substrates: sandy and clayey sediment, and in shallow and deep water. In a field study, four 250×250 m sections belonging to different types (sandy–shallow, clayey–shallow, sandy–deep and clayey–deep) were delineated. Here tubers were sampled with sediment corers in three years, both before and after swan exploitation in autumn, and swans were observed and mapped from a hide in two of these years. Giving-up tuber biomass densities varied among sections. Substitution of these giving-up densities in the derived patch-type-specific functional responses yielded the quitting net energy intake rates in the four sections. As expected from the marginal value theorem, the quitting net energy intake rates did not vary among sections. Moreover, the observed foraging pressure (total foraging time per area) per patch type was in quantitative agreement with the integrated functional responses. These results suggest that in spatially heterogeneous environments, patch exploitation by foragers can be predicted from their functional responses after accounting for foraging substrate.     

Costs and Benefits of Subadult Plumage in Mute Swans: Testing Hypotheses for the Evolution of Delayed Plumage Maturation

In some avian species, young birds capable of reproducing diminish their prospects of doing so by molting into a subadult plumage that accurately signals their subadult status. Several hypotheses have been proposed to explain the evolution of delayed plumage maturation, but testing them usually has involved interspecific comparisons that are hard to interpret. Mute swans (Cygnus olor) exhibit two phenotypes that differ in whether the birds have a gray subadult plumage (SAP phenotype) or molt immediately into an all white adult plumage (AP phenotype). The AP phenotype results from a recessive allele on the X chromosome; both phenotypes occur in the same population and even in the same brood. We compared costs and benefits of both phenotypes in mute swans on the Chesapeake Bay in 1972-1980 and on Long Island Sound in 1982-1989. Swans with the SAP phenotype had higher survival rates from hatching to fledging than AP swans. In the fall, when AP cygnets began to molt into their white plumage, their parents often attacked and drove them off while allowing SAP cygnets from the same brood to remain on their territories for several more months. SAP males had higher survival rates during their first 2 yr of life than AP males, but AP swans bred at a younger age than SAP swans. The only proposed hypothesis for the evolution of delayed plumage maturation that can explain its occurrence in mute swans is the status-signaling hypothesis. This hypothesis argues that males with subadult plumage honestly advertise their age and subordinate status while AP swans are cheaters and engaging in dishonest communication. SAP males acquire a longer period of parental care, suffer less aggression from older birds, and increase their survival but forgo the opportunity to breed at an early age. This is a unique example of how a single gene resulted in either honest or dishonest communication, changed a bird's relationship with its parents and potential mates, and altered the bird's chances to survive and to reproduce.     

Longer guts and higher food quality increase energy intake in migratory swans

1. Within the broad field of optimal foraging, it is increasingly acknowledged that animals often face digestive constraints rather than constraints on rates of food collection. This therefore calls for a formalization of how animals could optimize food absorption rates. 2. Here we generate predictions from a simple graphical optimal digestion model for foragers that aim to maximize their (true) metabolizable food intake over total time (i.e. including nonforaging bouts) under a digestive constraint. 3. The model predicts that such foragers should maintain a constant food retention time, even if gut length or food quality changes. For phenotypically flexible foragers, which are able to change the size of their digestive machinery, this means that an increase in gut length should go hand in hand with an increase in gross intake rate. It also means that better quality food should be digested more efficiently. 4. These latter two predictions are tested in a large avian long-distance migrant, the Bewick's swan (Cygnus columbianus bewickii), feeding on grasslands in its Dutch wintering quarters. 5. Throughout winter, free-ranging Bewick's swans, growing a longer gut and experiencing improved food quality, increased their gross intake rate (i.e. bite rate) and showed a higher digestive efficiency. These responses were in accordance with the model and suggest maintenance of a constant food retention time. 6. These changes doubled the birds' absorption rate. Had only food quality changed (and not gut length), then absorption rate would have increased by only 67%; absorption rate would have increased by only 17% had only gut length changed (and not food quality). 7. The prediction that gross intake rate should go up with gut length parallels the mechanism included in some proximate models of foraging that feeding motivation scales inversely to gut fullness. We plea for a tighter integration between ultimate and proximate foraging models.     

The use of a flexible patch leaving rule under exploitative competition: a field test with swans

Learning animals are predicted to use a flexible patch-leaving threshold (PLT) while foraging in a depletable environment under exploitative competition. This prediction was tested in flock-feeding Bewick's swans ( Cygnus columbianus bewickii ) depleting hidden tubers of fennel pondweed ( Potamogeton pectinatus ) in a two-dimensional, continuous environment. The swans' patch residence time was measured by combining recordings of the foraging behaviour and movement paths. The tuber biomass density was measured before and after the period of exploitation, using the presumable foraging window of the swans as the scale of measurement. Swan foraging was simulated in order to predict the effects of flexible and fixed PLTs, respectively, on the patch residence time and the spatial heterogeneity of the tuber biomass density. Flexible PLTs were predicted to lead to short and decreasing patch residence times and a decrease in the coefficient of variation in tuber biomass densities, whereas the reverse was generally the case for fixed PLTs. Observed patch residence times did not decrease with time and were intermediate between those predicted for swans with flexible and fixed PLTs. Furthermore, an increase of the coefficient of variation in the tuber biomass density was observed. Given the observed giving-up biomass densities the most likely model was one with swans with a fixed rather than a flexible PLT. These results point at factors that may affect the spacing behaviour or constrain the use of a flexible PLT in swans.     

Contrasting Parental Tasks Influence Parental Roles for Paired and Single Biparental Cichlid Fish

Biparental care of young occurs when both parents provide some sort of care for offspring and can include a wide variety of behaviors, yet often studies focus on single aspects of parental care when trying to determine how each parent contributes. Here, we presented the biparental convict cichlid fish (Amatitlania nigrofasciata) with two conflicting parental behaviors: retrieval of non‐swimming offspring that have been displaced from the nest and defense against a conspecific intruder, a potential brood predator. We examined single males, single females, and pairs of parents to determine how males and females each contributed to overall parental care. Traditionally in this species, parents exhibit a division of labor (in which each parent contributes to all parental activities), but also exhibit a division of roles (in which males tend to favor the role of defense and females tend to favor more direct care, spending more time with offspring). We hypothesized that single parents would compensate for their absent mate, but that males and females would still favor preferred roles. Additionally, we hypothesized that there would be an asymmetrical expansion of roles, with females being more flexible. Our results show that the preferred roles of both parents were evident even when parents were without their mates and that males and females differed in their compensatory levels, at least when compared to the behaviors of the intact pair. Contrary to our prediction, females seem unable to fully compensate for the defensive behaviors usually exhibited by males, while males shifted completely to retrieve displaced offspring.     

Genetically based polymorphisms in morphology and life history associated with putative host races of the water lily leaf beetle,Galerucella nymphaeae

A host race is a population that is partially reproductively isolated from other conspecific populations as a direct consequence of adaptation to a specific host. The initial step in host race formation is the establishment of genetically based polymorphisms in, for example, morphology, preference, or performance. In this study we investigated whether polymorphisms observed in Galerucella nymphaeae have a genetic component. Galerucella nymphaeae, the water lily leaf beetle, is a herbivore which feeds and oviposits on the plant hosts Nuphar lutea and Nymphaea alba (both Nymphaeaceae) and Rumex hydrolapathum and Polygonum amphibium (both Polygonaceae). A full reciprocal crossing scheme (16 crosses, each replicated 10 times) and subsequent transplantation of 1,001 egg clutches revealed a genetic basis for differences in body length and mandibular width. The heritability value of these traits, based on midparent-offspring regression, ranged between 0.53 and 0.83 for the different diets. Offspring from Nymphaeaceae parents were on average 12% larger and had on average 18% larger mandibles than offspring from Polygonaceae parents. Furthermore, highly significant correlations were found between feeding preference of the offspring and the feeding preference of their parents. Finally, two fitness components were measured: development time and survival. Development time was influenced by diet, survival both by cross type and diet, the latter of which suggest adaptation of the beetles. This suggestion is strengthened by a highly significant cross x diet interaction effect for development time as well as for survival, which is generally believed to indicate local adaptation. Although no absolute genetic incompatibility among putative host races was observed, survival of the between-host family offspring, on each diet separately, was lower than the survival of the within-host family offspring on that particular host. Survival of offspring of two Nymphaeaceae parents was about two times higher on Nymphaeaceae than on Polygonaceae, whereas survival of offspring of two Polygonaceae parents was 11 times higher on Polygonaceae than on Nymphaeaceae (based on untransformed data). Based on these results, we conclude that genetically determined polymorphisms in morphology and feeding preference exist in G. nymphaeae, resulting in differential performance. Furthermore, in each diet separately, offspring of between-host family crosses were less fit than offspring of within-host family crosses. These results support the hypothesis that within this species two host races can be distinguished.     

The pay‐offs of maternal care increase as offspring develop,favouring extended provisioning in an egg‐feeding frog

Offspring quantity and quality are components of parental fitness that cannot be maximized simultaneously. When the benefits of investing in offspring quality decline, parents are expected to shift investment towards offspring quantity (other reproductive opportunities). Even when mothers retain complete control of resource allocation, offspring control whether to allocate investment to growth or development towards independence, and this shared control may generate parent–offspring conflict over the duration of care. We examined these predictions by, in a captive colony, experimentally removing tadpoles of the strawberry poison frog (Oophaga pumilio) from the mothers that provision them with trophic eggs throughout development. Tadpoles removed from their mothers were no less likely to survive to nutritional independence (i.e. through metamorphosis) than were those that remained with their mothers, but these offspring were smaller at metamorphosis and were less likely to survive to reach adult size, even though they were fed ad libitum. Tadpoles that remained with their mothers developed more slowly than those not receiving care, a pattern that might suggest that offspring extracted more care than was in mothers’ best interests. However, the fitness returns of providing care increased with offspring development, suggesting that mothers would be best off continuing care until tadpoles initiated metamorphosis. Although the benefits of parental investment in offspring quality are often thought to asymptote at high levels, driving parent–offspring conflict over weaning, this assumption may not hold over natural ranges of investment, with selection on both parents and offspring favouring extended durations of parental care.