Communal suckling in the cavy Galea musteloides

We quantified the extent of communal suckling in the cavy Galea musteloides. Six groups of animals were held in large indoor enclosures and suckling behavior was recorded over 113 h of observation. The groups contained 2–6 lactating females and 3–14 sucking pups. Due to the relative synchronization of births, 73% of the pups present in each group during lactation were non-offspring. Each of the 22 lactating females in the six groups suckled non-offspring in addition to her own offspring. On average, females suckled 86% of non-offspring present in their groups. Thus, 98% of all pups (n = 47) received milk from non-mothers. Although suckling frequencies were significantly higher for mothers with their own individual offspring than with non-offspring individuals, females invested more total time suckling all non-offspring than did suckling just their own; this was possible because for each mother many more non-offspring than offspring pups were present during lactation. Suckling bouts were significantly longer for mothers with their own individual offspring than with non-offspring individuals. The proportion of non-offspring suckling of mothers correlated negatively with the proportion of own young among the pups of a group. Non-offspring suckling did not affect future reproduction of females. Our observations demonstrate extensive practice of communal suckling in G. musteloides under laboratory conditions. Probably because all mothers of a group participated more or less equally in communal suckling behavior, the obvious cost of giving energetically expensive milk to non-offspring did not result in reduced (future) reproductive success. Potential benefits directly involved with communal suckling are unclear. More indirectly, communal suckling as well as birth synchrony might contribute to the formation of advantageous multi-litter kindergardens.     

Communal nursing in prairie dogs

Summary Within a natural population of blacktailed prairie dogs (Cynomys ludovicianus), 68% of sampled juveniles received milk from foster mothers via communal nursing (Table 1). In proximate terms, communal nursing may result because prairie dog mothers seem unable to discriminate between their own and others' offspring. In ultimate terms, both indirect selection and reduced predation on juveniles resulting from the formation of multilitter groupings have probably been important in the evolution of communal nursing.     

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     

Familiarity with adults,but not relatedness,affects the growth of juvenile red-backed salamanders (<Emphasis Type="Italic">Plethodon cinereus</Emphasis>)

The relative roles of kinship and familiarity in affecting an individual’s growth and fitness are not easy to disentangle. Not only is an individual more likely to have prior behavioral interactions with conspecifics in close proximity, it may also be related (in terms of kinship) to those nearby conspecifics. While some studies have inferred that kin discrimination affects fitness correlates, other studies found that familiarity alone can reduce aggressive interactions, thus increasing fitness. These studies have all focused on intra-age class pairs or groups. However, many animals interact with conspecifics from different cohorts. In many populations, adults of Plethodon cinereus territorially defend rocks and logs that retain moisture and food resources. We investigated whether juveniles of P. cinereus grew more in the presence of adults that were relatives or familiar. We collected pairs of juveniles and adults found under the same cover objects in the forest (familiar) and pairs of juveniles and adults found under different cover objects, approximately 10 m apart (unfamiliar). We determined parentage and relatedness of the adult–juvenile pairs and then placed these pairs in semi-natural mesocosms for 17 days. We found that juveniles housed with familiar adults had significantly greater increases in mass and snout–vent length than juveniles housed with unfamiliar adults in 2006 but not in 2007. Relatedness had no effect on growth. In addition, juveniles cohabitating with adults were not more likely to be their offspring. At least under certain environmental conditions, familiarity with adults, independent of relatedness or parentage, increased the growth of juvenile salamanders.     

Factors influencing length of maternal care in brown bears (<Emphasis Type="Italic">Ursus arctos</Emphasis>) and its effect on offspring

Length of maternal care, i.e. the interval between successfully raised litters, is the most important factor explaining the variation in reproductive rate among brown-bear (Ursus arctos) populations. In this paper, we examine the variation in length of maternal care in radio-marked brown bears and its effect on their offspring in northern Sweden. Young stayed with their mothers for 1.4–1.5 or 2.4–2.5 (in one case 3.5) years and were weaned with body masses varying from 17 to 69 kg. The probability of yearling litters staying with their mother for a 2nd year increased with decreasing yearling body mass, and was higher for litters with two offspring than for litters with one or three to four offspring. Staying with their mothers for a 2nd year had a positive effect on mass gain in yearlings and this effect was more pronounced in litters with two than three to four offspring. Body mass of 2-year-olds was not related to age of weaning, suggesting that keeping offspring for an additional year mainly compensated for low yearling body mass. If large offspring body mass positively affects later offspring survival and reproduction, mothers may be able to optimize the length of maternal care according to the litter size and the size of their yearlings.Communicated by F. Trillmich     

Milk ejection solicitations and non-nutritive nursings: an honest signaling system of need in domestic pigs?

In domestic pigs, about 20% of nursing episodes end without milk transfer (non-nutritive nursings, NNNs). The function of NNNs has not been satisfactorily explained yet. Here, we suggest that NNNs may be a part of an honest signaling system that enables the sow to provide more frequent nutritive nursings (NNs) to those litters that can prove their need through exceptionally frequent milk ejection solicitations. We further propose that the system is kept stable through the accelerating costs attached to the solicitation in the form of NNNs. Based on this hypothesis, we predicted that (P1) with an increasing number of all nursings (ALL = NNNs + NNs) the number of NNs should increase and that (P2) with an increasing number of ALL the proportion of NNNs should increase. We tested P1 and P2 using a meta-analysis applied to data from eight studies that recorded the number of NNs and NNNs in domestic pigs. We confirmed both P1 (NNs increasing with ALL) and P2 (proportion of NNNs increasing with ALL). In combination, these results show a steeply accelerating cost of each additional nutritive nursing that piglets instigate. This cost sets limits to the piglets' ability to solicit higher maternal investment through more frequent nursing solicitations.     

Reproductive biology of a deposit-feeding amphipod, Casco bigelowi, with extended parental care

The reproductive traits of a deposit-feeding amphipod that engages in extended parental care were examined. At the study site in Lowes Cove, Maine, USA, Casco bigelowi (Blake, 1929) occurred in highest densities in soft sediments just below mean low water (MLW). During most months, the sex ratio was ≃1. Many females hosted males in their burrows throughout the summer, but after fertilization of females in September, all adult males disappeared from the study area. In October almost 80% of the females were ovigerous, and in November about the same percentage was parental, i.e. caring for juveniles in their burrows. The females produced only one brood each in late fall which they accommodated in their burrows for 2 mo or longer. The average number of juveniles per female was ∼20 in November, and continuously decreased until January. Juveniles reached sizes >10 mm length in the maternal burrows. In early December the first juveniles were found in their own burrows, but major recruitment took place in late December and January. It is concluded that for C. bigelowi, the delay of recruitment into the winter months with low predation pressure and the large offspring size at this time are major advantages gained by extended parental care. C. bigelowi is host to the peritrich ciliate Cothurnia sp. on its gills, and during the summer months >70% of all amphipods had ciliates on their gills. Juveniles still living in their mother's burrows showed infestation rates similar to that of the parent; those of highly infested mothers were more heavily infested than those of “clean” mothers. Facilitated epibiont transmission during intimate and long-lasting (2␣mo) parent–offspring associations may be a consequence of extended parental care. Received: 25 November 1997 / Accepted: 14 April 1998     

Costs and benefits of communal rearing to female prairie voles (<Emphasis Type="Italic">Microtus ochrogaster</Emphasis>)

Communal rearing of offspring may help mothers maximize their investment in offspring at a reduced cost to their own bodily condition, thus maximizing their potential for reproductive success. The objective of this study was to quantify the costs and benefits of communal rearing to prairie vole (Microtus ochrogaster) pups and mothers. Mothers were assigned to one of three social units: solitary mothers, singularly breeding groups (i.e. one mother and one non-reproductive sister) and plurally breeding groups (i.e. two lactating sisters). For each type of social unit, some replicates were provided with food ad libitum, while others were provided with limited food. The body mass of focal mothers (i.e. the first mother to produce a litter) was a significant predictor of pup growth. Regardless of food availability, litters of focal mothers in plurally breeding groups gained more weight than litters reared by solitary mothers. Pups reared in singularly breeding groups were intermediate in weight gain, but did not gain significantly more weight than solitary offspring. There was no difference in the body mass of focal mothers from each type of social unit, regardless of food availability. Within plurally breeding groups, the weight gain of the two litters and body mass of focal and second mothers did not differ. However, focal mothers from plurally breeding groups nursed fewer pups than solitary mothers and also fewer pups than their nestmates when food was limited. Our results suggest that plural breeding results in greater fitness to mothers than solitary and singular breeding.Communicated by E. Korpimäki     

Maternal response to neonatal sibling conflict in the spotted hyena, <Emphasis Type="Italic">Crocuta crocuta</Emphasis>

Among spotted hyenas, Crocuta crocuta, neonatal aggression in twins is a well-known phenomenon and serves to establish intra-litter dominance soon after birth. As the stronger more aggressive cub presumably attains dominance over its twin, intra-litter dominance presents mothers with an ideal opportunity to assess individual cub fitness and, thereafter, to selectively favor one cub over the other. This study quantified maternal response to sibling conflict in 26 sets of twins born to 16 wild-living females to determine whether mothers of different social ranks exhibited favoritism towards sons or daughters, or in the case of same-sex twins, the dominant or subordinate cub. Maternal response to sibling conflict did not vary with litter sex composition, suggesting that mothers do not favor offspring of one sex over the other. All mothers intervened when their cubs fought and sometimes punished their cubs. Higher-ranking mothers more often punished both cubs, while lower-ranking mothers were more selective and punished the dominant cub. Where sibling aggression was most extreme, rather than favor the dominant sibling, mothers of all ranks made concessions to the subordinate cub that included procuring private nursing bouts for the subordinate and temporarily housing twins in separate dens, presumably to decrease sibling conflict. These findings represent a complex example of parent–offspring conflict and support both the insurance cub hypothesis and resource tracking hypothesis that mothers endeavor to keep all offspring alive for as long as possible in the event that the dominant sibling dies or that resources provide for the rearing of twins. This contribution is part of the special issue “Sibling competition and cooperation in mammals” (guest editors: Robyn Hudson and Fritz Trillmich).     

Strong maternal effects and extreme heterogeneity of progeny development in the caridean shrimp Sclerocrangon boreas (Crangonidae)

Sclerocrangon boreas is uncommon among marine coastal carideans in having a non-dispersing, abbreviated (2-stage) larval phase. We investigated the implications of this strategy in terms of fecundity, offspring provisioning and brood care in S. boreas from the St. Lawrence Gulf and Estuary in 2009–2010. Fecundity scaled positively to female body size but was low due to the production of large, lipid-rich eggs. Offspring size at all stages of development was positively related to female size. Larval traits and lipid dynamics indicate obligatory lecithotrophic development from hatching to juvenile. The larva becomes a juvenile on the mother and remains associated with her for sometime after. The co-occurrence of early egg stages among many juveniles in some clutches raises the possibility that maternal care of juveniles includes the provisioning of trophic eggs or eggs reclaimed from other females.     

Paternity alone does not predict long-term investment in juveniles by male baboons

Adult male chacma baboons (Papio hamadryas ursinus) form preferential associations, or friendships, with particular lactating females. Males exhibit high levels of affiliative contact with their friends’ infants and defend them from potentially infanticidal attacks (Palombit et al. 1997). Little is known about males’ associations with juveniles once they have passed the period of infanticidal risk. We conducted an observational, experimental, and genetic study of adult male and juvenile chacma baboons in the Moremi Reserve, Botswana. We identified preferential associations between males and juveniles and used behavioral data and a playback experiment to explore whether those associations have potential fitness benefits for juveniles. We determined whether males preferentially invest in care of their own offspring. We also determined how often males invest in care of their former friends’ offspring. The majority of juveniles exhibited preferential associations with one or two males, who had almost always been their mother’s friend during infancy. However, in only a subset of these relationships was the male the actual father, in part because many fathers died or disappeared before their offspring were weaned. Male caretakers intervened on behalf of their juvenile associates in social conflicts more often than they intervened on behalf of unconnected juveniles, and they did not appear to differentiate between genetic offspring and unrelated associates. Playbacks of juveniles’ distress calls elicited a stronger response from their caretakers than from control males. Chacma males may provide care to unrelated offspring of former friends because the costs associated with such care are low compared with the potentially high fitness costs of refusing aid to a juvenile who is a possible offspring.     

Variation in offspring sex ratio among individual Weddell seal (<Emphasis Type="Italic">Leptonychotes weddellii</Emphasis>) females of different quality

The Trivers–Willard model predicts that in polygynous species, superior-quality females will maximize their fitness by producing male offspring. Using a sample of 1,780 Weddell seal (Leptonychotes weddellii) pups recorded over 31 years, we investigated relationships between offspring sex ratio and maternal age, reproductive experience, an index of maternal lifetime reproductive output, and annual environmental variations. We found evidence that females with higher index of lifetime reproductive output were more likely to produce male than female offspring but found only weak evidence that large-scale environmental variations influenced sex ratios. Our results suggest that mothers manipulate offspring sex to maximize their own fitness, and inherent maternal quality may influence offspring sex. These findings support the Trivers–Willard sex-allocation model. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Otolith record of age, growth, and ontogeny in larval and pelagic juvenile Stephanolepishispidus (Pisces: Monacanthidae)

Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S. hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed that increment formation was not significantly different than one increment per day, and thus, increment number was used to estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain, South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition. All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40% conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population level, but unresolved at the individual level. Received: 1 November 1999 / Accepted: 18 December 2000     

Communal nesting, kinship, and maternal success in a social primate

Communal nesting, where several mothers regularly pool and cooperatively rear offspring, is unusual in mammals. This type of crèching behavior is especially rare among primates, with the notable exceptions of humans, some nocturnal strepsirrhines, and—as we show in this study—black-and-white ruffed lemurs (Varecia variegata). Here, we combine data on nesting behavior, genetic relatedness, and infant survivorship to describe variation in ruffed lemur infant care and to examine the potential benefits of ruffed lemur communal breeding. Reproductive events were rare, and females produced litters (synchronously) only once in 6 years of observation. We show that not all mothers participate in communal crèches, but those that did had greater maternal success; communal breeders spent more time feeding and their offspring were more likely to survive. Although cooperating mothers were often related, females also cooperated with non-kin, and those who shared infant care responsibilities had greater maternal success than mothers who did not participate. If there is indeed a causal link between maternal cooperation and reproductive success, this unusual behavior, like that of human communal rearing, may have evolved via some combination of kin selection and mutualism.     

Effect of an organophosphorus insecticide, fenitrothion, on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg⁻¹, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC₅₀s ranged from 32.9 μg l⁻¹ (Zoeae 2) to 10.7 μg l⁻¹ (Mysis 3), and from 3.9 μg l⁻¹ (Zoeae 3) to 2.0 μg l⁻¹ (Mysis 3), respectively; 48 and 96 h  LC₅₀s in postlarvae (PL) at the same salinity ranged from 1.8 μg l⁻¹ (PL1) to 0.6 μg l⁻¹ (PL5), and from 0.3 μg l⁻¹ (PL7) to 0.4 μg l⁻¹ (PL15). In juveniles, 96 h LC₅₀s were 0.8 μg l⁻¹ in seawater and 1.5 μg l⁻¹ in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC₅₀. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal and sublethal concentrations of fenitrothion. Received: 7 October 1996 / Accepted: 13 November 1996     

Consequences of communal gall occupation and a test for kin discrimination in the aphid Tamalia coweni (Cockerell) (Homoptera: Aphididae)

This study investigated the consequences of communal gall induction on individual and group fitness in the aphid Tamaliacoweni. The possibilities that kin discrimination and foundress density are factors favoring communal gall occupation were examined. Clonally produced aphid foundresses were collected to create two treatments: clonal groups and groups of less closely related individuals. These were confined on suitable host plant tissue to compare their respective propensities towards communal behavior. There were no significant differences in the frequencies of communal gall occupation; therefore, active kin discrimination by T.coweni foundresses apparently does not play a role in their communal behavior, within the context of this experiment. In a second experiment, aphid foundress density on the host plant was manipulated in three treatments and was correlated with the frequency of communal gall occupation. Individual fitness was inversely related to the mean number of foundresses per gall. These results suggest that communal gall occupation does not necessarily represent mutual cooperation but may instead be the outcome of competition for limited gall sites on the host plant. However, natural selection at the clonal level may favor communal gall occupation under the conditions of resource limitation and high within-group relatedness. Received: 26 September 1997 / Accepted after revision: 28 March 1998     

Offspring number in pygmy marmosets, Cebuella pygmaea *, in relation to group size and the number of adult males

In many species of birds and mammals with a co-operative breeding and rearing system, offspring survival is positively related to the number of helpers. In the New World callitrichine primates (marmosets and tamarins), adult males are considered as particularly valuable helpers, and female reproductive success may depend strongly on the males' contribution to infant care. We analysed the number of offspring (infants, juveniles) in groups of wild pygmy marmosets, Cebuella pygmaea (Callitrichinae, Cebidae, Primates), in relation to the number of adult males and to the number of adult and subadult group members. In contrast to other callitrichines with a co-operative system of infant care, no relationship was found between the number of adult males and the number of infants and offspring. However, there was a significant positive relationship between the number of juveniles and the number of adult and subadult group members. The lack of a relationship between infant and adult-male number is interpreted as resulting from the reduced importance of adult males as helpers in pygmy marmosets in comparison to other callitrichines, probably due to the reduced costs of infant care. The relationship between the number of juveniles and the number of adult and subadult group members is in accordance with increased offspring survival in larger groups, as observed in other primates. Received: 1 February 1999 / Received in revised form: 5 June 1999 / Accepted: 29 June 1999     

Family insurance: kin selection and cooperative breeding in a solitary primate (Microcebus murinus)

Lactation imposes substantial physiological costs on mothers and should therefore not be directed towards foreign offspring. Such allonursing, however, is common in mammal species that share roosts. Hypotheses to explain allonursing among such plural breeders include misdirected parental care, milk evacuation, brood parasitism, reciprocity, and kin selection. The necessary behavioral data, in combination with data on kinship and kin recognition, have rarely been available to distinguish among these explanations, however. In this study, we provide evidence for cooperative nursing and adoption by plural-breeding females in a nocturnal primate, the gray mouse lemur (Microcebus murinus), in which females forage solitarily during the night, but form day-time sleeping groups with one to two other females. We observed 34 resident females in an 8 ha study area in Kirindy Forest, Madagascar, over three consecutive annual breeding seasons and determined genetic relationships among all members of this population. Five sleeping groups of adult females were filmed inside their roosts during one breeding season after females gave birth. The composition of groups changed substantially across years, but they always consisted of close maternal relatives. All females within a group gave birth to one to three infants. They regularly transferred only their own offspring among roosting sites, demonstrating an ability to discriminate between their own and other’s offspring, but they regularly groomed and nursed related offspring other than their own and adopted related dependent young after their mother’s death. Kin selection may therefore be the main selective force behind cooperative breeding among these closely related females with a high mortality risk, providing each of them with family insurance.     

Birth sex ratios in toque macaques and other mammals: integrating the effects of maternal condition and competition

Mammalian life histories suggest that maternal body condition and social dominance (a measure of resource-holding potential) influence the physical and social development of offspring, and thereby their reproductive success. Predictably, a mother should produce that sex of offspring which contributes most to her fitness (as measured by the number of her grandchildren) and that she is best able to raise within the constraints imposed by her condition, social rank, and environment. Such combined effects were investigated by monitoring variations in body condition (weight) and behavior of female toque macaques, Macaca sinica of Sri Lanka, in a changing forest environment over 18 years. Maternal rank, by itself, had no influence on offspring sex, but did affect maternal body condition. The combined effects of rank and condition indicated the following: mothers in robust condition bore more sons, whereas those in moderate condition bore more daughters, but both effects were expressed most strongly among mothers of high rank. Where the consequences of low rank were felt most acutely, as shown by poor condition, mothers underproduced daughters. Environmental quality directly influenced rank and condition interactions, and thus sex ratios. These relationships, and data from other mammals suggest an empirically and theoretically consistent pattern of sex allocation in mammals. New predictions integrate effects, proposed by Trivers and Willard, that are rooted in male mate competition, which is universal among polygynous mammals, with those of local resource competition (and/or female reproductive competition), which are not universal and differ in intensity between the socioecologies and local environments of different species. Received: 30 May 1998 / Accepted after revision: 29 August 1998     

Sequestration of As by iron plaque on the roots of three rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) cultivars in a low-P soil with or without P fertilizer

A pot experiment was carried out in a greenhouse to investigate the sequestration of As in iron plaques on root surface of three rice (Oryza sativa L.) cultivars. Phosphate (P) fertilization increased both plant biomass and tissue P concentrations significantly, indicating that the soils used in this study was highly P-deficient. Results from this study confirmed that low P supply improved the formation of iron plaque on rice roots. As a consequence, arsenic (As) concentrations in DCB-extracts with no P addition were significantly higher than those with P fertilization. Arsenic was highly sequestrated in iron plaque; arsenic concentration in iron was up to nearly 120 mg kg⁻¹, while arsenic concentrations in roots were just several mg kg⁻¹. Both arsenic and phosphate concentrations in iron plaque were highly positively correlated with the amounts of iron plaque (DCB-extractable Fe). Contrary to normal understanding that increasing P supply could reduced As accumulation in plants, results from the present study showed that P fertilization did not inhibit the As uptake by plants (As accumulation in aboveground), which was probably due to the fact that iron plaque formation was improved under low P conditions, thus leading to more As sequestration in the iron plaque. Thus results obtained in this study indicated that the iron plaque may inhibit the transfer of As from roots to shoots, and thus alter the P–As interaction in plant As uptake processes.