Cytochrome b sequence analysis reveals differential molecular evolution in African mole-rats of the chromosomally hyperdiverse genus Fukomys (Bathyergidae, Rodentia) from the Zambezian region

African mole-rats (Bathyergidae, Rodentia) of the (eu)social genus Fukomys are one of the most speciose mammal genera endemic to Sub-Saharan Africa. Fukomys distributed in the Zambezian phytochorion is characterized by extreme chromosomal variation (2n=40-78). We inferred a molecular phylogeny of Zambezian Fukomys to resolve the interrelationships and the evolutionary history of the known chromosomal races. We sequenced the entire cytochrome b gene (1140bp) for a total of 66 specimens representing 18 karyotypical races from Zambia. An additional 31 sequences were retrieved from GenBank including data on all other chromosomal races. The haplotypes belonging to a small chromosomal race from Salujinga cluster with the Fukomys mechowii (Giant mole-rat) haplotypes. Differential degrees of chromosomal variation are observed among the major mole-rat clades, which is most pertinent when comparing the central Zambezian Fukomys micklemi and the northern Zambezian Fukomys whytei clades. The karyotypically hyper-diverse (12 known chromosomal races) Fukomys micklemi clade shows low levels of cytochrome b sequence divergence. Within the F. whytei clade we find a more conservative pattern of chromosomal diversification (three known chromosomal races) while the levels of sequence divergence are much higher then in the F. micklemi clade. Our results suggest that chromosomal changes may drive phyletic divergence and, eventually, speciation. The observed cladogenetic events during the Plio-Pleistocene within the F. mechowii, F. whytei, F. damarensis and F. micklemi clades appear to coincide with climatically mediated speciation bursts in other savannah dwelling mammals, including hominids. Based on the molecular data presented, combined with morphological and chromosomal data, the taxonomic implication seems to be that Fukomys may contain several (undescribed) cryptic species.     

Stress in an underground empire

The naked mole-rat (Heterocephalus glaber) and the Damaraland mole-rat (Fukomys damarensis) live in large colonies in underground tunnel systems in sub-Saharan Africa. Most members of the colonies are suppressed from reproduction and they are unlikely to reproduce during their lifetime. Only one female and a small number of males reproduce. This extreme cooperative social system has fascinated researchers since the naked mole-rat was first described as eusocial. Despite much research into the mechanisms of social suppression, the exact mechanisms are still unclear. Much evidence points towards high glucocorticoid concentrations caused by agonistic behaviour by the breeding female suppressing reproduction of non-breeders, but laboratory studies have not found any differences in glucocorticoids between breeders and non-breeders. There is, however, considerable evidence from field studies and other social mole-rats that social stress may indeed be an important factor of social suppression in social mole-rats and that those mechanisms are affected by the stability of the colony and environmental conditions. This review aims to provide a summary of the current knowledge of the relationship between environmental conditions, colony stability, glucocorticoids and reproductive suppression in social mole-rat species and suggests some avenues for future research.     

Vocal repertoire of the social Mashona mole-rat (Fukomys darlingi) and how it compares with other mole-rats

Vocalizations play a major role in communication of mammals with subterranean lifestyles since other senses are dramatically restricted in the environment of below ground burrows. In our study, we recorded vocalizations of 10 adult males and 10 adult females of a social bathyergid, the Mashona mole-rat (Fukomys darlingi) in different behavioural contexts. Vocalizations were divided into four categories according to behavioural contexts. Similar to other subterranean mammals, the range of Mashona mole-rat calls is shifted towards lower frequencies. We described 10 types of true vocal signals and 2 mechanical sounds. The vocal repertoire of the Mashona mole-rat is less rich compared to other social mole-rats, corresponding with its low mean family size. Interestingly, this species has a higher diversity in contact and distress calls, while using a relatively low number of aggressive signals.     

Light Perception in Two Strictly Subterranean Rodents: Life in the Dark or Blue?

Background

The African mole-rats (Bathyergidae, Rodentia) are strictly subterranean, congenitally microphthalmic rodents that are hardly ever exposed to environmental light. Because of the lack of an overt behavioural reaction to light, they have long been considered to be blind. However, recent anatomical studies have suggested retention of basic visual capabilities. In this study, we employed behavioural tests to find out if two mole-rat species are able to discriminate between light and dark, if they are able to discriminate colours and, finally, if the presence of light in burrows provokes plugging behaviour, which is assumed to have a primarily anti-predatory function.

Methodology/Principal Finding

We used a binary choice test to show that the silvery mole-rat Heliophobius argenteocinereus and the giant mole-rat Fukomys mechowii exhibit a clear photoavoidance response to full-spectrum (“white”), blue and green-yellow light, but no significant reaction to ultraviolet or red light during nest building. The mole-rats thus retain dark/light discrimination capabilities and a capacity to perceive short to medium-wavelength light in the photopic range of intensities. These findings further suggest that the mole-rat S opsin has its absorption maximum in the violet/blue part of the spectrum. The assay did not yield conclusive evidence regarding colour discrimination. To test the putative role of vision in bathyergid anti-predatory behaviour, we examined the reaction of mole-rats to the incidence of light in an artificial burrow system. The presence of light in the burrow effectively induced plugging of the illuminated tunnel.

Conclusion/Significance

Our findings suggest that the photopic vision is conserved and that low acuity residual vision plays an important role in predator avoidance and tunnel maintenance in the African mole-rats.     

Poikilothermic traits in Mashona mole-rat (Fukomys darlingi). Reality or myth?

The African mole-rats (Bathyergidae, Rodentia) is a mammalian family well known for a variety of ecophysiological adaptations for strictly belowground life. The smallest bathyergid, the hairless naked mole-rat from arid areas in Eastern Africa, is even famous as the only truly poikilothermic mammal. Another bathyergid, the Mashona mole-rat (Fukomys darlingi) from Zimbabwe, is supposed to have strong poikilothermic traits, because it is not able to maintain a stable body temperature at ambient temperatures below 20 °C. This is surprising because, compared to the naked mole-rat, this species, together with all congenerics, is larger, haired, and living in more seasonal environment. In addition, other Fukomys mole-rats show typical mammalian pattern in resting metabolic rates. In our study, we measured resting metabolic rate and body temperature of Mashona mole-rats from Malawi across a gradient of ambient temperatures to test its poikilothermic traits. We found that the adult mass specific resting metabolic rate was 0.76±0.20 ml O₂ g⁻¹ h⁻¹ and body temperature 34.8±1.1 °C in the thermoneutral zone (27–34 °C). Body temperature was stable (33.0±0.5 °C) at ambient temperatures from 10 to 25 °C. We thus cannot confirm poikilothermic traits in this species, at least for its Malawian population. Factors potentially explaining the observed discrepancy in Mashona mole-rat energetics are discussed.     

Spatial and Temporal Activity Patterns of the Free-Living Giant Mole-Rat (Fukomys mechowii), the Largest Social Bathyergid

Despite the considerable attention devoted to the biology of social species of African mole-rats (Bathyergidae, Rodentia), knowledge is lacking about their behaviour under natural conditions. We studied activity of the largest social bathyergid, the giant mole-rat Fukomys mechowii, in its natural habitat in Zambia using radio-telemetry. We radio-tracked six individuals during three continuous 72-h sessions. Five of these individuals, including a breeding male, belonged to a single family group; the remaining female was probably a solitary disperser. The non-breeders of the family were active (i.e. outside the nest) 5.8 hours per 24h-day with the activity split into 6.5 short bouts. The activity was more concentrated in the night hours, when the animals also travelled longer distances from the nest. The breeding male spent only 3.2 hours per day outside the nest, utilizing less than 20% of the whole family home range. The dispersing female displayed a much different activity pattern than the family members. Her 8.0 hours of outside-nest activity per day were split into 4.6 bouts which were twice as long as in the family non-breeders. Her activity peak in the late afternoon coincided with the temperature maximum in the depth of 10 cm (roughly the depth of the foraging tunnels). Our results suggest that the breeding individuals (at least males) contribute very little to the work of the family group. Nevertheless, the amount of an individual''s activity and its daily pattern are probably flexible in this species and can be modified in response to actual environmental and social conditions.     

Unusual Ratio between Free Thyroxine and Free Triiodothyronine in a Long-Lived Mole-Rat Species with Bimodal Ageing

Ansell''s mole-rats (Fukomys anselli) are subterranean, long-lived rodents, which live in eusocial families, where the maximum lifespan of breeders is twice as long as that of non-breeders. Their metabolic rate is significantly lower than expected based on allometry, and their retinae show a high density of S-cone opsins. Both features may indicate naturally low thyroid hormone levels. In the present study, we sequenced several major components of the thyroid hormone pathways and analyzed free and total thyroxine and triiodothyronine in serum samples of breeding and non-breeding F. anselli to examine whether a) their thyroid hormone system shows any peculiarities on the genetic level, b) these animals have lower hormone levels compared to euthyroid rodents (rats and guinea pigs), and c) reproductive status, lifespan and free hormone levels are correlated. Genetic analyses confirmed that Ansell''s mole-rats have a conserved thyroid hormone system as known from other mammalian species. Interspecific comparisons revealed that free thyroxine levels of F. anselli were about ten times lower than of guinea pigs and rats, whereas the free triiodothyronine levels, the main biologically active form, did not differ significantly amongst species. The resulting fT4:fT3 ratio is unusual for a mammal and potentially represents a case of natural hypothyroxinemia. Comparisons with total thyroxine levels suggest that mole-rats seem to possess two distinct mechanisms that work hand in hand to downregulate fT4 levels reliably. We could not find any correlation between free hormone levels and reproductive status, gender or weight. Free thyroxine may slightly increase with age, based on sub-significant evidence. Hence, thyroid hormones do not seem to explain the different ageing rates of breeders and non-breeders. Further research is required to investigate the regulatory mechanisms responsible for the unusual proportion of free thyroxine and free triiodothyronine.     

Burrow architecture,family composition and habitat characteristics of the largest social African mole-rat: the giant mole-rat constructs really giant burrow systems

Among African mole-rats, the giant mole-rat Fukomys mechowii is the largest social species. Despite several attempts to study a free-living population, information on its biology from natural habitats is very scarce. We mapped two neighbouring burrow systems of the giant mole-rat in a miombo woodland in Zambia. We provide information on the size and kin structure of the respective mole-rat families, architecture of their burrow systems, and characteristics of the food supply and soil around the two mapped and additional ten burrow systems. Both uncovered burrow systems were very large (total lengths, 2,245 and 743 m), making them the largest burrow systems ever mapped. Food resources around the additional ten burrow systems had a clumped distribution (standardized Morisita index of dispersion = 0.526), but a relatively high biomass (298 ± 455 g m⁻²). This, together with favourable soil conditions even in the advanced dry season (cone resistance, 328 ± 50 N m⁻²; soil density, 1.36 ± 0.06 g cm⁻³) indicates relatively hospitable ecological conditions. Both food supply and soil conditions were comparable with the conditions found in a miombo habitat of the solitary silvery mole-rat in Malawi. This suggests that there are no ecological constraints which would preclude the solitary life of a subterranean herbivore from the examined habitat. Microsatellite analysis supported the assumption that giant mole-rats live in monogamous multigenerational families with only one breeding pair of non-related animals and their offspring. The mean family size is consistent with previous findings on this species and comparable to that found in other Fukomys species studied thus far.     

Eusociality in African mole-rats: new insights from patterns of genetic relatedness in the Damaraland mole-rat (Cryptomys damarensis)

After the discovery of eusociality in the naked mole-rat, it was proposed that inbreeding and high colony relatedness in this species were the major underlying factors driving cooperative breeding in African molerats. By contrast, field and laboratory studies of the eusocial Damaraland mole-rat (Cryptomys damarensis) have raised the possibility that this species is an obligate outbreeder, although the build-up of inbreeding over several generations could still occur. Using microsatellite markers, we show that most breeding pairs in wild colonies of the Damaraland mole-rat are indeed unrelated (R = 0.02 +/- 0.04) and that mean colony relatedness (R = 0.46 +/- 0.01), determined across 15 colonies from three separate populations, is little more than half that previously identified in naked mole-rats. This finding demonstrates that normal familial levels of relatedness are sufficient for the occurrence of eusociality in mammals. Variation in the mean colony relatedness among populations provides support both for the central role played by ecological constraints in cooperative breeding and for the suggestion that inbreeding in naked mole-rats is a response to extreme constraints on dispersal. Approaches that determine the relative importance of an array of extrinsic factors in driving social evolution in African mole-rats are now required.     

Non-Breeding Eusocial Mole-Rats Produce Viable Sperm—Spermiogram and Functional Testicular Morphology of Fukomys anselli

Ansell’s mole-rats (Fukomys anselli) are subterranean rodents living in families composed of about 20 members with a single breeding pair and their non-breeding offspring. Most of them remain with their parents for their lifetime and help to maintain and defend the natal burrow system, forage, and care for younger siblings. Since incest avoidance is based on individual recognition (and not on social suppression) we expect that non-breeders produce viable sperm spontaneously. We compared the sperm of breeding and non-breeding males, obtained by electroejaculation and found no significant differences in sperm parameters between both groups. Here, we used electroejaculation to obtain semen for the first time in a subterranean mammal. Spermiogram analysis revealed no significant differences in sperm parameters between breeders and non-breeders. We found significantly larger testes (measured on autopsies and on living animals per ultrasonography) of breeders compared to non-breeders (with body mass having a significant effect). There were no marked histological differences between breeding and non-breeding males, and the relative area occupied by Leydig cells and seminiferous tubules on histological sections, respectively, was not significantly different between both groups. The seminiferous epithelium and to a lesser degree the interstitial testicular tissue are characterized by lesions (vacuolar degenerations), however, this feature does not hinder fertilization even in advanced stages of life. The continuous production of viable sperm also in sexually abstinent non-breeders might be best understood in light of the mating and social system of Fukomys anselli, and the potential to found a new family following an unpredictable and rare encounter with an unfamiliar female (“provoked or induced dispersal”). Apparently, the non-breeders do not reproduce because they do not copulate but not because they would be physiologically infertile. The significantly increased testes volume of breeding males (compared to non-breeders) is in agreement with previously found higher testosterone levels of breeders.     

Reproductive state does not influence activity budgets of eusocial Ansell's mole-rats, Fukomys anselli (Rodentia, Bathyergidae): A study of locomotor activity by means of RFID

Ansell's mole-rats (Fukomys anselli) live in families of a breeding pair and several overlapping generations of their non-breeding offspring. Locomotor activity of 47 Ansell's mole-rats from six laboratory families was recorded for a week using radio frequency identification (RFID). This technique allowed monitoring each animal's activity without isolating them from other members of their family. Animals were active about 17% of the recording time, and older animals were significantly less active than younger ones. Females tended to be slightly more active than males. There was no significant difference in the amount of activity between breeding and non-breeding individuals. Consequently, the activity pattern does not seem to account for previously reported differences in longevity between breeding and non-breeding animals.     

Social Structure Predicts Genital Morphology in African Mole-Rats

Background

African mole-rats (Bathyergidae, Rodentia) exhibit a wide range of social structures, from solitary to eusocial. We previously found a lack of sex differences in the external genitalia and morphology of the perineal muscles associated with the phallus in the eusocial naked mole-rat. This was quite surprising, as the external genitalia and perineal muscles are sexually dimorphic in all other mammals examined. We hypothesized that the lack of sex differences in naked mole-rats might be related to their unusual social structure.

Methodology/Principal Findings

We compared the genitalia and perineal muscles in three African mole-rat species: the naked mole-rat, the solitary silvery mole-rat, and the Damaraland mole-rat, a species considered to be eusocial, but with less reproductive skew than naked mole-rats. Our findings support a relationship between social structure, mating system, and sexual differentiation. Naked mole-rats lack sex differences in genitalia and perineal morphology, silvery mole-rats exhibit sex differences, and Damaraland mole-rats are intermediate.

Conclusions/Significance

The lack of sex differences in naked mole-rats is not an attribute of all African mole-rats, but appears to have evolved in relation to their unusual social structure and reproductive biology.     

Reproductive senescence in a cooperatively breeding mammal

1. Senescence (or 'ageing') is a widespread and important process in wild animal populations, but variation in ageing patterns within and between species is poorly understood.
2. In cooperatively breeding species, the costs of reproduction are shared between breeders and one or more helpers. The effects of ageing in breeders may therefore be moderated by the presence of helpers, but there have been very few studies of senescence patterns in natural populations of cooperative breeders.
3. Here, we use 13 years of data from a long-term study population of wild meerkats ( Suricata suricatta ) to investigate age-related changes in several traits known to be key components of reproductive success in females of this species.
4. Four of the six traits studied exhibited significant declines with age, indicating senescence. Litter size, the number of litters produced per year and the number of pups that survived to emergence from the natal burrow per year all increased with female age up to a peak at c. 4 years, and declined steeply thereafter; the mean pup weight at emergence in a given litter declined steadily from age zero.
5. These results provide the first evidence of reproductive senescence in a wild population of a cooperatively breeding vertebrate. Breeding success declined with age despite the sharing of reproductive costs in this species, but further study is needed to investigate whether helping affects other aspects of senescence, including survival.     

Testis size depends on social status and the presence of male helpers in the cooperatively breeding cichlid Julidochromis ornatus

Cooperatively breeding animals, in which helpers may participatein reproduction with dominant breeders, are ideal species forexamining intraspecific variation in testis size because theyoften exhibit both monogamous breeding (low risk of sperm competition)and polyandrous breeding (high risk) within a population. However,little is known about testis investment as a result of spermcompetition in these animals. The substrate-brooding cichlidfish Julidochromis ornatus has a cooperatively breeding system,in which some males mate monogamously and other males reproduceas dominant breeders or helpers within cooperatively breedinggroups, in which male helpers frequently sire young. We examinedthe relationship between testis investment and male social statusin relation to the risk of sperm competition. As predicted fromsperm competition models, in groups with male helpers, boththe male breeders and the male helpers invested more in testesmass, compared to breeding males without male helpers. We alsofound a positive relationship between the testes mass of malebreeders and their male helpers, suggesting that males increasetheir investment in reproductive capability under the risk ofsperm competition. Sperm competition models also predict thatlarger testes are associated with increased siring success.Our paternity analysis supported this prediction; we found apositive relationship between testis investment by male helpersand the number of offspring they sired.     

Thermoregulatory differences in African mole-rat species from disparate habitats: Responses and limitations

Individuals and populations possess physiological adaptations to survive local environmental conditions. To occur in different regions where ambient temperature varies, animals must adopt appropriate thermoregulatory mechanisms. Failure to adjust to environmental challenges may result in species distributional range shifts or decreased viability. African mole-rats (Bathyergidae) occupy various habitats in sub-Saharan Africa from deserts to montane regions to mesic coastal areas. We examined thermoregulatory characteristics of three African mole-rat species originating from disparate (montane, savannah, and arid/semi-arid) habitats. Animals were exposed to various ambient temperatures, whilst core body temperature and the surface temperature of different body parts were measured. Oxygen consumption was determined as a measure of heat production. Core body temperatures of Natal (montane) mole-rats (Cryptomys hottentotus natalensis) increased significantly at ambient temperatures >24.5 °C, while those of the highveld (Cryptomys hottentotus pretoriae) (savannah) and Damaraland (Fukomys damarensis) (arid/semi-arid) mole-rats remained within narrower ranges. In terms of surface temperature variation, while pedal surfaces were important in regulating heat loss in Natal and Damaraland mole-rats at high ambient temperatures, the ventral surface was important for heat dissipation in Damaraland and highveld mole-rats. This study provides evidence of the variation and limitations of thermo-physiological mechanisms for three mole-rat species relative to their habitats. Information on physiological adaptations to particular habitats may inform predictive modelling of species movements, declines, and extinctions in response to a changing environment, such as climate change.     

Evolution of African mole-rat sociality: burrow architecture, rainfall and foraging in colonies of the cooperatively breeding Fukomys mechowii

African mole rats (Bathyergidae) offer an excellent system with which to test theories relating to the evolution and maintenance of sociality in mammals. The aridity food distribution hypothesis (AFDH) suggests that, within the bathyergids, sociality has evolved in response to patterns of rainfall, its effects on food distribution, and the subsequent costs and risks of foraging and dispersal. Here, in the first detailed study of burrow architecture in a social mole-rat species, with data from 32 burrows, we show that in the giant mole-rat Fukomys mechowii burrow fractal dimension increases with colony size and is higher during the rainy season than during the dry season. The mass of food in the burrow increases with fractal dimension and is higher during the rainy season than during the dry season. These results link for the first time colony size, burrow architecture, rainfall and foraging success and provide support for two assumptions of the AFDH, namely that (1) in arid conditions burrowing may be severely constrained by the high costs of digging; and (2) the potential risks of failing to locate food may be mitigated by increases in colony size.     

Group Structure,Nest Size and Reproductive Success in the Cooperatively Breeding Cichlid Julidochromis ornatus: A Correlation Study

The effect of group size on reproductive success has long been studied in cooperatively breeding species, as it might provide an adaptive explanation for group‐living in social species. Numerous studies have shown positive effects of subordinates on reproductive success (‘helper effect’), but these studies have also revealed the importance of controlling statistically, or experimentally, for the effect of other factors that might affect reproductive success. Here, we first examine the relationships between group size, body size of group members and nest size in the cooperatively breeding cichlid Julidochromis ornatus, in which unrelated helpers frequently participate in reproduction and their breeding nests inside rock crevices may be crucial for reproduction and survival of all group members. Then, we subsequently investigate the relationship between group size and reproductive success, while controlling for these factors. The results showed that group size was significantly related to body size of group members rather than nest size; and larger breeders had larger helpers. It was found that group size significantly increased group reproductive output. More importantly, reproductive success of male breeders did not depend on the presence of mature helpers, whereas female reproductive success increased when two males assisted her and tended to decrease when two females bred cooperatively. We conclude that breeding groups of J. ornatus have size hierarchical societies that relate to group size, and group composition of genetically unrelated and co‐breeding members affects their reproductive success.     

Family values: group dynamics and social control of reproduction in African mole-rats

To exploit ecological niches where constraints have favoured selection for group living and cooperation, both vertebrates and invertebrates have evolved elaborate social systems. In mammals, numerous divergent taxa have converged at similar solutions to these ecological challenges (such as food distribution and predator avoidance), culminating in the social insect-like behaviour of the naked mole-rat. Characteristically, breeding is partitioned unequally in such groups, resulting in a 'reproductive skew'. New research linking studies of physiology, behaviour and molecular ecology in African mole-rats is helping us to elucidate why different proximate mechanisms that control groups of cooperative breeders might have evolved.     

Reproductive parasitism of broodcare helpers in a cooperatively breeding fish

Large male helpers in the cooperatively breeding cichlid Neolamprologus pulchergain reproductive success by parasitizing the reproductive effort ofmale territory owners. Under controlled, experimental conditionswe examined the genetic relatedness between the members of broodpairs (n = 14), their male helpers (n = 8), and offspring (n= 292) in seven families. We used multilocus DNA fingerprintingto check for potential reproductive parasitism by male helpersand to assess their fertilization success. Of offspring producedin these families, 10.3% were sired by helpers. In parasitizedbroods, helper fertilization success varied between 12.5% and35.8%. Male helpers parasitized parental reproduction when theirbody size exceeded 4.5 cm standard length (SL), even thoughsexual maturity may be reached much earlier (3.5 cm SL). Twoof three parasitic helpers were punished by severe aggressiveattacks when parasitizing the reproduction of breeders, whichled to their expulsion from the territory. This study demonstratesa potential fitness benefit to broodcare helpers that is oftenneglected. It also points to the delicate balance that may exist betweencooperative and competitive behavior in cooperatively breeding species.     

Cichlids do not adjust reproductive skew to the availability of independent breeding options

Helpers in cooperatively breeding species forego all or partof their reproduction when remaining at home and assisting breedersto raise offspring. Different models of reproductive skew generatealternative predictions about the share of reproduction unrelatedsubordinates will get depending on the degree of ecologicalconstraints. Concession models predict a larger share when independentbreeding options are good, whereas restraint and tug-of-warmodels predict no effects on reproductive skew. We tested thesepredictions by determining the share of reproduction by unrelatedmale and female helpers in the Lake Tanganyika cichlid Neolamprologuspulcher depending on experimentally manipulated possibilitiesfor helper dispersal and independent breeding and dependingon helper size and sex. We created 32 breeding groups in thelaboratory, consisting of two breeders and two helpers each,where only the helpers had access to a nearby dispersal compartmentwith (treatment) or without (control) breeding substrate, usinga repeated measures design. We determined the paternity andmaternity of 1185 offspring from 47 broods using five to nineDNA microsatellite loci and found that: (1) helpers participatedin reproduction equally across the treatments, (2) large malehelpers were significantly more likely to reproduce than smallhelpers, and (3) male helpers engaged in significantly morereproduction than female helpers. Interestingly, in four broods,extragroup helper males had fertilized part of the brood. Nohelper evictions from the group after helper reproduction wereobserved. Our results suggest that tug-of-war models based oncompetition over reproduction within groups describe best thereproductive skew observed in our study system. Female breedersproduced larger clutches in the treatment compared to the controlsituation when the large helpers were males. This suggests thatmale breeder-male helper reproductive conflicts may be alleviatedby females producing larger clutches with helpers around.