Brood guarding and the evolution of male parental care in burying beetles

Summary Parental behavior that has an impact on the increased survival of offspring, an important factor in the evolution of parental care, can include both guarding and provisioning. The effects of these two components of parental care can be separated and quantified in the burying beetle Nicrophorus orbicollis in which both male and female cooperate to rear young. Although in the absence of competition, reproductive success is reduced by the presence of the second parent in the brood chamber, two parents dramatically reduce the probability that conspecifics will usurp the resource, replace either the male or female, kill the newly hatched brood, and produce a replacement clutch. After the establishment of the burial chamber (but not before) beetles appear to assist their mates in driving off intrasexual competitors. Male assistance in burial does not account for very much of the variance in the speed in which the carcass can be concealed nor are two parents essential to guard against insect predators. There were no significant differences in the duration of parental care by males paired with virgin and non-virgin females suggesting that paternity of the brood for which the male provides care is not a factor determining the length of care. Since male and female reproductive success is limited in Nicrophorus by access to suitable carcasses, many of the typical asymmetries in the costs and benefits of parental care are lacking. However since sperm displacement is not complete, paternity of the replacement clutch, for which the male does not provide care, may be a factor encouraging male desertion before female desertion. Other factors important in the evolution of paternal care, especially the probability of additional reproductive opportunities, are discussed.     

Replacement males in the western bluebird: opportunity for paternity, chick-feeding rules, and fitness consequences of male parental care

In western bluebirds (Sialia mexicana), most pairs remain together for life and share equally in post-hatching parental care. We removed resident males of socially monogamous pairs during laying and after clutch completion to examine chick-feeding rules used by replacement males and current and future fitness consequences of paternal care. Replacement males were not infanticidal and 7 (47%) fed nestlings. Feeding replacement males and the females they joined fed at rates similar to controls. Females without a feeding replacement male compensated by feeding more themselves so that overall feeding rates were not compromised, but they reduced their brooding time. Unlike assisted females, unassisted females exhibited reduced nesting success and their 14-day-old chicks weighed less than controls. Field metabolic rates of unassisted females were 17% higher than those of control females, but the difference was not statistically significant. Older females were better able to raise young without the male's help than were yearling females. Female condition was not affected by male provisioning and unassisted females were as likely to survive to the next breeding season as assisted females. We found no future benefits of provisioning by replacement males; those that fed were no more likely to breed with the female on her subsequent attempt than were males that did not feed, and subsequent clutch sizes were not reduced for females rearing young without the male's help. These experiments suggest that male parental care increases nesting success in western bluebirds and that replacement males use an all-or-none rule to determine whether or not to feed chicks: if they are present during the fertile period they feed at typical rates; if they are not, they usually do not feed at all. Because chick-feeding by males is tied to opportunity for paternity, influences success in the current nest, and does not affect the male's future breeding success, it appears to be parental rather than mating effort. Received: 8 May 1998 / Accepted after revision: 23 July 1998     

Parental conflict and brood desertion by females in blue-headed vireos

We investigated sexual conflict over parental care in blue-headed vireos (Vireo solitarius) and documented the first example of unvarying unisexual brood desertion in passerines. Females at all nests (N = 24) that were monitored closely near fledgling, deserted their broods on or near the day of fledging leaving males alone to complete parental care of young. No males deserted. This observational evidence was confirmed with radiotracking of females (2004, 2007) and both pair members (2008). Radiotracked females began visiting distant males 1–4 days before young left the nest, subsequently paired with males 355–802 m away, and laid first eggs in new nests less than 5 days after deserting. In contrast, females suffering nest predation did not desert and renested with the same male. We suggest equal parental care (nest building, incubation, feeding) in the sexes, genetic monogamy, and an adult sex ratio biased towards males has led to female control of brood desertion in this species. Unisexual desertion may be more important in altricial birds than generally realized and we discuss prerequisites to predict its occurrence. One is genetic monogamy, which may be a female tactic that reduces the likelihood of males evolving counter-adaptations to female desertion.     

Defending young biparentally: female risk-taking with and without a male in the burying beetle, <Emphasis Type="Italic">Nicrophorus pustulatus</Emphasis>

A positive correlation between the parental effort of a male and female should promote stable biparental care. Risk-taking (as assessed by injuries) against infanticidal intruders by Nicrophorus pustulatus females was expected to be low when females had a low probability of successful defense of the young. I tested the hypothesis that when the presence of a male partner increased the probability of successful defense from low to moderate that female risk-taking would increase. Single females and pairs with first instar larvae were confronted by potentially infanticidal male and female conspecific intruders. Male intruders routinely took over nests from unpaired females (30 of 36 trials). Unpaired females and male intruders were injured infrequently, indicating less intense fights despite the high probability of infanticide. A resident female defending against a male intruder was injured more often when paired than unpaired, suggesting greater risk-taking. A male parent that delays desertion, therefore, receives fitness benefits not only from his own defense of the young, but from greater female defense against male intruders as well. It is hypothesized that the threat of infanticidal takeovers by males promotes extended biparental care in burying beetles. When the intruder was female, on the other hand, a female parent on her own had a moderate probability of successfully defending the brood (22 of 36 trials). The presence of a male partner against female intruders almost guaranteed successful defense (35 of 36 trials) and female intruders did not appear to contest pairs vigorously. Against female intruders the presence of a male partner did not significantly change injury rates of the defending female.     

Sequential polyandry by brood desertion increases female fitness in a bird with obligatory bi-parental care

Parental care may be costly to parents because it decreases resources allocated to self-maintenance and may thus reduce survival and future reproductive success. An inter-sexual conflict may exist in animals with obligatory bi-parental care, such as birds of prey, in which females incubate and brood, whereas males provision food for their families. We analysed 29 years of data (1981–2009) from a study population of Tengmalm’s owls Aegolius funereus in western Finland to examine the occurrence and timing of brood desertion and sequential polyandry, and recorded a total of 1,123 monogamous and 12 polyandrous females. These data were supplemented with the 29-year nationwide Finnish ringing data, which included 11,590 monogamous and 20 polyandrous females. The 12 polyandrous females started egg-laying in their two nests at intervals of 54–68 days (mean 60 days), thus deserting their first broods when the age of oldest young averaged 21 days. Thirty-two polyandrous females re-mated and raised a second brood at a median distance of 4.5 km (range 1–196 km). These females produced 79% more eggs, 93% more hatchlings and 73% more fledglings than did females that laid simultaneously but remained monogamous. Our results show that not only males, but also females of altricial species with bi-parental care can increase their fitness by deserting their first brood when it will be cared for by the males. Earlier studies have shown that male owls can increase their lifetime reproductive success by simultaneous polygyny, and we suggest that an inter-sexual “tug-of-war” over bi-parental care exists in Tengmalm’s owls.     

Sex ratio and the sexual conflict about brood care in a biparental mouthbrooder

The pay-off of deserting and leaving a mate to care for the offspring alone is generally assumed to depend mainly on the availability of alternative mating partners and on the potential spawning rate of males and females. Eretmodus cyanostictus is a monogamous mouthbrooding cichlid in which the clutch is successively incubated first by the female and then by the male. It has been suggested that parents are constrained to monogamy due to low remating probabilities for both sexes. We tested this hypothesis by varying the sex ratio experimentally. Mate desertion by either sex was not significantly higher when additional potential mates were present (males: 8.3%, females: 0%) than when there were no other same-sex conspecifics present (males: 0%, females: 0%). Males lost their mate to a male intruder during their incubation in 26.7% of cases. Pair members were more active and showed more aggression when same-sex conspecifics were present. Behavioural differences between treatments were strongest during the incubation period of a given sex. If no desertion takes place, sexual conflict may be expressed also on a second level, the amount of parental care each parent provides. Indeed, males took the offspring later when additional females were present, although male incubation time did not differ between treatments. A hitherto undescribed display behaviour of females was clear evidence of a conflict about the timing of shift of young. In conclusion, offering alternative mating opportunities did not strongly favour mate desertion in E. cyanostictus. It rather revealed a conflict between mates about when to shift the young.Communicated by M. Abrahams     

Parental care of nestlings by male red-winged blackbirds

Summary Nestling feeding by males is less common among birds with polygynous mating systems than in monogamous species, because of the pronounced trade-off between parental behavior and the attraction of additional mates. In this study, however, we found that male red-winged blackbirds (Agelaius phoeniceus) commonly assisted females in feeding nestlings in several Ontario marshes. Male parental care was additional to that provided by females, and it significantly enhanced the fledging success of nests (Table 2). Male redwings did not help to feed all nests on their territories: primary and secondary nests were much more likely to receive male parental care than tertiary and later nests. Contrary to expectation, male parental care was not restricted to the nests of primary females: a greater proportion of secondary than primary nests were assisted (Tables 4a and b). The presence of new females settling on the territory at the same time that a resident female had nestlings, resulted in males deferring parental care until a later brood. This suggests that males trade off the recruitment of females against parental care to an existing brood. Although the number of nestlings fledging from a male's territory was strongly influenced by the number of females in the harem, males could additionally increase their reproductive success by feeding nestlings in one or more nests on their territories (Fig. 2). The reproductive success of females was significantly enhanced by male assistance in feeding nestlings (Table 3). However, those females not receiving male assistance on territories of feeding males did not suffer a significantly reduced reproductive success in comparison to females on territories of non-feeding males (Table 2). Males varied considerably in the quality of brood care given. We therefore suggest that the quality of male parental care may be a factor considered by females in choosing a breeding situation.     

Food and the deceptive acquisition of mates by polygynous male harriers

Summary Female northern harriers Circus cyaneus are polygynous, marsh-nesting raptors, whose mate choices are enigmatic. I determined the mate choice cues employed by females by correlating the order in which males were chosen with characters that 1) significantly influenced reproductive success; 2) were assessable prior to settlement; and 3) varied between breeding situations. Only nest sites and male provisioning performance met all these conditions: wet nest sites significantly (P<0.05) increased nest survival and high provisioning rates significantly (P<0.01) enhanced brood survival. The order in which females settled was strongly correlated with provisioning performance in both years (r _s -0.65, and r _s -0.84), but not with nest site quality. Females thus apperared to choose males principally on provisioning performance. Despite using the same cue, however, females choosing mated males reared only 0.28 young for every nestling raised by concurrently settling monogamous females (the lowest ratio recorded for any avian species). Extrapolation of male courtship provisioning patterns from clutch sizes and laying date indicated that females received similar proportions prior to and during egg-laying, but that males later preferentially fed females. Secondary females therefore chose mated males on the basis of a temporally changing and unreliable cue. The polyterritoriality, cooperative harems, skewed sex ratio, and sexy-son hypotheses were all inadequate in explaining polygyny in harriers. Female choice of mated males among harriers is best explained by the deceitful provisioning of food by males.     

Testosterone-induced depression of male parental behavior in the barn swallow: female compensation and effects on seasonal fitness

In birds, many aspects of male socio-sexual and parental behavior are influenced by androgens, most notably testosterone (T). We report the effects of subcutaneous T-implants in male barn swallows (Hirundo rustica) on male and female parental behavior and on seasonal reproductive success. Males were assigned to one of three experimental groups: (i) implanted with a T-filled Silastic tube; (ii) implanted with an empty Silastic tube; and (iii) not implanted. T-implanted males provided a smaller proportion of feedings (number of feedings by the male/total number of feedings by both parents) and fed nestlings less frequently (number of feedings/h) than males of the other two groups. Females paired to T-implanted males fed nestlings significantly more often than females paired with unimplanted males. Females almost fully compensated for their mates' shortfall, and this resulted in similar combined feeding efforts among treatments. Reproductive success in their first broods or during the entire breeding season was unaffected by T- treatment. These results confirm earlier reports of the suppressive effects of T on male parental behavior. However, they are inconsistent with current ESS models that predict partial compensation as the optimal response by one individual to reduction of parental effort by its mate in monogamous, biparental systems.     

Variance in male and female reproductive success in a harem-polygynous mammal,the black-tailed prairie dog (Sciuridae: Cynomys ludovicianus)

Summary Black-tailed prairie dogs are colonial rodents that live in contiguous social groups called coteries. A typical coterie contains one adult (2 years old) male, three or four adult females, and several yearlings and juveniles of both sexes. A large coterie sometimes contains two or more adult males. Using detailed behavioral observations on 164 females (of which 160 copulated) and data from four polymorphic loci from parents and offspring of 121 litters, we examined the black-tail mating system.Most females (101/164=62%) copulated with a single adult male, and only 3 of the 102 litters with 2 offspring (3%) showed unequivocal evidence of multiple paternity. Adult males usually copulated with several different adult females.In one-male coteries, females usually copulated exclusively with the resident adult male (RAM) (82/112=73%); this trend was confirmed by electrophoresis of blood smaples. In multimale coteries, each female frequently copulated with at least two different RAMs (28/52=54%); in 4 of 5 multimale coteries (80%) which produced two or more litters whose paternities could be unequivocally resolved by electrophoresis, two different RAMs each sired at least one litter.Of the 164 females, 30 (18%) copulated with both the RAM (or one of the RAMs, in multimale coteries) and an extracoterie adult male, but only 3 (2%) copulated exclusively with an extracoterie adult male. Electrophoresis showed that 9 of 121 litters (7%) were sired by an extracoterie adult male.Intersexual comparisons of annual reproductive success and lifetime reproductive success both indicate that black-tails are polygynous (i.e., that variance in reproductive success is greater for males than for females).     

Mixed reproductive strategy and mate guarding in a semi-colonial passerine,the swallow Hirundo rustica

Summary Both male and female swallows Hirundo rustica have a mixed reproductive strategy (parental care for offspring and extra-pair couplations). Mate guarding protects females from male harassment and male swallows from being cuckolded. Females hide their fertile period by copulating successfully with their mates for an extended period during first clutches. Males guard in the pre-fertile period, when many unpaired males are present. Early breeding swallows guard more than late breeders since more sexual chases of females by non-mate males take place in the early period. Solitarily breeding females experience few chases by strange males; copulation frequency, length of copulation period and mate guarding is adjusted to a lower level than among colonial birds. Male guarding activity is more intense in the fertile than in the pre-fertile period. Guarding reduces success of extra-pair copulation attempts.Three female swallows each paired and copulated with a single male and later changed to a new male before starting to breed. Extra-pair copulations most often take place between neighbouring swallows in the fertile period of the female. Many old, early breeding males and many young, late breeding females participate in extra-pair couplations. Successful extra-pair copulations peak in the fertile period contrary to success of pair copulations which does not change during the copulation period.     

Foraging decisions of American robins: somatic and reproductive tradeoffs

Summary Breeding units (occupants of a nest including at least one reproductive female) within two free-living populations of the prairie vole, Microtus ochrogaster, were monitored by live-trapping at nest during two 28-h periods each week from October 1980 to March 1984. Data are presented for 281 breeding units from all seasons, at high and low population densities and during breeding and nonbreeding periods. Fifty percent of the breeding units were monogamous (single resident reproductive male and female), 27% consisted of a single reproductive female with no resident adult male and 23% included more than one resident adult male and/or female (complex units). Monogamous units were present in the same proportions during breeding and nonbreeding periods. The number of monogamous units was significantly greater at low population densities than at high densities. During winter there were relatively more complex units and fewer single female units than during the rest of the year. Monogamous pairs remained together for an average of 42 days. Seventy-eight percent of these pairs were disbanded by the death of one or both members. There were few overlaps of the home ranges of adjacent breeding units. Significantly more nests were visited by nonresident males than by females, and the intervals between visits by males were significantly shorter than those for visits by females. Males visited single female units significantly more often than units with one or more resident males. Survival of juveniles was generally very low; 38% and 34% of young males and females, respectively, that were trapped survived until 30 days of age. Of young females remaining at the natal nest at low population densities, only 17.6% were reproductively activated; 77.1% of such females became reproductively activated at high densities. All young females that dispersed from the natal nest became reproductive.     

Species divergence and seasonal succession in rates of mate desertion in closely related Neotropical cichlid fishes

Across animal taxa, exclusive female offspring care has evolved repeatedly from biparental care, suggesting that the latter becomes evolutionarily unstable under certain conditions. Both the attributes of a species and the environment it experiences can help to predict shifts from one particular care mode to another. Nevertheless, factors inducing differences in care strategies among closely related species, or seasonal variation within species, have been subject to surprisingly little empirical testing. Here, we report the results of a field-based study that examined both among and within species variation in mate desertion in five species of closely related Nicaraguan cichlid fish in the genera Amphilophus and Amatitlania. The results show a link between female body size and male involvement in offspring care. Specifically, the larger the species the less often males were found to provide extended care. Furthermore, we found that solitary females became more common towards the end of the breeding season. We discuss the implications of this finding in the context of previous theoretical and empirical contributions regarding the frequency of offspring desertion by males.     

Manipulation of sex differences in parental care

Summary In a species with biparental care two parents cooperate to provide the appropriate amount of care for the young. Recent theoretical treatments consider the evolutionarily stable investment strategy. Under most conditions, the parental investment of the two partners should be negatively correlated, with the shortfall of one partner being partially compensated for by the other. Previous experimental manipulations of biparental care have involved removal of one partner, yet the response of a widowed bird may differ from that of a mated bird whose partner is doing less than its fair share of parental care. We present the first data involving subtle manipulations of sex differences in parental care where both partners continue to care for the young. This study involves pairs in a nestbox colony of european starlings (Sturnus vulgaris L.) with all brood sizes manipulated to five chicks. Pairs were randomly assigned to three groups: (i) male parental care reduced; (ii) female parental care reduce; and (iii) control pairs. Parental care was manipulated by attaching small weights to the base of a bird's tail feathers. Regardless of sex, nest visitation rate was reduced in the weighted birds with an incomplete compensatory increase by their unweighted partner. Additional parental duties were also considered, including shifts in prey type delivered to the nest, in both weighted birds and their partners. The shift in diet and the overall lower total visitation rate in experimental nests contributed to slower chick growth and lower chick weights than in control nests. The data accord with models suggesting that equality of invesment in biparental species is evolutionarily stable, but reveal new dimensions of parental response that need to be taken into account in theoretical treatments.     

Experimental increase in food supply influences the outcome of within-family conflicts in Tengmalm’s owl

Within a family there are conflicts of interest between parents and offspring, and between male and female parents, over the supply of parental care. The observed pattern of parental care is the outcome of negotiations within the family, and may be influenced by environmental factors such as food abundance. We experimentally increased food supply to ten Tengmalm’s owl (Aegolius funereus) nests from hatching to fledging, mimicking natural cached prey. Ten un-supplemented nests served as controls. Parents and offspring were fitted with radio-tags. Food provisioning by parents was measured both in the (1) mid- and (2) late nestling stage and in the (3) early and (4) late post-fledging stage. In response to food supplementation, both males and females reduced food provisioning, but the effect was more pronounced in females. Females generally contributed much less to food provisioning than males, and food supplementation increased the difference between the sexes. Mass loss during the brooding stage was substantially lower for supplemented than for control females. Food supplementation did not improve offspring survival, and had no effect on body measurements of nestlings. In conclusion, parents of both sexes used the increased food supply to reduce the costs of caring for their current offspring, but females responded more strongly than males.     

Pair and extra-pair mating success relative to male quality in red-winged blackbirds

We tested whether the reproductive success of male red-winged blackbirds (Agelaius phoeniceus) varied with male secondary sexual traits or with haematozoa prevalence, and whether these patterns were consistent with females preferring genetically superior males. We also determined whether the traits that correlated with male success on their own territories were also correlated with male success at siring young on other males territories. Our analysis included data from a 6-year study involving 617 nestlings for which paternity was determined by DNA profiling. Larger males sired more young on their territories, principally because they obtained larger harems. The success of larger males at acquiring more mates did not appear to be a consequence of larger males holding larger or better-quality territories. Older and longer-lived males sired more young by extra-pair fertilizations. Larger males sired the most offspring overall (on territory + off territory). Variation in epaulet size and color, responses to male and female models, nest defence and parasitism was not correlated with male success either on or off their territories or overall. Male success in a given year was significantly correlated with success the previous year, as expected if females were selecting genetically superior males. The male that was by far the most successful individual in this study was highly consistent from year to year. Because male body size is positively correlated with survival in this population (although not within the sample of males included in this study), female preference for larger males may have reflected a general preference for males with superior Survival ability. We propose that the direct advantage realized by older males in extra-pair matings might indicate that experience is important, such that experienced males are better at creating or exploiting the opportunities for extra-pair mating. This hypothesis is consistent with a pairwise analysis of cuckoldry that showed that cuckolders were most often older than the males they cuckolded.     

Polygyny and male parental care in Savannah sparrows: effects on female fitness

Summary To determine the effects of male mating status on female fitness, we compared the reproductive success, survival, and future fecundity of female Savannah sparrows (Passerculus sandwichensis) mated to monogamous vs. polygynous males in a 5-year study on Kent Island, New Brunswick, Canada. The proportion of males with more than one mate varied from 15 to 43% between years and sites. Polygynous and monogamous males fledged young of equal size in every year of the study. Females who shared paternal care with other females laid as many eggs per clutch and clutches per season as monogamously mated females. In most years polygynously mated females showed no delay in laying a second clutch, and they suffered no reduction in fecundity the following year. Recruitment of a female's offspring into the breeding population was generally independent of her mating status. Fitness costs of being mated to a polygynous male were only apparent in one year of the study, during which females mated to polygynous males had higher over-winter mortality than those mated to monogamous males. That same year, young raised by polygynous males were only one-third as likely to survive to reproductive maturity (as inferred by returns) as those raised by monogamous males. A male's mating status had no effect on his own survivorship. A male's mating status did not necessarily reflect his contributions to raising nestlings, which may partially explain why monogamously and polygynously mated females had equal fitness. At 35 nests the proportion of food deliveries brought by individual males varied from 0 to 75%; on average, males brought fewer than 30% of all food deliveries. Yet parental care by polygynous males was no less than that of monogamous males, at least at the nests of their primary females. Secondary females tended to receive less male assistance during the nestling stage, but their reproductive success was indistinguishable from that of primary females. Females feeding young without male assistance made as many food deliveries/h as did pairs in which males brought at least 30% of all food deliveries. Unassisted females did not suffer diminished fledging success or produce smaller fledglings. The benefits of polygyny for male Savannah sparrows are clear: polygynous males recruit more surviving offspring into the breeding population than monogamous males. The fitness of females, on the other hand, appears to be unaffected by whether their mate was monogamous or polygynous except in occasional years. Polygyny may be maintained in this population by the constraints of a female-biased sex ratio, the inability of females to predict a male's paternal care based on his morphology or behavior, the poor correlation between a male's mating status and his assistance at the nest, and inconsistent natural selection against mating with a polygynous male. Correspondence to: N.T. Wheelwright     

Male limitation of female reproductive success in a pipefish: effects of body-size differences

Summary In the pipefish Syngnathus typhle, a species with exclusive male parental care, males limit female reproductive success because of their limited brood pouch space and long pregnancy. Sexual size dimorphism is absent in these 1-year-old animals but increases with age so that older females are larger than similarly aged males. Because fecundity is related to size in both sexes and increases more rapidly with body size in females than in males, the difference in growth increases female fecundity more, relative to male fecundity, as the fish get older. We therefore predicted that male limitation of female reproductive success is even more severe when all age classes are considered. To measure a female's maximum reproductive rate, she was provided with three males. Small 1-year-old females produced as many eggs, or produced eggs at the same rate, as a male of similar size could care for. Small females filled on average 1.06 males within the time span of one male pregnancy and actually produced on average 10 eggs fewer than needed to fill a similarly sized male. Large 2-year-old females, in contrast, produced on average a surplus of 149 eggs and filled 2.7 similarly sized males within the course of one pregnancy. The difference between females of the two size classes was highly significant. Males prefer to mate with larger females if given a choice. In nature sex ratios are equal, and males limit female reproductive success in the whole population. Therefore, small females are more severely constrained by mate availability than are larger females because males choose to mate with larger females. Offprint requests to: A Berglund     

Behavioral strategies of American kestrels during mate replacement

Summary To determine the influence of mate replacement on the behavior and reproductive success of wild American kestrels (Falco sparverius) we removed 4 female and 16 male members of breeding pairs during incubation in 1983 and 1984. Eight males and 1 female were replaced within a mean time of 43 h. Widowed females that received a replacement spent less time hunting, but incubated and performed aerial displays more frequently than females that did not receive a replacement. After replacement, widowed females continued to incubate the original clutch, yet copulated and performed other courtship behaviors with the incoming male. Overlapping of normal temporally separate behavioral cues may be a female strategy to gain assistance from a replacement mate. However, none of the original clutches was successfully hatched. Of 8 pairs with replacement males, 2 pairs abandoned their territory, two remained on territory but did not renest, and 4 renested within a mean interval of 18 days. The lone female replacement and her mate copulated and performed nest inspections but then abandoned the territory. Incubation behavior was similar between replacement and control pairs; however, replacement males fed more invertebrate prey to nestling and made many more nest visits. All 3 replacement nests that hatched young failed within 8 days.     

Maternal nutrition affects offspring performance via maternal care in a subsocial spider

Provisioning of nutrients to the young during parental care is one of the mechanisms by which parents can affect growth and survival of their young and thus their reproductive success. We examined the hypothesis that food quality, i.e., ratio of macronutrients, provided to the young via maternal care affects their performance and the female’s reproductive success. The subsocial spider Stegodyphus lineatus exhibits intensive maternal care behaviors, including feeding the young and matriphagy (consumption of the mother). Our results showed that a protein-enriched diet resulted in larger females at maturation and higher survival of young, relative to intermediate or lipid-enriched diets. However, fecundity was not affected by female diet. We suggest that most of the nutrients are provided to the young during maternal care rather than deposited in the eggs, allowing females to economize on limited nutritional reserves. Females before maternal care showed a low protein and high lipid content relative to females before maturation and oviposition, suggesting a change in the nutritional requirement of females before maternal care. This change in macronutrient composition may be adaptive for the success of the young in the wild and shows a novel approach to animals’ ability to increase their reproductive success. Field-collected females showed a similar macronutrient composition as that of protein-enriched females in the lab, suggesting a high reproductive success of females in the wild. To our knowledge, this is the first time the importance of different macronutrients to females’ reproductive success is examined during reproduction.