Payoffs of the two alternative nesting tactics in the African dung beetle, Scarabaeus catenatus

1. Scarabaeus catenatus is a ball-rolling scarab in the subfamily Scarabaeinae. This species, however, makes use of two tactics for nest building: rolling and tunnelling. The tunnelling tactic differs substantially from the rolling tactic in that (1) it always involves repeated movements to and from the dung source and the nest, whereas rolling does not, and (2) it involves a shorter distance between the two sites.
2. Brood-nest founders were usually males and less often females, with about 25% adopting the rolling tactic and 75% adopting the tunnelling tactic. During nest building, the founder paired off with a scarab of the opposite sex, and they co-operated in the work. The female made one to four brood balls from the dung in the nest, each of which contained one egg.
3. Each scarab seemed to be able to employ both tactics. The tactic employed was independent of an individual's status, e.g. body size and timing of nest founding.
4. The rolling tactic offered only male founders a greater nest-defence success than the tunnelling tactic due to a lower intrusion into the rolled nest and a higher intensity of male–male fighting. The tunnelling tactic offered both male and female founders a larger number of brood balls than the rolling tactic because it enabled scarabs to take a larger amount of dung into the nest.
5. The reproductive success for the two tactics was estimated from the product of nest-defence success and the number of brood balls. As a result, the two tactics had equal fitness payoffs for males, but unequal payoffs for females.
6. The results suggest that male alternation of tactics is controlled by a mixed strategy. Female alternation, however, cannot be explained by mixed strategy, alternative strategies or conditional strategy.     

The benefit of large broods in barnacle geese: a study using natural and experimental manipulations

1. In precocial birds, where the young feed themselves, the costs and benefits of brood size are still poorly understood. An experimental manipulation of brood size was employed to examine the effects of brood size on both parents and young in a wild population of barnacle geese [ Branta leucopsis (Bechstein)] during brood-rearing on Svalbard.
2. Social dominance of the family unit, the amount of vigilance behaviour of the parents, the growth of the goslings in the family unit and an index of body condition for female parents during moult were all positively correlated with brood size.
3. When brood size changed as a result of natural events (i.e. predation or adoption) or experimental manipulation, rates of dominance, parental vigilance, gosling growth and female parent condition changed in a similar direction to the observed relation between the variable and brood size in unchanged broods.
4. After fledging, the fast-growing goslings in large broods survived better during autumn migration, while there was no apparent net cost in survival or next-year breeding for the parents.
5. Via a direct effect of brood size on dominance of the family unit, large broods were beneficial for both parent and young in a situation where there was strong intraspecific competition for the available food resources.
6. This study provides a clear demonstration of a causal relationship between brood size and various components of both gosling and adult fitness and is of direct relevance to the phenomenon of adoption and the evolution of brood size in this species.     

Burying beetles: intraspecific interactions and reproductive success in the field

Abstract. 1. The discovery and utilization of small carcasses by burying beetles (Silphidae, Nicrophorus ) was studied by placing dead mice at random points on large grids at two Iocations in Michigan, U.S.A.
2. The majority of mice are found within 24 h by more beetles than ultimately will utilize the carcass. If a carcass is likely to be usurped by a larger species of beetle or by a vertebrate, then intraspecific competition may be postponed until the carcass is concealed and buried.
3. Both males and females practice parental care. Maturing broods are tended by no adults, a single female, a single male, or a male—female pair. No differences in brood success were observed among these categories.
4. The female lays a larger clutch than ultimately will survive. Brood size is regulated after the egg stage, such that offspring number varies, but individual offspring size does not.
5. A large amount of unexplained variation exists in brood size, in both the laboratory and the field. This variation is probably caused by the environment, and not the reproductive physiology of the beetles. Competition with microbes is a likely candidate.
6. Differences exist not only between Nicrophorus species, but also between localities for a single species, suggesting adaptation to local environments.     

Normal and atypical nesting behaviour of Copris lunaris (L.): comparison with related species (Coleoptera, Scarabaeidae)

Abstract. 1. The lifecycle, mating and larval behaviour of Clunaris are described. Adults appeared in the autumn and nested in the following spring. The female beetle remained in the nest with the brood and could nest again the following year.
2. Nesting was initiated when virgin females were mated in the spring. Brood balls were formed by techniques sirnilar to those used by Scarabaeini. The female beetle left the nest soon after the first imagos broke out of the brood balls.
3. Nesting behaviour was readily modified by external conditions. Many parts of the sequence could be repeated or omitted. The female beetle left the nest if the brood was removed, but she remained for longer than usual if younger brood was substituted near the end of the normal nesting period.
4. Certain experimental conditions released behaviour patterns typical of other species. These were formation of superficial nests or of two-chambered nests, oviposition before completing the brood ball, and coating of the brood balls with soil (all found in other Coprina), as well as ball rolling and ball burial (found in Scarabaeini). The results are discussed in relation to the evolution of Copris nesting behaviour.     

Costs and consequences of superparasitism in the polyembryonic parasitoid Copidosoma koehleri (Hymenoptera: Encyrtidae)

Abstract.  1. Polyembryonic wasps provide dramatic examples of intra-specific developmental conflict. In these parasitoids, each egg proliferates into a clonal lineage of genetically identical larvae. If more than one egg is laid in a host (superparasitism), individuals of different clones may compete for food resources.
2. In the polyembryonic encyrtid Copidosoma koehleri , one larva per clone can differentiate into a sterile soldier. It is shown that soldiers are always females, and that they attack intra-specific competitors.
3. Research hypotheses were that (a) clones that develop in superparasitised hosts suffer heavier mortality than clones that develop in singly parasitised hosts, and (b) female clones cause higher mortality to their competitors than male clones, hence larval survival is lower in superparasitised hosts that contain females than in male-only broods.
4. The potential frequency of superparasitism in C. koehleri was manipulated by varying parasitoid–host ratios and exposure durations.
5. As parasitoid densities and exposure durations increased, the frequency of superparasitism rose, brood sizes increased, but the number of hosts that completed development was reduced. The number of offspring per parasitoid female decreased with increasing parasitoid–host ratios. Offspring size and longevity were inversely correlated with brood size. As superparasitism rates increased, fewer all-male broods were produced. Male–female broods were female-biased, suggesting selective killing of males by female soldiers. All-female broods were significantly smaller than all-male broods at high parasitoid densities only, possibly reflecting aggression among soldiers of competing clones.
6. The results support the working hypotheses, and suggest that female larvae outcompete males in superparasitised hosts.     

Brood ball size but not egg size correlates with maternal size in a dung beetle,Onthophagus atripennis

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Female size and fitness in the leaf-cutter bee Megachile apicalis

1. The effects of female size on fitness of the leaf-cutter bee Megachile apicalis Spinola (Hymenoptera: Megachilidae) were examined using artificial nesting sites in the field.
2. Although female size had no significant effect on female longevity or sex ratio of progeny, it did have a significant effect on fecundity; larger females attained greater realized fecundity than did smaller females.
3. This significant effect of female size on fecundity occurred because larger females produced cells faster than did smaller females.
4. Female size also had a significant effect on egg size; larger females laid larger eggs than did smaller females.
5. Female size had a significant effect on the size of investment in each progeny. The size of investment estimated by brood cell weight was greater for larger females than for smaller females. This pattern was largely absent, however, when the size of investment was estimated by adult progeny weight.
6. Female size had a significant effect on nest usurpation behaviour; larger females had a higher capacity to usurp nests than did smaller females.     

Parental behaviour in Copris lunaris (Coleoptera, Scarabaeidae): care and defence of brood balls and nest

Abstract. 1. Nesting female beetles righted brood balls (so as to replace the egg or larva in the uppermost position) and repaired damaged balls. This behaviour required the presence of an egg or larva in the ball, or of a short-lasting material found just after oviposition. The shape of the ball was also a righting stimulus since artificial ellipsoids were stood on end.
2. Balls containing dichloromethane extracts of C.lunaris brood were righted and repaired. Eggs and larvae of several other Scarabaeidae did not release these responses but were destroyed.
3. Righting behaviour was released when brood was absent from the top of the ball. The beetle then crawled vertically downwards and, if it encountered the displaced apex, a novel rolling action followed which automatically turned the ball towards the correct position.
4. An opening made in the nest was repaired with soil excavated from the chamber floor. Clunaris adults and Aphodius fossor larvae were attacked if they were encountered in the nest.     

Host selection and egg allocation behaviour by Aphytis melinus and A.lingnanensis: comparison of two facultatively gregarious parasitoids

Abstract. 1. The ovipositional and egg allocation behaviour of individual females of Aphytis melinus DeBach and A.lingnunensis Compere were compared.
2. Both Aphytis species exhibit the same behavioural sequence during oviposition.
3. Aphytis melinus laid most of its female eggs on the dorsum of a scale-insect beneath its cover, and most of its male eggs under the scale-insect's body. Aphytis lingnanensis also oviposited both dorsally and ventrally on scale-insect hosts, but female and male progeny arose with equal frequency from eggs laid in both locations.
4. Both A.melinus and A. lingnanensis are facultatively gregarious parasitoids. The degree of gregariousness depends on host size, i.e. the larger the host, the more the Iikelihood that several eggs will be deposited at each visit by the parasitoid.
5. When two eggs were laid during the same host visit, both A.melinus and A.lingnanensis laid one female and one male egg more often than would be expected under an assumption of random allocation of sexes.
6. Because A.melinus successfulIy utilize smaller hosts than A.lingnanensis to produce progeny, these parasitoids should not be considered ecological homo-logues, as suggested by DeBach & Sundby (1963).     

Parental care of Tilapia mariae in the field and in aquaria

Synopsis Parental care of Tilapia mariae was observed in nature (Ethiop River, Nigeria) and in aquaria with or without intruders present. In the field, 25–30% of nests are guarded by one parent, normally the female. It is assumed that most missing males have deserted. Males who participate in brood care exhibit both close brood guarding and brood defence at a lower level than females, and hence seem to invest less than females. Broods were guarded under three distinct types: (1) female at the brood, male in surroundings, (2) parents take turns, or (3) parents stay together at the brood. Each pair used predominantly one type until the young swam freely, thereafter type 3. Females defended most in type 3, but male attack rate did not differ among the types. Type 3 seems related to increased risk of brood predation and type 2 to the female's foraging needs, being more common when she is small and the mates do not differ much in size. The unequal guarding times of type 1 indicate rather a low parental investment by the male (and thus risk of desertion) than specialization in roles on equal investment basis. Parental behaviour exhibited in aquaria differed in many ways from that in nature. The role types were indistinct and there were more signs of motivational conflict between the mates. Isolated pairs avoided joint guarding in the embryo period and while switching, female turns were much longer than male turns, unlike in nature. When intruders were added, males attacked them more than did females.     

Carcass maintenance and biparental brood care in burying beetles: are males redundant?

1. Burying beetles inter small vertebrate carcasses that ultimately serve as a food source for their developing young. The male remains with the female on the carcass after the brood has been produced, purportedly to aid in the feeding and protection of larvae. However, numerous laboratory experiments have failed to demonstrate a beneficial effect of the male on the growth and survival of offspring.
2. A potential difficulty with laboratory studies is that beetles are typically held under relatively benign conditions, protected from the biotic and environmental challenges that they normally encounter. In nature, males may enhance offspring survival by aiding the female in ridding the carcass of mould, and by helping to preserve the carcass through the secretion of antibiotic substances in the beetles' saliva. To examine more rigorously the potential benefits of male parental care, an experiment was conducted under field conditions in which the reproductive output of male–female pairs was compared to that of single females.
3. Beetles were induced to bury carcasses in soil inside rigid plastic tubes that had been inserted into the ground. The experiment was a paired design involving pairs of sisters reproducing in adjacent tubes; one sister reproduced alone, whereas the other reproduced with the assistance of a male. Soil cores were recovered about 1 month later, and examined for viable pupae.
4. There was no significant difference in the number of offspring produced by single females and those reproducing with the assistance of the male, nor was there any significant difference in total brood mass. These results suggest that any benefits of extended male residency on the carcass do not stem from male participation in carcass maintenance or provisioning young.     

Risk taking in relation to reproductive investments and future reproductive opportunities: field experiments on nest-guarding common gobies, Pomatoschistus microps

The common goby, Pomatoschistus microps, has parental care,with males building nests and guarding the fertilized eggs untilhatching. We carried out field experiments to estimate the responseof males to predation risk in relation to developmental stageof their brood and time of the season. Artificial nest substrateswere placed in a shallow bay with soft substrate. After thenest had been built and eggs laid in it, a glass jar containinga potential predator (an eelpout, Zoarces viviparus) was placed15 cm from the goby's nest. We subsequently chased the malegoby away from the nest and measured his flight distance andtime until return. This was repeated once a day in May, June,and August. Time away from the nest decreased in the courseof one brood cycle, with a steeper slope in May compared tothe other months, as a result of longer times away from thenest in the beginning of the experiment. Flight distance decreasedslightly over one brood cycle and was longer in June than inMay and August. In another experiment, a male P. microps waspresented to the nest-guarding male, simulating a potentialcompetitor for the nest. Again, we found a decrease in returntime with advancement of the brood cycle, but the fish returnedfaster than when facing a predator, especially in the beginningof the brood cycle. No effect of habituation to the treatmentwas found, but there seemed to be a slight influence of developmentstage of the eggs. Thus, risk taking by nest-guarding male P.microps appears to be influenced by time already spent guardingone particular brood and the prospect for future reproductiveopportunities. [Behav Ecol 1991 ;2:351–359]     

Intraspecific female brood parasitism in the dung beetle Onthophagus taurus

Abstract.  1. Brood parasitism occurs when individuals parasitise each others' investment into parental care, and has been documented primarily as an interspecific interaction. Intraspecific brood parasitism, in contrast, is often difficult to detect and quantify, and evidence for it is comparatively scarce. The present study documents the occurrence of intraspecific brood parasitism by females of the tunnelling dung beetle Onthophagus taurus , and investigates the contributions of two variables to the propensity of female brood parasitism: female body size and dung desiccation rate.
2. Female O. taurus were found to routinely utilise brood balls made by conspecific females as food provisions for their own offspring.
3. Contrary to expectations, large and small females did not differ in the likelihood of engaging in brood-parasitic behaviour.
4. Dung desiccation rate appeared to influence likelihood of brood parasitism. Females that were given access to rapidly drying dung were significantly more likely to detect and utilise brood balls produced by conspecific females.
5. While interspecific brood parasitism has been documented in dung beetles before, the present study is among the first to present evidence for intraspecific brood parasitism as an alternative reproductive tactic of female dung beetles. Results are discussed in the context of the evolutionary ecology of onthophagine beetles.     

Courtship feeding in Ospreys Pandion haliaetus: a criterion for mate assessment?

In many bird species males provision their mates prior to egg-laying. Courtship feeding has been suggested to function in several ways: to advance laying date by improving female condition, to induce a female to copulate or to allow a female to assess her mate. The role of courtship feeding in Ospreys Pandion haliaetus was investigated in British Columbia, Canada. Courtship feeding rate affected the probability of a pair initiating a clutch. Pairs that laid eggs had higher rates of courtship feeding than pairs that did not lay eggs in both 1991 and 1992. Male courtship feeding rate also correlated negatively with the duration of the courtship period. Experimentally increasing the amount of food available to females prior to egg-laying resulted in a nonsignificant reduction in the duration of the courtship period. This study found no evidence to support the suggestion that female Ospreys trade copulations for food during the courtship period; only 63 of 385 copulations observed were associated with feeds, and courtship feeding rate did not correlate with the copulation rate of a pair. Male provisioning rates, however, were predictable; courtship feeding rate correlated with both male delivery rate to the nest when chicks were 1–2 weeks old and mean brood growth rate. Female Ospreys therefore may be able to predict the quality of subsequent paternal care using courtship feeding rate. As predicted if optimal hatching asynchrony is dependent on food availability, mean brood growth rate, an indirect measure of male parental care, was negatively correlated with hatching asynchrony. This suggests that female Ospreys may manipulate hatching asynchrony in response to male courtship feeding rate, thereby maximizing the productivity of their brood at predicted food levels.     

Brood burrow construction and brood care by Heliocopris japetus (Klug) and Heliocopris hamadryas (Fabricius) (Coleoptera, Scarabaeidae)

• 1 Brood burrow construction and brood care were studied by excavating burrows of different ages and by re-excavating certain burrows after a defined interval.
• 2 Brood burrows consisted of tunnels running via an upper chamber to a lower chamber 0.55–1.3 m below ground.
• 3 The female excavated the upper chamber, filled it with dung, then excavated the lower chamber and packed it with dung from the upper chamber.
• 4 Soil was removed from around the dung to give adungmasslying free in the lower chamber. The male was present during and just before this stage, and may cooperate in pushing soil out through the tunnel. Later the tunnel was filled with soil, excluding the male from the lower chamber.
• 5 The female formed the dung mass into balls each of which contained an egg. Development of the larvae led to an expansion at the upper pole, producing a pear shape. Third instar larvae were found in pears with a soil covering.
• 6 In the case of H.japetus the pears later became soil-covered balls containing the new adults, and the female remained in the chamber and died after the young had emerged.
• 7 The push-ups of H.japetus and of H.hamadryas were distinguishable, reflecting slight differences in the technique of burrow construction. H.hamadryas burrows were deeper and contained smaller brood balls.

     

Oviposition behavior and progeny allocation of the polyembryonic waspCopidosoma floridanum (Hymenoptera: Encyrtidae)

Oviposition behavior was used to determine the primary clutch size and sex ratio of the polyembryonic wasp Copidosoma floridanumAshmead (Hymenoptera: Encyrtidae) parasitizing Pseudoplusia includens(Walker) (Lepidoptera: Noctuidae). The laying of a female egg was associated with a pause in abdominal contractions during oviposition, while the laying of a male egg was associated with uninterrupted abdominal contractions. Although unmated females produced only male broods, they also displayed male and female egg oviposition movements. Wasps always laid a primary clutch of one or two eggs. For mated females if only one egg was laid, the emerging secondary clutch was all male or female, but if two eggs were laid a mixed brood of males and females was almost always produced. The secondary clutch of single sex broods was usually between 1000 and 1200 individuals, but the secondary clutch of mixed broods averaged 1143 females and 49 males. Thus, the primary sex ratio for mixed broods was 0.5 (frequency males), but the secondary sex ratio was 0.042. Manipulation of the sequence of male and female egg oviposition or of the primary clutch did not produce major alterations in the secondary clutch size or sex ratio.     

The frequency and fitness consequences of communal breeding in a natural population of burying beetles: a test of reproductive skew

Abstract.  1. Reproductive cooperation occurs in diverse taxa and a defining characteristic of these social systems is how reproduction is shared. Both male and female burying beetles ( Nicrophorus spp.) facultatively form associations to bury a carcass and rear a single brood, making burying beetles a model system for testing skew theory.
2. In this study, 50% of 40–45 g carcasses and 75% of 55–60 g ones were buried by more than one male and/or female Nicrophorus tomentosus .
3. Females were significantly more likely to cooperate on 55–60 g carcasses than on 40–45 g ones.
4. Analysis of parentage of 13 broods using microsatellite loci as genetic markers showed that maternity analysis of only 2% of the young excluded all females captured leaving the brood chamber after burial. Males previously mated with resident females or displaced by resident males fathered 7% of the young.
5. The male and female remaining the longest were usually the parents of the most offspring, and reproductively dominant individuals also tended to be the largest.
6. Although all but two or three individuals that helped to bury the carcass produced some offspring, reproduction was often not shared equitably. Reproduction of females was significantly skewed on six of nine 40–45 g carcasses but shared fairly equitably on all three 55–60 g ones. Reproduction was skewed among males on 7 of 10 broods.
7. Both males and females relinquished a greater proportion of the brood as the days of assistance from all consexuals increased.     

Sex ratio and maternal investment in the multivoltine large carpenter bee Xylocopa sulcatipes (Apoideh: Anthophoridae)

Abstract. 1. Females of the multivoltine carpenter bee Xylocopa sulcutipes (Maa) (Hymenoptera: Anthophoridae) usually excavate a straight tunnel in dead twigs and mass provision a linear array of up to ten brood cells with pollen and nectar. An egg is deposited upon each food mass within one cell.
2. Female offspring generally receive a higher provisioning mass (0.180 ± 0.048 g) than males, a significant difference ( P > 0.001). There are, however, male larvae that receive as much food or more as their sisters or female larvae reared in another nest.
3. There is a close positive association between the size of a mother and the weight of provisions for individual daughters, but not for sons.
4. Female offspring are positioned in the innermost brood cells (Gositions 1, 2 and 3). The sex ratio of the outer cells is either significantly male biased (positions 4–6) or skewed towards males (positions 8 and 9). Positions 7 and 10 are in equilibrium.
5. Solitary females produce a significantly female biased sex ratio ( P < 0.01). Sex ratio in social nests is skewed toward females, but not significantly so ( P < 0.2). There is no significant difference between the sex ratio of solitary and social nests ( P = 0.361). The population sex ratio (pooled sex ratio of all broods produced) is significantly female biased ( P = 0.003).
6. Females kept in the laboratory produced female biased sex ratios whilst unmated females produced all-male broods indicating that insemination and ovarian development are not causally related.
7. The expected sex ratio (ESR) under equal investment, calculated as 1/CR (CR = mean male provision weight/mean female provision weight), is 137.5:117.5 (males:females), and differs significantly from that observed, 104:151 (males:females) ( P < 0.001). The 'Local Resource Enhlancement' hypothesis best explains the female biased sex ratio found in X.sulcatipes and its maintenance in the population.     

Effects of mating order and male size on embryo survival in a pipefish

In species that provide parental care, individuals should invest adaptively in their offspring in relation to the pre‐ and post‐zygotic care provided by their partners. In the broad‐nosed pipefish, Syngnathus typhle L., females transfer large, nutrient‐rich eggs into the male brood pouch during mating. The male broods and nourishes the embryos for several weeks before independent juveniles emerge at parturition. Given a choice, females clearly prefer large partners. Yet, females provide protein‐richer eggs when the same individual mates with a smaller than a larger male. In the present study, we allowed each female to mate with one small and one large male, in alternated order. We found a strong effect of female mating order, with larger clutches and higher embryo mortality in first‐ than second‐laid broods, which may suggest that eggs over‐ripen in the ovaries or reflect the negative effects of high embryo density in the brood pouch. In either case, this effect should put constraints on the possibility of a female being selective in mate choice. We also found that small and large males produced embryos of similar size and survival, consistent with the reproductive compensation hypothesis, suggesting that, in this species, larger males provide better nourishment to the embryos than smaller males. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 639–645.     

The effect of partial brood loss on male desertion in a cichlid fish: an experimental test

There is little experimental evidence testing whether currentbrood size and past brood mortality influence mate desertion.In the cichlid Aequidens coeruleopunctatus both parents initiallydefend offspring. In a field study, all experimental broods,irrespective of initial brood size (222.9 ± 60.4, mean± SD), were manipulated to a size of 100 fry. Neitherthe duration nor investment of females in parental care differed between control and brood reduced pairs, even though care seemedcostly. On average, females lost 5.1 ± 4.8% of initialweight while guarding a brood until independence. In contrast,males with experimentally reduced broods guarded fry for significantlyfewer days before deserting their mate than did males fromcontrol pairs with natural-sized broods (20.5 ± 7.5 vs. 14.2 ± 6.2 days). In at least 20% of cases (n = 9/45),the deserting male immediately mated with another female. Maleswith experimentally reduced broods also spent less time guardingfry before deserting and attacked fewer brood predators thandid males with control broods. For broods manipulated to have100 fry, there was a significant negative relationship betweenthe days until male desertion and the proportion of the initialbrood removed. This indicates that male assessment of the futuresuccess of the current brood (hence its reproductive value)is based on past mortality and/or that there is variation amongmales in the expected size of future broods. Both current broodsize and brood size relative to initial brood size are thereforepredictors of male, but not female, parental behavior and matedesertion. Female care may be unaffected by brood reductiondue to limited breeding opportunities and partial compensationfor reduced male care.