Game theoretic model of brood parasitism in a dung beetle Onthophagus taurus

We present a game theoretic model of brood parasitism in the dung beetle Onthophagus taurus. Female O. taurus engage in brood parasitism when they attack a brood ball made by another female, destroy the existing egg and place one of their own eggs to develop within the existing dung ball. Brood parasitism is more costly than other forms of kleptoparasitism because an individual loses the total investment in an offspring. In this paper, we outline the behaviors involved in brood ball production and provide time estimates of those behaviors. The model is then used to predict when it is beneficial to steal the brood ball created by another female and when it is beneficial for a female to create her own. We also investigate how long a female should guard her eggs.     

Wild yellow dung fly females may not select sperm based on dung pat microclimate but could nevertheless benefit from polyandry

Molecular techniques have substantially improved our knowledge of postcopulatory sexual selection. Nevertheless, studies examining sperm utilization in natural populations of nonsocial insects are rare, support for sperm selection (biased use of stored sperm, e.g. to match offspring genotypes to prevailing environmental conditions) is elusive, and its relevance within natural populations unknown. We performed an oviposition site choice experiment in the field where female yellow dung flies Scathophaga stercoraria could deposit eggs into three different microenvironments on a dung pat (the east–west ridge, north- or south-exposed side), and genotyped the offspring and sperm remaining in storage after oviposition. Females exhibited plasticity in the number of eggs deposited according to pat age. Additionally, temperature strongly influenced egg placement: the warmer the temperature, the higher the proportion of eggs laid into the north-exposed side of dung. The number of ejaculates in storage differed amongst spermathecae, and females stored sperm from more males than fathered their offspring (2.11 sires vs. 2.84 males within sperm stores). Mean last male paternity was 83.4%, roughly matching previous laboratory estimates. Importantly, we found no evidence that females selectively lay eggs of different genotypes, by biasing paternity towards certain males, depending on offspring’s microclimate. Thus, while we show female choice over number of eggs and where these are deposited, there was no evidence for sperm selection. We further revealed positive effects of multiple mating on total number of offspring and proportion of offspring emerging from the dung. We argue that the integration of field studies and laboratory experiments is essential to promote our understanding of polyandry and cryptic female choice.     

The behaviour of laying workers and the morphology and viability of their eggs in Melipona bicolor bicolor

Abstract. As in many other stingless bees, Melipona bicolor bicolor Lepeletier (Apidae: Meliponinae) workers lay two morphologically distinct types of eggs: slender ones that have a typical patterned chorion, and larger ones that lack this pattern. In this paper we report on the relation between egg morphology and the behaviour of the workers that lay such eggs. In most cases, the laying of each of these egg types is accompanied by a unique sequence of behaviours. After a worker has laid the unpatterned type of egg, she generally leaves the cell, giving the queen the possibility of eating this egg. In the case of the patterned egg type, the worker usually closes the cell immediately after her egg laying. When worker egg laying occurs right after a series of regurgitations, it stops the queen from ovipositing. When, instead, a worker lays an egg after queen oviposition, the cell contains two eggs. This study also revealed cases in which workers laid slender, patterned eggs without closing the cell, and other cases where workers laid large, spherical, unpatterned eggs and instantly closed the cell. Experiments in which worker eggs, destined to be eaten by the queen, were protected by covering the cell artificially with a piece of wax showed that some of these eggs developed into larvae, although they were occasionally relatively small. The occurrence of a range of combinations of egg-laying behaviours and egg morphologies in M. b. bicolor workers is discussed from the perspective of worker egg laying in other stingless bees.     

Resource quality and the colonisation and succession of coprophagous dung beetles

In order to examine the degree of resource selectivity in a north temperate dung beetle assemblage und to identify major parameters that influence such selectivity, the occurrence of adult dung beetles ( Aphodius. Geotrupes and Sphaeridium ) in up to five different types of dung over a period of up to 25 d was examined in a series of field experiments using standardised dung pats. There were significant physical and chemical differences in dung quality between dung types and over time during succession. Dung beetle species showed distinct preferences for particular types of dung which were generally similar in data sets from both pitfall traps and dung pat samples. Species also showed distinct patterns of successional occurrence. Ordinations produced by Canonical Correspondence Analysis, based on species occurrences in dung types and over time, usually selected dung pat age as the most important environmental variable influencing dung beetle assemblages. Dung quality parameters contributed a significant element of structure to the species ordinations but ordinations using dung types or dung quality parameter values as the environmental variables were very similar in terms of sample and species placement within the ordination for each data set. Most importantly the CCA ordinations clearly grouped species according to their breeding behaviour. Early-successional species laid eggs in the soil, or in silken egg cocoons, which allowed them to exploit wet dung. Mid and late-successional species laid eggs in the dung pat: late-successional species could exploit normally wetter dung types than mid-successional species, probably due to increased crust formation and drying as the dung pat ages. Thus, species appear to be differentially adapted to exploit varying types of dung microhabitats. Therefore, where two or more species of large herbivores are present, dung quality preferences probably constitute an important niche dimension.     

Temperature effects on egg size and their fitness consequences in the yellow dung fly Scathophaga stercoraria

Organisms and parts of an organism like eggs or individual cells developing in colder environments tend to grow bigger. A unifying explanation for this Bergmann's rule extended to ectotherms has not been found, and whether this is an adaptive response or a physiological constraint is debated. The dependence of egg and clutch size on the mother's temperature environment were investigated in the yellow dung fly Scathophaga stercoraria. Smaller eggs were laid at warmer temperatures in the field and the laboratory, where possible confounding variables were controlled for. As clutch size at the same time was unaffected by temperature, this effect was not due to a trade-off between egg size and number. Temperature-dependent egg sizes even persisted within individuals: when females were transferred to a cooler (warmer) environment, they laid third-clutch eggs that were larger (smaller) than their first-clutch eggs. The fitness consequences of these temperature-mediated egg sizes were further investigated in two laboratory experiments. Neither egg and pre-adult survivorship nor larval growth rate were maximized, nor was development time minimized, at the ambient temperature corresponding to the mother's temperature environment. This does not support the beneficial acclimation hypothesis. Instead, this study yielded some, but by no means conclusive indications of best performance by offspring from eggs laid at intermediate temperatures, weakly supporting the optimal temperature hypothesis. In one experiment the smaller eggs laid at 24 °C had reduced survivorship at all ambient temperatures tested. Smaller eggs thus generally performed poorly. The most parsimonious interpretation of these results is that temperature-mediated variation in egg size is a maternal physiological response (perhaps even a constraint) of unclear adaptive value. This revised version was published online in November 2006 with corrections to the Cover Date.     

Oviposition behaviour and response of Monochamus scutellatus (Coleoptera: Cerambycidae) to conspecific eggs and larvae

• 1 The oviposition behaviour of white‐spotted sawyer beetle Monochamus scutellatus (Say) (Coleoptera: Cerambycidae) females was studied under laboratory and field conditions.
• 2 Females walked over the bark surface and stopped to palpate it with their labial and maxillary palpi. Once a potential oviposition site was located, the female excavated a scar in the bark with her mandibles, deposited an egg and brown plug in the scar and inserted her mandibles again into the scar prior to leaving the area.
• 3 Female M. scutellatus preferred to lay eggs on bolts containing no eggs (control) to those containing eggs from other females, but did not show this preference when provided with control bolts and those containing their own eggs. When females were provided with bolts containing their own eggs and bolts containing eggs from other females, they laid more eggs on bolts containing their own eggs. Females laid more eggs on control bolts than on bolts containing their own larvae or larvae from other females.
• 4 The brown plug in the oviposition scar may provide a protective barrier to the egg, a chemical message that the site is occupied, or both.

     

Egg characteristics are unreliable in determining maternity in communal clutches of guira cuckoos Guira guira

Egg characteristics have been used to determine egg maternity for birds in situations where two or more females lay eggs in a single nest (as in communal breeders and intraspecific parasites). We assessed the applicability of egg morphometry and eggshell appearance in ascribing egg ownership in communal clutches of guira cuckoos Guira guira , a species where up to seven females may lay eggs in a joint nest. We used both combined variables (including egg mass, length, width, shape and two eggshell variables), and a shape index to test whether eggs laid by each female were similar but different from eggs laid by other females. Also, we conducted discriminant function analyses to verify if eggs could be correctly classified to their mothers based on their characteristics. The correct maternity was determined by yolk protein electrophoresis of freshly-laid eggs. Individual female chutches were separated through egg characteristics or shape alone in 29% and 41% of the groups tested, respectively. Differences were mostly due to a single female that differed from her nest-mates in a unique egg variable. On average, 55% of the eggs analyzed were not assigned to the correct mother using egg dimensions and eggshell speckling pattern. In conclusion, the egg characteristics used do not reliably indicate maternity in guira cuckoo communal clutches. We therefore recommend a protein-based verification of egg appearance characteristics for assigning maternity in other species in which multiple female laying occurs.     

Egg Carrying Attracts Enemies in a Cryptic Coreid Bug (Phyllomorpha laciniata )

In the golden egg bug (Phyllomorpha laciniata) eggs are laid mainly on the backs of conspecifics, and in many habitats eggs do not survive unless carried by bugs. Bugs are covered with small spines that may make them unpalatable. They are also cryptic, at least if not carrying eggs. We used domestic chicks as predators to examine if egg carrying influences susceptibility to avian predators. The special morphology of the bugs and/or possible chemical defense may make the bugs unattractive, as chicks that picked up bugs often rejected them. Eggs made bugs more attractive to chicks. The total number of attacks and the probability of being attacked at all increased significantly when bugs carried eggs. If mating with an egg-carrying bug, a female without eggs suffered as much as her egg-carrying partner when attacked. This study, together with previous results on ant predation, suggests that carrying eggs as well as mating with an egg-loadedbug are costly in terms of predation risk.     

Factors affecting egg maturation in the bean weevil Callosobruchus maculatus

Abstract. This paper concerns the effects of mate and seed availability on the rate of egg maturation in the bean weevil Callosobruchus maculatus (F.). Egg maturation starts before emergence from the seed and, provided that both oviposition sites and mates are available, eggs are laid at a rate determined by the number of oviposition sites, and mature at a similar rate. If seeds or mates are absent then a small number of eggs are laid, but oocytes continue to mature until the oviduct-capacity is approached. The number of eggs that a female can store is dependent on her body weight and does not correlate with the number of ovarioles. If, after a period in which oocyte development has been halted, conditions for egg-laying become suitable, then egg maturation can be re-started, but only after the oviducts have been emptied of eggs. The rate of egg maturation is then similar to that for females of the same age which have been maturing eggs since emergence.     

Consequences of prenatal androgen exposure for the reproductive performance of female pheasants (Phasianus colchicus)

Maternal hormones in vertebrate eggs can mediate important forms of maternal effects. However, the function of hormone transfer to the eggs is still debated, especially because long-term fitness consequences have been little studied. We investigated the effect of prenatal exposure to physiologically elevated yolk testosterone (T) levels on reproduction of female pheasants (Phasianus colchicus) in captivity. We found that females hatching from T-injected eggs (T-females) had a lower egg-laying rate than controls, and their eggs were more frequently infertile than those laid by control females. There were no effects of prenatal maternal treatment on egg size and yolk T concentration, but eggs carrying a female embryo laid by T-females had smaller yolks than eggs with a male embryo, while there was no sex difference in yolk size among the eggs laid by control females. Progeny sex ratio was unaffected by maternal treatment. These findings suggest that the transfer of high androgen levels to the eggs by the mother is constrained by complex trade-offs between direct effects on her daughters' reproduction and by trans-generational differential consequences on male and female descendants.     

Reproductive properties of two sympatric dung beetles,Aphodius haroldianus andA. Elegans (Coleoptera: Scarabaeidae)

1. Reproductive properties of two sympatric dung beetles, Aphodius haroldianus and A. elegans, were studied at a pasture in the central Japan.
2. Overwintered adults of A. haroldianus came flying to dung pats from May to early August and bred from June to July. A. elegans overwintered as larvae, new adults came to dung pats from mid May to mid June. After aestivation, they reproduced from October to November.
3. A. haroldianus was a species with low fecundity and large food reserve for larvae. Female of this species had short duration of residence and laid fewer number of eggs in one dung pat. On the other hand, A. elegans was a species with high fecundity and small food reserve for larvae. Female of this species had long duration of residence and laid larger number of eggs in one dung pat.
4. The daily egg production in A. haroldianus reached a peak (0.40 eggs/female/day) at middle of oviposition period, but, that in A. elegans reached a peak (6.49 eggs/female/ day) at the beginning of oviposition period. The mortality of A. haroldianus female occurred after the daily egg production reached a peak and then rapidly increased, whereas that of A. elegans began soon after the beginning of oviposition and then gradually increased.

     

Factors affecting captive whooping crane egg fertility: A retrospective analysis

The whooping crane (Grus americana) has been managed in captivity since the 1960s following a substantial genetic bottleneck in the wild population. Through major ex situ conservation efforts, there are 158 whooping cranes managed in North American institutions and chicks are released annually into the wild. Current reintroduction goals for the whooping crane however, are impeded by poor reproduction within the ex situ population, in part because of low egg fertility. Development of improved management techniques to overcome low egg fertility requires a better understanding of factors that influence egg fertility. We collected data for eggs laid at Patuxent Wildlife Research Center from 2005–2014 (n = 438 eggs; n = 23 pairs). We constructed 5 sets of generalized linear mixed-models, with a Bernoulli-distributed response variable (fertile or infertile), to address the effects of egg-specific variables (month laid, sequence, and clutch order of the egg), life-history events of the male and female (age, rearing method, wing condition, age at first pairing, age at current pairing, and female age at first laying), pair-specific characteristics (kinship, years paired, chick-rearing experience, and previous pairings), and captive management decisions (inclusion in the artificial insemination program and pair experience chick-rearing) on the probability of egg fertility. Our results indicate that female-specific factors (especially age, age at current pairing, and wing status) and pair-specific factors of kinship, chick-rearing experience, copulation, and inclusion in the artificial insemination program influenced fertile egg production. Specifically, the younger a female is when paired with her current social mate, the higher probability that her eggs will be fertile. Furthermore, high kinship reduced fertility, whereas chick-rearing experience and artificial insemination of females with a donor male other than her social mate increased fertility. Further research on mate selection and reproductive mechanisms is needed to better understand egg laying and egg fertility in the whooping crane. © 2019 The Wildlife Society.     

Oviposition Behavior and Offspring Emergence Patterns in Succinea thaanumi, an Endemic Hawaiian Land Snail

In this field study, newly laid egg clutches of Succinea thaanumi, an endemic Hawaiian land snail, were labeled and observed weekly over a 12‐mo period. Snails usually laid their clutches under leaf tips and, moreover, this placement affected snail emergence by mitigating the effects of dehydration through the leaf‐drip phenomenon. During droughts, the gel surrounding egg clutches dehydrated, pasting the embryos to the backs of leaves. The hygroscopic gel rehydrated once rains resumed. The majority of newly laid clutches contained shell‐less embryos which required more time for emergence than embryos laid with visible shells. More shelled embryos were laid subsequent to a 3‐wk drought, indicating that snails retained their eggs during adverse environmental conditions and laid them when conditions improved. The snails’ abilities to retain eggs in adverse conditions, but to lay more unshelled embryos over their lifetimes, contributed to their overall reproductive success.     

Chemical properties allow stingless bees to place their eggs upright on liquid larval food

Abstract. Queen-laid eggs of Melipona bees stand upright on their larval food, in part because the upper part of the egg is covered with a water-repellent layer of fatty acids and C₂₁ to C₂₉ hydrocarbons. The lower, wettable portion does not have these materials. Trophic eggs laid by workers are essentially devoid of this coating and tend to sink in the food, when not detected and consumed by the queen. Reproductive workers' eggs, which have about 50% of the water-repellent coating in comparison with the queen's eggs, are usually laid in the cell after oviposition by the queen, and therefore there are two eggs in the cell. Surface tension forces cause the two eggs to float towards each other so they become attached. When alone inside the cell, the reproductive worker egg often floats at an angle to the surface, reflecting the instability of this kind of egg. Attachment to a queen's egg therefore compensates this instability and enhances the reproductive worker egg's chances to develop. Such reproductive worker eggs have about 50% of the water-repellent coating in comparison with the queen's eggs. The surface of an 'undetermined' egg laid by a worker was much closer in composition to that of a queen's egg, from which it is deduced that this was the rarer type of reproductive worker egg, namely those that are laid before queen oviposition has taken place. The layer of hydrophobic material on a queen's egg is about one molecule thick, and probably orientated with the carboxyl groups toward the chorion of the egg and the hydrocarbon chains perpendicular to the surface.     

Reduced realised fecundity in the pine looper Bupalus piniarius caused by host plant defoliation

1. Whether the potential fecundity of herbivorous insects is realised or not may depend on female behaviour, which in turn may be influenced by host plant acceptability. Female Bupalus piniarius were observed to discriminate against needles growing out the year following defoliation (current‐year needles) of its host plant Pinus sylvestris. 2. It was hypothesised that the discriminatory behaviour was due to current‐year needles being less secure as a substrate. Field and laboratory experiments were designed to test this hypothesis and to estimate the discrepancy between potential and realised fecundity when females were offered defoliated branches. 3. In a laboratory oviposition experiment, B. piniarius females were exposed to branches bearing either current‐year needles only or both mature and current‐year needles. Daily oviposition rate, egg batch size, longevity, and mature eggs and fat retained at death were recorded for each female. In field experiments, the rate at which eggs dropped from expanding needles and the capacity of neonate larvae hatching from the dropped eggs to colonise a tree were assessed. 4. Significantly fewer eggs were laid when females were exposed to defoliated branches. 5. Twenty‐six and 16% of the eggs laid on current‐year needles dropped from the needles in 1998 and 1999 respectively, whereas no eggs dropped from mature needles in 1998 and only one egg (< 1%) dropped in 1999. 6. A very small proportion of larvae hatching on the forest floor (simulated egg drop) was able to recolonise host trees. 7. These results emphasise the importance of oviposition behaviour on realised fecundity when analysing insect population dynamics. In the case of B. piniarius, egg placement, although a minor detail during the normal course of events, became of key importance when defoliation deprived females of their preferred egg attachment site.     

Genetic variation in male effects on female reproduction and the genetic covariance between the sexes

Abstract.— Males of many insect species increase the fecundity and/or egg size of their mates through the amount or composition of their nuptial gifts or ejaculate. The genetic bases of such male effects on fecundity or egg size are generally unknown, and thus their ability to evolve remains speculative. Likewise, the genetic relationship between male and female investment into reproduction in dioecious species, which is expected to be positive if effects on fecundity are controlled by at least some of the same genes in males and females, is also unknown. Males of the seed beetle Stator limbatus contribute large ejaculates to females during mating, and the amount of donated ejaculate is positively correlated with male body mass. Females mated to large males lay more eggs in their lifetime than females mated to small males. We describe an experiment in which we quantify genetic variation in the number of eggs sired by males (mated to a single female) and found that a significant proportion of the phenotypic variance in the number of eggs sired by males was explained by their genotype. Additionally, the number of eggs sired by a male was highly positively genetically correlated with his body mass. The between-sex genetic correlation, that is, the genetic correlation between the number of eggs sired by males and the number of eggs laid by females, was highly positive when eggs were laid on Acacia greggii seeds. This indicates that males that sire many eggs have sisters that lay many eggs. Thus, some of the genes that control male ejaculate size (or some other fecundity-enhancing factor) when expressed in males appear to control fecundity when expressed in females. We found no significant interaction between male and female genotype on fecundity.     

The importance of temperature and moisture to the egg-laying behaviour of a pest slug, Deroceras reticulatum

Oviposition behaviour is important when modelling the population dynamics of many invertebrates. The numbers of eggs laid are frequently used to describe fecundity, but this measure may differ significantly from realised fecundity. Oviposition has been shown to be important when describing the dynamics of slug populations, which are important agricultural pests. The numbers of eggs laid by Deroceras reticulatum and their viability were measured across a range of 16 temperature (4, 10, 15 and 23°C) by moisture (33%, 42%, 53% and 58% by dry soil weight) experimental combinations. A fitted quadratic response surface model was used to estimate how D. reticulatum adjusted its egg laying to the surrounding temperature and moisture conditions, with most eggs being laid at a combination of 53% soil moisture and 18°C. The number and proportion of viable eggs also covaried with temperature and moisture, suggesting that D. reticulatum may alter their investment in reproduction to maximise their fitness. We have shown that the number of viable eggs differs from the total number of eggs laid by D. reticulatum . Changes in egg viability with temperature and moisture may also be seen in other species and should be considered when modelling populations of egg-laying invertebrates.     

THE EVOLUTIONARY GENETICS OF AN ADAPTIVE MATERNAL EFFECT: EGG SIZE PLASTICITY IN A SEED BEETLE

In many organisms, a female's environment provides a reliable indicator of the environmental conditions that her progeny will encounter. In such cases, maternal effects may evolve as mechanisms for transgenerational phenotypic plasticity whereby, in response to a predictive environmental cue, a mother can change the type of eggs that she makes or can program a developmental switch in her offspring, which produces offspring prepared for the environmental conditions predicted by the cue. One potentially common mechanism by which females manipulate the phenotype of their progeny is egg size plasticity, in which females vary egg size in response to environmental cues. We describe an experiment in which we quantify genetic variation in egg size and egg size plasticity in a seed beetle, Stator limbatus, and measure the genetic constraints on the evolution of egg size plasticity, quantified as the genetic correlation between the size of eggs laid across host plants. We found that genetic variation is present within populations for the size of eggs laid on seeds of two host plants (Acacia greggii and Cercidium floridum; h² ranged between 0.217 and 0.908), and that the heritability of egg size differed between populations and hosts (higher on A. greggii than on C. floridum). We also found that the evolution of egg size plasticity (the maternal effect) is in part constrained by a high genetic correlation across host plants (r_G > 0.6). However, the cross-environment genetic correlation is less than 1.0, which indicates that the size of eggs laid on these two hosts can diverge in response to natural selection and that egg size plasticity is thus capable of evolving in response to natural selection.     

中华蜜蜂卵表面微观结构及化学成分初步研究

为认识蜜蜂的工蜂监督机制,利用扫描电镜分别观察了中华蜜蜂Apis cerana cerana不同类型卵（蜂王产的受精卵、未受精卵以及工蜂产的未受精卵）的表面超微结构,同时用气 质联用技术测定了各类型卵新产卵（0 h）和5 h卵的表面化学信息素成分。结果表明：中华蜜蜂3种卵表面均覆有六边形的结构,结构内充满小突起,3种卵的大小及表面超微结构无显著差异。受精卵表面化学信息素种类比未受精卵更为丰富,C27∶2和C27∶1可能是卵带有的标记化学信息素。     

INTRACLUTCH DIFFERENCES IN EGG CHARACTERISTICS MITIGATE THE CONSEQUENCES OF AGE‐RELATED HIERARCHIES IN A WILD PASSERINE

The relative age of an individual's siblings is a major cause of fitness variation in many species. In Blue tits (Cyanistes caeruleus), we show that age hierarchies are predominantly caused by incubation preclutch completion, such that last laid eggs hatch later than early laid eggs. However, after statistically controlling for incubation behavior late laid eggs are shown to hatch more quickly than early laid eggs reducing the amount of asynchrony. By experimentally switching early and late laid eggs between nests on the day they were laid, we controlled for the effect of differential incubation and found that the faster hatching times of late laid eggs remains. Chicks that hatched earlier were heavier and had higher probability of fledgling, and chicks that hatched from experimental eggs had patterns of growth and survival consistent with this. Egg mass explained a small part of this variation, but the remainder must be due to egg composition. These results are consistent with the idea that intrinsic differences between eggs across the laying sequence serve to mitigate the effects of age‐related hierarchies. We also show that between‐clutch variation in prenatal developmental rate exists and that it is mainly environmental in origin rather than genetic.