Avian eggshell thickness in relation to egg morphometrics,embryonic development,and mercury contamination

Eggshell thickness is important for physiological, ecological, and ecotoxicological studies on birds; however, empirical eggshell thickness measurements for many species and regions are limited. We measured eggshell thickness at the equator and the egg poles for 12 avian species and related eggshell thickness to egg morphometrics, embryonic development, egg status, and mercury contamination. Within an egg, eggshells were approximately 5.1% thicker at the equator than the sharp pole of the egg, although this difference varied among species (0.6%–9.8%). Within Forster's tern (Sterna forsteri), where eggshell thickness was measured at 5 equally spaced positions along the longitude of the egg, eggshell thickness changed more rapidly near the sharp pole of the egg compared to near the blunt pole of the egg. Within species, eggshell thickness was related to egg width and egg volume for six of the 12 species but was not related to egg length for any species. Among species, mean eggshell thickness was strongly related to species mean egg width, egg length, egg volume, and bird body mass, although species mean body mass was the strongest predictor of species mean eggshell thickness. Using three species (American avocet [Recurvirostra americana], black‐necked stilt [Himantopus mexicanus], and Forster's tern), whose nests were carefully monitored, eggshell thickness (including the eggshell membrane) did not differ among viable, naturally abandoned, dead, or failed‐to‐hatch eggs; was not related to total mercury concentrations of the egg content; and did not decrease with embryonic age. Our study also provides a review of all existing eggshell thickness data for these 12 species.     

Regulation of Trpm activation and calcium wave initiation during Drosophila egg activation

The transition from a developmentally arrested mature oocyte to a developing embryo requires a series of highly conserved events, collectively known as egg activation. All of these events are preceded by a ubiquitous rise of intracellular calcium, which results from influx of external calcium and/or calcium release from internal storage. In Drosophila, this calcium rise initiates from the pole(s) of the oocyte by influx of external calcium in response to mechanical triggers. It is thought to trigger calcium responsive kinases and/or phosphatases, which in turn alter the oocyte phospho‐proteome to initiate downstream events. Recent studies revealed that external calcium enters the activating Drosophila oocyte through Trpm channels, a feature conserved in mouse. The local entry of calcium raises the question of whether Trpm channels are found locally at the poles of the oocyte or are localized around the oocyte periphery, but activated only at the poles. Here, we show that Trpm is distributed all around the oocyte. This requires that it thus be specially regulated at the poles to allow calcium wave initiation. We show that neither egg shape nor local pressure is sufficient to explain this local activation of Trpm channels.     

The cortical contraction related to the ooplasmic segregation inCiona intestinalis eggs

Summary The egg cytoplasm of ascidian,Ciona intestinalis, segregates towards both the animal and vegetal poles within a few minutes of fertilization or parthenogetic activation with ionophore A23187. A constriction appears first on the egg surface near the animal pole and then moves to the vegetal pole. Carmine granules and spermatozoa attached to the egg surface move towards the vegetal pole with the movement of the constriction. Microvilli, which are distributed uniformly in unfertilized egg, disappear on the animal side of the constriction and became more dense on the vegetal side of the constriction. Transmission electron microscopy revealed that sub-cortical cytoplasm, containing numerous mitochondria and sub-cortical granules, moves towards the vegetal pole with the movement of the constriction and then concentrates into a cytoplasmic cap at the vegetal pole. An electron-dense layer appears in the cortex of the cap. The ooplasmic segregation and the cortical contraction were inhibited by cytochalasin B and induced by ionophore A23187. These observations suggest that ooplasmic segregation is caused by the cortical contraction which is characterised by a surface constriction and by the formation of an electron-dense layer.     

Calculating egg volume when shape differs: when are equations appropriate?

ABSTRACT Egg volume is often calculated from length and breadth, assuming little variation in egg shape within species. However, egg shape may vary among females, over time, or within clutches. If this variation is not predictable, volume should be estimated using another method. For example, in some species, egg shape changes consistently with laying order and volume can be estimated using laying‐order specific equations. We measured the length, breadth, volume, and mass of 249 Magellanic Penguin (Spheniscus magellanicus) eggs and regressed volume on length and breadth for first and second eggs separately. Differences between measured and calculated volume averaged <1% for both eggs. Using linear measurements, we calculated egg volume for 7085 clutches from 1983 to 2006. First and second eggs had similar calculated volumes (P > 0.05) in 19 of 24 yr; when they differed, the second egg was larger. In contrast, using single equations typically employed to compute egg volume, we erroneously concluded that first eggs were usually (20 of 24 yr) significantly larger than second eggs. Our regression equations should be applicable to other Spheniscus penguins because ratios of elongation coefficients (length divided by breadth) of first and second eggs are similar among these species. In other species of birds where egg shape changes with laying order, the volume of a sample of eggs should be measured to develop regression equations specific to the species and laying order. Slight variation in egg volume can have important evolutionary and ecological implications that would be erroneously interpreted without field tests to measure volume.     

Protective function of maternal care against egg predators in the shield bug Sastragala esakii (Hemiptera: Acanthosomatidae)

Females of many acanthosomatid shield bugs attend eggs and young nymphs by covering them with their bodies. Although such form of maternal care has been suggested to have evolved independently in four genera, Elasmucha, Sastragala, Acanthosoma and Sinopla, previous studies exploring its adaptive function have solely focused on species of Elasmucha. This study pioneered an experimental examination of maternal care in the Japanese species Sastragala esakii. Field experiments demonstrated that unattended egg masses suffered intense predation, whereas egg masses attended by their mothers were rarely preyed upon. The ant Crematogaster sp. was the most common egg predator, while two other insect species were also observed to prey on eggs. The exclusion of ant workers and other walking predators from accessing egg masses through the utilization of a sticky trap resulted in a remarkably improved egg survival rate in orphaned egg masses, suggesting that, at least in our study site, maternal care of S. esakii primarily functions to protect eggs from walking predators. Laboratory observations revealed that egg protection against predators was achieved through at least two distinctive defensive behaviors shown by egg-tending females: (i) tilting their bodies when approached by predators; and (ii) fanning their wings when in contact with predators. However, females displayed a limited response to predators approaching from the posterior direction, suggesting that visual cues play a significant role in predator recognition. These results indicate a similarity in the maternal care functions between Elasmucha and Sastragala, and suggest the parallel evolution of female defensive behaviors.     

Developmental asynchrony caused by steep temperature gradients does not impair pattern formation in the wasp,Pimpla turionellae L.

Generating developmental gradients by temperature gradients established within a developing organism is an easy, non-invasive technique to study physiological interdependencies between locally separated subsystems. A linear temperature gradient of about 10° C/mm was maintained up to 5 h in either direction along the long axis of a long-germ-type hymenopteran egg, which was simultaneously filmed by the 16 mm timelapse technique. The result was a dramatic desynchronization of development, which between the egg poles could reach up to 9.3 h relative to normal development. Within the same egg, up to seven mitotic waves (i.e. eight different nuclear generations) were observed at the same time, and the subsequent cellularization process was extremely asynchronous. The initial regions of the mitotic waves, the fountain flow of the ooplasm, and the gastrulation process were shifted towards the egg pole kept at higher temperatures. Developmental processes occurring successively in normal development now took place simultaneously, with either direction of the temperature gradient. For instance, while gastrulation had started in the warm region, midblastula transition and cellularization were in progress in the middle of the egg, and intravitelline nuclear multiplication occurred at the cold pole, by rapid and still biphasic cell cycles. In some respects, development resembled that of a short-germ-type insect egg. Nevertheless, the developmental processes were resynchronized after the temperature gradient was switched off. Surprisingly, the extreme desynchronization during early development did not affect the segment pattern of the resulting embryos. The technique of inducing well-defined developmental asynchronies might be applied in Drosophila to analyse the subtle interplay between maternal and zygotic gene activities described in this species.     

Egg size and composition in an ageing capital breeder – consequences for offspring performance

1. Egg size is often used as a proxy of egg quality although size and composition may vary, e.g. in insects egg size usually decreases as female ages. Whether this decrease in size reflects reduced concentrations of essential nutrients such as lipids and proteins of eggs laid by ageing females, or does reduced size per se explain often observed lower fitness of later laid eggs is poorly explored. 2. Egg properties were compared with fitness parameters of offspring laid on the first and fourth night during the oviposition period of a capital breeding moth, Cleorodes lichenaria (Hufnagel). The study aim was to explore whether decreased egg size is caused by decreased provisioning into later laid eggs measured as egg protein and lipid concentration, and whether it results in lower fitness of later laid offspring. 3. The fresh and dry weight of eggs decreased over the oviposition period, but the protein and lipid concentration remained constant. Survival of larvae was lower among the fourth night laid offspring on a low quality host Parmelia sulcata Taylor compared to a high quality host Ramalina fraxinea (L.) Ach. No differences were observed in egg fertility or hatchability, neonate survival without food and pupal mass between the offspring produced on different nights. 4. Decreased survival of offspring produced later was rather attributable to absolute provisioning (i.e. lower weight of eggs) than relative provisioning (i.e. decreased concentrations of nutrients in eggs). It is argued that lower survival of later laid smaller eggs on low quality diet is likely attributable to physical and chemical characteristics of host lichens and/or physical properties of tiny neonate larvae.     

Blunt egg pole holds cues for alien egg discrimination: experimental evidence

Eggshell colour patterns play a crucial role in avian host–parasite coevolution. In contrast to many experiments investigating general host egg discrimination abilities, studies testing where specific recognition cues are located on the eggshells (on blunt, sharp or both egg poles) are lacking. Previous studies suggested that discrimination cues might be located at the blunt egg pole, where the shell patterning is typically concentrated. We tested this hypothesis experimentally in species subject to interspecific (great reed warblers Acrocephalus arundinaceus, reed warblers A. scirpaceus), and also intraspecific parasitism (song thrushes Turdus philomelos, blackbirds T. merula). We examined host responses towards two types of intraspecific eggs painted non‐mimetic immaculate blue either at blunt or sharp poles. All four species rejected eggs manipulated at the blunt pole at significantly higher rates, indicating that they perceive the critical recognition cues in the same egg part. Thus, the presence of egg recognition cues at the blunt egg pole may be a general phenomenon in birds parasitized by both intraspecific and interspecific parasites.     

Counterstrategy to Egg Dumping in a Coreid Bug: Recipient Individuals Discard Eggs from Their Backs

The golden egg bug, Phyllomorpha laciniata Vill. (Heteroptera: Coreidae), is the only terrestrial insect in which females oviposit on the backs of female and male conspecifics. Eggs do not survive unless carried by a bug. Herein, I report laboratory observations that egg-carrying individuals actively brush their backs against the host plant seemingly in an effort to rub off eggs. Egg scraping is more common among individuals carrying many eggs than among those carrying only a few eggs. The most recently received eggs were rubbed off first. Females did not avoid laying eggs on the backs of egg-loaded individuals, nor did bugs carrying several eggs resist oviposition attempts more often than unloaded ones. Some males were likely to have fertilized the eggs they scraped off their backs. Laboratory results of active egg removal correspond with egg loss in the field, suggesting that egg scraping may explain egg loss in nature. The data indicate a cost of egg carrying to an individual and an evolutionary arms race between oviposition and discarding behavior.     

Evidence of selection for egg crypsis in conspicuous nests

ABSTRACT The value of egg coloration as crypsis, once accepted as a general principle, has recently been questioned because most experiments have failed to show that egg coloration deters predation. The nest‐crypsis hypothesis postulates that, among species that build conspicuous nests, selection for egg crypsis is relaxed or absent because visually searching predators detect nests prior to eggs. I tested the nest‐crypsis hypothesis using the large, relatively conspicuous nests of American Robins (Turdus migratorius), and eggs that differed markedly in color that were collected from the nests of Red‐winged Blackbirds (Agelaius phoeniceus), Brewer's Blackbirds (Euphagus cyanocephalus), and Yellow‐headed Blackbirds (Xanthocephalus xanthocephalus). Each nest (N= 22) received a clutch of each species during three sequential predation trials that were 16 d in duration. The order of clutch presentation was randomized for each nest. Survival trends for Brewer's and Yellow‐headed Blackbirds were similar, and higher than those for clutches of Red‐winged Blackbirds. By the end of trials, overall survival of the three clutch types was roughly equivalent. However, clutches of Red‐winged Blackbird eggs, the most conspicuous egg type to the human eye, were discovered sooner by predators. Because the experimental design controlled for effects of nest crypsis, nest location, and nest size, this difference in egg survival can be attributed to differences in egg pigmentation. Thus, my results support a role for egg coloration as camouflage in conspicuous nests.     

Effect of host diet and adult parasitoid diet on egg load dynamics and egg size of braconid parasitoids attacking Anastrepha ludens

The quantity and quality of host nutrients can affect fitness‐related traits in hymenopteran parasitoids, including oogenesis. The present study tested the prediction that a high host quality will influence oogenesis‐related traits positively in synovigenic parasitoids, and that a high‐quality adult parasitoid diet can positively affect the same parameters, potentially compensating for development on low‐quality hosts. Four braconid parasitoid species with contrasting life histories are reared on a low‐quality diet [Anastrepha ludens Loew (Diptera: Tephritidae) larvae reared on mango] or a high‐quality (artificial) diet. Adult parasitoids are provided with a high‐quality (honey ad libitum), moderate‐quality (honey every other day) or low‐quality (guava pulp) diet. Generalist species that encounter high variation in host quality naturally are predicted to be more flexible in dealing with nutrient shortfalls than specialist species. By contrast to the predictions, low‐quality hosts yield parasitoids with higher egg loads in two species: Opius hirtus Fisher and Diachasmimorpha longicaudata Ashmead. However, as predicted, a high‐quality adult diet exerts a positive effect on egg load (Utetes anastrephae Viereck), egg size (Doryctobracon crawfordi Viereck) and egg maturation rate (D. longicaudata, O. hirtus and U. anastrephae). The generalist D. longicaudata varies in egg load and maturation rate depending on host quality and adult diet, respectively. Evidence of the combined effect of both factors on parasitoid fertility is presented for the specialist O. hirtus. The theoretical and practical implications of these findings are discussed.     

Effect of host deprivation on egg quality,egg load,and oviposition in a solitary parasitoid,Chetogena edwardsii (Diptera: Tachinidae)

Solitary parasitoids are limited to laying one egg per host because larvae compete within hosts. If host encounter rate is low, females should not increase the number of eggs/host in response. The tachinid fly, Chetogena edwardsii,was used to evaluate the effect of host deprivation on egg accumulation, oviposition behavior, and egg quality in a solitary parasitoid. Females deprived of hosts for 2– 7 days accumulate about 1 day's supply of eggs. Egg output of deprived females once hosts are restored does not differ from that of control females. Deprived females retain one egg in the uterus where it undergoes embryogenesis. Maggots emerging from retained eggs are more likely to survive in hosts molting in 40 h or less after receipt of an egg than are maggots emerging from eggs fertilized shortly before oviposition. Egg retention is a consequence of host deprivation that permits females to broaden the range of hosts they can exploit to include soon-to-molt hosts and possibly multiply parasitized hosts.     

Geographic variation in offspring size of a widespread lizard (Takydromus septentrionalis): importance of maternal investment

Geographic variation in offspring size is widespread, but the proximate causes of this variation have not yet been explicitly determined. We compared egg size and egg contents among five populations of a lizard (Takydromus septentrionalis, Günther, 1864) along a latitudinal gradient, and incubated eggs at two temperatures to determine the influence of maternal investment and incubation temperature on offspring size. The mean values for female size and egg size were both greater in the two northern populations (Chuzhou and Anji) than in the three southern populations (Lishui, Dongtou, and Ningde). The larger eggs were entirely attributable to the body size of females in the Anji population, but their increased size also stemmed from further enlargement of egg size relative to female body size in Chuzhou, the northernmost population sampled in this study. Eggs of the Chuzhou population contained more yolk and less water than those of southern populations. Despite the lower lipid content in the yolk, eggs from the Chuzhou population had higher energy contents than those from the two southern populations, owing to the larger egg size and increased volume of yolk. Hatchling size was not affected by incubation temperature, but differed significantly among populations, with hatchlings being larger in the Chuzhou population than in the other populations. Our data provide an inference that oviparous reptiles from cold climates may produce larger offspring, not only by increasing egg size but also by investing more energy into their eggs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 59–67.     

Avian egg collections: museum collection bias driven by shape and size

Avian eggs exhibit substantial intra- and interspecific variation in shape, size and colour. Considerable efforts have been made to better understand the evolutionary drivers behind such variation, often using museum egg collections. Usually it is assumed that museum collections accurately represent the variation seen in natural populations, but this may not be the case if there is collection bias. Collection bias may lead to the over-representation of certain egg traits in collections, due to the aesthetic (or other) preferences of collectors. The aim of this study is to begin to look for the occurrence of potential collection bias in museum egg collections by comparing three shape indices (pointedness/asymmetry, elongation and polar asymmetry) and egg volume between subsets of eggs in museum collections with those of recently sampled eggs in the field for three different bird species: common guillemot Uria aalge, razorbill Alca torda and northern fulmar Fulmarus glacialis. We found no evidence of collection bias in our sampled razorbill and northern fulmar museum collection eggs, but some evidence for a bias in sampled museum collection eggs of common guillemots. Since the guillemot's egg differs from most bird eggs in being pyriform, we suggest that collection bias by historic egg collectors may be more prevalent in species with extreme egg traits. Researchers using museum egg collections to examine questions relating to egg shape should be aware of collection bias risks and consider how to minimise the effect of these possible biases on accumulated datasets.     

Egg size,fertility, hatchability,and chick survivability in captive California condors (Gymnogyps californianus)

California condors are one of the most endangered species native to the mainland United States and are subject of intense effort regarding captive breeding and reintroduction. We analyzed 20 years of California condor egg records from the wild and from three captive propagation facilities for fertility, hatchability, and chick survivability, along with changes in egg size due to multiple clutching. Overall annual mean percent of fertile eggs was 80.2%, hatchability was 87.3%, and chick survivability to ≥60 days was 95.5%. One egg-laying site had a significantly lower fertility rate (P ≤ 0.0001) than the other sites, which was probably due to pair incompatibility rather than any physiological factors. Egg volume of the first egg was significantly greater than both the second (t=6.73, P=0.0001) and third egg (t=6.62, P ≤ 0.0001) of the season, while the second egg had a significantly greater volume (t=3.20, P=0.0084) than the third egg. Chicks from the second egg (t=3.24, P=0.029) and third egg (t=7.94, P=0.0014) of the season were significantly smaller than chicks from the first egg of the season. The decrease in egg measures and chick hatch weight due to multiple clutching did not affect hatchability or chick survivability. There were significant positive relationships (P<0.0001) between fresh egg weight and chick hatch weight and between egg volume and chick hatch weight, as well as between fresh egg weight and egg volume. In spite of the decrease in fresh egg weight, egg volume and chick hatch weights, due to egg removal to stimulate double and sometimes triple clutching, the captive propagation program has been successful in producing birds for the restoration of this species. Zoo Biol 23:489–500, 2004. © 2004 Wiley-Liss, Inc.     

Semiochemical and physical stimuli involved in host recognition by Telenomus podisi (Hymenoptera: Scelionidae) toward Euschistus heros (Heteroptera: Pentatomidae)

The egg parasitoid, Telenomus podisi, was shown to recognize its host, Euschistus heros, through both chemical and physical cues. These were determined in short-range bioassays. The cues comprised fertile and infertile host eggs, egg extracts, crude extracts of adult males and females and successive dilutions of the synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a male-produced pheromone of E. heros. Some of the treatments used induced a selection process in T. podisi, through host recognition behaviour, indicating a consistent response of this species to E. heros. The possibility that some of these compounds could be exploited as long-range kairomones, by T. podisi, is discussed. Using GC analysis, an unidentified compound (Rt 24.8 min), possibly from the egg adhesive material, was detected from E. heros egg extracts. Its retention time compared to the methyl 2,6,10-trimethyltridecanoate showed a lower volatility, suggesting that the egg adhesive may act as a short-range kairomone. Physical cues appeared to be an important component in the host selection process by T. podisi. The parasitoid discriminated infertile eggs which are differently shaped and smaller than fertile eggs.     

Ooplasmic segregation in theTubifex egg: Mode of pole plasm accumulation and possible involvement of microfilaments

Summary Ooplasmic segregation, i.e. the accumulation of pole plasm in theTubifex egg, consists of two steps: (1) Cytoplasm devoid of yolk granules and lipid droplets migrates toward the egg periphery and forms a continuous subcortical layer around the whole egg; (2) the subcortical cytoplasm moves along the surface toward the animal pole in the animal hemisphere and toward the vegetal pole in the vegetal hemisphere, and finally accumulates at both poles of the egg to form the animal and vegetal pole plasms. Whereas the subcortical layer increases in volume during the first step, it decreases during the second step. This is ascribed to the compact rearrangement in the subcortical layer of membraneous organelles such as endoplasmic reticulum and mitochondria. The number of membraneous organelles associated with the cortical layer increases during the second step. Electron microscopy reveals the presence of microfilaments not only in the cortical layer but also in the subcortical layer. Subcortical microfilaments link membraneous organelles to form networks; some are associated with bundles of cortical microfilaments. The thickness of the cortical layer differs regionally. The pattern of this difference does not change during the second step. On the other hand, the subcortical cytoplasm moves ahead of the stationary cortical layer. The accumulation of pole plasm is blocked by cytochalasin B but not by colchicine. The first step of this process is less sensitive to cytochalasin B than the second step, suggesting that these two steps are controlled by differnt mechanisms. The mechanical aspects of ooplasmic segregation in theTubifex egg are discussed in the light of the present observations.     

Drosophila centrosomes are unable to trigger parthenogenetic development of Xenopus eggs

Centrosomes are powerful and exclusive parthenogenetic agents in the Xenopus egg. We have previously shown that heterologous centrosomes from various vertebrate species were able to promote egg cleavage in Xenopus and that human centrosome activity was associated with an insoluble proteinacious structure that is not significantly simpler than the native centrosome. In this work, we have investigated the parthenogenetic capacity of more evolutionary distant centrosomes. We show that centrosomes devoid of centrioles, such as SPBs isolated from Saccharomyces cerevisiae, do not form asters of microtubules in cytoplasmic extracts from Xenopus eggs, and are inactive in the parthenogenetic test. We further show that Drosophila centrosomes which possess a typical centriole architecture, and are quite active to nucleate microtubules in Xenopus cytoplasmic extracts, are unable to trigger egg cleavage. This was observed both with centrosomes isolated from Drosophila syncytial embryos and nucleus-centrosome complexes from the Drosophila Kc23 cell line. We demonstrate that this inability could not be restored after pre-incubation of Drosophila centrosomes in the egg cytoplasm before injection. We conclude that the parthenogenetic activity of a centrosome is not directly linked to its capacity to nucleate microtubules from the egg tubulin, and that the evolutionary conserved nine-fold symmetrical structure of the centriole cannot be considered as sufficient for triggering procentriole assembly.     

Effects of Enterococcus faecalis on egg production,egg quality and caecal microbiota of hens during the late laying period

This study was conducted to determine the effects of diet supplementation of laying hens with Enterococcus faecalis (EF) on egg production, egg quality and caecal microbiota. A total of 360 Hy-Line Brown laying hens (72 weeks old) were divided into three groups with four replicates of 30 birds each. The laying hens were fed with the basal diet (Control), the basal diet + 3.75 · 10⁸ cfu EF/kg (Group I) or the basal diet + 7.5 · 10⁸ cfu EF/kg (Group II). The experiment lasted for 45 d. Eggs and caecal samples were collected at the end of the experiment. Results showed that dietary supplementation with EF did not affect the average daily egg weight, cracked egg rate, mortality and egg quality. However, EF supplementation caused a significantly increased laying rate and decreased feed/egg ratio (p < 0.05). The differences in caecal microbiota between Group II and the Control were significant. The relative abundance of Verrucomicrobia and Cyanobacteria at the phylum level, Rikenellaceae, Christensenellaceae and Veillonellaceae at the family level, and the Faecalibacterium, Christensenellaceae R-7 group and Eubacterium coprostanoligenes group at the genus level changed significantly in Group II compared with the Control (p < 0.05). In conclusion, the tested dietary supplementations with EF improved product performance and affected the caecal microbial community structure of laying hens during the late laying period.     

Do Egg Carrying and Protracted Copulation Affect Mobility in the Golden Egg Bug?

Golden egg bug Phyllomorpha laciniata (Heteroptera, Coreidae) females oviposit on male and female conspecifics that carry ova until they hatch. Embryos benefit from being carried because of diminished risks of predation. Female carriers are never the parents of carried eggs, and males are only rarely the fathers of any carried eggs. Eggs develop and hatch without being carried in the laboratory. Egg carriers may be viewed as victims, exploited by females that encumber them with eggs. The intensity of selection favouring resistance to egg carrying should be proportional to the costs of this behaviour. One possible cost could be a reduction in mobility caused by carried eggs. We compare movement rates among encumbered and unencumbered golden egg bugs of both sexes. Protracted copulations (often exceeding 20 h) typical of this species and mating may also cause reduction in bugs mobility. Therefore, we also evaluate rates of movement of coupled pairs of bugs. Our results indicate that egg loads do not affect the mobility and speed of either males or females. However, copulating pairs are significantly slowed as compared to single bugs. Thus protracted copulations have a clear cost in rates of movement and possibly risks of predation, but there are no apparent mobility costs for egg carrying.