Egg Dumping Research Articles

Alternative mating strategies in Eurasian Reed Warblers: extra-pair paternity and egg dumping

Alternative mating strategies, involving mating outside a social pair bond, have been studied intensively during the last few decades. However, we are still far from understanding what factors affect their frequencies in wild bird populations. In 2006–2011 we studied Eurasian Reed Warblers breeding in the nature reserve “Stawy Milickie” in SW Poland, and analysed the frequency of extra-pair paternity (EPP) and intra-specific brood parasitism (IBP). We genotyped a total of 786 nestlings from 259 nests. EPP offspring constituted 13.40% of all young (from 7.63% to 22.82% in different study years), and they were found in 21.62% of the broods (from 14.6% to 32.7% annually). The mean proportion of females with EPP young was 24.2% (from 16.2 to 41.7% annually). The proportion of EPP young in nests containing any EPP offspring ranged from 25% to 100% (on average 60%) and was not related to brood size. EPP young in one nest were sired usually by one or two males (92% of all cases), but we recorded one brood with three EPP fathers and one brood of four, where each young was sired by a different EPP male, and none by a social male. We found only one case of intra-specific brood parasitism (IBP). The brood with IBP constituted 0.39% of all examined broods, while the nestling that hatched from the dumped egg constituted 0.13% of all young whose parents were genotyped. We conclude that extra-pair paternity is a relatively common and regularly occurring alternative mating strategy in our study population of Reed Warblers, while intra-specific brood parasitism is extremely rare.

Extra-pair paternity in a species with frequent extra-pair courtship feedings, few extra-pair copulations, and male-biased parental care

Patterns of extra pair paternity (EPP) and intraspecific brood parasitism (IBP) were studied in a Whiskered Tern Chlidonias hybrida population characterized by female brood desertion, a high level of extra pair courtship feedings (10%) and a low level of extra pair copulation (EPC; 0.6%). In this study, we used a set of microsatellite loci to analyse parentage in 56 Whiskered Tern families from southern Poland. Depending on the method, we detected that 1.4%–3.6% of chicks were sired by an extra-pair male, and extra-pair chicks were present in 3.6%–8.9% of broods. IBP was observed in 8.9%–14.3% of broods, corresponding to 3.6%–6.4% of the chicks. The low rate of EPP is in agreement with the hypothesis that in species with high male parental investment, females should avoid EPC. The low level of IBP indicates that intraspecific egg dumping is not a common female strategy in Whiskered Tern, similar to many other colonial waterbird species.

Fitness costs of female choosiness are low in a socially monogamous songbird.

Female mate choice is thought to be responsible for the evolution of many extravagant male ornaments and displays, but the costs of being too selective may hinder the evolution of choosiness. Selection against choosiness may be particularly strong in socially monogamous mating systems, because females may end up without a partner and forego reproduction, especially when many females prefer the same few partners (frequency-dependent selection). Here, we quantify the fitness costs of having mating preferences that are difficult to satisfy, by manipulating the availability of preferred males. We capitalize on the recent discovery that female zebra finches (Taeniopygia guttata) prefer males of familiar song dialect. We measured female fitness in captive breeding colonies in which one-third of females were given ample opportunity to choose a mate of their preferred dialect (two-thirds of all males; "relaxed competition"), while two-thirds of the females had to compete over a limited pool of mates they preferred (one-third of all males; "high competition"). As expected, social pairings were strongly assortative with regard to song dialect. In the high-competition group, 26% of the females remained unpaired, yet they still obtained relatively high fitness by using brood parasitism as an alternative reproductive tactic. Another 31% of high-competition females paired disassortatively for song dialect. These females showed increased levels of extra-pair paternity, mostly with same-dialect males as sires, suggesting that preferences were not abolished after social pairing. However, females that paired disassortatively for song dialect did not have lower reproductive success. Overall, females in the high-competition group reached equal fitness to those that experienced relaxed competition. Our study suggests that alternative reproductive tactics such as egg dumping can help overcome the frequency-dependent costs of being selective in a monogamous mating system, thereby facilitating the evolution of female choosiness.

Cases of occasional interspecific brood parasitism and egg dumping in Hungary

Abstract There are numerous publications in the ornithological literature on mixed-species broods, i.e. on cases when a species lays some or all of its eggs into the nests of other species. This phenomenon, known as brood parasitism, has not yet been studied in Hungary. Here, I use the term brood parasitism, but I could not separate cases of egg dumping, a reproductive error by females. Based on literature and my own observations, I found evidence for interspecific brood parasitism in 28 species breeding in Hungary, not including the cases of the obligate interspecific brood parasite, the Common Cuckoo (Cuculus canorus). Only one of these belongs to passerines, while in the rest of the cases, this phenomenon occurred in representatives of non-passerine families. However, cases of brood parasitism and nest parasitism have to be treated separately. The latter refers to cases when a species occupies a nest, usually a nesthole or nestbox, already containing eggs of another species, and lays its own eggs next to the foreign eggs. The present study provides data on European Roller (Coracias garrulus), Northern Goshawk (Accipiter gentilis), Common Kestrel (Falco tinnunculus), Red-footed Falcon (Falco vespertinus), Eurasian Hobby (Falco subbuteo), tit species (Parus, Cyanistes, Poecile spp.), Eurasian Nuthatch (Sitta europaea) and Eurasian Tree Sparrow (Passer montanus), but in all likelihood the number of species involved is much higher.

Age of Both Parents Influences Reproduction and Egg Dumping Behavior in Drosophila melanogaster.

Trans-generational maternal effects have been shown to influence a broad range of offspring phenotypes. However, very little is known about paternal trans-generational effects. Here, we tested the trans-generational effects of maternal and paternal age, and their interaction, on daughter and son reproductive fitness in Drosophila melanogaster. We found significant effects of parent ages on offspring reproductive fitness during a 10 day postfertilization period. In daughters, older (45 days old) mothers conferred lower reproductive fitness compared with younger mothers (3 days old). In sons, father’s age significantly affected reproductive fitness. The effects of 2 old parents were additive in both sexes and reproductive fitness was lowest when the focal individual had 2 old parents. Interestingly, daughter fertility was sensitive to father’s age but son fertility was insensitive to mother’s age, suggesting a sexual asymmetry in trans-generational effects. We found the egg-laying dynamics in daughters dramatically shaped this relationship. Daughters with 2 old parents demonstrated an extreme egg dumping behavior on day 1 and laid >2.35× the number of eggs than the other 3 age class treatments. Our study reveals significant trans-generational maternal and paternal age effects on fertility and an association with a novel egg laying behavioral phenotype in Drosophila.

Diversity of social-genetic relationships in the socially monogamous pied flycatcher (Ficedula hypoleuca) breeding in Western Siberia.

We explored the genetic background of social interactions in two breeding metapopulations of the pied flycatcher (Ficedula hypoleuca) in Western Siberia. In 2005, we sampled blood from birds breeding in study areas located in the city of Tomsk and in a natural forest 13 km southward of Tomsk (Western Siberia, Russia). We sampled 30 males, 46 females, 268 nestlings (46 nests) in the urban settlement of pied flycatcher, and 232 males, 250 females, 1,485 nestlings (250 nests) in the woodland plot. DNA fingerprinting was carried out using eight microsatellite loci, which were amplified by two multiplex-PCRs and analyzed by capillary electrophoresis. About 50–58% of all couples were socially and genetically monogamous in both study plots. However, almost all possible social and genetic interactions were detected for non-monogamous couples: polygamy, polyandry, helping, adoption, and egg dumping. Differences in the rate of polygyny and the rate of extra-pair paternity between both study sites could be explained by differences in environmental heterogeneity and breeding density. Our findings suggest that egg dumping, adoption, polygamy, extra pair copulation, and other types of social-genetic interactions are modifications of the monogamous social system caused by patchy environment, breeding density, and birds’ breeding status.

Floating bird nests provide resources for wildlife: ecological roles of vertebrates using Aechmophorus grebe nests at Clear Lake, California

Floating bird nests occur ephemerally in many wetlands, providing resources for wildlife, but the species using such nests and their ecological roles are poorly studied. Grebes (Podicipedidae) construct floating nests anchored to vegetation. During 2010–2017 we studied the vertebrates using nests of the colonially-nesting western grebe (Aechmophorus occidentalis) and Clark’s grebe (A. clarkii) at Clear Lake, California. In addition to both grebe species using each other’s nests for copulation and egg dumping, we identified 47 other species of vertebrates using Aechmophorus grebe nests, including one fish, one amphibian, two turtles, one snake, 39 birds, and three mammals. Ecological roles of vertebrates using grebe nests included: egg dumping (one bird); predation on grebe eggs, chicks, or adults (four birds and three mammals); scavenging on broken grebe eggs (five birds); resting (one amphibian, three reptiles, and 15 birds); foraging for non-avian prey on nests (13 birds) or in adjacent water (five birds); and incidental destruction of grebe eggs (one fish and two reptiles) and nests (many species). Floating grebe nests undergo a process of ecological succession. Egg dumping, predation, and scavenging occur during early stages of nest development and maintenance. Once abandoned, older nests are used for resting or foraging for prey in nearby water. Decomposing nests are colonized by arthropods which are preyed upon by birds. Because floating bird nests increase food web complexity by attracting aquatic, semiaquatic, and terrestrial organisms at all trophic levels, protecting the engineers and their nests should be considered a conservation priority by wetland managers.

Impact of sexually antagonistic genital morphologies on female reproduction and wild population demography.

Sexual conflict is a strong driver of evolution. The evolutionary outcomes of sexual conflict can, in turn, influence ecological processes within populations, for example, demography. However, evidence for the latter hypothesis is scarce, especially in the wild. Here, we show that sexual conflict is associated with demographic processes determining population size in the ground beetle Carabus insulicola with elaborate male and female genitalia based on individual- and population-level analyses. We found that sexually antagonistic selection can operate on the genitalia: longer male genitalia can be beneficial in sperm competition but decrease female reproductive success with increased egg dumping, whereas longer female genitalia are resistant to this male harassment via decreased egg dumping and increased fertilization rate. As expected from sexually antagonistic coevolution due to sexual conflict, we detected coevolutionary divergence between male and female genital sizes among populations. In parallel with decrease in female reproductive success, more harmful males with longer genitalia and less resistant females with shorter genitalia were related to small effective population sizes. Thus, sexual conflict may promote coevolutionary diversification between sexual traits, and this was associated with a demographic process. Our findings provide an insight into sex-driven eco-evolutionary dynamics in the wild.

An Interspecific Mixed Clutch of Semipalmated Sandpiper and Lapland Longspur Eggs

Abstract. Semipalmated Sandpipers (Calidris pusilla) and Lapland Longspurs (Calcarius lapponicus) share similar nesting habitat preferences on small islands in the Mackenzie River Delta, Northwest Territories, Canada. A Semipalmated Sandpiper was observed incubating a mixed clutch of its own eggs with two smaller eggs presumed to be from a Lapland Longspur. This is a unique combination of a precocial and an altricial species' eggs in the same nest. Possible explanations for the occurrence of this interspecific mixed clutch include nest parasitism, accidental laying, opportunistic egg dumping, or nest usurpation.

Behavioral and physiological responses of the bean weevil Zabrotes subfasciatus to intraspecific competition

Zabrotes subfasciatus uses Phaseolus vulgaris seeds as its main host and reacts to variations in the availability of seeds by adjusting egg size and number. When faced to choose among different hosts, however, this insect shows the following preference hierarchy: bean > soy > lentil > chickpea, meaning that it is quite able to use species initially rejected as hosts for oviposition. Here, we investigated how this insect would react when placed in environments with different insect densities and allowed to choose between two types of seeds with contrasting levels of acceptability as substrates for oviposition. The experimental setting compared four levels of resource competition (density) by placing 1, 2, 4, or 6 couples within a Petri dish with 2 grains of P. vulgaris and 2 grains of Cicer arietinum. During the 7-day oviposition period, the following four behaviors were identified and quantified: fleeing, mating, inspecting P. vulgaris, and inspecting C. arietinum. We correlated these behaviors with fecundity. The most common behavior revealed by correspondence analyses plots was fleeing (searching for a new resource), followed by inspecting and mating (p < 0.001). Increasing competition diminished the inspecting behavior (of both hosts), reduced oviposition on P. vulgaris (the preferred host) and increased oviposition on C. arietinum (the less-preferred host), promoted fleeing and augmented the number of eggs glued to Petri dishes (egg dumping, p < 0.0001). Mating occurred mainly in situations of intermediate density. We previously demonstrated the existence of a preference hierarchy for different hosts and showed that artificial selection increases the oviposition preference for the less-preferred host. Here, we found that fleeing and egg dumping are the main strategies for avoiding competition and that these behaviors may support niche broadening in Z. subfasciatus.

Parent-environmental interactions shape acoustic signatures in tree swallows: a cross-fostering experiment

Acoustic signatures are common components of avian vocalizations and are important for the recognition of individuals and groups. The proximate mechanisms by which these signatures develop are poorly understood, however. The development of acoustic signatures in nestling birds is of particular interest, because high rates of extra-pair paternity or egg dumping can cause nestlings to be unrelated to at least one of the adults that are caring for them. In such cases, nestlings might conceal their genetic origins, by developing acoustic signatures through environmental rather than genetic mechanisms. In a cross-fostering experiment with tree swallows Tachycineta bicolor, we investigated whether brood signatures of nestlings that were about to fledge were attributable to their genetic/maternal origins or to their rearing environment. We found that the calls of cross-fostered nestlings did not vary based on their genetic/maternal origin, but did show some variation based on their rearing environment. Control nestlings that were not swapped, however, showed stronger brood signatures than either experimental group, suggesting that acoustic signatures develop through an interaction between rearing environment and genetic/maternal effects.

Supernormal clutches in southern African Kelp Gulls Larus dominicanus vetula

The Kelp Gull Larus dominicanus typically lays clutches of 1–3 eggs, but larger clutches have been recorded occasionally. We report that four- and five-egg clutches comprise 0.3% of clutches among the southern African subspecies L. d. vetula, with a higher incidence in edges of the species’ breeding range (southern Namibia and the south-eastern Cape) than in the south-western Cape. Supernormal clutches tend to be clustered in specific years and are associated with low hatching success in some but not all cases. Further observations are needed to assess whether such clutches result from female–female pairs, egg dumping, or unusually large clutches laid by a single female.

Worker drift and egg dumping by queens in wild Bombus terrestris colonies

Wild bumblebee colonies are hard to find and often inaccessible, so there have been few studies of the genetic structure of bumblebees within natural colonies, and hence, it is not clear how frequently events such as worker reproduction, worker drift and queen usurpation take place. This study aimed to quantify the occurrence of natal-worker reproduction, worker drift and drifter reproduction within 14 wild colonies of Bombus terrestris in Central Scotland. Four unlinked microsatellites were used to identify patterns of relatedness of the colonies’ adults and broods. In colonies with queens (queenright colonies), worker reproduction accounted for just 0.83 % of males, increasing to 12.11 % in queenless colonies. Four colonies contained a total of six workers which were not daughters of the queen, and were assumed to be drifters, and four male offspring of drifters. Drifting is clearly not common and results in few drifter offspring overall, although drifters produced approximately seven times more offspring per capita than workers that remained in their natal colony. Unexpectedly, two colonies contained clusters of sister workers and juvenile offspring that were not sisters to the rest of the adults or brood found in the colonies, demonstrating probable egg dumping by queens. A third colony contained a queen which was not a sister or daughter to the other bees in the colony. Although usurping of bumblebee colonies by queens in early season is well documented, this appears to be the first record of egg dumping, and it remains unclear whether it is being carried out by old queens or newly mated young queens.

Coping with an unpredictable and stressful environment: The life history and metabolic response to variable food and host availability in a polyphagous tephritid fly

The way energy resources are used under variable environmental conditions lies at the heart of our understanding of resource management and opportunism in many organisms. Here we sought to determine how a time-limited, synovigenic and polyphagous insect with a high reproductive-potential ( Anastrepha ludens), copes behaviourally and metabolically with environmental unpredictability represented by constant and variable regimes of host availability and variation in food quality. We hypothesized that an adaptive response to a windfall of nutritious food would be the rapid accumulation of energy metabolites (whole body lipids, glycogen and proteins) in the female. We also studied patterns of oogenesis as an indicator of egg-reabsorption under stressful environmental conditions. As predicted, patterns of energy metabolites were mainly driven by the quality and temporal pattern of food availability. In contrast, patterns of host availability had a lower impact upon metabolites. When given constant access to high quality nutrients, after an initial increase early in life, whole body lipids and glycogen were regulated downward to a steady-state level and somatic protein levels did not vary. In contrast, when food uncertainty was introduced, whole body lipid, glycogen and protein oscillated sharply with peaks associated with pulses of high-quality food. Production of eggs was highest when offered continuous access to hosts and high quality food. Importantly, females fully recovered their reproductive capacity when fruit became available following a period of host deprivation. With no evidence of egg resorption and high levels of egg dumping, it appears that egg dumping may favour the continuous production of eggs such that the female’s reproductive tissues are ready to respond to rapid changes in the availability of hosts. Our results exemplify the capacity of insects to maximize reproduction under variable and stressful environmental conditions.

Egg-Dumping Behavior is Not Correlated with Wider Host Acceptance in the Seed Beetle Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae)

Abstract If typical host plants are absent, some herbivorous insects “dump” eggs on unsuitable substrates, even though this can cause complete larval mortality and reduced maternal life span. In the seed beetle Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae), the tendency to dump eggs varies genetically both within and between populations. A previous study hypothesized that egg-dumping behavior facilitates host-range expansions, and suggested that such expansions have served to maintain “dumper” genotypes in beetle populations. We tested this hypothesis in two experiments. For both African and Asian beetle populations, full-sib females from &amp;gt;60 families were split among three treatments: no seeds, a less-preferred novel host, and a preferred host. Within each population, we found no correlation among families between the tendency to dump eggs and the tendency to accept the novel host. We also compared egg dumping between selection lines that had adapted to a novel host and a line that had remained on the ancestral host. Females from lines that had evolved greater acceptance of the novel host did not dump more eggs if hosts were absent. Thus, neither experiment supported the host-range expansion hypothesis. Egg distributions on the preferred host in the first experiment provided weak support for a more proximate explanation: family-level variation in the tendency to dump eggs is inversely related to the tendency to avoid superparasitism of seeds. Such a relationship is also evident in comparisons between populations. Given the considerable short-term costs of egg dumping, we suggest that the host-range expansion hypothesis requires unrealistically high frequencies of host deprivation and subsequent host shifts in C. maculatus.

Geographical variation in patterns of parentage and relatedness in the co‐operatively breeding Ground TitParus humilis

The Ground Tit is a large parid species endemic to the Tibetan Plateau. Here we describe its genetic breeding system based on 2 years of fieldwork on a population from Damshung, Tibet. Genetic relatedness and parentage were analysed using 16 microsatellite markers and sex was determined with a marker on the Z and W chromosomes. We established that 16 of 75 families (21%) were assisted by one or occasionally two male helpers, which in most cases were young from a previous brood of one or both of the breeding adults. The helpers typically stayed with their families throughout the breeding season. Helpers never obtained any paternity in their own families, but one helper was identified as the sire in the only instance of extra‐group (and extra‐pair) parentage detected. Thus, the level of extra‐group/extra‐pair parentage appears to be very low in this Ground Tit population, and sharing of reproduction within family groups is apparently absent. Our results contrast with the findings from another Ground Tit population in Gansu, further northeast in China, with respect to both the number and sex of helpers and the division of parentage within and among family groups. In Gansu, helpers regularly produced offspring and both extra‐pair and extra‐group paternity as well as maternity (egg dumping) was common. Differences in family structure, philopatry, territoriality and potential inclusive fitness benefits can probably explain this contrast, and are likely to reflect the relative costs and benefits of co‐operative breeding.

Egg dumping by predatory insects

Synovigenic insects resorb oocytes when food is scarce and mature oocytes when food is plentiful. These two antagonistic processes allow an optimal allocation of resources to reproduction and somatic functions. Unlike hymenopteran parasitoids, ladybirds cannot resorb mature oocytes present in the oviducts. Is the energy contained in these oocytes lost or is there a mechanism for recovering it when needed? Females of two species of ladybird beetles Adalia bipunctata (L.) and Adalia decempunctata (L.) that are starved for &gt;24 h lay single infertile eggs, which they immediately eat, and these eggs comprise the mature oocytes in the oviducts at the onset of starvation. This behaviour has some similarities to egg dumping reported in herbivorous insects and is part, in ladybird beetles, of a process to retrieve energy invested in reproduction. Such behaviour may exist in other predatory synovigenic insects species that do not invest in maternal care.

Conspecific brood parasitism and anti-parasite strategies in relation to breeding density in female bearded tits

Within the animal kingdom conspecific brood parasitism (CBP) is particularly frequent in birds and parasitic individuals mainly save parental costs. Host counterstrategies and their efficiency may be influenced by environmental or socio-ecological factors like breeding density. Breeding density in particular may influence the opportunities for parasitism and the number of parasites. Here we examine the rate and efficiency of parasitism in relation to breeding density in socially monogamous bearded tits Panurus biarmicus. We differentiate between CBP attempts and realized CBP which means genetic representation of parasitic chicks in a brood and relate these to breeding density. Furthermore we investigate anti-parasite strategies of female bearded tits including egg ejection, nest abandonment and manipulation of egg position. Almost 40% of the females suffer from conspecific brood parasitism but there is significant increase with breeding density. Finally, only half of all egg dumping attempts have been successful, which implies high costs for parasites as well. Hence CBP is a 'make the best of a bad job' strategy rather than a strategy to increase reproductive success. Females desert their nests especially when clutch size is larger than normal. Egg ejection occurs less frequently and host females do not move parasitic eggs to less favourable incubation positions.

Egg-dumping behaviour in the seed beetle Acanthoscelides obtectus (Coleoptera: Chrysomelidae: Bruchinae) selected for early and late reproduction

In the present study the egg dumping behaviour in short (E)- and long (L)-lived lines of the seed beetle Acanthoscelides obtectus was analyzed. Females of the short-lived E line exhibited substantially higher egg dumping than long-lived L line females. We hypothesize that, since cessation of egg dumping enhances longevity, non-dumping females were selectively favoured in the L regime. Our study also produced evidence that the selection regime affected the male's ability to influence female egg-dumping behaviour. The females mated to males from the lines that were selected for extended longevity and of which the females exhibited little egg-dumping dumped fewer eggs. We suggest that in the L selection regime, where offspring produced at the end of the females' reproductive period were recruited to the next generation, selection operated against those males that stimulated female ovi- position in the absence of seeds. This is the first study to provide evidence that selection for long-lived insects results in the reduced potency of male seminal products to stimulate female oviposition.

Low or no occurrence of extra-pair paternity in the Black Guillemot Cepphus grylle

We investigated extra-pair paternity (EPP) among 46 young in 32 broods of 19 social pairs of Black Guillemot Cepphus grylle, using a combination of three polymorphic microsatellite markers. The analysis was based on blood samples collected over eight years from a population of individually colour-ringed birds in North Norway. All chicks shared an allele on all three loci with both social parents. Hence, there were no cases of extra-pair parentage. Given our sample sizes, the upper 95% confidence limit of EPP was estimated to 6.2% of the young and 8.9% of the broods. Among seven extra chicks, for which we lacked a DNA sample from the social mother, there was one case of genotype mismatch with the social father, but this could also be because of egg dumping. Low occurrence of EPP has now been documented in five of the six species of Atlantic auks.