Abstract Cryptic female choice (CFC) is a component of postcopulatory sexual selection that allows females to influence the fertilization success of sperm from different males. While its precise ...mechanisms remain unclear, they may involve the influence of the protein composition of the female reproductive fluids on sperm functionality. This study maps the protein composition of the cloacal fluid across different phases of female reproductive cycle in a sexually promiscuous passerine, the barn swallow. Similar to mammals, the protein composition in the female reproductive tract differed between receptive (when females copulate) and nonreceptive phases. With the change in the protein background, the enriched gene ontology terms also shifted. Within the receptive phase, distinctions were observed between proteomes sampled just before and during egg laying. However, three proteins exhibited increased abundance during the entire receptive phase compared to nonreceptive phases. These proteins are candidates in cryptic female choice, as all of them can influence the functionality of sperm or sperm-egg interaction. Our study demonstrates dynamic changes in the cloacal environment throughout the avian breeding cycle, emphasizing the importance of considering these fluctuations in studies of cryptic female choice.
Interspecific brood parasitism represents a prime example of the coevolutionary arms race where each party has evolved strategies in response to the other. Here, we investigated whether common ...cuckoos (Cuculus canorus) actively select nests within a host population to match the egg appearance of a particular host clutch. To achieve this goal, we quantified the degree of egg matching using the avian vision modelling approach. Randomization tests revealed that cuckoo eggs in naturally parasitized nests showed lower chromatic contrast to host eggs than those assigned randomly to other nests with egg-laying date similar to naturally parasitized clutches. Moreover, egg matching in terms of chromaticity was better in naturally parasitized nests than it would be in the nests of the nearest active non-parasitized neighbour. However, there was no indication of matching in achromatic spectral characteristics whatsoever. Thus, our results clearly indicate that cuckoos select certain host nests to increase matching of their own eggs with host clutches, but only in chromatic characteristics. Our results suggest that the ability of cuckoos to actively choose host nests based on the eggshell appearance imposes a strong selection pressure on host egg recognition.
Extended phenotypes with signalling function are mostly restricted to animal taxa that use construction behaviour during courtship displays. However, they can be used also as post‐mating signals of ...mate quality, allowing individuals to obtain reliable information about their partners. Nest size may have such a signalling function and a lot of indirect evidence supports this view. However, direct evidence based on an experimental approach is still widely missing. Here we test the role of nest size in post‐mating signalling of mate quality in the great reed warbler Acrocephalus arundinaceus, a passerine with female‐restricted nest‐building behaviour. Based on observational data, clutch size, nestling weight, brood size and fledglings’ propensity to return to their natal site positively correlated with nest size. Moreover, we experimentally enlarged great reed warbler nests to investigate whether this manipulation affects male investment in feeding. We found that males fed their nestlings significantly more intensively on enlarged nests than those on control nests. This suggests that nest size in this species serves as a signal of female quality or willingness to invest in reproduction and that it pays males to enhance their feeding effort according to this signal. Thus, we provide convincing evidence that animal communication takes place through the extended phenotypes and that post‐mating signalling of quality is not restricted only to males, but may function equally well in females.
In some populations of the host of brood parasites, more than two parasite eggs may be laid in a single nest. This phenomenon is known as multiple parasitism, representing a cost to both the host and ...parasite. In this study, we analysed a long-term dataset (2007–2021) focusing on multiple parasitism of the common cuckoo (
Cuculus canorus
) parasitizing the great reed warbler (
Acrocephalus arundinaceus
). The annual parasitism rate was on average 54.3% and varied between 5.8% and 92.2%, depending on the year. Out of 720 parasitized nests, double parasitism was recorded in 172 (23.9%) nests, triple in 51 (7.1%) nests, quadruple in 10 (1.3%) nests, and, exceptionally, in the years of heavy parasitism (about 90%), quintuple parasitism was recorded in three (0.4%) nests. The rate of multiple parasitism ranged from 0 to 63% inter-annually and strongly correlated with the parasitism rate and the total number of parasite eggs found. Furthermore, the number of cuckoo eggs laid per one nest increased with the decreasing daily availability of host nests that were at a suitable breeding stage for parasitism. Both genetic and egg phenotype analyses revealed that no cuckoo female laid more than one egg in the same host nest. Using data on long-term parasite–host interactions and from continuous video recording, as well as progressive methods to assign parasite offspring thus helped us better understand various aspects of multiple parasitism in hosts heavily parasitized by an evictor brood parasite.
Significance statement
Laying more parasite eggs in one host nest (i.e. multiple parasitism) is common in brood parasites whose nestlings share the nest with nestmates. In the species where the parasite’s nestling kills its nest mates, multiple parasitism should be rare because it is costly for the parasite. However, in host populations with high parasitism rates, multiple parasitism occurs more often than predicted. Using long-term and video-recording data, we quantified multiple parasitism in the common cuckoo across years and host egg-laying sequences. We found that the rate of multiple parasitism is positively related to the parasitism rate and that the lower the number of nests suitable for parasitism, the higher the number of parasite eggs in one nest. Based on genetic and egg phenotype analyses, we also showed that individual parasitic females avoid laying in the nests they had already parasitized.
Returning to a breeding site and decision where to breed belong to the key life-history traits, especially in migratory birds. Yet, we still lack knowledge about the drivers of adult return rates and ...breeding dispersal distances in populations under pressure of brood parasitism. We explored these issues in a trans-Saharan migratory passerine, the great reed warbler (Acrocephalus arundinaceus), in a population parasitized by the common cuckoo (Cuculus canorus)—an evicting brood parasite. In 2008-2012, a total of 563 great reed warblers were colour-marked and 185 of them were reencountered 303 times in a year following their breeding at a fishpond area in the Czech Republic. We tested how brood parasitism and host breeding parameters in 1 year affect host return rate and dispersal distances in a following year. Return rate was lower in females fledging a cuckoo and in both sexes that failed to produce any offspring than in birds that fledged own chicks in the preceding year. Individual brood parasitism had a negative effect on the probability of female returning, but this relationship disappeared when excluding females fledging cuckoos. Although return rates did not differ between females that rejected and those that accepted cuckoo eggs, rejecter females dispersed less than acceptors. We conclude that brood parasitism and fostering the parasite might be negatively related to host female survival. The other breeding conditions might rather be related to the decision where to breed in the future. Establishing new long-term studies monitoring parasitized populations might open up avenues for future research.
In many animal species, organismal performance declines with age in a process known as aging or senescence. Senescence typically leads to a deterioration of physiological functionality and can impact ...the development of primary sexual phenotypes. Sperm production is a complex and costly process that is sensitive to changes in individual physiological state, yet remarkably little is known about age-related changes in sperm performance and aging costs of sperm production. Here we use a non-linear generalized additive mixed models (GAMM) modelling to evaluate age-related changes in postcopulatory sexual traits in the European barn swallow (
Hirundo rustica rustica
), a relatively short lived sexually promiscuous passerine species, where male extra-pair fertilization success has been shown to increase with age. We confirmed a positive relationship between sperm midpiece length and sperm velocity in this species. Within-male changes in sperm morphology and sperm velocity were in general absent, with only sperm length decreasing linearly with increasing age, although this change was negligible compared to the overall variation in sperm size among males. In contrast, the cloacal protuberance (CP) size changed nonlinearly with age, with an initial increase between the first and third year of life followed by a plateau. The results further indicate the existence of a trade-off between investments in sperm production and survival as males with large CP tended to have a reduced lifespan. This seems consistent with the idea of expensive sperm production and survival aging costs associated with investments in post-copulatory traits in this sexually promiscuous species.
In many bird species, return rates tend to be greatest in the vicinity of their hatching site, thus natal philopatry is an important trait in avian demography. In the present study, we examined how ...conditions in natal nests affect return rates and dispersal distances of a long-distance migratory passerine. From 2008 to 2016, we studied a colour-ringed population of the Great Reed Warbler
Acrocephalus arundinaceus
breeding in southeastern Czech Republic. Almost 10% of the 1430 ringed individuals returned to the study site within 2 years after fledging. Birds originating from earlier broods were more likely to return than birds from delayed broods. The variation in local dispersal distances was explained by the sex of the recruits: males dispersed shorter distances than females. There was no evidence that return rates and dispersal distances in Great Reed Warbler are related to other factors closely linked to the condition in the natal nest, namely brood social status and brood size. While the higher return rates of the juveniles from earlier broods is in concordance with the findings of other studies, the sex-related difference in dispersal distances does not correspond with what was found in Great Reed Warbler juveniles in other studies and adults at the same study site. Our results show that early breeding produces more local recruits and that sex-biased dispersal may be site specific.
Breeding dispersal, defined as the movement of adults from one breeding locality to another, varies widely between individuals, sexes and species. Birds of the genus Acrocephalus are characterised by ...short breeding-dispersal distances. In this note we describe a case of a very long breeding dispersal in the Eurasian Reed Warbler A. scirpaceus. The male recorded at a nest containing a Cuckoo chick in the southeastern Czech Republic in 2013 was found two years later in southern Poland. In 2015 the male was observed singing in a territory and later with a female carrying nest material. The distance between the two breeding sites was 160 km. This is the longest breeding dispersal recorded in the species, considering the cases when breeding status at both sites was confirmed.
Geographic variation in avian clutch size is thought to be related to the variation in nest predation rate and food availability. We studied predation on artificial ground nests along a large-scale ...geographic gradient in South Africa characterised by increasing productivity from the deserts in the west to humid savannas in the east, and calculated mean clutch sizes of birds occurring in atlas quadrates surrounding our study sites. Clutch sizes generally increased with increasing productivity and seasonality. The least productive desert site was characterised also by the highest predation rate, whereas all the other sites located in savannas revealed much lower and more or less constant predation rate. We found no evidence for relationship between nest predation rates and clutch sizes of ground-nesting birds. This indicates that food availability is the major factor responsible for geographical variation in bird clutch sizes across South Africa, though high predation rate might also contribute to low clutch size in least productive arid environments.
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