Project description:Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.
Project description:Brood parasitism by cuckoos relies on manipulating hosts to raise their offspring and has evolved stunning adaptations to aid in their deception. The fact that cuckoos usually but not always, remove one or two host eggs while laying their eggs has been a longstanding focus of intensive research. However, the benefit of this behavior remains elusive. Moreover, the recently proposed help delivery hypothesis, predicting that egg removal by cuckoos may decrease the egg-laying duration in the parasitism process caused by biting action, lacks experimental verification. Therefore, in this study, we examined the effects of egg removal/biting on the egg-laying speed in the common cuckoo (Cuculus canorus) to experimentally test this hypothesis. We compared the duration of cuckoo egg-laying in empty nests, nests with host eggs, and nests with artificial blue stick models to test whether cuckoos biting an egg/stick can significantly hasten the egg-laying speed than no biting action. Our results showed that biting an egg or an object is associated with cuckoos laying approximately 37% faster than when they do not bite an egg or an object. This study provides the first experimental evidence for the help delivery hypothesis and demonstrates that when cuckoos bite eggs or other objects in the nest, they lay eggs more quickly and thereby avoid suffering the hosts' injurious attack.
Project description:Male sexually-selected traits can evolve through different mechanisms: conspicuous and colorful ornaments usually evolve through inter-sexual selection, while weapons usually evolve through intra-sexual selection. Male ornaments are rare among mammals in comparison to birds, leading to the notion that female mate choice generally plays little role in trait evolution in this taxon. Supporting this view, when ornaments are present in mammals they typically indicate social status and are products of male-male competition. This general mammalian pattern, however, may not apply to rhesus macaques (Macaca mulatta). Males of this species display conspicuous skin coloration, but this expression is not correlated to dominance rank, and is therefore unlikely to have evolved due to male-male competition. Here, we investigate whether male color expression influences female proceptivity towards males in the Cayo Santiago free-ranging rhesus macaque population. We collected face images of 24 adult males varying in dominance rank and age at the peak of the mating season, and modeled these to rhesus macaque visual perception. We also recorded female socio-sexual behaviors towards these males. Results show that dark red males received more sexual solicitations, by more females, than pale pink ones. Together with previous results, our study suggests that male color ornaments are more likely to be a product of inter- rather than intra-sexual selection. This may especially be the case in rhesus macaques due to the particular characteristics of male-male competition in this species.
Project description:The eggs of the parasitic blood fluke, Schistosoma, are the main drivers of the chronic pathologies associated with schistosomiasis, a disease of poverty afflicting approximately 220 million people worldwide. Eggs laid by Schistosoma mansoni in the bloodstream of the host are encapsulated by vascular endothelial cells (VECs), the first step in the migration of the egg from the blood stream into the lumen of the gut and eventual exit from the body. The biomechanics associated with encapsulation and extravasation of the egg are poorly understood. We demonstrate that S. mansoni eggs induce VECs to form two types of membrane extensions during encapsulation; filopodia that probe eggshell surfaces and intercellular nanotubes that presumably facilitate VEC communication. Encapsulation efficiency, the number of filopodia and intercellular nanotubes, and the length of these structures depend on the egg's vitality and, to a lesser degree, its maturation state. During encapsulation, live eggs induce VEC contractility and membranous structures formation in a Rho/ROCK pathway-dependent manner. Using elastic hydrogels embedded with fluorescent microbeads as substrates to culture VECs, live eggs induce VECs to exert significantly greater contractile forces during encapsulation than dead eggs, which leads to 3D deformations on both the VEC monolayer and the flexible substrate underneath. These significant mechanical deformations cause the VEC monolayer tension to fluctuate with the eventual rupture of VEC junctions, thus facilitating egg transit out of the blood vessel. Overall, our data on the mechanical interplay between host VECs and the schistosome egg improve our understanding of how this parasite manipulates its immediate environment to maintain disease transmission.
Project description:Egg retrieval in birds may help ensure the survival of eggs and improve reproductive success. However, with the risk of brood parasitism, for ground-nesting or cavity-nesting bird hosts, there is a significant reproductive cost and thus a reduction in fitness if the host wrongly retrieved the parasitic eggs. The south rock bunting (Emberiza yunnanensis) and yellow-throated bunting (E. elegans) are hosts for common cuckoos (Cuculus canorus), which coexist within the study area and breed sympatrically in ground nests. Previous studies have found that these two species exhibit strong egg recognition and egg rejection of non-mimetic eggs. In this study, red model eggs, budgerigar eggs, and the host's own eggs were used to assess the recognition and retrieval behavior of two bunting hosts, particularly in response to different types of eggs placed at the nest edge. The results showed that both bunting hosts retrieved ca. 80% of own eggs and did not retrieve any red model eggs. This indicated that both species could distinguish non-mimetic model eggs from their own eggs and make appropriate decisions, which is consistent with their responses when encountering foreign eggs in the nest. However, both species simultaneously retrieved some (8.3% for the yellow-throated bunting and 19% for south rock bunting) of the highly mimetic budgerigar eggs, indicating that the degree of mimicry of foreign eggs affects their egg recognition and egg retrieval behavior. Factors such as parasitism risk, nest predation pressure, age differences, and experience of parent birds may combine to influence egg retrieval behavior of the host.
Project description:Virulent brood parasites refrain from arduous parental care, often kill host progeny and inflict rearing costs upon their hosts. Quantifying the magnitude of such costs across the whole period of care (from incubation through to parasite fledgling independence) is essential for understanding the selection pressures on hosts to evolve antiparasitic defences. Despite the central importance of such costs for our understanding of coevolutionary dynamics, they have not yet been comprehensively quantified in any host of any avian brood parasite. We quantified parasite-rearing costs in common redstarts Phoenicurus phoenicurus raising either parasitic common cuckoo Cuculus canorus or their own chicks throughout the complete breeding cycle, and used multiple cost parameters for each breeding stage: incubation, brooding and feeding effort; length of parental/host care; parent/host body condition; and heterophil/lymphocyte ratio (stress-level indicator). Contrary to traditional assumptions, rearing the parasite per se was not associated with overall higher physiological or physical costs to hosts above the natural levels imposed by efforts to rear their own progeny. The low parasite-rearing costs imposed on hosts may, in part, explain the low levels of known host counter-defences in this unusually frequently parasitized cuckoo host.
Project description:Sexual selection produces extravagant male traits, such as colorful ornaments, via female mate choice. More rarely, in mating systems in which males allocate mating effort between multiple females, female ornaments may evolve via male mate choice. Females of many anthropoid primates exhibit ornaments that indicate intraindividual cyclical fertility, but which have also been proposed to function as interindividual quality signals. Rhesus macaque females are one such species, exhibiting cyclical facial color variation that indicates ovulatory status, but in which the function of interindividual variation is unknown. We collected digital images of the faces of 32 rhesus macaque adult females. We assessed mating rates, and consortship by males, according to female face coloration. We also assessed whether female coloration was linked to physical (skinfold fat, body mass index) or physiological (fecal glucocorticoid metabolite [fGCM], urinary C-peptide concentrations) condition. We found that redder-faced females were mated more frequently, and consorted for longer periods by top-ranked males. Redder females had higher fGCM concentrations, perhaps related to their increased mating activity and consequent energy mobilization, and blood flow. Prior analyses have shown that female facial redness is a heritable trait, and that redder-faced females have higher annual fecundity, while other evidence suggests that color expression is likely to be a signal rather than a cue. Collectively, the available evidence suggests that female coloration has evolved at least in part via male mate choice. Its evolution as a sexually selected ornament attractive to males is probably attributable to the high female reproductive synchrony found in this species.
Project description:Animals that create structures often display non-random patterns in the direction of their constructions. This tendency of oriented construction is widely presumed to be an adaptive trait of the constructor's extended phenotype, but there is little empirical support for this hypothesis. Particularly, for cavity nesting-birds there is a lack of studies examining this issue. In this study of a primary cavity excavator, the endangered red-cockaded woodpecker (Dryobates borealis), we show that cavity entrances exhibited a strong westward bias in all 11 of the populations examined throughout the geographic range of the species in the southeastern United States. This species requires cavities in living pine trees for roosting and nesting that often take many years to complete, resulting in many incomplete excavations on the landscape. We used population monitoring data to show that orientation was stronger among completed cavities than incomplete cavities. There was a significant correlation between latitude and average cavity direction among populations, turning northward with increasing latitude, suggesting adaptation to local conditions. Long-term monitoring data showed that cavity orientation and breeding group size are correlated with egg hatching rates, fledging rates, and the total number of fledglings produced per nest. Our results provide empirical evidence from extensive long-term data that directional orientation in animal constructions is an important feature of the extended animal phenotype and have immediate implications for animal ecology and the conservation of endangered species.
Project description:Bees require distinct foraging and nesting resources to occur in close proximity. However, spatial and temporal patterns in the availability and quantity of these resources can be affected by disturbances like wildfire. The potential for spatial or temporal separation of foraging and nesting resources is of particular concern for solitary wood-cavity-nesting bees as they are central-place, short-distance foragers once they have established their nest. Often the importance of nesting resources for bees have been tested by sampling foraging bees as a proxy, and nesting bees have rarely been studied in a community context, particularly postdisturbance. We tested how wood-cavity-nesting bee species richness, nesting success, and nesting and floral resources varied across gradients of wildfire severity and time-since-burn. We sampled nesting bees via nesting boxes within four wildfires in southwest Montana, USA, using a space-for-time substitution chronosequence approach spanning 3-25 years postburn and including an unburned control. We found that bee nesting success and species richness declined with increasing time postburn, with a complete lack of successful bee nesting in unburned areas. Nesting and floral resources were highly variable across both burn severity and time-since-burn, yet generally did not have strong effects on nesting success. Our results together suggest that burned areas may provide important habitat for wood-cavity-nesting bees in this system. Given ongoing fire regime shifts as well as other threats facing wild bee communities, this work helps provide essential information necessary for the management and conservation of wood-cavity-nesting bees.
Project description:Avian brood parasites lay their eggs in the nests of other birds, and impose the costs associated with rearing parasitic young onto these hosts. Many hosts of brood parasites defend against parasitism by removing foreign eggs from the nest. In systems where parasitic eggs mimic host eggs in coloration and patterning, extensive intraclutch variation in egg appearances may impair the host's ability to recognize and reject parasitic eggs, but experimental investigation of this effect has produced conflicting results. The cognitive mechanism by which hosts recognize parasitic eggs may vary across brood parasite hosts, and this may explain variation in experimental outcome across studies investigating egg rejection in hosts of egg-mimicking brood parasites. In contrast, for hosts of non-egg-mimetic parasites, intraclutch egg color variation is not predicted to co-vary with foreign egg rejection, irrespective of cognitive mechanism. Here we tested for effects of intraclutch egg color variation in a host of nonmimetic brood parasite by manipulating egg color in American robins (Turdus migratorius), hosts of brown-headed cowbirds (Molothrus ater). We recorded robins' behavioral responses to simulated cowbird parasitism in nests where color variation was artificially enhanced or reduced. We also quantified egg color variation within and between unmanipulated robin clutches as perceived by robins themselves using spectrophotometric measures and avian visual modeling. In unmanipulated nests, egg color varied more between than within robin clutches. As predicted, however, manipulation of color variation did not affect rejection rates. Overall, our results best support the scenario wherein egg rejection is the outcome of selective pressure by a nonmimetic brood parasite, because robins are efficient rejecters of foreign eggs, irrespective of the color variation within their own clutch.