Egg spottiness reflects female condition, physiological stress, and ornament expression in a common rallid species

Lay Summary • There is equivocal support for direct associations between maternal quality and deposition of protoporphyrin pigmentation (dark spots and blotches) in avian eggshells. • Research on protoporphyrin eggshell pigmentation has primarily focused on a single avian order (Passeriformes). • We examined associations of protoporphyrin-based eggshell pigmentation with female phenotypic and genetic traits in a non-passerine species, the Eurasian Coot. • Deposition of protoporphyrin in eggshells (total number per area of egg spots) positively correlated with female condition and expression of a putative bare-part ornament (frontal shield), while it was negatively associated with the level of physiological stress. • Protoporphyrin-based eggshell pigmentation acts as a reliable signal of female phenotypic (but not genetic) traits in the Eurasian Coot. • Signaling properties of protoporphyrin-based egg coloration are likely to largely differ between different evolutionary lineages of birds.

Coevolution of song and egg coloration: multimodal mating signals?

The divergence of reproductive traits frequently underpins the evolution of reproductive isolation. One of the most enduring puzzles on this subject concerns the variability in egg coloration among species of tinamou (Tinamidae) —a group of birds endemic to neotropics (Cabot 1992). Specifically, some tinamous lay glossy and colorful eggs while others lay less colorful eggs. Here I tested the hypothesis that tinamou egg coloration is a mating signal and its diversification was driven by reinforcement. For most tinamou species, the male guard the nest that is sequentially visited and laid eggs in by multiple females. The colorations of the existing eggs in the nest could signal mate quality and species identities to the upcoming females to the nest, preventing costly hybridization, thus were selected to diverge among species. If so, egg colors should coevolve with the known mating signals as the tinamou lineages diverged. The tinamou songs are important mating signals and are highly divergent among species. I found that the egg luminance was significantly associated with the first principle component of the song variables among 31 tinamou species (after correcting for phylogenetic signal). Egg color and songs could be multimodal mating signals that are divergently selected as different tinamou species diverged. Mating signal evolution could be opportunistic and even exploit post-mating trait as premating signals.

The Relationship Between Digital Egg Coloration and Egg Survival in Landlocked Fall Chinook

Digital color values were collected from the eggs of 128 spawns from individual landlocked fall Chinook salmon Oncorhynchus tshawytscha females from Lake Oahe, South Dakota, USA, in 2008, 2009, 2015 and 2016. For all spawns, the mean (SE) a* value, a measure of red-green chromaticness, was 10.99 (0.27), and ranged from 3.98 to 18.71. Mean (SE) b* (yellow-green) was 20.27 (0.32), and ranged from 9.28 to 28.50. Mean (SE) L* (white-black) was 20.73 (0.48), and ranged from 3.98 to 18.71. Egg total color index also showed considerable variation, with a mean (SE) of 23.05 (0.37) and range from 11.70 to 31.64. Egg survival to the eyed-stage was weakly, but significantly, correlated to b* (r = 0.206), L* (r = 0.185), Chroma (r = 0.211), and Entire Color Index (r = 0.211). Spawns with no egg survival had eggs with significantly lower a* values compared to spawns where at least some of the eggs survived to the eyed stage. L*, a*, b*, Chroma, and Entire Color Index varied significantly among the years, but Hue and egg survival to the eyed stage did not. The results of this study indicate a possible link between egg color and landlocked fall Chinook salmon egg survival, possibly due to differences in the diets of feral broodstock females or their ability to deposit bodily carotenoids in the developing eggs.

THE NEST AND EGGS OF BLACK-CAPPED SPARROW ARREMON A. ABEILLEI (PASSERELLIDAE) IN SOUTHWESTERN ECUADOR

I describe the nest and egg of Black-capped Sparrow (Arremon a. abeillei), providing the first substantiated information on its reproductive biology and the first report of brood parasitism by Shiny Cowbird (Molothrus bonariensis). I studied 7 nests at two locations in southwestern Ecuador. Nests are enclosed, oven-shaped structures with a side entrance, concealed amongst leaf litter on either flat sloping ground. Confirmed clutch size at one nest was 4 eggs, and 13 eggs varied from very pale buff to pure white, sparsely marked with dark brown or black flecks, small spots, and short scrawls. Nest architecture is similar to that of congeners traditionally placed within Arremon and Lysurus, and to members of the genus Arremonops, but differs from the open-cup nests of congeners historically placed in the genera Buarremon or Atlapetes. Egg coloration reflects similar relationships within these genera.

Dinosaur origin of egg color: oviraptors laid blue-green eggs

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 parataxonMacroolithus yaotunensiscan be assigned to the oviraptorHeyuannia huangibased 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.

A scenario for the evolution of selective egg coloration: the roles of enemy-free space, camouflage, thermoregulation and pigment limitation

Behavioural plasticity can drive the evolution of new traits in animals. In oviparous species, plasticity in oviposition behaviour could promote the evolution of new egg traits by exposing them to different selective pressures in novel oviposition sites. Individual females of the predatory stink bug Podisus maculiventris are able to selectively colour their eggs depending on leaf side, laying lightly pigmented eggs on leaf undersides and more pigmented eggs, which are more resistant to ultraviolet (UV) radiation damage, on leaf tops. Here, we propose an evolutionary scenario for P. maculiventris egg pigmentation and its selective application. We experimentally tested the influence of several ecological factors that: (i) could have favoured a behavioural shift towards laying eggs on leaf tops and thus the evolution of a UV-protective egg pigment (i.e. exploitation of enemy-reduced space or a thermoregulatory benefit) and (ii) could have subsequently led to the evolution of selective pigment application (i.e. camouflage or costly pigment production). We found evidence that a higher predation pressure on leaf undersides could have caused a shift in oviposition effort towards leaf tops. We also found the first evidence of an insect egg pigment providing a thermoregulatory advantage. Our study contributes to an understanding of how plasticity in oviposition behaviour could shape the responses of organisms to ecological factors affecting their reproductive success, spurring the evolution of new morphological traits.

Comment on “Vegetation height and egg coloration differentially affect predation rate and overheating risk: an experimental test mimicking a ground-nesting bird” 1Appears in Can. J. Zool. 90(6): 694–703. doi: 10.1139/z2012-035.

It is often assumed that darker colored avian eggs are more at risk from overheating in direct sunlight than paler eggs. In fact, the evidence for this lies solely in studies using unnatural pigments; studies with natural pigments find no such effect. I argue that risk of egg overheating likely affects the behaviour of birds nesting in hot environments, but there is no evidence or physical reason to expect it to have a strong influence on egg coloration.