Evolution of avian egg shape: underlying mechanisms and the importance of taxonomic scale

Stoddard, Mary Caswell; Sheard, Catherine; Akkaynak, Derya; Yong, Ee Hou; Mahadevan, L.; Tobias, Joe

doi:10.1111/ibi.12755

Cited by 30 publications

(33 citation statements)

References 27 publications

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“…Why, in evolutionary terms, an egg is the shape that it is, is surprisingly under-studied. That is, although there are some previous investigations in the field of egg shape evolution ( Andersson, 1978; Stoddard et al, 2017, 2019; Birkhead et al, 2019 ), we do not know how exactly this process occurred. In this context, it is the pyriform eggs (the ones that, in this study, we have incorporated in order to make the formula universal) that have attracted the most attention.…”

Section: Discussionmentioning

confidence: 84%

A universal formula for avian egg shape

Narushin

Romanov

Griffin

2020

Preprint

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The bird's oomorphology has far escaped mathematical formulation universally applicable. All bird egg shapes can be laid in four basic geometric figures: sphere, ellipsoid, ovoid, and pyriform (conical/pear-shaped). The first three have a clear mathematical definition, each derived from expression of the previous, but a formula for the pyriform profile has yet to be inferred. To rectify this, we introduced an additional function into the ovoid formula. The subsequent mathematical model fits a completely novel geometric shape that can be characterized as the last stage in the evolution of the sphere-ellipsoid-Hügelschäffer's ovoid transformation applicable to any avian egg shape geometry. Required measurements are the egg length, maximum breadth, and diameter at the terminus from the pointed end. This mathematical description is invariably a significant step in understanding not only the egg shape itself, but how and why it evolved, thus making widespread biological and technological applications theoretically possible.

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Section: Discussionmentioning

confidence: 84%

A universal formula for avian egg shape

Narushin

Romanov

Griffin

2020

Preprint

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“…It was clear that there was substantial variation in allometric coefficients among orders, among families within orders, and even between orders and their families. This suggests the prospect that different processes are important at different taxonomic scales, as observed in avian egg shape evolution (Birkhead et al 2019, Stoddard et al 2019. In that example, Stoddard et al (2017Stoddard et al ( , 2019 performed a class-wide analysis that concluded that, over a broad phylogenetic scale that spanned 34 orders, adaptations for flight might be important drivers of egg shape variation.…”

Section: Discussionmentioning

confidence: 99%

“…This suggests the prospect that different processes are important at different taxonomic scales, as observed in avian egg shape evolution (Birkhead et al 2019, Stoddard et al 2019. In that example, Stoddard et al (2017Stoddard et al ( , 2019 performed a class-wide analysis that concluded that, over a broad phylogenetic scale that spanned 34 orders, adaptations for flight might be important drivers of egg shape variation. However, within each of 2 families of distantly related but ecologically similar species (Alcidae and Spheniscidae), Birkhead et al (2019) observed that incubation site explained the majority of variation in egg shape.…”

Section: Discussionmentioning

confidence: 99%

Estimating egg mass–body mass relationships in birds

Rotenberry

Balasubramaniam²

2020

The Auk

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The mass of a bird’s egg is a critical attribute of the species’ life history and represents a fundamental component of reproductive effort. Indeed, the tradeoff between the number of eggs in a clutch and clutch mass lies at the heart of understanding how environmental attributes such as nest predation or adult mortality influence reproductive investment. However, egg masses have not been reported for the majority of avian species. We capitalized on the strong allometric relationship between avian body mass and egg mass to produce egg mass estimates for over 5,500 species previously lacking such information. These estimates are accompanied by measures of the robustness of the regressions used to produce them (e.g., sample size, root mean square error [RMSE] of estimation, coefficient of determination, and degree of extrapolation), thus allowing independent evaluation of the suitability of any estimate to address a particular research question relating to avian life history. Most estimates (~5,000) were based on family-level egg mass–body mass regressions, with the remainder derived from other relationships such as ordinal regressions. We compared estimating regressions based on adult vs. female body masses and, after finding little difference between the 2, based our final estimates on adult masses as those were more numerous in the literature. What small differences between adult- and female-based regressions that did occur were not related to sexual size dimorphism across families. These new estimates, coupled with ~5,000 egg masses reported in the literature, provide a foundation of over 10,000 species for wider investigations assessing variation in reproductive effort in birds over a broad array of ecological and evolutionary contexts.

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“…Across and within bird species there is considerable variation in egg shape, colour and maculation (shape: Hewitson , Thompson , Thomson , Stoddard et al , and colour and maculation: Wallace , Gaston and Nettleship , Kilner , Cassey et al , Cherry and Gosler , Stevens , also see Birkhead ). Variation in both intra‐ and interspecific egg traits has long intrigued researchers (Hewitson , Wallace , Newton , Swynnerton , Thompson , Schönwetter 1960–), but the drivers of egg trait variation remain poorly understood (Underwood and Sealy , Cassey et al , Deeming and Ruta , Birkhead , Stoddard et al , Birkhead et al , Stoddard et al ). Recent studies have started to fill this gap in our understanding by examining patterns of egg trait diversity at different taxonomic scales (e.g.…”

Section: Introductionmentioning

confidence: 99%

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

Thompson

Birkhead

2020

Journal of Avian Biology

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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.

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Evolution of avian egg shape: underlying mechanisms and the importance of taxonomic scale

Cited by 30 publications

References 27 publications

A universal formula for avian egg shape

A universal formula for avian egg shape

Estimating egg mass–body mass relationships in birds

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

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