Latitudinal variation in biophysical characteristics of avian eggshells to cope with differential effects of solar radiation

Abstract

Solar radiation is an important driver of animal coloration, not only because of the effects of coloration on body temperature but also because coloration may protect from the deleterious effects of UV radiation. Indeed, dark coloration may protect from UV, but may increase the risk of overheating. In addition, the effect of coloration on thermoregulation should change with egg size, as smaller eggs have higher surface‐volume ratios and greater convective coefficients than larger eggs, so that small eggs can dissipate heat quickly. We tested whether the reflectance of eggshells, egg spottiness, and egg size of the ground‐nesting Kentish plover Charadrius alexandrinus is affected by maximum ambient temperature and solar radiation at breeding sites. We measured reflectance, both in the UV and human visible spectrum, spottiness, and egg size in photographs from a museum collection of plover eggshells. Eggshells of lower reflectance (darker) were found at higher latitudes. However, in southern localities where solar radiation is very high, eggshells are also of dark coloration. Eggshell coloration had no significant relationship with ambient temperature. Spotiness was site‐specific. Small eggs tended to be light‐colored. Thermal constraints may drive the observed spatial variation in eggshell coloration, which may be lighter in lower latitudes to diminish the risk of overheating as a result of higher levels of solar radiation. However, in southern localities with very high levels of UV radiation, eggshells are of dark coloration likely to protect embryos from more intense UV radiation. Egg size exhibited variation in relation to coloration, likely through the effect of surface area‐to‐volume ratios on overheating and cooling rates of eggs. Therefore, differential effects of solar radiation on functions of coloration and size of eggshells may shape latitudinal variations in egg appearance in the Kentish plover.

Egg recognition: The importance of quantifying multiple repeatable features as visual identity signals

“…Such discrepancies among studies were expected under an evolutionary perspective, since there is no single evolutionary pathway to develop individual egg recognition. Each species has phenotypic traits more prone to evolve towards identity signals than others, as egg phenotypic traits may be also constrained by other important functions [ 79 , 84 , 85 ], such as camouflage [ 80 , 86 ], protection against radiation [ 87 ], or flight biomechanics [ 88 ]. This fact may explain why in some species most variation among eggs arises in colour [ 42 , 43 , 46 , 81 ], while in others the eggs primarily vary in shell marks [ 28 , 55 , 80 ], shape and size [ 82 , 83 ], or a combination of different traits [ 21 , 30 , 60 , 89 ].…”

Four‐legged foes: dogs disturb nesting plovers more than people do on tourist beaches

“…2009, Gómez et al . 2018), but the gain or loss of heat that eggs may experience depends on various factors such as ambient temperature, wind speed, type of substrate (Saalfeld et al . 2012a), type and colour of nest lining (Mayer et al .…”

“…2010) and the effects of thermal stress on unattended eggs (Yasué & Dearden 2006a, Gómez et al . 2018). Nevertheless, given that climate change has a high potential to exacerbate the impact that thermal risk can have on breeding success, more studies are needed to better quantify the impact of a probable interaction between disturbance and temperature after hatching.…”

Climate Predicts UV Floral Pattern Size, Anthocyanin Concentration, and Pollen Performance in Clarkia unguiculata

“…We used the "Multispectral Image Analysis Toolbox" (Troscianko and Stevens, 2015), which is a plugin for ImageJ (Schneider et al, 2012). Several studies have used this toolkit (Stevens et al, 2017;Gómez et al, 2018;van den Berg et al, 2019;Hawkes et al, 2019;Price et al, 2019;Šulc et al, 2019), which has many advantages including; easy linearization, high precision, and low data loss in image analysis due to 32-bit floating-point image processing (Troscianko and Stevens, 2015). The image frame included a fixed position ruler and Spectralon TM diffuse reflectance standard with a flat reflectance value of 20% across the entire light spectrum, including red, blue, green, and UV wavelengths 9 (North Sutton, NH, United States).…”