An Insect with Selective Control of Egg Coloration

Abstract

The color and patterning of animal eggs has important consequences for offspring survival. There are examples of between-species and polymorphic differences in egg coloration in birds and amphibians [1-3], as well as cases of birds and insects whose nutritional status or age can cause within-individual variation in egg pigmentation [4-6]. However, no studies to date have demonstrated that individual animals can selectively control the color of their eggs. Here, we show that individual females of the predatory stink bug Podisus maculiventris can control the pigmentation of their eggs during oviposition, as a response to environmental conditions. The color of egg masses produced by individual females can range from pale yellow to dark black/brown. Females tend to lay darker eggs, which are more resistant to UV radiation, on the upper surface of leaves where UV exposure is highest in nature. Conversely, they lay lighter eggs on the undersides of leaves. However, egg color is not determined by the intensity of UV radiation falling on the surface where they are laid. Rather, female stink bugs appear to use a visual assessment of oviposition substrate reflectance to determine egg color. Unexpectedly, biochemical analyses revealed that the egg pigment is not melanin, the most ubiquitous light-absorbing pigment in animals. Our study offers the first example of an animal able to selectively control the color of its eggs.

Diversity in warning coloration: selective paradox or the norm?

“…Melanin also has benefits associated with ultraviolet (UV) protection (Ortonne, 2002), immunocompetence (Dubovskiy et al, 2013), and desiccation (King & Sinclair, 2015) and its abundance is plastically adjusted in response to increases in these challenges (Wilson et al, 2001;Abram et al, 2015;Välimäki et al, 2015). Variation in these factors may act, like temperature, to enable the persistence of variation in the abundance of melanic morphs across spatial (polytypism) and temporal (polymorphism) scales.…”

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

“…Populations of African village weaverbirds Ploceus cucullatus changed in egg appearance after being introduced in sites where they experienced different levels of solar radiation compared to those in their original sites (Lahti, ). However, the variation described in these studies can also be interpreted either as local adaptation (evolution), or environmental constraints affecting egg coloration by modifying the state (nutritional status/stress level) of the female bird, and it remains to be demonstrated whether birds plastically adjust egg coloration to match environmental conditions, as it has been shown in insects (Abram et al., ; Torres‐Campos, Abram, Guerra‐Grenier, Boivin, & Brodeur, ). Individual phenotypic plasticity may be adaptive, as there may be differences in the effects of solar radiation throughout the long nesting season of the Kentish plover (individual females may lay up to four clutches in a season [Fraga & Amat, ]), as well as between sites at which individual plovers may breed during successive nesting attempts.…”

“…In ground-nesting birds, darker eggs can sometimes have better camouflage than lighter eggs (Gómez et al, 2016;Troscianko et al, 2016), which suggests that ground-nesting birds may face trade-offs between the level of egg camouflage and dealing with high levels of solar radiation (Gómez et al, 2016;Wilson-Aggarwal et al, 2016). However, in sites where solar radiation is very high (>0.8 kW/m 2 ), lighter colors may not be advantageous because of the higher transmittance of light-colored eggshells, assuming no variation in eggshell thickness, as this increases the risk of UV radiation reaching the embryo (Abram et al, 2015;Brulez et al, 2015;Gaudreau et al, 2017;Lahti & Ardia, 2016;Maurer et al, 2015). Such high UV radiation levels are found at low latitudes, and this may be a reason for the occurrence of eggs of dark coloration at such latitudes in spite of high levels of solar radiation.…”

“…Because the eggs contain the DNA, harmful mutations could be inherited by the next generation (e.g., Flenley, 2011). Darker colors reduce light transmittance through eggshells, thus protecting the embryo from UV radiation (Abram et al, 2015;Brulez, Pike, & Reynolds, 2015;Gaudreau, Abram, & Brodeur, 2017;Lahti & Ardia, 2016;Maurer et al, 2015;Shafey, Ghannam, Al-Batshan, & Al-Ayed, 2004). Because the absorptance by darker colors is higher than that of lighter colors, this may result in a trade-off between the risk of egg overheating and the risk of UV radiation on embryos if ambient temperature and solar radiation are positively related (Lahti & Ardia, 2016): Darker eggshells would protect the embryo from UV radiation, but in turn would increase the risk of overheating.…”

Darker eggs resist more to desiccation: the case of melanin inAedes,AnophelesandCulexmosquito vectors

“…Females of the bug Podisus maculiventris selectively control egg color during oviposition: darker and lighter eggs are laid on the upper and lower surface of leaves, respectively. The dark pigment protects eggs against the deleterious effects of UV light emitted from the sun (Abram et al, 2015).…”