Guest Speakers - Camille Duval & Kaat Brulez

Hosted by the Global Ecology Laboratory

The Global Ecology Lab presented Camille Duval and Kaat Brulez, visiting researchers from the University of Birmingham, UK on Thursday 28th February 2013.

Each candidate gave a 30 minute presentation on their research. Camille's talk is titled 'Condition-dependent strategies of eggshell pigmentation: an experimental study in Japanese quail' and Kaat's 'Does calcium supplementation offer new insights into eggshell coloration?' (See individual abstracts below)

Camille Duval

Camille is a PhD student at the Centre for Ornithology, School of Biosciences, at the University of Birmingham, UK. Her research is into the effects of stressful environments on eggshell pigmentation and the implications for eggs crypsis in Japanese quail (Coturnix coturnix japonica).

ABSTRACT
A relationship has been suggested between eggshell colour and female body condition based on the opposing antioxidant properties of the two main eggshell pigments: the antioxidant biliverdin (blue-green) and the pro-oxidant protoporphyrin (brown). We hypothesized that experimentally food-restricted females with low antioxidant capacity would deposit more protoporphyrin and less biliverdin in their eggshells, resulting in eggshells of reduced brightness but increased colour intensity. Two eggs were collected at the beginning and two at the end of a 2week period from each of 24 female Japanese quails that were either food restricted or receiving ad libitum food (i.e. controls) during that time. Reflectance spectra were recorded and analysed using spectral shape descriptors, chromatic and achromatic contrasts were computed accounting for avian visual sensitivities, and eggshell pigments were quantified. We examined both spot and background pigmentation and found no significant effect of food restriction on eggshell reflectance. However, food-restricted females in lower body condition increased the deposition of protoporphyrin and decreased the amount of biliverdin invested in their eggshells. We hypothesize that in species laying brown-spotted eggshells, females modulate eggshell pigment investment in response to their body condition. According to this hypothesis, we predict that females maintain eggshell colour to limit visible changes that could be detected by predators and thereby conceal their eggs, although this work has yet to be conducted. We suggest that further experimental work on egg camouflage under different environmental conditions will elaborate on the process of pigment deposition and the physiological costs to females of laying heavily pigmented eggshells.

Kaat Brulez

Kaat Brulez is a PhD candidate at the University of Birmingham, UK. Her research uses calcium supplementation as a tool to explore eggshell colouration. She is currently a visiting researcher at the University of Adelaide.

ABSTRACT
Many small passerine species have diets that are low in calcium. During egg production female birds shift their dietary preferences to include foods rich in calcium. Recent work has focused on the deposition of the protoporphyrin, the main pigment that constitutes maculation of the eggshell of many small passerines. Owing to its hypothetical shock-absorbing properties, protoporphyrin is postulated by the structural-function hypothesis to reinforce the structural integrity of eggshells under conditions when dietary calcium is scarce. Here, we investigated the effects of calcium-supplementation on the eggshell characteristics (thickness, calcium content, protoporphyrin content) of both great tits (Parus major) and blue tits (Cyanistes caeruleus), focusing on the predictions outlined by the structural-function hypothesis. Pigment spots occurred in thinner areas of the eggshell laid by control female great tits but this was not the case with supplemented birds. Supplemented female blue tits laid eggs with thinner shells than control females. Pigmented eggshell was thinner than adjacent unpigmented eggshell regardless of whether birds were supplemented. In both species, no significant relationships were found between eggshell protoporphyrin content and calcium content although larger eggs laid by blue tits were found to contain greater quantities of protoporphyrin. Our results do not fully support the predictions outlined by the structural-function hypothesis, suggesting that protoporphyrin pigmentation may have multiple functions. Especially in great tits, eggshell maculation may only be superficially deposited perhaps suggesting functionality beyond structural strengthening.