Intraspecific egg variation
The basic function of why bird eggs are coloured and/or patterned has been debated for hundreds of years. The distinctive evolutionary shift from white, subterranean reptilian eggs has driven biologists to discover the principle function behind birds’ exceptional capacity to lay pigmented eggs (Stoddard, M.C. et al. 2011). Scientists hypothesise it being due to either signalling properties (i.e. to avoid predation through camouflage and aposematism, to solicit parental care, to facilitate own egg recognition and provide a form of mimicry/crypsis to protect from brood parasites) or structural properties (i.e. to protect embryo from solar radiation, reinforced shell strength, thermoregulation and antimicrobial defence), or both (Cassey, P. et al. 2010).
Generally intra-specific variation in egg colour is very low however, some species show significant variation. This study will focus on on the Australian Magpie (Cracticus tibicen) based on the high variability in their eggs, their vast range across the continent, and the extensive collections of recovered eggs in Australian Museums. The collection i have used is the Museum in Melbourne- who have one of the most unbelievable collection of eggs, including H.L. White’s exclusive collection.
Image: One of the many trays of Australian Magpie eggs from the H.L. White Collection. Imagine a human embryo, so safely kept within the womb of a mother… Well this is all created within 24 hours of reproducing. With the most unbelievable creativity. The shells vary so much, it’s hard to keep track, it makes sciences exciting, and after all… isn’t what science is about? To be eggited about your topic?
My aim is to conduct a spatial analysis to determine whether the variation is due to genetic structuring (subspecies), or due to environmental pressures. I will assess the level of variation for:
- Same subspecies in different environments
- Different subspecies in same environment
I’m also incorporating the factor of brood parasitism of the Channel Billed Cuckoo (Scythrops novaehollandiae) to magpies, and the possible variations in egg patterning for recognition between females to avoid parasitism. It’s been reported before in African Prinia to adjust the variability between females to outwit the Cuckoo-finch (Anomalospiza imberbis), and due to collecting naturalists we conclusively observe a change over time.
Such a spatial analysis is yet to be performed in Australia, and would contribute towards a rich source of information about avian egg structure and appearance. Once I manage to establish the basic source of the variation, it will enable further studies to dig deeper into the function of such variability.
The inspiration for this is from Tim Birkhead’s book “The Most Perfect Thing” and in it this quote (by the abolitionist and mentor to Emily Dickinson) Thomas Wentworth Higginson) sums up the reason I am utterly consumed by the topic…:
“I think that, if required on pain of death to name instantly the most perfect thing in the universe, I should risk my fate on a bird’s egg.”
Environmental influences on maternal investment in a cooperatively-breeding bird
Understanding environmental impacts on animal behaviour and ecology is increasingly important as anthropogenic effects on natural habitats, weather, and climate become more pronounced. How species respond to these environmental shifts is closely linked to their resilience and ability to recover from disturbance, which ultimately determines their future success and range under permanent changes. One important aspect of a species’ response to environmental conditions are the decisions made by mothers when producing and rearing offspring, as the investment strategy the mother adopts can have important effects on adult offspring behaviour and life-history.
Maternal effects are the consequences of maternal investment strategies on offspring phenotype, and can influence morphology, anatomy, physiology or behaviour (Wolf and Wade 2009; Russell and Lummaa 2009).There is abundant evidence that maternal effects can have a major effect on offspring fitness (Mousseau and Fox 1998; Marshall and Uller 2007; Pilakouta and Smiseth 2016), and that mothers adaptively adjust their investment in offspring according to the social environment (Russell et al. 2008; Canestrari et al. 2011). However, while tactical maternal investment in response to local environmental conditions has been found in plants (Galloway 2005), comparable research on animals living in heterogeneous environments is limited. The proposed research project will address this gap by studying the influence of environmental conditions on maternal strategies in detail within a well-understood natural model system.
My aim is to explore the interaction between climatic variability and female investment in egg size and composition. Social environment has been shown to be a driver of reduced egg investment in other cooperative birds (Russell et al. 2007), however the relationship between egg investment and the natural environment remains unclear. I hope to address this question by supplementing the existing 13 years of egg and climate data with more detailed measures of female investment in eggs, such as their composition. Smaller eggs are generally assumed to be of lower quality, producing smaller offspring, however this assumption relies upon egg nutritive value scaling strictly with size. I would investigate egg composition of clutches of different sized eggs under different environmental conditions. This information would illuminate why mothers decide to produce bigger or smaller eggs and validate future research on female investment in this system.
Study system- The Chestnut-Crowned Babbler
My study system will be the Chestnut-crowned Babbler (Pomatostomus ruficeps), a medium-sized (~50g) passerine bird endemic to semi-arid southern and central eastern Australia (Russell et al. 2010). Babblers breed 1-3 times per year (late winter–early spring) in groups of 2–13 comprised of a breeding female, 1–3 breeding males, and a highly variable number of non-breeding helpers (Russell 2016). Babblers have high breeding success, are rarely predated, and can live at least 13 years in the wild, making them an excellent prospect for studying maternal investment across environmentally heterogeneous years and habitats. Cooperative breeding systems, wherein non-breeding helpers as well as parents provide care to the offspring , are often studied to understand the complex interactions presented by their social environment. This project would instead focus on the less-understood but equally important effects of unpredictable environments, and the corresponding plastic decisions made by the female for her offspring’s optimal development.
Testing the developmental basis of Bergmann’s rule using an altitudinal gradient
With a radical temperature increase predicted over the next century, the majority of organisms will be required to adapt at a faster rate than ever previously experienced. Body size has recently become of interest due to the link scientists have been able to draw between temporal changes in size and temperature in relation to climate change, often referred to in the context of Bergmann’s rule. The unanswered debate on the mechanisms behind these morphological changes. It raises a multitude of questions on the likely outcome for species in the face of rapid environmental changes, their potential ability for rapid acclimation, or susceptibility to mass extinction. My study focused was based in the French Pyrenees and was carried out in association with the University of Exeter and the CNRS. It focused on a single population of breeding Blue Tits (Cyanistes caeruleus) along an steep altitudinal cline over a period of three years. The altitudinal cline was used as a proxy for climate change. Results indicate that body size was negatively correlated with temperature increase, and that phenotypic plasticity was the mediating mechanism driving these changes.