Evolution of embryonic development and egg physiology in avian brood parasites

Stephanie Mcclelland

Research output: ThesisDoctoral Thesis

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Brood parasites are species that parasitise the parental care of other species, to avoid the costs of raising their own young. For birds this involved laying their eggs in another bird’s nest. This reproductive strategy involves behavioural and physiological adaptation to successfully exploit their hosts. After laying their egg, the parasite female has no control over their offspring development. As such there is strong selection on producing an egg and embryo that will develop optimally in the hosts nest and obtain the hosts’ parental care.

This thesis investigates the evolution of specialised adaptations of the eggs and embryos in avian brood parasites, from multiple evolutionarily distinct lineages of this behaviour, using up-to-date phylogenetic comparative statistical methods. A combination of laboratory and field-based methods are employed to collect data on a diverse range of species.

Firstly, I investigate the structural traits of parasite eggshells, with comparison to non-parasite species and the parasites hosts. This includes eggshell water vapour conductance, calcium carbonate content and eggshell surface properties such as surface roughness and hydrophobicity. Although there were no differences between parasites and hosts in most of the eggshell traits investigated, we found that parasites had lower eggshell conductance, potentially as an adaptation to increasing their aerobic fitness or a constraint of thicker eggshells. Secondly, I investigated embryo muscular activity and metabolic rate development as potential adaptations for the early hatching of parasite young and their unique and energetically costly nestling behaviour. We found that brood parasite embryos move significantly more during development compared to non-parasites, which is potential to increase muscle mass prior to hatching. Metabolic rate of embryos was measured in-situ using flow-through respirometry. We see that in high virulence species, where the parasitic chick activity kills the host offspring, there is a higher embryo metabolic rate during development, with similarities in the pattern of metabolic rate development seen in more precocial bird species.

Overall, this thesis fills a gap in our knowledge on the evolution of physiological traits to the early life stages of this exceptional group of birds. Furthermore, the results of this thesis provide new insights on embryo development which will be of wider interest to the field of animal physiology.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Portugal, Steve, Supervisor
  • Leadbeater, Elli, Supervisor
Thesis sponsors
Award date1 Feb 2022
Publication statusPublished - 25 Apr 2018

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