Macroevolutionary outcomes of coevolution between avian brood parasites and their hosts
Date
2016
Authors
Medina-Guzman, Iliana
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Abstract
Almost one hundred bird species in the world are known to be
obligate interspecific brood parasites. These lay their eggs in
the nests of other species, their hosts, which take care of a
usually larger parasitic chick. Brood parasitism constitutes one
of the best examples of coevolution in the animal kingdom. This
strategy is usually costly to the host, and has led to the
evolution of a suite of adaptations in hosts, in order to defend
themselves against parasitism, and in parasites, in order to
effectively parasitize their hosts. In this thesis I explore the
effects of brood parasitism on macro-evolutionary patterns in
both hosts and parasites.
In the first six chapters of my thesis I explore how defences
evolve in hosts. First I present a literature review about the
evolution of egg acceptance and tolerance mechanisms in hosts of
brood parasites, in which I discuss how other co-evolutionary
interactions, such as those between plants and herbivores, may be
informative for understanding brood parasitic systems. In the
second chapter I perform a large-scale comparative analysis on
the evolution of clutch size as a tolerance mechanism in hosts.
This chapter also incorporates a mathematical model and a field
experiment on the Horsfield’s bronze-cuckoo Chalcites basalis.
In the third chapter I investigate why one type of defence, egg
rejection, evolves in some host species and not in others. In the
fourth chapter I present a comparative analysis which tests the
idea that the benefits of group defence against brood parasites
has led to the evolution of cooperative breeding in hosts. For
the fifth and sixth chapters, I describe field experiments to
test the evolution of defences in the yellow-rumped thornbill
(Acanthiza chrysorrhoa), the main host of the shining
bronze-cuckoo (Chalcites lucidus) in Australia. My main aim is to
understand which types of defences have evolved in this major
host. I also perform field experiments to understand which
factors constrain the evolution of defences in this species.
In the second part of my thesis I study how brood parasitism can
be associated with the evolution of diversity in both hosts and
parasites, especially in traits that are likely to be under
selective pressures, such as the egg phenotype. In chapter 7 I
study how egg phenotype has evolved to be more diverse within and
among species that are hosts of brood parasites. In chapter 8 I
explore whether a brood parasitic breeding strategy promotes the
generation of new species and phenotypic diversity. Specifically,
I test whether brood parasitic lineages have faster rates of
speciation and phenotypic evolution.
Finally, in chapter 9, I discuss how together, these chapters
offer a broad evolutionary landscape that demonstrate the diverse
impacts of brood parasitism as a co-evolutionary interaction. I
provide evidence that brood parasitism, besides driving the
evolution of defenses, is linked to trait diversity, and may be
an important force behind the evolution of clutch size,
cooperative breeding, egg pattern, egg size and plumage
diversity.
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brood parasitism, host, defences, coevolution, arms race, macroevolution, birds, cuckoos, parasites
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Thesis (PhD)
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