Research


Damseldead.jpgPredator-Prey Interactions 
Interactions between predators and prey, particularly in the context of receiver psychology, are a mainstay of research in the lab.  Particular areas of interest include:

Crypsis - a number of different strategies exist for avoiding detection by a predator.  These include (i) background-matching, where an individual resembles the substrate on which it occurs, (ii) disruptive colouration, where an individual possesses areas of high contrast to break up its outline and (iii) countershading, where the upper surface of an individual is darker than the lower surface, resulting in confusing patterns of shading.  The lab is conducting field experiments on the effects of varying disruptive colouration and background-matching on predation on artificial prey by woodland birds.

Background evolution - it is generally considered that either the prey evolve to conceal themselves from predators or predators evolve to conceal themselves from prey.  However, in some cases the background against which the individual is camouflaged is also an organism (usually trees and flowers).  In cases such as polllination, the background (e.g. flowers) may have an interest in preventing predators (e.g. spiders) from concealing themselves and increasing their predation on pollinators (e.g. hoverflies).  This produces a selective pressure for an evolving background which will hinder the camouflage of the predator.

Aposematism -many organisms (particularly insects) possess traits which make them unpalatable or dangerous to consume by predators. These defences are often accompanied by traits that make the individuals easily perceptible by predators, an association that is known as “aposematism”. The lab has done a lot of work to test theories as to why the association between defence and conspicuous signals has evolved. We are currentlyHoverflydaisy.JPG conducting extensive experiments in the field to investigate relative levels of predation on artificial prey items in by woodland birds.  These artificial prey vary in their conspicuousness and palatability.

Mimicry -The Sherratt Lab research into mimicry occurs in two contexts.  The first is predator-prey interactions where a potential prey species possesses traits which result in a predator perceiving it as less profitable.  Most commonly this is seen in pigmentation patterns such as in hoverflies which mimic wasps.  The lab is interested not only in the similarity of appearance between models and mimics but also potential behavioural similarities which may enhance mimicry or compensate for imperfect mimicry.  Previous research has also looked at the similarity of the sounds produced by models and their mimics.

elegansandro.jpg eleganshetero.jpgThe second context within which we carry out research into mimicry is that of intraspecific polymorphisms. Many examples of this phenomenon occur in the damselflies (Odonata: Zygoptera), although not everyone believes that it is based in mimicry.  In most cases there are multiple female morphs, one which differs from the male ("heterochrome") and one which resembles the male ("androchrome").  An example is given here, with Ischnura elegans males mating with heterochrome female (left) and androchrome female (right).  We are interested in both how these polymorphisms evolved and how they are maintained in natural populations.





Death feigning
- some organisms have been shown to adopt behaviours which may be designed to deceive a predator into thinking that the organism is dead or incapacitated.  However, little experimental work has been done to describe the phenomenon within individuals and populations.  The lab is working on lab-reared populations of beetles to look at consistency of death-feigning within individuals, heritability of death-feigning between generations and relationships between death-feigning and chemical defense.




Ford_Model_T.jpgSenescence
The question "why do we age" is a fundamental issue in evolution.  The lab works both on theoretical and empirical models of ageing.  In particular, we have made attempts to place explanations of ageing based on reliability theory in an evolutionary context. In so doing, we have turned up a few surprises.   Ageing.jpgFor example, the apparently logical economic case for equalising the durability of components (advocated by Henry Ford in relation to the kingpins of the Model-T) turns out not to be the best strategy as a result of the varying costs of investment in different components.

Age-dependent mortality has been described in a large number of long-lived vertebrate species but similar studies have not been carried out in many invertebrate species.  Using Odonata as model systems, we investigate patterns in mortality using modern statistical approaches (MARK) combined with data from extensive mark-release-recapture experiments.  This has been used to demonstrate conclusively the existence of age-dependent mortality in Odonata.  The lab also works on comparative data collected from the literature, investigating interspecific variation in rates of mortality in relation to other biological traits.







Ants.jpgThe Evolution of Cooperation
Why do individuals appear to accept the costs of helping others (for example, in food sharing or grooming) when they would apparently do better by accepting such help without giving it? Over the past few years the Sherratt lab has been collaborating to develop and test biologically relevant theories of cooperation.  In an early paper with Gilbert Roberts we sought to identify the types of strategies that would be competitively successful when individuals can decide not just whether they cooperate, but also by how much.  Recent work has involved game-theoretic analyses of optimal investment rules (e.g., for food storage, or extracellular enzymes) when competitors may also benefit from these investments.  Working with renowned game theorist Mike Mesterton-Gibbons, we have attempted to elucidate the conditions under which individuals might form fighting coalitions, and when it may pay an individual to be a “Good Samaritan” and intervene to help a neighbour ward off a challenger.








Funding


We are extremely grateful to all our funders over the years:

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