Biomedical subjects

Daniel W Franks

Publications and source records attributed to Daniel W Franks.

4 recordsLinked to original sources

PubMed2006

The evolution of multicomponent mimicry.

The relative sizes of phenotypic mutations contributing to evolutionary change has long been the subject of debate. We describe how mimicry research can shed light on this debate, and frame mimicry studies within the general context of macromutationism and micromutationism, and punctuated versus gradual evolution. Balogh and Leimar [Müllerian mimicry: an examination of Fisher's theory of gradual evolutionary change. Proc. Roy. Soc. Lond. B Biol. Sci. 272, 2269-2275] have recently used a model to readdress the question of whether or not mimicry evolves gradually along a single dimension. We extend their approach, and present the first model to consider the effect of predator generalization along multiple components on the evolution of mimicry. We find that the gradual evolution of mimicry becomes increasingly less likely as the number of signal components increases, unless predators generalize widely over all components. However, we show that the contemporary two-step hypothesis (punctuated evolution followed by gradual refinement) can explain the evolution of Müllerian mimicry under all tested conditions. Thus, although the gradual evolution of mimicry is possible, the two-step hypothesis appears more generally applicable.

Adaptation, Physiological↗

PubMed2005

Do unprofitable prey evolve traits that profitable prey find difficult to exploit?

Prey that are unprofitable to attack (for example, those containing noxious chemicals) are often conspicuously patterned and move in a slower and more predictable manner than species lacking these defences. Contemporary theories suggest these traits have evolved as warning signals because they can facilitate both associative and discriminative avoidance learning in predators. However, it is unclear why these particular traits and not others have tended to evolve in unprofitable prey. Here we show using a signal detection model that unprofitable prey will evolve conspicuous colours and patterns partly because these characteristics cannot readily evolve in profitable prey without close mimicry. The stability of this signal is maintained through the costs of dishonesty in profitable prey. Indeed, unprofitable prey will sometimes evolve a conspicuous form to reduce mimetic parasitism, even in the unlikely event that this form can be more closely mimicked. This is one of the first mathematical models of the evolution of warning signals to allow for the possibility of mimicry, yet our analyses suggest it may offer a general explanation as to why warning signals take the form that they do. Warning signals and mimicry may therefore be more closely related than is currently supposed.

Animals↗

PubMed2004

Warning signals and predator-prey coevolution.

Theories of the evolution of warning signals are typically expressed using analytic and computational models, most of which attribute aspects of predator psychology as the key factors facilitating the evolution of warning signals. Sherratt provides a novel and promising perspective with a model that considers the coevolution of predator and prey populations, showing how predators may develop a bias towards attacking cryptic prey in preference to conspicuous prey. Here, we replicate the model as an individual-based simulation and find, in accordance with Sherratt, that predators evolve a bias towards attacking cryptic prey. We then use a Monte Carlo simulation to calculate the relative survivorships of cryptic and conspicuous prey and stress that, as it stands, the model does not predict the evolution or stability of warning signals. We extend the model by giving predators continuous attack strategies and by allowing the evolution of prey conspicuousness: results are robust to the first modification but, in all cases, cryptic prey always enjoy a higher survivorship than conspicuous prey. When conspicuousness is allowed to evolve, prey quickly evolve towards crypsis, even when runaway coevolution is enabled. Sherratt's approach is promising, but other aspects of predator psychology, besides their innate response, remain vital to our understanding of warning signals.

Animals↗

PubMed2004

Batesian mimics influence mimicry ring evolution.

Mathematical models of mimicry typically involve artificial prey species with fixed colorations or appearances; this enables a comparison of predation rates to demonstrate the level of protection a mimic might be afforded. Fruitful theoretical results have been produced using this method, but it is also useful to examine the possible evolutionary consequences of mimicry. To that end, we present individual-based evolutionary simulation models where prey colorations are free to evolve. We use the models to examine the effect of Batesian mimics on Müllerian mimics and mimicry rings. Results show that Batesian mimics can potentially incite Müllerian mimicry relationships and encourage mimicry ring convergence.

Animals↗