Causes and consequences of signal divergence across species

Introduction


I am broadly interested in why signals differ across species and the consequences of this variation for important evolutionary processes, such as the evolution of reproductive isolation, cooperation, and sensory biases.

I've used a variety of songbird systems to answer these questions:

What factors lead to signal divergence across species?

How do individuals come to recognize the (variable) signals of other species?

What mechanisms focus learning onto relevant signals?

I am currently a postdoctoral researcher at Uppsala University working with Anna Qvarnström. In 2012, I completed my PhD in Trevor Price's lab at the University of Chicago and, from 2012-2014, completed a NSF research fellowship in Anna Qvarnström's lab in Uppsala.

Contact me at: davidjameswheatcroft "at" gmail "dot" com

1)
Associative learning and the evolution of alarm calls


During my PhD work, I studied the formation of cooperative anti-predator groups comprised of individuals from many species, called mobs, that are formed when surrounding birds are attracted to characteristic calls signaling alarm. In multi-species communities, the formation of mobs depends on individuals from one species recognizing the calls produced by co-occurring species.

Calls generally vary greatly across even closely related species (Wheatcroft and Price 2013, 2014), potentially because they are also used in a variety of species-specific contexts that may promote divergence across species (Wheatcroft 2015). Despite dissimilarity across species, a combination of learning (Wheatcroft and Price 2013) and recognition of common acoustic features allows widespread communication (Wheatcroft and Price 2013, 2014; Wheatcroft 2015).

My work also addressed the evolutionary rate of alarm calls using recently developed methods to compare rates of evolution of multiple traits shared by the same species. We demonstrated that the number and variety of receivers may strongly influence the rate and nature of signal divergence: alarm calls directed at a narrower set of receivers evolve at slower rates than those directed at a more diverse set of receivers (Wheatcroft and Price 2014). In extreme cases, communication between a pair of species may even promote call convergence through copying or mimicry (Wheatcroft and Price 2013).
2) Innate auditory predispositions, song learning, and speciation

Learning is thought to underlie the tremendous diversity in songs across songbird species by increasing transmission errors and by fixing rare variants through cultural conformity. Remarkably, despite the variability introduced by learning, adults almost invariably produce and prefer species-specific songs, implying that the learning process is at least partly guided.

I am using playback experiments, acoustic analysis, and neurobiological methods to study the genetic and neural basis of auditory predispositions in two species of closely related, co-occurring songbirds, the pied (Ficedula hypoleuca) and collared flycatcher (F. albicollis).

First, to establish the social and genetic influences on early auditory discrimination, I play back songs to very young nestlings raised from the embryonic phase either by their natural parents or by adults from the other species and compare the nestlings' activity in response to songs from both flycatcher species. In addition, in collaboration with Eryn MacFarlane, we are using measurements of metabolic rate to determine the earliest developmental stages during which song responses develop.

Second, I have played back songs to adult males from both flycatcher species in sympatry, where both species co-occur, and to pied flycatchers in allopatry, where each flycatcher