Showing papers by "Trevor D. Price published in 2008"

Density-dependent cladogenesis in birds.

Abstract: A characteristic signature of adaptive radiation is a slowing of the rate of speciation toward the present. On the basis of molecular phylogenies, studies of single clades have frequently found evidence for a slowdown in diversification rate and have interpreted this as evidence for density dependent speciation. However, we demonstrated via simulation that large clades are expected to show stronger slowdowns than small clades, even if the probability of speciation and extinction remains constant through time. This is a consequence of exponential growth: clades, which, by chance, diversify at above the average rate early in their history, will tend to be large. They will also tend to regress back to the average diversification rate later on, and therefore show a slowdown. We conducted a meta-analysis of the distribution of speciation events through time, focusing on sequence-based phylogenies for 45 clades of birds. Thirteen of the 23 clades (57%) that include more than 20 species show significant slowdowns. The high frequency of slowdowns observed in large clades is even more extreme than expected under a purely stochastic constant-rate model, but is consistent with the adaptive radiation model. Taken together, our data strongly support a model of density-dependent speciation in birds, whereby speciation slows as ecological opportunities and geographical space place limits on clade growth.

Phenotypic Plasticity and the Evolution of a Socially Selected Trait Following Colonization of a Novel Environment

Abstract: Novel selection pressures in new environments arise through two distinct processes. First, environmental conditions directly affect the fitness of different phenotypes. Second, phenotypic plasticity alters the distribution of phenotypes, thereby placing populations in new selective regimes. A small isolated population of dark-eyed juncos Junco hyemalis became established in San Diego, probably in the early 1980s and probably from the nearby mountains. The relatively mild coastal climate has resulted in an increase in both the mean and the variance of the length of time females breed each year, and this is assumed to be a result of phenotypic plasticity. The population has evolved reduced white in the tail. We studied contemporary patterns of selection on tail white, in the context of the altered breeding season length. Late-hatched nestlings had higher survival and were in better condition than early-hatched nestlings, but among survivors, late-hatched birds had less tail white. We suggest this reflects juvenile mortality favoring individuals with less tail white. In adults, we found weak sexual selection and no viability selection but positive selection on female tail white in association with fecundity. We argue that altered breeding season length had a major impact on patterns of selection and evolution in this population.

Song Frequency Does Not Reflect Differences in Body Size among Males in Two Oscine Species

Abstract: Large animals, having large vocal organs, produce low sound frequencies more efficiently. Accordingly, the frequency of vocalizations is often negatively related to body size across species, and also among individuals of many species, including several non-oscine birds (non-songbirds). Little is known about whether song frequency reveals information about body size within oscine species, which are characterized by song learning and large repertoires. We asked whether song frequency is related to body size in two oscines that differ in repertoire size: the dark-eyed junco (Junco hyemalis) and the serin (Serinus serinus). We also asked whether the extent to which receivers sample repertoires might influence the reliability of their assessment of body size. We found that none of the frequency traits of song that we investigated was related to male body size, nor did more extensive sampling of repertoires lead to any relationship between frequency and body size. Possible reasons for these results are the small range of variation in size within species, or the elaborate vocal physiology of oscines that gives them great control over a wide frequency range. We discuss these results as they relate to female preferences for high-frequency song that have been previously reported for oscine species.

Brain size and the diversification of body size in birds.

Abstract: Large brains are associated with increased cognitive skills, enabling animals to use new environments and resources more successfully. Such behavioral flexibility is theoretically expected to have macroevolutionary consequences. First, populations of big‐brained individuals should more easily become established in new locations, increasing opportunities for allopatric speciation and decreasing chances that the species as a whole becomes extinct. Second, the ability to use new resources should place new selection pressures on populations, promoting adaptive diversification, a process termed “behavioral drive.” In this article, we show that the average brain size of a bird family explains a significant fraction ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\c...

Reciprocal cooperation in avian mobbing: playing nice pays

Abstract: Unrelated passerine birds often join together while mobbing, a widespread antipredator behavior during which birds harass a predator. Although previous analyses concluded that mobbing could not have evolved via reciprocity, Krams and colleagues' field experiments show that birds preferentially join mobs with neighbors that have aided them previously, suggesting that these birds utilize reciprocity-based strategies involving individual recognition and recollection of previous interactions with others. This implies a level of sophistication in bird communities greater than had previously been realized.

Introduction: genetics of colonizing species.

Abstract: Successful colonization of a new location involves a fourstep process: departure from the source, dispersal across a barrier, establishment, and range expansion in the new region. The hurdles at each step mean that a restricted subset of potential source species become established in the new location (Whittaker and Fernandez-Palacios 2007). Further, among the species that do successfully colonize, these same four hurdles result in genetic differentiation from the source (Lee 2002; Gilchrist and Lee 2007). Taking advantage of the many human-aided invasions throughout the world, a massive research program now focuses on the third and fourth stages of the colonization process (i.e., establishment and range expansion in the new location). Several book-length reviews on these stages have recently appeared (Sax et al. 2005; Allen and Lee 2006; Gilchrist and Lee 2007; Lockwood et al. 2007; Nentwig 2007). New Zealand has been particularly affected by invasive species (Allen and Lee 2006), and in the classic volume Genetics of Colonizing Species, Wodzicki (1965, p. 456) noted that it “offers an excellent opportunity to study the results of a large scale introduction of exotic species and their adaptation to a new environment.” The 2007 American Society of Naturalists symposium in New Zealand therefore seemed an ideal setting to discuss advances in the genetic changes underlying invasion. We asked contributors to this symposium to focus on original research, covering the spectrum of all four stages of the colonization process.

Song Variation in a Recently Founded Population of the Dark-Eyed Junco (Junco hyemalis)

Abstract: During natural colonization events, songs are expected to change as a result of both selection and drift-like processes. We studied song variation within a small isolated population of dark-eyed juncos, Junco hyemalis, which became established in an unusual environment on the University of California at San Diego (UCSD) campus in the early 1980’s, and compared this variation with the native range. At UCSD, the average repertoire size is 4.2 song types/male, which is similar to that in the native range. There is a low level of song-type sharing across the population. Typically a male shares at least one song type with on average 40% of his neighbors, and song-type sharing decreases rapidly with distance. Thus song-type diversity is high, and in this respect appears similar to that in ancestral mountain populations. These results suggest a moderate to large number of males founded and/or subsequently immigrated into the UCSD population, but several selection mechanisms, if coupled with a high cultural mutation rate, may also favor high song-type diversity. When combined with results from a previous study, songs are significantly shorter at UCSD than in the mountain population we studied. It appears that founder effects have not influenced the evolution of songs in this population. More generally, if song-type diversity and other features of song result from various social and natural selection pressures, many of these pressures may have remained similar between the native and the recently established population.

Sensory ecology: In sight of speciation

Abstract: Adaptation of a fish's eyes to its visual environment can bias females to mate with different males according to their coloration. This sensory preference can contribute to the formation of new species.