Pattern and process in sexual selection in birds
Much of my research has involved the role of sexual dimorphic 'ornaments' in the interactions between individual animals. In particular, most of this work was done in the context of determining whether sexual ornaments are signals of individual condition and how ornaments influence the behaviors of competitors and potential mates.
Some completed projects:
1. With David Ligon, my PhD supervisor at the University of New Mexico, I demonstrated the central role played by social interactions in determining steroid hormone levels and the expression of sexual signals in red junglefowl (Gallus gallus).
2. In collaboration with Dany Garant, I identified and quantified heritability of comb size in red junglefowl and its strong genetic correlation with a body condition index, as predicted by the hypothesis of capture of genetic variance in condition by sexually-selected signals.
3. I demonstrated that female red junglefowl adjust maternal investment in response to experimentally manipulated mate appearance by laying larger clutches of eggs for more attractive males.
4. I found that the area of melanin-pigmented black plumage on the cap of Kentucky Warblers (Oporornis formosus) was greater in older males and in heavier males (controlling for body size), and that males with more black on their caps were more likely to attract a mate.
5. As my portion of a collaborative effort with Simon Griffith and Valerie Olson, I used meta-analysis to demonstrate that melanin-pigmented and carotenoid-pigmented plumage ornaments in birds did not differ in their susceptibility to experimental manipulations of condition. Further I found evidence of a bias against the publication of results that failed to support predictions of condition-dependent signaling.
6. Iain Barr and I, in collaboration with Simon Griffith showed that a number of song variables previously identified as condition signals in the blue tit (Cyanistes caeruleus) do not show consistent relationships to condition across studies, and that the limited set of song variables which may signal condition do so only weakly.
7. My collaborators and I showed that fecundity selection on plumage color in our population of blue tits (Cyanistes caeruleus) was weak and variable. Selection varied as a function of nesting density and oak density, but not in a consistent pattern. Further, selection gradients typically were neither positive nor stabilizing, and were thus counter to prediction.
Patch area and edge effects on the occurrence patterns of forest songbirds
In 2002-2003 I worked closely with Brooke Stansberry, an MS student I supervised at Kansas State University, studying forest-nesting, migrant birds. The most important part of this work ended up being a meta-analysis of published studies to determine edge and small-patch avoidance patterns across a large number of migrant forest bird species in Eastern North America. See my publication list for a link to the appendices to our Conservation Biology paper on this topic. A major result included our observations that in forest dominated landscapes, almost no forest-nesting bird species appear to avoid edges, but in landscapes not dominated by forests, many forest-nesting bird species appear to avoid smaller forest patches and/or edges.
Several alternative explanations exist for this result. One hypothesis we proposed is that larger forest patches end up with higher densities of forest birds through the process of conspecific attraction - preferential recruitment into already occupied locations. Since the publication of our paper, empirical support for this mechanism as a link between patch area and bird density has been growing.
Nest abandonment by Bell's Vireos: an adaptation to brood parastism?
When conducting my MS thesis work I observed that Bell's Vireo (Vireo bellii) frequently abandoned their nests when brood-parasitic Brown-headed Cowbird (Molothrus ater) eggs appeared. If a cowbird hatches in a vireo nest, the cowbird chick usually obtains more or less all the food, and the vireo chicks typically starve to death. Thus I first thought that the vireos were abandoning parasitized nests as an adaptation evolved in response to this strong selection pressure. However, the number of cowbird eggs laid in a nest was not a good predictor of abandonment. Instead, the number of vireo eggs remaining in the nest (cowbirds often remove host eggs) predicted abandonment, suggesting that vireo behavior might best be explained as a response to egg loss. Vireos typically failed to abandon parasitized nests, and thus resigned themselves to tending a doomed nest, unless cowbirds removed a sufficient proportion of the clutch. Because abandonment in response to egg loss is a behavior shared by most bird species, it is likely an ancestral trait in Bell's vireos and not evolved as a unique response to cowbird parasitism.
In 2005-2006 I collaborated with Karl Kosciuch, whose dissertation focused on this system, and Karl's PhD supervisor Brett Sandercock. Karl's large correlative data set supported my original observations, and experiments we designed and implemented in spring 2005 supported the conclusion that Bell's Vireos do not recognize or respond to cowbird eggs, but instead abandon their nests when a sufficient proportion of the clutch is removed by cowbirds. Remarkably, loss of host eggs explained nearly all the variation in abandonment of parasitized nests within and among pairs. This raises the interesting question of why a species that pays such a high cost of being parasitized by cowbirds, and has presumably co-existed with cowbirds for a long time, has not evolved behaviors that would more effectively reduce the costs of cowbird parasitism.
Cultural evolution in a landscape context
-Geographic patterns of song sharing in dickcissels
In many bird species, distinct vocal neighborhoods develop in which neighbors closely resemble each other in song types. We know that social learning coupled with limited dispersal are sufficient to promote the development of this phenomenon, but there has been only limited empirical exploration of the habitat or population processes that lead to the strikingly different patterns and scales of song sharing among, and even within, species.
Since 2005, Bill Jensen and I, along with a series of undergraduate students, have been exploring song sharing in the dickcissel (Spiza americana), a Neotropical migrant songbird and one of the most common grassland birds breeding in the central United States. The students who have worked on this project, Perry Williams, Derek Schook, Anthony Dalisio, Amy Strauss, Cory Castro, Gabriella Sterne, Brian Kearns, Cecily Foo, Kristin Ballinger, Hanna Kahl, Eric Ross, and Marci Parra have all participated through an REU program in the Division of Biology at Kansas State University. Thanks to their hard work, we have started to develop a more sophisticated understanding of geographic variation in dickcissel song. Within an area of continuous habitat (Konza Prairie Biological Station) adjacent dickcissel males sing nearly identical songs, but there is a steady decline in similarity with distance such that males several km apart have many differences in their songs. These differences are both qualitative, in the form of different elements, and quantitative, in the form of changes in note frequency and duration within elements. Furthermore, we found dramatically different patterns of song sharing in different landscapes with different patterns of habitat.
We have continued to investigate song sharing in dickcissels, and we are currently analyzing our extensive data sets.
-We have shown that male dickcissels respond equally strongly to playback of foreign and local song, suggesting that dialect conformity does not confer an advantage when defending a territory. This work is in press.
-We found that male dickcissels direct much less aggression towards playback of song from adjacent neighbors than non-neighbor local song or foreign song, demonstrating that male dickcissels can discriminate among songs even from within dialects in which songs vary very little from male to male. This work is in press.
We are currently analyzing data to answer questions such as the following:
-How do different habitat patterns influence dickcissel population processes potentially relevant to song learning, and how does this lead to different patterns of song sharing among landscapes?
-How does vocal culture change over time as a function of habitat effects on population processes such as site fidelity and territory connectivity?
-Is their a role for female choice promoting conformity to neighborhood dialect?
This work has also led to an ongoing cross-species meta-analaysis to explain variation in the responses of territorial songbirds to playback of local vs. foreign dialects.
Obstacles to robust inference in biology
While examining the extensive literature on sexual selection in blue tits, it seemed to me that published results did not produce a coherent picture of the signaling role of plumage color in this species. I like quantification, so I decided to conduct meta-analyses to see if I could derive robust conclusions from this literature. With >50 papers published containing >1000 statistical effects, there appeared to be ample material for such analyses. Remarkably, the meta-analyses did not strongly support any conclusions beyond the almost trivial observation that male blue tits are more intensely colored than females.
So how could we have spent so much time and money studying this species and not have learned more? There's no one answer to this question, but I've identified several issues that appear to plague this body of research and probably hinder progress throughout evolutionary biology and beyond. These problems include insufficient replication and a variety of frequent practices expected to make Type I error (acceptance of false hypotheses) common.
In my paper (Biological Reviews 2013), I review some ideas for increasing the quality of inference and thus the effectiveness of progress in evolutionary biology. Human behavior is influenced by incentives, and the current incentive structures facing evolutionary biologists do not favor decisions that optimize empirical progress. It is within our power as a scientific community to change these incentive structures, for instance by adopting editorial and funding policies that more highly value replication, changing data reporting standards at journals, and developing and promoting hypothesis registries.
Since publishing this paper, I have been working towards improving incentive structures in evolutionary biology and ecology. To this end, Shinichi Nakagawa and I published a paper (Frontiers in Ecology and Evolution 2014) describing efforts underway in psychology and elsewhere to reduce type I error and promote replication. We followed this up with another article making the case for the importance of replication and the need to shape incentive structures to promote more replication (BMC Biology 2015). The two of us joined with Jessica Gurevich to organize a workshop to further this agenda. At the workshop, attended by editors of many high profile journals in ecology and evolution as well as researchers interested in transparency, there was strong support for the recently published Transparency and Opennness Promotion (TOP) guideiness designed to be useful across empirical disciplines. The workshop also produced the Tools for Transparency in Ecology and Evolution (TTEE), designed to help journals in ecology and evolutionary biology implement TOP guidelines. At this point, a number of journals represented at the workshop have become signatories to TOP, and most of these have also agreed to either sign on to a joint editorial or to publish their own editorial endorsing TOP. Editors of most other journals represented at the workshop are currently assessing how best to promote transparency. In a related effort to raise awareness of these issues, I worked with several collaborators to write a paper, now published in Trends in Ecology and Evolution, that presents empirical evidence indicating that insufficient transparency is a widespread and serious problem through much of ecology and evolutionary biology. That TREE paper also describes how institutions can adopt policies, such as TOP, to promote transparency. Although most of my work on transparency has focussed on promoting institutional change, I was also happy to join an effort led by Wolfgang Forstmeier to provide guidance to individual scientists on how to best avoid the bias that often results from insufficient transparency. This resulted in a paper now in press at Biological Reviews.
I am also working on other collaborative projects that emerged from the workshop as well as a replication case study, again using blue tits. With the blue tits, I'm comparing field data from my collaborative work with Simon Griffith and others with previously published work on the costs of reproduction in this species to explore challeges to replication and to generate a more robust understanding of reproductive costs as measured through brood size manipulations. Much of my other ongoing empirical work on transparency involves collaboartive 'meta-research' with Fiona Fidler and Shinichi Nakagawa. These projects are mostly in their early stages.
I'm now also involved in several formal efforts to promote transparency in ecology, evolutionary biology, and beyond.