Phenotypic selection exerted by a seed predator is replicated in space and time and among prey species

Although consistent phenotypic selection arising from biotic interactions is thought to be the primary cause of adaptive diversification, studies documenting such selection are relatively few. Here we analyze 12 episodes of phenotypic selection exerted by a predispersal seed predator, the red crossbill (Loxia curvirostra complex), on five species of pines (Pinus). We find that even though the intensity of selection for some traits increased with the strength of the interaction (i.e., proportion of seeds eaten), the relative strength of selection exerted by crossbills on cone and seed traits is replicated across space and time and among species. Such selection (1) can account for repeated patterns of conifer cone evolution and escalation in seed defenses with time and (2) suggests that variation in selection is less the result of variation intrinsic to pairwise biotic interactions than, for example, variation in relative densities of the interacting species, community context, and abiotic factorsNational Science Foundation (DEB-0212271 and DEB-0344503), the Robert B. Berry Endowed Chair, and the Ministry of Science and Innovation of Spain (CGL2010- 15687) for financial support for our researc

Forest and cone structure influence where crossbills forage in a managed Scots pine forest

The structure of forests is a fundamental attribute that impacts biodiversity and ecosystem services and in turn is influenced by natural disturbances and management practices. Here, we examine spatial variation in the interaction between a specialized predispersal seed predator, common crossbills (Loxia curvirostra), and Scots pine (Pinus sylvestris) in relation to forest structure and tree features in a managed Mediterranean forest. Crossbills preferred to forage in pine stands that were more open, which correspond to older stands or regeneration stands with scattered old seed trees. More open older stands with larger trees tend to produce more cones that are attractive to crossbills, although their use was also consistent with crossbills reducing their risk of predation. Within these patches, crossbills selectively foraged on trees having many small, thin-scaled cones, which require less effort and time to extract the seeds. Crossbills were apparently limited to only a very small subset of the closed Scots pine cones because they have relatively small and ineffective bills for foraging on Scots pine. Given that crossbills foraged on only a small subset of the cones within more open stands, a management strategy that would aid common crossbills is to thin middle-aged stands. This would accelerate the development of older stand structure, which would benefit crossbills by increasing the occurrence of suitably open woodlands, benefit other species that rely on older more open stand structure, and potentially decrease the vulnerability of the forest to fire and droughtWe thank C. Ferrini, E. García and P. Acebes for field assistance, P. Edelaar and R. Summers for helpful comments on the manuscript, and Centro de Montes y Aserradero de Valsaín (Organismo Autónomo de Parques Nacionales) for providing information and the LiDAR data. The REMEDINAL 3-CM research network (S2013/mae-2719) partially funded this research. ETM was supported by “Convenio Comunidad de Madrid y Universidad Autónoma de Madrid en Línea 3: Excelencia del Profesorado Universitario” during the writing and publication process

Survival and population size of a resident bird species are declining as temperature increases

Summary 1. A large number of migratory bird species appear to be declining as the result of climate change, but whether resident bird species have or will be adversely affected by climate change is less clear. We focus on the South Hills crossbill (Loxia curvirostra complex), which is endemic to about 70 km 2 of Rocky Mountain lodgepole pine (Pinus contorta latifolia) forest in southern Idaho, USA. 2. Our results indicate that the South Hills crossbill has declined by over 60% between 2003 and 2008, and that decreasing adult survival drives this population decline. 3. We evaluated the relative support for multiple hypotheses linking crossbill survival to climate, an ectoparasitic mite (scaly-leg mites Knemidokoptes jamaicensis), and the recent emergence of West Nile virus. Changes in adult apparent survival rate were closely associated with average spring and annual temperatures, and with high temperatures ( ‡32°C) during summer, which have increased during the last decade. In contrast, there was little evidence that scaly-leg mites or West Nile virus contributed to recent declines in adult survival. 4. The most probable mechanism causing the decline in adult survival and population size is a decrease in the availability of their primary food resource, seeds in serotinous pine cones. Cone production has declined with increasing annual temperatures, and these cones appear to be prematurely opening owing to increasingly hot summer conditions releasing their seeds and reducing the carrying capacity for crossbills later in the year. 5. In light of regional climate change forecasts, which include an increase in both annual temperature and hot days (>32°C), and the likely disappearance of lodgepole pine from southern Idaho by the end of this century, additional research is needed to determine how to maintain lodgepole pine forests and their supply of seeds to conserve one of the few bird species endemic to the continental United States

Transcriptome sequencing in an ecologically important tree species: assembly, annotation, and marker discovery

<p>Abstract</p> <p>Background</p> <p>Massively parallel sequencing of cDNA is now an efficient route for generating enormous sequence collections that represent expressed genes. This approach provides a valuable starting point for characterizing functional genetic variation in non-model organisms, especially where whole genome sequencing efforts are currently cost and time prohibitive. The large and complex genomes of pines (<it>Pinus </it>spp.) have hindered the development of genomic resources, despite the ecological and economical importance of the group. While most genomic studies have focused on a single species (<it>P. taeda</it>), genomic level resources for other pines are insufficiently developed to facilitate ecological genomic research. Lodgepole pine (<it>P. contorta</it>) is an ecologically important foundation species of montane forest ecosystems and exhibits substantial adaptive variation across its range in western North America. Here we describe a sequencing study of expressed genes from <it>P. contorta</it>, including their assembly and annotation, and their potential for molecular marker development to support population and association genetic studies.</p> <p>Results</p> <p>We obtained 586,732 sequencing reads from a 454 GS XLR70 Titanium pyrosequencer (mean length: 306 base pairs). A combination of reference-based and <it>de novo </it>assemblies yielded 63,657 contigs, with 239,793 reads remaining as singletons. Based on sequence similarity with known proteins, these sequences represent approximately 17,000 unique genes, many of which are well covered by contig sequences. This sequence collection also included a surprisingly large number of retrotransposon sequences, suggesting that they are highly transcriptionally active in the tissues we sampled. We located and characterized thousands of simple sequence repeats and single nucleotide polymorphisms as potential molecular markers in our assembled and annotated sequences. High quality PCR primers were designed for a substantial number of the SSR loci, and a large number of these were amplified successfully in initial screening.</p> <p>Conclusions</p> <p>This sequence collection represents a major genomic resource for <it>P. contorta</it>, and the large number of genetic markers characterized should contribute to future research in this and other pines. Our results illustrate the utility of next generation sequencing as a basis for marker development and population genomics in non-model species.</p

The Auk FEEDING BEHAVIOR, FLOCK-SIZE DYNAMICS, AND VARIATION IN SEXUAL SELECTION IN CROSSBILLS

ABSTRACT.--I present field data on feeding and scanning behavior of White-winged Crossbills (Loxia leucoptera) in relation to flock size. Feeding rates increased and individual levels of vigilance decreased as flock size increased from one to two. Further increases in flock size did not correspond with substantial reductions in individual vigilance, but did correspond with frequent agonistic interactions. As rates of agonistic interactions increased, feeding rates of subordinate age-sex classes (e.g. adult females) declined relative to those of dominant age-sex classes (e.g. adult males). Females (and immatures) may have reduced this effect by avoiding flocks composed mostly of adult males. Assortative flocking occurred in the nonbreeding period (late November to December), but during breeding periods (September and potentially rest of year) the numbers of each age-sex class tended to be positively correlated. Rates of agonistic interactions were higher when crossbills foraged on conifers whose cones were compactly dispersed. Flocks were smaller when rates of agonistic interactions were high and conifers had compact cone dispersions. Flock size increased as seed density declined. Larger flocks, with high levels of collective vigilance, were favored because feeding rate and the time spent scanning while seeds were husked also declined. Crossbills (Loxia spp-) that forage on small-crowned conifers are more sexually dichromatic and have other traits indicating stronger sexual selection than crossbills that forage on large-crowned conifers. I suggest that these differences result from differences in rates of agonistic interactions, which influence female feeding rates compared with male feeding rates, and likely have a differential effect on female mortality rates and the population sex ratio. Received 21 June 1996, accepted 17 December 1996. FORAGING COSTS AND BENEFITS, as a function of group size, have been the focus of many studie

Basal area of lodgepole pine at 67 locations in South Hills

This file contains the data used to estimate basal area at 67 locations in the South Hills, Idaho in 2002 and 2013. The first column is plot identifier, then its latitude, longitude, numbers of lodgepole pine within a 20-m radius in 2002 and 2013, the mean DBH of the these trees, and estimated basal areas

Data from: Matching habitat choice in nomadic crossbills appears most pronounced when food is most limiting

Of the various forms of non-random dispersal, matching habitat choice, whereby individuals preferentially reside in habitats where they are best adapted, has relatively little empirical support. Here I use mark-recapture data to test for matching habitat choice in two nomadic ecotypes of North American Red Crossbills (Loxia curvirostra complex) that occur in the lodgepole pine (Pinus contorta) forests in the South Hills, Idaho every summer. Crossbills are adapted for foraging on seeds in conifer cones, and in the South Hills the cones are distinctive, favoring a relatively large bill. During a period when seed was most limiting, only the largest individuals approximating the average size of the locally adapted ecotype remained for a year or more. During a period when seed was less limiting, proportionately more individuals remained and the trend for larger individuals to remain was weaker. Although matching habitat choice is difficult to demonstrate, it likely contributed to the observed patterns. Otherwise, nearly unprecedented intensities of natural selection would be needed. Given the nomadic behavior of most crossbill ecotypes and the heterogeneous nature of conifer seed crops, matching habitat choice should be favored and likely contributes to their adaptation to alternative conifers and rapid diversification

Data from: The natural history of the South Hills crossbill in relation to its impending extinction

Increasingly, the species that we discover will be uncommon, area restricted, and vulnerable to extinction. I describe the natural history of a newly discovered seed-eating finch from the Rocky Mountain region, the South Hills crossbill (Loxia curvirostra complex). It relies on seeds in the closed cones of the fire-adapted Rocky Mountain lodgepole pine (Pinus contorta latifolia) and is found only in the higher elevations of two small mountain ranges in southern Idaho. Here crossbills and pine are engaged in a coevolutionary arms race. Although most of the seeds remain secured within the cones for decades until the heat of a stand-replacing fire causes the cone scales to separate, seeds become accessible to crossbills slowly as cones weather and gaps form between some of the scales. However, hot days (≥32°C), especially four or more hot days, seem to mimic the effect of fire, apparently causing the immediate release of a fraction of the seeds. Such events caused a 20% annual decline in crossbills that lasted up to 4 years and an 80% decline in the population between 2003 and 2011. This is an example of a novel trophic mismatch between a consumer and its resource caused by a shift in the phenology of the resource arising from climate change. Not only do these phenological shifts have the potential to cause seed consumers to decline, these shifts are also likely to cause reduced recruitment of the plants. The South Hills crossbill is especially vulnerable and will likely go extinct this century before lodgepole pine is extirpated from the South Hills