| diversifying coevolution between crossbills and black spruce on newfoundland. | coevolution is increasingly recognized as an important process structuring geographic variation in the form of selection for many populations. here we consider the importance of a geographic mosaic of coevolution to patterns of crossbill (loxia) diversity in the northern boreal forests of north america. we examine the relationships between geographic variation in cone morphology, bill morphology, and feeding performance to test the hypothesis that, in the absence of red squirrels (tamiasciurus h ... | 2002 | 12353759 |
| physiological responses to photoperiod in three cardueline finch species. | cardueline finches (canaries, goldfinches, and rosefinches, etc.) vary widely in the degree to which their natural reproductive schedules track seasonal changes in photoperiod. in this study, we tested for photo-induction of reproductive development and photorefractoriness in males of three cardueline finch species: pine siskins (carduelis pinus), common redpolls (carduelis flammea), and white-winged crossbills (loxia leucoptera). exposure to long days (20l:4d) in winter induced gonadal growth a ... | 2004 | 15094340 |
| interspecific variation in photo-induced gnrh plasticity among nomadic cardueline finches. | changes in response to photoperiod are of fundamental importance to seasonal cycles in avian reproductive development. in this study we present data on photo-induced changes in gonadotropin-releasing hormone (gnrh) immunoreactivity associated with the development of photorefractoriness in males of 3 closely related species of cardueline finch: common redpoll (carduelis flammea), pine siskin (c. pinus) and white-winged crossbill (loxia leucoptera). all are nomadic, mid- to high-latitude breeders ... | 2005 | 15821347 |
| patterns of genetic variation in the adaptive radiation of new world crossbills (aves: loxia). | incipient species groups or young adaptive radiations such as crossbills (aves: loxia) present the opportunity to investigate directly the processes occurring during speciation. new world crossbills include white-winged crossbills (loxia leucoptera), hispaniolan crossbills (loxia megaplaga), and red crossbills (loxia curvirostra complex), the last of which is comprised of at least nine morphologically and vocally differentiated forms ('call types') where divergent natural selection for specializ ... | 2006 | 16689904 |
| coevolution between hispaniolan crossbills and pine: does more time allow for greater phenotypic escalation at lower latitude? | crossbills (aves: loxia) and several conifers have coevolved in predator-prey arms races over the last 10,000 years. however, the extent to which coevolutionary arms races have contributed to the adaptive radiation of crossbills or to any other adaptive radiation is largely unknown. here we extend our previous studies of geographically structured coevolution by considering a crossbill-conifer interaction that has persisted for a much longer time period and involves a conifer with more variable a ... | 2007 | 17767586 |
| blood parasitaemia in a high latitude flexible breeder, the white-winged crossbill, loxia leucoptera: contribution of seasonal relapse versus new inoculations. | we measured seasonal changes in the prevalence of haematozoa (leucocytozoon fringillinarum, haemoproteus fringillae, and trypanosoma avium) in free-ranging white-winged crossbills, loxia leucoptera, over 1.5 year in fairbanks, alaska, usa. this prevalence was low during early winter. l. fringillinarum prevalence increased in late winter/early spring, in the absence of vectors, suggesting relapse of latent infection. by contrast, the prevalence of t. avium and h. fringillae did not increase until ... | 2010 | 19849885 |
| seasonal changes in brain gnrh immunoreactivity and song-control nuclei volumes in an opportunistically breeding songbird. | white-winged crossbills (loxia leucoptera) are opportunistic breeders that can nest at almost any time of year if there is sufficient food. other cardueline finches that have been shown to breed on a strictly seasonal schedule become absolutely refractory to the stimulatory effects of long-day photoperiod, dramatically down-regulate hypothalamic gonadotropin-releasing hormone (gnrh), and reduce the volume of several song-control nuclei in autumn. this study examined whether changes in photoperio ... | 2001 | 11799277 |
| reproductive endocrinology of a free-living, opportunistically breeding passerine (white-winged crossbill, loxia leucoptera). | the aim of the study was to investigate, in a free-living opportunistic breeder, the white-winged crossbill (loxia leucoptera), the degree to which annual changes in photoperiod and differences in the timing of breeding in different years correlate with the secretion of reproductive hormones. seasonal changes in concentrations of luteinizing hormone (lh) and prolactin were compared in white-winged crossbills in interior alaska (64 degrees 50'n, 147 degrees 50'w) in plasma samples taken in may-de ... | 2001 | 11589628 |