Assortative mating also indicates that common crossbill Loxia curvirostra vocal types are species

Abstract

Compared to most other birds, the taxonomy of crossbills (Loxia) is still highly unsettled. However, much progress seems to be achievable when data on vocalisations is included. In a recent paper, Summers et al. (2007) argued that strong assortative mating indicated that parrot crossbill Loxia pytyopsittacus, Scottish crossbill Loxia scotica and common crossbill Loxia curvirostra behave as good species when breeding in sympatry. Here I argue that their data, when placed in the context of other studies, also indicate that three vocally differentiated European populations within the common crossbill are species (following the biological species concept of Mayr (1963): species are groups of interbreeding natural populations that are reproductively isolated from other such groups). If this tentative conclusion remains to be upheld, it might have large repercussions for our understanding of the speciation process as well as for a number of more applied issues such as the discovery and description of biodiversity and the conversation of mobile, cryptic species.The common (red) crossbill Loxia curvirostra has long challenged taxonomic stability and customs, and seems to continue to do so. In North America various treatments have tried to mould morphological variability into geographically defined subspecific units. However, a frequent finding was that birds collected at the same locality often varied much more in morphology than did birds collected at opposite ends of the continent, or that birds collected one year differed dramatically from birds collected another year at the same locality (reviewed in Groth 1993a). The inclusion of vocal characters has proven to be a major step forward in unravelling these unusual patterns, as is often the case for morphologically similar birds with overlapping distributions (Remsen 2005). Work by Groth and Benkman has shown that at least 9 vocal types are involved. These types differ in vocalisations, morphology, ecology and genetic markers

The multiple applications of DNA barcodes in avian evolutionary studies

“…One such case is that of the crossbills (Loxia curvirostra and L. pytyopsittacus, Johnsen et al 2010), which experienced a recent ecological speciation process with assortative mating among members within clades in relation to their bill size and calls, but with no differentiation in mitochondrial markers and microsatellites and occasional hybridization (Piertney et al 2001;Parchman et al 2006;Summers et al 2007;Edelaar 2008).…”

Repeated Evolution of Fused Thoracic Vertebrae in Songbirds

“…The notarium in Loxia has a unique developmental pattern in which the vertebral bodies fuse late or not at all, and in addition the notarium in the L. curvirostra species group is distinct from that in L. leucoptera. Further survey of the form of the notarium in this group could assist with understanding the complex pattern of population segregation and speciation in crossbills (e.g., Benkman 1993, Groth 1993, Summers et al 2007, Edelaar 2008.…”

Vocal types in crossbill populations (Loxia spp.) of Southwest Europe

“…This is especially important since recent evidence from genetic analyses suggests that there is a much lower genetic differentiation between crossbill forms than expected, even between the morphologically and behaviourally rather distinct Parrot Crossbills and Common Crossbills (Questiau et al 1999;Piertney et al 2001). It is debatable whether full species status should be given to the different crossbill forms on the basis of only vocal types (Summers et al 2007;Edelaar 2008). Interestingly, in a study on partially isolated Citril Finches Carduelis citrinella with a similar distribution to the crossbills described in this study, vocalisation patterns also differed considerably (Förschler and Kalko 2007).…”

“…The classification of crossbills has been disputed for a long time (Nethersole-Thompson 1975;Murray 1978;Tyrberg 1991;Groth 1988Groth , 1993, and is still strongly debated (Parkin 2003;Edelaar and Terpestra 2004;Parchmann et al 2006;Smith and Benkman 2007;Edelaar et al 2008;Edelaar 2008). In Europe, until the first half of the last century, three species were recognized based on morphological (bill and body size, wing pattern) and behavioural characteristics (food selection and migratory behaviour): the Common Crossbill L. curvirostra, the Parrot Crossbill L. pytyopsittacus, and the TwoBarred Crossbill L. leucoptera bifasciata.…”

“…Subsequently, six distinct vocal types, based mainly on the frequently uttered flight calls, were discovered by Robb (2000) The occurrence of these seven vocal types in the Benelux, probably representing distinct populations of crossbills, varies considerably from year to year (Edelaar and Terpestra 2004). Biometric data from crossbills captured in different years suggest that birds with different vocal types also differ in functional traits (especially in bill depth) and are apparently mating assortatively (Edelaar 2008;Edelaar et al 2008). Although it has been argued that this divergence in vocalisation and morphology might be associated with the presence of multiple, cryptic species in Europe, recent genetic analyses did not reveal any evidence for a high degree of differentiation, neither between the European subspecies and vocal types (including Scottish crossbills) nor between the distinct vocal types found in North America (Questiau et al 1999;Piertney et al 2001).…”