Palaeobiogeography of Crossbills (Loxia spp.) and their Food Plants

Abstract

Crossbills (Loxia spp.) are members of the finch family (Fringillidae) and have a primarily granivorous diet, feeding on the seeds of conifers, specifically members of the family Pinaceae. Studies of the five extant crossbill species are abundant due to the distinctive evolution of their crossed mandibles, specifically adapted for a coniferous seed diet. Many have attempted to understand their evolutionary origins and speciation but the complexity of Loxia’s phylogeography and movement patterns have made it difficult to gain an accurate understanding. Although many hypotheses have been proposed, substantial evidence has yet to be found.

This study aims investigates the palaeobiogeography of the five species of crossbill, as well as their specific food trees, in order to better understand their past movements and the impacts of these on the evolutionary history of the genus. By combining several different techniques of climate-based niche modelling with global palaeoclimatic simulations, potential ranges of crossbills and their food plants have been simulated for the last 120 thousand years. These simulations have also been compared to available crossbill fossil records, pollen data and other palaeovegetation models.

The results indicate that significant species’ specific population range shifts are likely to have occurred in response to climatic change throughout this period. The simulations have provided valuable insight into the evolution of Loxia taxa, particularly isolated island populations or races, supporting existing evolutionary theories in addition to introducing novel hypotheses.