Beak and skull shapes of human commensal and non-commensal house sparrows Passer domesticus

這一篇挺有趣的。家麻雀(Passer domesticus)從一萬年前中亞農業起源時就與人類生存在一起。並且數千年來與人類及農業的發展，擴張到歐亞各地(註: 美洲的家麻雀是引進種)。其中一個亞種 P. d. bactrianus分布於中亞，維持得古老的生活史特徵，棲息於原生草地及溼地，只取食野草的種子。隨著農業的發展，稻穀的顆粒越來越大顆且飽滿，作者群認為家麻雀的鳥喙和顱骨應該會變得更大更強壯，才有辦法吃這些人類種出來的穀粒。於是他們在伊朗量了五個家麻雀亞種(包含 P. d. bactrianus)的顱骨和鳥喙，發現與人類共存的亞種，鳥喙和顱骨確實比 P. d. bactrianus來的大且強壯。人類的農業發展，牽引了鳥類的演化。

Abstract
Background
The granivorous house sparrow Passer domesticus is thought to have developed its commensal relationship with humans with the rise of agriculture in the Middle East some 10,000 years ago, and to have expanded with the spread of agriculture in Eurasia during the last few thousand years. One subspecies, P. d. bactrianus, residing in Central Asia, has apparently maintained the ancestral ecology, however. This subspecies is not associated with human settlements; it is migratory and lives in natural grass- and wetland habitats feeding on wild grass seeds. It is well documented that the agricultural revolution was associated with an increase in grain size and changes in seed structure in cultivated cereals, the preferred food source of commensal house sparrow. Accordingly, we hypothesize that correlated changes may have occurred in beak and skull morphology as adaptive responses to the change in diet. Here, we test this hypothesis by comparing the skull shapes of 101 house sparrows from Iran, belonging to five different subspecies, including the non-commensal P. d. bactrianus, using geometric morphometrics.

Results
The various commensal house sparrow subspecies share subtle but consistent skeletal features that differ significantly from those of the non-commensal P. d. bactrianus. Although there is a marked overall size allometry in the data set, the shape difference between the ecologically differentiated sparrows cannot be explained by differences in size alone. Relative to the size allometry commensal house sparrows exhibit a skull shape consistent with accelerated development (heterochrony), resulting in a more robust facial cranium and a larger, more pointed beak.

Conclusion

The difference in skull shape and robustness of the beak between commensal and non-commensal house sparrows is consistent with adaptations to process the larger and rachis encapsulated seeds of domesticated cereals among human associated populations.