Still working on my review of Science and Human Origins (yes, I have been somewhat lazy when it comes to blogging) in the meantime enjoy the following items.
PNAS has an interesting article on the development of beaks in Darwin’s finches – and related species – called Closely related bird species demonstrate flexibility between beak morphology and underlying developmental programs. Here is the abstract:
The astonishing variation in the shape and size of bird beaks reflects a wide range of dietary specializations that played an important role in avian diversification. Among Darwin’s finches, ground finches (Geospiza spp.) have beaks that represent scaling variations of the same shape, which are generated by alterations in the signaling pathways that regulate growth of the two skeletal components of the beak: the prenasal cartilage (pnc) and the premaxillary bone (pmx). Whether this developmental mechanism is responsible for variation within groups of other closely related bird species, however, has remained unknown. Here, we report that the Caribbean bullfinches (Loxigilla spp.), which are closely related to Darwin’s finches, have independently evolved beaks of a novel shape, different from Geospiza, but also varying from each other only in scaling. However, despite sharing the same beak shape, the signaling pathways and tissues patterning Loxigilla beaks differ among the three species. In Loxigilla noctis, as in Geospiza, the pnc develops first, shaped by Bmp4 and CaM signaling, followed by the development of the pmx, regulated by TGFβIIr, β-catenin, and Dkk3 signaling. In contrast, beak morphogenesis in Loxigilla violacea and Loxigilla portoricensis is generated almost exclusively by the pmx through a mechanism in which Ihh and Bmp4 synergize to promote expansion of bone tissue. Together, our results demonstrate high flexibility in the relationship between morphology and underlying developmental causes, where different developmental programs can generate identical shapes, and similar developmental programs can pattern different shapes.
Nature Communications has an interesting paper called Genetic architecture supports mosaic brain evolution and independent brain–body size regulation. Here is the abstract:
The mammalian brain consists of distinct parts that fulfil different functions. Finlay and Darlington have argued that evolution of the mammalian brain is constrained by developmental programs, suggesting that different brain parts are not free to respond individually to selection and evolve independent of other parts or overall brain size. However, comparisons among mammals with matched brain weights often reveal greater differences in brain part size, arguing against strong developmental constraints. Here we test these hypotheses using a quantitative genetic approach involving over 10,000 mice. We identify independent loci for size variation in seven key parts of the brain, and observe that brain parts show low or no phenotypic correlation, as is predicted by a mosaic scenario. We also demonstrate that variation in brain size is independently regulated from body size. The allometric relations seen at higher phylogenetic levels are thus unlikely to be the product of strong developmental constraints.
The relevance to human evolution is obvious.
Finally, Evolutionary Ecology has an interesting paper called Geographic distribution of the anti-parasite trait “slave rebellion”. Here is the abstract:
Social parasites exploit the brood care behavior of other species and can exert strong selection pressures on their hosts. As a consequence, hosts have developed defenses to circumvent or to lower the costs of parasitism. Recently, a novel, indirect defense trait, termed slave rebellion, has been described for hosts of a slave-making ant: Enslaved Temnothorax longispinosus workers reduce local parasite pressure by regularly killing pupae of their obligatory slavemaking parasite Protomognathus americanus. Subsequently, growth of social parasite nests is reduced, which leads to fewer raids and likely increases fitness of neighboring related host colonies. In this study, we investigate the presence and expression the slave rebellion trait in four communities. We report its presence in all parasitized communities, document strong variation in its expression between different geographic sites and discuss potential explanations for this observed variation.