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New and Exciting in PLoS Biology

Loss of Egg Yolk Genes in Mammals and the Origin of Lactation and Placentation:

Egg yolk contains the nutrients required for the development of the nonmammalian vertebrate embryo. These nutrients derive by and large from a single set of proteins, vitellogenins, which are produced in the liver and provide or transport amino acids, lipids, phosphorous, and calcium to the egg. Mammals have evolved new nutritional resources for their developing and early offspring, such as lactation and placentation. However, the evolutionary timing and molecular events associated with this major phenotypic transition are not well understood. In this study, we have investigated the evolutionary fate of the three ancestral vitellogenin-encoding genes in mammals. Using detailed evolutionary analyses of genomes from the three major mammalian lineages (eutherian “placental” mammals, marsupials, and monotremes), we found that these genes progressively lost their functions and became pseudogenes relatively recently during mammalian evolution (the most recent inactivation event occurred roughly 30-70 million years ago). Monotremes, which lactate yet lay small parchment-shelled eggs, even retained a functional vitellogenin gene, consistent with their intermediate reproductive state. Our analyses also provide evidence that the major milk resource genes, caseins, which have similar functional properties as vitellogenins, appeared in the common mammalian ancestor ∼200-310 million years ago. Based on our data, we suggest that the emergence of the alternative resources for the mammalian young–lactation and then placentation–only gradually reduced the need for egg yolk resources (and hence functional vitellogenin genes) in mammals.

See also the synopsis, For Mammals, Loss of Yolk and Gain of Milk Went Hand in Hand, and blog posts, Got Milk? Lactation and Placentation Replace Yolky Eggs, Got yolk?, Which came first, the mammalian breast or the placenta? and Reproductive history writ in the genome

Change the IUCN Protected Area Categories to Reflect Biodiversity Outcomes:

In 1872, United States President Ulysses Grant set aside 2.2 million acres of wilderness, primarily for recreational purposes, as the first formally recognized protected area (PA)–Yellowstone National Park. The concept took hold slowly over the next hundred years, and PAs are now recognized as essential to biodiversity conservation [1] and as irreplaceable tools for species and habitat management and recovery. Today, over 100,000 sites (11.5% of the Earth’s land surface) are listed in the World Database on Protected Areas [2]. PAs have always been recognized as having broad roles, but it wasn’t until the 1990s that the International Union for the Conservation of Nature (IUCN) included the role of conserving biodiversity in its definition: “An area of land and/or sea especially dedicated to the protection and maintenance of biological diversity, and of natural and associated cultural resources, and managed through legal or other effective means” [3].

See also this blog post: Issues for the IUCN: Redefining Protected Areas

Social Context-Induced Song Variation Affects Female Behavior and Gene Expression:

Vocal communication in many species, including humans, is affected by social cues. In the zebra finch, for example, males make subtle changes to the length, tempo, and variability of their courtship songs (directed songs) relative to songs performed in isolation (undirected songs). Using a behavioral approach assay, we found that female zebra finches strongly prefer the sound of directed over undirected song. Interestingly, female preferences were influenced by the variability of note pitch, showing stronger preferences for directed songs when they were less variable in pitch than the undirected songs. Pitch variability is controlled by a forebrain-basal ganglia circuit, which may represent a neural substrate on which selection acts to shape behavior. Preference for directed song was also increased when the singer was familiar to the listener, suggesting that song preferences are enhanced by experience. Based on the expression of an immediate early gene associated with memory formation and plasticity, we found that two high-level auditory areas were differentially responsive to the category of song females heard, with one area responding to whether songs were directed or undirected, and a second area to whether songs were familiar or unfamiliar. Together, these data demonstrate that females detect and prefer the male’s changed performance during courtship singing and suggest that neurons in high-level auditory areas are involved in this social perception.