Contributions of the hippocampus and medial prefrontal cortex to energy and body weight regulation

The effects of selective ibotenate lesions of the complete hippocampus (CHip), the hippocampal ventral pole (VP), or the medial prefrontal cortex (mPFC) in male rats were assessed on several measures related to energy regulation (i.e., body weight gain, food intake, body adiposity, metabolic activity, general behavioral activity, conditioned appetitive responding). The testing conditions were designed to minimize the nonspecific debilitating effects of these surgeries on intake and body weight. Rats with CHip and VP lesions exhibited significantly greater weight gain and food intake compared with controls. Furthermore, CHip-lesioned rats, but not rats with VP lesions, showed elevated metabolic activity, general activity in the dark phase of the light-dark cycle, and greater conditioned appetitive behavior, compared with control rats without these brain lesions. In contrast, rats with mPFC lesions were not different from controls on any of these measures. These results indicate that hippocampal damage interferes with energy and body weight regulation, perhaps by disrupting higher-order learning and memory processes that contribute to the control of appetitive and consummatory behavior.     

Innate development of acoustic signals for host parent–offspring recognition in the brood‐parasitic Screaming Cowbird Molothrus rufoaxillaris

Young birds communicate their need to parents through complex begging displays that include visual and acoustic cues. Nestlings of interspecific brood parasites must ‘tune’ into these communication channels to secure parental care from their hosts. Various studies show that parasitic nestlings can effectively manipulate host parental behaviour through their begging calls, but how these manipulative acoustic signals develop in growing parasites remains poorly understood. We investigated the influence of social experience on begging call development in a host‐specialist brood parasite, the Screaming Cowbird Molothrus rufoaxillaris. Screaming Cowbird nestlings look and sound similar to those of the primary host, the Greyish Baywing Agelaioides badius. This resemblance is likely to be adaptive because Baywings discriminate against fledglings unlike their own and provision nests at higher rates in response to Baywing‐like begging calls than to non‐mimetic begging calls. By means of cross‐fostering and playback experiments, we tested whether the acoustic cues that elicit recognition by Baywings develop innately in Screaming Cowbird nestlings or are acquired through social experience with host parents or nest mates. Our results suggest that begging call structure was partially modulated by experience because Baywing‐reared Screaming Cowbird and host nestlings were acoustically more similar as age increased, whereas acoustic similarity between cross‐fostered and Baywing‐reared Screaming Cowbird nestlings decreased from 4–5 to 8–10 days of age. Cross‐fostered Screaming Cowbirds developed begging calls of lower minimum frequency and broader bandwidth than those of Baywing‐reared Screaming Cowbirds by the age of 8–10 days. Despite the observed differences in begging call structure, however, adult Baywings responded similarly to begging calls of 8‐ to 10‐day‐old cross‐fostered and Baywing‐reared Screaming Cowbirds, suggesting that these were functionally equivalent from the host's perspective. These findings support the idea that, although rearing environment can influence certain begging call parameters, the acoustic cues that serve for offspring recognition by Baywings develop in young Screaming Cowbirds independently of social experience.     

Recent horizontal transfer of a mariner transposable element among and between Diptera and Neuroptera

Transposable elements of the mariner family are widespread among insects and other invertebrates, and initial analyses of their relationships indicated frequent occurrence of horizontal transfers between hosts. A specific PCR assay was used to screen for additional members of the irritans subfamily of mariners in more than 400 arthropod species. Phylogenetic analysis of cloned PCR fragments indicated that relatively recent horizontal transfers had occurred into the lineages of a fruit fly Drosophila ananassae, the horn fly Haematobia irritans, the African malaria vector mosquito Anopheles gambiae, and a green lacewing Chrysoperla plorabunda. Genomic dot-blot analysis revealed that the copy number in these species varies widely, from about 17,000 copies in the horn fly to three copies in D. ananassae. Multiple copies were sequenced from genomic clones from each of these species and four others with related elements. These sequences confirmed the PCR results, revealing extremely similar elements in each of these four species (greater than 88% DNA and 95% amino acid identity). In particular, the consensus sequence of the transposase gene of the horn fly elements differs by just two base pairs out of 1,044 from that of the lacewing elements. The mosquito lineage has diverged from the other Diptera for over 200 Myr, and the neuropteran last shared a common ancestor with them more than 265 Myr ago, so this high similarity implies that these transposons recently transferred horizontally into each lineage. Their presence in only the closest relatives in at least the lacewing lineage supports this hypothesis. Such horizontal transfers provide an explanation for the evolutionary persistence and widespread distribution of mariner transposons. We propose that the ability to transfer horizontally to new hosts before extinction by mutation in the current host constitutes the primary selective constraint maintaining the sequence conservation of mariners and perhaps other DNA-mediated elements.      

Seasonal Changes in the Distribution of Photo-assimilated C in Young Pine Plants

Pinus strobus L. plants in their third year of growth were permitted to photoassimilate ¹⁴CO₂ for about 1 hour at monthly intervals between April and October, and the subsequent distribution of ¹⁴C in these plants was determined 8 hours, 1 month, 2 months or 4 months after photo-assimilation. In this way, the fate of ¹⁴CO₂ photo-assimilated during different months of the growing season was observed.

In the spring, old needles played a significant role in photo-assimilating ¹⁴CO₂ and exporting current photosynthate to the developing new shoots and roots. By July, the new shoot had replaced the old shoot both as the primary photo-assimilating part of the plant and as an exporter, particularly to the root.

The root received current photosynthate from the shoot throughout the entire growing season, although plant analysis only 8 hours after photo-assimilation did not always reveal this. Translocation of recent photosynthate from shoot to root was particularly high in August, September, and October.

The amounts of photo-assimilated ¹⁴C lost from the plants over a 4 month interval, principally through respiration and photorespiration, were about one-half of that absorbed during photo-assimilation, with the greatest loss occurring within the first month.

     

Actin filaments elongate from their membrane-associated ends

In limulus sperm an actin filament bundle 55 mum in length extends from the acrosomal vacuole membrane through a canal in the nucleus and then coils in a regular fashion around the base of the nucleus. The bundle expands systematically from 15 filaments near the acrosomal vacuole to 85 filaments at the basal end. Thin sections of sperm fixed during stages in spermatid maturation reveal that the filament bundle begins to assemble on dense material attached to the acrosomal vacuole membrane. In micrographs fo these early stages in maturation, short bundles are seen extending posteriorly from the dense material. The significance is that these short, developing bundles have about 85 filaments, suggesting that the 85-filament end of the bundle is assembled first. By using filament bundles isolated and incubated in vitro with G actin from muscle, we can determine the end “preferred” for addition of actin monomers during polymerization. The end that would be associated with the acrosomal vacuole membrane, a membrane destined to be continuous with the plasma membrane, is preferred about 10 times over the other, thicker end. Decoration of the newly polymerized portions of the filament bundle with subfragment 1 of myosin reveals that the arrowheads point away from the acrosomal vacuole membrane, as is true of other actin filament bundles attached to membranes. From these observations we conclude that the bundle is nucleated from the dense material associated with the acrosomal vacuole and that monomers are added to the membrane-associated end. As monomers are added at the dense material, the thick first-made end of the filament bundle is pushed down through the nucleus where, upon reaching the base of the nucleus, it coils up. Tapering is brought about by the capping of the peripheral filaments in the bundle.