Lateralization and motor stereotype of song production in the brown-headed cowbird

Song production in adult brown-headed cowbirds(Molothrus ater ater) is lateralized, with a slight right syringeal dominance. The left size of the syrinx produces low-frequency (200–2000 Hz) notes within the introductory note clusters, while the right side produces the higher-frequency (1500–6000 Hz) introductory notes, the interphrase unit (10–12 kHz), and the final high-frequency whistle (5–13 kHz). Cross-correlation analyses reveal that individual cowbirds produce each of their four to seven song types with a distinct stereotyped motor pattern–as judged by the patterns of syringeal airflow and subsyringeal pressure. The acoustic differences across song types are reflected in the differences in the bronchial airflow and air sac pressure patterns associated with song production. These motor differences are particularly striking within the second and third introductory note clusters where there is a rapid switching back and forth between the two sides of the syrinx in the production of notes. These motor skills may be especially important in producing behaviorally effective song. 1994 John Wiley & Sons, Inc.     

The development of the human spleen

Summary Splenic tissue of human fetuses from the 14^th to the 24^th week of gestation (menstrual age) were investigated by light- and electron microscopy to describe the development of the red and white pulp in close relationship to the differentiation of the vascular tree. Special interest is focussed on the differentiation of the T-cell- and the B-cell regions and their specific stationary cells.The preliminary stage, here called the primary vascular reticulum, lasts up to the 14^th gestational week (gw). Numerous erythrocytes, normoblasts and macrophages are seen among a network of mesenchymal cells and argyrophilic fibers. Hematopoiesis, especially erythropoiesis, can be recognized.The characteristic organ structure becomes established during the subsequent transformation stage of the fetal spleen, beginning with the 15^th gw. Splenic lobules begin to form during the 15^th to 17^th gw. They consist of a central artery, surrounded by a sheath of lightly stained stationary cells which resemble myofibroblasts. At the periphery of these lobules the red pulp forms. Initially mobile cells are distributed throughout the reticulum. Soon they begin to accumulate in the venous sinuses, which develop from lacunae among the reticular network and come into contact with the venous system. The endothelial wall of these sinuses remains discontinuous, confirming the theory of the open vascularization of the spleen. The development of the larger veins is correlated with the differentiation of the splenic trabeculae.The development of the white pulp is correlated with the stage of lymphoid colonization within the spleen, beginning around the 18^th gw. An accumulation of lymphocytes around the central arteries can be recognized during the 19^th and 20^th gw. These lymphoid cells show morphological and immunohistochemical characteristics of T-precursor cells. Within the now assembling periarterial lymphoid sheath (PALS) a few precursors of interdigitating cells (IDC) are recognizable, giving evidence for the differentiation of the T-cell region.Around the 23^rd gw the assemblage of primary follicles is discernible at the periphery of the PALS. Precursors of the follicular dendritic reticulum cell (FDRC), the specific stationary cell of the B-cell region, have been recognized. This observation leads to the conclusion that the small primary follicles represent the beginning formation of the B-cell region.The significance of the vascular system for the differentiation of the specific splenic organization is discussed.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft (Sonderforschungsbereich 111)The authors appreciate the contribution of human fetal material from Dr. von Hollweg and Dr. Körner from the Hospital Heidberg, Hamburg, and the excellent technical assistance of Mrs. H. Hansen, Mrs. I. Knauer, Mrs. M.v. Kolszynski, Mrs. J. Quitzau, Mrs. H. Siebke and Mrs. H. Waluk     

Winter dialects in the bronzed cowbird and their relationship to breeding-season dialects

Studies of geographical variation in animal signals generally focus on breeding-season behaviour but, in many species, signalling persists throughout the year. In passerine birds, patterns of variation in the nonbreeding season might provide opportunities for vocal learning that have been neglected by a historic focus on breeding-season behaviour. This study provides the first example of dialect variation outside of the breeding season. Quantitative analysis of acoustic similarity showed discrete differences between the songs of bronzed cowbirds, Molothrus aeneus, in four winter flocks. Most songs produced by members of a given flock were classified as belonging to the same dialect. Songs from one of the four winter dialects were indistinguishable from songs recorded in the breeding season in the same region. Depending on migratory patterns, dialects in one season may be a consequence of dialects in the other season, or the two seasonal patterns may be the result of independent social or evolutionary forces. Because the nonbreeding season is an important period of vocal learning in some bird species, winter dialects might limit the range of signals available for individuals to learn to produce. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

脾脏的免疫功能及脾脏对血流变影响的研究

脾脏是人体最大的免疫器官,含有多种免疫活性细胞和细胞因子,脾脏的解剖组织学特点使其成为免疫应答的重要场所和重要调节器官.脾脏具有抗感染和抗肿瘤作用;脾脏还具有清除衰老红细胞及降低血小板,降低血小板粘度从而引起血流变改变的功能.本文将从脾脏的组织学结构及相应的功能加以论述.     

The importance of the spleen in malaria

There are several malaria vaccine candidates at various stages of development. Many of these target blood stages of Plasmodium falciparum. The spleen is a key site for removal of parasitized red blood cells, generation of immunity and production of new red blood cells during malaria. This article describes how all of these processes are modified following infection, and suggests that until we fully understand how these processes function and are modulated by infection, appropriate malaria vaccine design and delivery will be extremely difficult to achieve.     

The role of the spleen in malaria

The spleen is a complex organ that is perfectly adapted to selectively filtering and destroying senescent red blood cells (RBCs), infectious microorganisms and Plasmodium-parasitized RBCs. Infection by malaria is the most common cause of spleen rupture and splenomegaly, albeit variably, a landmark of malaria infection. Here, the role of the spleen in malaria is reviewed with special emphasis in lessons learned from human infections and mouse models.     

Stereometry of the red pulp on the human spleen. II) The normal spleen

The stereometric measurements obtained in three human normal spleens surgically removed for trauma have been submitted to statistical evaluation. On the basis of the original counts, some stereometric measures of the normal splenic red pulp have been determined, namely per cent volume of sinuses, per cent volume of cords, breadth of the cords, mean sectional area of sinuses and the volume of sinuses:volume of cords ratio. These data can constitute a series of parameters to which compare the measures of the pathologic spleens.     

Fitness costs and benefits of cowbird egg ejection by gray catbirds

Gray catbirds (Dumetella carolinensis) eject over 95% of brown-headedcowbird (Molothrus ater) eggs placed into their nests. Ejectionbehavior could be maintained by selection from either: (1) cowbird parasitism, if the costs of accepting a cowbird egg outweighthe costs of ejecting it, or (2) conspecific parasitism, ifsuch parasitism occurs naturally and results in ejection. Thisstudy tested the above hypotheses by measuring the cost ofacceptance of cowbird parasitism (n= 38 experimentally introducedcowbird chicks) and of cowbird egg ejection (n = 94 experiments),as well as the frequency of natural conspecific parasitismamong 229 catbird nests observed and the frequency of conspecific egg ejection (n = 27 experiments). The conspecific parasitism hypothesis was not supported because catbirds accepted all foreignconspecific eggs placed into their nests, and no natural conspecificbrood parasitism was detected at any nests. The cowbird parasitismhypothesis was strongly supported because the cost of acceptinga cowbird chick (0.79 catbird fledglings) is much greater thanthe cost of ejecting a cowbird egg (0.0022 catbird fledglingsper ejection).     

Prolactin secretion in a brood parasite, the brown-headed cowbird, Molothrus ater

Blood samples were collected from a free-living population of male and female brown-headed cowbirds, Molothrus ater , during the breeding season and plasma levels of prolactin were measured by radioimmunoassay. Prolactin concentrations in both sexes increased significantly in mid to late May; peak levels were reached by June and were maintained throughout June and into July. Prolactin levels in juveniles were significantly lower than in adults but were still elevated. Prolactin has been implicated in parental care in several avian species; however, cowbirds are brood parasites with complete absence of parental behaviour, suggesting that prolactin must function in another capacity in cowbirds, or that cowbirds have developed target tissue insensitivity to this hormone.     

The dynamics of spleen morphogenesis

The mammalian spleen has important functions in immunity and haematopoiesis but little is known about the events that occur during its early embryonic development. Here we analyse the origin of the cells that gives rise to the splenic mesenchyme and the process by which the precursors assume their position along the left lateral side of the stomach. We report a highly conserved regulatory element that regulates the Nkx2-5 gene throughout early spleen development. A transgenic mouse line carrying this element driving a reporter gene was used to show that morphogenesis of the spleen initiates bilaterally and posterior to the stomach, before the splenic precursors grow preferentially leftward. In addition the transgenic line was used in an organ culture system to track spleen precursor cells during development. Spleen cells were shown to move from the posterior mesenchyme and track along the left side of the stomach. Removal of tissue from the anterior stomach resulted in splenic cells randomly scattering suggesting a guidance role for the anterior stomach. Using a mouse line carrying a conditional Cre recombinase to mark early precursor cell populations, the spleen was found to derive from posterior mesenchyme distinct from the closely adjacent stomach mesenchyme.     

Patterns of courtship between cowbird subspecies: evidence for positive assortment

The courtship and mating behaviour of captive individuals from allopatric populations of two cowbird subspecies (Molothrus ater ater and Molothrus ater obscurus) were observed in a large indoor-outdoor aviary, using a multiple-choice design in order to assess whether they would selectively pair with members of their own subspecies. Twenty-nine of the 42 consortships observed were between consubspecifics, and 10 of the 15 copulating pairs were homogamic. Individuals tended to pair with consubspecifics whether or not they had had prior breeding experience with consubspecifics or winter contact with heterosubspecifics. This demonstration of selective courtship between individuals of widely separated populations is one of the first quantified examples, to our knowledge, of the development of assortative pairing in allopatry for a passerine species. These data place in perspective previous findings on the female cowbird's preferential response to playback of her own subspecies' song, thereby suggesting that song may be an important cue for selective mating between passerine populations.