Comparative analysis of avian hearts provides little evidence for variation among species with acquired endothermy. (22nd January 2019)

• Record Type: Journal Article
• Authors: Kroneman, Jelle G. H.; Faber, Jaeike W.; Schouten, Jacobine C.M.; Wolschrijn, Claudia F.; Christoffels, Vincent M.; Jensen, Bjarke
• Is Part Of: Journal of morphology. Volume 280:Number 3(2019)
• Page Start: 395
• Page End: 410
• Publication Date: 2019-01-22
• Subjects: anatomy -- bird -- evolution -- heart; Morphology -- Periodicals; Physiology -- Periodicals; Anatomy -- Periodicals; 571.3
• DOI: 10.1002/jmor.20952
• Languages: English
• ISSNs: 0362-2525

Abstract

Abstract: Mammals and birds acquired high performance hearts and endothermy during their independent evolution from amniotes with many sauropsid features. A literature review shows that the variation in atrial morphology is greater in mammals than in ectothermic sauropsids. We therefore hypothesized that the transition from ectothermy to endothermy was associated with greater variation in cardiac structure. We tested the hypothesis in 14 orders of birds by assessing the variation in 15 cardiac structures by macroscopic inspection and histology, with an emphasis on the atria as they have multiple features that lend themselves to quantification. We found bird hearts to have multiple features in common with ectothermic sauropsids (synapomorphies), such as the presence of three sinus horns. Convergent features were shared with crocodylians and mammals, such as the cranial offset of the left atrioventricular junction. Other convergent features, like the compact organization of the atrial walls, were shared with mammals only. Pacemaker myocardium, identified by Isl1 expression, was anatomically node‐like (Mallard), thickened (Chicken), or indistinct (Lesser redpoll, Jackdaw). Some features were distinctly avian, (autapomorphies) including the presence of a left atrial antechamber and the ventral merger of the left and right atrial auricles, which was found in some species of parrots and passerines. Most features, however, exhibited little variation. For instance, there were always three systemic veins and two pulmonary veins, whereas among mammals there are 2–3 and 1–7, respectively. Our findings suggest that the transition to high cardiac performance does not necessarily lead to a greater variation in cardiac structure. Abstract : Birds and mammals evolved independently from ectotherm‐sauropsid‐like ancestors and acquired endothermy supported by a high‐performance heart. Because the mammal heart exhibits much variation in morphology, we hypothesized the variation relates to the evolution of endothermy. We tested the hypothesis in a comparative study of bird hearts. We find little variation in cardiac morphology and reject the hypothesis.