Metabolic Capacity and the Evolution of Biogeographic Patterns in Oscine and Suboscine Passerine Birds Author(S): David L

Metabolic Capacity and the Evolution of Biogeographic Patterns in Oscine and Suboscine Passerine Birds Author(s): David L. Swanson and Francisco Bozinovic Source: Physiological and Biochemical Zoology, Vol. 84, No. 2 (March 2011), pp. 185-194 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/10.1086/658291 . Accessed: 23/02/2011 15:48 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at . http://www.jstor.org/action/showPublisher?publisherCode=ucpress. 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Swanson1,2,* Introduction Francisco Bozinovic2,† Birds of the order Passeriformes are classified into two major 1Department of Biology, University of South Dakota, 414 suborders, the suboscines and the oscines (Sibley and Ahlquist East Clark Street, Vermillion, South Dakota 57069; 2Center 1990; Barker et al. 2004). The suboscines are the more ancient for Advanced Studies in Ecology and Biodiversity and lineage and are generally outcompeted by the oscines wherever Departamento de Ecologıá, Pontificia Universidad Cato´lica the two groups come into contact (Feduccia 1999). Biogeo- de Chile, Santiago, CP 6513677, Chile graphic analyses of passerine birds demonstrate that oscines are dominant in Europe, Asia, North America, Africa, and Aus- Accepted 10/24/2011; Electronically Published 1/6/2011 tralia, whereas suboscines are dominant in South America. In general, suboscines flourish as a group principally in tropical Online enhancement: appendix. and subtropical regions of the New World, where over 90% of living suboscines are found (Newton 2003). The likely reason that suboscine dominance persists in South America is that the ABSTRACT opportunity for interaction between oscines and suboscines has Biogeographic analyses of passerine birds demonstrate that sub- been limited until recently geologically because of the long oscines are numerically dominant in South America, whereas isolation of South America from other continents, where os- oscines are dominant elsewhere. This suggests that oscines gen- cines have diversified. The opportunity for large-scale faunal erally outcompete suboscines and that suboscine dominance exchange between North and South America has existed only likely persists in South America because of its long isolation since the formation of the Central American land bridge in the from other continents, where oscines have diversified. One hy- late Pliocene, between 2 and 4 mya (Feduccia 1999). Even so, pothesis for oscine competitive superiority is that oscines pos- Ricklefs (2002) notes that within South America, oscines are sess higher metabolic capacities than suboscines, and this favors typically dominant in forest canopy and open habitats, whereas oscines in most habitats. We tested this hypothesis by com- suboscines are dominant within the forest understory, so the Great American Faunal Interchange following the formation of paring summit metabolic rates (Msum, maximum thermoregulatory metabolic rate) between oscines and suboscines using the Central American land bridge favored North American os- conventional and phylogenetically informed statistical ap- cines, which likely displaced South American suboscines from proaches. We predicted that if the metabolic-capacity hypoth- forest canopy and open habitats. Feduccia (1999) posits that the relatively limited biogeo- esis is valid, then oscines should have higher Msum than suboscines. Both conventional and phylogenetically informed graphic “distribution of suboscines is related more to their early acquisition of restrictive tropical physiological adaptations than ANCOVA on regressions of log Msum against log mass showed to any inability to expand their ranges” (p. 369). Feduccia that oscines had higher Msum than suboscines: least squares continues, “It was the oscines, with their advanced, more flex- mean Msum was 74% greater for oscines. Moreover, conventional and phylogenetically informed multiple regressions identified ible neural parameters, physiological tolerance, and high re- log mass, winter-range temperature, and clade (oscines vs. sub- productive potential ... that were capable of occupying both temperate and tropical zones” (pp. 369–370). Because this hy- oscines) as significant effectors of log Msum. Thus, oscines have pothesis focuses on differences in physiological capacities as generally higher Msum than suboscines, which is consistent with the metabolic-capacity hypothesis and suggests that metabolic drivers of passerine biogeographic patterns, we term this hy- capacity is one factor influencing the evolution of broad bio- pothesis the “metabolic-capacity hypothesis.” In addition to the geographical patterns in passerines. metabolic-capacity hypothesis, Ricklefs (2002) proposed several other potential hypotheses for why oscine invaders of South America were able to replace suboscines in forest canopy and open habitats. These include differences in morphology (longer legs and toes in oscines) that permit oscines to engage in more * Corresponding author; e-mail: [email protected]. active movement through vegetation, more generalized behav- † E-mail: [email protected]. iors and diets in oscines that may have been advantageous during the deteriorating climates of the late Tertiary, and the Physiological and Biochemical Zoology 84(2):185–194. 2011. ᭧ 2011 by The University of Chicago. All rights reserved. 1522-2152/2011/8402-0092$15.00. ability of oscines to respond more rapidly to resource fluctu- DOI: 10.1086/658291 ation (as evidenced by shorter incubation periods and lower 186 D. L. Swanson and F. Bozinovic investment in immune activity; Ricklefs 2002). These factors this study, we measured metabolic capacities (as Msum) for eight are also likely related to metabolic capacities because higher temperate-zone suboscine species and collected additional Msum activity levels, shorter incubation periods, and reduced im- values from the literature for oscines and suboscines. We then mune-system function are associated with a faster pace of life used both conventional and phylogenetically informed com- and elevated basal metabolic rate (BMR) and summit metabolic parative analyses to test whether Msum differs between suboscine p rate (Msum maximum thermoregulatory metabolic rate) in and oscine passerines. Thus, these data provide the first test of temperate relative to tropical birds (Wiersma et al. 2007b). the metabolic-capacity hypothesis for the comparative bioge- Moreover, not only would more generalized behaviors and diets ography of suboscine and oscine passerines. be beneficial during the climatic cooling of the late Tertiary, but elevated cold tolerance, which is positively correlated with Material and Methods increased M (Swanson 2001; Swanson and Liknes 2006), sum Study Species would also be advantageous under such conditions (Swanson and Garland 2009). Thus, differences in metabolic capacities We measured Msum for eight summer-acclimatized suboscine could be an important factor influencing the evolution of bio- passerine species from central Chile, namely thorn-tailed ray- geographic patterns in oscines and suboscines. However, com- adito (Aphrastura spinicauda), plain-mantled tit-spinetail (Lep- parative studies of metabolic capacities of oscines and subos- tasthenura aegithaloides), dusky-tailed canastero (Asthenes hu- cines have not been undertaken, so no direct tests of the milis), wren-like rushbird (Phleocryptes melanops), fire-eyed metabolic-capacity hypothesis for passerine biogeography are diucon (Xolmis pyrope), white-crested elaenia (Elaenia albiceps), available. tufted tit-tyrant (Anairetes parulus), and many-colored rush- The broad questions of how physiological traits covary with tyrant (Tachuris rubigastra). All of these species except white- environmental variability over large geographic distances and crested elaenia are permanent residents of the south temperate how such traits might influence patterns of distribution are zone of central Chile (Jaramillo 2003), so these data supplement significant and have yet to be fully resolved. Consequently, we literature values for Msum in suboscines, which mostly are ob- ask what tropical physiological adaptations might function to tained from tropical resident or tropical-wintering species restrict suboscine birds largely to tropical and subtropical

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