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Rohwer VG, Hagler SJ, Van Doren BM, Fuentes M, Billerman SM. Lower survival of hybrid grosbeaks, but not towhees, suggests a molt divide disfavors hybrids. Evolution 2023; 77:1956-1966. [PMID: 37345673 DOI: 10.1093/evolut/qpad112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2022] [Revised: 05/29/2023] [Accepted: 06/21/2023] [Indexed: 06/23/2023]
Abstract
Although avian hybrid zones in the Great Plains have been studied for almost 70 years, we know surprisingly little about the fitness costs to hybrids that keep these zones narrow. We compare age ratios in grosbeaks (Pheucticus ludovicianus and P. melanocephalus) and towhees (Pipilo erythropthalums and P. maculatus), two species pairs that differ in their life histories and molt schedules, to evaluate survival between hybrids and parentals. We then contrast molt and migratory divides as possible sources of selection against hybrids. Hybrid grosbeaks had 27%-33% lower survival relative to their parentals, whereas hybrid towhees had survival rates similar to parentals. Age ratio data for hybrid grosbeaks suggest high mortality in older birds, as expected if selection operates after the first year of life. This pattern is consistent with parental species of grosbeaks having contrasting molt schedules relative to migration, suggesting high mortality costs to hybrids driven by molt biology, which are expressed later in life. Contrasts in molt schedules are absent in towhees. While migratory divides may exist for towhees and grosbeaks, the low adult survival of hybrid grosbeaks suggest that molt may be an important and underappreciated source of selection maintaining this and other narrow avian hybrid zones.
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Affiliation(s)
- Vanya G Rohwer
- Cornell University Museum of Vertebrates, Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, United States
| | - Samantha J Hagler
- Cornell University Museum of Vertebrates, Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, United States
- Cornell Lab of Ornithology, Ithaca, NY, United States
| | - Benjamin M Van Doren
- Cornell Lab of Ornithology, Ithaca, NY, United States
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, United States
| | - Miguel Fuentes
- Manning College of Information and Computer Sciences, University of Massachusetts-Amherst, Amherst, MA, United States
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2
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Walsh J, Billerman SM, Butcher BG, Rohwer VG, Toews DPL, Vila-Coury V, Lovette IJ. A complex genomic architecture underlies reproductive isolation in a North American oriole hybrid zone. Commun Biol 2023; 6:154. [PMID: 36747071 PMCID: PMC9902562 DOI: 10.1038/s42003-023-04532-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Accepted: 01/26/2023] [Indexed: 02/08/2023] Open
Abstract
Natural hybrid zones provide powerful opportunities for identifying the mechanisms that facilitate and inhibit speciation. Documenting the extent of genomic admixture allows us to discern the architecture of reproductive isolation through the identification of isolating barriers. This approach is particularly powerful for characterizing the accumulation of isolating barriers in systems exhibiting varying levels of genomic divergence. Here, we use a hybrid zone between two species-the Baltimore (Icterus galbula) and Bullock's (I. bullockii) orioles-to investigate this architecture of reproductive isolation. We combine whole genome re-sequencing with data from an additional 313 individuals amplityped at ancestry-informative markers to characterize fine-scale patterns of admixture, and to quantify links between genes and the plumage traits. On a genome-wide scale, we document several putative barriers to reproduction, including elevated peaks of divergence above a generally high genomic baseline, a large putative inversion on the Z chromosome, and complex interactions between melanogenesis-pathway candidate genes. Concordant and coincident clines for these different genomic regions further suggest the coupling of pre- and post-mating barriers. Our findings of complex and coupled interactions between pre- and post-mating barriers suggest a relatively rapid accumulation of barriers between these species, and they demonstrate the complexities of the speciation process.
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Affiliation(s)
- Jennifer Walsh
- Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY, USA.
| | - Shawn M. Billerman
- grid.5386.8000000041936877XFuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY USA
| | - Bronwyn G. Butcher
- grid.5386.8000000041936877XFuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY USA
| | - Vanya G. Rohwer
- grid.5386.8000000041936877XFuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY USA
| | - David P. L. Toews
- grid.29857.310000 0001 2097 4281Department of Biology, Penn State University, University Park, Pennsylvania, USA
| | - Vicens Vila-Coury
- grid.5386.8000000041936877XFuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY USA
| | - Irby J. Lovette
- grid.5386.8000000041936877XFuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, NY USA ,grid.5386.8000000041936877XDepartment of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY USA
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3
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Suh YH, Ligon RA, Rohwer VG. Revisiting the Baltimore-Bullock's Oriole hybrid zone reveals changing plumage colour in Bullock's Orioles. R Soc Open Sci 2022; 9:221211. [PMID: 36533198 PMCID: PMC9748506 DOI: 10.1098/rsos.221211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 11/18/2022] [Indexed: 06/17/2023]
Abstract
Hybrid zones are dynamic areas where populations of two or more interbreeding species may change through an influx of novel genetic material resulting from hybridization or selection on standing genetic variation. Documenting changes in populations through time, however, is challenging because repeated samples are often missing or because long-term storage can affect trait morphologies, especially colour traits that may fade through time. We document a change in carotenoid-based orange breast feathers of Bullock's Orioles (Icterus bullockii) from the Great Plains hybrid zone, USA. Contemporary Bullock's Orioles are more orange than historic individuals from the same location sampled approximately 60 years ago. Spectrophotometry revealed that contemporary Bullock's Orioles resemble orange colour profiles of Baltimore Orioles (I. galbula), the species with which they hybridize. Fading or changes in diet hypotheses do not appear to explain the shift in colour we report for Bullock's Orioles. We propose that these changes in colour are facilitated through introgression with Baltimore Orioles, and favoured by females that choose brighter, more orange males. Our study highlights the long memory of natural history collections and how they offer new insights to the dynamic roll of hybrid zones in trait evolution between interacting species.
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Affiliation(s)
- Young Ha Suh
- Department of Ecology and Evolutionary Biology, Cornell University Museum of Vertebrates, Ithaca, NY 14853, USA
- Cornell Lab of Ornithology, Ithaca, NY 14850, USA
| | | | - Vanya G. Rohwer
- Department of Ecology and Evolutionary Biology, Cornell University Museum of Vertebrates, Ithaca, NY 14853, USA
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4
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Aguillon SM, Rohwer VG. Revisiting a classic hybrid zone: Movement of the northern flicker hybrid zone in contemporary times. Evolution 2022; 76:1082-1090. [PMID: 35318662 DOI: 10.1111/evo.14474] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Revised: 02/10/2022] [Accepted: 02/15/2022] [Indexed: 01/22/2023]
Abstract
Natural hybrid zones have provided important insights into the evolutionary process, and their geographic dynamics over time can help to disentangle the underlying biological processes that maintain them. Here, we leverage replicated sampling of an identical transect across the hybrid zone between yellow-shafted and red-shafted flickers in the Great Plains to assess its stability over ∼60 years (1955-1957 to 2016-2018). We identify a ∼73-km westward shift in the hybrid zone center toward the range of the red-shafted flicker, but find no associated changes in width over our sampling period. In fact, the hybrid zone remains remarkably narrow, suggesting some kind of selective pressure maintains the zone. By comparing to previous work in the same geographic region, it appears likely that the movement in the hybrid zone has occurred in the years since the early 1980s. This recent movement may be related to changes in climate or land management practices that have allowed westward movement of yellow-shafted flickers into the Great Plains.
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Affiliation(s)
- Stepfanie M Aguillon
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853.,Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Ithaca, New York, 14850.,Current Address: Department of Biology, Stanford University, Stanford, California, 94305
| | - Vanya G Rohwer
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853.,Cornell University Museum of Vertebrates, Ithaca, New York, 14850
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Abstract
The growth of natural history collections is declining. We need to reverse this decline to effectively facilitate the discovery of new knowledge and inform future societies about their past.
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Affiliation(s)
- Vanya G. Rohwer
- Cornell University Museum of Vertebrates, Department of Ecology and Evolutionary Biology, Ithaca, New York, United States of America
- * E-mail:
| | - Yasha Rohwer
- Oregon Institute of Technology, Klamath Falls, Oregon, United States of America
| | - Casey B. Dillman
- Cornell University Museum of Vertebrates, Department of Ecology and Evolutionary Biology, Ithaca, New York, United States of America
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6
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Dzielski SA, Razavi NR, Twining CW, Cleckner LB, Rohwer VG. Reconstructing avian mercury concentrations through time using museum specimens from New York State. Ecotoxicology 2020; 29:1802-1814. [PMID: 31729602 DOI: 10.1007/s10646-019-02123-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 10/04/2019] [Indexed: 06/10/2023]
Abstract
We examined how variation in MeHg concentrations through time is reflected in birds, a taxon commonly used as a biological indicator of ecosystem health. Using museum specimens collected from 1880 to 2016, we measured feather MeHg concentrations in six species of birds that breed in New York State and have distinct dietary and habitat preferences. We predicted that MeHg concentrations in feathers would mirror Hg emission patterns in New York State and increase through time until 1980 then decrease thereafter in response to increased regulation of anthropogenic Hg emissions. We found that MeHg concentrations increased with δ15N, and that MeHg feather concentrations for some individuals from four of the six species examined exceeded concentrations known to cause negative sublethal effects in birds. In contrast to our prediction, MeHg concentrations in feathers did not parallel global or local Hg emissions through time and varied by species, even after controlling for possible changes in diet and habitat. MeHg concentrations varied substantially within species and individual specimens, suggesting that high within-individual variation in feather MeHg concentrations caused by spatiotemporal variation in molt, environmental Hg exposure, or mobility decoupling Hg uptake from breeding sites, may obscure trends in MeHg through time. Our study provides a unique assessment of feather MeHg in six species not typically analyzed using this retrospective approach.
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Affiliation(s)
- Sarah A Dzielski
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14850, USA.
- Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, NY, 13210, USA.
- Cornell University Museum of Vertebrates, 159 Sapsucker Woods Road, Ithaca, NY, 14850, USA.
| | - N Roxanna Razavi
- Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, NY, 13210, USA
- Finger Lakes Institute, Hobart and William Smith Colleges, Geneva, NY, 14556, USA
| | - Cornelia W Twining
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14850, USA
- Max Planck Institute for Animal Behavior, 78315, Radolfzell, Germany
- Limnological Institute, University of Konstanz, 78464, Konstanz, Germany
| | - Lisa B Cleckner
- Finger Lakes Institute, Hobart and William Smith Colleges, Geneva, NY, 14556, USA
| | - Vanya G Rohwer
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14850, USA
- Cornell University Museum of Vertebrates, 159 Sapsucker Woods Road, Ithaca, NY, 14850, USA
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Rohwer VG, Rohwer S, Wingfield JC. Despotic aggression in pre-moulting painted buntings. R Soc Open Sci 2020; 7:191510. [PMID: 32257318 PMCID: PMC7062092 DOI: 10.1098/rsos.191510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 01/07/2020] [Indexed: 06/11/2023]
Abstract
Aggression in territorial social systems is easy to interpret because the benefits of territorial defence mostly accrue to the territorial holder. However, in non-territorial systems, high aggression seems puzzling and raises intriguing evolutionary questions. We describe extreme rates of despotism between age classes in a passerine bird, the painted bunting (Passerina ciris), during the pre-moulting period. Aggressive encounters were not associated with aggressors gaining immediate access to resources. Instead, conspecifics, and even other species, were pursued as though being harassed; this aggression generated an ideal despotic habitat distribution such that densities of adult males were higher in high-quality sites. Aggression was not a by-product of elevated testosterone carried over from the breeding season but, rather, appeared associated with dehydroepiandrosterone, a hormone that changes rates of aggression in non-breeding birds without generating the detrimental effects of high testosterone titres that control aggression in the breeding season. This extraordinary pre-moult aggression seems puzzling because individual buntings do not hold defined territories during their moult. We speculate that this high aggression evolved as a means of regulating the number of conspecifics that moulted in what were historically small habitat patches with limited food for supporting the extremely rapid moults of painted buntings.
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Affiliation(s)
- Vanya G. Rohwer
- Cornell University Museum of Vertebrates, Ithaca, NY 14850, USA
| | - Sievert Rohwer
- Burke Museum of Natural History and Culture and Department of Biology, University of Washington, Seattle, WA 98195, USA
| | - John C. Wingfield
- Department of Neurobiology, Physiology and Behavior, University of California, One Shields Avenue, Davis, CA 95616, USA
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Abstract
Incubating birds must trade-off leaving the nest to forage with staying on the nest to maintain optimal temperatures for developing embryos. This trade-off is expressed through incubation behavior, which can be heavily influenced by climate, food availability, attentiveness of their mates, and nest predation risk. Comparative studies across species have shown that incubation behavior varies across latitude, but few studies have explored how incubation behavior varies across sites within species. We might expect incubation behavior to be flexible and respond to local environmental challenges; alternatively, behavior may be relatively fixed and vary little across a species’ range. We explored four incubation behaviors (male feeding rate, female off-bout duration, female off-bout frequency, and the proportion of time incubating females spent on the nest) in a widespread songbird, the yellow warbler (Setophaga petechia), breeding at a temperate and subarctic site. As temperatures warmed at both sites, males fed females less often, and as male feeding rates decreased, off-bout durations and frequencies increased causing the proportion of time on the nest to decrease. While incubation behaviors changed in similar ways between sites, off-bout durations shortened with increasing male feeding rates most strongly at the temperate site. Overall, these results show flexibility in incubation behaviors in response to different environmental cues, which likely minimize costs associated with provisioning incubating parents and maintaining warm nest temperatures, and suggests that male feeding may be especially important for breeding in cold regions.
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Affiliation(s)
- Vanya G. Rohwer
- Cornell University Museum of Vertebrates, Ithaca, NY
- * E-mail:
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9
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Callan LM, La Sorte FA, Martin TE, Rohwer VG. Higher Nest Predation Favors Rapid Fledging at the Cost of Plumage Quality in Nestling Birds. Am Nat 2019; 193:717-724. [PMID: 31002573 DOI: 10.1086/702856] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
High predation risk can favor rapid offspring development at the expense of offspring quality. Impacts of rapid development on phenotypic quality should be most readily expressed in traits that minimize fitness costs. We hypothesize that ephemeral traits that are replaced or repaired after a short period of life might express trade-offs in quality as a result of rapid development more strongly than traits used throughout life. We explored this idea for plumage quality in nestling body feathers, an ephemeral trait. We found a strong trade-off whereby nestlings that spend less time in the nest produced lower-quality plumage with less dense barbs relative to adults across 123 temperate and tropical species. For a subset of these species ( n=67 ), we found that variation in the risk of nest predation explained additional variation in plumage quality beyond development time. Ultimately, the fitness costs of a poor-quality ephemeral trait, such as nestling body feathers, may be outweighed by the fitness benefits of shorter development times that reduce predation risk. At the same time, reduced resource allocation to traits with small fitness costs, such as ephemeral traits, may ameliorate resource constraints from rapid development on traits with larger fitness impacts.
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Abstract
Molt summary tables reveal the sequence and mode of flight-feather replacement and how these feathers are divided into independent replacement series. Tables for summarizing molt are relatively new, and the rules for generating them were first formally illustrated using data from a temperate passerine. However, this first illustration failed to address (i) species with primaries divided into more than one replacement series, (ii) species with stepwise primary replacement, which almost always involves incomplete annual replacement of the primaries, and (iii) species with incomplete annual replacement within molt series characterized by single-wave replacement. Here, we review complications that arise in developing molt summary tables for such cases and we offer solutions that remove ambiguity about the direction that molt proceeds within a replacement series and about the recognition of nodal and terminal feathers that mark the beginning and end of molt series. We use these modified molt summary tables to describe the sequence of primary replacement in four groups of Gruiform birds, a group for which primary replacement has been reported to proceed from the outermost primary toward the body, unlike most other birds. Eighty molting Grey-winged Trumpeters, Psophia crepitans, and 124 molting Limpkins, Aramus guarauna, show the sequence of primary replacement is proximal in both groups; furthermore, the primaries of trumpeters are divided into two replacement series, one beginning at the outermost primary P10, and the other beginning at P3. To further evaluate the extent of this highly unusual direction of replacement in Gruiforms, we cast the data (Stresemann & Stresemann, 1966) on primary replacement in upland rails (Rallidae) and flufftails (Sarothruridae) into molt summary tables; both also replace their primaries proximally, from outermost to innermost, suggesting that this mode of primary replacement may be characteristic of Gruiformes.
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Affiliation(s)
- Sievert Rohwer
- Burke Museum of Natural History and Culture and Department of Biology, University of Washington, Seattle, WA, United States of America
| | - Vanya G Rohwer
- Cornell University Museum of Vertebrates, Ithaca, NY, United States of America
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11
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Rohwer S, Rohwer VG. Breeding and multiple waves of primary molt in common ground doves of coastal Sinaloa. PeerJ 2018; 6:e4243. [PMID: 29379683 PMCID: PMC5787347 DOI: 10.7717/peerj.4243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 12/18/2017] [Indexed: 11/24/2022] Open
Abstract
For adult Common Ground Doves from Sinaloa we demonstrate that the primaries are a single molt series, which sometimes feature two (in one case three) waves of feather replacement. Such stepwise primary replacement is found in many large birds but, at 40 g, this dove is much the smallest species reported to have multiple waves of replacement proceeding through its primaries simultaneously. Pre-breeding juvenile Common Ground Doves never feature two waves of primary replacement. Juveniles usually have more than two adjacent feathers growing simultaneously and replace their primaries in about 100 days. In contrast adults, which extensively overlap molt and breeding, usually grow just a single primary at a time, and require at least 145 days to replace their primaries. Molt arrests are thought to drive the generation of new waves of primary replacement in a diversity of large birds. For adult Common Ground Doves, we found molt arrests to be strongly associated with active crop glands, suggesting that the demands of parental care cause arrests in primary replacement in this dove. For those adults with two primary molt waves, initiation of an inner wave was most frequently observed once the outer wave had reached P10. Thus, unlike reports for large birds, Common Ground Doves usually suppress the initiation of a new wave of molt starting at P1 when the preceding wave arrests before reaching the distal primaries. This assures that relatively fresh inner primaries are not replaced redundantly, overcoming a serious flaw in stepwise molting in large birds (Rohwer, 1999).
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Affiliation(s)
- Sievert Rohwer
- Burke Museum of Natural History and Culture and Department of Biology, University of Washington, Seattle, WA, United States of America
| | - Vanya G Rohwer
- Museum of Vertebrates, Cornell University, Ithaca, NY, United States of America
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12
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Abstract
Characterizing many species interactions as mutualisms can be misleading because some members of the interaction derive greater fitness benefits at the expense of other members. We provide detailed natural history data on a suspected bird-plant mutualism in South Africa where many species of birds use fluffy Eriocephalus seed material to construct their nests, potentially dispersing seeds for the plant. We focus on a common bird, Prinia maculosa, which invests heavily in gathering Eriocephalus material. Prinias spent 5 of their median 6-day nest construction period adding seed material to their nests and frequently travelled outside their territory boundary to gather Eriocephalus material. Yet, prinias gathered primarily Eriocephalus fluff and actively avoided gathering seeds. The average prinia nest contained only 6.6 seeds, but contained fluff from 579 seeds. These data suggest that prinias provide limited dispersal benefits to Eriocephalus plants. By contrast, the large amounts of Eriocephalus fluff in prinia nests, and the effort that prinias invest in gathering it, suggest that prinias benefit from constructing their nests with Eriocephalus material. We end by outlining hypotheses for possible fitness benefits that Eriocephalus material could provide prinias and other birds.
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Affiliation(s)
- Vanya G. Rohwer
- Department of Biology, Queen's University, Kingston, Ontario, CanadaK7 L 3N6
| | - Anton Pauw
- Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa
| | - Paul R. Martin
- Department of Biology, Queen's University, Kingston, Ontario, CanadaK7 L 3N6
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13
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Rohwer VG, Bonier F, Martin PR. Conflict between biotic and climatic selective pressures acting on an extended phenotype in a subarctic, but not temperate, environment. Proc Biol Sci 2016; 282:20151585. [PMID: 26490789 DOI: 10.1098/rspb.2015.1585] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Climatic selective pressures are thought to dominate biotic selective pressures at higher latitudes. However, few studies have experimentally tested how these selective pressures differentially act on traits across latitudes because traits can rarely be manipulated independently of the organism in nature. We overcame this challenge by using an extended phenotype-active bird nests-and conducted reciprocal transplant experiments between a subarctic and temperate site, separated by 14° of latitude. At the subarctic site, biotic selective pressures (nest predation) favoured smaller, non-local temperate nests, whereas climatic selective pressures (temperature) favoured larger local nests, particularly at colder temperatures. By contrast, at the temperate site, climatic and biotic selective pressures acted similarly on temperate and subarctic nests. Our results illustrate a functional trade-off in the subarctic between nest morphologies favoured by biotic versus climatic selective pressures, with climate favouring local nest morphologies. At our temperate site, however, allocative trade-offs in the time and effort devoted to nest construction favour smaller, local nests. Our findings illustrate a conflict between biotic and climatic selective pressures at the northern extremes of a species geographical range, and suggest that trade-offs between trait function and trait elaboration act differentially across latitude to create broad geographic variation in traits.
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Affiliation(s)
- V G Rohwer
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - F Bonier
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
| | - P R Martin
- Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6
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15
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Bura VL, Rohwer VG, Martin PR, Yack JE. Whistling in caterpillars (Amorpha juglandis, Bombycoidea): sound-producing mechanism and function. J Exp Biol 2011; 214:30-7. [DOI: 10.1242/jeb.046805] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
Caterpillar defenses have been researched extensively, and, although most studies focus on visually communicated signals, little is known about the role that sounds play in defense. We report on whistling, a novel form of sound production for caterpillars and rare for insects in general. The North American walnut sphinx (Amorpha juglandis) produces whistle ‘trains’ ranging from 44 to 2060 ms in duration and comprising one to eight whistles. Sounds were categorized into three types: broadband, pure whistles and multi-harmonic plus broadband, with mean dominant frequencies at 15 kHz, 9 kHz and 22 kHz, respectively. The mechanism of sound production was determined by selectively obstructing abdominal spiracles, monitoring air flow at different spiracles using a laser vibrometer and recording body movements associated with sound production using high-speed video. Contractions of the anterior body segments always accompanied sound production, forcing air through a pair of enlarged spiracles on the eighth abdominal segment. We tested the hypothesis that sounds function in defense using simulated attacks with blunt forceps and natural attacks with an avian predator – the yellow warbler (Dendroica petechia). In simulated attacks, 94% of caterpillars responded with whistle trains that were frequently accompanied by directed thrashing but no obvious chemical defense. In predator trials, all birds readily attacked the caterpillar, eliciting whistle trains each time. Birds responded to whistling by hesitating, jumping back or diving away from the sound source. We conclude that caterpillar whistles are defensive and propose that they function specifically as acoustic ‘eye spots’ to startle predators.
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Affiliation(s)
- Veronica L. Bura
- Department of Biology, Carleton University, Ottawa, ON, Canada, K1S 5B6
| | - Vanya G. Rohwer
- Department of Biology, Queen's University, Kingston, ON, Canada, K7L 3N6
| | - Paul R. Martin
- Department of Biology, Queen's University, Kingston, ON, Canada, K7L 3N6
| | - Jayne E. Yack
- Department of Biology, Carleton University, Ottawa, ON, Canada, K1S 5B6
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Abstract
Replacement of flight feathers takes disproportionately more time for large birds than it does for small birds, because feather length increases with body size almost twice as fast as feather growth rate increases. We used allometric scaling to explain why the regular replacement of the primary flight feathers requires disproportionately more time for large birds. Primary growth rate scales to mass (M) as M0.171, whereas the summed length of the primaries scales almost twice as fast (M0.316). The ratio of length (mm) to rate (mm/day), which would be the time needed to replace all the primaries one by one, increases as the 0.14 power of mass (M0.316/M0.171 = M0.145), illustrating why the time required to replace the primaries is so important to life history evolution in large birds. Smaller birds generally replace all their flight feathers annually, but larger birds that fly while renewing their primaries often extend the primary molt over two or more years. Most flying birds exhibit one of three fundamentally different modes of primary replacement, and the size distributions of birds associated with these replacement modes suggest that birds that replace their primaries in a single wave of molt cannot approach the size of the largest flying birds without first transitioning to a more complex mode of primary replacement. Finally, we propose two models that could account for the 1/6 power allometry between feather growth rate and body mass, both based on a length-to-surface relationship that transforms the linear, cylindrical growing region responsible for producing feather tissue into an essentially two-dimensional structure. These allometric relationships offer a general explanation for flight feather replacement requiring disproportionately more time for large birds. The pace of life varies with body size and is generally slower among larger organisms. Larger size creates opportunities but also establishes constraints on time-dependent processes. Flying birds depend on large wing feathers that deteriorate over time and must be replaced through molting. The lengths of flight feathers increase as the 1/3 power of body mass, as one expects for a length-to-volume ratio. However, feather growth rate increases as only the 1/6 power of body mass, possibly because a two-dimensional feather is produced by a one-dimensional growing region. The longer time required to grow a longer feather constrains the way in which birds molt, because partially grown feathers reduce flight efficiency. Small birds quickly replace their flight feathers, often growing several feathers at a time in each wing. Larger species either prolong molt over two or more years, adopt complex patterns of multiple feather replacement to minimize gaps in the flight surface, or, among species that do not rely on flight for feeding, simultaneously molt all their flight feathers. We speculate that the extinct 70-kg raptor, Argentavis magnificens, must have undergone such a simultaneous molt, living off fat reserves for the duration.
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Affiliation(s)
- Sievert Rohwer
- Burke Museum and Department of Biology, University of Washington, Seattle, United States of America.
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