An Interspecific Test of Allen's Rule: Evolutionary Implications for Endothermic Species

Nudds, Robert L.; Oswald, Stephen A.

doi:10.1111/j.1558-5646.2007.00242.x

Cited by 82 publications

(85 citation statements)

References 40 publications

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“…Although bill size is known to vary seasonally in many birds [18], [24], the magnitude of this variation is quite small. So a single bill size might only be able to maximize heat dissipation or minimize heat loss (for a discussion of this trade-off for avian tarsi see [25]). Historically, the relationship between climate and bill size has focused on heat conservation [13], [14], with the argument that smaller bills evolve in areas with colder winters.…”

Section: Introductionmentioning

confidence: 99%

Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats

et al. 2012

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BackgroundResearch on variation in bill morphology has focused on the role of diet. Bills have other functions, however, including a role in heat and water balance. The role of the bill in heat loss may be particularly important in birds where water is limiting. Song sparrows localized in coastal dunes and salt marsh edge (Melospiza melodia atlantica) are similar in size to, but have bills with a 17% greater surface area than, those that live in mesic habitats (M. m. melodia), a pattern shared with other coastal sparrows. We tested the hypotheses that sparrows can use their bills to dissipate “dry” heat, and that heat loss from the bill is higher in M. m. atlantica than M. m. melodia, which would indicate a role of heat loss and water conservation in selection for bill size.Methodology/Principal FindingsBill, tarsus, and body surface temperatures were measured using thermal imaging of sparrows exposed to temperatures from 15–37°C and combined with surface area and physical modeling to estimate the contribution of each body part to total heat loss. Song sparrow bills averaged 5–10°C hotter than ambient. The bill of M. m atlantica dissipated up to 33% more heat and 38% greater proportion of total heat than that of M. m. melodia. This could potentially reduce water loss requirements by approximately 7.7%.Conclusions/SignificanceThis >30% higher heat loss in the bill of M. m. atlantica is independent of evaporative water loss and thus could play an important role in the water balance of sparrows occupying the hot and exposed dune/salt marsh environments during the summer. Heat loss capacity and water conservation could play an important role in the selection for bill size differences between bird populations and should be considered along with trophic adaptations when studying variation in bill size.

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Section: Introductionmentioning

confidence: 99%

Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats

et al. 2012

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“…Allen's rule is an eco-geographical hypothesis, relating climate to body size proportion in endotherms [15][16][17], and has been established within and among numerous avian groups [9,[18][19][20]. The rule proposes that protruding morphological features, such as limbs, digits and ears, vary in proportion to body mass, and to the environmental temperatures in which the animal normally resides.…”

Section: Introductionmentioning

confidence: 99%

Post-hatch heat warms adult beaks: irreversible physiological plasticity in Japanese quail

et al. 2013

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Across taxa, the early rearing environment contributes to adult morphological and physiological variation. For example, in birds, environmental temperature plays a key role in shaping bill size and clinal trends across latitudinal/thermal gradients. Such patterns support the role of the bill as a thermal window and in thermal balance. It remains unknown whether bill size and thermal function are reversibly plastic. We raised Japanese quail in warm (308C) or cold (158C) environments and then at a common intermediate temperature. We predicted that birds raised in cold temperatures would develop smaller bills than warm-reared individuals, and that regulation of blood flow to the bill in response to changing temperatures would parallel the bill's role in thermal balance. Cold-reared birds developed shorter bills, although bill size exhibited 'catch-up' growth once adults were placed at a common temperature. Despite having lived in a common thermal environment as adults, individuals that were initially reared in the warmth had higher bill surface temperatures than coldreared individuals, particularly under cold conditions. This suggests that blood vessel density and/or the control over blood flow in the bill retained a memory of early thermal ontogeny. We conclude that post-hatch temperature reversibly affects adult bill morphology but irreversibly influences the thermal physiological role of bills and may play an underappreciated role in avian energetics.

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“…For instance, relative to individuals from low latitudes, high-latitude individuals tend to have higher growth rates and larger body size (1,2), produce larger eggs (3), have relatively shorter extremities (4), and more vertebrae (5). Lifespan also varies with latitude in a wide variety of ectotherms.…”

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confidence: 99%

Latitudinal variation in lifespan within species is explained by the metabolic theory of ecology

Munch

Salinas

2009

Proc. Natl. Acad. Sci. U.S.A.

174

165

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Many ectotherms exhibit striking latitudinal gradients in lifespan. However, it is unclear whether lifespan gradients in distantly related taxa share a common mechanistic explanation. We compiled data on geographic variation in lifespan in ectotherms from around the globe to determine how much of this intraspecific variation in lifespan may be explained by temperature using the simple predictions of the metabolic theory of ecology. We found that the metabolic theory accurately predicts how lifespan varies with temperature within species in a wide range of ectotherms in both controlled laboratory experiments and free-living populations. After removing the effect of temperature, only a small fraction of species showed significant trends with latitude. There was, however, considerable residual intraspecific variation indicating that other, more local factors are likely to be important in determining lifespan within species. These findings suggest that, given predicted increases in global temperature, lifespan of ectotherms may be substantially shortened in the future.any phenotypic traits covary with latitude, particularly among ectotherms. For instance, relative to individuals from low latitudes, high-latitude individuals tend to have higher growth rates and larger body size (1, 2), produce larger eggs (3), have relatively shorter extremities (4), and more vertebrae (5). Lifespan also varies with latitude in a wide variety of ectotherms. For example, lifespan increases with latitude in the yellow clam (Mesodesma mactroides) (6), oegopsin squid (suborder Oegospina) (7), and many fish species (8-11). One example is particularly striking: pearl mussels (Margaritifera margaritifera) found in Spain (43°N) have maximum lifespans of 29 years, whereas those in Russia (66°N) live nearly 200 years (12, 13). The purpose of our study is to determine whether this ubiquitous geographical variation in lifespan has a common physiological basis in temperature.Temperature has long been known to influence lifespan (14, 15). For example, Drosophila melanogaster from Brazil raised at 31.2°C lived up to 29 days, whereas flies from the same population reared at 12°C lived up to 247 days (16). Although the temperature-lifespan relationship has been known for nearly a century, most of our knowledge on this relationship is derived from laboratory experiments on short-lived invertebrates (e.g., 17). Studies on natural variation in lifespan with temperature have largely been limited to cross-taxa comparisons (18,19). As a consequence, the role of temperature in controlling geographic variation in lifespan within species is unclear. It is easy to imagine how geographic variation in the abundance of predators, availability of resources, fluctuations in environmental conditions, and local adaptation might obscure any relationship between temperature and lifespan in wild populations.The metabolic theory of ecology (MTE) (20) has been used to link metabolism to a wide range of physiological and macroecological processes. Growth trajectories and l...

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An Interspecific Test of Allen's Rule: Evolutionary Implications for Endothermic Species

Cited by 82 publications

References 40 publications

Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats

Heat Loss May Explain Bill Size Differences between Birds Occupying Different Habitats

Post-hatch heat warms adult beaks: irreversible physiological plasticity in Japanese quail

Latitudinal variation in lifespan within species is explained by the metabolic theory of ecology

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