Changing patterns of natural selection on morphology of Cliff Swallows during severe weather

Brown, Charles R.; Brown, Mary Bomberger; Hannebaum, Stacey L.; Hosack, Patricia K.; Kucera, Abigail J.; Page, Catherine E.; Strickler, Stephanie A.; Wagnon, Gigi S.

doi:10.1676/17-00057.1

Cited by 2 publications

(5 citation statements)

References 32 publications

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“…If, as predicted, the frequency of bad weather events in the Nebraska study area increases with global climate change [19,32], more frequent episodic selection for larger brains could lead to permanent microevolutionary change in brain size over time, as we have seen for other traits [16]. However, such a directional shift is so far not evident in our data: year had no significant effect on brain size over the 37 years of our study.…”

Section: Discussionsupporting

confidence: 41%

“…Multiple-day periods of cold and rainy weather in late-spring (when insects are not active) lead to cliff swallow mortality owing to starvation that varies in severity depending on how long the cold weather lasts [14,19]. We documented that cold weather caused mortality in 1988, 1992, 1996, 2004 and 2017; that of 1996 was the most severe, with at least 53% of the population perishing over a 6-day period [14].…”

Section: (B) Specimen Collection and Weather Eventsmentioning

confidence: 87%

“…Empirical tests of the cognitive-buffer hypothesis have mostly involved cross-species comparisons, yet the same selective pressures on brain size should also apply within species whenever individuals are exposed to extreme conditions. One component of environmental variability is unusually severe weather, which can lead to intense selection on morphological traits such as body size or behavioural traits such as spring arrival time [13][14][15][16][17][18][19], but occurs so rarely that often only long-term studies can detect its effects. Consequently, little is known about how unusually harsh conditions might affect selection on cognitive abilities as reflected in brain size within a species.…”

Section: Introductionmentioning

confidence: 99%

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Smaller brained cliff swallows are more likely to die during harsh weather

Wagnon

Brown

2020

Biol. Lett.

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The cognitive-buffer hypothesis proposes that more harsh and unpredictable environments favour animals with larger brains and resulting greater cognitive skills. Comparisons across taxa have supported the hypothesis, but it has rarely been tested within a species. We measured brain size, as inferred from head dimensions, for 1141 cliff swallow specimens collected in western Nebraska, 1982–2018. Cliff swallows starving to death during unusual late-spring cold snaps had significantly smaller brains than those dying from other causes, suggesting that brain size in this species can affect foraging success and that greater cognitive ability may confer advantages when conditions exceed normal environmental extremes. Brain size declined significantly with the size of the breeding colony from which a specimen came. Larger brains may be favoured in smaller colonies that represent more unpredictable and more challenging social environments where there is less public information on food sources and less collective vigilance against predators, even in relatively normal conditions. Our results provide intraspecific support for the cognitive-buffer hypothesis and emphasize the potential evolutionary impact of rare climatic events.

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Section: Discussionsupporting

confidence: 41%

Section: (B) Specimen Collection and Weather Eventsmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

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Smaller brained cliff swallows are more likely to die during harsh weather

Wagnon

Brown

2020

Biol. Lett.

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“…Although we detected five unusual climatic events that resulted in cliff swallow mortality in our study area from 1982 to 2018 (Brown and Brown , Brown et al. ), in only one of these (1996) was mortality widespread enough for us to measure effects of colony size. However, with unusual climatic events predicted to increase in frequency in the future (Bailey and van de Pol , Kingsolver and Buckley ), their effect on social behavior should be closely monitored.…”

Section: Discussionmentioning

confidence: 93%

“…Based on climatic records, we could identify only two weather events of that likely severity between 1875 and the present (Brown and Brown , Brown et al. ).…”

Section: Methodsmentioning

confidence: 99%

Extreme group sizes in a colonial bird favored during a rare climatic event

Brown

2018

Ecosphere

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What maintains stasis in animal group‐size distributions is an unresolved problem in behavioral ecology. One potential driver could be rare climatic events that favor certain group sizes in ways that do not occur in normal conditions. We investigated mortality among colonially nesting cliff swallows (Petrochelidon pyrrhonota) during a rare climatic event in western Nebraska in 1996 that led to the starvation of thousands of adult birds. Colonies at the extreme end of the size distribution exhibited less size reduction (higher adult survival) than those of intermediate size. That this event resulted in disruptive selection on colony size was suggested by an underrepresentation of locally produced yearling birds that recruited into colonies of intermediate size the following year. There was no evidence that the colony‐size‐related mortality could be explained by differential sorting of birds among colonies based on body size or differing patterns of selection on morphology. The selection on colony size was likely driven by lower competition for food in the smallest colonies and better quality foraging habitat associated with the largest colonies, with these advantages enhanced in severe weather. Selection on colony size during rare climatic events can reinforce or oppose selection occurring during other times of the annual cycle. Whether such selection results in long‐term change in the colony‐size distribution may depend on the frequency and severity of these climatic events.

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Changing patterns of natural selection on morphology of Cliff Swallows during severe weather

Cited by 2 publications

References 32 publications

Smaller brained cliff swallows are more likely to die during harsh weather

Smaller brained cliff swallows are more likely to die during harsh weather

Extreme group sizes in a colonial bird favored during a rare climatic event

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