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1. Spatial and temporal variation in phenotypes and fitness in response to developmental thermal environments

   https://doi.org/10.1111/1365-2435.13910  

   Pruett, Jenna E. ; Warner, Daniel A. ( October 2021 , Functional Ecology)

   Phenotypic variation within populations is influenced by the environment via plasticity and natural selection. How phenotypes respond to the environment can vary among traits, populations and life stages in ways that can influence fitness.

   Plastic responses during early development are particularly important because they can affect components of fitness throughout an individual's life. Consequently, how natural selection shapes developmental plasticity could be influenced by fitness consequences across different life stages. Moreover, spatial variation in selection pressures could generate differences in plastic responses among populations.

   To gain insight into sources of variation in phenotypes and survival, we used a laboratory egg incubation experiment using brown anole lizardsAnolis sagreifrom mainland (ancestral) and island (descendent) populations, combined with a mark–release–recapture experiment in the field. Our study was designed to (a) quantify the effects developmental temperature on embryo development and offspring morphology, (b) assess how developmental temperature influences offspring survival across different life stages and (c) quantify how thermal reaction norms vary among ancestral and descendant populations.

   Developmental temperature influenced offspring morphology, but thermal reaction norms of embryos showed little variation among populations. Developmental temperature influenced offspring survival, but the patterns differed between embryo and hatchling stages; the optimal temperature for embryos was about 5℃ lower than that for hatchlings. High temperatures were thermally stressful to embryos, but they reduced incubation duration and led to early hatching. In turn, earlier hatching increased the probability of survival to adulthood. Moreover, the effect of developmental temperature on hatchling survival was most pronounced for offspring that hatched late in the season.

   The difference in optimal developmental temperatures between life stages may be driven by physiological tolerance for embryos and by ecological factors for hatchlings. Moreover, the fitness consequences of the developmental environment depend on the phenology of hatching. Overall, these results highlight how the developmental environment can differentially affect fitness across life stages and show that temporal thermal heterogeneity can influence survival of embryos, but the consequences on post‐hatching stages may vary at different times of the season.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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2. Breadth of the thermal response captures individual and geographic variation in temperature‐dependent sex determination

   https://doi.org/10.1111/1365-2435.13410  

   Carter, Anna L. ; Bodensteiner, Brooke L. ; Iverson, John B. ; Milne‐Zelman, Carrie L. ; Mitchell, Timothy S. ; Refsnider, Jeanine M. ; Warner, Daniel A. ; Janzen, Fredric J. ; White, ed., Craig ( August 2019 , Functional Ecology)

   Population‐scale responses of key ecological traits to local environmental conditions provide insight into their adaptive potential. In species with temperature‐dependent sex determination (TSD), short‐term, individual developmental responses to the incubation environment have long‐term consequences for populations.

   We took a model‐based approach to study within‐ and among‐population variation in the physiological components of TSD in 12 populations of painted turtles (Chrysemys picta). We used laboratory and field incubation data to quantify variation in thermal reaction norms at both population and clutch scales, focusing on the pivotal temperature that produces a 1:1 sex ratio (P) and the transitional range of incubation temperatures (TRTs) that produce mixed sex ratios.

   Defying theoretical expectations, among‐population variation inPwas not convincingly explained by geography or local thermal conditions. However, within some populations,Pvaried by >5°C at the clutch scale, indicating that the temperature sensitivity of gonadal differentiation can vary substantially among individual nesting females. In addition, the TRT was wider at lower latitudes, suggesting responsiveness to local incubation conditions.

   Our results provide a potential explanation for discrepancies observed between constant‐temperature experimental results and outcomes of fluctuating incubation conditions experienced in natural nests, exposing important knowledge gaps in our understanding of local adaptation in TSD and identifying shortcomings of traditional laboratory studies. Understanding individual variation and the timing of gonadal differentiation is likely to be far more useful in understanding local adaptation than previously acknowledged.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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3. Intraspecific variation in incubation behaviours along a latitudinal gradient is driven by nest microclimate and selection on neonate quality

   https://doi.org/10.1111/1365-2435.13772  

   Lundblad, Carl G. ; Conway, Courtney J. ; Sandercock, ed., Brett ( March 2021 , Functional Ecology)

   The strategies by which animals allocate reproductive effort across their lifetimes vary, and the causes of variation in those strategies are actively debated. In birds, most research has focused heavily on variation in clutch size and fecundity, but incubation behaviour and other functionally related traits have received less attention. Variation in incubation period duration is notable because time‐dependent sources of clutch mortality should impose strong directional selection to minimize the incubation period. However, life‐history theory predicts multiple mechanisms by which inter‐ and intraspecific variation in incubation behaviours may be adaptive.

   We conducted one of the first studies of intraspecific latitudinal variation in avian incubation behaviours across a large portion of a single species’ range. We placed motion‐activated nest cameras inside burrowing owl nests at five study sites to quantify variation in daily nest attentiveness, cumulative nest attendance and incubation period duration. We tested predictions of two alterative hypotheses that have been proposed to explain variation in incubation periods: theparental risk tolerance hypothesisand theneonate quality hypothesis.

   Daily nest attentiveness, cumulative nest attendance and incubation period duration in burrowing owls were all positively correlated with latitude. Burrowing owls reduced their daily nest attentiveness at low latitudes and on days when the average nest temperature was within the range that is optimal for embryo development. Further, longer incubation periods were most strongly associated with greater cumulative nest attendance instead of reduced daily nest attentiveness.

   These results support predictions of theneonate quality hypothesis:longer incubation periods result from stronger selection on neonate quality rather than selection to reduce reproductive effort in response to low extrinsic mortality risk. However, some owls facultatively reduced their daily nest attentiveness, and this result supports the general hypothesis that incubation decisions reflect a trade‐off between reproduction and self‐maintenance, and that the optimal solution to that trade‐off varies systematically in response to latitudinal gradients in adult mortality.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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4. Environmental drivers of female reproductive investment in egg quantity and quality in a grassland sparrow

   https://doi.org/10.1111/ibi.13379  

   Sroor, Elizabeth_N ; Boyle, W_Alice ; Castro‐Miller, Henry_N ; Hobbs, Kristen_S ; Reynaldo, Miriam_D ; Silber, Katy_M ; Mohankumar, Narmadha_M ; Wright, Nathalie_A ; Freeman, Nikole_E ( November 2024 , Ibis)

   Female investment in reproduction is a critical component of life history that influences both the fitness of the female and her offspring. Oviparous females can allocate energy into egg size and/or clutch size, and this allocation can vary over lifetimes, within populations and among species. However, we know little about whether investment decisions shift within breeding seasons and the factors that influence female reproductive strategies. We studied endogenous and exogenous factors associated with variation in female reproductive investment by measuring 860 eggs from 240 clutches laid by Grasshopper SparrowsAmmodramus savannarumbetween 2014 and 2019 at the Konza Prairie Biological Station in Manhattan, Kansas, USA. As the breeding season progressed, females laid smaller clutches of heavier eggs, indicating a shift in investment towards fewer but higher quality young. Females that were heavier than expected given their body size laid heavier and larger eggs, but maternal body condition was not related to clutch size. Brood parasitism by Brown‐headed CowbirdsMolothrus aterreduced the number of Grasshopper Sparrow eggs in nests, but was unrelated to host egg size or the total number of eggs that a female incubated, implying that sparrows do not adjust investment in response to parasitism risk. Pre‐laying ambient temperature and precipitation were not associated with egg size, yet females tended to lay more eggs under rainier conditions. Overall, we provide evidence that both endogenous and exogenous factors shape female reproductive investment. Understanding the flexibility of reproductive strategies in response to multiple sources of selection, and how this mediates key trade‐offs that influence demographic rates, can be used in forecasting population growth of bird species affected by anthropogenic changes to breeding areas.

    

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5. Nest structure affects auditory and visual detectability, but not predation risk, in a tropical songbird community

   https://doi.org/10.1111/1365-2435.13405  

   Mouton, James C. ; Martin, Thomas E. ; Galván, ed., Ismael ( August 2019 , Functional Ecology)

   Offspring mortality varies dramatically among species with critical demographic and evolutionary ramifications, yet the causes of this variation remain unclear. Nests are widely used for breeding across taxa and thought to influence offspring mortality risk. Traditionally, more complex, enclosed nest structures are thought to reduce offspring predation by reducing the visibility of nest contents and muffling offspring sounds compared to open nests. Direct tests of the functional bases for nest structure influence on predation risk are lacking.

   We used experiments and 10 years of observational data to examine how nest structure influences nest predation risk in a diverse community of tropical songbirds. First, we examined how nest size was related to nest structure and nest predation rates across species. Second, we assessed how nest structure influences the detectability of nestling begging calls both in field and in laboratory settings. Finally, we examined how the acoustic properties of different nest structures influence nest predation risk. Specifically, we experimentally broadcast begging calls from open and enclosed nests to determine how auditory cues and nest structure interact to affect predation on plasticine and quail eggs. We also tested whether nest structure was associated with differences in nest predation rates between the incubation (no begging cues) and nestling (begging cues) stages.

   We found that enclosed nests are larger than open nests after accounting for adult size, and larger nests had increased predation rates. Moreover, enclosed nests did not consistently alter nestling begging calls in ways that reduce the likelihood of predation compared to open nests. Indeed, begging cues increased predation rates for enclosed but not open‐cup nests in our playback experiment, and nest predation rates showed greater increases after hatching in enclosed than open‐cup nests.

   Ultimately, enclosed nests do not necessarily provide greater predation benefits than open nests in contrast to long‐standing theory.

   A freeplain language summarycan be found within the Supporting Information of this article.

    

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