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1. Adaptive seasonal shift towards investment in fewer, larger offspring: Evidence from field and laboratory studies

   https://doi.org/10.1111/1365-2656.13182  

   Hall, Joshua M. ; Mitchell, Timothy S. ; Thawley, Christopher J. ; Stroud, James T. ; Warner, Daniel A. ; Dantzer, ed., Ben ( March 2020 , Journal of Animal Ecology)

   Seasonal changes in reproduction have been described for many taxa. As reproductive seasons progress, females often shift from greater energetic investment in many small offspring towards investing less total energy into fewer, better provisioned (i.e. larger) offspring. The underlying causes of this pattern have not been assessed in many systems.

   Two primary hypotheses have been proposed to explain these patterns. The first is an adaptive hypothesis from life‐history theory: early offspring have a survival advantage over those produced later. Accordingly, selection favours females that invest in offspring quantity early in the season and offspring quality later. The second hypothesis suggests these patterns are not intrinsic but result from passive responses to seasonal changes in the environment experienced by reproducing females (i.e. maternal environment).

   To disentangle the causes underlying this pattern, which has been reported in brown anole lizards (Anolis sagrei), we performed complementary field and laboratory studies. The laboratory study carefully controlled maternal environments and quantified reproductive patterns throughout the reproductive season for each female. The field study measured similar metrics from free ranging lizards across an entire reproductive season.

   In the laboratory, females increased relative effort per offspring as the reproductive season progressed; smaller eggs were laid earlier, larger eggs were laid later. Moreover, we observed significant among‐individual variation in seasonal changes in reproduction, which is necessary for traits to evolve via natural selection. Because these patterns consistently emerge under controlled laboratory conditions, they likely represent an intrinsic and potentially adaptive adjustment of reproductive effort as predicted by life‐history theory.

   The field study revealed similar trends, further suggesting that intrinsic patterns observed in the laboratory are strong enough to persist despite the environmental variability that characterizes natural habitats. The observed patterns are indicative of an adaptive seasonal shift in parental investment in response to a deteriorating offspring environment: allocating greater resources to late‐produced offspring likely enhances maternal fitness.

    

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2. Visitation rate, but not foraging range, responds to brood size manipulation in an aerial insectivore

   https://doi.org/10.1007/s00265-022-03244-z  

   Madden, Sage A. ; McDermott, Molly T. ; Safran, Rebecca J. ( September 2022 , Behavioral Ecology and Sociobiology)

   Life history theory predicts that increased investment in current offspring decreases future fecundity or survival. Avian parental investment decisions have been studied either via brood size manipulation or direct manipulation of parental energetic costs (also known as handicapping). However, we have limited experimental data on the potential interactive effects of these manipulations on parent behavior. Additionally, we know little about how these manipulations affect spatial foraging behavior away from the nest. We simultaneously manipulated brood size and parental costs (via added weight in the form of a GPS tag) in wild female barn swallows (Hirundo rustica). We measured multiple aspects of parent behavior at and away from the nest while controlling for measures of weather conditions. We found no significant interactive effects of manipulated brood size and parental costs. Both sexes increased their visitation rate with brood size, but nestlings in enlarged broods grew significantly less post-brood size manipulation than those in reduced broods. Foraging range area was highly variable among GPS-tagged females but was unaffected by brood size. As such, increased visitation rate in response to brood size may be more energetically costly for far-ranging females. GPS-tagged females did not alter their visitation rate relative to un-tagged birds, but their mates had higher visitation rates. This suggests that GPS tagging may affect some unmeasured aspect of female behavior, such as prey delivery. Our findings indicate that investigation of foraging tactics alongside visitation rate is critical to understanding parental investment and the benefits and costs of reproduction.

   Avian parental investment decisions have been studied by either brood size manipulation or direct manipulation of parental costs, but rarely both simultaneously. We simultaneously manipulated brood size and parental costs (via addition of a GPS tag) in a wild avian system, allowing us to examine interactive effects of these manipulations. Additionally, studies of parental investment often examine behaviors at the nest, but measurements of parental care behavior away from the nest are rare. Our study is unique in that we measured multiple aspects of parental care, including spatial foraging behavior tracked with GPS tags. We found no interactive effects of manipulated brood size and parental costs on visitation rate or nestling growth, and spatial foraging behavior of females was individually variable. Documenting foraging tactics alongside visitation rate is critical to understanding parental investment because the same visitation rate might be more costly for far-ranging females.

    

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3. Greater opportunities for sexual selection in male than in female obligate brood parasitic birds

   https://doi.org/10.1111/jeb.13537  

   Louder, Matthew I. M. ; Hauber, Mark E. ; Louder, Amber N. A. ; Hoover, Jeffrey P. ; Schelsky, Wendy M. ( September 2019 , Journal of Evolutionary Biology)

   Females are expected to have evolved to be more discriminatory in mate choice than males as a result of greater reproductive investment into larger gametes (eggs vs. sperm). In turn, males are predicted to be more promiscuous than females, showing both a larger variance in the number of mates and a greater increase in reproductive success with more mates, yielding more intense sexual selection on males vs. females (Bateman's Paradigm). However, sex differences in costly parental care strategies can either reinforce or counteract the initial asymmetry in reproductive investment, which may be one cause for some studies failing to conform with predictions of Bateman's Paradigm. For example, in many bird species with small female‐biased initial investment but extensive biparental care, both sexes should be subject to similar strengths of sexual selection because males and females are similarly restricted in their ability to pursue additional mates. Unlike 99% of avian species, however, obligate brood parasitic birds lack any parental care in either sex, predicting a conformation to Bateman's Paradigm. Here we use microsatellite genotyping to demonstrate that in brood parasitic brown‐headed cowbirds (Molothrus ater), per capita annual reproductive success increases with the number of mates in males, but not in females. Furthermore, also as predicted, the variance of the number of mates and offspring is greater in males than in females. Thus, contrary to previous findings in this species, our results conform to predictions of the Bateman's Paradigm for taxa without parental care.

    

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4. Marine heatwave temperatures enhance larval performance but are meditated by paternal thermal history and inter-individual differences in the purple sea urchin, Strongylocentrotus purpuratus

   https://doi.org/10.3389/fphys.2023.1230590  

   Leach, Terence S. ; Hofmann, Gretchen E. ( August 2023 , Frontiers in Physiology)

   Marine heatwave (MHW) events, characterized by periods of anomalous temperatures, are an increasingly prevalent threat to coastal marine ecosystems. Given the seasonal phenology of MHWs, the full extent of their biological consequences may depend on how these thermal stress events align with an organism’s reproductive cycle. In organisms with more complex life cycles (e.g., many marine invertebrate species) the alignment of adult and larval environments may be an important factor determining offspring success, setting the stage for MHW events to influence reproduction and development in situ . Here, the influence of MHW-like temperatures on the early development of the California purple sea urchin, Strongylocentrotus purpuratus , were explored within the context of paternal thermal history. Based on temperature data collected during MHW events seen in Southern California from 2014–2020, adult urchins were acclimated to either MHW or non-MHW temperatures for 28 days before their sperm was used to produce embryos that were subsequently raised under varying thermal conditions. Once offspring reached an early larval stage, the impact of paternal and offspring environments were assessed on two aspects of offspring performance: larval size and thermal tolerance. Exposure to elevated temperatures during early development resulted in larger, more thermally tolerant larvae, with further influences of paternal identity and thermal history, respectively. The alignment of paternal and offspring exposure to MHW temperatures had additional positive benefits on larval thermal tolerance, but this tolerance significantly decreased when their thermal experience mismatched. As the highest recorded temperatures within past MHW events have occurred during the gametogenesis of many kelp forest benthic marine invertebrate species, such as the purple sea urchin, such parental mediated impacts may represent important drivers of future recruitment and population composition for these species. 

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5. Within‐ and transgenerational stress legacy effects of ocean acidification on red abalone ( Haliotis rufescens ) growth and survival

   https://doi.org/10.1111/gcb.17048  

   Neylan, Isabelle P. ; Swezey, Daniel S. ; Boles, Sara E. ; Gross, Jackson A. ; Sih, Andrew ; Stachowicz, John J. ( November 2023 , Global Change Biology)

   Understanding the mechanisms by which individual organisms respond and populations adapt to global climate change is a critical challenge. The role of plasticity and acclimation, within and across generations, may be essential given the pace of change. We investigated plasticity across generations and life stages in response to ocean acidification (OA), which poses a growing threat to both wild populations and the sustainable aquaculture of shellfish. Most studies of OA on shellfish focus on acute effects, and less is known regarding the longer term carryover effects that may manifest within or across generations. We assessed these longer term effects in red abalone (Haliotis rufescens) using a multi‐generational split‐brood experiment. We spawned adults raised in ambient conditions to create offspring that we then exposed to high pCO₂(1180 μatm; simulating OA) or low pCO₂(450 μatm; control or ambient conditions) during the first 3 months of life. We then allowed these animals to reach maturity in ambient common garden conditions for 4 years before returning the adults into high or low pCO₂treatments for 11 months and measuring growth and reproductive potential. Early‐life exposure to OA in the F1 generation decreased adult growth rate even after 5 years especially when abalone were re‐exposed to OA as adults. Adult but not early‐life exposure to OA negatively impacted fecundity. We then exposed the F2 offspring to high or low pCO₂treatments for the first 3 months of life in a fully factorial, split‐brood design. We found negative transgenerational effects of parental OA exposure on survival and growth of F2 offspring, in addition to significant direct effects of OA on F2 survival. These results show that the negative impacts of OA can last within and across generations, but that buffering against OA conditions at critical life‐history windows can mitigate these effects.

    

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