The adaptive evolution of herbivory in freshwater systems

Herbivory is thought to be nutritionally inefficient relative to carnivory and omnivory, but herbivory evolved from carnivory in many terrestrial and aquatic lineages, suggesting that there are advantages of eating plants. Herbivory has been well-studied in both terrestrial and aquatic systems, and there is abundant information on feedbacks between herbivores and plants, coevolution of plant and herbivore defenses, mechanisms for mediating nutrient limitation, effects of nutrient limitation on herbivore life history, and, more recently, the origins of the herbivorous diet. Researchers have sufficiently defined the ecological context and evolutionary origins of the herbivorous diet, and these main areas of research have laid the groundwork for studying herbivory as an adaptation. However, we have yet to synthesize this information in a way that allows us to establish a framework of testable adaptive hypotheses. To understand the adaptive significance of this diet transition, we review the current literature and use evidence from these works as support for five hypotheses on the evolution of herbivory from carnivory: (1) intake efficiency—herbivores use part of their food source as habitat, thus minimizing the energy/time spent searching for food and avoiding predators; (2) suboptimal habitat—herbivory allows organisms to invade and establish populations in habitats that have high primary production but low abundance of animal prey; (3) heterotroph facilitation—herbivory is adaptive because herbivores consume microbes associated with producers; (4) lipid allocation—herbivory is adaptive because producers are rich in fatty acids, which fuel reproduction and storage; and (5) disease avoidance—herbivory minimizes animal-facilitated disease transmission. Due to the extensive literature, we have limited this review to discussing herbivory in freshwater systems. To our knowledge, no prior work has compiled a comprehensive list of conditions that favor an herbivorous diet in nature. With backgrounds in both theoretical and experimental ecology, the incorporation of these hypotheses to the current literature will provide information about diet evolution, where it is currently lacking

Optimal timing of introduction of complementary feeding: A systematic review and meta-analysis

Context: The timing of introducing complementary feeding (CF) is crucial because premature or delayed CF can be associated with adverse health outcomes in childhood and adulthood.Objective: This systematic review aims to evaluate the impact of the timing of CF introduction on health, nutrition, and developmental outcomes among normal-term infants.Data sources: Electronic databases and trial registries were searched, along with the reference lists of the included studies and relevant systematic reviews.Data extraction: Two investigators independently extracted data from the included studies on a standardized data-extraction form.Data analysis: Data were meta-analyzed separately for randomized controlled trials (RCTs) and observational studies on the basis of early introduction of CF (\u3c 3 months, \u3c 4 months, \u3c 6 months of age) or late introduction of CF (\u3e 6 months, \u3e 8 months of age). Evidence was summarized according to GRADE criteria. In total, 268 documents were included in the review, of which 7 were RCTs (from 24 articles) and 217 were observational studies (from 244 articles). Evidence from RCTs did not suggest an impact of early introduction, while low-certainty evidence from observational studies suggested that early introduction of CF (\u3c 6 months) might increase body mass index (BMI) z score and overweight/obesity. Early introduction at \u3c 3 months might increase BMI and odds of lower respiratory tract infection (LRTI), and early introduction at \u3c 4 months might increase height, LRTI, and systolic and diastolic blood pressure (BP). For late introduction of CF, there was a lack of evidence from RCTs, but low-certainty evidence from observational studies suggests that late introduction of CF (\u3e 6 months) might decrease height, BMI, and systolic and diastolic BP and might increase odds of intestinal helminth infection, while late introduction of CF (\u3e 8 months) might increase height-for-age z score.Conclusion: Insufficient evidence does suggest increased adiposity with early introduction of CF. Hence, the current recommendation of introduction of CF should stand, though more robust studies, especially from low- and middle-income settings, are needed.Systematic review registration: PROSPERO registration number CRD42020218517